Examples of enthalpy-temperature conversion law (usthht.f90)

The usthht subroutine is used to encapsulate a simple enthalpy-temperature conversion law and its inverse.

Introduction

The usthht function allows one to define a simple enthalpy-temperature conversion law and its inverse. The parameters mode allows one to know in which direction the conversion will be made.

Examples

The following code blocks show two examples of entahlpy-temperature conversion law.

Example 1

The first example corresponds to a simple law :

 
! First example, corresponding to H = CpT with Cp = 4000
! ======================================================
 
! --- Mode H -> T
if (mode .eq.  1) then
  temper = enthal / 4000.d0
 
! --- Mode T -> H
else
  enthal = temper * 4000.d0
 
endif
 

Example 2

The second example corresponds to a simple interpolation based on a tabulation defined hereafter and declared as a variable :

 
! For the second example below,
!   input of ntab > 1 (fictitious) tabulated values of H (=HT)
!   as a function of NTAB values of T (=TH) (be careful with unit K or C)
 
integer          ntab
parameter(ntab=5)
double precision ht(ntab), th(ntab)
data             ht /100000.d0,200000.d0,300000.d0,               &
                               400000.d0,500000.d0 /
data             th /   100.d0,   200.d0,   300.d0,               &
                                  400.d0,   500.d0 /
 

The enthalpy-temperature conversion law is then defined :

 
! Second example, corresponding to a simple interpolation
! based on a tabulation H = f(T) entered as DATA
! ======================================================
 
! --- Mode H -> T
if (mode .eq.  1) then
 
  ! Default initialization
  temper = 0.d0
 
  ! If H is smaller than the smallest tabulated value,
  ! set T to smallest temperature.
  if (enthal.le.ht(1)) then
    temper = th(1)
 
  ! If H is larger than the largest tabulated value,
  ! set T to largest temperature.
  else if (enthal.ge.ht(ntab)) then
    temper = th(ntab)
 
  ! Otherwise, use piecewise linear interpolation
  else
    do it = 2, ntab
      if(enthal.le.ht(it)) then
        temper = th(it-1)                                         &
          +(enthal-ht(it-1))*(th(it)-th(it-1))/(ht(it)-ht(it-1))
      endif
    enddo
  endif
 
! --- Mode T -> H
else
 
  ! Default initialization
  enthal = 0.d0
 
  ! If T is smaller than the smallest tabulated value,
  ! set H to smallest enthalpy.
  if (temper.le.th(1)) then
    enthal = ht(1)
 
  ! If T is larger than the largest tabulated value,
  ! set H to largest enthalpy.
  else if (temper.ge.th(ntab)) then
    enthal = ht(ntab)
 
  ! Otherwise, use piecewise linear interpolation
  else
    do it = 2, ntab
      if(temper.le.th(it)) then
        enthal = ht(it-1)                                         &
          +(temper-th(it-1))*(ht(it)-ht(it-1))/(th(it)-th(it-1))
      endif
    enddo
  endif
endif