Modeling heat exchange in recovery direct-flow boiler of auxiliary power plant based on organic Rankine cycle

Currently, there are many ways to improve the energy efficiency of different technological processes. The article presents the results of heat transfer simulating in a recovery direct-flow boiler of a ship auxiliary power plant using the organic Rankine cycle. There has been illustrated the basic circuit of the organic Rankine cycle unit. The parameters of the studied working bodies (pentane, ethanol, methanol) have been given. The process of the coolant boiling (for methanol) is considered, the process (5 s) of the coolant boiling from the liquid state to the steady state is modeled. There are presented the graphs of the dependence of the heat transfer coefficient on the length of the evaporator tube, on the specific heat of vaporization, on the surface tension, on the physical properties of the heat carrier material. There have been summarized the results of studying the dependence of the heat transfer coefficient during organic coolant boiling on such physical properties of the coolant as heat of vaporization and surface tension. Obtaining a numerical dependence that allows to calculate the heat transfer coefficient during the boiling of organic heat carriers, taking into account the physical properties of these heat carriers has been analyzed. The study was carried out by creating a numerical model of the evaporator in the ANSYS Fluent software. It has been found out that with the increasing ratio of the surface tension force to the specific heat of vaporization, the heat transfer coefficient increases. The empirical equation was also obtained for calculating the heat transfer coefficient during the organic heat carrier boiling.