! Choosing sizes of a series of heat exchangers.
 We want to heat a cold stream through a series
 of heat exchangers, using some available hot
 streams, assigned one to each exchanger;
! Keywords: Process Industry, Petroleum Industry, Heat Exchanger;
  HX : AREA, U, TH, TC;
DATA: T0 = 100; ! Temperature of initial cold stream; TF = 500; ! Temp required of final output cold stream; U = 120 80 40; ! Heat transfer coefficient of exchanger; TH= 300 400 600; ! Temperature of hot streams; HFLO = 100000; ! Heat flow of cold stream in (BTU/degree)/hour; ENDDATA ! Decision variables: AREA(i) = area of exchanger i, TC(i)= temperature of the cold stream upon exit of exchanger i (and entry to i+1); NX = @SIZE(HX); ! Number of heat exchangers; ! Minimize total area; Min = @SUM(HX(i): AREA(i)); ! The input and output temperatures of the stream being heated are related to the areas by; HFLO*(TC(1) - T0) = U(1)*AREA(1)*(TH(1)-TC(1)); @FOR( HX(i)| i #GT# 1: HFLO*(TC(i) - TC(i-1)) = U(i)*AREA(i)*(TH(i)-TC(i)); ); ! Must meet final target temp; TC(NX) = TF;