Performance Analysis And Working Fluid Selection Of Organic Rankine Cycle For Low-temperature Heat Recovery

The industrial energy consumption about60%-65%in China is converted to waste heat with different carriers at different temperatures, among which the quantity of low-temperature waste heat is extremely large. In the thermoelectric conversion field of utilizing medium-and-low temperature waste heat, organic Rankine cycles adopting low-boiling-point working fluids are a recommended method to recover the waste heat efficiently. The effiency of an organic Rankine cycle for waste heat recovery is closely related to its cycle parameters and working fluid. It has important practical significance and comprehensive application prospects to analyze the performance of organic Rankine cycle recovering low-temperature wast heat and to select its optimal working fluid.This paper optimized the heat transfer model of the heat exchangers to improve the model of the organic Rankine cycle. The computation methods of the heat exchange area of the evaporator and the condenser were proposed by combining the calculation method of the convective heat-transfer coefficient for single-phase flow and for two-phase flow. The latter calculation method was based on two-phase flow pattern, which has high degree of accuracy and good adaptability for working fluid and work condition. Expressions of performance parameters of the improved organic Rankine cycle were given by analyzing the cyclic process and were programmed using Matlab software.Effects of cycle parameters and hot fluid characteristic parameters on the performance of the improved organic Rankine cycle were explored. The cycle parameters studied are evaporation temperature, degree of superheated, and condensation temperature. The characteristic parameters of the hot fluid studied are its inlet temperature, mass flow rate, and specific heat capacity. Finally, selection of working fluid for low-temperature heat recovery using organic Rankine cycle was carried out. The results show that:1) Effects of evaporation temperature on some performance of the improved organic Rankine cycle for dry fluid expanded at saturated state and at superheated state and for wet fluid expanded at superheated state are nearly identical, which is valid for effects of condensation temperature.2) Effects of degree of superheated on most performance parameters of the improved organic Rankine cycle using dry fluid and using wet fluid are nearly identical.3) Effects of inlet temperature of hot fluid on some performance of the improved organic Rankine cycle for dry fluid expanded at saturated state and at superheated state and for wet fluid expanded at superheated state are nearly identical, which is valid for mass flow rate and specific heat capacity of hot fluid.4) Evaporation temperature, degree of superheated, condensation temperature, and inlet temperature of hot fluid have an effect on the position of the minimal temperature difference in evaporator and the effects are different for different working fluid.5) The maximum of net power per unit heat exchanger area has a relationship with critical temperature of working fluid.6)1-butene, heptane, octane, R245fa, and R245ca are recommended, because they are outstanding in response to the higher net power per unit heat exchanger area for the low-temperature heat resource below503.15K.