Part I. Reynolds' analogy between heat transfer and friction leads to the wellknown equationh=1/2fc _pϱv. According to improved theories, for turbulent flow of gases in long straight ducts, the factor 1/2 is to be replaced byc=0.55 It is shown that for laminar flow in long ductsc is equal to 0.3 for a circular, and equal to 0.4 for a flat rectangular cross-section. Further in very short ducts an approximate theory is shown to give values that are of the same order of magnitude. Though the equationh=cfc _pϱv has an approximative character, it has the advantage of being simple and generally valid for gases flowing in ducts. Applications and experimental data will be given in a subsequent article.

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heat transfer wellknown equationh12fc sub classapluspluspsubv flat rectangular flow friction

B. H. Schultz,.On the application of Reynolds' analogy and the heat-exchange factor to the design of heat exchangers I. 1 (1),387-399.

B. H. Schultz,"On the application of Reynolds' analogy and the heat-exchange factor to the design of heat exchangers I" 1

B. H. Schultz,"On the application of Reynolds' analogy and the heat-exchange factor to the design of heat exchangers I"