Development of a Hybrid Empirical-Analytical Method to Predict Adiabatic Flow Properties in Capillary Tubes

Capillary tubes have been used in household refrigerators and other cooling systems for several decades. Complicated geometry, inevitable manufacturing variations, and complex two-phase phenomena have been major prohibitory factors in the development of reliable and efficient modeling tools to analyze the flow properties inside capillary tubes. Friction factor correlations as are available in the open literature (as examined by the authors) unanimously fail to give accurate analysis of the refrigerant flow. The delicate operation of a capillary tube makes experimentation cumbersome, time and cost intensive, and prone to errors. The present study introduces a method to utilize the data from a standard Nitrogen flow test for a given capillary tube to develop a model specific to that tube which can predict the refrigerant flow properties through the tube at any desired spatial resolution, inlet state, and flow rate. Thereby, exploratory studies and capillary tube modifications for the purpose of system optimization can be greatly simplified.