Liquid-phase region of working fluid

The controlling equations for the energy balance of working fluid and conduction oil are as follows:


UnDi (Th – Tf)



mfCp, f

T =

UnDi (Th – Tf)



mhCp, h

Total heat transfer coefficient is calculated by the following:

Подпись: (18)U = 1 (i + ±

hi K


The convectional heat transfer coefficient can be calculated using the Dittus-Boelter equation [17]. When flow of the outer fluid is laminar, the concentric tube is considered isothermal at the inner annulus of the cross-section; it is insulated at the outer annulus, thus obtaining the heat transfer coefficient, according to the Handbook of Heat Transfer [18].

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