Authors
Abstract
A numerical and experimental study was performed to predict the flow and
thermal performance of a capillary tube that used in air conditioning and
refrigeration systems. In the numerical study, the (CFD) technique was employed
to model the problem using the finite volume method for a two-phase, two
dimensional flow in the pipe. In the experimental part, an experimental rig was
constructed using a split unite to measure the temperature and pressure along the
capillary tube. These measurements were taken for (R-22) refrigerant with
different ambient temperatures. It was found that for a fixed length and diameter
of capillary tube the mass flow rate of (R-22) increases as the inlet temperature
increases. The numerical study was then applied to predict the flow and heat
transfer along several types of capillary tube, i.e. several lengths, diameters, and
refrigerants, for cooled and non cooled tube. In the non cooled capillary results,
the capillary tube length of R-407C (R-32/125/134a(23/25/52)) was found to be
shorter than that required for (R-22). It was also found that (R-22) vaporized later
than its corresponding (R-407C). The same condition was found for (R-12) and its
alternative R-134a (CF3CH2F). The numerical results show a large effect of the
length of capillary tube on the refrigeration system performance. When the length
increases, the drop in pressure, temperature, and density decreases, while the
velocity and dryness fraction increases.
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