• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.1
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• pp.28-35
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• 2007

In this study the seasonal performance of a residential air conditioning system having either a fin-and-tube condenser or a microchannel condenser is experimentally investigated. A commercially available 7 kW capacity residential air conditioning system having a fin-and-tube condenser served as the base system. The test results show that the system with a microchannel heat exchanger has a reduced refrigerant charge amount of 10%, the coefficient of performance is increased by 6% to 10%, and the SEER is increased by 7% as compared with those of the base system. Moreover, the condensing pressure of the system is decreased by 100 kPa and the pressure drop across the condenser is decreased by 84%. The microchannel heat exchanger enhances the SEER of the residential air conditioning system by providing better heat transfers at reduced pressure drops.

• Journal of the Korean Society for Heat Treatment
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• v.37 no.3
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• pp.128-137
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• 2024

In this study, the carburizing heat treatment process used in aircraft gear manufacturing was compared with the general carburizing heat treatment process using AISI 9310 steel. The process of carburizing followed by slow cooling, and then quenching after austenitizing(Process A) showed less compressive residual stress and less retained austenite in the surface layer compared to the process of quenching directly after carburizing(Process B). In prpcess B, there was a large amount of retained austenite when quenched immediately after carburization, and when treated with subzero, martensite rapidly increased and the compressive residual stress increased significantly, but at the same time, there is a risk of cracking due to severe expansion in volume. Therefore, in the case of aviation parts, it is believed that a step-by-step heat treatment cycle was adopted to ensure stability against heat treatment cracks. As a result of the final tempering after sub-zero treatment, the A process specimen showed a deeper effective case depth and HV700 depth and a higher hardness value above HV700 than the B process specimen.

• Magazine of the Korean Society of Agricultural Engineers
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• v.43 no.6
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• pp.120-126
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• 2001

This experiment was carried out to analyse on the cooling and dehumidifying effects of greenhouse by air-to-water heat pump system employing the air as cooling source. following results were obtained ; 1. The coefficients of performance (COP) of heat pump itself and total heat pump system were approximately 2.71~2.88 and 1.99~2.22, respectively. 2. The night-time cooling load of experimental greenhouse was 64.9 MJ/h, and the heat absorbed (cooling load) from heat pump system was 816.3~1,004.6 MJ/day. 3. The dehumidified moisture amount from experimental greenhouse was 7.0~15.0 kg/h. 4. The night time temperature of experimental greenhouse cooled by heat pump system could be maintained 4~6$^{\circ}C$ lower than that of control greenhouse which was almost equal to outside air temperature.

• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2464-2476
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• 2021

Direct-contact heat transfer of a single saturated droplet upon colliding with a heated wall in the regime of film boiling was experimentally investigated using high-resolution infrared thermometry technique. This technique provides transient local wall heat flux distributions during the entire collision period. In addition, various physical parameters relevant to the mechanistic modelling of these phenomena can be measured. The obtained results show that when single droplets dynamically collide with a heated surface during film boiling above the Leidenfrost point temperature, typically determined by droplet collision dynamics without considering thermal interactions, small spots of high heat flux due to localized wetting during the collision appear as increasing We_n. A systematic comparison revealed that existing theoretical models do not consider these observed physical phenomena and have lacks in accurately predicting the amount of direct-contact heat transfer. The necessity of developing an improved model to account for the effects of local wetting during the direct-contact heat transfer process is emphasized.

• Journal of Biosystems Engineering
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• v.26 no.4
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• pp.385-390
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• 2001

The Ondol system using both air-to-water heat pump and PCM(Phase Change Material) was constructed, and the effects of ambient air temperature on COP(Coefficient of Performance) of heat pump, the amount of heat supplied to the Ondol in the heating process, the heat storage in the PCM and the variation of Ondol room temperature were analyzed. The results from this study could be summarized as follows: 1. The COP of the heat pump (3 PS) was in proportion to the ambient air temperature. 2. When the ambient air temperature was varied between -10$^{\circ}C$ and -7$^{\circ}C$, the air temperature in the Ondol room was maintained between 16$^{\circ}C$ and 22$^{\circ}C$. As the results, it was certified that the heat pump-latent heat storage type Ondol system could be a comfortable residential heating system in the winter. 3. The maximum radiation and convection heat transfer from Ondol surface was 206.2 kJ/㎥hr and 82.6 kJ/㎥hr respectively. As the results, it could be confirmed that the radiation was major heat transfer mechanism for the Ondol room heating.

• 제어로봇시스템학회:학술대회논문집
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• 1990.10b
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• pp.1259-1264
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• 1990

During the past two decades, a lot of researches have been done on the synthesis of grassroot heat exchanger networks(HEN). However, few have been dedicated to retrofit of existing heat exchanger networks, which usually use more amount of utilities (i.e. steam and/or cooling water) than the minimum requirements. This excess gives motivation of trades-off between energy saving and rearranging investment. In this paper, an algorithmic-evolutionary synthesis procedure for retrofitting heat exchanger networks is proposed. It consists of two stages. First, after the amount of maximum energy recovery(MER) is computed, a grass-root network featuring minimum number of units(MNU) is synthesized. In this stage, a systematic procedure of synthesizing MNU networks is presented. It is based upon the concept of pinch, from which networks are synthesized in a logical way by the heuristics verified by the pinch technology. In the second stage, since an initial feasible network is synthesized based on the pre-analysis result of MER and must-matches, an assignment problem between new and existing units is solved to minimize total required additional areas. After the existing units are assigned, the network can be improved by switching some units. For this purpose, an improvement problem is formulated and solved to utilize the areas of existing units as much as possible. An example is used to demonstrate the effectiveness of the proposed method.

• Journal of Welding and Joining
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• v.6 no.2
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• pp.40-46
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• 1988

The effect of heat input on the content of residual .delta.-ferrite and the hot cracking susceptibility in the austenitic stainless steel overlaid on the carbon steel was studied in the range of heat input from 7.5 to 15.1 KJ/cm. Present study shows that residual .delta.-ferrite content in the overlay is mainly determined by the dilution of the base metal (carbon steel) which is in turn affected by heat input, i.e. the amount of dilution decreases as heat input increase. Accordingly, higher heat input results in a substantial increase in Cr equivalent but a little increase in Ni equivalent due to the less dilution of carbon from base metal. This fact can explain the result obtained in this study, i, e, the higher content of .delta.-ferrite in the weld deposit made with higher heat input. This in turn causes more resistant overlaying weld metal to hot cracking.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.4
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• pp.273-280
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• 2011

In this study, the steady state performance of a $CO_2$ heat pump water heater was measured with a variation of operating conditions such as refrigerant charge amount, compressor frequency, EEV opening, and water mass flow rate. Transient state performance tests were also conducted to investigate major system effects associated with the interaction between the $CO_2$ heat pump water heater and the water tank. Optimum refrigerant charge amount for the system was 1600 g. At compressor frequencies of 50 Hz and 60 Hz, water mass flow rates of 95 kg/h and 105 kg/h, and EEV opening of 8% and 16%, the water heating temperatures were $65^{\circ}C$ and $68^{\circ}C$ and COPs were 3.0 and 2.8, respectively. In the transient condition, the instantaneous COP decreased with an increase in the inlet water temperature.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.1
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• pp.44-55
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• 1998

The evaluation of aluminum flat tube and louver fin heat exchangers for a condenser in residential air-conditioning applications has been conducted. A series of tests for two-different brazed aluminum heat exchangers was performed and the results were compared with conventional fin and tube heat exchangers for residential air-conditioning system. Refrigerant charge amount for a window-system air-conditioner with the brazed aluminum condenser is decreased by 35% and the volume and material of heat exchanger can be reduced by 50% compared to the conventional fin and tube heat exchangers.

• Journal of the Korean institute of surface engineering
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• v.26 no.6
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• pp.327-333
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• 1993

The effect of heat treatment on the adhesion between Cu-18wt% Cr film and polyimide has been studied by using T-peel test, AES, and XRD. Cu-18wt% Cr alloy and pure Cu films were sputter deposited onto pol-yimide. Cu was electroplated before and after heat treatment at $400^{\circ}C$ for 0.5 hr and 2 hrs respectively. The adhesion of metal film onto polyimide was considerably good before heat treatment, but heat treatment re-duced the peel adhesion strength in all specimens. The reduction in adhesion in adhesion strength values in the specimens which were plated after heat treatment was mainly due to Cr-O rich pahse formed in the metal/polyimide in-terface. In the specimens which were heat treated after plating, the enhanced ductility in the metal films con-tributes the peel adhesion strength by increasing the amount of deformation in metal strips.