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limited study that specifically discusses the relation between thermophysical properties of a Heat Transfer Fluid (HTF) and pumping performance. This study aims to find the effect of the change in thermophysical properties of HTF on the pumping performance, particularly for the delivery rate, slip factor coefficient, and volumetric efficiency. In this study, five different HTFs are used to assess the effect of working temperature and pumping speed on the pumping performance. Delivery rate is evaluated by setting the pumping speed from 0 to 1300 RPM where the working fluid temperature is set at 40, 140, and 200 °C. It shows that the HTF with a lower viscosity has a better delivery rate. The slip coefficient for all working fluid is ranging between 0.11–0.31 at temperature 200 °C. It is found that a higher working temperature for the fluid increases the slip coefficient and delivery rate. The volumetric efficiency is directly affected by the slip ranging from 69 – 89% at 200 °C. The heat transfer rate ranges from 40 – 98 °C for all fluids, which is mainly affected by the volumetric efficiency of the pump and also pumping speed where a higher pumping speed decreases the heat transfer rate. It can be concluded that the change in thermophysical properties of the working fluid will change the pumping performance. Therefore, it is important to adjust the pumping operation according to the temperature and properties of the working fluid to achieve the highest heat transfer rate for a convective heat transfer system.

Pump as Turbine (PAT) is one of a hydropower plant that applies a pump with a reversed flow, working as a turbine to generate electrical power. It has the advantages of low-cost, widely available in the market and user-friendly. However, like other hydropower plants, PAT technology has low performance in term of power output. The impeller surface roughness is one of critical aspect, which influences PAT performance because poor surface roughness causes losses and cavitation. The objective of the research is to increase the PAT performance by improving the quality of the surface roughness and validate by the experimental tests. A low-cost and customize hand grinding process was applied to produce five impellers with three different levels of surface roughness (average surface roughness of 0.16 mm, 0.24 mm, and 0.40 mm), an edge rounded impeller, and a varnish lacquer coated impeller. All of the impellers undergo performance testing. The performance of the original impeller (without modification) used as a comparison. The experiment result shows that an impeller with a lower surface roughness (lower Ra number) has a higher performance. An impeller with an average surface roughness of 0.16 mm improved 10.9% of its initial performance. Additional edge rounding for a 0.16 mm surface roughness impeller would improve its performance by 13.1%.  The optimum turbine efficiency of 15.45% was achieve-able by implementing an impeller with the lowest surface roughness.

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