Enhancement of power efficiency of evaporating-condensing heat exchangers

The aspects of heat transfer in evaporating-condensing heat exchangers conditioning their thermophysical merits and advantages as regards routine heat transferring devices are determined and analyzed. It is shown that implementation of one of these aspects which is transformation of heat flux density in its transferring from “hot” medium to “cold” one by changing the ratio of the lengths of the evaporation and condensation zones of evaporating-condensing heat transferring elements (positioning of tube plate separating the channels with heat exchanging media) allows studying optimization of the said ratio in respect to getting the minimal thermal and aerodynamic resistances of evaporating-condensing heat exchangers. Thus, the concerned work on one of the parts of such study is aimed to derive the correlations for optimal ratio of evaporation and condensation zones in gas-to-gas heat exchangers based on vertical transversely finned tubular thermosiphons to spend the minimal power required to pump heat-exchanging media under the specified conditions of heat transfer. As an objective function of optimization the dimensionless ratio of transferred heat flux to the sum of the powers provided to pump the heat-exchanging media through the heat-exchanger channels is accepted. This ratio is called a factor of heat exchanger power efficiency. In the concerned study the functional dependence of dimensionless power efficiency factor of evaporating-condensing heat exchanger upon dimensionless ratio of the lengths of evaporation and condensation zones is derived. The performed extremum research of the dependence revealed that it has an extremum for an actual range of the determining parameters and this extremum is the maximum. The study resulted in an equation of optimal relationship between the zone lengths (the heights of the channels occupied by flowing heat-exchanging media) that corresponds to the maximal factor of power efficiency.