Condensation in a horizontal tube: If a vapor is condensing in a horizontal tube, then assuming the flow is stratified with laminar film condensation, the heat transfer coefficient can be found as

Where L = length of the tube; W = steam condensation rate; μ = viscosity of condensate;

ρ = density of condensate; n = number of segments

It is suggested that this value should be corrected by a factor h/h_c that depends on condensate loading. This factor is reported as a function of two parameters, Reynolds number, and A_s where

Example 5.13: Calculate the effective condensate coefficient for a horizontal tube with an inside diameter of 0.62 in and a length of 9 ft for a fluid at a rate of 126 lb/h.

Use the following data:

Density of condensate, ρ = 50 lb/ft³; absolute viscosity, μ = 0.25 lb/(ft·h)

Thermal conductivity, k = 0.08 Btu/(h·ft·°F); specific heat, c = 0.55 Btu/(lb·°F)

Internal diameter of tube, d_i = 0.62 in; number of tubes, n = 1

Condensation rate, W = 126 lb/h; length of a tube, L = 9 ft; g_c = 4.18´10⁸ ft/h².

Solution: For steam condensing in a horizontal tube, and assuming that flow is stratified, heat transfer coefficient can be found to be

The parameter, A_s, can be calculated as

Now this value of A_s gives h/h_c of 0.92 (Table on page 7-50, Chopey) and we can find h as 374 Btu/(h·ft²·°F).