How is the Reynolds number on the air side of a finned heat exchanger calculated?
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When calculating the air-side Reynolds number for finned heat exchangers (such as packaged air-cooled condensers), how is it specifically defined and distinguished? In the foreign algorithms for the heat transfer factor j cited in the paper \"Experimental Research Progress on Heat Transfer and Pressure Drop Characteristics of Finned Tube Heat Exchangers _ Correlation Equations\", there are two different notations for the Reynolds number on the air side: ReDo is mentioned in Kim’s (1996) paper, while ReDc is mentioned in C.C. Wang’s papers from 1999 and 2002. Do = outer diameter of the tube; Dc = outer diameter of the fin sleeve. Dc = Do + 2 * fin thickness. In the original paper, it’s unlikely that these two diameters are used directly for the calculations (mainly because the algorithm for calculating the Reynolds number isn’t available in the original text)… According to the method for calculating the Reynolds number, the fin channels on the air side are not circular, so it’s necessary to convert them to an equivalent ventilation diameter De, or equivalent diameter, for calculation. Why did those two experts come up with two different ways of expressing the Reynolds number? What is the purpose behind this difference? I really can’t figure it out; please give me some analysis and advice. Thank you.
The Reynolds number is defined as the ratio of inertial force to viscous force.
This post was last edited by wiseboy on 2015-12-30 09:17, version 1. “The term “air side” is ambiguous, as air can be present on both sides; you cannot consider your own operating conditions as the universal standard ； 2. The algorithm for the Reynolds number is not that difficult to understand; different Reynolds numbers correspond to different formulas for calculating heat transfer and fluid resistance. So it’s not possible to ask generally how it is calculated; it depends on the Reynolds number corresponding to the heat transfer and fluid resistance calculation formulas. In finned tube calculations, the “Heat Exchanger Master” software defines 5 Reynolds numbers, which correspond to the software’s formulas for heat transfer and fluid resistance calculations. \"Heat Exchanger Master\" defines the finned tube as follows: Re0h – the Reynolds number based on the outer diameter do of the base tube, used to represent the heat transfer coefficient ； Refh — Heat transfer coefficient based on the fin outer diameter (do+2h) using the Reynolds number ； Re0f——Reynolds number based on the external diameter do of the base tube for the drag coefficient ； Reff —— Drag coefficient based on the outer diameter of the fin (do+2h) using the Reynolds number ； . . . . . . But all of the Reynolds number algorithms in \"Heat Exchanger Master\" are useless to you, because you don’t have the heat transfer and fluid resistance calculation formulas from \"Heat Exchanger Master\". So when looking for a method to calculate the Reynolds number, you must find it together with those formulas for heat transfer and fluid resistance: they go hand in hand, and it’s very difficult for others to understand the details.
Is the Reynolds number the boundary that distinguishes turbulent flow from chaotic flow?
This post was last edited by wiseboy on 2015-12-30 09:21. Yes. However, different geometric structures have different boundaries. In a smooth circular tube,