João F. P. DE LARA
Cláudio Melo
Joel Boeng

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The aim of this research was to study the expansion process of HFC-134a through two distinct expansion devices applied in compact cooling systems, the so-called meso-scale cooling systems. To this end, an experimental apparatus was designed and built to mimic the running conditions of such systems. The experiments were planned according to the factorial design technique. The first part of this work was focused on small diameter adiabatic capillary tubes and showed that the capillary tube I.D. plays a major role in determining the refrigerant mass flow rate. It was also found that the models developed predicted 90% of the experimental data points within a band of error of ±10%. Visualization studies were also carried out and it was found that vapor bubbles at the entrance of the capillary tubes have a critical effect in meso-scale cooling systems. The second part of this work was focused on pulsating capillary tubes (series association of a PWM-driven metering valve, an intermediate chamber and an adiabatic capillary tube) and showed that the refrigerant mass flow rate is determined by the valve duty cycle. Unfortunately, the fluid flow phenomenon for this particular expansion device was not well captured by the model, with deviations of the order of ±30%.

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