HYDRAULIC EFFICIENCY MEASUREMENT OF CENTRIFUGAL PUMP BY THERMODYNAMIC METHOD

Abstract

The thermodynamic method is one of the most reliable and accurate method of measuring hydraulic efficiency of hydraulic machines. Thermodynamic method is based on the principle of conservation of energy, i.e. first law of thermodynamics. This method is based on a very simple principle that the energy lost in the hydraulic machine due to viscous effect and rotating component heats up the water passing through. The measurement of rise of temperature gives the measure of the losses. The efficiency is calculated directly from the specific hydraulic energy and specific mechanical energy equations. The temperature difference between the inlet and outlet of the machine is very small, typically of the order of a few milli-Kelvins. Hence it is very difficult to measure the temperature rise accurately. For temperature measurement SBE 38 temperature thermometer is used. The SBE 38’s measurement range is -5 to +35 °C. Absolute accuracy is better than ± 0.001 °C (1 mK) and resolution is approximately 0.00025 °C (0.25 mK) having response time 500 millisecond and self-heating error less than 200 μk. Experiment carried out suggest that the thermodynamic method would give much better result for the head more than 100 m because at low head uncertainty is very high. Also this method will give much better result if circulation of water in the same water tank is avoided.