Steady-state performance of capillary tubes for small-scale vapour compression systems using different refrigerants

Abstract

• Fixed capillary tube geometry with straight, helical and SLHX sections. • A model was proposed to determine the steady-state operation of the capillary tubes. • Refrigerant velocity was shown to increase with the capillary tubes elongation. • Refrigerant outlet state of the capillary tube is determined. • Refrigerants R134a, R1234yf, R1234ze (E), R513A, R600, R600a are investigated. The operational performance of small-scale refrigeration systems is mainly decided by their capillary tubes outlet parameters, wherein an accurate determination of the pressure and vapour quality is a prerequisite. Experiments have been performed for a capillary tube (CT) with specified geometry consisting of a straight, a helical and a suction line heat exchanger (SLHX) section. The capillary tube is incorporated in a small refrigeration system operated with R600a. In addition, a model was developed to determine the steady-state operation of the capillary tubes (activated with R134a, R1234yf, R1234ze(E), R600, R600a, R152a and R513A refrigerants) and validated. The highest and lowest value of the vapour quality was discerned to be 0.3132 (for R1234yf) and 0.2124 (for R600), respectively. The relative errors between the experimental and model results for the CT outlet pressure and temperature were ranged from 1.16 to 5.35% and 0.12–0.81%, respectively. It is asserted that the present strategy may contribute towards the precise estimation of the pressure and vapour quality to customize the working performance of small scale refrigeration systems.