Two Functions Used in the Analysis of Crossflow Exchangers, Regenerators and Related Equipment

a response exhibits a step when t = P and thus t' = t a . The first cross-sectional fluid a lamina that enters at time zero with a temperature of unity sees fluid b at zero temperature. (The wall is "transparent" when its thermal capacitance is zero.) This lamina therefore has a temperature of exp(-AOc). When it reaches its exit plane {x -1) at time /" its temperature is exp (-N), which is the magnitude of the jumps seen in The solution with zero core capacitance is much easier and faster to compute than the Spiga and Spiga solution. It is therefore of interest to estimate the upper range of V a or V b that is reasonable for an exchanger. Suppose that fluid a flows inside tubes. Then for thin wall tubes V a -£>y/(4A) in which D and A are the tube diameter and wall thickness and v is the ratio of the volummetric heat capacities of the fluid and tube materials. This ratio has the exceptionally large value of 1.7 for water and aluminum. Using this material combination gives V a -0.4D/A. Thus an aluminum tube with 25 mm diameter and 1 mm wall thickness gives V a = 10. The parameters V a and V b can, of course, vary over a wide range, but this illustration indicates that the simplicity of the zero core capacitance solution can sometimes be enjoyed with acceptable accuracy. References Anzelius, A., 1926 Introduction This note focuses on the transport in aiding laminar mixed convection flow adjacent to a vertical isothermal surface. The direction of forced flow is taken to be upward for the heated surface. This situation causes the flow to be predominantly forced at the leading edge, primarily natural far downstream, and mixed in the middle. In the intermediate region of mixed convection Merkin (1969) reported a finite difference solution for Pr = 1