CORRELATIONS AND NEURAL NETWORKS AS MODELS FOR THE LOCAL HEAT TRANSFER COEFFICIENT ON CONDENSATION FOR R1234YF IN Ø 0.96MM DUCTS

Due to global warming considerations, the European Union has banned the use of refrigerants with a GWP greater than 150 in new passenger cars (air-conditioning systems) and 750 for fluids used in residential heat exchangers starting on January 1, 2017 (E. UNION, 2006). In this sense, the R1234yf was developed which consists of a hydrofluorolefin derived from alkenes and commercialized with the name of Opteon YF. Given the need for research related to the use of this fluid, this work has the objective of comparing the data of the local heat transfer coefficient in condensation extracted from the work of Del Col et al. (2010) for flow in a mini channel of 0.96 mm internal diameter, with mass flux of 200, 300, 400, 600, 800 and 1000 kg·(m²·s)-1 at saturation temperature of 40ºC with ten different correlations from literature as well as one neural network. It is verified that among the correlations analyzed the one which best suited the experimental data was presented by Cavallini and Zecchin (1974), with MRD, MARD, and Accuracy values equal to 5.42%, 7.81%, and 96.96%, respectively. The neural network used as a prediction model presents values of MRD, MARD, and Accuracy equals to 2.53%, 3.66%, and 100%, respectively

Consideration on Local Heat Transfer Measurement of Plate Heat Exchanger with the Aid of Simulation

In this study, the local heat transfer coefficient of boiling and condensation were obtained by an experimental set up using vertical stainless-steel type brazed plate heat exchanger. A series of 8 vertical brazed plates are used as the major components of the test section of experimental set up and are fabricated into layers so that flow channels are formed between the plates through which water and refrigerants are flowing through. The experiments are carried out at the mass flux of 10, 20 and 50 kg/(m2žs). In order to measure the local heat transfer coefficient, flat stainless-steel plates of 10 mm in thickness are installed attached to the vertical plates onto which the thermocouples are positioned to measure the temperature distributions at the surface of the plates. By performing the experiment, the direction of the heat flux across the plate tends to deviate downward especially at the lower part of the plate due to the non-uniform temperature distributions across the plate. The results are analyzed and validated at the mass flux of 10 kg/(m2žs) by the aid of the simulation tool by using ANSYS FLUENT 19.1 to estimate the local heat transfer coefficient and the heat flux across the plate. The analysis result shows that the simulation model can assist to track the deviation of the direction of the heat flow from the horizontal direction across the plate and the experimental results of the local heat transfer coefficient have similar trends with that of the simulation results.