Experimental study on flow boiling heat transfer characteristics of R134a, R245fa and R134a/R245fa mixture at high saturation temperatures
Section snippets
Instruction
The working fluid R245fa is usually selected as working fluid in organic Rankine cycle (ORC) and high temperature heat pump system due to its high critical temperature (154 °C), which is benefit to be used in high temperature heat pump and ORC systems. Kang [1], Usman et al. [2] and Galloni et al. [3] used R245fa as ORC system circulation working substance in their experimental research work, of which results show that the safety of R245fa could be guaranteed in the system operation process,
Experimental apparatus
In this study, the experimental system mainly includes the preheating segment, the test section, visual segment, condenser, data acquisition system, pressure acquisition, electric heating section and power meter, as shown in Fig. 1(a). Fig. 1(b) shows the actual system and equipment layout.
The experimental test section is a copper tube with 10 mm inner diameter, of which tube thickness is 1 mm. The electric heating wire was placed outside the surface of the tube which was covered by insulation
Experiment results at high saturation temperatures
The experimental results of this work were compared with some data from literature. It can be seen in Fig. 6 that the results in this study are coincided with Kattan et al.'s [20], which can determine the reliability of the experimental system. And the dryout took place at the vapor quality of 0.765.
Fig. 7(a) shows the wall temperature variations of different locations of R134a at 65 °C. At low and medium vapor qualities, the wall temperatures on the top of the tube were higher than those of
Comparison of pure refrigerant and mixture refrigerant
Fig. 10 shows the mixture temperature comparison between Refprop9.1 [23] and experimental data, the result shows the temperature difference was less than 0.2 K.
Two-phase pressure drop results
The fractional pressure drop was obtained from the measured total pressure, then subtracted the momentum contribution and the gravity gradient:
Since the tube was horizontal, the gravity contribution could be ignored.
The momentum pressure gradients were:
The void fraction was from Rouhani et al.'s [27] study.
In Fig. 16, the
Conclusions
In this paper, the heat transfer characteristics of R134a and R134a/R245fa mixture at high evaporation temperatures were studied, and the following conclusions were obtained.
- (1)
The heat transfer coefficient of the mixture (R34a/R245fa with 33%/67% by mass) is much lower than that of pure R134a and is very close to that of pure R245fa.
- (2)
The heat transfer coefficients of three working fluids are increased slightly when the saturated temperatures change within 10 °C.
- (3)
The pressure drop of the mixture
Declaration of competing interest
The authors declared that they have no conflicts of interest to this work.
We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.
Acknowledgements
This work was supported by National Natural Science Foundation of China (No. 51876135) and Shanghai Hanbell CO., LTD.
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