A Study of R113 Refrigerant Boiling Processes in a Horizontal Tube Bundle under High Heat Flux Conditions

Energy-saving technologies are among the priority development lines of Russia’s power industry. In recovering the rejected heat from geothermal sources, especially those located in cold climatic zones in which there is no access to service cooling water resources, it is profitable to use organic coolants, e.g., CFC refrigerants, as working fluid for dry cooling towers. The properties of such coolants have, as a rule, been studied to a sufficient detail in the region of low temperatures, because they are mainly used as working fluids for refrigeration systems at moderate heat fluxes. To obtain data on the boiling of organic coolants on a tube bundle for taking into account the influence of bundle lower tubes on the heat transfer in the upper tubes, a vapor generator mockup with a horizontal tube bundle was developed. High-pressure water served as the heating medium; and electric heaters were provided for additionally heating the CFC refrigerant to a level close to the saturation temperature. The tube bundle includes twelve tubes arranged in three rows along the height: the central row consists of four measurement tubes, and two lateral rows consist of auxiliary tubes. Eight thermocouples are installed at the top and bottom in the slots of the central row heat-transfer tubes for measuring the surface temperature. For the lower and upper rows in the bundle, boiling heat-transfer coefficients were obtained in a wide range of specific heat fluxes. It is shown that the boiling on the upper rows is significantly more (by 30–35%) intense than it is on the lower rows.