| Abstract |
The purpose of the review is the analysis of investigations on boiling heat transfer of paraffin hydrocarbons in channels having different orientation in space. These hydrocarbons are considered as promising coolant and working media [1] for binary power plants [1]. Forecasting and calculating of boiling crisis is a complex problem. The crisis divides the vapor generating channel in two zones, which considerably differ as to heat transfer intensity. They are: the sub-crisis zone with a high level of heat transfer and the post-crisis one with a low level of heat transfer. For the first zone (the bubble and annular flow regimes), rather reliable correlations to calculate heat transfer are well known. For the second zone (the disperse regime of flow), reliable experimental and calculation data on heat transfer of hydrocarbons are absent in the literature, and it is necessary to conduct special experimental studies. We performed the comparative analysis of the thermal and hydraulic characteristics of vapor-generating channels, using isobutane and Freon-142b as examples of working medium for binary plants. It was shown that the use of hydrocarbons results in approximately two-fold reduction of the mass flow rate of the coolant and in a considerable decrease in energy consumption for its pumping as compared to using freons. At the same time, the intensities of heat transfer under nucleate boiling of isobutane and Freon-142b are approximately the same because the evaporation velocities q / r and the Pr number are close for both substances, with the pressure and the heat flux being equal in both cases. The effect of different factors, such as the presence of oxygen, inert gases, binary mixtures of different hydrocarbons, and other, on heat transfer of hydrocarbons in two-phase flows is analized. These factors considerably influence characteristics of heat transfer equipment. [1]. Shpilrain E.E., Popel O.S., Director L.B., Frid S.E. A choice and testing of the equation of the state of natural hydrocarbons - promising working media for geothermal binary power plants. IVTRAN Report. Moscow. 2000. |