No abstract

An experimental study of the effects of three jet-induced crossflow schemes on impingement heat transfer was made. The schemes, referred to as minimum, intermediate, and maximum crossflow correspond, successively, to unrestricted flow of spent air away from the target surface, restriction of the flow to leave through two opposite sides, and through one side of a rectangular impingement surface. The study covered jet Reynolds number, jet-to-surface spacing, and open area of 1000–21,000, 2–16 jet hole diameters, and 1–4 percent, respectively. The best heat transfer performance is obtained with the minimum scheme, intermediate and complete crossflow being associated with varying degrees of degradation. For a given blower power, heat transfer can be enhanced markedly by having greater number of jets over a fixed target area; notably when working with the minimum scheme at narrow jet-to-target spacings.

molecule (Pedram and Hines, 1983; Gupta and Bhatia, 1969), we estimated the surface are for adsorption to be 170 m2/g of com grits. This estimate is comparable to the values of 210 m2/g reported for starch (Gupta and Bhatia, 1969) and 263 m2/g for shelled corn (Hall and Rodriguez-Arias, 1958), which were also obtained by using water adsorption data. ConclusionsCorn grits adsorb water in the range of 323-373 K.Experimental adsorption data were fitted to a modified Henderson's equilibrium equation. The equation was modified by assuming that one of its parameters, n, was temperature independent. The second parameter, K, was found to have an Arrhenius-type dependence on temperature. The modified equation may be useful for extrapolations to lower temperatures as well. The calculated heats of adsorption (10.8-14.6 kcal/g-mol) are close to the latent heats of condensation (9.7-10 kcal/g-mol), thus indicating a physical adsorption phenomenon.

It has been demonstrated conclusively that the widely observed differences in data for frictional pressure coefficient between circular and noncircular passages derive from the inseparably connected effects of transition and the choice of a length scale. A relatively simple approach, the critical friction method (CFM), has been developed and when applied to triangular, rectangular, and concentric annular passages, the reduced data lie with remarkable consistency on the circular tube relations. In accordance with the theory of dynamical similarity, it has also been shown that noncircular duct data can be reduced using the hydraulic diameter or any arbitrarily defined length scale. The proposed method is what is needed to reconcile such data with those for circular tubes. With the hydraulic diameter, the critical friction factor almost converges to a universal value for all passages and the correction is simply that required to account for the difference in critical Reynolds number. By contrast, with any other linear parameter, two corrections are needed to compensate for variations in critical friction factor and Reynolds number. Application of the method to roughened passages is discussed.

No abstract