Experimental study on condensation heat transfer and pressure drop in horizontal smooth tube for R1234ze(E), R32 and R410AEtude expérimentale sur le transfert de chaleur et la chute de pression du R1234ze(E), du R32 et du R410A lors de la condensation à l'intérieur d'un tube lisse horizontal

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Abstract

Experimental condensation heat transfer and pressure drop of R1234ze(E), trans-1, 3, 3, 3-tetrafluoropropene (trans-CHFdouble bondCHCF3) in a horizontal smooth tube are measured and compared with R32 and the nearly azeotropic HFC refrigerant blend R410A. The effects of mass flux and saturation temperature on heat transfer and pressure drop have been conducted and analyzed. The copper tube with inner diameter of 4.35 mm and length of 3.6 m was used as the test sections. The tests were conducted for mass fluxes varying from 150 to 400 kg (m−2 s−1) and the saturation temperature ranging between 35 and 45 °C over the vapor quality range 0.0–1.0. It was found that the experimental heat transfer performance of R1234ze(E) was about 20–45% lower than R32 but 10–30% higher than R410A for saturation temperature 40 °C. The experimental results are compared with some well-known existing prediction methods of condensation of pure refrigerant.

Highlights

► We have measured heat transfer and pressure drop of new refrigerant R1234ze(E). ► The data was compared with conventional refrigerants R410A and R32. ► Well-known correlations have been evaluated for heat transfer and pressure drop.

Introduction

Chlorofluorocarbons (CFCs) had been phased out under the Montreal Protocol; CFC alternative refrigerants are searching for based on the condition of no chlorine atoms because of zero ODP. It seemed that conversion from CFC refrigerant to HFC refrigerant or natural refrigerant have been progressed smoothly in the two decades. However, next serious global environmental problem is concerning the refrigerant. It is the global warming problem. Although HFCs do not include chlorine atoms and are very stable materials, the GWP value is high. As the result of their higher GWP values, not only HFC-134a but also other HFCs have to convert to lower GWP refrigerants in order to keep the F-gas regulation in EU countries to be started from 2011.

As for the low GWP refrigerants, hydrofluoro-olefins (HFOs), especially, HFO-1234yf (CF3CFdouble bondCH2: 2, 3, 3, 3-tetrafluoropropene) and HFO-1234ze(E) are recently focusing in the world. Both of these HFOs have low GWP values (HFO-1234yf is 4 (Nielsen et al., 2007) and HFO-1234ze(E) is 6 (Honeywell Fluorine Products, 2008), and expecting as the next generation refrigerant. Many works have been done relating to thermophysical properties of R1234ze(E). A few of those studies (Brown et al., 2009, Grebenkov et al., 2009, Higashi, 2010, Matsuguchi et al., 2010, Miyara et al., 2010, Motta et al., 2010, Tanaka et al., 2010) are listed in the references that have been done to measure the thermophysical properties of HFOs and HFO + HFC mixtures. Miyara et al., 2010, Miyara et al., in press experimentally measured the thermal conductivities of saturated liquid of HFO-1234ze(E), HFC-32, and their mixture. The thermal conductivity of HFO-1234ze(E) is about 40% lower than that of HFC-32. For HFO-1234ze(E) + HFC-32 mixture with 50/50 mass%, thermal conductivity is between those of HFO-1234ze(E) and HFC-32. A new thermodynamic property model is presented by Akasaka (2010) for HFO-1234ze(E) based upon available experimental data. HFO-1234yf is, especially, focused as a refrigerant of mobile air-conditioners. On the other hand, HFO-1234ze(E) is also becoming an influential candidate. Horie et al. (2010) studied system performance of heat pumps using HFC-32, HFC410A, and HFO-1234yf by considering the effect of pressure drop. Park et al. (2011) built a new test facility to conduct condensation heat transfer tests in vertical microchannels, in particular an aluminum multi-port tube. First, they measured the single-phase heat transfer and pressure drop data to validate the measurement systems. Then, a series of experiments covering a wide range of two-phase test conditions were conducted, targeting two-phase computer and electronic cooling system applications, comprising R134a, R236fa and R1234ze(E) condensation heat transfer in vertically aligned multi-minichannels. Dong et al. (2011) measured isothermal VLE data for R1234ze(E) + propane (R290) systems by a recirculation apparatus with view windows at four temperatures (258.150, 263.150, 273.150 and 283.150 K), and found the azeotropic behavior at each measured temperature.

Dalkilic and Wongwises (2009) reviewed a large number of existing studies of heat transfer and pressure drop during in-tube condensation according to the tube orientation (horizontal, vertical, inclined tubes) and tube geometry (smooth and enhanced tubes), flow pattern studies of condensation, void fraction studies, and refrigerants with the effect of oil. Miyara (2008) reviewed condensation of hydrocarbons and Cavallinia et al. (2003) reviewed some research relating to condensation inside and outside smooth and enhanced tubes. Cavallini et al. (2001) experimentally measured the heat transfer coefficient and pressure drop of pure HFC refrigerants (R134a, R125, R236ea, R32) and the nearly azeotropic HFC refrigerant blend R410A inside a smooth tube of diameter 8 mm. The experiment was carried out in a saturation temperature ranging between 30 and 50 °C, and mass velocities varying from 100 to 750 kg (m−2 s−1), over the vapor quality range 0.15–0.85. They found that, during condensation of pure fluids and nearly azeotropic mixtures, in the annular flow regime the heat transfer coefficient varies with mass velocity G, vapor quality x and saturation temperature; only in the stratified regimes the measured heat transfer coefficient was affected by temperature difference between saturation and tube wall (Ts  Tw). Jung et al. (2003) also found that flow condensation heat transfer coefficients increase as the quality and mass flux increase. They carried out the experiment for R12, R22, R32, R123, R125, R134a, and R142b on a horizontal plain tube of outside diameter 9.52 mm with saturation temperature 40 °C and mass fluxes of 100, 200 and 300 kg (m−2 s−1).

In HVACR and heat pump system, before the commercial use of a new refrigerant the design engineers require the heat transfer and pressure drop data of heat exchanger and the necessary prediction methods for analysis the refrigerant. But till now no available data relating to condensation heat transfer and pressure drop of R1234ze(E) in horizontal smooth tube.

In the present study, we experimentally investigate the effect of mass velocity, vapor quality and saturation temperature on condensation heat transfer coefficient (HTC) and pressure drop of R1234ze(E) inside a smooth horizontal tube of ID 4.35 and OD 6.35 mm with different experimental conditions and compare the results with two refrigerants R32 and R410A for the same tube. In this study, experimental results also compare with some well-known prediction methods.

Section snippets

Experimental apparatus

Fig. 1 shows the schematic diagram of the experimental apparatus which is a vapor compression heat pump cycle comprising a inverter controlled compressor, an oil separator, a test condenser, a subcooler, an expansion valve and an evaporator. Cooling water kept at a constant temperature is supplied to the test condenser from a heat source unit. The refrigerant flow rate is regulated by varying the rotating speed of the compressor and opening the expansion valve and is measured by a Coriolis type

Data reduction

The sensible heat gain of the coolant from the inlet to the exit of the whole test section isQC=MCCP,C(TC,OTC,I)

The heat release of refrigerant from the inlet to the exit of the whole test section isQR=MR(hR,IhR,O)

The heat balance factor isηHB=QRQCasshowninFig.3

The heat transfer rate of the coolant side of each subsection isqC=MCCP,C(TC,oTC,i)

The heat flux of each subsection is calculated with qC and ηHB.qR=qCηHBπdiΔz

Because of the good agreement of heat balance as shown in Fig. 3 was

Results and discussion

Table 3 lists the thermodynamic and transportation properties of the three refrigerants R1234ze(E), R32 and R410A at 40 °C which was calculated by REFPROP 9.0. It is notable that among the three refrigerants, R1234ze(E) is a low pressure, high liquid density, low vapor density, low thermal conductivity, high viscosity and high surface tension refrigerant. A total of 242 experimental data for condensation in a horizontal smooth tube for R1234ze(E), R32 and R410A ranging in mass fluxes from 160 to

Conclusion

Condensation heat transfer and pressure drop were experimentally investigated inside a smooth tube with R1234ze(E), R32, and R410A for different refrigerant mass fluxes. For R1234ze(E), the experiment was conducted for three different saturation temperatures of 35, 40 and 45 °C. The effects of vapor qualities, mass fluxes and saturation temperature on heat transfer coefficient and pressure drop are discussed and compared with some well-known correlations in the paper and we found the following

Acknowledgment

This study was supported by Toshiba Carrier Co., Toshiba Home Appliances Co. and Sumitomo Light Metal Industries Ltd.

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