Capillary Tube Flow Dynamics in Refrigeration Systems
Summary
Capillary tubes serve as simple, fixed-geometry throttling devices in vapour compression refrigeration systems, creating a controlled pressure drop that drives refrigerant expansion from the condenser to the evaporator. Within the narrow bore of the tube, refrigerant undergoes a transition from single-phase liquid to two-phase mixture, exhibiting complex flow regimes such as slug, annular and stratified flow. The inner diameter, length, surface roughness and coil configuration of the tube all influence local pressure gradients, heat transfer with surrounding lines and consequently mass flow rate. Small changes in geometry or boundary conditions can markedly alter the degree of superheat entering the compressor, system capacity and overall energy efficiency. Predictive modelling of capillary flow remains challenging owing to the interplay of fluid properties, phase change kinetics and non-adiabatic heat exchange with adjacent piping. Recent efforts have focussed on integrating suction-line heat recovery, novel tube geometries and advanced flow models to improve performance, stability and manufacturability in residential and mobile air-conditioning, water cooler and heat-pump applications.
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Capillary Tube Flow Dynamics in Refrigeration Systems publication trend
The graph below shows the total number of articles in capillary tube flow dynamics in refrigeration systems across all publications each year (not limited to Nature Index journals).
Technical terms
Capillary tube: small-bore tube that serves as a fixed-geometry throttling device to induce pressure drop and vapour formation between condenser and evaporator.
Two-phase flow: simultaneous flow of liquid and vapour phases within the capillary, exhibiting regimes such as slug, annular or stratified flow.
Superheat: temperature of vapour above its saturation temperature at a given pressure, used to prevent liquid carry-over into the compressor.
Coefficient of performance (COP): ratio of refrigeration effect to input work, a key metric of system efficiency.
Separated flow model: predictive approach treating liquid and vapour phases as distinct streams with different velocities and distributions.
Homogeneous flow model: simplified formulation that assumes uniform mixture properties and equal phase velocities within the capillary.
References
- Role of Non-Adiabatic Capillary Tube in Water Cooler Performance. Energies (2023).
- Jadhav P., Sahu A., Ballal S. Numerical study on the straight, helical and spiral capillary tube for the CO2 refrigerant. Journal Scientific and Technical Of Information Technologies, Mechanics and Optics (2022).
- Comparison between homogeneous and separated flow models of isobutane flowing through adiabatic capillary tubes. JUSTC (2022).
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