Modified efficiency-NTU method (m-ε-NTU) for calculating air coolers in dehumidifying or frost conditions. Part II

Abstract

This study presents a calculation method that can be applied to counterflow and straight-through air coolers operating in “dry” (without condensation), “wet” (with condensation on the entire surface), or “nonbinary” (with condensation on a part of the surface) modes for cases with and without the cooling medium undergoing a phase transition. Comparing the results obtained from the proposed method with those obtained from the method of segmental division of the heat exchange apparatus showed good convergence, with the proposed method requiring considerable lesser time for their execution. Hence, the novel proposed method can be widely used for the selection, verification, and structural calculations related to air coolers.

In the second part of this study, the main mathematical relations used for stationary calculations related to air coolers are provided. These dependencies are applicable to the dry, wet, and combined conditions. The method used for performing calculations related to air coolers operating in “dry” conditions is described herein. Formulas for determining the heat exchange surface with respect to the cooling fluid and humid air are derived herein. Moreover, these formulas can be used for calculations related to air coolers with or without a phase transition of the cooling fluid. Moreover, the criterion of transition of the air cooler from the “dry” operating mode to the “wet” or “combined” mode is provided in this study.

Keywords

heat transfer / mass transfer / air coolers / fin-and-tube heat exchangers / cooling of humid air / dehumidifying conditions / frost conditions / efficiency-NTU method

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