Prediction of Heat Transfer Coefficients for Flow Boiling of Refrigerant-Oil Mixtures in Horizontal Evaporator Tubes

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Prediction of Heat Transfer Coefficients for Flow Boiling of Refrigerant-Oil Mixtures in Horizontal Evaporator Tubes

Format:
Grant
Kyushu Univ. Production Kyushu Univ. Production
Title(Other Language):
油を含む冷媒の水平蒸発管内熱伝達係数の予測方法の確立
Responsibility:
吉田 駿(九州大学・工学部・教授)
YOSHIDA Suguru(九州大学・工学部・教授)
Language:
Japanese
Project Year:
1988-1989
Latest Report:
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. Read more
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