1989 Fiscal Year Final Research Report Summary
Prediction of Heat Transfer Coefficients for Flow Boiling of Refrigerant-Oil Mixtures in Horizontal Evaporator Tubes
| Project/Area Number |
63550167
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Thermal engineering
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| Research Institution | Kyushu University |
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Principal Investigator |
YOSHIDA Suguru Kyushu Univ., Fac. of Engng., Professor, 工学部, 教授 (30037741)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUNAGA Takashi Kurume Coll. of Tech., Associate Professor, 助教授 (60117249)
MORI Hideo Kyushu Univ., Fac. of Engng., Associate Professor, 工学部, 助教授 (70150505)
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| Project Period (FY) |
1988 – 1989
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| Keywords | Boiling Heat Transfer / Refrigerant-Oil Mixtures / Horizontal Evaporator Tube / Heat Transfer Coefficient / Prediction Method / Heat Transfer Enhancement / 伝熱促進 |
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| Research Abstract |
1. Experiments and theoretical analyses were carried out on the heat transfer to Refrigerant-22 with 0 to 6 percent by mass of oil contained, flowing in horizontal smooth evaporator tubes. Following results were obtained. (1) The addition of oil produced an increase in heat transfer coefficient over a wide range of quality at low mass velocities and in the low quality region at high mass velocities because of an intensive foaming action. (2) The heat transfer coefficient decreased in the high quality region at high mass velocities, where an annular flow prevailed. This reduction of the heat transfer coefficient was attributed to a deterioration in local heat transfer near the tube top due to the formation of oil-rich and thereby highly viscous liquid film. (3) When the heat flux is low at a high mass velocity, the circumferentially averaged heat transfer coefficient for refrigerant-oil mixtures can be evaluated from a correlation equation for pure refrigerants by using the liquid properties of the mixtures. At a low mass velocity or at a high heat flux and high mass velocity, however, the circumferential variation of the oil mass fraction in the liquid film must be taken into account to predict the circumferentially averaged heat transfer coefficient.
2. Following results were experimentally obtained for refrigerant-oil mixtures in a horizontal, spirally grooved evaporator tube. (1) The addition of the oil generally deteriorated the heat transfer, but improved in low quality region at high mass velocities and high heat fluxes. The deterioration was more remarkable with increasing quality and oil mass fraction. (2) The heat transfer enhancement at a low mass velocity was reduced by two-thirds of that for oil-free refrigerant. When the mass velocity, heat flux and oil mass fraction were high, the heat transfer was considerably enhanced in high quality region.
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