Performance analysis of a feasible air-cycle refrigeration system for road transport

The performance of an air-cycle refrigeration unit for road transport, which had been previously reported, was analysed in detail and compared with the original design model and an equivalent Thermo King SL200 vapour-cycle refrigeration unit. Poor heat exchanger performance was found to be the major contributor to low coefficient of performance values. Using state-of-the-art, but achievable performance levels for turbomachinery and heat exchangers, the performance of an optimised air-cycle refrigeration unit for the same application was predicted. The power requirement of the optimised air-cycle unit was 7% greater than the equivalent vapour-cycle unit at full-load operation. However, at part-load operation the air-cycle unit was estimated to absorb 35% less power than the vapour-cycle unit. The analysis demonstrated that the air-cycle system could potentially match the overall fuel consumption of the vapour-cycle transport refrigeration unit, while delivering the benefit of a completely refrigerant free system.

Design, construction and testing of an air-cycle refrigeration system for road transport

The environmental attractions of air-cycle refrigeration are considerable. Following a thermodynamic design analysis, an air-cycle demonstrator plant was constructed within the restricted physical envelope of an existing Thermo King SL200 trailer refrigeration unit. This unique plant operated satisfactorily, delivering sustainable cooling for refrigerated trailers using a completely natural and safe working fluid. The full load capacity of the air-cycle unit at -20 °C was 7,8 kW, 8% greater than the equivalent vapour-cycle unit, but the fuel consumption of the air-cycle plant was excessively high. However, at part load operation the disparity in fuel consumption dropped from approximately 200% to around 80%. The components used in the air-cycle demonstrator were not optimised and considerable potential exists for efficiency improvements, possibly to the point where the air-cycle system could rival the efficiency of the standard vapour-cycle system at part-load operation, which represents the biggest proportion of operating time for most units.

An Investigation of the Flow Field through a Variable Geometry Turbine Stator with Vane Endwall Clearance

Variable geometry turbines provide an extra degree of flexibility in air management in turbocharged engines. The pivoting stator vanes used to achieve the variable turbine geometry necessitate the inclusion of stator vane endwall clearances. The consequent leakage flow through the endwall clearances impacts the flow in the stator vane passages and an understanding of the impact of the leakage flow on stator loss is required. A numerical model of a typical variable geometry turbine was developed using the commercial CFX-10 computational fluid dynamics software, and validated using laser doppler velocimetry and static pressure measurements from a variable geometry turbine with stator vane endwall clearance. Two different stator vane positions were investigated, each at three different operating conditions representing different vane loadings. The vane endwall leakage was found to have a significant impact on the stator loss and on the uniformity of flow entering the turbine rotor. The leakage flow changed considerably at different vane positions and flow incidence at vane inlet was found to have a significant impact.

Gaining Access to Data Sources in Statutory Social Work Agencies: The Long and Winding Road

This paper details a researcher's experience of gaining access to three statutory social work agencies in order to conduct a study examining how social workers respond to family support cases and how parents and carers experience the intervention of social workers in these cases. The stages in gaining access are outlined, the gate-keepers involved at each stage are identified and some of the difficulties encountered are highlighted and discussed. The paper concludes that researchers need to give greater priority to access considerations and that social work agencies need to give greater priority to co-operation with researchers.