Influence of eccentricity on heat transfer in borehole counterflow heat exchanger of tube-in-tube type
Keywords:
borehole heat exchanger, counterflow heat exchanger, eccentricity, geothermal power engineeringAbstract
Heat exchangers of tube-in-tube type are widely used in the vertical borehole heat exchangers and other technical equipments. In practice, because of the design features of the channels or assembly inaccuracies appear eccentricity. In the cross-section integral value of the heat flux through the inner tube becomes different from the similar value in the case of concentric tubes. In this paper, investigated the influence of eccentricity on the magnitude of the heat flux through the inner tube of counterflow heat exchanger of "tube in tube" type. This problem is considered as an example of vertical borehole heat exchanger. Mathematical model of thermal processes, is based on a system of equations which includes the equations of thermal conduction, the continuity equation, the energy equation, Reynolds-averaged Navier–Stokes equation. The standard k-ε turbulence model was used to close the system of equations. The calculations were performed for different variants of displacement of the inner tube and the coolant rate. As a result, a series of computing experiments obtained functional dependence of the heat flux from the value of displacement. In case of ignoring the eccentricity during the thermal calculation the inaccuracy can be up to 12%. The received results can be used for thermal calculations in annular channels with eccentric of borehole heat exchangers and other technical devices.
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