Optimal heat pipe heat exchanger design

Abstract

A typical heat pipe heat exchanger with continuous planar fins and a staggered equilateral triangular pitch of the tubes is subject to optimization from the point of view of the ratio heat flow/weight and heat transfer effectiveness. Different optimization procedures are explained in detail and numerical results are given in the application. The procedures are as follows. 1. A. If hot and cold fluid mass flow velocities in the minimum free flow areas are given, one obtains the maximum of the ratio heat flow, Q /mass, M for optimal values of fin density and equilateral triangular pitch. The ratio of evaporator to condenser lengths observes a relation which allows Q/M to be permanently at its peak with respect to the dimensionless saturation temperature. 2. B.1. One obtains the maximum of the ratio heat flow/evaporator mass for optimal fin and triangular pitches. 2. One selects the cold fluid mass flow velocity G 2 so as to obtain equality between evaporator and condenser fin side heat transfer coefficients. The optimal pitches found at the evaporator also lead to the maximum of heat flow/condenser mass. 3. There is an optimal value of the ratio of evaporator to condenser lengths which ensures Q/M to be a maximum with respect to the dimensionless saturation temperature. 3. C.1. As B.1.2. G 2 remains variable. A condenser with maximal heat exchanger heat transfer effectiveness is “linked” to the optimized evaporator. One obtains the ratio of evaporator to condenser lengths and the ratio of hot and cold fluid heat capacities as optimal functions of G 2 . 4. D.1. As B.1.2. G 2 remains variable. The ratio of evaporator to condenser lengths is selected from the condition: Q/M maximum with respect to the dimensionless saturation temperature. It follows that this ratio becomes an optimal function of G 2 . The ratio of the heat capacities is derived as an optimal function of G 2 too. The heat flow value, the number of tubes in a row and the number of rows do not affect optimization results. The optimization procedures presented in this paper may be used, with adequate transformations, for other heat pipe heat exchanger configurations.