Convective and Radiative Heat Losses of a Cylindrical Accumulator for Solar Water Heating Collectors

A new method for approximate numerical calculation of the temperature field and heat losses by convection and radiation (Q) of a two-layer cylindrical heat accumulator (HA) with symmetrical boundary conditions is presented and its software implementation is given. We estimate the accuracy of an approximate solution with a known analytical solution for the case with convective heat losses only and with a constant heat transfer coefficient and we reveal that the error of the approximate method starts to exceed 1% when Fo > 2 or when the HA temperature is already less than a half of the HA initial temperature (90°C). It is shown that under permissible heat loss of 10% for 10 h for a HA with R = 0.2 m, the thermal insulation thickness should be about of 5 cm, and the relative heat loss depends greatly on the HA volume. It is important to investigate the effect of thermal insulation emissivity under a small insulation thickness: if thermal insulation thickness is higher than 2 cm, its influence is only of about 5–6%.

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