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Air Cooler / Finned Tube
Core Numerical Engine in Fortran 90 • 49 total downloads
hx_finned.f90
! =========================================================================
! Source File: hx_finned.f90
! =========================================================================
program hx_finned
implicit none
! Inputs
integer :: FinType
double precision :: m_a, T_in_a
double precision :: rho_a, Cp_a, mu_a, k_a
double precision :: m_t, T_in_t
double precision :: rho_t, Cp_t, mu_t, k_t
double precision :: do_val, di, L
integer :: Nrows, Nt_row
double precision :: Pt, Pl
double precision :: tf, pf, kf, hf
double precision :: ktube
integer :: Npasses
! Calculated properties
integer :: Nt, iostat_val
double precision :: Nf, s, df, Ab, Af, A_total, r_o, r_eq
double precision :: Amin, v_max, G_max, Re_a, Pr_a, Nu_a, h_air
double precision :: m_val, h_term, eta_f, eta_o
double precision :: Aat, v_t, Re_t, Pr_t, Nu_t, h_tube
double precision :: Rw, U_inv, U_o
double precision :: C_air, C_tube, C_min, C_max, Cr, NTU, epsilon, Q
double precision :: T_out_a, T_out_t, fa, dP_air
double precision, parameter :: pi = 3.141592653589793d0
! Read all variables from stdin in order
read(*,*,iostat=iostat_val) FinType
if (iostat_val /= 0) then
write(*,*) 'ERROR: Invalid inputs'
stop
end if
read(*,*,iostat=iostat_val) m_a
read(*,*,iostat=iostat_val) T_in_a
read(*,*,iostat=iostat_val) rho_a
read(*,*,iostat=iostat_val) Cp_a
read(*,*,iostat=iostat_val) mu_a
read(*,*,iostat=iostat_val) k_a
read(*,*,iostat=iostat_val) m_t
read(*,*,iostat=iostat_val) T_in_t
read(*,*,iostat=iostat_val) rho_t
read(*,*,iostat=iostat_val) Cp_t
read(*,*,iostat=iostat_val) mu_t
read(*,*,iostat=iostat_val) k_t
read(*,*,iostat=iostat_val) do_val
read(*,*,iostat=iostat_val) di
read(*,*,iostat=iostat_val) L
read(*,*,iostat=iostat_val) Nrows
read(*,*,iostat=iostat_val) Nt_row
read(*,*,iostat=iostat_val) Pt
read(*,*,iostat=iostat_val) Pl
read(*,*,iostat=iostat_val) tf
read(*,*,iostat=iostat_val) pf
read(*,*,iostat=iostat_val) kf
read(*,*,iostat=iostat_val) hf
read(*,*,iostat=iostat_val) ktube
read(*,*,iostat=iostat_val) Npasses
! Basic sanity checks
if (do_val <= 0.0d0 .or. di <= 0.0d0 .or. L <= 0.0d0 .or. pf <= 0.0d0 .or. tf <= 0.0d0) then
write(*,*) 'ERROR: Geometrical tube/fin values must be positive and non-zero.'
stop
end if
Nt = Nrows * Nt_row
Nf = L / pf
s = pf - tf
r_o = do_val / 2.0d0
! Bare exposed area
Ab = pi * do_val * (L - Nf * tf) * dble(Nt)
! Fin diameter and Area
df = do_val + 2.0d0 * hf
if (FinType == 1) then
! Plate Fins: Continuous
Af = 2.0d0 * Nf * (Pt * Pl - pi * do_val**2 / 4.0d0) * dble(Nt)
r_eq = sqrt(Pt * Pl / pi)
else
! Spiral Fins: Helical
Af = dble(Nt) * Nf * pi * ((df**2 - do_val**2) / 2.0d0 + df * tf)
r_eq = df / 2.0d0
end if
A_total = Af + Ab
! Minimum air-flow area
if (FinType == 1) then
Amin = dble(Nt_row) * (Pt * L - do_val * (L - Nf * tf) - Pt * Nf * tf)
else
Amin = dble(Nt_row) * (Pt * L - do_val * (L - Nf * tf) - df * Nf * tf)
end if
if (Amin <= 0.0d0) Amin = 1.0d-6
! Air flow properties
v_max = m_a / (rho_a * Amin)
G_max = rho_a * v_max
Re_a = G_max * do_val / mu_a
Pr_a = mu_a * Cp_a / k_a
! Briggs & Young Nusselt correlation
if (Re_a > 0.0d0) then
Nu_a = 0.134d0 * (Re_a**0.681d0) * (Pr_a**(1.0d0/3.0d0)) * (s / tf)**0.2d0 * (s / do_val)**0.1134d0
else
Nu_a = 0.0d0
end if
h_air = Nu_a * k_a / do_val
! Fin efficiency
m_val = sqrt(2.0d0 * h_air / (kf * tf))
h_term = m_val * (r_eq - r_o)
if (h_term > 1.0d-8) then
eta_f = tanh(h_term) / h_term
else
eta_f = 1.0d0
end if
eta_o = 1.0d0 - (Af / A_total) * (1.0d0 - eta_f)
! Tube-side film coefficient
Aat = dble(Nt) * pi * di**2 / (4.0d0 * dble(Npasses))
if (Aat <= 0.0d0) Aat = 1.0d-6
v_t = m_t / (rho_t * Aat)
Re_t = rho_t * v_t * di / mu_t
Pr_t = mu_t * Cp_t / k_t
if (Re_t >= 2100.0d0) then
Nu_t = 0.027d0 * (Re_t**0.8d0) * (Pr_t**(1.0d0/3.0d0))
else
if (Re_t > 0.0d0) then
Nu_t = 1.86d0 * (Re_t * Pr_t * di / L)**(1.0d0/3.0d0)
else
Nu_t = 3.66d0
end if
if (Nu_t < 3.66d0) Nu_t = 3.66d0
end if
h_tube = Nu_t * k_t / di
! Tube wall resistance
Rw = (do_val * log(do_val / di)) / (2.0d0 * ktube)
! Overall HTC (referred to outside area)
U_inv = 1.0d0 / (eta_o * h_air) + Rw + do_val / (di * h_tube)
U_o = 1.0d0 / U_inv
! Heat capacities
C_air = m_a * Cp_a
C_tube = m_t * Cp_t
if (C_air < C_tube) then
C_min = C_air
C_max = C_tube
else
C_min = C_tube
C_max = C_air
end if
Cr = C_min / C_max
if (Cr <= 0.0d0) Cr = 1.0d-6
! NTU & Effectiveness for unmixed-mixed crossflow
NTU = U_o * A_total / C_min
if (C_air <= C_tube) then
! Air (mixed) has C_min
epsilon = 1.0d0 - exp(-(1.0d0 / Cr) * (1.0d0 - exp(-Cr * NTU)))
else
! Tubes (unmixed) has C_min
epsilon = (1.0d0 / Cr) * (1.0d0 - exp(-Cr * (1.0d0 - exp(-NTU))))
end if
Q = epsilon * C_min * abs(T_in_t - T_in_a)
! Outlet temperatures
if (T_in_t > T_in_a) then
! Cooling tube fluid
T_out_t = T_in_t - Q / C_tube
T_out_a = T_in_a + Q / C_air
else
! Heating tube fluid
T_out_t = T_in_t + Q / C_tube
T_out_a = T_in_a - Q / C_air
end if
! Air-side pressure drop (Robinson & Briggs)
if (Re_a > 0.0d0) then
fa = 18.93d0 * Re_a**(-0.316d0) * (Pt / do_val)**(-0.927d0)
else
fa = 0.0d0
end if
dP_air = fa * G_max**2 * dble(Nrows) / (2.0d0 * rho_a)
! Output results to stdout in KEY=value format
write(*,'(A,I2)') 'FINTYPE=', FinType
write(*,'(A,F18.4)') 'AF=', Af
write(*,'(A,F18.4)') 'AB=', Ab
write(*,'(A,F18.4)') 'A_TOTAL=', A_total
write(*,'(A,F18.4)') 'AMIN=', Amin
write(*,'(A,F18.4)') 'V_MAX_AIR=', v_max
write(*,'(A,F18.4)') 'RE_AIR=', Re_a
write(*,'(A,F18.4)') 'H_AIR=', h_air
write(*,'(A,F18.4)') 'ETA_F=', eta_f
write(*,'(A,F18.4)') 'ETA_O=', eta_o
write(*,'(A,F18.4)') 'V_TUBE=', v_t
write(*,'(A,F18.4)') 'RE_TUBE=', Re_t
write(*,'(A,F18.4)') 'H_TUBE=', h_tube
write(*,'(A,F18.4)') 'U_OVERALL=', U_o
write(*,'(A,F18.4)') 'EPSILON=', epsilon * 100.0d0
write(*,'(A,F18.4)') 'Q=', Q
write(*,'(A,F18.4)') 'T_OUT_AIR=', T_out_a
write(*,'(A,F18.4)') 'T_OUT_TUBE=', T_out_t
write(*,'(A,F18.4)') 'DP_AIR=', dP_air
write(*,'(A,F18.6)') 'FA=', fa
end program hx_finned
Solver Description
Design and rate finned-tube crossflow heat exchangers. Evaluates bare and finned heat transfer areas, air-side film coefficient via Briggs & Young correlation, Schmidt fin efficiency, Sieder-Tate tube film coefficient, unmixed-mixed crossflow effectiveness ($\epsilon$-NTU), and air-side pressure drops via Robinson & Briggs.
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 hx_finned.f90 -o hx_finned
Execution Command:
Execute the program by feeding the sample input file into the program using stdin redirection:
hx_finned < input.txt
📥 Downloads & Local Files
Preview of the required input file (input.txt):
! Fin Type (1=Plate Fins, 2=Spiral Fins)
2
! Air mass flow rate ma [kg/s]
5.0
! Air inlet temperature Tin_a [°C]
30.0
! Air density [kg/m3]
1.16
! Air specific heat [J/kg-K]
1007.0
! Air viscosity [Pa-s]
0.0000185
! Air thermal conductivity [W/m-K]
0.0263
! Tube fluid mass flow rate mt [kg/s]
2.5
! Tube fluid inlet temperature Tin_t [°C]
90.0
! Tube fluid density [kg/m3]
980.0
! Tube fluid specific heat [J/kg-K]
4180.0
! Tube fluid viscosity [Pa-s]
0.00035
! Tube fluid thermal conductivity [W/m-K]
0.67
! Tube outer diameter do [m]
0.0254
! Tube inner diameter di [m]
0.022
! Tubes active length L [m]
4.0
! Number of rows Nrows
4
! Tubes per row Nt_row
12
! Transverse tube pitch Pt [m]
0.060
! Longitudinal tube pitch Pl [m]
0.052
! Fin thickness tf [m]
0.0003
! Fin pitch pf [m]
0.0028
! Fin thermal conductivity kf [W/m-K]
200.0
! Fin height hf [m]
0.0125
! Tube wall conductivity ktube [W/m-K]
50.0
! Number of tube passes Npasses
2
2
! Air mass flow rate ma [kg/s]
5.0
! Air inlet temperature Tin_a [°C]
30.0
! Air density [kg/m3]
1.16
! Air specific heat [J/kg-K]
1007.0
! Air viscosity [Pa-s]
0.0000185
! Air thermal conductivity [W/m-K]
0.0263
! Tube fluid mass flow rate mt [kg/s]
2.5
! Tube fluid inlet temperature Tin_t [°C]
90.0
! Tube fluid density [kg/m3]
980.0
! Tube fluid specific heat [J/kg-K]
4180.0
! Tube fluid viscosity [Pa-s]
0.00035
! Tube fluid thermal conductivity [W/m-K]
0.67
! Tube outer diameter do [m]
0.0254
! Tube inner diameter di [m]
0.022
! Tubes active length L [m]
4.0
! Number of rows Nrows
4
! Tubes per row Nt_row
12
! Transverse tube pitch Pt [m]
0.060
! Longitudinal tube pitch Pl [m]
0.052
! Fin thickness tf [m]
0.0003
! Fin pitch pf [m]
0.0028
! Fin thermal conductivity kf [W/m-K]
200.0
! Fin height hf [m]
0.0125
! Tube wall conductivity ktube [W/m-K]
50.0
! Number of tube passes Npasses
2