Heat transfer and fluid flow in spray evaporators with application to reducing refrigerant inventory

As the phase-out of chlorofluorocarbons (CFC's) approaches, there is a current need for the development of new vapor compression chillers which can operate with non-CFC refrigerants while still maintaining high operating efficiencies. Redesign of the traditional flooded evaporator used in refrigeration chillers so as to incorporate a spray evaporation capability offers both a potential for increased heat transfer performance and a reduction in refrigerant inventory for a given chiller capacity relative to that found with existing industrial units. This study is an evaluation of the spray evaporation heat transfer performance of refrigerants HFC-134a, HCFC-22, and HCFC-123 with commercially available copper alloy tubes. In addition, the effects of small concentrations of oil on the spray evaporation heat transfer process are also investigated. Two different spray evaporation heat transfer facilities were designed and constructed, namely, a multi-tube facility and a large scale bundle facility. Testing of HFC-134a was conducted on the multi-tube test facility with six different enhanced and low-fmned surface copper tubes. These initial tests indicated that enhanced condensation surfaces were better suited for the spray evaporation environment than enhanced boiling surfaces. The pure refngerant work was followed by lubricant effects testing with two different viscosity polyol-