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System-Level Refrigeration Cycle (2P)

System-level, two-phase refrigeration block in a moist air, thermal liquid, or two-phase fluid network

Since R2023a

  • System-Level Refrigeration Cycle (2P) block diagram

Libraries:
Simscape / Fluids / Two-Phase Fluid / Thermodynamic Cycles

Description

The System-Level Refrigeration Cycle (2P) block models a basic refrigeration cycle consisting of a compressor, a condenser, a liquid receiver, a thermostatic expansion valve, and an evaporator. The block models the refrigerant loop within the block in the two-phase fluid domain using the fluid properties specified at port F. The condenser and evaporator external fluids can be part of a moist air, thermal liquid, or two-phase fluid network. The external fluids are the fluids in the condenser and evaporator opposite the refrigerant.

When the compressor is on, the refrigeration cycle consumes power to transfer heat from the evaporator external fluid to the condenser external fluid. The subcomponents provide the specified nominal heat transfer under nominal operating conditions.

Block Structure

This block behaves as a simplified version of this refrigeration cycle made from Simscape™ Fluids™ blocks that model the condenser, compressor, evaporator, expansion device, and liquid receiver:

Diagram of refrigeration cycle consisting of condenser, compressor, evaporator, expansion device, and liquid receiver

The refrigerant flows through the loop counterclockwise. The compressor, which is controlled by the signal at port S, sucks in refrigerant vapor and produces a hot, high-pressure vapor, which moves to the condenser. The condenser rejects heat from the refrigerant to the external fluid to condense the refrigerant. The liquid receiver acts as a storage tank for the refrigerant and only allows liquid flow to exit, which helps maintain normal operation even if fluctuating external conditions cause the condenser output to vary. From the tank, the refrigerant flows to the expansion device, which is typically a valve or capillary tube that produces a large pressure loss. The drop in pressure partially vaporizes the refrigerant, which chills it. The refrigerant moves to the evaporator, which absorbs heat from the external fluid to the cold refrigerant to vaporize the refrigerant.

The subcomponents of the System-Level Refrigeration Cycle (2P) block behave the same as these Simscape Fluids blocks in this model, but the equations for the positive displacement compressor, expansion valve, receiver component, and condenser and evaporator subcomponents vary. For more information on the individual components of a refrigeration system, see:

The compressor and evaporator components depend on the External fluid for condenser heat transfer and External fluid for evaporator heat transfer parameters. For more information, see:

Positive Displacement Compressor Subcomponent

The compressor subcomponent determines the refrigerant mass flow rate for the system. The physical signal input port S controls the compressor operation. When the value at port S is 0, the compressor is off and the mass flow rate is 0. When the value at port S is 1, the compressor runs at the nominal shaft speed, which produces the nominal mass flow rate under nominal operating conditions. To prevent reverse flow, the value of S must be greater than or equal to 0.

The mass flow rate in the compressor is

m˙=ηvV˙nominalSvin,

where:

  • ηv is the volumetric efficiency.

  • S is the value of the signal at port S.

  • vin is the inlet specific volume.

  • V˙nominal is the nominal volumetric flow rate, which the block determines from the nominal mass flow rate, m˙nominal, which depends on the setting of the Capacity specification parameter:

    • When the Capacity specification parameter is Cooling load,

      m˙nominal=Qcoolingh1h4,

      where Qcooling is the Nominal evaporator heat transfer parameter, h1 is the evaporator outlet specific enthalpy, and h4 is the valve outlet specific enthalpy.

    • When the Capacity specification parameter is Heating load,

      m˙nominal=Qheatingh2h3,

      where Qcooling is the Nominal condenser heat transfer parameter, h2 is the compressor outlet specific enthalpy, and h3 is the condenser outlet specific enthalpy.

    • When the Capacity specification parameter is Refrigerant mass flow rate, m˙nominal is the value of the Nominal mass flow rate parameter.

The fluid power that the compressor adds to the flow is

Φfluid=m˙hout,isenhinηs,

where:

  • hout,isem is the specific enthalpy evaluated at the output pressure for an isentropic process.

  • hin is the inlet specific enthalpy.

  • ηs is the isentropic efficiency.

    • When Performance specification is Coefficient of performance for cooling or Coefficient of performance for heating, the block solves for ηs by calculating h2 and using the relation

      h2=h2isenh1ηs+h1,

      where h2isen is the compressor outlet specific enthalpy assuming an isentropic process.

      • When Performance specification is Coefficient of performance for cooling, the block solves for h2 with CoPcooling=h1h4h2h1, where CoPcooling is the Coefficient of performance at nominal conditions parameter.

      • When Performance specification is Coefficient of performance for heating, the block solves for h2 with CoPheating=h2h3h2h1=h2h4h2h1=CoPcooling+1, where CoPheating is the Coefficient of performance at nominal conditions parameter.

    • When Performance specification is Compressor isentropic efficiency, ηs is the value of the Compressor isentropic efficiency parameter.

The block calculates the volumetric efficiency directly from the inlet and outlet specific volumes

ηv=1+CCvinvout,

where:

  • C is the clearance volume fraction that the block determines from the nominal operating conditions.

  • vin and vout are the inlet and outlet specific volumes evaluated at the inlet and outlet pressures.

The compressor subcomponent does not have mechanical rotational ports and does not need to calculate shaft torque. The mechanical power is

Φmech=Φfluidηm,

where ηm is the mechanical efficiency.

Expansion Valve Subcomponent

The relationship between mass flow rate, which the compressor determines, and the pressure drop across the thermostatic expansion valve subcomponent is

m˙=Seff2vinΔp(Δp2Δplam2)0.25,

where:

  • vin is the inlet specific volume.

  • Δp is the pressure differential over the valve.

  • Δplam is the pressure threshold for transitional flow. Below this value, the flow is laminar.

The effective valve area depends on the pressure difference between the measured pressure, pbulb, and the equalization pressure, peq

Seff=β[(pbulbpeq)(psat(Tevap+ΔTstatic)psat(Tevap))],

where:

  • β is a valve constant the block determines from the nominal operating conditions.

  • Tevap is the evaporating temperature, which depends on the Pressure specification setting:

    • When Pressure specification is Pressure at specified saturation temperature, Tevap is the value of the Nominal evaporating (saturation) temperature parameter.

    • When Pressure specification is Specified pressure, Tevap is the saturation temperature that corresponds to the value of the Nominal evaporator pressure parameter.

  • ΔTstatic is the Static (minimum) evaporator superheat parameter.

  • psat(Tevap) is the fluid saturation pressure as a function of Tevap.

  • psat(Tevap+ΔTstatic) is the fluid saturation pressure as a function of Tevap+ΔTstatic.

  • pbulb is the fluid pressure of the bulb. This pressure is the saturation pressure at the evaporator outlet temperature.

  • peq is the equalization pressure, which is the evaporator pressure for this block.

The effective valve area has limits. The minimum effective valve area, Seff,min, is

Seff,min=fleakSeff,nom,

where fleak is the value of the Ratio of leakage to nominal expansion valve opening parameter. The maximum effective valve area, Seff,mmax, is

Seff,max=fmaxSeff,nom,

where fmax is the value of the Ratio of maximum to nominal expansion valve opening parameter.

Receiver Subcomponent

Excluding the receiver, the block assumes that the refrigerant mass flow rate is the same value through the loop. In the receiver, the total mass is based on the balance between the mass flow rate produced by the compressor and the mass flow rate metered by the expansion valve. The outflow from the receiver subcomponent is always liquid and perfectly insulated from the environment.

The liquid mass fraction in the receiver subcomponent is

dxliqdt=m˙liq,inm˙outm˙vaporization+m˙condensation,

where:

  • xliq is the liquid mass fraction.

  • m˙liq,in is the portion of the flow in that is liquid.

  • m˙out is the mass flow rate out of the receiver.

  • m˙vaporization is the rate of vaporization from the liquid volume to the vapor volume.

  • m˙condensation is the rate of condensation from the vapor volume to the liquid volume.

The pressure relates to the total mass via the specific volume using the relation

M(xliqvliq+(1xliq)vvap)=V,

where:

  • V is the total receiver volume.

  • vliq is the is the specific volume of the liquid volume.

  • vvap is the is the specific volume of the vapor volume.

Condenser and Evaporator Subcomponents

The condenser and evaporator subcomponents model the refrigerant thermal mass, but do not model fluid volume. For the condenser and evaporator, the energy conservation equation is

dhIdt=m˙(hinhout)+Q,

where:

  • M is the constant mass of refrigerant in the component.

  • hI is the refrigerant specific enthalpy at the component internal node.

  • m˙ is the refrigerant mass flow rate.

  • Q is the rate of heat transfer from the external fluid to the refrigerant.

  • hin and hout are the refrigerant specific enthalpy in and out of the component.

Visualize the P-H Diagram

To visualize the refrigeration cycle, use a Probe block from the Simscape > Utilities library to output the variables p_cycle and h_cycle. These variables contain the four pressure and specific enthalpy points of the refrigeration cycle. Connect the variables to the P-H Diagram (2P) block to visualize the refrigeration cycle.

This diagram shows the fluid attributes throughout the system for the refrigerant R-410a. Segment 1 to 2 is the compressor, segment 2 to 3 is the condenser, point 3 is the receiver, segment 3 to 4 is the expansion valve, and segment 4 to 1 is the evaporator.

P-H diagram for the refrigeration cycle

Assumptions and Limitations

  • The block does not model reverse flow and limits the refrigeration cycle to zero and forward flow only. To prevent reverse flow, the block limits the compressor control to zero or forward operation and only models fluid volume in the liquid receiver subcomponent.

  • Excluding the liquid receiver, the subcomponents do not model refrigerant fluid volume, which prevents the accumulation of mass in subcomponents. As a result, the refrigerant mass flow rate is the same through the evaporator, compressor, and condenser subcomponents.

  • There is no refrigerant pressure loss in the evaporator or condenser.

  • The block does not model kinetic energy changes in the refrigerant flow.

  • The evaporator subcomponent models approximate pressure dynamics to maintain numerical robustness. However, the condenser subcomponent does not model approximate pressure dynamics, because the condenser pressure is equal to the receiver pressure, which does model pressure dynamics.

  • The condenser and evaporator subcomponents only model counter flow because the refrigerant is primarily in the two-phase mixture state within the condenser and evaporator. Consequently, the temperature is uniform across most of the condenser and evaporator, and there is no significant difference between counter flow and cross flow.

Ports

Input

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Physical signal input that operates the compressor. A value of 0 means the compressor is off. A value of 1 means the compressor is operating at the nominal capacity.

Conserving

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Two-phase fluid conserving port associated with the refrigerant properties. Connect a Two-Phase Fluid Properties (2P) or Two-Phase Fluid Predefined Properties (2P) block to this port. Do not connect any other Two-Phase Fluid blocks to port F because this port acts as an absolute reference.

Moist air, thermal liquid, or two-phase fluid conserving port associated with the condenser external fluid inlet. The block assumes that the condenser external fluid flows from port Ac to port Bc. The External fluid for condenser heat transfer parameter controls the port fluid.

Moist air, thermal liquid, or two-phase fluid conserving port associated with the condenser external fluid outlet. The block assumes that the condenser external fluid flows from port Ac to port Bc. The External fluid for condenser heat transfer parameter controls the port fluid.

Moist air, thermal liquid, or two-phase fluid conserving port associated with the evaporator external fluid inlet. The block assumes that the evaporator external fluid flows from port Ae to port Be. The External fluid for evaporator heat transfer parameter controls the port fluid.

Moist air, thermal liquid, or two-phase fluid conserving port associated with the evaporator external fluid outlet. The block assumes that the evaporator external fluid flows from port Ae to port Be. The External fluid for evaporator heat transfer parameter controls the port fluid.

Output

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Physical signal output port that measures the heat rejected by the refrigerant in the condenser, in W.

Physical signal output port that measures the heat absorbed by the refrigerant in the evaporator, in W.

Physical signal output port that measures the mechanical power consumed by the compressor, in W.

Physical signal output port that measures rate of condensation in the evaporator external fluid, in kg/s, if the External fluid for evaporator heat transfer parameter is Moist air. If the External fluid for evaporator heat transfer parameter is not moist air, this port outputs 0.

Parameters

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Refrigeration Cycle

Method for specifying the size of the system. You can specify the cooling load, heating load, or the refrigerant mass flow rate.

Rate of heat transfer from the refrigerant to the external fluid in the condenser.

Dependencies

To enable this parameter, set Capacity specification to Heating load.

Rate of heat transfer from the external fluid to the refrigerant in the evaporator.

Dependencies

To enable this parameter, set Capacity specification to Cooling load.

Refrigerant mass flow rate through the cycle.

Dependencies

To enable this parameter, set Capacity specification to Refrigerant mass flow rate.

Method for providing condenser and evaporator pressures. Select whether to directly provide the pressures or provide the corresponding saturation temperatures.

Pressure of refrigerant in the condenser.

Dependencies

To enable this parameter, set Pressure specification to Specified pressure.

Pressure of refrigerant in the evaporator.

Dependencies

To enable this parameter, set Pressure specification to Specified pressure.

Saturation temperature of refrigerant in the condenser.

Dependencies

To enable this parameter, set Pressure specification to Pressure at specified saturation temperature.

Saturation temperature of refrigerant in the evaporator.

Dependencies

To enable this parameter, set Pressure specification to Pressure at specified saturation temperature.

Degrees of temperature below saturation temperature at the condenser outlet.

Degrees of temperature above saturation temperature at the evaporator outlet. The expansion valve adjusts its valve area to try to maintain this superheat.

Superheat threshold to close the expansion valve.

Method to specify the refrigeration cycle efficiency. Choose based on the coefficient of performance of the cycle for heating, cooling, or the compressor efficiency.

Ratio of useful cooling or heating by the refrigeration cycle to the power consumed by the compressor.

Dependencies

To enable this parameter, set Performance specification to Coefficient of performance for cooling or Coefficient of performance for heating.

Ratio of ideal, or isentropic, change in specific enthalpy to the actual change in specific enthalpy across the compressor.

Dependencies

To enable this parameter, set Performance specification to Compressor isentropic efficiency.

Ratio of actual volumetric flow rate to the displacement rate of the compressor.

Ratio of the power delivered to the fluid flow to the power driving the mechanical shaft.

Ratio of the fully opened valve area to the valve area needed to maintain superheat at nominal conditions.

Ratio of the closed valve area to the valve area needed to maintain superheat at nominal conditions

Smoothing factor that introduces a layer of gradual change to the flow response when the valve is in near-open or near-closed positions. Set this value to a nonzero value less than one to increase the stability of your simulation in these regimes.

Volume of refrigerant in the condenser.

Volume of refrigerant in the evaporator.

Total physical volume of liquid receiver tank, including both the volume of liquid and vapor phases.

Liquid volume fraction in the receiver tank at the start of simulation.

Whether refrigerant in the cycle starts simulation at the nominal operating conditions based on the nominal operating parameters or specified explicitly with initial condition parameters.

Pressure of the refrigerant in the condenser and liquid receiver at the start of simulation.

Dependencies

To enable this parameter, clear the Initialize refrigerant to nominal operating conditions check box.

Pressure of the refrigerant in the evaporator at the start of simulation.

Dependencies

To enable this parameter, clear the Initialize refrigerant to nominal operating conditions check box.

Specific enthalpy of the refrigerant in the condenser at the start of simulation. If you specify this parameter as a vector of two values, the first element is the inlet specific enthalpy value and the second element is the outlet specific enthalpy value. If you enter a scalar, the block assumes that the inlet and outlet specific enthalpy are the same value.

Dependencies

To enable this parameter, clear the Initialize refrigerant to nominal operating conditions check box.

Specific enthalpy of the refrigerant in the evaporator at the start of simulation. If you specify this parameter as a vector of two values, the first element is the inlet specific enthalpy value and the second element is the outlet specific enthalpy value. If you enter a scalar, the block assumes that the inlet and outlet specific enthalpy are the same value.

Dependencies

To enable this parameter, clear the Initialize refrigerant to nominal operating conditions check box.

Whether the receiver starts the simulation at the saturation equilibrium, meaning the liquid and vapor volumes are both at the saturated state, or uses explicitly specified initial conditions.

Dependencies

To enable this parameter, clear the Initialize refrigerant to nominal operating conditions check box.

Specific enthalpy of the liquid portion of the refrigerant in the receiver at the start of simulation.

Dependencies

To enable this parameter, clear the Initialize refrigerant to nominal operating conditions and Initial receiver liquid and vapor fully saturated check boxes.

Specific enthalpy of the vapor portion of the refrigerant in the receiver at the start of simulation.

Dependencies

To enable this parameter, clear the Initialize refrigerant to nominal operating conditions and Initial receiver liquid and vapor fully saturated check boxes.

Condenser External Fluid

External fluid for heat transfer in the condenser.

Mass flow rate from port Ac to port Bc during nominal operating conditions.

Pressure drop from port Ac to port Bc during nominal operating conditions.

Method of pressure specification:

  • Specified pressure — Specify the nominal inlet pressure.

  • Pressure at specified saturation temperature — Specify the nominal saturation temperature that corresponds to the inlet pressure.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Two-phase fluid.

Pressure at the inlet of the condenser on the external fluid side of the heat exchanger during the nominal operating condition.

Dependencies

To enable this parameter, set either:

  • External fluid for condenser heat transfer to Moist air or Thermal liquid.

  • External fluid for condenser heat transfer to Two-phase fluid, and set Pressure specification to Specific pressure.

Saturation temperature at the outlet of the condenser external fluid side of the heat exchanger during the nominal operating condition. The pressure in the condenser is the corresponding saturation pressure.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Two-phase fluid and Pressure specification to Pressure at specified saturation temperature.

Method the block uses to describe the inlet condition of the condenser external fluid at the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Two-phase fluid.

Temperature at the inlet of the external fluid side of the condenser during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Two-phase fluid and Initial condition specification to Temperature.

Specific enthalpy at the inlet of the external fluid side of the condenser during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Two-phase fluid and Initial condition specification to Specific enthalpy.

Vapor quality, defined as the mass fraction of vapor in a liquid-vapor mixture, at the inlet of the external fluid side of the condenser during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Two-phase fluid and Initial condition specification to Vapor quality.

Method the block uses to describe the moisture level at the inlet during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air.

Relative humidity at the inlet of the external fluid side of the condenser during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air and Inlet moisture specification to Relative humidity.

Specific humidity, defined as the mass fraction of water vapor in a moist air mixture, at the inlet of the external fluid side of the condenser during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air and Inlet moisture specification to Specific humidity.

Mole fraction of the water vapor in a moist air mixture at the inlet of the external fluid side of the condenser during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air and Inlet moisture specification to Mole fraction.

Humidity ratio, defined as the mass ratio of water vapor to dry air and trace gas, at the inlet of the external fluid side of the condenser during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air and Inlet moisture specification to Humidity ratio.

Wet-bulb temperature at the inlet of the external fluid side of the condenser during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air and Inlet moisture specification to Wet-bulb temperature.

Method the block uses to describe the trace gas level at the external fluid side inlet of the condenser during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air.

Mass fraction of trace gas in a moist air mixture at the inlet of the external fluid side of the condenser during the nominal operating condition.

The block ignores this parameter if the Trace gas model parameter in the Moist Air Properties (MA) block is None.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air and Inlet trace gas specification to Mass fraction.

Mole fraction of the trace gas in a moist air mixture at the inlet of the external fluid side of the condenser during the nominal operating condition.

The block ignores this parameter if the Trace gas model parameter in the Moist Air Properties (MA) block is None.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air and Inlet trace gas specification to Mole fraction.

Total volume of external fluid in the condenser.

Flow area at the condenser external fluid port Ac.

Flow area at the condenser external fluid port Bc.

Whether to include the temperature dynamics of the heat transfer surface.

Total mass of the condenser heat transfer surface.

Dependencies

To enable this parameter, select Condenser wall thermal mass.

Specific heat of the condenser heat transfer surface.

Dependencies

To enable this parameter, select Condenser wall thermal mass.

Whether to start the simulation at the nominal operating condition or specify a different set of initial conditions using additional parameters.

Condenser external fluid pressure at the start of the simulation.

Dependencies

To enable this parameter, clear the Initialize to nominal operating conditions check box.

Quantity used to describe the initial state of the condenser external fluid.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Two-phase fluid and clear the Initialize to nominal operating conditions check box.

Temperature at the start of simulation. If the value is a scalar, then the block assumes that the initial temperature is uniform. If the value is a two-element vector, then the block assumes that the initial temperature varies linearly between the ports condenser ports, with the first element corresponding to port Ac and the second element corresponding to port Bc.

Dependencies

To enable this parameter, set either:

  • External fluid for condenser heat transfer to Moist air or Thermal liquid and clear the Initialize to nominal operating conditions check box.

  • External fluid for condenser heat transfer to Two-phase fluid, clear the Initialize to nominal operating conditions check box, and set Initial fluid energy specification to Temperature.

Condenser external fluid vapor quality, defined as the mass fraction of vapor in a liquid-vapor mixture, at the start of simulation. If the value is a scalar, then the block assumes that the initial vapor quality is uniform. If the value is a two-element vector, then the block assumes that the initial vapor quality varies between the condenser ports, with the first element corresponding to port Ac and the second element corresponding to port Bc.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Two-phase fluid, clear the Initialize to nominal operating conditions check box, and set Initial fluid energy specification to Vapor quality.

Condenser external fluid vapor void fraction, defined as the volume fraction of vapor in a liquid-vapor mixture, at the start of simulation. If the value is a scalar, then the block assumes that the initial vapor void fraction is uniform. If the value is a two-element vector, then the block assumes that the initial vapor void quality varies between the condenser ports, with the first element corresponding to port Ac and the second element corresponding to port Bc.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Two-phase fluid, clear the Initialize to nominal operating conditions check box, and set Initial fluid energy specification to Vapor void fraction.

Condenser external fluid specific enthalpy at the start of simulation. If the value is a scalar, then the block assumes that the initial specific enthalpy is uniform. If the value is a two-element vector, then the block assumes that the initial specific enthalpy varies between the condenser ports, with the first element corresponding to port Ac and the second element corresponding to port Bc.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Two-phase fluid, clear the Initialize to nominal operating conditions check box, and set Initial fluid energy specification to Specific enthalpy.

Condenser external fluid specific internal energy at the start of simulation. If the value is a scalar, then the block assumes that the initial specific internal energy is uniform. If the value is a two-element vector, then the block assumes that the initial specific internal energy varies between the condenser ports, with the first element corresponding to port Ac and the second element corresponding to port Bc.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Two-phase fluid, clear the Initialize to nominal operating conditions check box, and set Initial fluid energy specification to Specific internal energy.

Method used to describe the initial moisture level in condenser external fluid.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air and clear the Initialize to nominal operating conditions check box.

Condenser external fluid relative humidity at the start of simulation. If the value is a scalar, then the block assumes that the initial relative humidity is uniform. If the value is a two-element vector, then the block assumes that the initial relative humidity varies linearly between the ports, with the first element corresponding to port Ac and the second element corresponding to port Bc.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air, clear the Initialize to nominal operating conditions check box, and set Initial moisture specification to Relative humidity.

Condenser external fluid specific humidity, defined as the mass fraction of water vapor in a moist air mixture, at the start of simulation. If the value is a scalar, then the block assumes that the initial specific humidity is uniform. If the value is a two-element vector, then the block assumes that the initial specific humidity varies linearly between the ports, with the first element corresponding to port Ac and the second element corresponding to port Bc.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air, clear the Initialize to nominal operating conditions check box, and set Initial moisture specification to Specific humidity.

Mole fraction of the water vapor in the condenser external fluid at the start of simulation. If the value is a scalar, then the block assumes that the initial water vapor mole fraction is uniform. If the value is a two-element vector, then the block assumes that the initial water vapor mole fraction varies linearly between the ports, with the first element corresponding to port Ac and the second element corresponding to port Bc.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air, clear the Initialize to nominal operating conditions check box, and set Initial moisture specification to Mole fraction.

Condenser external fluid humidity ratio, defined as the mass ratio of water vapor to dry air and trace gas, at the start of simulation. If the value is a scalar, then the block assumes that the initial humidity ratio is uniform. If the value is a two-element vector, then the block assumes that the initial humidity ratio varies linearly between the ports, with the first element corresponding to port Ac and the second element corresponding to port Bc.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air, clear the Initialize to nominal operating conditions check box, and set Initial moisture specification to Humidity ratio.

Condenser wet-bulb temperature at the start of the simulation.

If the value is a scalar, then the block assumes that the initial wet-bulb temperature is uniform. If the value is a two-element vector, then the block assumes that the initial wet-bulb temperature varies linearly between the ports, with the first element corresponding to port Ac and the second element corresponding to port Bc.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air, clear the Initialize to nominal operating conditions check box, and set Initial moisture specification to Wet-bulb temperature.

Method used to describe the trace gas level at the start of simulation.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air and clear the Initialize to nominal operating conditions check box.

Mass fraction of trace gas in a moist air mixture at the start of simulation. If the value is a scalar, then the block assumes that the initial mass fraction is uniform. If the value is a two-element vector, then the block assumes that the initial mass fraction varies linearly between the ports, with the first element corresponding to port Ac and the second element corresponding to port Bc.

The block ignores this parameter if the Trace gas model parameter in the Moist Air Properties (MA) block is None.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air, clear the Initialize to nominal operating conditions check box, and set Initial trace gas specification to Mass fraction.

Mole fraction of the trace gas in a moist air mixture at the start of simulation. If the value is a scalar, then the block assumes that the initial mole fraction is uniform. If the value is a two-element vector, then the block assumes that the initial mole fraction varies linearly between the ports, with the first element corresponding to port Ac and the second element corresponding to port Bc.

The block ignores this parameter if the Trace gas model parameter in the Moist Air Properties (MA) block is None.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air, clear the Initialize to nominal operating conditions check box, and set Initial trace gas specification to Mole fraction.

Heat transfer surface temperature at the start of simulation. If this value is a scalar, the block assumes that the initial temperature is uniform. If this value is a two-element vector, then the block assumes that the temperature varies linearly between ports Ac and Bc with the first element corresponding to Ac and second element corresponding to Bc.

Dependencies

To enable this parameter, clear the Initialize to nominal operating conditions check box.

Relative humidity point of condensation. Condensation occurs above this value. In most cases, this value is 1, which is equivalent to 100%. A value greater than 1 indicates a supersaturated vapor.

Dependencies

To enable this parameter, set External fluid for condenser heat transfer to Moist air and clear the Initialize to nominal operating conditions check box.

Evaporator External Fluid

External fluid for heat transfer in the evaporator.

Mass flow rate from port Ae to port Be during nominal operating conditions.

Pressure drop from port Ae to port Be during nominal operating conditions.

Method of pressure specification:

  • Specified pressure — Specify the nominal inlet pressure.

  • Pressure at specified saturation temperature — Specify the nominal saturation temperature that corresponds to the inlet pressure.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Two-phase fluid.

Pressure at the inlet of the evaporator on the external fluid side of the heat exchanger during the nominal operating condition.

Dependencies

To enable this parameter, set either:

  • External fluid for evaporator heat transfer to Moist air or Thermal liquid.

  • External fluid for evaporator heat transfer to Two-phase fluid, and set Pressure specification to Specific pressure.

Saturation temperature at the outlet of the evaporator external fluid side of the heat exchanger during the nominal operating condition. The pressure in the evaporator is the corresponding saturation pressure.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Two-phase fluid and Pressure specification to Pressure at specified saturation temperature.

Method the block uses to describe the inlet condition of the evaporator external fluid at the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Two-phase fluid.

Temperature at the inlet of the external fluid side of the evaporator during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Two-phase fluid and Initial condition specification to Temperature.

Specific enthalpy at the inlet of the external fluid side of the evaporator during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Two-phase fluid and Initial condition specification to Specific enthalpy.

Vapor quality, defined as the mass fraction of vapor in a liquid-vapor mixture, at the inlet of the external fluid side of the evaporator during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Two-phase fluid and Initial condition specification to Vapor quality.

Method the block uses to describe the moisture level at the inlet during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air.

Relative humidity at the inlet of the external fluid side of the evaporator during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air and Inlet moisture specification to Relative humidity.

Specific humidity, defined as the mass fraction of water vapor in a moist air mixture, at the inlet of the external fluid side of the evaporator during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air and Inlet moisture specification to Specific humidity.

Mole fraction of the water vapor in a moist air mixture at the inlet of the external fluid side of the evaporator during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air and Inlet moisture specification to Mole fraction.

Humidity ratio, defined as the mass ratio of water vapor to dry air and trace gas, at the inlet of the external fluid side of the evaporator during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air and Inlet moisture specification to Humidity ratio.

Evaporator wet-bulb temperature in a moist air mixture at the inlet of the external fluid side of the evaporator during the nominal operating condition.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air and Inlet moisture specification to Wet-bulb temperature.

Method the block uses to describe the trace gas level at the external fluid side inlet of the evaporator during the nominal operating condition.

Mass fraction of the trace gas in a moist air mixture at the inlet of the external fluid side of the evaporator during the nominal operating condition.

The block ignores this parameter if the Trace gas model parameter in the Moist Air Properties (MA) block is None.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air and Inlet trace gas specification to Mass fraction.

Mole fraction of the trace gas in a moist air mixture at the inlet of the external fluid side of the evaporator during the nominal operating condition.

The block ignores this parameter if the Trace gas model parameter in the Moist Air Properties (MA) block is None.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air and Inlet trace gas specification to Mole fraction.

Total volume of external fluid in the evaporator.

Flow area at the evaporator external fluid port Ae.

Flow area at the evaporator external fluid port Be.

Whether to include the temperature dynamics of the heat transfer surface.

Total mass of the evaporator heat transfer surface.

Dependencies

To enable this parameter, select Evaporator wall thermal mass.

Specific heat of the evaporator heat transfer surface.

Dependencies

To enable this parameter, select Evaporator wall thermal mass.

Whether to start the simulation at the nominal operating condition or specify a different set of initial conditions using additional parameters.

Evaporator external fluid pressure at the start of the simulation.

Dependencies

To enable this parameter, clear the Initialize to nominal operating conditions check box.

Quantity used to describe the initial state of the evaporator external fluid.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Two-phase fluid and clear the Initialize to nominal operating conditions check box.

Temperature at the start of simulation. If the value is a scalar, then the block assumes that the initial temperature is uniform. If the value is a two-element vector, then the block assumes that the initial temperature varies linearly between the ports evaporator ports, with the first element corresponding to port Ae and the second element corresponding to port Be.

Dependencies

To enable this parameter, set either:

  • External fluid for evaporator heat transfer to Moist air or Thermal liquid and clear the Initialize to nominal operating conditions check box.

  • External fluid for evaporator heat transfer to Two-phase fluid, clear the Initialize to nominal operating conditions check box, and set Initial fluid energy specification to Temperature.

Evaporator external fluid vapor quality, defined as the mass fraction of vapor in a liquid-vapor mixture, at the start of simulation. If the value is a scalar, then the block assumes that the initial vapor quality is uniform. If the value is a two-element vector, then the block assumes that the initial vapor quality varies between the evaporator ports, with the first element corresponding to port Ae and the second element corresponding to port Be.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Two-phase fluid, clear the Initialize to nominal operating conditions check box, and set Initial fluid energy specification to Vapor quality.

Evaporator external fluid vapor void fraction, defined as the volume fraction of vapor in a liquid-vapor mixture, at the start of simulation. If the value is a scalar, then the block assumes that the initial vapor void fraction is uniform. If the value is a two-element vector, then the block assumes that the initial vapor void quality varies between the evaporator ports, with the first element corresponding to port Ae and the second element corresponding to port Be.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Two-phase fluid, clear the Initialize to nominal operating conditions check box, and set Initial fluid energy specification to Vapor void fraction.

Evaporator external fluid specific enthalpy at the start of simulation. If the value is a scalar, then the block assumes that the initial specific enthalpy is uniform. If the value is a two-element vector, then the block assumes that the initial specific enthalpy varies between the evaporator ports, with the first element corresponding to port Ae and the second element corresponding to port Be.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Two-phase fluid, clear the Initialize to nominal operating conditions check box, and set Initial fluid energy specification to Specific enthalpy.

Evaporator external fluid specific internal energy at the start of simulation. If the value is a scalar, then the block assumes that the initial specific internal energy is uniform. If the value is a two-element vector, then the block assumes that the initial specific internal energy varies between the evaporator ports, with the first element corresponding to port Ae and the second element corresponding to port Be.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Two-phase fluid, clear the Initialize to nominal operating conditions check box, and set Initial fluid energy specification to Specific internal energy.

Method used to describe the initial moisture level in evaporator external fluid.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air and clear the Initialize to nominal operating conditions check box.

Evaporator external fluid relative humidity at the start of simulation. If the value is a scalar, then the block assumes that the initial relative humidity is uniform. If the value is a two-element vector, then the block assumes that the initial relative humidity varies linearly between the ports, with the first element corresponding to port Ae and the second element corresponding to port Be.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air, clear the Initialize to nominal operating conditions check box, and set Initial moisture specification to Relative humidity.

Evaporator external fluid specific humidity, defined as the mass fraction of water vapor in a moist air mixture, at the start of simulation. If the value is a scalar, then the block assumes that the initial specific humidity is uniform. If the value is a two-element vector, then the block assumes that the initial specific humidity varies linearly between the ports, with the first element corresponding to port Ae and the second element corresponding to port Be.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air, clear the Initialize to nominal operating conditions check box, and set Initial moisture specification to Specific humidity.

Mole fraction of the water vapor in the evaporator external fluid at the start of simulation. If the value is a scalar, then the block assumes that the initial water vapor mole fraction is uniform. If the value is a two-element vector, then the block assumes that the initial water vapor mole fraction varies linearly between the ports, with the first element corresponding to port Ae and the second element corresponding to port Be.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air, clear the Initialize to nominal operating conditions check box, and set Initial moisture specification Mole fraction.

Evaporator external fluid humidity ratio, defined as the mass ratio of water vapor to dry air and trace gas, at the start of simulation. If the value is a scalar, then the block assumes that the initial humidity ratio is uniform. If the value is a two-element vector, then the block assumes that the initial humidity ratio varies linearly between the ports, with the first element corresponding to port Ae and the second element corresponding to port Be.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air, clear the Initialize to nominal operating conditions check box, and set Initial moisture specification Humidity ratio.

Wet-bulb temperature at the start of the simulation. The block uses this value to calculate moisture.

If the value is a scalar, then the block assumes that the initial wet-bulb temperature is uniform. If the value is a two-element vector, then the block assumes that the initial wet-bulb temperature varies linearly between the ports, with the first element corresponding to port Ae and the second element corresponding to port Be.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air, clear the Initialize to nominal operating conditions check box, and set Initial moisture specification to Wet-bulb temperature.

Method used to describe the trace gas level at the start of simulation.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air and clear the Initialize to nominal operating conditions check box.

Mass fraction of trace gas in a moist air mixture at the start of simulation. If the value is a scalar, then the block assumes that the initial mass fraction is uniform. If the value is a two-element vector, then the block assumes that the initial mass fraction varies linearly between the ports, with the first element corresponding to port Ae and the second element corresponding to port Be.

The block ignores this parameter if the Trace gas model parameter in the Moist Air Properties (MA) block is None.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air, clear the Initialize to nominal operating conditions check box, and set Initial trace gas specification to Mass fraction.

Mole fraction of the trace gas in a moist air mixture at the start of simulation. If the value is a scalar, then the block assumes that the initial mole fraction is uniform. If the value is a two-element vector, then the block assumes that the initial mole fraction varies linearly between the ports, with the first element corresponding to port Ae and the second element corresponding to port Be.

The block ignores this parameter if the Trace gas model parameter in the Moist Air Properties (MA) block is None.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air, clear the Initialize to nominal operating conditions check box, and set Initial trace gas specification to Mole fraction.

Heat transfer surface temperature at the start of simulation. If it this value is a scalar, the block assumes that the initial temperature is uniform. If this value is a two-element vector, then the block assumes that the temperature varies linearly between ports Ae and Be with the first element corresponding to Ae and second element corresponding to Be.

Dependencies

To enable this parameter, clear the Initialize to nominal operating conditions check box.

Relative humidity point of condensation. Condensation occurs above this value. In most cases, this value is 1, which is equivalent to 100%. A value greater than 1 indicates a supersaturated vapor.

Dependencies

To enable this parameter, set External fluid for evaporator heat transfer to Moist air and clear the Initialize to nominal operating conditions check box.

Correlation Coefficients

Whether to manually modify the condenser Nusselt number correlation coefficients. Select this parameter to adjust the off-design performance of the condenser.

Proportionality constant in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for a subcooled liquid for the condenser. The default value is based on the Colburn equation.

Dependencies

To enable this parameter, select Modify condenser Nusselt number correlation coefficients.

Proportionality constant in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for the liquid-vapor mixture for the condenser. The default value is based on the Cavallini and Zecchin correlation.

Dependencies

To enable this parameter, select Modify condenser Nusselt number correlation coefficients.

Proportionality constant in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for the superheated vapor for the condenser. The default value is based on the Colburn equation.

Dependencies

To enable this parameter, select Modify condenser Nusselt number correlation coefficients.

Reynolds number exponent in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for the condenser refrigerant. The same value applies to subcooled liquid, liquid-vapor mixture, and superheated vapor.

Dependencies

To enable this parameter, select Modify condenser Nusselt number correlation coefficients.

Prandtl number exponent in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for condenser refrigerant. The same value applies to subcooled liquid, liquid-vapor mixture, and superheated vapor.

Dependencies

To enable this parameter, select Modify condenser Nusselt number correlation coefficients.

Proportionality constant in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for the subcooled condenser external fluid. The default value is based on the Colburn equation.

Dependencies

To enable this parameter, select Modify condenser Nusselt number correlation coefficients and set External fluid for condenser heat transfer to Two-phase fluid.

Proportionality constant in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for liquid-vapor mixture in the condenser external fluid. The default value is based on the Cavallini and Zecchin correlation.

Dependencies

To enable this parameter, select Modify condenser Nusselt number correlation coefficients and set External fluid for condenser heat transfer to Two-phase fluid.

Proportionality constant in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for superheated vapor in the condenser external fluid. The default value is based on the Colburn equation.

Dependencies

To enable this parameter, select Modify condenser Nusselt number correlation coefficients and set External fluid for condenser heat transfer to Two-phase fluid.

Proportionality constant in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for the condenser external fluid. The default value is based on the Colburn equation.

Dependencies

To enable this parameter, select Modify condenser Nusselt number correlation coefficients and set External fluid for condenser heat transfer to Moist air or Thermal liquid.

Reynolds number exponent in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for the condenser external fluid. The default value is based on the Colburn equation.

Dependencies

To enable this parameter, select Modify condenser Nusselt number correlation coefficients.

Prandtl number exponent in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for the condenser external fluid. The default value is based on the Colburn equation.

Dependencies

To enable this parameter, select Modify condenser Nusselt number correlation coefficients.

Whether to manually modify the evaporator Nusselt number correlation coefficients. Select this parameter to adjust the off-design performance of the evaporator.

Proportionality constant in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for a subcooled liquid for the evaporator. The default value is based on the Colburn equation.

Dependencies

To enable this parameter, select Modify evaporator Nusselt number correlation coefficients.

Proportionality constant in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for the liquid-vapor mixture for the evaporator. The default value is based on the Cavallini and Zecchin correlation.

Dependencies

To enable this parameter, select Modify evaporator Nusselt number correlation coefficients.

Proportionality constant in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for the superheated vapor for the condenser. The default value is based on the Colburn equation.

Dependencies

To enable this parameter, select Modify evaporator Nusselt number correlation coefficients.

Reynolds number exponent in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for the evaporator refrigerant. The same value applies to subcooled liquid, liquid-vapor mixture, and superheated vapor.

Dependencies

To enable this parameter, select Modify evaporator Nusselt number correlation coefficients.

Prandtl number exponent in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for evaporator refrigerant. The same value applies to subcooled liquid, liquid-vapor mixture, and superheated vapor.

Dependencies

To enable this parameter, select External fluid for evaporator heat transfer.

Proportionality constant in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for the subcooled evaporator external fluid. The default value is based on the Colburn equation.

Dependencies

To enable this parameter, select Modify evaporator Nusselt number correlation coefficients and set External fluid for evaporator heat transfer to Two-phase fluid.

Proportionality constant in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for liquid-vapor mixture in the evaporator external fluid. The default value is based on the Cavallini and Zecchin correlation.

Dependencies

To enable this parameter, select Modify evaporator Nusselt number correlation coefficients and set External fluid for evaporator heat transfer to Two-phase fluid.

Proportionality constant in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for superheated vapor in the evaporator external fluid. The default value is based on the Colburn equation.

Dependencies

To enable this parameter, select Modify evaporator Nusselt number correlation coefficients and set External fluid for evaporator heat transfer to Two-phase fluid.

Proportionality constant in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for the evaporator external fluid. The default value is based on the Colburn equation.

Dependencies

To enable this parameter, select Modify evaporator Nusselt number correlation coefficients and set External fluid for evaporator heat transfer to Moist air or Thermal liquid.

Reynolds number exponent in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for the evaporator external fluid. The default value is based on the Colburn equation.

Dependencies

To enable this parameter, select Modify evaporator Nusselt number correlation coefficients.

Prandtl number exponent in the correlation of the Nusselt number as a function of the Reynolds number and Prandtl number for the evaporator external fluid. The default value is based on the Colburn equation.

Dependencies

To enable this parameter, select Modify evaporator Nusselt number correlation coefficients.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2023a

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