• 설비공학논문집
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• 제18권11호
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• pp.941-946
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• 2006

Nowadays heat exchangers that have been applied for freon refrigerating systems, a shell and tube type condenser, but because of their large size, large space for installation and more amount of refrigerants are needed. Therefore, in this study, we will find the most suitable operating condition through the comparison of performance between the shell & tube type and shell & disk type heat exchanger with R22. The experiments are carried out for the condensing pressure of refrigeration system from 1,500 kPa to 1,600 kPa and for the degree of superheat from 0 to $10^{\circ}C$ at each condensing pressure. As a result of experiment, if the shell & disk type heat exchanger is applied for R22 refrigerating systems, minimized input of refrigerants and space required for installation will be secured, which will have a great contribute to financial improvement for industry.

• 한국지열·수열에너지학회논문집
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• 제17권3호
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• pp.30-40
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• 2021

This paper compares the annual energy performance of four different types of air-conditioning systems in a medium-sized office building. Chiller and boiler, air-cooled VRF, ground-source VRF, and ground-source heat pump systems were selected as the systems to be compared. Specifically, the energy performance of the GSHP system and the ground-source VRF system were compared with each other and also with conventional HVAC systems including the chiller and boiler system and air-cooled VRF system. In order to evaluate and compare the energy performances of four systems for the office building, EnergyPlus, a whole-building energy simulation program, was used. The EnergyPlus simulation results show that both the GSHP and the ground-source VRF systems not only save more energy than the other two systems but also significantly reduce the electric peak demand. These make the GSHP and the VRF systems more desirable energy-efficient HVAC technologies for the utility companies and their clients. It is necessary to analyze the impact of partial load performance of ground-source heat pump and ground-source VRF on the long-term (more than 20 years) performance of ground heat exchangers and entire systems.

• 대한건축학회논문집:구조계
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• 제35권3호
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• pp.43-48
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• 2019

Since the revision of the Rationalization of Energy Use Law, the spread of new and renewable energy in buildings has been promoted. In addition, the production of electric power and thermal energy is an important issue in the change of energy paradigm centered on the use of distributed energy. Among them, geothermal energy is attracting attention as a high-performance energy-saving technology capable of coping with heating / cooling and hot water load by utilizing the constant temperature zone of the earth. However, there is a disadvantage that the initial investment cost is high as a method of calculating the capacity of a geothermal facility by calculating the maximum load. The disadvantages of these disadvantages are that the geothermal energy supply is getting stagnant and the design of the geothermal system needs to be supplemented. In this study, optimization design of geothermal system was carried out using optimization tool. As a result of the optimization, the ground heat exchanger decreased by 30.8%, the capacity of the heat pump decreased by 7.7%, and the capacity of the heat storage tank decreased by about 40%. The simulation was performed by applying the optimized value to the program and confirmed that it corresponds to the load of the building. We also confirmed that all of the constraints used in the optimization design were satisfied. The initial investment cost of the optimized geothermal system is about 18.6% lower than the initial investment cost.

• Journal of Biosystems Engineering
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• 제8권2호
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• pp.49-61
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• 1983

U shape multitube heat exchanger was equipped in the flue to recover the exhaust heat from the boiler system. The fluids of the exhaust heat recovery equipment were the flue gas as the hot fluid, and the water as the cold fluid. The flow geometry of the fluids was cross flow - two pass, the hot fluid being mixed and the cold fluid unmixed. The results of the theoretical and the experimental analysis and the economic evaluation are summarized as follows. 1) The heat exchanger effectiveness and the temperature efficiency of the hot fluid were about 35% when the fuel consumption rate was 140 - 150 L/15min. The temperature efficiency for the cold fluid ranged from 3.0% to 4.5%. The insulation efficiency ranged from 85% to 98%, which was better than the KS air preheater insulation efficiency of 90%. 2) The relationship between the fuel consumption rate, F, and the outlet temperature, $T_{h2}$, of the flue gas from the heat exchanger was $T_{h2}$ = 0.927F + 110. In order to prevent the low temperature corrosion from the coagulation of $SO_3$, it is necessary to maintain the fuel consumption rate above 82 L/15min. 3) The ratio of the exhaust heat from the boiler system to the total energy consumption was about 14.5%. With the installation of the exhaust heat recovery equipment, the energy recovery ratio to the exhaust heat was about 25%. Accordingly, about 3.6% of the total fuel consumption was estimated to be saved. 4) Economic analysis indicated that the installation of the exhaust heat recovery equipment was feasible to save the energy, because the capital reocvery period was only 10 months when the fuel consumption rate was 80 L/15min. 4 months when it was 160 L/15min. 5) Based on the theoretical and the experimental analysis, it was estimated to save the energy of about 18 million Won per year, if four heat exchangers are installed in a factory. 6) A further study is recommended to identify the relationship among the flow rate of the exhaust gas, the size of the heat exchanger and the capacity of the air preheater. For a maximum heat recovery from the exhaust gas an automatic control system is required to control the flow rate of the cold fluid depending on the boiler load.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2315-2320
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• 2007

This paper presents an investigative study on the efficacy of a new physical water treatment (PWT) technology using an oscillating electric field to mitigate mineral fouling in heat exchangers. Parallel graphite electrode plates immersed in water were used to generate the electric field directly in water. Artificial hard water at 500 ppm hardness was used in all fouling tests. The inlet temperatures were maintained at 23.5${\pm}$0.5$^{\circ}C$ and 85${\pm}$0.5$^{\circ}C$ for cold and hot water sides, respectively. The results at a cold water-side velocity of 0.3 m/s showed a 16-60% drop in fouling resistances from the baseline test depending on the frequency of the electric field for the PWT-treated cases.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.379-380
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• 2002

Steam generators (S/G) of pressurized water reactors are large heat exchangers that use the heat from the primary reactor coolant to make steam in the secondary side for driving turbine generators. Reciprocating sliding wear experiments have been performed to examine the wear properties of Incoloy 800 and Inconel 690 steam generator tubes in high temperature water. In present study, the test rig was designed to examine the reciprocating and rolling wear properties in high temperature (room temperature - $300^{\circ}C$) water. The test was performed at constant applied load and sliding distance to investigate the effect of test temperature on wear properties of steam generator tube materials. To investigate the wear mechanism of material, the worn surfaces were observed using scanning electron microscopy. At $290^{\circ}C$, wear rate of Inconel 690 was higher than that of Incoloy 800. It was assumed to be resulted from the oxide layer property difference due to the a\loy composition difference. Between 25 and $150^{\circ}C$ the wear loss increased with increasing temperature. Beyond $150^{\circ}C$, the wear loss decreased with increasing temperature. The wear loss change with temperature were due to the formation of wear protective oxide layer. From the worn surface observation, texture patterns and wear particle layers were found. As test temperature increased, the proportion of particle layer increased.

• 설비공학논문집
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• 제9권2호
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• pp.198-209
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• 1997

This paper is concerned about the performance of alternative refrigerants of R-502 which has been widely used in transport and low temperature refrigeration. A breadboard heat pump was constructed with counterflow heat exchangers and tested with R-502 and transitional alternatives of R-402A and R-402B and long-term alternatives of R-404A and R-507 to compare the performance of each refrigerant. Measurements were conducted at two different condensing temperatures of $43.3^{\circ}C$ and $52.0^{\circ}C$ and the evaporating temperature was varied over a range from $-25^{\circ}C$ to $-5^{\circ}C$. The evaporator superheat and condenser subcooling were maintained constant at about $5^{\circ}C$ for all tests. Test results showed that all alternative fluids tested in this research work can be used as 'drop-in' fluids to replace R-502 without any major problem. It is also found that in the long run HFC alternatives are to be used due to their favorable environmental characteristics and better performance.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 1998년도 춘계 학술발표회 논문집
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• pp.235-242
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• 1998

Aiming at one of decisive alternatives for long term aspect of nuclear power concerns, an integral and closed nuclear system, AMBIDEXTER (Advanced Molten-salt Break-even Inherently-safe Dual-mission Experimental and TEst Reactor) concept is under development. The AMBIDEXTER complex essentially comprises two mutually independent loops of the radiation/material transport and the heat/energy conversion, centered at the integrated reactor assembly, which enables one to utilize maximum benefits of nuclear energy under minimum risks of nuclear radiation. And it provides precious radioisotopes and radiation sources from its waste stream. Also the reactor operates at very low level of fission products inventory throughout its lifetime. The nuclear and thermalhydraulic characteristics of the molten TH/$^{233}$ U fuel salt extend the capability of the self-sustaining AMBIDEXTER fuel cycle to enhance resource security and safeguard transparency. The reactor system is consisted of a single component module of the core, heat exchangers and recirculation pumps with neither pipe connections nor active valves in between, which will significantly improve inherent features of nuclear safety. States of the core technologies associated with designing and developing the AMBIDEXTER concept are mostly available in commercialized form and thus demonstration of integral aspects of the concept should be the prime area in future R＆D programs.

• Journal of Welding and Joining
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• 제33권5호
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• pp.1-8
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• 2015

Aluminium and its alloys are widely used in brazing various components in automotive industries due to their properties like lightweight, excellent ductility, malleability and formability, high oxidation and corrosion resistance, and high electrical and thermal conductivity. However, high machinability and strength of aluminium alloys are a serious concern during casting operations. The generation of porosity caused by dissolved gases and modifiers affects seriously the strength and quality of cast product. Brazing of Al and its alloys requires careful monitoring of temperature since theses alloys are brazed at around the melting temperature in most of the aluminium alloys. Therefore, the development of low temperature brazing filler alloys as well as superior strength Al alloys for various engineering applications is always in demand. In various heat exchangers and automotive applications, poor strength of Al alloys is due to the inherent porosities and casting defects. The unstable mechanical properties is therefore needed to be controlled by adding various additive elements in the aluminium and its alloys, by a change in the heat treatment procedure or by modifying the microstructure. In this regard, this article reports the effect of various elements added in aluminium alloys to improve microstructure, brazeability, machinability, castability as well as to stabilize the mechanical properties.

• 설비공학논문집
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• 제23권1호
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• pp.73-79
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• 2011

A portion of oil for lubrication of compressor flows together with refrigerant in the refrigeration system. If the oil discharge from a compressor is increased in the refrigeration system, not only pressure drop is increased in other components, such as evaporator and gas cooler, but also heat transfer coefficient in the heat exchangers is decreased. Oil discharge rate from a compressor may strongly depend on operating conditions of a compressor. In this study, one stage single rotary compressor is employed for measuring oil circulation ratio(OCR). Carbon dioxide and PAG oil are used as refrigerant and lubricant. Using a U-tube densimeter, mixture density is measured. Oil circulation ratio(OCR) can be estimated by measured mixture density. The results obtained indicate that the oil circulation ratio(OCR) is increased as the suction temperature or compressor operating frequency is increased. Oil circulation ratio(OCR) correlation of the compressor is also suggested.