• Journal of the Korean Society of Combustion
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• v.18 no.2
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• pp.23-31
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• 2013

Compact steam boiler is a useful heat exchanger in a space-intensive system. There are some constraints in terms of sizing and designing the space confined in the system which is usually used in vessels. In this study, design considerations for heavy duty heat exchangers of compact steam boilers are presented and evaluated. Especially, evaporator tubes of marine boiler which are exposed to a high temperature environment are considered. Also, extended surface designs with a high temperature are examined. In order to determine the criteria with considerations of both heat transfer rate and pressure drop in the heat exchanger, they are evaluated with major variables, such as the tube diameter, the number of tubes, and the tube length. Finally, the design parameters are estimated as the bare tubes are installed instead of the finned tubes.

• Journal of Welding and Joining
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• v.10 no.3
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• pp.40-53
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• 1992

고온고압장치(High Temperature and Pressure Vessels)의 적용을 위한 기초연구로서 9Cr-1Mo강 용접부의 연화특성에 대하여 검토하였다. 9Cr-1Mo 강재에 Bead-on-Plate용접을 실시한 후, 용접부의 기계적 성질과 그 현미경조직관찰 및 미세경도를 측정한 결과, As-Welded 및 용접 후열처리(PWHT)등의 조건에 관계없이 용접열향부의 변태역과 템퍼링역의 경계에서 모재의 경 도보다 낮은 경도값(연화역)을 나타내었으며 이러한 원인은 결정립계(Grain boundary)에 석출 되는 탄화물의 형성에 의한 뜨임 현상임이 판명되었다.

• Progress in Superconductivity and Cryogenics
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• v.9 no.4
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• pp.46-49
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• 2007

This paper describes the sensitive cooling performance change of J-T refrigerator for cryosurgical probe due to its working fluid. The analytical results of using 50 bar nitrous oxide are compared with the case of 300 bar argon. Bio-heat equation is numerically solved to investigate the effect of the probe temperature and the cooling power of the J-T refrigerator. The refrigerator using 50 bar nitrous oxide has larger cooling power above 185 K than the one with 300 bar argon, which enables fast cooling at early stage of cryosurgery, but the biological tissue away from the probe tends to be cooled slowly after the probe reaches its lowest operating temperature. When the repeated freeze-thaw cycle is employed for main tissue destruction mechanism, using high pressure nitrous oxide is more advantageous than argon if the freezing operation is within 2-3 minutes. The probe with high pressure argon is more suitable for the case of longer freeze-thaw cycle with fewer repetitions.

• Progress in Superconductivity and Cryogenics
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• v.4 no.2
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• pp.1-4
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• 2002

Electrical properties of liquid nitrogen ($LN_2$) and gaseous nitrogen($GN_2$) have become of great interest again since the discovery of high temperature superconductors . It is very important from a point of superconducting apparatus protection to elucidate breakdown characteristics in $LN_2$ and $GN_2$ at atmospheric and pressurized conditions Therefore. this paper studies the effect of pressure on the breakdown characteristics in $LN_2$ and $GN_2$. Af high voltage is applied to electrode system with uniform and non-unform field in various gap length. And Breakdown voltages of $LN_2$ and $GN_2$ are investigated under AC voltage for Pressure ranging from 0 and 0.5 MPa. This research presented basis information of electrical insulation design for liquid nitrogen immersed HTS power apparatus.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.6
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• pp.74-79
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• 2004

The effects of change in injection pressure on spray structure have been investigated in high temperature and pressure field. To analyze the structure of evaporative diesel spray is important in speculation of mixture formation process. Also emissions of diesel engines can be controlled by the analyzed results. Therefore, this study examines the evaporating spray structure by using a constant volume vessel. The injection pressure is selected as the experimental parameter, is changed from 72 MPa to 112 MPa with a high pressure injection system(ECD-U2). The PIV(Particle Image Velocimetry) technique was used to capture flow variation of the evaporative diesel spray. A study on the mixture formation process of diesel spray was executed by the results of flow analysis in this study. Consequentially the large-scale vortex flow could be found in downstream spray and the formed vortex governs the mixture formation process in diesel spray.

• Journal of Industrial Technology
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• v.20 no.B
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• pp.15-20
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• 2000

High pressure, pressure ratio, refrigerating effect, heat transfer from the condenser and the power of the compressor etc. of a self-made refrigeration equipment for R-12 are investigated when R-12 and R-134a are used as the coolants. The comparison between the performance for R-12 and that for R-134a is made. As a result, R-134a is better than R-12 in the view of high pressure, refrigerating effect and the coefficient of performance and vice versa in the view of pressure ratio, exit gas temperature from the compressor and heat transfer from the condenser.

• Bulletin of the Korean Chemical Society
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• v.30 no.6
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• pp.1337-1340
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• 2009

Electrical properties of a fluorinated carbon black (CB)-filled high-density polyethylene (HDPE) polymeric switch were investigated as a function of fluorination pressure at 0.1 ~ 0.4 MPa. From the FT-IR results, the absorption spectra of the fluorinated CB show an absorption band at 1400 ~ 1000 $cm^{-1}\;for\;{\nu}_{C-F}$ and the peak intensity increased with increasing fluorination pressure. Also, the analysis of XPS spectra of the fluorinated CB indicated that fluorine content increased with increasing fluorination pressure. Meanwhile, the surface free energy of the fluorinated CB decreased with increasing fluorination pressure. Consequently, the increase of fluorine contents of CB made a disappearance of negative temperature coefficient (NTC) behavior of the polymeric switch, which was probably due to the reduction of CB reaggregation after melting point of the HDPE, resulted from the decreasing of London dispersive component of the surface free energy for CB particles.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.9
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• pp.671-678
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• 2012

The objective of this study is to analyze theoretically the performance of an open air-cycle refrigeration system in which environmental concerns increase. The pressure ratio of the external compressor and efficiencies of the components that compose of the system are selected as important parameters. As the pressure ratio of the external compressor increases, the pressure ratio of the ACM compressor is determined high, the refrigerating temperature and capacity increase, the COP decreases, and the total entropy production rate increases. The effect of heat exchanger effectiveness and turbine efficiency on the performance are greater than that of the ACM compressor efficiency. Also the performance of the air-cycle refrigeration system with two heat exchangers has been enhanced like high COP and low total entropy production rate, compared to the system with one heat exchanger.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.5 no.1
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• pp.1-8
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• 2009

Nuclear hydrogen production using high temperature heat of a very high temperature reactor(VHTR) is one of the most attractive ways of mass hydrogen production without greenhouse gas emission. In many countries, sulfur-iodine(S-I) thermochemical process and high temperature steam electrolysis(HTSE) process are being investigated. In such processes, corrosion behavior of Intermediate heat exchanger materials are the most critical issues. Especially in a HTSE system, several heat exchangers will be facing hot steam conditions. In this paper, the status of high temperature corrosion researches in hot steam and supercritical water conditions are reviewed in view of the implication to HTSE conditions. Based on the review, test condition and plan of the hot steam corrosion of the candidate materials are formulated and described in some details along with the schematics of the test set-up. The test results and subsequent evaluation will be used in development of a interface system between the HTSE hydrogen production system and the VHTR.

• Nuclear Engineering and Technology
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• v.54 no.8
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• pp.2792-2800
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• 2022

In the core of the WWR-K reactor, a long-term irradiation of tristructural isotopic (TRISO)-coated fuel particles (CFPs) with a UO₂ kernel was carried out under high-temperature gas-cooled reactor (HTGR)-like operating conditions. The temperature of this TRISO fuel during irradiation varied in the range of 950-1100 ℃. A fission per initial metal atom (FIMA) of uranium burnup of 9.9% was reached. The release of gaseous fission products was measured in-pile. The release-to-birth ratio (R/B) for the fission product isotopes was calculated. Aspects of fuel safety while achieving deep fuel burnup are important and relevant, including maintaining the integrity of the fuel coatings. The main mechanisms of fuel failure are kernel migration, silicon carbide corrosion by palladium, and gas pressure increase inside the CFP. The formation of gaseous fission products and carbon monoxide leads to an increase in the internal pressure in the CFP, which is a dominant failure mechanism of the coatings under this level of burnup. Irradiated fuel compacts were subjected to electric dissociation to isolate the CFPs from the fuel compacts. In addition, nondestructive methods, such as X-ray radiography and gamma spectrometry, were used. The predicted R/B ratio was evaluated using the fission gas release model developed in the high-temperature test reactor (HTTR) project. In the model, both the through-coatings of failed CFPs and as-fabricated uranium contamination were assumed to be sources of the fission gas. The obtained R/B ratio for gaseous fission products allows the finalization and validation of the model for the release of fission products from the CFPs and fuel compacts. The success of the integrity of TRISO fuel irradiated at approximately 9.9% FIMA was demonstrated. A low fuel failure fraction and R/B ratios indicated good performance and reliability of the studied TRISO fuel.