A THEORETICAL AND EXPERIMENTAL ANALYSIS OF CAPILLARY TUBE-SUCTION LINE HEAT EXCHANGERS
Abstract
Every household refrigerator and freezer operates with a capillary tube-suction line heat exchanger. The proper design of these heat exchangers is thus an important factor in energy conservation. The capillary tube is a long length of small diameter (0.028 inch for this study) drawn, copper tubing which restricts and regulates the refrigerant flow in a refrigeration system. The suction line is a lesser length of larger diameter (0.25 inch for this study) copper tubing which acts as the return line from the evaporator to the compressor. The capillary tube and suction line are soldered together to form the capillary tube-suction line heat exchanger. A literature survey showed that substantial literature and information exists for designing adiabatic capillary tubes (zero heat transfer with the suction line), but there is very little information that can be used to design capillary tube-suction line heat exchangers. An experimental test loop was designed and built for testing the capillary tube-suction line heat exchanger. This test loop completely simulated a refrigeration system while providing easily controlled test conditions. A capillary tube-suction line heat exchanger was also instrumented with pressure taps and thermocouples. A capillary tube-suction line heat exchanger was experimentally tested for a wide range of conditions including; variable heat exchanger length conditions, subcooled inlet, quality inlet and choked flow. The resulting experimental data was used to calculate the thermo-dynamic state along the capillary tube-suction line heat exchanger, to verify the theoretical model, and to make design decisions. The capillary tube-suction line heat exchanger was theoretically modeled by dividing the capillary tube flow into two regions, subcooled and two-phase. Each of the two regions was described by four governing differential equations and boundary conditions. The governing differential equations were solved by an implicit finite difference method that marched the solution along the heat exchanger from a known initial condition. The results of the theoretical models compared satisfactorily with measured experimental data when initial conditions were accurately known.
Degree
Ph.D.
Subject Area
Mechanical engineering
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