• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.12
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• pp.971-976
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• 2006

The objectives of this paper are to study the characteristics of pool boiling heat transfer for enhanced tubes used in the evaporator of turbo chiller and to provide a guideline for optimum design of an evaporator using HFC134a. Three different enhanced tubes are tested at 4 different saturation temperatures. The wall super heated temperature difference ranges from $0.5^{\circ}C\;to\;3.5^{\circ}C$. The refrigerant, HFC134a evaporates on the outside of the tube while the chilled water flows inside the tube. This study provides experimental heat transfer coefficients for evaporation on the enhanced tubes. It is found that the turbo-II tube provides the highest heat transfer coefficient.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.7
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• pp.315-321
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• 2014

In this study, external condensation heat transfer coefficients (HTCs) of two non-azeotropic refrigerant mixtures of HFC32/HFC152a at various compositions were measured on both 26 fpi low-fin and Turbo-C enhanced tubes, of 19.0 mm outside diameter. All data were taken at the vapor temperature of $39^{\circ}C$, with a wall subcooling of 3~8 K. Test results showed that the HTCs of the tested mixtures on the enhanced tubes were much lower than the ideal values calculated by mass fraction weighting of the pure component HTCs. Also, the reduction of HTCs due to the diffusion vapor film was much larger than that of a plain tube. Unlike HTCs of pure fluids, HTCs of the mixtures measured on enhanced tubes increased, as the wall subcooling increased, which was due to the sudden break-up of the vapor diffusion film with an increase in wall subcooling. Finally, the heat transfer enhancement ratios for mixtures were found to be much lower, than those of pure fluids.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.808-814
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• 1999

Pool boiling performance of a metal-formed enhanced tube for a flooded refrigerant evaporator was experimentally investigated. Tests were performed for three different refrigerants(R-11, R-123, R-l34a), at two different saturation temperatures $4.4^{\circ}C \;and \;26.7^{\circ}C$ .Heat flux was varied from 10㎾/$m^2\;to\ 50㎾/$m^2$. Compared with the heat transfer coefficients of the smooth tube, the heat transfer coefficients of the enhanced tube were 6.6 times higher for R-11, 6.0 tines higher for R-123 and 3.5 times higher for R-l34a. The enhancements are comparable with those of foreign products. The heat transfer coefficients of R-l34a were higher than those of R-11 and R-123, either for the enhanced tube or for the smooth tube. At $4.4^{\circ}Csaturation temperature, however, the heat transfer coefficients of R-l34a were approximately the same as those of R-11, The effect of the saturation pressure on the boiling performance was similar to that of the smooth tube - the heat transfer coefficient increases as the saturation pressure increases.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.3
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• pp.382-388
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• 2006

This study experimented to understand the effect of transporting ice slurry through in pipe with valve. And at this experiment it used ethylene glycol-water solution and a concentration is 30wt%. The experimental apparatus was constructed of ice slurry generation tank, turbo flow meter, manometers for differential pressure measuring, PIV system for flow pattern measuring. illumination and along a horizontal circular tube with valve as test section. The experiments were carried out under various conditions, with velocity of fluid at the entry ranging from 0.5 to 1.5 m/s and concentration of IPF is 30%. Also valve open rate is 50%, 75%, 100%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.12
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• pp.1017-1024
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• 2006

In this work, pool boiling heat transfer coefficients (HTCs) of five hydrocarbon refrigerants of propylene, propane, isobutane, butane and dimethylether (DME) were measured at the liquid temperature of $7^{\circ}C$ on a 26 fpi low fin tube, Turbo-B, and Thermoexcel-E tubes. All data were taken from 80 to $10kW/m^2$ in the decreasing order of heat flux. The data of hydrocarbon refrigerants showed a typical trend that nucleate boiling HTCs obtained on enhanced tubes also increase with the vapor pressure. Fluids with lower reduced pressure such as DME, isobutane, and butane took more advantage of the heat transfer enhancement mechanism of enhanced tubes than those enhancement ratios of $2.3\sim9.4$ among the tubes tested due to its sub-channels and re-entrant cavities.

• Journal of Fisheries and Marine Sciences Education
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• v.6 no.1
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• pp.58-76
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• 1994

Heat transfer and pressure drop measurements are made on low integral-fin tubes in turbulent water flow condition. The integral-fin tubes investigated in this paper are nominally 19mm in diameter. Eight tubes have been used with trapezoidally shaped integral-fins having fin density from 748 to 1654 fpm and 10, 30 grooves. Plain tube having same diameter as finned tube is also tested for comparison. Experiments are carried out using R-11 as working fluid. The refrigerant condensates at a saturation state of $30^{\circ}C$ on the outside tube surface cooled by coolant. The amount of noncondensable gases present in the test loop is reduced to a negligible value by repeated purging. For a given heat input to the boiler and given cooling water flow rate, all test data are taken on steady state. The heat transfer loop is used for testing single long tubes and cooling water is pumped from a storage tank through filters and flowmeters to the horizontal test section where it is heated by steam condensing on the outside of the tube. The pressure drop across the test section is measured by means of pressure gauge and manometer. Each tube tested is cleaned with sodium dichromate pickling solution and well rinsed with water prior to installation in the test section. The results obtained in this study is as follows : 1. Based on inside diameter and nominal inside area, heat transfer of finned tube is enhanced up to 4 times as that of a plain tube at constant Reynolds number and up to 2 times at constant pumping power. 2. Friction factors are up to 1.6~2.1 times those of plain tube. 3. At a given Reynolds number, Nusselt number decrease with increasing pitch to diameter. 4. The constant pumping power ratio for low integral-fin tubes increase directly with the effective area to the nominal area ratio, and with the effective area diameter ratio.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.1
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• pp.124-131
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• 2000

In this study, pool boiling performance of Turbo/B-type metal-formed tubes was investigated. Tubes with three different cavity gap width(0.04 mm, 0.07 mm, 0.1 mm) were manufactured and tested using R-11, R-123 and R-134a. Tests were conducted at two different saturation temperatures $4.4^{\circ}C$ and $26.7^{\circ}C.$ Heat flux was varied from 10 kW/m2 to 50 kW/m2. It was found that optimum gap width varied for different refrigerants. For low-pressure refrigerants such as R-11 or R-123, optimum gap width was 0.07 mm. For high-pressure refrigerant R-134a, however, the optimum value was 0.1 mm. Compared with the heat transfer performance of the smooth tube, the metal-formed tubes enhanced the heat transfer coefficients significantly - 6.5 times for R-11, 6.0 times for R-123 and 5.0 times for R-134a (at $4.4^{\circ}C$ saturation temperature and 40 kW/m2 heat flux), which are comparable with the performance of foreign products. The heat transfer coefficients of R-134a were larger than those of R-11 or R-123, and they increased as the saturation temperature increased.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.5
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• pp.231-238
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• 2017

HFO refrigerants have recently come to be regarded as promising alternatives to R134a for use in turbo chillers. This study provides results from experiments evaluating the film condensation heat transfer characteristics of HFO refrigerants R1234ze(E) and R1233zd(E) on smooth horizontal laboratory tubes. The experiments were conducted at a saturation vapor temperature of $38.0^{\circ}C$ with surface sub-cooling temperatures in the range of $3{\sim}15^{\circ}C$. We observe that the film condensation heat transfer coefficient decreases as surface sub-cooling temperatures increase. In the case of laboratory tubes with a diameter of 19.05 mm, the film condensation heat transfer coefficients of R1234ze(E) and R1233zd(E) were approximately 11% and 20% lower than those of R134a, respectively. Furthermore, our investigation of the effect of tube diameter on film condensation heat transfer coefficients, demonstrates an inverse relationship where the film condensation heat transfer coefficient increases as laboratory tube diameter decreases. We propose experimental correlations of Nusselt number for R1234ze(E) and R1233zd(E), which yield a ${\pm}20%$ error band.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.2
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• pp.161-167
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• 2002

In this study, external condensation heat transfer coefficients (HTCs) of two non-azeotropic refrigerant mixtures of HFC32/HFC134a and HF0134a/HCF0123 at various compositions were measured on both low fin and Turbo-C enhanced tubes of 19.0 mm outside diameter All data were taken at the vapor temperature of 39$^{\circ}C$ with a wall subcooling of 3- 8 K. Test results showed that HTCs of the tested mixtures on the enhanced tubes were much lower than the ideal values calculated by the mass fraction weighting of the pure compo- nents'HTCs. Also the reduction of HTCs due to the diffusion vapor film was much larger than that of a plain tube. Unlike HTCs of pure fluids, HTCs of the mixtures measured on enhanced tubes increased as the wall subcooling increased, which was due to the sudden break up of the vapor diffusion film with an increase in wall subcooling. Finally, heat transfer enhancement ratios for mixtures were found to be much lower than those of pure fluids.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.7
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• pp.980-991
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• 1998

In this study, nucleate pool boiling heat transfer coefficients of alternative refrigerants on a plain, low fin, and two enhanced tubes were measured and compared against each other. To obtain data at conditions similar to the actual evaporator, a fluid heating method was employed instead of an electric heating method in the experiments. R123, R134a, R22 and R410a were used as working fluids and data were taken at 7 deg.C ar heat fluxes of 20 ~ 100 kW/m$\^$2/. Comparison of the plain tube data against some correlations showed that the simplest correlation of Cooper based on reduced pressure predicted the data for all fluids tested with a 10% deviation. For all refrigerants, enhanced tubes composed of subsurface and subtunnels, especially Thermoexcel-E tube, showed the highest heat transfer coefficients among the tubes tested with one exception that the low fin tube's performance was better than those of enhanced tubes for high vapor pressure fluid such as R410a at high heat flux. Finally, a low fin and enhanced tubes showed higher heat transfer enhancement for low vapor pressure of R123 than for high vapor pressure fluisd. For R123, the enhancement factors for Turbo-B and Thermoexcel-E tubes were 2.8 ~ 4.8 and 4.6 ~ 8.1 respectively.