Pressure drop heat exchanger tubes

Friction Coefficient. In the design of a heat exchanger, the pumping requirement is an important consideration. For a fully developed laminar flow, the pressure drop inside a tube is inversely proportional to the fourth power of the inside tube diameter. For a turbulent flow, the pressure drop is inversely proportional to D where n Hes between 4.8 and 5. In general, the internal tube diameter, plays the most important role in the deterrnination of the pumping requirement. It can be calculated using the Darcy friction coefficient,, defined as... 

When a fluid flows over a stationary or moving surface, the pressure of the fluid decreases along the length of the surface due to friction. This is commonly called the pressure drop of the system. Of particular interest are the pressure drops in pipes (tubes) and in heat exchanger shells. 

Figure 10-138. Pressure drop for water in smooth tubes at 68°F. (Used by permission Scovill Heat Exchanger Tube Manual, 3 Ed. Scovill Manufacturing Co.)...

Pressure drop in heat exchangers Tube-side... 

Neeraas, B.O. Condensation of hydrocarbon mixtures in coil-wound LNG heat exchangers, tube-side heat transfer and pressure drop , Dr.ing. thesis, NTH, 1993... 

In heat-exchanger applications, it is frequently important to match heat-transfer requirements with pressure-drop limitations. Assuming a fixed total heat-transfer requirement and a fixed temperature difference between wall and bulk conditions as well as a fixed pressure drop through the tube, derive expressions for the length and diameter of the tube, assuming turbulent flow of a gas with the Prandtl number near unity. 

All calculations are carried out at a window cut of 20%. This seems to be an optimum figure as it produces the maximum heat transfer coefficient at a given pressure drop for all tested heat exchangers. It is further assumed that TEMA standard clearances would exist between the tubes and baffles and between the shell inside diameter and baffle outside diameter. The various numbers in Figures 2-33a and b denote the fluids, pressure drops and exchanger dimensions given in Table 2-6. 

Examination of equations (6.30) and (6.32) for heat transfer, and equations (6.36) and (6.40) for pressure drop, indicates that for a given heat exchanger and fluids, the fluid velocity is the most important parameter affecting heat transfer and pressure drop on both tube and shell sides. Thus, with increasing velocity, both pressure drop and heat transfer coefficient increase. The rate of pressure drop increase is faster than... 

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