• International Journal of Air-Conditioning and Refrigeration
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• 제13권2호
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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.

• 설비공학논문집
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• 제16권12호
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• pp.1197-1203
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• 2004

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

• 한국초전도ㆍ저온공학회논문지
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• 제22권1호
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• pp.24-28
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• 2020

Heat leakage is an important parameter to reflect heat insulated performance of cryogenic vessel. According to the current standard requirements, it needs to measure the daily evaporation rate to indicate heat leakage. The test needs-over 24h after cryogenic vessel in heat equilibrium as standard required, therefore test efficiency is poor and new efficient method is required to cut test time. First of all, the volume of instantaneous evaporated gas and heat leakage are calculated by the current standard corresponding to the maximum allowable daily evaporation rate of cryogenic vessel. Depending on the relationship between real daily evaporation rate and maximum allowable daily evaporation rate of cryogenic vessel, we designed a new test method based on the pressure changes over time in cryogenic vessel to determine whether its heat insulated performance meets requirements or not. Secondly, the heat transfer process was analyzed in measurement of cryogenic vessel, and the heat transfer equations of whole system were established. Finally, the test was completed in four hours; meanwhile the heat leakage and daily evaporation rate of cryogenic vessel are calculated basing on test data.

• 한국초전도ㆍ저온공학회논문지
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• 제23권1호
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• pp.7-11
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• 2021

Cryogenic vessels are special equipment that requires periodic evaluation of their thermal insulation performance. At the current standard, the test is considered as the loss product or heat leakage of cryogenic vessel, which takes over 72 h to evaluate; consequently, a large amount of working medium is discharged to the environment in the process. However, hydrogen is flammable and explosive, and the discharged gas may be dangerous. If liquid hydrogen is replaced with liquid nitrogen before testing, the operation then becomes complicated, and the loss product or heat leakage cannot respond to the thermal insulation performance of cryogenic vessels for liquid hydrogen. Therefore, a novel method is proposed to evaluate the heat leakage of cryogenic vessels for liquid hydrogen in self-pressurization. In contrast to the current testing methods, the method proposed in this study does not require discharge or exchange of working medium in all test processes. The proposed method is based on one-dimensional heat transfer analysis of cryogenic vessels, which is verified by experiment. When this method is used to predict the heat leakage, the comparison with the experimental data of the standard method shows that the maximum error of heat leakage is less than 5.0%.

• 설비공학논문집
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• 제20권1호
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• pp.26-34
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• 2008

Heat recovery ventilator(HRV) is recommended to improve indoor air quarlity (IAQ) and energy conservation in apartment houses. Recently, in Korea, HRV is produced from many manufacturers. However, there have been not so many experiences to apply HRV in apartment houses and verification on the performance such as heat exchange efficiency, carry-over rate, internal leakage, etc. have not been carried out sufficiently. So in this study, fan performance, heat exchange efficiency, air leakage, internal exhaust leakage, external leakage and sound level of HRV were examined for selected HRV models under domestic and international standard. Results of performance test, there were need to improve latent heat exchange efficiency and sound level of HRV.

• 대한기계학회논문집A
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• 제24권10호
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• pp.2428-2437
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• 2000

In general, it is known that the portion of leakage loss is more than 20 % of total loss in scroll compressor. So far many studies have been done to improve the leakage problem and volumetric efficiency. In order to do this it is necessary that the leakage is exactly evaluated for conventional scroll model. Almost all studies that have been done were assumed that the clearance remains constant while operating. But in actual operating conditions, scroll wrap is deformed due to elevated refrigerant gas temperature. And this makes the leakage clearance change, so the leakage mass flow and the volumetric efficiency are also changed. In this study we assumed the steady state operating condition and obtain the average temperature and convection heat transfer coefficient in terms of involute angle. With these results, using finite element method we analyzed the heat transfer of scroll wrap, then did thermal deformation analysis. Then we obtain the leakage clearance and do the leakage and volumetric efficiency analysis. Compared with undeformed feature, we examine the effect of the thermal deformation on the leakage. The results say that the leakage mass flow for the case of considering thermal deformation is less than that for the unconsidered one, and this means that the leakage clearance is reduced due to thermal deformation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.187-192
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• 2003

The heat (mass) transfer characteristics in the tip-leakage flow region of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. The heat transfer data in the tip-leakage flow area for the tip clearance-to-span ratio, h/s, of 2.0% are compared with those in endwall three-dimensional flow region without tip clearance (h/s = 0.0 %). The result shows that the thermal load in the tip-leakage flow region for h/s = 2.0% is more severe than that in the endwall flow region for h/s = 0.0%. The thermal loads even at the leading and trailing edges for h/s = 2.0% are found larger than those for h/s = 0.0%. The tip-leakage flow results in heat transfer augmentations near the tip on both pressure and suction sides in comparison with the mid-span results.

• 대한기계학회논문집B
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• 제28권5호
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• pp.535-544
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• 2004

The heat (mass) transfer characteristics in the tip-leakage flow region of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. The heat transfer data in the tip-leakage flow area for the tip clearance-to-span ratio, h/s, of 2.0% are compared with those in endwall three-dimensional flow region without tip clearance (h/s : 0.0 %). The result shows that the thermal load in the tip-leakage flow region for h/s = 2.0% is more severe than that in the endwall flow region for h/s : 0.0%. The thermal loads even at the leading and trailing edges for h/s = 2.0% are found larger than those for h/s = 0.0%. The tip-leakage flow results in heat transfer augmentations near the tip on both pressure and suction sides in comparison with the mid-span results.

• 대한기계학회논문집B
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• 제30권11호
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• pp.1074-1083
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• 2006

In the present study, the effect of blade rotation on blade heat transfer is investigated by comparing with the heat transfer results for the stationary blade. The experiments are conducted in a low speed annular cascade with a single stage turbine and the turbine stage is composed of sixteen guide vanes and blades. The chord length and the height of the tested blade are 150 mm and about 125 mm, respectively. The blade has a flat tip and the mean tip clearance is 2.5% of the blade chord. A naphthalene sublimation method is used to measure detailed mass transfer coefficient on the blade. For the experiments, the inlet Reynolds number is $Re_c=1.5{\times}10^5$, which results in the blade rotation speed of 255.8 rpm. Blade rotation induces a relative motion between the blade and the shroud as well as a periodic variation of incoming flow. Therefore, different heat/mass transfer patterns are observed on the rotating blade, especially near the tip and on the tip. The relative motion reduces the tip leakage flow through the tip gap, which results in the reduction of the tip heat transfer. However, the effect of the tip leakage flow on the blade surface is increased because the tip leakage vortex is formed closer to the surface than the stationary case. The overall heat/mass transfer on the shroud is not affected much by the blade rotation.

• Journal of Advanced Marine Engineering and Technology
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• 제22권6호
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• pp.871-879
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• 1998

The refrigerator consists of many components such as compressor condenser expansion valve evaporator and the cabinet which filled by urethane foam. In this paper the heat leakage of refriger-ator is measured by the new experiment method which is different from a present method, The devi-ation of the UA(overall heat transfer coefficient times area) between the simulation and experiments is about 7-8%. Using the modeling of various components of refrigeration system a performance analysos of CFC 12 and HFC 134a is performed numerically on the UA. As the results of this study according to increase the heat leakage the refrigeration load and mass flow rate of refrigerant are increased. And the increase of the mass flow rate results in the increase of the condensing and evapo-rating temperature. Therefore according to increase of the heat leakage the COP leads to increase because the increase of refrigeration capacity is larger than the increase if compressor power.