SHELLSIDE HEAT TRANSFER TO AIR IN FOUR X-SHELL HEAT EXCHANGER CONFIGURATIONS VIA 2D CFD SIMULATION
Two-dimensional CFD simulations of turbulent air downflow cooling in TEMA X shells have been completed for four inlet velocities for a one-pass and a two-pass configuration, both with and without sealing devices−sixteen cases in all. The detailed results show a significant variation of the heat transfer coefficient around the circumference of the tubes. For an interior tube, this variation approaches 14:1. Tubes on the
boundaries between the crossflow B- and bypass C-streams or between the B- and bypass F-streams have the largest heat transfer coefficient−approximately twice the bundle average. The tube-by-tube duty and MTD (mean temperature difference) values are more disparate; the maximum value can be two orders of magnitude greater than the minimum. Most of the heat transfer occurs in the first three or four rows of the
bundle. One effect of bypass streams is a penalty on the MTD and thus the heat transfer capability of the exchanger. This penalty can be formulated as a knockdown multiplier (called the delta correction factor) on the MTD. In the absence of relevant experimental data, the CFD simulations reported here allow one to formulate a correlation of flow and geometry parameters that can be applied to new designs. The detailed simulations also identify where gap velocities have been elevated by leakage streams and blockage from adjacent seal strips and seal rods, possibly exacerbating the potential for flow-induced vibration.