function tgh = hotsim(var,twh,qrloss)
% evaluate heater average heat transfer performance
% Israel Urieli, 7/22/2002
% Modified 2/6/2010 to include regenerator qrloss
% Arguments:
%   var(22,37) array of variable values every 10 degrees (0 - 360)
%   twh - heater wall temperature [K]
%   qrloss - heat loss due to imperfect regenerator [J]
% Returned values: 
%   tgh - heater average gas temperature [K]

% Row indices of the var, array:
 TC = 1;  % Compression space temperature (K)
 TE = 2;  % Expansion space temperature (K)
 QK = 3;  % Heat transferred to the cooler (J)
 QR = 4;  % Heat transferred to the regenerator (J)
 QH = 5;  % Heat transferred to the heater (J)
 WC = 6;  % Work done by the compression space (J)
 WE = 7;  % Work done by the expansion space (J)
 W  = 8;  % Total work done (WC + WE) (J)
 P  = 9;  % Pressure (Pa)
 VC = 10; % Compression space volume (m^3)
 VE = 11; % Expansion space volume (m^3)
 MC = 12; % Mass of gas in the compression space (kg)
 MK = 13; % Mass of gas in the cooler (kg)
 MR = 14; % Mass of gas in the regenerator (kg)
 MH = 15; % Mass of gas in the heater (kg)
 ME = 16; % Mass of gas in the expansion space (kg)
 TCK = 17; % Conditional temperature compression space / cooler (K)
 THE = 18; % Conditional temeprature heater / expansion space (K)
 GACK = 19; % Conditional mass flow compression space / cooler (kg/rad)
 GAKR = 20; % Conditional mass flow cooler / regenerator (kg/rad)
 GARH = 21; % Conditional mass flow regenerator / heater (kg/rad)
 GAHE = 22; % Conditional mass flow heater / expansion space (kg/rad)

global th % heater temperature [K]
global freq omega % cycle frequency [herz], [rads/s]
global ah % heater internal free flow area [m^2]
global awgh % heater internal wetted area [m^2]
global dh % heater hydraulic diameter [m]

% Calculating the Reynolds number over the cycle
for(i = 1:1:37)
      gah(i) = (var(GARH,i) + var(GAHE,i))*omega/2;
      gh = gah(i)/ah;
      [mu,kgas,re(i)] = reynum(th,gh,dh);
end

% Average and maximum Reynolds number
sumre=0;
remax=re(1);
for (i=1:1:36)
      sumre=sumre + re(i);
      if (re(i) > remax)
            remax = re(i);
      end
end
reavg = sumre/36;

[ht,fr] = pipefr(dh,mu,reavg); % Heat transfer coefficient
tgh = twh - (var(QH,37)+qrloss)*freq/(ht*awgh); % Heater gas temperature [K]

fprintf('============ Heater Simple analysis =============\n')
fprintf(' Average Reynolds number : %.1f\n',reavg)
fprintf(' Maximum Reynolds number : %.1f\n',remax)
fprintf(' Heat transfer coefficient [W/m^2*K] : %.2f\n',ht)
fprintf('heater wall/gas temperatures: Twh = %.1f[K], Tgh = %.1f[K]\n',twh,tgh);