• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.3
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• pp.512-520
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• 1995

This study investigates the simultanceous heat and mass transfer between a falling desiccant film and air in cross flow at the interface. The application of this work is the optimization of falling film evaporators for use in potential hybrid air conditioning systems. The specific geometry considered is liquid TEG films falling along the vertical cooled surfaces of a channel with air in cross flow. The equations to describe the coupled heat and mass transfer between a falling desiccant film and air in cross flow for a falling film evaporator have been presented and solved numerically. The effects of important design and operating variables on the evaporator performance predicted by the parametric numerical analysis and suggestions for performance improvements of the evaporator are presented.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.10
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• pp.657-664
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• 2010

The theoretical analysis of performance characteristics in a $CO_2$ cycle with the heat exchanger type was carried out. The size and performance of the fin-tube and microchannel heat exchanger were compared with operating conditions. As a result, the performance of the fin-tube gascooler and evaporator were more sensitive to the variation of operating condition compared to that of the microchannel gascooler and evaporator. Beside, the sizes of microchannel gascooler and evaporator could be decreased by 73% and 76%, respectively, compared to those of the fin-tube type gascooler and evaporator with the similar capacity. The COP and reliability of the $CO_2$ system can be increased by using a microchannel heat exchanger.

• Journal of the Semiconductor & Display Technology
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• v.16 no.1
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• pp.116-119
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• 2017

In this paper, natural convection around the ambient evaporator was numerically studied using commercial computational fluid dynamics software. From the simulations, temperature and velocity fields around the evaporator were found as a function of evaporator size and liquefied gas flow rate. The heat transfer coefficient at the external surface of the evaporator was also calculated from the simulation results. In order to give the heat transfer coefficient for various conditions, correlation between Rayleigh number and Nusselt number was proposed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.9
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• pp.818-826
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• 2001

In this study, in-situ performance test of a wet surface finned-tube evaporator of an air source heat pump which has a rating capacity of 20RT is carried out. Since test conditions, such as indoor and outdoor air conditions cannot be controlled to satisfy the standard test conditions, experiments are done with the inlet air conditions as they exist, From the experimental data, air side heat and mass transfer coefficients were calculated by the well known heat and mass transfer analogy and tube-by-tube method. since current procedure underpredicted the experimental sensible heat factor(SHF), a proper empirical parameter was introduced to predict the experimental data with satisfactory results. This study provides the method of evaluating the heat and mass transfer coefficients of a wet surface finned-tube evaporator of which in-situ performance test in necessary.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.11
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• pp.1020-1030
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• 2000

A crossflow finned tube evaporator has been investigated using tube-by-tube method. The refrigerant flows inside tubes while the air passes outside the finned tue. R134a for a refrigerant and wet air were used in this analysis. Three refrigerant circuitries, complex or simple, were compared. The effects of refrigerant circuitry and airside condensation on thermal performance such as heat transfer rate, enthalpy of refrigerant, temperature of refrigerant and air, pressure of refrigerant and average condensate layer thickness were investigated. It was found that this method could be applied to the analysis of finned tube evaporator for dehumidification and air conditioning.

• International Journal of Air-Conditioning and Refrigeration
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• v.10 no.4
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• pp.211-219
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• 2002

In this study, in-situ performance test of a wet surface finned-tube evaporator of an air source heat pump which has a rating capacity of 20 RT is carried out. Since test conditions, such as indoor and outdoor air conditions cannot be controlled to satisfy the standard test conditions, experiments are done with the inlet air conditions as they exist. From the experimental data, air side heat and mass transfer coefficients were calculated by the well known heat and mass transfer analogy and tube-by-tube method. Since current procedure underpredicted the experimental sensible heat factor (SHF), a proper empirical parameter was introduced to predict the experimental data with satisfactory results. This study provides the method of evaluating the heat and mass transfer coefficients of a wet surface finned-tube evaporator of which in-situ performance test is necessary.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.46-51
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• 1999

This paper describes the control charcteristics of thermal/flow systems. In thermal/flow systems, the transport lag plays as a dead time causing a deterioration of the controllability. Besides this, such many parameters including the temperature, pressure, and flow rate affect the system response that a control scheme which can deal with multi-input is required. Particularly in a refrigerant compressor test facility, the evaporator and condenser interact each other so that the change in the evaporator pressure cause the condenser pressure to change or vice versa. Therefore, to control the evaporator pressure, not only the cooling water flow rate in the evaporator but also the coolant flow rate in the condenser is considered. Meanwhile, the conventional PID controllers, which is suitable for a single input system, shows a large overshoot for a disturbance input. In this work, the predictive control scheme is introduced and its applicability is discussed for thermal/flow systems.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.3
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• pp.277-284
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• 2001

One of the problems in a refrigerator operation is the frost formation on a cold surface of the evaporator. The frost layer is formed by the sublimation of water vapor when the surface temperature is below the freezing point. This frost layer is usually porous and formed on the cold surface of the evaporator. The frost layer on the surface of a evaporator will make side effect such as thermal resistance. However, these important factors have not been used in determining the defrosting period. Therefore, the proper defrosting operation period based on the new defrosting method is very important, and make a comparison between conventional method like electric defrost and new method in compression work, evaporation pressure, evaporation temperature.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.211-218
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• 2002

It has been investigated for the temperature profile in a planar evaporator of micro-cooler subject to a uniform heat flux prior to tole initiation of boiling. The results of the analysis allow for the determination of applied power levels fur which nucleation is likely to occur only within the vapor grooves of the evaporator while maintaining subcooling in the liquid core, thereby increasing the likelihood of a successful startup. Also, limits are fecund for which additional increases in the applied heat flux do not increase the temperature difference between the vapor grooves and the wick-liquid core interface. This analysis is appropriate for the microscale evaporators of micro-cooler during a fully-flooded startup as well as starter pump designs and micro-CPLs(capillary pumped loops). The results are useful in the initial basic design of microscale heat transfer devices.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.7
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• pp.645-651
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• 2004

Fin-tube evaporator for carbon dioxide has been investigated both by experiment and simulation. Inside refrigerant heat transfer and outside heat and mass transfer of a wet surface heat exchanger were modeled using appropriate correlations. The results estimated by the calculation were in good agreement with the experimental results. The simulation errors were less than 7.9% for estimating capacity, 0.6$^{\circ}C$ for air exit temperature, 1.2% for air exit humidity and 17% for $CO_2$ exit pressure. The simulation program was used to study the effect of air flow direction, number of rows and refrigerant circuits. For a 2-row evaporator, parallel flow showed better performance for low air velocity but for high air velocity, counter-flow was better. Refrigerant circuits, however, showed insignificant effect on the performance.