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custom phase changing material does not release heat.

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Berkay Paksoy
Berkay Paksoy 2023-10-26
回答： Shishir Reddy 2024-8-23，6:46
Problem:
When I adjust the latent heat, there's no change in the temperature curve of the XPS material. I anticipate a stable temperature, ranging between 305K and 320K. So the problem is that the material does not release the absorbed heat.
equations
assert(Cps > 0 && Cpl > 0)
assert(T > 0, 'Temperature must be greater than absolute zero')
T == M.T;
if T >= Tmelt_start && T <= Tmelt_end
phaseChangeRate == {0.001, '1/s'};
else
phaseChangeRate == {0, '1/s'};
end
if phase < 1 && phase > 0
Q == m * Cps * T.der + m * L * phaseChangeRate;
phase.der == phaseChangeRate;
else
Q == m * Cpl * T.der;
phase.der == {0, '1/s'};
end
end
explanation of the full code:
This code describes a thermal component that models internal energy storage in a thermal network. Here's a breakdown of the main parts of this code:
1. **Nodes**: These are points where other components can connect. Two thermal nodes are defined: `M` (top) and `N` (bottom).
2. **Inputs**: These values can be supplied from outside. `Mdot` represents the mass flow rate (in kg/s) and `T_in` is the input temperature (in Kelvin).
3. **Parameters**: These values determine the behavior of the component. They include:
- `mass_type`: Type of mass (constant or variable).
- `mass`: The mass of the thermal component.
- `Cps` and `Cpl`: Specific heat capacity for solid and liquid, respectively.
- `Tmelt_start` and `Tmelt_end`: The temperature range where the material starts melting and stops melting.
- `L`: Specific latent heat.
- `mass_min`: Minimum mass.
- `num_ports`: The number of graphical ports.
4. **Annotations**: These are metadata that provide additional information about the component or dictate how it is displayed in a GUI. Here, it is primarily used to indicate which parameters can be modified externally and to define the component's icon.
5. **Variables**: These represent the internal states of the component. They include:
- `m`: The mass.
- `T`: The temperature.
- `phase`: The phase (0 for solid, 1 for liquid, and values in between for a mixed phase).
- `phaseChangeRate`: The rate of phase change.
- `Q`: Heat flow rate.
6. **Branches**: These are connections between different parts of the network. Here, the heat flow `Q` from node `M` to another part of the network is defined.
7. **Equations**: These describe the mathematical relationships between the different variables and parameters. They include:
- Relationships between `T`, `Q`, `m`, and other variables, especially around phase change.
- Constraints on certain values (like that `Cps`, `Cpl`, and `T` must be positive).
8. **Connections**: These are the actual connections between the different nodes within the component. Here, node `M` is connected to node `N`.
The essence of this component is that it models a thermal mass that can store and release energy. It also accounts for phase changes, meaning it can melt or solidify within a certain temperature range.
component derdecomponent
% Thermal Mass
% This block models internal energy storage in a thermal network.
nodes
M = foundation.thermal.thermal; % :top
end
inputs(ExternalAccess = none)
Mdot = {0, 'kg/s'}; % Mdot:bottom
T_in = {300, 'K'}; % Tin:bottom
end
nodes(ExternalAccess = none)
N = foundation.thermal.thermal; % :bottom
end
parameters
mass_type = foundation.enum.constant_variable.constant; % Mass type
end
parameters (ExternalAccess = none)
mass = {1, 'kg'}; % Mass
end
parameters
Cps = {200, 'J/(kg*K)'}; % Specific heat solid
Cpl = {1000, 'J/(kg*K)'}; % Specific heat liquid
Tmelt_start = {320, 'K'}; % Start Melting Temperature
Tmelt_end = {305, 'K'}; % End Melting Temperature
L = {100, 'J/(kg)'}; % Specific Latent Heat
end
parameters (ExternalAccess = none)
mass_min = {1e-6,'kg'}; % Minimum mass
end
parameters
num_ports = foundation.enum.numPorts2.one; % Number of graphical ports
end
if num_ports == 2
annotations
N : ExternalAccess=modify
end
if mass_type == foundation.enum.constant_variable.constant
annotations
% Icon = 'mass2.svg'
end
else
annotations
% Icon = 'mass4.svg'
end
end
else
if mass_type == foundation.enum.constant_variable.variable
annotations
% Icon = 'mass3.svg'
end
end
end
if mass_type == foundation.enum.constant_variable.constant
annotations
mass : ExternalAccess=modify
end
equations
m == {1,'kg'};
end
else
annotations
[Mdot, T_in, m, mass_min] : ExternalAccess=modify
end
equations
assert(mass_min > 0)
end
end
variables (ExternalAccess=none)
m = {value = {1,'kg'}, priority=priority.high}; % Mass
end
variables
T = {value = {300, 'K'}, priority = priority.high}; % Temperature
phase = {value = {0, '1'}, priority = priority.high}; % Phase
phaseChangeRate = {0, '1/s'}; % Rate of phase change
end
variables (Access=private)
Q = {0, 'W'}; % Heat flow rate
end
branches
Q : M.Q -> *;
end
equations
assert(Cps > 0 && Cpl > 0)
assert(T > 0, 'Temperature must be greater than absolute zero')
T == M.T;
if T >= Tmelt_start && T <= Tmelt_end
phaseChangeRate == {0.001, '1/s'};
else
phaseChangeRate == {0, '1/s'};
end
if phase < 1 && phase > 0
Q == m * Cps * T.der + m * L * phaseChangeRate;
phase.der == phaseChangeRate;
else
Q == m * Cpl * T.der;
phase.der == {0, '1/s'};
end
end
connections
connect(M,N)
end
end

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回答（1 个）

Shishir Reddy
Shishir Reddy 2024-8-23，6:46
Hi Berkay
The issue seems to be related to the logic in the phase change model.
‘Tmelt_start’ has been set to 320K and ‘Tmelt_end’is set to 305K. This is inverted, typically the melting process starts at a lower temperature and ends at high temperature. So, the values must be swapped.
Tmelt_start = {305, 'K'};
Tmelt_end = {320, 'K'};
In calculating ‘’phaseChangeRate‘ - (T >= Tmelt_start && T <= Tmelt_end)’ – This condition only checks if the temperature T is within the range where phase change can occur. But it should also be ensured that ‘phaseChangeRate’ should be applied only when the material is neither fully solid (phase == 0) nor fully liquid (phase == 1).
For example, consider a material that starts melting at 305 K and finishes at 320 K. If the temperature is 310 K, it is within the range, but if ‘phase’== 0’ or ‘phase == 1’, the material is not currently undergoing a phase change. Conversely, if ‘phase’ is between 0 and 1 but the temperature is outside 305-320 K, the phase change should not be active.
So, the code should be modified as follows.
if T >= Tmelt_start && T <= Tmelt_end && phase < 1 && phase > 0
phaseChangeRate == {0.001, '1/s'};
else
phaseChangeRate == {0, '1/s'};
end
I hope this helps.

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