• Proceedings of the KSME Conference
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• 2001.06e
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• pp.175-178
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• 2001

In a clothes dryer, various thermo-fluid flow phenomena occur such as the heat and mass transfer in the process of removing moisture from clothes, the flow field generated by the fan, and the various flow characteristics from the complex flow paths. The study and understanding of such phenomena is an important factor in increasing the performance of dryers. In this study, as part of a dryer research, the flow field inside a vented dryer was measured using PIV, which the result will be used as the basic material in analyzing the various flow phenomena.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.29-35
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• 1996

For the Reactor Coolant System(RCS) flow rate measurement by the secondary calorimetric heat balance method, the coolant temperature of the hot leg is needed. Several Resistance Temperature Detectors(RTD) are installed in the hot leg to measure the temperature, but the average value of RTDs does not correctly represent the energy-averaged(bulk) temperature because of the thermal stratification phenomenon. Therefore some correction is introduced to predict the bulk temperature, but the correction inevitably contains uncertainty because the stratification is not defined well quantitatively yet. Therefore a large uncertainty for the correction has been used for the conservative estimation. But unrealistically large uncertainty causes degradation of the measurement method and yields difficulty to meet the acceptance criterion in start-up flow measurement test. In this paper, an analytical estimation is made on the correction and the related uncertainty using the measured hot leg velocity profile of System 80 reactor flow model test and the measured temperatures of YGN 3&4 and PVNGS 1&2 start-up tests. The results reveal that the magnitude of the correction uncertainty is much smaller than that used in the previous design. Therefore, the confidence on the flow rate measurement method can be improved and the difficulty in start-up flow measurement test can be lessened if the smaller correction uncertainty obtained through this estimation is applied.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.581-586
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• 2009

Knowledge of ground thermal properties is most important for the proper design of large scale BHE(borehole heat exchanger) systems. The type, pipe size and thermal performance of the BHE is highly dependent on the ground source heatpump system-efficiency and instruction cost. Thermal response tests with mobile measurement devices were developed primarily for insitu determination of design data for large diameter BHE for triple-U spacer apply. The main purpose has been to determine insitu values of effective ground thermal conductivity and thermal resistance, including the effect of ground-water flow and natural convection in the boreholes. The test rig is set up on a some trailer, and contains a circulation pump, a inline heater, temperature sensors, flow meter, power analysis meter and a data logger for recording the temperature, fluid flow data. A constant heat power is injected into the borehole through the tripl-U pipes system of test rig and the resulting temperature change in the borehole is recorded. The recorded temperature data are analysed with a line-source model, which gives the effective insitu values of rock thermal conductivity and borehole thermal resistance of large diameter BHE for spacer apply.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.1
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• pp.105-110
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• 2018

The flow boiling heat transfer of water was experimentally investigated on plain and sintered microporous surfaces in a mini-channel. The effects of microporous coating on flow boiling heat transfer of subcooled water were investigated in a 300 mm long mini-channel with a cross section of $20{\times}10mm^2$. The test section has sufficiently long entrance length of 300 mm which provides a fully-developed flow before the channel inlet. The bottom side of the channel was heated by a copper block assembled with a high-density cartridge heater and other sides of the channel were insulated. The microporous surface was fabricated by sintering copper particles with the average particle size of $50{\mu}m$ on the top side of the copper block. Heat transfer measurement was conducted at the mass flux of $208kg/m^2s$ and the heat flux up to $500kW/m^2$. Microporous coated surface showed an earlier boiling incipience compared with plain surface regardless of the mass flux. Microporous coating were significantly attributed to local wall temperature and local heat transfer coefficient for flow boiling.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.4
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• pp.368-373
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• 2004

A flow field in a passage with periodically converging-diverging cross-section is investigated experimentally by PIV measurement. A tube with a sinusoidally wavy cross section is one of several devices employed for enhancing the heat and mass transfer efficiency due to turbulence promotion and unsteady vortical motion. While the numerical flow visualization results have been limited to the fully developed cases, existing experimental results of this flow were simple qualitative ones by smoke or dye streak test. Therefore, the main purpose of this study is to produce quantitative flow data for fully developed and transient flow regime by the Correlation Based Correction PIV (CBC PIV) and to conjecture the analogy between flow characteristics and heat transfer enhancement with low pumping power. Another purpose of this paper is to examine the onset position of the transition and the global mixing, which results in transfer enhancement. At Re=2000, evidences of the global mixing are captured at 2.5 wavy module through the variation of RMS values and instantaneous velocity plot.

• Transactions of the Korean hydrogen and new energy society
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• v.10 no.1
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• pp.19-26
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• 1999

The effectiveness of a double-tube heat exchanger has been investigated experimentally. This problem is of particular interest in the design of the heat exchanger in a hydrogen liquefaction system. Temperature, pressure, and mass flow rate for hydrogen were measured both in inner tube and in annulus of a double-tube heat exchanger. The effectiveness could be evaluated from the measured temperature and mass flow rate. It is found that the effectiveness increases with an increase in the heat transfer area of a double-tube heat exchanger and with a decrease of the heat capacity ratio. But the increase rate of the effectiveness decreased with a decrease of the heat capacity ratio. Therefore, it is presented that a criterion for selecting the heat exchanger length and heat capacity ratio to obtain the effectiveness required in a hydrogen liquefaction system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.8
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• pp.1051-1060
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• 2003

The heat and mass transfer on two kinds of tube surfaces (bare stainless steel tube and Teflon coated tube) in steam-air mixture flow are experimentally studied to obtain design data for the heat exchanger of the latent heat recovery from flue gas. In the test section, 3-tubes are horizontally installed, and steam-air mixture is vertically flowed from the top to the bottom. The pitch between tubes is 67mm, the out-diameter of tube is 25.4mm, and the thickness is 1.2mm ; blockage factor (cross sectional tube area over the cross sectional area of the test section) is about 0.38. All of sensors and measurement systems (RTD, pressure sensor, flow-meter, relative humidity sensor, etc.) are calibrated with certificated standard sensors and the uncertainty for the heat transfer measurement is surveyed to have the uncertainty within 7%. As experimental results, overall heat transfer coefficient of the Teflon (FEP) coated tube is degraded about 20% compared to bare stainless tube. The degradation of overall heat transfer coefficient of Teflon coated tube comes from the additional heat transfer resistance due to Teflon coating. Its magnitude of heat transfer resistance is comparable to the in-tube heat transfer resistance. Nusselt and Sherwood numbers on Teflon (FEP) coated surface and bare stainless steel surface are discussed in detail with the contact angles of the condensate.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.339-344
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• 2001

The present study investigates convective heat/mass transfer and flow characteristics in wavy ducts of primary surface heat exchanger. Experiments using a naphthalene technique are carried out to determine the local transfer characteristics for flow in the corrugated wall duct. The aspect ratios of the rectangular duct cross-section are 7.3, 4.7 and 1.8 with a corrugation angle of $145^{\circ}$. The Reynolds numbers, based on the duct hydraulic diameter, are ranged from 1000 to 5000. The local heat/mass transfer measurement is conducted in the spanwise directions. The results show that Tayler-Gortler vortices exist on the pressure surface. Flow separation on the suction surface appears at a high Reynolds number resulting in a sharp decrease in the local transfer rates, but relatively high transfer rates are obtained in the reattachment region.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.9
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• pp.447-454
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• 2017

In this study, local velocity distribution of cooling air in a heat exchanger used in an air compressor for a railway car was measured and heat transfer characteristics of the heat exchanger were analyzed. First, heat transfer coefficient and fin performance of the cooling air side were predicted and was checked if the fin of the heat exchanger was effectively used. Distribution of air flow rate at high temperature side was predicted through pipe network analysis and heat resistance at high temperature and low temperature side were predicted and compared. Spatial distribution of temperature in the interior and surface of the square channel constituting high-temperature side was predicted and appropriateness of the size of the heat exchanger was examined. As a result of the analysis, the present size of the heat exchanger could be reduced and it could be effective to promote heat transfer inside the heat exchanger rather than outside to improve performance of the heat exchanger.

• Journal of the Korean Society of Visualization
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• v.7 no.1
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• pp.21-28
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• 2009

The study of swirling flow is of technical and scientific interest because it has an internal recirculation field, and its tangential velocity is related to the curvature of streamline. The fluid flow for tubes and elbow of heat exchangers has been studied largely through experiments and numerical methods, but studies about swirling flow have been insufficient. Using the particle image velocimetry(PTV) method, this study found the time averaged velocity distribution with swirl and without swirl along longitude sections and the results appear to be physically reasonable. In addition, streamwise mean velocity distribution was compares with that of other. Furthermore, other experimental investigation was performed to study the characteristics of turbulent water flow in a horizontal circular tube by using liquid crystal. 2D PIV technique is employed for velocity measurement and liquid crystal is used for heat transfer experiments in water. Temperature visualization was made quantitatively by calibrating the colour of the liquid crystal versus temperature using various approaches.