Investigation of flow inside the capillary tubes used in refrigeration systems

Increasing energy demand and the decrease of existing fossil fuel reserves, has led to worldwide research that concentrates on efforts relevant to energy economics. The reduction of the energy index every year for household refrigerator manufacturers, which is determined by CECED, has also played a part in convincing researchers to work on energy economy. A related aspect is the damage to the ozone layer and to the environment in general caused by refrigerants used in refrigeration. Under the Montreal Protocol, which took effect in 1989, the chlorine-containing non-halogenated hydrocarbons (CFCs), and hydrogen-containing halogenated hydrocarbons (HFC) were gradually abandoned and hydrocarbon (HC) based refrigerants have been adopted in their place. In this context, nowadays, manufacturers halted or reduced production of systems using commonly used refrigerants like R11, R12, R22 and have begun to use alternative refrigerants like R600a(isobutane) and R744 (CO2) that have a much lower impact on the environment. During the process of transition to alternative refrigerants, the resizing of the system components of refrigeration cycle that provide desired mechanical and thermal properties is important. The aim of this study is to investigate the flow characteristics and to visualize the flow types through the adiabatic capillary tube which is used as a throttling device for cooling systems working with R600a. Within this study, firstly, a comprehensive literature review has been conducted. Secondly , an experimental and visualization setup which is capable of providing different cycle parameters in steady-state condition, has been designed and built to determine the behaviour of alternative refrigerant R600a inside the adiabatic capillary tube with different dimensional properties. During the experiments, the effects of the main parameters of cooling cycle, condensation temperature, sub-cooling degree and dimensional parameters, the diameter and length of the capillary tube to pressure drop and mass flow rate along the capillary tube have all been investigated. Other experiments have been carried out to determine the additional pressure drop required for the bubble growth and transition from single-phase flow to two-phase flow (under pressure of vaporization) through capillary tube. As well as the determination of the thermodynamic properties of two-phase flow and flow visualization in the capillary tube, in order to examine the effects of bubble collapse on flow induced vibration and acoustics, collaborative research has been made with Arçelik A.Ş. Vibration and Acoustics Division.