Flow Boiling Heat Transfer Characteristics In Helically Coiled Tube With Circumferentially Non-Uniform Heating

Helically coiled tubes are widely used in HVAC, refrigeration and cryogenics, biomedicine, power energy, oil and chemical industry, metallurgy, mineral, aerospace and other industries for the advantages of good heat transfer performance, high efficiency and the simple manufacturing process. At present, researches of two-phase flow boiling heat transfer in horizontal helically coiled tubes are mainly focused on uniform heat flux or constant temperature of outer wall of the helically coiled tubes. However, researches of non uniform heat flux in the outer wall of the helically coiled tubes are rarely reported. The flow boiling heat transfer characteristics in helically coiled tubes with two non-uniform heat flux and one uniform heat flux conditions were carried out in this thesis and corresponding experimental heat transfer correlations were also proposed.1. The flow boiling heat transfer coefficients of horizontal helically coiled tubes with four different curvature( ? =0.0672? ? =0.0642? ? =0.0369? ? =0.0288) were studied experimentally under three different heating conditions. It were measured in a test condition range of mass flux G=80kg/(m2s)~420kg/(m2s),heat flux q=2.990kW/m2~5.981kW/m2, and mass quality 0.12~0.53. It is concluded that the pressure drop increases obviously with the increase of the average mass quality. When the saturation pressure of the system decreases, the pressure drop increases obviously. The pressure drop of the uniform heating condition is very close to the non-uniform heating conditions, but the pressure drop under the condition of the outer half heated and the inner half adiabatic is slightly higher than that of the other two heating conditions.2. No matter under the condition of uniform heat flux or non-uniform heat flux, four helically coiled tubes with different curvature present a common heat transfer characteristic. Under the same mass quality condition, the flow boiling heat transfer coefficient increases with the increase of heat flux and mass flux. When the mass flux, heat flux and mass quality are constant, the flow boiling heat transfer coefficient increases with the increase of curvature. The effect of non uniform heat flux on the flow boiling heat transfer coefficient is also analyzed. The flow boiling heat transfer coefficients under three different heating conditions have little difference. But the boiling heat transfer coefficient with outer half circumference heating and the inner half circumference adiabatic condition is 4%~10% higher than the other two kinds of heating conditions in the helically coiled tubes.3. Flow boiling heat transfer correlations are proposed in this thesis under two kinds of non uniform heating and one uniform heating condition based on the experimental data. For the two kinds of non uniform heat flux conditions, the average absolute error between the calculated and experimental heat transfer coefficients are 9.66% and 8.47%, respectively, and 8.24% for the uniform heating condition.