How to make goal seek with 3 unknown varible that interconnected each other?

3 次查看（过去 30 天）
Muhammad Rizki Nasution
Hai, i want to search the output of Tb_of and Tb_hf in every iteration, but we just know both of the input value and the input value had a different enter region. to search that value in excel i have 3 stopping criteria, the first one is when absolute value of deltaTb_of is no more than 10^-5, second is when the value of Tb_hf iteration comes to more than input value of Tb_hf, and the third is when the last iteration value of Tb_hf more or less 10^-5 from Tb_hf input value or absolute deltaTB_hf is no more than 10^-5. as far as i wrote the code, i have some problem, the bigger problem is guessing value and iteration of Tb_hf never come to a convergence value so iteration for delta Tb_of and delta Tb_hf never reach the condition.
here is my calculation sheet in excel
and here is my iteration code now
while abs(deltaTb_hf)>=10^-5 %Stopping criterion of calculation
Tb_of_0=Tin_of; %Declare initial bulk temperature of organic fluid is equal to inlet temperature of organic fluid
DB(1,1)=L0; %Record value of initial length
DB(1,3)=Tb_of_0; %Record value of inlet temperature of organic refrigerant
DB(1,7)=(refpropm('H','T',(Tin_of+273.15),'P',pressure.*1000,refrigerant))/1000; %Record value of initial enthalpy of organic fluid
i=1; %Iteration 0
Tb_hf_0= Tb_hf_0+deltaTb_hf; %Iteration for outlet bulk temperature of hot fluid
DB(1,17)=Tb_hf_0; %Record value of outlet temperature of hot fluid
i=2; %Re-declare calculation
Tb_hf_i=Tb_hf_0+deltaTb_hf; %Declare bulk temperature of hot fluid for start column iteration
while Tb_hf_i<=Tin_hf %Column iteration
Lnew=Lnew+Delta_L; %Total Length
deltaTb_of=1; %Starting criteria to enter row iteration
Tb_of_i=DB((i-1),3)+deltaTb_of; %Starting criteria to enter row iteration
if i==2
cp_hf_i=1.8363+(0.00392.*Tb_hf_i)-((1.5.*(10^-6)).*(Tb_hf_i^2)); %Starting heat capacity at constant pressure of hot fluid to enter row iteration
end
while absolute(deltaTb_of) >= 10^-5 %Row iteration
Tb_of_i=Tb_of_i+(deltaTb_of/2); %Correction for bulk temperature of organic fluid
Tf_of_i=273.15+((DB((i-1),3)+Tb_of_i)/2); %Calculate film temperature of organic fluid in a segment in K
h_of_i=(refpropm('H','T',(Tb_of_i+273.15),'P',pressure.*1000,refrigerant))/1000; %Enthalpy of organic fluid in a segment
Qdot_i=mdot_of.*(h_of_i-DB((i-1),7)); %Heat rate generate from organic fluid
Tb_hf_i=Tb_hf_i+(Qdot_i/(cp_hf_i.*mdot_hf)); %Bulk temperature of hot fluid in a segment
Tf_hf_i=(DB((i-1),17)+Tb_hf_i)/2; %Calculate film temperature of hot fluid in a segment in oC
%Physical properties of organic fluid from REFPROP
rho_of_i=refpropm('D','T',Tf_of_i,'P',pressure.*1000,refrigerant); %Density of organic fluid in a segment
k_of_i=refpropm('L','T',Tf_of_i,'P',pressure.*1000,refrigerant).*1000; %Thermal conductivity of organic fluid in a segment
nu_of_i=refpropm('$','T',Tf_of_i,'P',pressure.*1000,refrigerant); %Kinematic viscosity of organic fluid in a segment
Pr_of_i=refpropm('^','T',Tf_of_i,'P',pressure.*1000,refrigerant); %Prandtl number of organic fluid in a segment
%Physiscal properties of hot fluid from formulae
cp_hf_i=1.8363+(0.00392.*Tf_hf_i)-((1.5.*(10^-6)).*(Tf_hf_i^2)); %heat capacity at constant pressure of hot fluid in a segment
rho_hf_i=870.297-(0.684497.*Tf_hf_i)+(5.18441*(10^-5).*(Tf_hf_i^2))-(1.0695.*(10^-6).*(Tf_hf_i^3)); %Density of hot fluid in a segment
k_hf_i=0.1265-(0.000123.*Tf_hf_i)-(9.161.*(10^-8).*(Tf_hf_i^2)); %Thermal conductivity of hot fluid in a segment
nu_hf_i=exp((645.13/(Tf_hf_i+117.8))-2.662); %Kinematic viscosity of hot fluid in a segment
%Calculation for organic fluid parameter
vm_of_i=mdot_of/(rho_of_i.*A_ft); %Mean velocity of organic fluid in a segment
Re_of_i=(vm_of_i.*di.*10^4)/nu_of_i; %Reynold number of organic fluid in a segment
Nu_db_of_i=0.023.*(Re_of_i^0.8).*(Pr_of_i^0.4); %Nusselt number based on Dittus-Boelter of organic fluid in a segment
hc_of_i=(Nu_db_of_i.*k_of_i.*(10^-3))/di; %Heat transfer coefficient of convection of organic fluid in a segment
%Calculation for hot fluid parameter
vm_hf_i=mdot_hf/(A_an.*rho_hf_i); %Mean velocity of hot fluid in a segment
Re_hf_i=(vm_hf_i.*((Di+do)/2)/nu_hf_i).*(10^6); %Reynold number of hot fluid in a segment
alfa_hf_i=(k_hf_i/(rho_hf_i.*cp_hf_i.*(10^3))).*(10^6); %Thermal diffusivity of hot fluid in a segment
Pr_hf_i=nu_hf_i/alfa_hf_i; %Prandtl number of hot fluid in a segment
Nu_db_hf_i=0.023.*(Re_hf_i^0.8).*(Pr_hf_i^0.4); %Nusselt number based on Dittus-Boelter of hot fluid in a segment
hc_hf_i=(Nu_db_hf_i.*k_hf_i)/((Di+do)/2); %Heat transfer coefficient of convection of hot fluid in a segment
%Calculation for heat transfer between both fluids
Ln_T_i=log((DB((i-1),17)-DB((i-1),3))/(Tb_hf_i-Tb_of_i)); %Natural logarithmic bulk temperature in a segment
UAs_i=1/((1/(hc_of_i.*A_si_i))+(1/(hc_hf_i.*A_so_i))+((log(do/di))/(2.*pi.*k.*Delta_L))); %Overall heat transfer coefficient in a cylinder
%Check error
Tb_of_pivot_i=DB((i-1),3)+(Tb_hf_i-DB((i-1),17))+(((10^3).*Qdot_i/UAs_i).*Ln_T_i); %The first guess bulk temeperature of organic fluid in a segment that synchronize with bulk temperature of hot fluid in a segment
deltaTb_of=Tb_of_i-Tb_of_pivot_i; %Convergence check for bulk temperature of organic fluid in a segment
if abs(deltaTb_of) <= 10^-5
%Moving data
DB(i,1)=Lnew; %Length to column 1
DB(i,3)=Tb_of_i; %Bulk temperature of organic fluid to column 3
DB(i,4)=Tf_of_i; %Film temperature of organic fluid to column 4
DB(i,5)=rho_of_i; %Density of organic fluid to column 5
DB(i,6)=nu_of_i; %Kinematic viscosity of organic fluid to column 6
DB(i,7)=h_of_i; %Enthalpy of organic fluid to column 7
DB(i,8)=k_of_i; %Thermal conductivity of organic fluid to column 8
DB(i,9)=Pr_of_i; %Prandtl number of organic fluid to column 9
DB(i,10)=vm_of_i; %Mean temperature of organic fluid to column 10
DB(i,11)=Re_of_i; %Reynold number of organic fluid to column 11
DB(i,12)=Nu_db_of_i; %Nusselt number of organic fluid to column 12
DB(i,13)=hc_of_i; %Heat transfer coefficient of convection of organic fluid to column 13
DB(i,15)=Qdot_i; %Heat rate generate from organic fluid to column 15
DB(i,17)=Tb_hf_i; %Bulk temperature of hot fluid to column 17
DB(i,18)=Tf_hf_i; %Film temperature of hot fluid to column 18
DB(i,19)=cp_hf_i; %Heat capacity of hot fluid to column 19
DB(i,20)=rho_hf_i; %Density of hot fluid to column 20
DB(i,21)=nu_hf_i; %Kinematic viscosity of hot fluid to column 21
DB(i,22)=k_hf_i; %Thermal conductivity of hot fluid to column 22
DB(i,23)=alfa_hf_i; %Thermal diffusivity of hot fluid to column 23
DB(i,24)=Pr_hf_i; %Prandtl number of hot fluid to column 24
DB(i,25)=vm_hf_i; %Mean temperature of hot fluid to column 25
DB(i,26)=Re_hf_i; %Reynold number of hot fluid to column 26
DB(i,27)=Nu_db_hf_i; %Nusselt number of hot fluid to column 27
DB(i,28)=hc_hf_i; %Heat transfer coefficient of convection of hot fluid to column 28
DB(i,30)=UAs_i; %Overall heat transfer coefficient in a cylinder to column 30
DB(i,31)=Ln_T_i; %Natural logarithmic bulk temperature to column 31
DB(i,33)=deltaTb_of; %Error checking in row iteration to column 33
end
end
i=i+1; %New row iteration
Tb_hf_i=DB((i-1),17); %Stopping criteria for column iteration
end
deltaTb_hf=(Tin_hf-Tb_hf_i)/2; %stopping criteria
if abs(deltaTb_hf)>=10^-5
Lnew=0;
end
end

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