Abstract
To optimize a vertical flash tank separator, the characteristics of the flow entering the separator are required to be known. A flash tank separator improves the performance of a refrigeration cycle by separating the liquid from liquid-gas flow and providing the evaporator with only liquid refrigerant. This technique improves the effective area and enhances the heat transfer coefficient in the evaporator. This paper investigates the influence of the inlet operating conditions to an expansion device, on the adiabatic two-phase flow development in a horizontal pipe downstream from the expansion device. This work also compares three dimensional numerical simulations and experimental observations for the two-phase flow development after the expansion device in the horizontal pipe. A general trend of the two-phase flow after the expansion device was gradually developed and the expansion length was identified at less than 200 mm from the inlet. The two-phase flow behaviour was recorded using a digital camera recording the flow behaviour at the upstream and downstream of the horizontal tube. The results revealed that an increase of the mass flow rate causes an increase in the void fraction and a reduction in the slip ratio in the developed region. The simulations underestimate the expansion length and the mean difference between the experimental data and the numerical results is 8 %.
Highlights
Two-phase liquid-gas flow is involved in various processes including air conditioning systems refrigerators and the petroleum industry [1]
This is from the experiment with ṁ = 13.1 ± 0.2 g/s with vapour quality of 5.4 %. This is consistent with description by Hrnjak [3], who reported that the liquid and vapour move together at a certain velocity directly after the expansion device where both phases are uniformly mixed
In order to show the simulated two-phase flow development after the expansion device, contours of the liquid volume fraction were plotted along the axial vertical plane from the inlet of the tube as illustrated in Figure 17 for the case of ṁ = 23.4 g/s
Summary
Two-phase liquid-gas flow is involved in various processes including air conditioning systems refrigerators and the petroleum industry [1]. Numerical simulation and experimental investigations were conducted to investigate the two-phase flow development after the expansion device using water as the working fluid in a 25 mm inner diameter horizontal tube. Many numerical simulations of gas-liquid two-phase flow have used the Eulerian model in different geometries including sudden expansion [23] and flow in a horizontal tube [24] because it has proven to be more accurate than the VOF and Mixture models [23]. As the flow regime is gas-liquid two-phase flow and the phases under throttling process effect in the expansion device which provides an adiabatic mixed well two-phase flow these phases are being separated, the Eulerian model was used.
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