Experimental investigation of the refrigerant flow of isobutane (R600a) through adiabatic capillary tubes

Capillary tubes are widely used as expansion device in small scale refrigeration systems. Despite the simple geometry one finds complex physical processes during the throttling in the capillary tube, which were subject of many studies in the last decades. However, there is currently only one source of experimental data for the refrigerant isobutane (R600a) and adiabatic capillary tubes (Melo et al., 1999). In order to close this gap a test rig was built and experimental data in the range of typical small scale refrigeration systems was collected. The measured mass flow rates span from 0.64 kg h−1 to 1.93 kg h−1. Additionally, the effect of critical flows (Choked Flow) is shown by means of an extra performed test. The semi-algebraic equation from Hermes et al. (2010) showed a remarkable level of agreement by predicting 94% of all points within a ± 10% error band.