Refrigerant conditions at the capillary tube inlet of a household refrigerator.

Capillary tube-suction line heat exchanger (CT-SLHX) is a component widely used in household refrigerators. Recent works pointed out that even measuring subcooled conditions, the actual capillary tube inlet is two-phase flow. The main objective of this work is to visualize and assess experimentally the conditions taking place at the capillary tube inlet of a household refrigerator working with isobutane. The tube and wire condenser was replaced by a refrigerant-to-water heat exchanger in order to better assess the refrigerant conditions at the capillary tube inlet. Transparent tubes were set up at the condenser outlet and at the capillary tube inlet. The experiments confirmed the entrance of vapor and liquid in the capillary tube. Measurements indicated a non-equilibrium two-phase flow composed of subcooled vapor and liquid at the capillary tube inlet. The reason for the existence of two-phase flow seems to be the matching between the capillary tube and the compressor flow rates, meaning that the capillary tube is oversized. A smaller capillary tube diameter with different compressor speeds was tested, proving that at 2500 rpm the inlet of the capillary tube became full of liquid and clearly subcooled liquid conditions were measured.