Компьютерное моделирование и экспериментальное исследование теплообмена и гидродинамики в каналах компактных кожухотрубных теплообменников

В. Г. Горобец, Ю. О. Богдан

Анотація


 

COMPUTER MODELING AND EXPERIMENTAL STUDY OF HEAT TRANSFER AND HYDRODYNAMICS IN THE CHANNELS OF COMPACT CASING TUBE HEAT EXCHANGERS

V. Gorobets, Y. Bogdan

One of major directions energy- and resource saving on the modern stage of development of technique there is development of more perfect heat-exchange equipment which involve in power plants. At the same time, the heat exchangers of modern power plants must to meet more becoming tougher requirements to the new constructions: on reliability of work, minimum hydraulic resistance, comfort of operating, maintenance and overhauling, compactness, reduction of mass-size indexes and increase of durability and longevity. There is arise of interest development of the new improved constructions of heat exchangers that possess improved power, mass-size and price characteristics as compared to present analogues.

Shell-and-tube heat-exchangers (STHEX), found a wide use in industry, energy and transport, due to simplicity of constructions, small hydraulic resistance, high enough efficiency and durability. The increase of their efficiency directly depends on geometry and arrangement of basic element of such heat-exchangers – tube bundles. It is known that for shell-and-tube heat-exchangers maximal heat transfer in tube bundles is observed at the cross current of heat carriers, i.e. at the transversal flowing around of such bundles.

The aim of work consists of carry out numerical computer modeling and experimental research of processes of heat exchange and hydrodynamics, which occur in channels of compact bundles of tubes of small diameter and implementation of their comparative analysis with the bundles of tubes of the known arrangements.

In the paper the numerical computer modeling of heat- and mass transfer processes in the channels of ultimately compressed transversely streamlined smooth-tube bundles of inline arrangement was carried out in the absence of a gap between adjacent pipes in the direction of the heat carrier motion using the ANSYS Fluent software. The fields of velocities, temperatures and pressures in the investigated channels are obtained, the conditions of the hydrodynamic flow in them are analyzed and the intensity of heat transfer between the heat carriers through the wall separating them is estimated.

 It has been determined that the maximum value of the relative heat-transfer coefficient at the surface of the tubes of the 2d-4th rows αloc/αav.m in the sections of the connected flow (at Re = 6044) exceeds by 0.46 (29%) the maximum value αloc/αav.m 3d-7th rows in the inline arrangement of the tube bundles (with Re = 14000). It is shown that the investigated bundle of maximums αloc/αav.m is approximately in 2 times larger in comparison with the inline tube bundle, which causes an increase in the total heat-transfer coefficient for bundles of the new configuration.

 Experimental data of the processes taking place in the channels of the investigated tube bundles are obtained, which are presented in the form of the dependences of the heat exchange characteristics for compressed tube bundles on the dynamic and thermophysical parameters of the heat carriers.

 The comparative analysis of the results of numerical computer modeling and experimental data for channels with a compact arrangement of tube bundles is carried out. It is shown that the developed design is sufficiently effective at a relatively low hydraulic resistance and has improved mass and dimension parameters of the heat exchange surface at the same heat capacity of the heat exchangers.

 The compact design of a heat-exchanging tube bundle is proposed, which has high efficiency, low aerodynamic (1225 Pa) and hydraulic resistance (400 Pa), with Nusselt number on the surface of the investigated tube bundles, which are approximately in 2 times higher than their values for a bundle with a inline arrangement of tubes.

 


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