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I am trying to model fluid flow and losses through a component (e.g., pipe) using REAL GAS properties since 1) I have access to RefProp from NIST, and 2) I am dealing with refrigerants, which are far from ideal.

I have seen nowhere an analysis of fluid flow losses (e.g., drag, friction, incidence, pressure drop) using real gas properties. In every discussion and book I have examined, somewhere in the analysis the gas is assumed to be ideal or perfect or steam, or no velocity change is allowed (which happens due to density change, if nothing else).

However, I have access to real gas properties (as I am sure many of us do), and I would greatly appreciate someone with a firmer grasp on reality than I have double-checking my 1D analysis.

The procedure in general is:

Given inlet fluid conditions, and pressure out, change mass flow rate until h0_out = h0_in (i.e., specific enthalpy stagnation at component exit = specific enthalpy stagnation at component inlet).

The way I figure it, all the energy to accelerate the fluid (due to the change in density) and overcome the losses (shear forces due to viscosity) must come from the internal energy, resulting in a reduction in fluid temperature.

I know this is long, but all the formulas and results (including units) are given, so I hope it is at least clear. Thanks in advance.

I have seen nowhere an analysis of fluid flow losses (e.g., drag, friction, incidence, pressure drop) using real gas properties. In every discussion and book I have examined, somewhere in the analysis the gas is assumed to be ideal or perfect or steam, or no velocity change is allowed (which happens due to density change, if nothing else).

However, I have access to real gas properties (as I am sure many of us do), and I would greatly appreciate someone with a firmer grasp on reality than I have double-checking my 1D analysis.

The procedure in general is:

Given inlet fluid conditions, and pressure out, change mass flow rate until h0_out = h0_in (i.e., specific enthalpy stagnation at component exit = specific enthalpy stagnation at component inlet).

The way I figure it, all the energy to accelerate the fluid (due to the change in density) and overcome the losses (shear forces due to viscosity) must come from the internal energy, resulting in a reduction in fluid temperature.

I know this is long, but all the formulas and results (including units) are given, so I hope it is at least clear. Thanks in advance.

Code:

```
Inputs
Fluid = R134A
T_in_C Temperature at component inlet
= 5.0000 C
Cd Drag coefficient
= 0.50000
Area Characteristic area
= 0.10000 m²
PressureRatio p_out / p_in
= 0.90000
Calculations ƒ() => fluid function RefProp from NIST
Calculations Not Iterated
Fluid Properties at Component Inlet
T_in Temperature at component inlet
= T_in_C converted to K
= 278.15 K
p_in Pressure at component inlet
= Saturation pressure @ (T_in - 0.01 K) to ensure pure vapor = ƒ(T)
= 349.54 kPa
rho_in Density at component inlet
= ƒ(P_in,T_in)
= 17.124 kg/m³
s_in Specific entropy at component inlet
= ƒ(P_in,T_in)
= 1.7245 m²/(s²·K)
h_in Specific enthalpy at component inlet
= ƒ(P_in,T_in)
= 401.50 m²/s²
u_in Specific internal energy at component inlet
= ƒ(P_in,T_in)
= 381.08 m²/s²
u_in_reality_check u_in calculated differently
= h_in - p_in / rho_in
= 381.08 m²/s²
Fluid Properties at Component Exit
p_out Pressure at component exit
= p_in · PressureRatio
= 314.58 kPa
u_out_s Specific internal energy at component exit isentropic
= ƒ(P_out,s_in)
= 379.05 m²/s²
Iterated Calculations Solve for mdot
mdot Mass flow rate. Note circular iterative self-reference
= mdot · h0_target / h0_out_calculated
= 3.9505 kg/s
rho_out Density at component exit. Uses u_out calculated below.
= ƒ(P_out,u_out)
= 15.366 kg/m³
Vdot_in Volumetric flow rate at component inlet
= mdot / rho_in
= 0.23069 m³/s
c_in Relative fluid velocity at component inlet
= Vdot_in / Area
= 2.3069 m/s
ke_in Specific kinetic energy at component inlet
= c_in² / 2
= 2.6610 m²/s²
h0_in Specific enthalpy stagnation at component inlet
= h_in + ke_in
= 404.16 m²/s²
h0_out_target Specific enthalpy stagnation at component exit
= h0_in
= 404.16 m²/s²
Vdot_out Volumetric flow rate at component exit
= mdot / ρout
= 0.25709 m³/s
c_out Relative fluid velocity at component exit
= Vdot_out / Area
= 2.5709 m/s
ke_out Specific kinetic energy at component exit
= c_out² / 2
= 3.3047 m²/s²
F_drag Drag force
= Cd · rho_in · c_in² · area / 2
= 2.2784 kg·m/s²
Pwr_drag Drag power
= F_drag · c_in
= 5.2561 kg·m²/s³
Delta_u Δ specific internal energy due to drag
= Pwr_drag / mdot
= 1.3305 m²/s²
u_out Specific internal energy at component exit
= u_out_s + Delta_u
= 380.38 m²/s²
h0_out_calculated
= u_out + p_out / rho_out + ke_out
= 404.16 m²/s²/code]
```

Last edited: