Fundamentals of modelling a two-phase refrigerant heat exchanger- an industrial perspective

Abstract

A heat exchanger is the heart of any thermal or refrigeration system, and hence its proper design is of paramount importance to industry. Modelling is an economical and efficient way to design a thermal system (and hence a heat exchanger) and predict its performance without conducting detailed time intensive and costly physical experiments. Although the physics of two 'generic' modelling techniques, namely LMTD and NTU-e, is well covered in the basic heat transfer text books, applying these techniques can be quite an involved process in some difficult situations, such as complex heat exchanger geometries, one or both streams undergoing phase change or moisture removal from an air stream, heat exchanger experiencing a 'pinch point' etc. In some situations, models can also become quite sophisticated and use more advanced techniques, where a heat exchanger involving two-phase is modelled following a segment, zone by zone or an elemental approach. An elemental method is intensive but can be comprehensive and accurate. This paper reviews some of these modelling fundamentals for a two-phase heat exchanger, and presents two novel examples of heat exchangers that were optimised for their energy efficient use in domestic refrigerators. These were well received by the industry.Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21July, 2010.