• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.3
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• pp.137-142
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• 2013

A small air-conditioner or chiller for a constant temperature bath normally uses a constant speed compressor. The constant speed compressor is relatively inexpensive, but it uses on/off control for capacity modulation. The on/off control has several disadvantages, specifically energy loss and large temperature fluctuation. Continuous operation with a bypass system can be an alternative to on/off control, for capacity modulation. In this study, a heat pump system having a hot-gas bypass and a liquid bypass was adopted. The performance of the bypass-type heat pump was measured, by varying the bypass valve opening. The differences of the COP between the hot-gas bypass and the liquid bypass, in the cooling and heating operations, were within 2% and 1%, respectively. The liquid bypass showed a wider range of capacity control in the cooling operation but the hot-gas bypass showed a wider range of capacity control in the heating operation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.11
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• pp.3695-3705
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• 1996

We designed the hot wind tunnel to reproduce the conditions of utility boiler and carried out its performance test, in order to investigate the particulate two-phase flow behaviour, the fouling and heat transfer characteristics to the heat exchanger. The hot wind tunnel introduces the control system to control the temperature in the test section. The particle is injected into the hot gas stream. The fouling probe (cylindrical tube) is positioned normal to the particulate gas-particle two-phase flow and cooled by the air. The temperature of gas and cooling air, and temperature in the fouling probe are measured as a function of time, giving the local and averaged heat transfer and fouling factor. The shape of particulate deposition adhered to the fouling probe is also observed.

• Proceedings of the Safety Management and Science Conference
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• 2010.04a
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• pp.81-95
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• 2010

Gas turbines generating power operate in high temperature condition and use natural gas as fuel. For that reason, there are many cases where damage is done to the hot gas parts caused by the high temperature and many accidents occur like gas explosions, then various efforts are needed to maintain the hot gas parts and prevent accidents. It is difficult to find the root causes of damage to the hot gas parts from the gas explosion caused by gas leakage through rotor cooling air line from fuel gas heat exchanger during the shut down. To prevent gas turbine from damage, removal of gas leakage inside of gas turbine is required by purging the turbine before firing, improving the fuel gas heating system and installing alarm systems for detecting gas leakage from stop valve to turbine while the gas turbine has shut down.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.6
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• pp.493-502
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• 2002

During the defrosting process, the temperature in the cabinet of a showcase becomes high as compared to the setting point, which is not desirable for stored foods or materials. It is necessary to develop a more efficient defrosting method to prevent large temperature fluctuation. In this study, the performance of a showcase refrigeration system with three evaporators is investigated by employing a hot-gas bypass defrosting technology in the system under frosting and defrosting conditions. The operating characteristics are compared with those for the on-off defrosting method that has been widely used in current products. As a result, the hot-gas bypass defrosting method shows higher refrigerating capacity and less temperature fluctuation than the on-off method under frosting/defrosting conditions, while the power input is relatively high for the hot-gas bypass method.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.2
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• pp.127-133
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• 2002

The objectives of this paper are to develop an advanced GAX cycle named HGAX (Hybrid Generator Absorber heat exchanger) cycle, and to study the effect of key parameters on the cycle performance and the hot-water temperature from the condenser. New types of the HGAX cycle are developed by adding a compressor between the generator and the condenser- Type C (performance improvement and reduction of the generator temperature) and Type D (Hot-water temperature application). The solution temperature in the generator outlet is reduced to 168$^{\circ}C$ with the COP improvement of 19% compared to the standard GAX cycle. The hot-water temperature from the condenser is raised to 106$^{\circ}C$ for panel heating (Ondol heating) application.

• Journal of the Korea Safety Management & Science
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• v.12 no.2
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• pp.75-82
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• 2010

Gas turbines for power generating operate in a very high temperature condition and use natural gas for fuel. For this reason, many cases of damage happen at hot gas parts which are severely affected by high temperature gas and many cases of explosion occur by fuel gas. So a lot of efforts should be made to prevent hot gas parts damage and gas explosion accidents. Though there are many damage cases and explosion accidents, it is very difficult to find out the root causes of hot gas parts damage caused by gas explosion due to gas leakage in the heat exchanger for air cooling and gas heating. To prevent gas turbine from damage caused by gas explosion, removal of leakage gas from gas turbine is inevitably required before firing the gas turbine and installing alarm systems is also required for detecting gas leakage at stop valve to turbine while shut down.

• Journal of the Korean Society of Food Science and Nutrition
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• v.25 no.3
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• pp.453-459
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• 1996

This study was carried out to determine the changes in quality during the drying process and the optimum drying condition for utilizing soybean curd residue. The quality criteria for soybean curd residue were acid value, peroxide value, fatty acid composition and microbial concentration. The acid values of soybean curd residue were 7.5, 4.5 and 5.9 KOH mg/g upon 12 hour drying with open-air sun, ambient-air blast and warm-air blast, respectively. The numbers of total aerobic bacteria and molds increased remarkably during drying with open-air sunlight, ambient-air blast and warm-air blast except for hot air blast. Among different drying methods, the hot air blast drying(1kg of sample) was the most effective methods, which completed in three hours. Also, the drying method demonstrated a typical drying curve ; settling down, constant rate drying and falling rate drying period were shown within one hour, from one and three hours and after three hours, respectively. Moreover, there was significant variation in the constant drying period for the quality of soybean curd residue.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.9
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• pp.947-954
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• 2015

The homogeneous coating of a flexible film that is applied to dye-sensitized solar cells is related to the performance and durability of the product. The applied coating is obtained from the uniform temperature distribution and the mass flow rate in the nozzle of the hot air dryer. In this study, we determine the uniform temperature distribution and mass flow rate of each nozzle by performing numerical simulations to understand how various factors affect the performance of the hot air dryer. The numerical model is composed of the momentum equation for flow motion and the energy equation for temperature. In addition, we compare the numerical results to the experimental results to validate the model. Based on the results, the round-hole plate inside the hot air dryer significantly affects the uniform temperature and the mass flow rate.

• The Korean Journal of Food And Nutrition
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• v.33 no.1
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• pp.91-97
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• 2020

The purpose of this study was to provide the basic data of butternut squash (Cucurbita moschata) according to the drying methods. The proximate composition and chromaticity of freeze-dried and hot air-dried Cucurbita moschata powders were evaluated, and the antioxidant effects of these ethanolic extracts were analyzed by DPPH, ABTS, FRAP, reducing power activity, total phenolic, and flavonoid content. As a result, Cucurbita moschata was revealed to have high carbohydrate and crude protein contents, while crude ash and crude fat contents were relatively low. Also, it was confirmed that the hot air-dried Cucurbita moschata had lower L, a, and b values than the freeze-dried Cucurbita moschata. Additionally, as a result of analyzing the antioxidant activity of Cucurbita moschata ethanolic extracts, hot air-dried Cucurbita moschata ethanolic extract showed significantly superior antioxidant activity than freeze-dried Cucurbita moschata ethanolic extract. Also, hot air-dried Cucurbita moschata ethanolic extract was revealed to have a higher polyphenol content, but slightly lower flavonoid content than freeze-dried Cucurbita moschata ethanolic extract. Based on the data from this study, further experiments on Cucurbita moschata material are necessary.

• Journal of Physiology & Pathology in Korean Medicine
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• v.25 no.5
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• pp.823-829
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• 2011

This study was performed to obtain the good processing in the Rehmanniae Radix Preparata. In this study, we investigated the comparative analysis for steamed and hot-air dried Rehmanniae Radix Preparata. The results were obtained as follows : Through loss on drying analysis with each additional processing of Rehmanniae Radix preparata, there was gradual increase. Through ash analysis with each additional processing of Rehmanniae Radix preparata, there was slight increase. Rehmanniae Radix preparata had several inorganic components such as K, P, Mg, Ca, Cl, Al. P and Mg were increased gradually with each additional processing of Rehmanniae Radix Preparata. But Ca was decreased with each additional processing. We identitied 24 kinds of volatile components from extracts of various processed Rehmanniae Radix Preparata through componential analysis using GC/MS. From GC/MS analysis, we found out the content of 5-HMF Rehmanniae Radix Preparata steamed over 7 times was suitable. 5-HMF's content of 9 times steamed Rehmanniae Radix Preparata gained from GC/MS analysis is 70-fold higher than gained from HPLC. The more it is repeating steamed and hot-air dried, the more toxic volatile compound of Rehmanniae Radix Preparata is removed. Taken together, these results suggested that Rehmanniae Radix Preparata had component (especially 5-HMF) changes according to different processed steaming and hot-air drying.