• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.1
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• pp.16-25
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• 2004

The flow and heat/mass transfer in the falling-film of a heat exchanger can be influenced by the motion of the surrounding refrigerant vapor. In this study, the effect of the vapor flow direction on the absorption heat transfer has been investigated for a falling-film helical coil which is frequently used as the absorber of ammonia/water absorption refrigerators. The experiments were carried out for different solution concentration. The heat and mass transfer performance was measured for both parallel and counter-current flow. The effect of vapor flow on the heat and mass transfer is found to be increased with decreasing solution concentration. In the experiments with low solution concentration, whose vapor specific volume is great, the counter-current flow of vapor resulted in uneven distribution of falling-film and reduced the heat transfer performance of the absorber. The direction of the vapor flow hardly affected the thermal performance as the solution concentration became stronger since the specific volume of the ammonia/water vapor was much smaller than that of the water vapor.

• International Journal of Air-Conditioning and Refrigeration
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• v.6
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• pp.148-157
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• 1998

This study presents test results of a residential window air-conditioner using R22 and two potential alternative refrigerants, R407C and R410B. A series of performance tests has been carried out for the basic and liquid-suction heat exchange cycles in a psychometric calorimeter test facility. For R407C, the same rotary compressor was used as in the R22 system. However, compressor for the R410B system was modified to provide the similar cooling capacity. The evaporator circuit was changed to get a counter-cross flow heat exchanger to take advantage of zeotropic mixture's temperature glide, and liquid-suction heat exchange cycle was also considered to improve the system performance. Test results were compared with those for the basic R22 system. The modified system with a liquid-suction heat exchanger increased cooling capacity and energy efficiency by up to 5%.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.12
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• pp.915-923
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• 2008

The performance experiments for a microchannel printed circuit heat exchanger (PCHE) of high-performance and high-efficiency on the two technologies of micro photo-etching and diffusion bonding were performed in this study. The microchannel PCHE were experimentally investigated for Reynolds number in ranges of 100 $\sim$ 700 under various flow conditions in the hot side and the cold side. The inlet temperatures of the hot side were conducted in range of $40^{\circ}C\;{\sim}\;50^{\circ}C$ while that of the cold-side were fixed at $20^{\circ}C$. In the flow pattern, the counter flow was provided 6.8% and 10 $\sim$ 15% higher average heat transfer rate and heat transfer performance than the parallel flow, respectively. The average heat transfer rate, heat transfer performance and pressure drop increases with increasing Reynolds number in all the experiment. The increasing of inlet temperature in the experiment range has not an effect on the heat transfer performance while the pressure drop decrease slightly with that of inlet temperature. The experimental correlations to the heat transfer coefficient and pressure drop factor as a function of the Reynolds number have been suggested for the microchannel PCHE.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.3
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• pp.470-475
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• 2009

In the present study, the heat transfer characteristics of the fin-tube and PF heat exchangers and the performances of the air-conditioner are experimentally investigated. Also, Cooling Seasonal Performance Factor(CSPF) of the air-conditioner is evaluated. For the heat exchanger experiment, the heat transfer and pressure drop are obtained. For the air-conditioner experiment, the cooling capacity, input power and COP are obtained. The air-enthalpy calorimeter and the constant temperature water bath are used. As the inlet air velocity increases, the heat transfer rate and pressure drop of the heat exchanger increased. PF heat exchanger has smaller refrigerant weight and larger capacity and COP than the fin-tube heat exchanger. The performance of PF-2 heat exchanger with the squarer fin is more excellent than that of PF-1 heat exchanger with the triangler fin. Also, CSPF of the fm -tube and PF heat exchanger is evaluated.

• The KSFM Journal of Fluid Machinery
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• v.17 no.6
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• pp.77-83
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• 2014

The vessel of integral reactor contains its major primary components such as the fuel and core, pumps, steam generators, and a pressurizer, so its size is proportional to the required space for the installation of each component. The steam generators take up the largest volume of internal space of reactor vessel and their volumes is substantial for the overall size of reactor vessel. Reduction of installation space for steam generators can lead to much smaller reactor vessel with resultant decrease of overall cost for the components and related facilities. A printed circuit heat exchanger is one of the compact types of heat exchangers available as an alternative to conventional shell and tube heat exchangers. Its name is derived from the procedure used to manufacture the flat metal plates that form the core of the heat exchanger, which is done by chemical milling. These plates are then stacked and diffusion bonded, converting the plates into a solid metal block containing precisely engineered fluid flow passages. The overall heat transfer area and pressure drops are evaluated for the steam generator based on the concept of the printed circuit heat exchanger in this study. As the printed circuit heat exchanger is known to have much larger heat transfer area density per unit volume, we can expect significantly reduced steam generator compared to former shell and tube type of steam generator. For the introduction of new steam generator, two design requirements are considered: flow area ratio between primary and secondary flow paths, and secondary side parallel channel flow oscillation. The results show that the overall volume of the steam generator can be significantly reduced with printed circuit type of steam generator.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.10
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• pp.1017-1024
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• 2001

The optimum shape of header part in a PFHE (parallel-flow heat exchanger) is studied. The optimal values of each geometric parameter are proposed according to their order of influence with varying the four important parameters (the injection angle of working fluid ($\Theta$), the shape of inlet(S), the location of inlet ($y_c/D_{in}$) and the height of the protruding flat tube ( $y_{b/}$ $D_{in}$ )). The optimal geometric parameters are as follows:$\Theta= -21^{\circ}C,\; S=Type\; A \;an\;y_b/D_{in}$/=0. The heat transfer rate of the optimum model, compared to that of the reference model, is increased by about 55%. The optimal geometric parameters ran be applicable to the Reynolds number ranging from 5,000 to 20,000.0.

• Solar Energy
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• v.20 no.1
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• pp.97-108
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• 2000

The purpose of this study is to minimize the heat transfer surface area and cold fluid exit temperature of heat exchanger which applied to the refrigeration and air-conditioning system by utilizing the thermoelectric principle. Both uniform and non-uniform current distribution methods which applied to the analysis of the TE elements that incorporates heat exchanger were investigated. The non-uniform current distribution method had the better coefficient of performance and had the lower cold fluid exit temperature of the TE cooling system than the uniform current distribution method. It was found that if a TE cooling system incorporates a heat exchanger, a non-uniform current distribution should guarantee to the lowest cold fluid exit temperature. Also, the hybrid method (combination of the uniform and non-uniform current distribution method) is investigated to achieve the best results by combining the uniform and non-uniform current distributions. The results show that it can lower the cold fluid exit temperature and reduce the heat transfer surface area for the parallel flow arrangement if we apply the constant current in some entry region and the non-uniform increasing current in the direction of the cold fluid flow afterwards.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.11
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• pp.881-887
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• 2014

This paper presents numerical study on flow and heat transfer characteristics in micro-gap plate heat exchanger. In particular, we investigate the effect of flow inertia on the flow distribution from single main channel to multiple parallel micro-gaps. The flow regime of the main channel is varied from laminar regime (Reynolds number of 100) to turbulent regime (Reynolds number of 10000) by changing the flow rate, and non-uniformity of the flow distribution and temperature field is evaluated quantitatively based on the standard deviation. The flow distribution is found to be significantly affected by not only the header design but also the flow rate of the main channel. It is also observed that the non-uniformity of the temperature field has its maximum at the intermediate flow regime.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.6
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• pp.347-354
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• 2009

Experimental study on a cross-flow air-cooled plate heat exchanger (PHE) was performed. Two types of PHEs were manufactured either with single-wave plates or with double-wave plates in parallel. Cooling air flows through the PHEs in a crosswise direction against internal hot water. The heat exchanger aims to substitute open-loop cooling towers with closed-loop water circulation, which guarantees cleanliness and compactness. In this study, prototype single-wave and double-wave PHEs were designed and tested in a laboratory scale experiments. From the tests, the double-wave PHE shows approximately 50% enhanced heat transfer performance compared to the single-wave PHE. However, the double-wave PHE costs 30% additional pressure drop. For the commercialization, a wide channel design for air flow would be essential for performance and reliability.

• Journal of Power System Engineering
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• v.17 no.3
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• pp.50-56
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• 2013

The analysis of performance characteristics was carried out in the plate type evaporator with counter and parallel flow. To investigate performance of evaporator with water inlet temperature and refrigerant mass flow rate were changed. As a result, when the inlet temperature of water is $8^{\circ}C$, capacity of parallel flow evaporator higher than counter flow is 0.35%. But as the inlet temperature of water rises from $8^{\circ}C$ to $16^{\circ}C$, capacity of counter flow type evaporator higher than parallel flow type is 0.12%, 0.27%, 1.1%, 1.6%, respectively. The findings showed that counter flow type evaporator has a larger capacity than those that were parallel flow type evaporator. As the refrigerant mass flow rate rises, capacity and pressure drop increases in the counter and parallel flow type evaporator.