OPTIMIZATION OF IN-TUBE ENHANCEMENT FOR LARGE EVAPORATORS AND CONDENSERS

Introducing roughness in tubes increases the turbulent heat-transfer c oefficient but there is usually a much larger increase in friction fac tor for constant geometry and flow conditions. In this study, generali zed rib-tube correlations are used in optimizing the roughness geometr y for two different objective functions or performance evaluation crit eria (PEG). Considered are the maximum heat transfer for given pumping power and surface area (R-3) and the minimum surface area for constan t heat load and pumping power (R-5). Only tube-side flow was considere d. The PEG, with their associated constraint equations, were evaluated by using a simple iterative procedure over a wide range of parameters (Re = 10,000-100,000, Pr = 0.7-35, e/d = 0.01-0.1, p/d = 0.1-1.0, and alpha/90 = 0-1.0). The optimum rib geometry had e/d = 0.02, p/d = 0.1 , and alpha/90 = 1.0. The Reynolds and Prandtl numbers had little infl uence on hear-transfer augmentation. The improvement in the effectiven ess due to the ribbed tubes has been illustrated for different tube an d flow variables to aid in the preliminary design of enhanced heat exc hangers.