A difference of 2% or more in efficiency as determined by the usual mechanical testing method and thermodynamic method without heat transfer from the pump casing was demonstrated in the previous study.Heat accumulation in the glass wool fixed on the inner wall of the heat insulation box made of foam-styrol plate enclosing the test pump casing and thermometer setting block at the pump inlet and outlet may have been the reason for this.
The present experimental apparatus was improved ; the glass wool was removed, and a large insulation box covering the pump casing together with the thermometer setting block was made so as to control air temperature in the vicinity of the pump casing. Efficiency assessed by the present method was virtually the same as that by the mechanical testing method.
Air temperature surrounding the thermometer setting block affected oil temperature measured by the sensor in the block. The effect of air temperature near the stem of the thermometer was thus investigated, and the actual oil temperature at the pump inlet and outlet was determined. The effect of air temperature surrounding the inlet block on oil temperature distribution was also found. The oil temperature in the inlet rubber hose was not affected significantly by air temperature surrounding the hose.