This module is used to compute heat transfer coefficient due to fluid flow in a pipe. The pipe cross-section can be circular, annular or rectangular. Heat transfer due to laminar or turbulent flow of an incompressible fluid (gas or liquid) can be computed.

This module calculates convection heat transfer coefficient. For laminar flow conditions and constant temperature conditions on the pipe surface, the Nusselt number in a circular pipe is computed using equation (1)

(1)

where d is diameter of pipe, L is length of pipe and P_e is the Peclet number and is computed using equation (2)

(2)

where C_p is specific heat capacity, k is fluid thermal conductivity, r is fluid density and V is average velocity of fluid in pipe. For laminar flow conditions and constant heat flux conditions on the pipe surface the Nusselt number is computed using equation (3).

(3)

For turbulent flow conditions the Nusselt number is computed

(4)

where f is friction factor for flow in a pipe; f is computed using equation (5)

(5)

For laminar flow in a duct with rectangular cross-section Nusselt number is computed using equation (6)

(6)

where r is ratio of width to height.

For turbulent flow in a rectangular cross-section duct the Nusselt number is computed using equation (7)

(7)

where:

(8) (9)

For laminar flow in an annulus the Nusselt number is computed using equation (10)

(10)

where d_i is internal diameter, d_o is outer diameter of annulus and d_h is hydraulic diameter.

(11a)

(11b)

(11c)

The selection of equation (11a), (11b), or (11c) depends on the thermal boundary conditions on the surface of the annulus.

For turbulent flow the Nusselt number is computed using equation (12a), (12b), or (12c); the selection of equation depends on the thermal boundary conditions on the surface of the annulus.

(12a)

(12b)

(12c)

(13)

The inputs for this module are depicted in Figure 1. The inputs consist of pipe geometric dimensions, fluid flow properties and flow conditions.

Figure 1: ETBX inputs for heat transfer computations.

The results are displayed using standard ETBX output window shown in Figure 2. The outputs are Reynolds number, flow regime and heat transfer coefficient.

Figure 2: ETBX heat transfer coefficient module outputs.