The controlling equations for the energy balance of working fluid and conduction oil are as follows:
|
dTf |
UnDi (Th – Tf) |
(16) |
|
dY |
mfCp, f |
|
|
T = |
UnDi (Th – Tf) |
(17) |
|
dY |
mhCp, h |
Total heat transfer coefficient is calculated by the following:
U = 1 (i + ±
hi K
where
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].
