• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.341-346
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• 2009

The purpose of the present study is to investigate the flow resistance and the heat transfer characteristics of oval fin-tube heat exchanger. Six kinds of oval fin having the same fin area and the different diameter ratio tested numerically. Test data for the heat transfer, pressure drop and fin temperature were shown and discussed. The pressure drop and heat transfer increased for increasing the oval fin diameter ratio(diameter of span-wise direction to diameter of longitudinal diameter) up to 50% and 45% respectively.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1473-1478
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• 2003

Scale is formed when hard water is heated or cooled in heat transfer equipments such as heat exchangers, condensers, evaporators, cooling towers, boilers, and pipe walls. When scale deposits in a heat exchanger surface, it is traditionally called fouling. The objective of the present study is to investigate the formation of fouling in a heat exchanging system. A lab-scale heat exchanging system is built-up to observe and measure the formation of fouling experimentally. Water analyses are conducted to obtain the properties of HAN river water. In the present study a microscopic observation is conducted to visualize the process of scale formation. Hardness of HAN-river water is higher than that of tap water in Seoul.

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.2
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• pp.83-88
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• 2005

This study investigates the air leakage and heat transfer characteristics of a commercially available rotary-type air-to-air heat exchanger with a fiber polyester matrix. Crossover leakage between the exhaust and supply air is measured using a tracer gas method for various ventilation rates and rotational speeds of the wheel. A correlation equation for the leakage is obtained by summing up pressure leakage and carryover leakage. The pressure leakage is observed to be a function of ventilation rate only, and the carryover leakage is found to be a linear function of wheel speed. The real efficiency of the heat exchanger can be obtained from its apparent efficiency by taking into account the leakage ratio. The heat recovery efficiency decreases, as the ventilation rate increases. As the wheel speed increases, however, the efficiency increases initially but reaches a constant value for the speeds over 10rpm.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.8
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• pp.664-670
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• 2002

A heat sink (HS) system using heat pipes for electronics systems was studied. The experimental results indicate that a cooling capacity of up to 150w at an overall temperature difference of $50^{\circ}C$ can be attainable. The heat sink design program also showed that a computer simulation can predict the most of the parameters involved. To do so, however, the interior temperature distribution had to be verified by experimental results. The current simulation results were close to the experimental results in acceptable range. The simulation study showed that the design program can be a good tool to predict the effects of various parameters involved in the optimum design of the heat sink.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.799-807
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• 1999

Exergy analysis is widely used in energy system analysis for more efficient energy use. Pinch technology has focused on chemical plants, such as pure heat exchanger networks. In this study, the objective is to seek more effective means with integrating above two methods. In order to demonstrate effective result and to prove possibility for pinch analysis, the steam turbine is adopted to make heat recovery in the heat exchanger network. Three cases are introduced using the integration of exergy and pinch analysis. The standard steam turbine utility is the base case, and adding the heat pump to this system is the second case. The third case is the system with the heat pump and minimum utilities. The results show that the output power of steam turbine in the case(2) and case(3) are increased up to 42% and 46%, respectively, compared with that of base case.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.7
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• pp.639-644
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• 2004

This paper deals with the heat transfer characteristics of R-1270 (Propylene), R-600a (Iso-butane) and R-290 (Propane) as an environment friendly refrigerant and R-22 for condensing. The experimental apparatus has been set-up as a conventional vapor compression type heat pump system. The test section is a horizontal double pipe heat exchanger. A tube diameter of 12.70 mm with 1.32 mm wall thickness is used for this investigation. The test results showed that the local condensing heat transfer coefficients of hydrocarbon refrigerants were higher than that of R-22. The average condensing heat transfer coefficient was obtained with the maximum value in R-1270 and the minimum one in R-22. Comparing the heat transfer coefficient of experimental results with that of other correlations, the presented results had a good agreement with the Cavallini-Zecchin's correlation. It reveals that the natural refrigerants can be used as substitute for R-22.

• Nuclear Engineering and Technology
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• v.36 no.5
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• pp.460-474
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• 2004

Effects of liquid subcooling on pool boiling heat transfer in an annulus with an open bottom have been investigated experimentally. A tube of 19.1mm diameter and the water at atmospheric pressure have been used for the fest. Up to $50^{\circ}C$ of liquid subcooling has been tested and experimental data of the annulus have been compared with the data of a single unrestricted tube. Temperatures on the heated tube surface fluctuate only slightly regardless of the heat flux in the annulus, whereas high variation is observed on the surface of the single tube. An increase in the degree of subcooling decreases heat transfer coefficients greatly both for the single tube and the annulus. Heat transfer coefficients increase suddenly at ${\Delta}T_{sub}\;{\le}\;10^{\circ}C$ and much greater change in heat transfer coefficients is observed at the annulus. To obtain effects of subcooling on heat transfer quantitatively, two new empirical equations have been suggested, and the correlations predict the empirical data within ${\pm}30\%$ error bound excluding some data at lower heat transfer coefficients.

• Journal of the Korean Society of Visualization
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• v.17 no.1
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• pp.10-18
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• 2019

In this study, the temperature behavior of Pulsating Heat Pipe (PHP) according to the diameter change were studied by limiting the diameter change to only the evaporator. To investigate operation of PHP in various heat input, heat input power was increased from 10 to 120 W. The results show operation can be divided into 3 regimes by temperature behavior. Thermal resistance was increased before start-up and decreased with increasing heat input. At 110 W heat input, thermal conductivity of 2 mm PHP was 8 .times higher compare to thermal conductivity of copper. Further, to investigate details of temperature behavior in higher heat input, FFT analysis was conducted. Based on the results, when the deviation of peak frequency in each section is lowest, the thermal resistance has lowest value.

• Korean Journal of Materials Research
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• v.21 no.2
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• pp.73-77
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• 2011

Specific heat of a crystal is the sum of electronic specific heat, which is the specific heat of conduction electrons, and lattice specific heat, which is the specific heat of the lattice. Since properties such as crystal structure and Debye temperature do not change even in the superconducting state, the lattice specific heat may remain unchanged between the normal and the superconducting state. The difference of specific heat between the normal and superconducting state may be caused only by the electronic specific heat difference between the normal and superconducting states. Critical temperature, at which transition occurs, becomes lower than $T_{c0}$ under the influence of a magnetic field. It is well known that specific heat also changes abruptly at this critical temperature, but magnetic field dependence of jump of specific heat has not yet been developed theoretically. In this paper, specific heat jump of superconducting crystals at low temperature is derived as an explicit function of applied magnetic field H by using the thermodynamic relations of A. C. Rose-Innes and E. H. Rhoderick. The derived specific heat jump is compared with experimental data for superconducting crystals of $MgCNi_3$, $LiTi_2O_4$ and $Nd_{0.5}Ca_{0.5}MnO_3$. Our specific heat jump function well explains the jump up or down phenomena of superconducting crystals.

• Journal of Ocean Engineering and Technology
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• v.23 no.4
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• pp.85-90
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• 2009

Although most of existing hydration heat control methods show a certain degree of hydration heat control, generally, there are many problems as mentioned above. Therefore, our laboratory previously developed a hydration heat control method using an exposed heat pipe, which solves most of these problems and simultaneously displays excellent hydration heat control. Unfortunately, even this method had some problems such as the processing, transport, and assembly of heat pipes, and the surface treatment of a cut plane after pouring, and hardening concrete. Therefore, in this study, a hydration heat control method using an embedded pipe has been developed with the expectation that this method solves those problems in hydration heat control using an exposed heat pipe. As a result of the experiment, the peak temperature of ECHP and ICHP specimen about $4.5{\sim}6.5^{\circ}C$ than the OPC specimen and the probability of thermal cracked generated in ECHP and ICHP specimen decreased up to $13{\sim}20%$. Finally, it was confirmed in this study that the hydration heat control method using an embedded heat pipe is significantly more superior and cost effective than the existing method of an exposed one.