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Thermal Entry Length Calculator
Core Numerical Engine in Fortran 90 • 25 total downloads
entry_length.f90
! =========================================================================
! Source File: entry_length.f90
! =========================================================================
program entry_length
implicit none
double precision :: D, V, Ti, Tw, Lp, rho, mu, kf, Pr, cp, bc_val
integer :: fl_type, bc_type
double precision :: Tf, dT, nu, Re, Gz, Lh, Lt, Nufd, Nud, h, As, Q, To, g, f, pi
integer :: iostat_val, i
double precision :: temp_val(6)
double precision :: xs, Gzs, Nuds, hs
pi = 3.141592653589793d0
! Read inputs sequentially
read(*,*,iostat=iostat_val) D
read(*,*,iostat=iostat_val) V
read(*,*,iostat=iostat_val) Ti
read(*,*,iostat=iostat_val) Tw
read(*,*,iostat=iostat_val) Lp
read(*,*,iostat=iostat_val) fl_type
! Read custom parameters
read(*,*,iostat=iostat_val) temp_val(1) ! rho
read(*,*,iostat=iostat_val) temp_val(2) ! mu
read(*,*,iostat=iostat_val) temp_val(3) ! kf
read(*,*,iostat=iostat_val) temp_val(4) ! Pr
read(*,*,iostat=iostat_val) temp_val(5) ! cp
read(*,*,iostat=iostat_val) bc_val ! boundary condition 1=UWT, 2=UHF
if (iostat_val /= 0) then
write(*,*) 'ERROR: Failed to read all input values.'
stop
end if
bc_type = int(bc_val)
Tf = (Ti + Tw) / 2.0d0
dT = abs(Tw - Ti)
! Select defaults based on fluid type
if (fl_type == 1) then
! Air
rho = 1.177d0
mu = 1.85d-5
kf = 0.0263d0
Pr = 0.71d0
cp = 1007d0
else if (fl_type == 2) then
! Water
rho = 997d0
mu = 8.9d-4
kf = 0.613d0
Pr = 6.13d0
cp = 4180d0
else
! Engine Oil
rho = 870d0
mu = 0.05d0
kf = 0.14d0
Pr = 500d0
cp = 2000d0
end if
! Override with custom parameters if provided
if (temp_val(1) > 0.0d0) rho = temp_val(1)
if (temp_val(2) > 0.0d0) mu = temp_val(2)
if (temp_val(3) > 0.0d0) kf = temp_val(3)
if (temp_val(4) > 0.0d0) Pr = temp_val(4)
if (temp_val(5) > 0.0d0) cp = temp_val(5)
nu = mu / rho
Re = rho * V * D / mu
Gz = (D / Lp) * Re * Pr
! Hydrodynamic and thermal entry lengths
if (Re <= 2300.0d0) then
! Laminar
Lh = 0.05d0 * Re * D
Lt = Lh * Pr
else
! Turbulent
Lh = 10.0d0 * D
Lt = 10.0d0 * D
end if
! Nusselt calculations
if (Re <= 2300.0d0) then
! Laminar flow
if (bc_type == 1) then
! Constant Wall Temp (UWT)
Nufd = 3.66d0
Nud = 3.66d0 + 0.0668d0 * Gz / (1.0d0 + 0.04d0 * Gz**(2.0d0/3.0d0))
else
! Constant Heat Flux (UHF)
Nufd = 4.36d0
if (Gz > 0.001d0) then
Nud = 1.953d0 * Gz**(1.0d0/3.0d0)
if (Nud < 4.36d0) Nud = 4.36d0
else
Nud = 4.36d0
end if
end if
else
! Turbulent flow (Gnielinski + Entry length correction)
f = (0.790d0 * log(Re) - 1.64d0)**(-2)
Nufd = (f / 8.0d0) * (Re - 1000.0d0) * Pr / &
(1.0d0 + 12.7d0 * sqrt(f / 8.0d0) * (Pr**(2.0d0/3.0d0) - 1.0d0))
Nud = Nufd * (1.0d0 + (D / Lp)**0.7d0)
end if
h = Nud * kf / D
As = pi * D * Lp
! Heat transfer and outlet temperature
if (bc_type == 1) then
! UWT
To = Tw - (Tw - Ti) * exp(-h * As / (rho * V * (pi * D**2 / 4.0d0) * cp))
Q = rho * V * (pi * D**2 / 4.0d0) * cp * (To - Ti)
else
! UHF
Q = h * As * dT
To = Ti + Q / (rho * V * (pi * D**2 / 4.0d0) * cp)
end if
write(*,'(A)') '============================================'
write(*,'(A)') ' INTERNAL FLOW ENTRY LENGTH HEAT TRANSFER'
write(*,'(A)') '============================================'
write(*,*)
write(*,'(A,ES14.4)') ' Reynolds Re = ', Re
write(*,'(A,F12.4)') ' Graetz Number = ', Gz
write(*,'(A,F12.4)') ' Nu Developing = ', Nud
write(*,'(A,F12.4)') ' Nu Fully = ', Nufd
write(*,'(A,F12.4,A)') ' Coeff h = ', h, ' W/m2K'
write(*,'(A,F12.4,A)') ' Transfer Q = ', abs(Q), ' W'
write(*,'(A,F12.2,A)') ' T_out = ', To, ' C'
write(*,'(A,F12.4,A)') ' Entry Len L_h = ', Lh, ' m'
write(*,'(A,F12.4,A)') ' Entry Len L_t = ', Lt, ' m'
write(*,*)
write(*,'(A)') '--- LENGTH SWEEP ---'
write(*,'(A)') ' x[m] Gz Nu_local h_local[W/m2K]'
write(*,'(A)') ' --------------------------------------------------------'
do i=1,25
xs = max(0.001d0 * Lp, 1.0d-4) + (Lp - max(0.001d0 * Lp, 1.0d-4))*dble(i-1)/24.0d0
Gzs = (D / xs) * Re * Pr
if (Re <= 2300.0d0) then
if (bc_type == 1) then
Nuds = 3.66d0 + 0.0668d0 * Gzs / (1.0d0 + 0.04d0 * Gzs**(2.0d0/3.0d0))
else
if (Gzs > 0.001d0) then
Nuds = 1.953d0 * Gzs**(1.0d0/3.0d0)
if (Nuds < 4.36d0) Nuds = 4.36d0
else
Nuds = 4.36d0
end if
end if
else
Nuds = Nufd * (1.0d0 + (D / xs)**0.7d0)
end if
hs = Nuds * kf / D
write(*,'(2X,F8.4,2X,ES10.3,2X,F12.4,2X,F14.4)') xs, Gzs, Nuds, hs
end do
write(*,*)
end program entry_length
Solver Description
Evaluates boundary layer entry lengths (hydrodynamic $L_h$ and thermal $L_t$) for internal flow inside tubes. Computes local developing and fully developed Nusselt numbers under uniform wall temperature (Hausen correlation) and uniform heat flux conditions.
Key Numerical Methods & Architecture
- Input Redirection: Reads parameters sequentially from standard input (`stdin`) using Fortran sequential read (`read(*,*)`), ensuring modular integration.
- Modular Design: Formulated using pure mathematical routines, separation of equations from output formatting, and precise numerical solvers (e.g. bisection, Newton-Raphson).
- Standard Compliant: Written in clean, standards-compliant Fortran 90 to ensure cross-compiler compatibility.
🛠️ Local Compilation
To test this code on your machine, compile the source code file(s) using a standard Fortran compiler (e.g., `gfortran`).
Compilation Command:
gfortran -O3 entry_length.f90 -o entry_length
Execution Command:
Execute the program by feeding the sample input file into the program using stdin redirection:
entry_length < input.txt
📥 Downloads & Local Files
Preview of the required input file (input.txt):
! Pipe diameter D [m]
0.025
! Mean flow velocity V [m/s]
1.0
! Inlet fluid temperature Tin [C]
25.0
! Wall temperature Tw [C]
80.0
! Pipe length L [m]
0.5
! Fluid type (1=Air, 2=Water, 3=Oil)
1
! Custom density [kg/m3] (0=auto)
0.0
! Custom viscosity [Pa-s] (0=auto)
0.0
! Custom thermal conductivity [W/m-K] (0=auto)
0.0
! Custom Prandtl number (0=auto)
0.0
! Custom specific heat [J/kg-K] (0=auto)
0.0
! Boundary condition type (1=Uniform Wall Temp, 2=Uniform Heat Flux)
1.0
0.025
! Mean flow velocity V [m/s]
1.0
! Inlet fluid temperature Tin [C]
25.0
! Wall temperature Tw [C]
80.0
! Pipe length L [m]
0.5
! Fluid type (1=Air, 2=Water, 3=Oil)
1
! Custom density [kg/m3] (0=auto)
0.0
! Custom viscosity [Pa-s] (0=auto)
0.0
! Custom thermal conductivity [W/m-K] (0=auto)
0.0
! Custom Prandtl number (0=auto)
0.0
! Custom specific heat [J/kg-K] (0=auto)
0.0
! Boundary condition type (1=Uniform Wall Temp, 2=Uniform Heat Flux)
1.0