• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.153-160
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• 2010

A magnetocardiogram (MCG) is a recording of the biomagnetic signals generated by cardiac electrical activity. Biomagnetic instruments are based on superconducting quantum interference devices (SQUIDs). A liquid cryogenic Dewar flask was used to maintain the superconductors in a superconducting state at a very low temperature (4 K). In this study, the temperature distribution characteristics of the liquid helium in the Dewar flask was investigated. The Dewar flask used in this study has a 30 L liquid helium capacity with a hold time of 5 d. The Dewar flask has two thermal shields rated at 150 and 40 K. The temperatures measured at the end of the thermal shield and calculated from the computer model were compared. This study attempted to minimize the heat transfer rate of the cryogenic Dewar flask using an optimization method about the geometric variable to find the characteristics for the design geometric variables in terms of the stress distribution of the Dewar flask. For thermal and optimization analysis of the structure, the finite element method code ANSYS 10 was used. The computer model used for the cryogenic Dewar flask was useful to predict the temperature distribution for the area less affected by the thermal radiation.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.4
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• pp.324-331
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• 2013

All evacuated tube collector is being constantly studied since it can reduce the conductive heat loss in absorber by using vacuum technology and has advantage of heat transport capacity and quick thermal response in comparatively small temperature difference. This study investigated the dynamic thermal performance of the solar collector with the control condition of solar irradiance and fluid temperature by using performance experimental apparatus which is combined with solar collector and refrigerator, examined the thermal characteristics in definite temperature range of fluid in constant temperature tank by simultaneously measuring refrigerating performance. As a result of it, I deducted the related equation of collector efficiency and found that mean collector efficiency has increased through quick heat transfer characteristics according to increase of outdoor temperature and irradiance in case of outlet temperature of constant temperature tank $22^{\circ}C$ when set outlet temperature of solar collector $25^{\circ}C$ with outlet temperature of constant temperature tank $18^{\circ}C$ & $22^{\circ}C$. Also COP of refrigerator was acquired value of 6.2~7.1 at outlet temperature of constant temperature tank $18^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.5
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• pp.389-397
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• 2014

An absorption chiller-heater using only a natural refrigerant hardly causes any environmental pollution. In an absorption chiller-heater, the performance of its high-temperature generator, which uses exhaust gases, is essential to achieving superior system performance. To investigate the performance of such a high-temperature generator, a laboratory-scale high-temperature generator working with exhaust gases was designed and tested. Changes in the performance of the high-temperature generator as a function of inlet conditions of the absorbing solution, such as air inlet temperature and mass flow, were investigated. It was observed that when the air mass flow rate ratio was increased from 80% to 120%, the heat capacity was increased by 30%, 33%, 34%, and 37%, respectively. Additionally, when the air inlet temperature was elevated from $170^{\circ}C$ to $210^{\circ}C$ for absorption solution concentrations of 56%, 55%, 545, and 53%, the heat capacity increased by 140%, 160%, 220%, and 224%, respectively.

• Journal of Hydrogen and New Energy
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• v.5 no.2
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• pp.81-90
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• 1994

The hydrogen fuel tanks having hydrogen storing capacity of about 300g and 1200g are manufactured using $MmNi_{4.7}Al_{0.25}V_{0.05}Fe_{0.001}$ alloy. They are composed of several unit reactor made of Cu-tube(outer diameter = 50.1mm, thickness = 2mm). In order to increase the heat and mass transfer property of the hydride bed, Al-plates are inserted perpendicular to axial direction at intervals of 5mm and three arteries of diameter 8mm are installed symmetrically in each unit reactor. Hydrogen absorption is proceeded about 80% within 30 minute and is completed within 60 minute at the conditions of charging hydrogen pressure of 25atm and temperature of $22^{\circ}C$. On desorbing hydrogen at a constant rate of 30 slm at $20^{\circ}C$, discharging hydrogen pressure is sustained at 3~5atm for 120 minutes. The discharging pressure is increased upto 5~8atm as the increase of the reactor temperature to $30^{\circ}C$. From the experimental results and the brief discussions about the hydrogen absorption and disorption behaviors of the hydrogen storage tank, it is suggested that the behaviors of hydrogen charging and discharging could be controlled by adjusting the operating parameters and the reactor design parameters.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.1 s.34
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• pp.9-16
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• 2005

This paper presents the development of new anisotropic conductive adhesives with enhanced thermal conductivity for the wide use of adhesive flip chip technology with improved reliability under high current density condition. The continuing downscaling of structural profiles and increase in inter-connection density in flip chip packaging using ACAs has given rise to reliability problem under high current density. In detail, as the bump size is reduced, the current density through bump is also increased. This increased current density also causes new failure mechanism such as interface degradation due to inter-metallic compound formation and adhesive swelling due to high current stressing, especially in high current density interconnection, in which high junction temperature enhances such failure mechanism. Therefore, it is necessary for the ACA to become thermal transfer medium to improve the lifetime of ACA flip chip joint under high current stressing condition. We developed thermally conductive ACA of 0.63 W/m$\cdot$K thermal conductivity using the formulation incorporating $5 {\mu}m$ Ni and $0.2{\mu}m$ SiC-filled epoxy-bated binder system to achieve acceptable viscosity, curing property, and other thermo-mechanical properties such as low CTE and high modulus. The current carrying capability of ACA flip chip joints was improved up to 6.7 A by use of thermally conductive ACA compared to conventional ACA. Electrical reliability of thermally conductive ACA flip chip joint under current stressing condition was also improved showing stable electrical conductivity of flip chip joints. The high current carrying capability and improved electrical reliability of thermally conductive ACA flip chip joint under current stressing test is mainly due to the effective heat dissipation by thermally conductive adhesive around Au stud bumps/ACA/PCB pads structure.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.629-632
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• 2009

The polymeric desiccant rotor is made from the super absorbent polymer by ion modification. The moisture sorption capacity of the super desiccant polymer(SDP) is 4 to 5 times larger than those of common desiccant meterials such as silica gel or zeolite. It is also known that SDP can be regenerated even at the relatively low temperature. To fabricate the desiccant rotor, firstly the SDP was laminated by coating the SDP on polyethylene sheet. Then corrugated and rolled up into a rotor. The diameter, the depth, the dimensions of the corrugated channel, etc. were pre-determined from numerical simulation on the heat and mass transfer in the desiccant rotor. The dehumidification performance was tested in a climate chamber. The relevant tests were carried out at the process air inlet temperature of $32^{\circ}C$, the regeneration air inlet temperature of $60^{\circ}C$ and the inlet dew-point temperature of both the process air and the regeneration air of $18.5^{\circ}C$, when the rotation period is long, the moisture sorption is not effective. In the desiccant rotor developed in this study, the optimum rotation period is found about 350s at the regeneration temperature of $60^{\circ}C$. It was found from further experiments that the optimum rotation tends to decreases as the regeneration temperature increases. Meanwhile, the outlet temperature of the process air deceases monotonically as the rotation period increases.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.485-488
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• 2007

Riverbank filtration is a kind of artificial aquifer recharge for the fresh water supply. By construction of several production wells penetrating the riverbank, surface water withdrawn from the river would pass riverbed. This extracted water is well known to be cooler than surface water in summer and warmer than surface water in winter, showing more constant water temperature. This characteristic of extracted water is applied to geothermal energy utilization. Prediction of the annual temperature variation of filtrated water is the major concern in this study. In Daesan-myeon, Changwon-si, Gyeongsangnam-do, South Korea, riverbank filtration facility has been on its operation for municipal water supply and thermal energy utilization since 2006. Appropriate hydraulic and thermal properties were estimated for flow and heat transfer modeling with given pumping rate and location. With the calibrated material properties and boundary conditions, we numerically reproduced measured head and temperature variation with acceptable error range. In the numerical simulation, the change of saturation ratio and river stage caused by rainfall was calculated and the resulting variation of thermal capacity and thermal conductivity was considered. Simulated temperature profiles can be used to assess the possible efficiency of geothermal energy utilization using riverbank filtration facility. Influence of pumping rate, pumping location on the extracted water temperature will be studied.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.2 no.1
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• pp.1-7
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• 2006

This paper was studied for optimum design of the used vaporizer at a satellite station. Generally, the cold air is created by temperature drop on the vaporizer surface. In addition, the frost creates ice deposit layer, therefore, heat transfer on vaporizer decreases into the adiabatic condition. By this reason, recent vaporizer system is installed as parallel type, and it takes three times of vaporizer capacity. But this vaporizer system requires much installation costs and restricted by some space. It is very important to solve this problem. This study paper is regarding $LN_2$ vaporizer where the utilization increases recently. There are three variable conditions which are used in this study research. First, fin lengths of 4000mm, 6000mm, 8000mm and 0, 4, 8 fin types were applied rut each vaporizer. Second, we applied four season condition which consist of humidity, temperature and air velocity to the experimental environment. Finally, pressure was applied to get flow rate during experiment. This paper objective is to propose vaporizer type and length data for best performance of vaporizer through experiment.

• Journal of Hydrogen and New Energy
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• v.22 no.6
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• pp.859-867
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• 2011

The cold start problem is one of major obstacles to overcome for the commercialization of fuel cell vehicles. However, the cold start characteristics of fuel cell systems are very complicated since various phenomena, i.e. ice-blocking, electro-chemical reactions, heat transfer, and defrosting of BOP components, are involved in them. This paper presents a framework to approach the problem at a full stack scale using Axiomatic Design (AD). It was characterized in terms of Functional Requirements (FRs) and Design Parameters (DPs) while their relations were established in a design matrix. Considering the design matrix, the endplates should have low thermal conductivity and capacity without increase in weight or decrease in structural stiffness. Consequently, composite sandwich endplates were proposed and examined both through finite element analyses and experiments simulating cold start conditions. From the examinations, it was found that the composite sandwich endplates significantly contributed to improving the cold start characteristics of PEMFC.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.9
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• pp.505-512
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• 2009

A thermosiphon is utilized as a thermal shunt to reduce the cool-down time of a cryogenic system cooled by a two stage cryocooler. The cool-down time reduction by the thermosiphon is determined by the type of working fluid which is directly related to the operating temperature range of the thermosiphon. A mixed working fluid has a potential to widen the operation temperature range of the thermosipohon. In this study, the thermosiphon using N$_2$ and CF$_4$ mixture as the working fluid is fabricated and tested to verify its transient heat transfer performance. The thermosiphon with the mixed working fluid has no noticeable reduction of cool-down time compared with that of the thermosiphon with pure working fluid in this experiment. However, it seems that the thermosiphon with mixed working fluid may have an advantage according to the cooling capacity of a cryocooler, the cooling target temperature and the size of a cooling object.