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Title: Flow Boiling for HFC134a and Oil Mixtures
Author: Dabboussi, Ibrahim
ISNI:       0000 0004 2679 6692
Awarding Body: London South Bank University
Current Institution: London South Bank University
Date of Award: 2008
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Refrigerants containing chlorine are believed to deplete the ozone layer. They have been phased out and replaced by new ozone-safe refrigerants. This thesis concerns the heat transfer and pressure drop for chlorine-free refrigerant, HFC134a and with two Ester oil mixtures. A test facility was designed, constructed and operated to simulate the evaporator in a heat pump system. The ranges of heat flux, mass flux and evaporating temperature were between 3-40 kW / m2 , 40-375 kg / m2s and 5- 15'C respectively. The overall concentration of oil was varied from 0% to approximately 5% by mass. The results indicated that the nucleate boiling heat transfer in annular flow is dominant when the vapour quality is less than 30% to 50%; heat transfer coefficients were strongly dependent upon heat flux. However, at higher vapour quality values, the heat flux dependence disappeared and the convective heat transfer dominates in this region in which nucleate boiling is suppressed. Dry-out region was observed after the vapour quality was above 90%. The measured pressure drop for pure refrigerant increased with rising exit vapour quality and mass flux but decreased with evaporating temperature. Local heat transfer coefficients for refrigerant-oil mixtures were lower than for the pure refrigerant In most cases The pressure Drops Were always Higher. Data from the present study were compared with existing correlations. A new correlation for pure refrigerant was developed and the results yielded a good agreement with a mean deviation of only 10.55%.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available