program heat_exchanger_lmtd implicit none double precision :: T_hi, T_ho, T_ci, T_co double precision :: m_h, m_c, Cp_h, Cp_c double precision :: U, A_req double precision :: Q_h, Q_c, Q double precision :: dT1, dT2, LMTD_pf, LMTD_cf double precision :: LMTD_used double precision :: C_h, C_c, C_min, C_max, C_r double precision :: eff double precision :: NTU integer :: config integer :: i character(len=20) :: config_name ! Read inputs read(*,*) config ! 1=parallel flow, 2=counter flow read(*,*) T_hi ! Hot fluid inlet temp [C] read(*,*) T_ho ! Hot fluid outlet temp [C] read(*,*) T_ci ! Cold fluid inlet temp [C] read(*,*) T_co ! Cold fluid outlet temp [C] read(*,*) m_h ! Hot fluid mass flow rate [kg/s] read(*,*) m_c ! Cold fluid mass flow rate [kg/s] read(*,*) Cp_h ! Hot fluid specific heat [J/kg.K] read(*,*) Cp_c ! Cold fluid specific heat [J/kg.K] read(*,*) U ! Overall heat transfer coefficient [W/m2.K] ! Configuration name if (config == 1) then config_name = 'Parallel Flow' else config_name = 'Counter Flow' end if ! Heat capacity rates C_h = m_h * Cp_h C_c = m_c * Cp_c if (C_h < C_c) then C_min = C_h C_max = C_c else C_min = C_c C_max = C_h end if C_r = C_min / C_max ! Heat transfer rates Q_h = C_h * (T_hi - T_ho) Q_c = C_c * (T_co - T_ci) Q = (Q_h + Q_c) / 2.0d0 ! ============================================ ! LMTD CALCULATION ! ============================================ ! Parallel flow LMTD dT1 = T_hi - T_ci dT2 = T_ho - T_co if (abs(dT1 - dT2) < 1.0d-6) then LMTD_pf = dT1 else if (dT1 > 0 .and. dT2 > 0) then LMTD_pf = (dT1 - dT2) / log(dT1 / dT2) else LMTD_pf = 0.0d0 end if ! Counter flow LMTD dT1 = T_hi - T_co dT2 = T_ho - T_ci if (abs(dT1 - dT2) < 1.0d-6) then LMTD_cf = dT1 else if (dT1 > 0 .and. dT2 > 0) then LMTD_cf = (dT1 - dT2) / log(dT1 / dT2) else LMTD_cf = 0.0d0 end if ! Select LMTD based on configuration if (config == 1) then LMTD_used = LMTD_pf else LMTD_used = LMTD_cf end if ! Required area if (LMTD_used > 0 .and. U > 0) then A_req = Q / (U * LMTD_used) else A_req = 0.0d0 end if ! Effectiveness if (C_min * (T_hi - T_ci) > 0) then eff = Q / (C_min * (T_hi - T_ci)) else eff = 0.0d0 end if ! NTU if (C_min > 0 .and. A_req > 0) then NTU = U * A_req / C_min else NTU = 0.0d0 end if ! ============================================ ! OUTPUT ! ============================================ write(*,'(A)') '=============================================================' write(*,'(A)') ' HEAT EXCHANGER ANALYSIS - LMTD METHOD' write(*,'(A)') '=============================================================' write(*,*) write(*,'(A)') '--- CONFIGURATION -------------------------------------------' write(*,'(A,A)') ' Flow Arrangement = ', trim(config_name) write(*,*) write(*,'(A)') '--- INPUT PARAMETERS ----------------------------------------' write(*,'(A)') ' Hot Fluid:' write(*,'(A,F12.2,A)') ' Inlet Temperature = ', T_hi, ' C' write(*,'(A,F12.2,A)') ' Outlet Temperature = ', T_ho, ' C' write(*,'(A,F12.4,A)') ' Mass Flow Rate = ', m_h, ' kg/s' write(*,'(A,F12.2,A)') ' Specific Heat = ', Cp_h, ' J/kg.K' write(*,*) write(*,'(A)') ' Cold Fluid:' write(*,'(A,F12.2,A)') ' Inlet Temperature = ', T_ci, ' C' write(*,'(A,F12.2,A)') ' Outlet Temperature = ', T_co, ' C' write(*,'(A,F12.4,A)') ' Mass Flow Rate = ', m_c, ' kg/s' write(*,'(A,F12.2,A)') ' Specific Heat = ', Cp_c, ' J/kg.K' write(*,*) write(*,'(A,F12.2,A)') ' Overall U = ', U, ' W/m2.K' write(*,*) write(*,'(A)') '--- HEAT CAPACITY RATES -------------------------------------' write(*,'(A,F12.4,A)') ' C_hot = m_h x Cp_h = ', C_h, ' W/K' write(*,'(A,F12.4,A)') ' C_cold = m_c x Cp_c = ', C_c, ' W/K' write(*,'(A,F12.4,A)') ' C_min = ', C_min, ' W/K' write(*,'(A,F12.4,A)') ' C_max = ', C_max, ' W/K' write(*,'(A,F12.4)') ' C_r = C_min/C_max = ', C_r write(*,*) write(*,'(A)') '--- ENERGY BALANCE ------------------------------------------' write(*,'(A,F12.4,A)') ' Q_hot = C_h(T_hi-T_ho)= ', Q_h, ' W' write(*,'(A,F12.4,A)') ' Q_cold = C_c(T_co-T_ci)= ', Q_c, ' W' write(*,'(A,F12.4,A)') ' Q (average) = ', Q, ' W' write(*,'(A,F12.4,A)') ' Energy Balance Error = ', & abs(Q_h-Q_c)/max(Q_h,1.0d-10)*100, ' %' write(*,*) write(*,'(A)') '--- LMTD RESULTS --------------------------------------------' write(*,'(A,F12.4,A)') ' LMTD (parallel flow) = ', LMTD_pf, ' deg-C' write(*,'(A,F12.4,A)') ' LMTD (counter flow) = ', LMTD_cf, ' deg-C' write(*,'(A,F12.4,A)') ' LMTD (used) = ', LMTD_used, ' deg-C' write(*,*) write(*,'(A)') '--- DESIGN RESULTS ------------------------------------------' write(*,'(A,F12.4,A)') ' Required Area (A) = ', A_req, ' m2' write(*,'(A,F12.4)') ' NTU = UA/C_min = ', NTU write(*,'(A,F12.4,A)') ' Effectiveness (e) = ', eff*100, ' %' write(*,*) ! Temperature profiles for chart write(*,'(A)') '--- TEMPERATURE PROFILE ALONG EXCHANGER --------------------' write(*,'(A)') ' Position % T_hot [C] T_cold [C]' write(*,'(A)') ' --------------------------------------------------' do i = 0, 20 if (config == 1) then ! Parallel flow: both fluids travel same direction write(*,'(F10.1,4X,F10.2,4X,F10.2)') dble(i)/20.0d0*100, & T_hi - (T_hi - T_ho) * dble(i)/20.0d0, & T_ci + (T_co - T_ci) * dble(i)/20.0d0 else ! Counter flow: cold fluid travels opposite direction write(*,'(F10.1,4X,F10.2,4X,F10.2)') dble(i)/20.0d0*100, & T_hi - (T_hi - T_ho) * dble(i)/20.0d0, & T_co - (T_co - T_ci) * dble(i)/20.0d0 end if end do write(*,*) write(*,'(A)') '--- FORMULAS USED -------------------------------------------' write(*,'(A)') ' Q = U x A x LMTD' write(*,'(A)') ' LMTD = (DT1 - DT2) / ln(DT1/DT2)' write(*,'(A)') ' Effectiveness = Q / Q_max = Q / (C_min x (T_hi - T_ci))' write(*,'(A)') ' NTU = U x A / C_min' end program heat_exchanger_lmtd