Experimental investigation on Al2O3-R123 nanorefrigerant heat transfer performances in evaporator based on organic Rankine cycle.

Graphical abstract This paper presents an experimental investigation of heat transfer performances including heat transfer coefficient along flowing direction, log-mean temperature difference and differential pressure of pure R123 and four volume concentrations 20 nm Al 2 O 3 -R123 nanorefrigerants with various volume concentrations 0.03%, 0.13%, 0.18%, 0.23% flowing inside a double-tube counter flow heat exchanger of an organic Rankine cycle system under the conditions of various heat source temperatures and flow rates. A comparison has been made between pure R123 and four kinds of nanorefrigerants to find out the influences of different nanoparticles volume concentrations on local heat transfer coefficient and variation tendency (straight lines) along flowing direction in evaporator. By using polynomial fitting where polynomial order is 3, the polynomial fitting curves (dash lines) and the optimum of volume concentration has been acquired, which indicates the loading carrying capacity in each operation condition. Highlights • Effect of Al 2 O 3 nanoparticles on R123 heat transfer performances. • Variation tendency along flowing direction in evaporator of ORC. • Polynomial fitting curve. • Comparison of differential pressure and log-mean temperature difference of R123 and nanorefrigerants. Abstract This paper presents an experimental investigation of variation tendency of heat transfer coefficient, log-mean temperature difference and differential pressure of pure R123 and 20 nm Al 2 O 3 -R123 nanorefrigerants with four various volume concentrations, 0.03%, 0.13%, 0.18%, 0.23% flowing inside the evaporator of organic Rankine cycle system under the conditions of various heat source temperatures and flow rates. Heat source temperatures are in the range of 50–90 °C at an interval of 10 °C, and heat source flow rates are 0.7 m3/h, 1.3 m3/h and 1.8 m3/h. Results show an increment of heat transfer coefficient along flowing direction for both pure R123 and four Al 2 O 3 -R123 nanorefrigerants with the increment of heat source temperature and flow rate, and that of four nanorefrigerants are higher than that of pure R123. There is no optimum value of heat transfer coefficient when operation condition is changed for the loading carrying capacity increasing with the increasing intensity of operation condition. Meanwhile, suspending nanoparticles and increasing heat source temperature can change the variation tendency of heat transfer coefficient along flowing direction except pure R123 and 0.18 vol% nanorefrigerant. In addition, 0.13 vol% as a whole is the optimum volume concentration for both log-mean temperature difference and differential pressure. [ABSTRACT FROM AUTHOR]