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Transport Phenomena in Thermal Engineering. Volume 2

ISBN 印刷: 1-56700-015-0

A NUMERICAL STUDY ON INTERNAL FLOW IN AN UNMIXED HEAT EXCHANGER WITH RECTANGULAR CROSS SECTION PASSAGES

要約

In most of the former studies on heat exchangers, calculations of the efficiency studied by BULCK and XUAN(1).(9) or pressure losses in practical machines have been treated by using a simplified method such as NTU-method or LMTD-method(2). Heat and mass flows in heat exchangers have been scarcely studied before. It is useful for a designer to improve their performances and to make new arrangements by investigating the temperature and the velocity profiles of the working fluid. Then in this study, the inside detailed circumstances which can not be treated by NTU-method or LMTD-method are investigated.
Heat exchangers in use can be classified into several types: the bulkhead, the direction of the heat flow, or the geometory of a flow cross section. In an unmixed type heat exchanger, heat always flows from the hot fluid to the cold one through the bulkhead regardless of the flow direction or the shape of passage. If basic phenomena in a heat exchanger with a square section are understood, the results would be projected one with the other cross section.
An unmixed type parallel flow heat exchanger in which the passages of the hot and cold fluid are square or rectangular, placed side by side, was analyzed in this study. Considering the temperature dependency of physical properties of working fluid, an analysis was carried out.
With respect to heat exchangers, the following matters are well known: Temperature gredients of working fluid are significant at the boundaries of passage. The temperature profiles, the velocity ones and the physical properties of working fluid influence each other. Therefore, it is difficult to make a thermal equivalent model and to reproduce the phenomena. It is also difficult to examine the flow patterns in it by using a noncontact type device. In such a case, numerical analyses are often used for the investigations. Larger computation would be required if the numerical analysis is dealt with in three-dimensions. Therefore, in this study, flows in a heat exchanger were assumed to be an one-way flow as Patanker's. By use of the continuation of two-dimensional planes, a big reduction in computer memories and calculation times was accomplished.
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