MATLAB: For loop or if condition

for loopheatingif statementthermostat

Hi,

I solved system of differential equations that present temperature values in two rooms. Now, I want to apply thermostat control which is active if temperature drops below 18 or go above 20 degrees. Is this loop correct?

for i=1:t t(i)=84600; if(T(i)>=18 && T(i)<=20) go else stop end end

Or is better to use if statement?

Thanks in advance!

Best Answer

First of all, this is not a correctly asked question.

Put your code in a correct format and be of a more explanatory nature.

While you mention 'OR' in your question , the code contains '&&' which stands for "AND".

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MATLAB: How can get the value for each time step for a variable inside of a function

Hi,

you try this code (all in one file as nested function). The values you want to have in every iteration are now added to the solution and also saved in the results table. This should be what you want.

Result = main
function Result = main
%Initial conditions
Wads=0.045;
Tads=80;
Wdes=0.035;
Tdes=27;
Teva=7;
Tcond=27;
Mweva=0.65;         
Initial=[Wads Tads Wdes Tdes Mweva Teva Tcond 0 0 0 0];           
tspan=[1:1:800];
opts = odeset('RelTol',1e-6,'AbsTol',1e-6);
[t,Soln]=ode45(@(t,Soln)ODEdw(t,Soln),tspan,Initial,opts);
colNames = {'Time','Wads','Tads','Wdes','Tdes','Mweva', 'Teva','Tcond',...
    'Tcwaout', 'Thwdout', 'Tchwout', 'Tcwcout'};
Result = array2table([tspan',Soln],'VariableNames',colNames);
function [dYdt] =ODEdw(~,Soln)
Ea=4.2*10^4;         %Activation energy of surface diffusion, (J/mol)
R=8.314;             %Ideal gas constant, (j/mol.K)
Dso=2.54*10^-4;       %Pre-exponential constant, (m^2 S^-1)
Qs=2.8*10^6;         %Heat of adsorption, (J/kg)
%%%%%%%%%%%Operating conditions%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Thwdin=85;            %Inlet temperature of hot water in desorber, (oC)
Tcwain=27;            %Inlet temperature of cooling water in adsorber, (oC)
Tcwcin=27;            %Inlet temperature of cooling water in condenser, (oC)
Tchwin=14;            %Inlet temperature of chilling water in evaporator, (oC)
mcwa=8/60;            %Mass flow rate of cooling water in adsorber, (kg/s)
mcwc=20/60;           %Mass flow rate of cooling water in condenser, (kg/s)
mchw=1.6/60;          %Mass flow rate of chilling water in evaporator, (kg/s)
mhwd=7/60;            %Mass flow rate of hot water in desorber, (kg/s)
%%%%%%%%%Physical and thermal properties of adsorbent%%%%%%%%%%
Cps=924;              %Specific heat capacity of silica gel, (J/kg.K)
Ms=9;                 %Mass of silica, (kg)
Rp=5.6*10^-4;         %Radious of silica gel particle, (m)
ps=700;              %density of silica gel, (kg/m^3)
Por=0.3;              %Porosity of silica gel,
%%%%%%Physical and thermal properties of adsorbate%%%%%%%%%%%%%
Cpw=4200;             %Specific heat capcity of water, (J/kg.k)
Cpv=1900;             %Specific heat capacity of water vapor (J/kg.K)
M=18.02;              %Molar mass of water, (g/mol)
Lv=2500*10^3;         %Lantent heat of vaporization (J/kg) 
%%%%%%%%%Physical and thermal Properties of Condenser%%%%%%%%%%%%%
Acond=5.76;            %Surface area of condenser, (m^2)
Mhexcond=19.87;        %Mass of heat exchanger (Condenser), (kg)
Ucond=486.87;          %Heat transfer coefficient of condenser, (W/m^2.K)
UAcond=Acond*Ucond;
Mwcond=1.0;         %Mass of water in Condenser (kg)
%%%%%%%%%%Physical and thermal properties of adsorber/desorber   %%%%%%%
Mhex=65;             %Mass of heat exchanger (Adsorber/desorber), (kg)
Cphex=386;           %Heat capacity of heat excahgner, (J/kg.K)
Aad=2.11;            %Surface area of adsorber/desorber, (m^2)
Uads=189.60;         %Heat transfer coefficient of adsorber, (W/m^2.K)
Udes=203.99;         %Heat transfer coefficient of desorber, (W/m^2.K)
UAads=Aad*Uads;
UAdes=Aad*Udes;
Vt=0.5;              %volume of adsorber/desorber tank, (m^3)
%%%%%%%%%Physical and thermal Properties of Evaporator%%%%%%%%%%%%%%
Aeva=0.34;           %Surface area of evaporator, (m^2)
Mhexeva=16.1;        %Mass of heat exchanger (Evaporator), (kg)
Ueva=302.58;         %Heat transfer coefficient of evaporator, (W/m^2.K)
UAeva=Aeva*Ueva;
Wads=Soln(1);    
Tads=Soln(2);  
Wdes=Soln(3);    
Tdes=Soln(4);
Mweva=Soln(5);
Teva=Soln(6);
Tcond=Soln(7);
Kads=((15*Dso)/(Rp).^2)*exp(-Ea/(R*(Tads+273.16)));   %Overall mass tarsnfer coeffcient of adsorber

Pwa=133.32*exp(18.3-(3820/((Teva+273.16)-46.1))); % Saturated vapour pressure of waterm (vapour) at adsorbent temperature, (Pa)

Psga=133.32*exp(18.3-(3820/((Tads+273.16)-46.1))); % Saturated vapour pressure of water at adsorbent temperature, (Pa)

Weqa=0.346*(Pwa/Psga)^0.625;
Aads=(Kads*(Weqa-Wads));
TLads=(Ms*(Cpw+Cpw*Wads)+Mhex*Cphex); %Left hand side of adsorber equation
Tcwaout=Tads+(Tcwain-Tads)*exp((-UAads)/(mcwa*Cpw));
   
Kdes=((15*Dso)/(Rp).^2)*exp(-Ea/(R*(Tdes+273.16)));   %Overall mass tarsnfer coeffcient of adsorber
Pwd=133.32*exp(18.3-(3820/((Tcond+273.16)-46.1))); % Saturated vapour pressure of waterm (vapour) at adsorbent temperature, (Pa)
Psgd=133.32*exp(18.3-(3820/((Tdes+273.16)-46.1))); % Saturated vapour pressure of water at adsorbent temperature, (Pa)
Weqd=0.346*(Pwd/Psgd)^0.625;
Ades=(Kdes*(Weqd-Wdes));
TLdes=(Ms*(Cps+Cpw*Wdes)+Mhex*Cphex); %Left hand side of desorber equation
Thwdout=Tdes+(Thwdin-Tdes)*exp((-UAdes)/(mhwd*Cpw));
  
TLeva=(Mweva*Cpw+Mhexeva*Cphex); %Left hand side of evaporator equation

Tchwout=Teva+(Tchwin-Teva)*exp((-UAeva)/(mchw*Cpw));
  
TLcond=(Mwcond*Cpw+Mhexcond*Cphex); %Left hand side of evaporator equation
Tcwcout=Tcond+(Tcwcin-Tcond)*exp((-UAcond)/(mcwc*Cpw));
dYdt=[Kads*(Weqa-Wads);((Qs*Ms*Aads)+(Ms*Cpv*Aads*(Teva-Tads))+mcwa*Cpw*(Tcwain-Tcwaout))/TLads;
    Kdes*(Weqd-Wdes); ((Qs*Ms*Ades)+(mcwa*Cpw*(Thwdin-Thwdout)))/TLdes; 
    -Ms*((Kads*(Weqa-Wads))+(Kdes*(Weqd-Wdes)));((-Lv*Ms*Aads)+Ades*Ms*Cpw*(Tcond-Teva)+mchw*Cpw*(Tchwin-Tchwout))/TLeva;
    (Ades*Ms*Cpv*(Tdes-Tcond)+(Lv*Ms*Ades)+mcwc*Cpw*(Tcwcin-Tcwcout))/TLcond; Tcwaout; Thwdout; Tchwout; Tcwcout];
end
end

Best regards

Stephan

MATLAB: Nested functions procedure error

I am going to guess that you have missed out on telling us that your heat_sys function is being invoked by ode45 or similar. I am going to further guess that heat_sys is your main function, and that your thermostat function is needed to calculate non-linear constraints. If I am correct, then a handle to your thermostat function would need to be passed as an additional parameter to the ode call, and it would also have to be modified to return information for both equality constraints and inequality constraints (I cannot tell which you intend in your existing code.)

If I am correct so far, please have another look at the documentation for the ode function you are using.

Best Answer

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