Forced Convection Heat Transfer Inside Pipes

5 FORCED CONVECTION HEAT TRANSFER INSIDE PIPES 4.5A Introduction and Dimensionless Numbers 

In most situations involving a liquid or a gas in heat transfer, convective heat transfer usually occurs as well as conduction. In most industrial processes where heat transfer is occurring, heat is being transformed from one fluid through a solid wall to a second fluid. In Fig. 4.5-1 heat is being transferred from the hot flowing fluid to the cold flowing fluid. The temperature profile is shown. 

The velocity gradient, when the fluid is in turbulent flow, is very steep next to the wall in the thin viscous sublayer where turbulence is absent. Here the heat transfer is mainly by conduction with a large temperature difference of 7 — T3 in the warm fluid. 

4 Principles of Steady-State Heat Transfer 

As we move farther away from the wall, we approach the turbulent region, where rapidly moving eddies tend to equalize the temperature. Hence, the temperature gradient is less and the difference is small. The average temperature of fluid A is slightly less 

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Sec. 4.5 Forced Convection Heat Transfer Inside Pipes... 

Computation of inside heat transfer coefficient. The inside heat transfer coefficient involves internal forced convection in a circular pipe, and thus the use of Table 6.1. Following the five computational steps ... 

Natural convection heat transfer outside a vertical plane. In the case of natural-convection heat transfer from a vertical plane wall of length L to an adjacent fluid, different dimensionless groups should be expected when compared to forced convection inside a pipe since velocity is not a variable. The buoyant force due to the difference in density between the cold and heated fluid should be a factor. As seen in Eqs. (4.7-1) and (4.7-2), the buoyant force depends upon the variables p, g, p, and AT. Hence, the list of variables to be considered and their fundamental units are as follows ... 

The heat transfer coefficient at the inside wall and pressure drop through the coil can be estimated using the correlations for flow through pipes see Section 12.8 and Volume 1, Chapters 3 and 9. Correlations for forced convection in coiled pipes are also given in the Engineering Sciences Data Unit Design Guide, ESDU 78031 (2001). 

Micro heat pipe effect -l- two-phase forced convection in the coaxial gap (porous tube inside the glass tube) increase the heat transfer 2-2.5 times as higher as in liquid pool at low and moderate heat fluxes. 

Introduction. The use of fins or extended surfaces on the outside of a heat exchanger pipe wall to give relatively high heat-transfer coefficients in the exchanger is quite common. An automobile radiator is such a device, where hot water passes inside through a bank of tubes and loses heat to the air. On the outside of the tubes, extended surfaces receive heat from the tube walls and transmit it to the air by forced convection. 

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