Paper 26: The Wider Application of Roughened Heat Transfer Surfaces as Developed for Advanced Gas-Cooled Reactors

Review of developments in turbulence theory

“…It is sometimes argued that surface modification can only be helpful if St/f for the modified surface is greater than that for a smooth surface, since then the modification will reduce the ratio of pumping power to heat transfer (see eg Dipprey and Sabersky 1963). Walker and Wilkie (1967) showed that, because heat transfer is proportional to G while pressure drop is proportional to G3, the figure of merit is more nearly St3/f. On this revised criterion, the rib-roughened surface is almost four times better than a smooth one.…”

Performance Evaluation Criterion at Equal Pumping Power for Enhanced Performance Heat Transfer Surfaces

“…However, the enhancement in heat transfer is also associated with significant increase in pressure drop and pumping power. Various thermal performance evaluation criteria, which take account of both heat transfer enhancement and pumping power, have been suggested for these enhanced performance surfaces based on different design constraints and objectives [1][2][3][4][5][6]. However, the criterion based on equal pumping power for the roughened and smooth surfaces suggested by Webb and Eckert [2] has been most widely used .…”

“…One of the old references where an equation similar to (1) has been given is that of Walker and Wilkie [1] for flow along the axis of a cluster of heated roughened rods in a smooth channel for the fixed mass flow rate and pumping power as constraints and the flow area as variable. Webb and Eckert [2], while discussing three different design objectives for multitube heat exchangers, proposed (1) for the design objective of enhanced heat transfer rate at equal pumping power for the roughened and smooth tubes. However, they 2 Journal of Solar Energy developed this equation for a particular set of constraints and this equation is applicable only when a condition of specified ratio of mass velocities through the smooth and rough tubes is fulfilled.…”

“…These constraints and conditions are discussed later. Many investigators [8][9][10][11][12][13][14][15][16][17][18][19], while using (1), did not take notice of the condition specified by Webb and Eckert [2] or Walker and Wilkie [1], and some of them [11][12][13][14][15][16][17][18][19] have used the performance ratio 1 for the square and rectangular ducts without mentioning the modification of the original constraints and condition specified for the multitube exchangers.…”