tailieunhanh - Heat Transfer Handbook part 87

Heat Transfer Handbook part 87. The Heat Transfer Handbook provides succinct hard data, formulas, and specifications for the critical aspects of heat transfer, offering a reliable, hands-on resource for solving day-to-day issues across a variety of applications. | COMPACT HEAT EXCHANGERS 855 Ratio of free flow to frontal area on one side a. dimensionless Figure Entrance and exit loss coefficients for flow through plate fin exchanger cores. From Kays and London 1984 . Nu _ hde k _ h Re Pr deG c k GC The fluid properties in eqs. and are evaluated at the bulk temperature Tb 2 Ti T2 tb 2 t1 h 856 HEAT EXCHANGERS a D s a a x -0 1 . 3 D O is ü W - -80 Kc X . Laminar Re 2000 Re 3000 Re 5000 Re 10 000 if Ke xx Re 10 000 x X. Rn soon Re 3000 Re 2000 Laminar Ratio of free flow to frontal area on one side a dimensionless Figure Entrance and exit loss coefficients for flow through rectangular passages. From Kays and London 1984. Flow Friction Data Kays and London 1984 suggest that the pressure drop AP in a compact heat exchanger be computed from the equation AP PT G2 vi 2gPi 1 2 3 - 4 where 1 1 Kc - a2 V2 2 2 - V1 1 LONGITUDINAL FINNED DOUBLE-PIPE EXCHANGERS 857 S Vm T f-------m A Vi O4 1 - o2 - Ke - Vi Friction factors are correlated on an individual surface basis and are usually plotted as a function of the Reynolds number. The entrance and exit loss coefficients differ for the various types of passages and are plotted as functions of the parameter a and the Reynolds number. Four terms may be noted within the parentheses in eq. . These terms denote respectively the entrance or contraction loss as the fluid approaches the exchanger at line velocity and changes to the exchanger entrance velocity acceleration loss or acceleration gain as the fluid expands or contracts during its passage through the exchanger flow friction loss and exit loss. Kays and London 1984 have presented heat transfer and flow friction data for approximately 120 surfaces described by the foregoing. Some typical examples are shown in Figs. through . Entrance and exit loss coefficients for .