Method of Calculation and Comparative Characteristics of Heat Exchangers with Heat Transfer Enhancement by Various Random Elements

摘要

Consideration has been given to the method of enhancement of a heat-transfer process due to the use of small random metallic elements (packings) in channels of heat-exchange apparatuses. The packings ensure a laminar-to-turbulent transition and a considerable increase in heat-transfer coefficients (of 30 to 60 times). Structures of two modern packing elements and their technical data have been given, as well as expressions to calculate hydraulic-resistance and heat-transfer coefficients. On the basis of a modified method of the thermal number of transfer units, expressions have been obtained for calculation of the tube length and the heat-transfer surface when random packings are used as intensifiers of the process in the apparatuses. Basic parameters of the obtained expressions are the heat-transmission coefficient and modified Peclet (Bodenstein) numbers with the coefficients of reverse mixing of heat-transfer agents. Empirical coefficients at Peclet numbers have been identified using a diffusion model of the structure of a heat-transfer agent flow. The obtained expressions permit taking account of the influence of the reverse mixing of heat-transfer agents on the structural characteristics of a heat exchanger. Examples of calculations of heat exchangers without intensifiers and with random packings have been given. It has been shown that during the heat exchange with different media, the overall dimensions of the heat exchangers are reduced 20 to 25 times. The use of random packings in heat exchangers with media of high viscosity is pressing, since the packings initiate a turbulent regime of flow of heat-transfer agents.