• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2328-2333
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• 2008

The experimental study was carried out to evaluate the heat transfer performance on the shell side of shell-and-plate finned tube heat exchanger with three different tube numbers(9, 13 and 19). Oil flowing on the shell side was cooled by cold water flowing inside the tubes. A shell-and-tube heat exchanger of an oil cooler consisted of one shell pass and two tube passes with the inner tube diameter of 8.82 mm and the tube length of 575 mm. Mass flow rate was varied from 1.2 to $6.0\;m^3/h$ for oil and from 0.6 to $3.0\;m^3/h$ for cold water, respectively. From the experiment of shell-and-plate finned tube heat exchanger, the shell side heat transfer coefficient of heat exchanger with 9 tubes was compared with that of 13 and 19 tubes. It was found that the heat exchanger with 9 plate finned tubes showed more performance of heat transfer than that of 13 and 19 tubes.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.2
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• pp.166-174
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• 1994

An experimental study has been performed to identify the evaporation characteristics of HCFC-22 for transport refrigeration system. Heat transfer coefficients were measured in a horizontal, smooth evaporating tube with an inner diameter of 10.7mm and a length of 2.8m. The refrigerant was heated electrically by surface-wrapped heaters and uniform power is applied along the tube. The entire tube was divided into 7 sections. Surface temperatures of tube and refrigerant temperature in each test section were measured. Pressure drops in each section and the inlet pressure were also measured. The mass flowrate of the refrigerant was controlled and measured. A single tube evaporation test was conducted for different ranges of mass flux of refrigerant, heat flux of evaporator and condensing temperature of transport refrigeration system. The evaporation heat transfer coefficients of HCFC-22 were compared with predictions from the well known Chen's correlations. Averaged heat transfer coefficients in this experiment range from $2kW/m^2/^{\circ}C$ to $3kW/m^2/^{\circ}C$. Most of the experimental results differ from the predicted ones by less than ${\pm}30%$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.8
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• pp.612-620
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• 2008

New alternative refrigerants have been developed due to the ozone layer depletion and global warming. For this reason, carbon dioxide is believed to be a promising refrigerant for use in air conditioners and heat pumps. Evaporative heat transfer characteristics and pressure drop of $CO_2$ with outer diameter of 5 mm in inclined ($45^{\circ}$) smooth and micro-fin tubes have been investigated by the experiments with respect to several test conditions such as mass fluxes, heat fluxes, evaporation temperatures in this study. The inclined ($45^{\circ}$) smooth and micro-fin tubes with length of 1.44 m were installed to measure the evaporative heat transfer coefficients of $CO_2$ and heat was supplied to the refrigerant by direct heating method where the test tube was uniformly heated by electricity. The tests were conducted at mass fluxes from 212 to $656\;kg/m^2s$, heat fluxes from 15 to $60\;kW/m^2$ and evaporation temperatures from -10 to $20^{\circ}C$. The heat transfer coefficients of $CO_2$ are slightly increased with increasing mass flux, and the heat transfer characteristics in the inclined ($45^{\circ}$) tubes are enhanced about $5{\sim}10%$ compared with those in horizontal or vertical tubes.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.9
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• pp.1253-1262
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• 2001

Experimental study is conducted to investigate the heat/mass transfer and flow characteristics for the flow over backward-facing step and cavities. A naphthalene sublimation method has been employed to measure the mass transfer coefficients on the duct wall and LDV system has been used to obtain mean velocity profiles and turbulence intensities. Reynolds number based on the step height and free stream velocity is 20,000 and St numbers of acoustic excitations given to separated flow are 0.2 to 0.4. The spectra of streamwise velocity fluctuation show a sharp peak forcing frequency for an acoustically excited flow. The results reveal that the vortex pairing and overall turbulence level are enhanced by the acoustic excitation and a significant decrease in the reattachment length and the increased turbulence intensity are observed with the excitation. A certain acoustic excitation increases considerably the heat/mass transfer coefficient at the reattachment point and in the recirculation region. For the cavities, heat/mass transfer is enhanced by the acoustic excitation due to the elevated turbulence intensity. For the 10H cavity, the flow pattern is significantly changed with the acoustic excitation. However, for the 5H cavity, the acoustic excitation has little effect on the flow pattern in the cavity.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.6
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• pp.372-380
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• 2008

In order to control indoor air quality and save energy, it is needed to install a suitable ventilation system equipped with heat exchanger for heat recovery. Paper heat exchanger can recover $50{\sim}70%$ of the enthalpy difference between supply and exhaust air. The purpose of this research is to obtain the experimental correlations for the friction factor, heat transfer coefficient, mass transfer coefficient and permeance of paper heat exchanger, which can be used to predict the performance of the paper heat exchanger. Pressure drops at various velocities, and sensible and latent heat transfer rates at various dry-bulb temperatures, relative humidities and specific humidities are measured to derive experimental correlations. The results of prediction using correlations show fairly good agreement with the experimental data obtained in the actual operating conditions.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.3_1spc
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• pp.551-557
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• 2013

The heat transfer performance and pressure drop characteristics of brazed-plate heat exchangers with 20 and 30 plates were experimentally measured and analyzed in this study. The mass flow rates of the heat exchangers with 20 and 30 plates were fixed at 0.6 and 0.9 kg/s for the low temperature side, respectively. The mass flow rate for the high temperature side was controlled from 0.2 kg/s to 1.2 kg/s. The inlet temperatures for the high and low temperature sides were $10^{\circ}C$ and $7^{\circ}C$, respectively. The heat transfer characteristics were not influenced by the number of plates. The pressure drop at the heat exchanger with 30 plates was slightly higher than that with 20 plates. The values calculated from the correlations based on gasket plate heat exchangers were compared with the experimental results. It was found that the predicted Nusselt numbers for the gasket plate heat exchangers were about 5% to 20% lower than the measured Nusselt numbers for the brazed plate heat exchangers. However, a pressure drop comparison showed that the calculated pressure drops at the gasket plate heat exchangers were less than half of the measured pressure drops at the brazed plate heat exchangers.

• Journal of Energy Engineering
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• v.19 no.4
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• pp.234-239
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• 2010

Heat transfer characteristics were experimentally investigated for ice slurry which was made from 6.5% ethylene glycol-water solution flowing in the circular pipe. The test section was made of a copper tube of 13.84 mm inner diameter and 1,500 mm length. The ice slurry was heated by passing hot water through an annulus surrounding the test section. The ice packing factor(IPF) and the mass flux of the experiments were varied from 0 to 25% and from 1,000 to 3,000 kg/$m^2s$ respectively at a fixed hot water temperature and flow rate. The measured heat transfer rates increase with the mass flow rate and IPF; however the effect of IPF appears to be minor at high mass flow rate. At the low mass flow rate condition, a sharp increases in the heat transfer coefficient was observed when the IPF was above 15 ~ 20%. And finally the measured heat transfer coefficients were compared with those calculated from the correlations.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.7
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• pp.938-944
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• 2000

Recently, micro fin tube is widely used to heat exchanger for high performance. And, as the alternative refrigerants for R-22, hydrocarbons such as R-290, R-600 and R-600a are very promising because of their low GWP and ODP. Thus, R-290 was used as working fluid in this study. Most design of heat exchanger had been based on heat transfer characteristics of pure refrigerant although refrigerant oil exists in the refrigeration cycles. So, the influence of oil on heat transfer characteristics have to be considered for investigating exact evaporation heat transfer characteristics. But, this is an unresolved problem of refrigeration heat transfer. Therefore the influence of the refrigeration oil to the evaporation heat transfer characteristics of R-290 were conducted in a horizontal micro tin tube. The mineral oil was used as refrigeration oil. The experimental apparatus consisted of a basic refrigeration cycle and a system for oil concentration measurement. Test conditions are as the follows; evaporation temperature $5^{\circ}C$, mass velocity 100 $kg/m^2s$, heat flux 10 $kW/m^2$, oil concentration 0, 1.3, 3.3, 5.7 wt.%, and quality $0.07{\sim}1.0$. When refrigeration oil was entered, oil foaming was observed at the low quality region. And, very small bubbles were observed as quality was increased. Pressure drop and heat transfer coefficient increased as the concentration of refrigeration oil increased to 5 wt.%.. The performance index of heat exchanger was the highest near 3.3 wt.%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.1
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• pp.140-150
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• 1996

CFC-12, which has been used most widely in automobile air conditioners and household refrigerators is scheduled to be phased out soon because of its high ozone depletion potential. Now HFC-134a is suggested as an alternative refrigerant for CFC-12. In this Study, we intended to investigate how PAG oil influence evaporation heat transfer and flow pattern, using R-134a and PAG oil influences evaporation heat transfer and flow pattern, using R-134a and PAG oil in the horizontal miro-fin evaporation tube. Experiments were conducted under the flowing est conditions : mass velocity 86-250kg/$m^2$s, heat flux 5-30 ㎾/$m^2$, oil concentration 0-21 wt.% and saturation temperature 5$^{\circ}C$. Local evaporation heat transfer coefficients were found to be higher at the top, side and bottom of the tube in this order. Average heat transfer coefficients turned out to increase with oil concentration increment up to 3 wt.% oil concentration, whereas heat transfer coefficients gradually decreased over 3 wt.% oil concentration, because of oil-rich liquid film was formed on the heat transfer surface. Flow patterns were rapidly transitioned to annular regimes up to 3 wt.% oil concentration. In case of pure refrigerant, measured heat transfer coefficients in the experiments were similar to those of Kandlikar＇s correlation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.5
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• pp.633-641
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• 1999

Experiments were carried out to investigate the condensation heat transfer characteristics for R22 and its alternatives, R407C (R32/125/134a, 23/25/52wt%) and R410A (R32/125, 50/50wt%). A concentric tube heat exchanger was made to conduct condensation heat transfer tests. Mass flux and saturation temperature of refrigerants at the test section inlet were varied to get the corresponding heat transfer coefficients. Serial and parallel input of secondary fluid (water) were applied to the test subsections. Compared with existing correlations of condensation heat transfer, experimental heat transfer coefficients obtained in this study were generally higher than the predicted values, and mean absolute deviations from several correlations were shown. Wall subcooling was introduced to get a new correlation for condensation heat transfer coefficients by modifying Shah's equation. The RMS deviation of the measured heat transfer coefficients from the new correlation in this study for R22 is 9.9% and that for R407C and R410A are 10.2% and 14.6%, respectively.