The function performed by a direct contact heat exchanger is by definition a heat interaction between two media without an interfering wall between them. The direct contact heat exchanger analyzed herein refers to the restricted definition of systems in which temperatures of the contacted media vary without change of phase. This class involves the particulate systems of immiscible liquids, solid particles in fluids, gas bubbles in liquids, and droplets in gases. The applicability of direct contact heat exchangers has been considered for use in fouling and crystallizing systems, sea-water heating, geothermal brines, as well as in nuclear and MHD power plants. An analytic way to evaluate the performance of a direct contact heat exchanger is applied to examine the effects of operational variables upon length and diameter of a heat exchanger. The heat exchanger becomes shorter as the particle size decreases, and heat capacity ratio, flow rate ratio and approach temperature increase. The diameter of the column decreases with the particle size, and the density ratio of the contacted media. It increases with the flow rate ratio. All the evaluations made, correspond to the laminar bulk flow in the heat exchanger, and to particle Reynolds numbers in the range of 20–500.

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