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本文说明水力直径与当量直径是不同的概念。从理论上证明了水力直径对无角、无狭窄旁路断面中的通道紊流可以被当作当量直径直接用于阻力与换热计算;对层流,或对带有狭窄旁路断面通道中的紊流,水力直径只是一个形状参数,不能直接用来计算阻力与换热。从流动阻力与换热机理的角度给出水力直径的适用范围与误差,指出其误差大小完全取决于通道边壁的曲折程度和Re数的大小。此项研究的目的,在于为探索几何形状变化影响阻力与换热的一般规律进行理论准备。
This article shows that hydraulic diameter and equivalent diameter are different concepts. It is theoretically proved that the channel turbulence in the non-angular and non-stencil bypass section can be used as the equivalent diameter directly for the calculation of resistance and heat transfer. For laminar flow or in the channel with narrow bypass section Turbulence, hydraulic diameter is just a shape parameter, can not be used directly to calculate the resistance and heat transfer. From the perspective of flow resistance and heat transfer mechanism, the applicable range and error of hydraulic diameter are given. The error size is completely determined by the degree of tortuosity and the Reynolds number. The purpose of this study is to theoretically prepare for the exploration of the general laws of resistance and heat transfer that affect the geometry change.