Numerical Investigation of Air-Side Heat Transfer and Pressure Drop Characteristics of a New Triangular Finned Microchannel Evaporator with Water Drainage Slits

Brice Rogie,Jens Honore Walther,Wiebke Brix Markussen,Martin Ryhl Kærn

doi:10.3390/fluids4040205

Abstract

The present study investigated a new microchannel profile design encompassing condensate drainage slits for improved moisture removal with use of triangular shaped plain fins. Heat transfer and pressure drop correlations were developed using computational fluid dynamics (CFD) and defined in terms of Colburn j-factor and Fanning f-factor. The microchannels were square 2.00 × 2.00 mm and placed with 4.50 mm longitudinal tube pitch. The transverse tube pitch and the triangular fin pitch were varied from 9.00 to 21.00 mm and 2.50 to 10.00 mm, respectively. Frontal velocity ranged from 1.47 to 4.40 m·s−1. The chosen evaporator geometry corresponds to evaporators for industrial refrigeration systems with long frosting periods. Furthermore, the CFD simulations covered the complete thermal entrance and developed regions, and made it possible to extract virtually infinite longitudinal heat transfer and pressure drop characteristics. The developed Colburn j-factor and Fanning f-factor correlations are able to predict the numerical results with 3.41% and 3.95% deviation, respectively.

Highlights

Microchannel heat exchangers are attractive due to their high ratio of heat transfer area to internal volume
The new microchannel profile designs are made with specialized drain paths in between each microchannel port, which means that the coil becomes thicker in the airflow direction
The aim of the current work is to provide airside heat transfer and pressure drop correlations that are applicable for the design of novel ammonia microchannel evaporators for industrial refrigeration systems, e.g., cold stores, blast freezers etc., where the evaporator operates in freezing conditions

Summary

Introduction

Microchannel heat exchangers are attractive due to their high ratio of heat transfer area to internal volume. In recent years, they have gained increased market shares in many refrigeration and air-conditioning applications as air-cooled condensers, because of better thermo-hydraulic performance and compactness compared with traditional finned tube heat exchangers. They have gained increased market shares in many refrigeration and air-conditioning applications as air-cooled condensers, because of better thermo-hydraulic performance and compactness compared with traditional finned tube heat exchangers Their use as evaporators in refrigeration systems is challenged by (1) water condensate retention and (2) poor refrigerant distribution. The new microchannel profile designs are made with specialized drain paths in between each microchannel port, which means that the coil becomes thicker in the airflow direction

Objectives

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Results

Conclusion