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Npsh available
- 1. 1.(a)(i) NPSH available (NPSHa) is the net positive suction head resulting from system configuration and operation, it is the difference between the net inlet head and the head corresponding to the vapour pressure of the liquid required to make the liquid flow through the suction from the sump to the impeller .NPSH required(NPSHr) is an empirical quantity, obtained from the pump manufacturer’s tests,it is the total suction head ,varies with the pump design ,speed and capacity of the pump. Calculations to find NPSHa NPSHa = (absolute pressure head at inlet of pump)-(vapour pressure head)+ (velocity head at inlet of pump) = 𝑃 𝑎𝑡𝑚 𝜌𝑔 − 𝑃𝑣 𝜌𝑔 + 𝑣 𝑠 2 2𝑔 = 𝑃 𝑎𝑡𝑚 𝜌𝑔 − ( 𝑣 𝑠 2 2𝑔 + ℎ 𝑠 + ℎ 𝑓𝑠)− 𝑃𝑣 𝜌𝑔 + 𝑣 𝑠 2 2𝑔 = 𝑃 𝑎𝑡𝑚 𝜌𝑔 − ℎ 𝑠 − ℎ 𝑓𝑠 − 𝑃𝑣 𝜌𝑔 = Hatm- ℎ 𝑠 − ℎ 𝑓𝑠 − 𝐻v where 𝑃𝑎𝑡𝑚 = 𝑎𝑡𝑚𝑜𝑠𝑝ℎ𝑒𝑟𝑖𝑐 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑃𝑣 = 𝑣𝑎𝑝𝑜𝑢𝑟 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 ℎ 𝑠 = 𝑠𝑢𝑐𝑡𝑖𝑜𝑛 ℎ𝑒𝑎𝑑 ℎ 𝑓𝑠 = ℎ𝑒𝑎𝑑 𝑙𝑜𝑠𝑠 𝑖𝑛 𝑠𝑢𝑐𝑡𝑖𝑜𝑛 𝑝𝑖𝑝𝑒 𝐻 𝑎𝑡𝑚 = 𝑎𝑡𝑚𝑜𝑠𝑝ℎ𝑒𝑟𝑖𝑐 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 ℎ𝑒𝑎𝑑 𝐻𝑣 = 𝑣𝑎𝑝𝑜𝑢𝑟 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 ℎ𝑒𝑎𝑑 1.(a)(i) NPSHa = 99.929 1.03×9.81 − 5.2 − 0.457 − 3.4955 1.03×9.81 =3.887m Conclusion Since NPSHa =3.887m>NPSHr = 3.66m ,cavitation will not occur. 2(a) (i) Heat engines They receive heat from high temperature source. They convert part of this heat to work . They reject the remaining waste heat to a low temperature sink. They operate on a cycle, Measure of performance is called thermal