Heat transfer between conduction oil and working fluid

Thermal efficiency of FPCs can be calculated directly by the inlet and outlet temperatures of working fluid, according to Eq.14. On the other hand, thermal efficiency of CPC collectors is determined by the heat transfer process in the evaporator. The temperature relationship between working fluid and conduction oil must be established.

This section focuses on heat transfer in the evaporator, and the developed equations can easily be extended to the case of the condenser. Counter-current concentric tubes are adopted, and the parameters are listed in Table 2.

Подпись: Parameters Value Parameters Value Outer diameter Do mm 45 Generator efficiency є g 0.95 Inner diameter Di mm 25 Regenerator efficiency ЄГ 0.85 Turbine efficiency st 0.80 Pump efficiency Єp 0.75 Optical conversion of CPC n0 0.644 Optical conversion of FPC n0 0.857 First heat loss coefficient of collectors of CPC A wjm1 oC 0.749 First heat loss coefficient of collectors of FPC A Wjm2 oC 3.157 Second heat loss coefficient of collectors of CPC B W/m1 oC2 0.005 Second heat loss coefficient of collectors of FPC B Wjm1 oC2 0.014 Table 2. Specifications of the proposed low-temperature solar thermal electricity system

The following preconditions are assumed: 1) the influence of pressure drop on the saturated temperature arising from flow resistance in the evaporator is negligible; and 2) the two – phase flow is one-dimensional, that is, all parameters change only in the flow direction (Y).

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