The Experimental Study Of Flow Boiling Of R134a In Tube Under High-gravity Conditions

With the improvement of fighers’ capabilities and the increase of the electronic equipments’ power, the airborne vapor cycle refrigeration system has gained plenty of attention, as well as the flow characteristics and heat transfer characteristics of pipe flow boiling under high-gravity conditions, which is the difficulty in the system. This thesis contains the research of the pipe flow boiling frictional pressure drop characteristics and heat transfer characteristics of R134 a under high-gravity conditions.An experiment system has been set up successfully, in which the mass flow of refrigerant and the average pressure of the test section are adjustable. The reliability of the experimental system has been verified. The two test sections used in the experiment are both smooth and straight copper pipes, whose inner diameters are 4.065 mm and 2.168 mm respectively. In the experiment, both of the two test sections’ high-gravity ranges from 0 to 3g, their fluxes are 28.5kW/m2 and 19.0kW/m2. The 4.065 mm test section’s mass quality ranges from 0 to 0.9, it’s pressures are 5.8bar and 6.8bar, it’s mass flow rates are 185kg/m2 s and 295kg/m2s; The 2.168 mm test section’s mass quality ranges from 0 to 0.7, it’s pressures are 7.1bar and 8.2bar, it’s mass flow rates are 725kg/m2 s and 910kg/m2 s.Through the analysis of the experimental data, the influences caused by high-gravity、mass flow rate, heat flux, mass quality on the pipe flow boiling pressure drop and heat transfer characteristics are acquired. The experimental results indicate that high-gravity has a larger influence on the heat transfer characteristics than the flow characteristics of the flow boiling. The friction pressure drop under high-gravity is smaller than that under normal gravity when mass quality is small, it is larger under high-gravity than that under normal gravity when mass quality is large, the turning point is around the mass quality of 0.4. The convective heat transfer coefficient is larger under high-gravity conditions than that under normal gravity condition, and the huger the high-gravity is, the larger the convective heat transfer coefficient emerges. With the experimental data under high-gravity conditions, flow boiling heat transfer correlations under normal gravity condition have been evaluated, it has been found that Fang correlation can preferably forecast the flow boiling heat transfer coefficient under high-gravity conditions in the experimental parameters region.