• Title/Summary/Keyword: heat modification

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The Inprovement of the Heat Exchanger Performance by Shape Modification(I)-Experimental Analysis of the Heat Transfer Enhancement by Attached Wires in a Double Pipe Heat Exchanger- (형상변화 에 의한 열교환기 의 열전달 성능 향상 (I) -이중 동심원관내에 와이어 부착시의 열전달 촉진에 대한 실험적 해석-)

  • 노승탁;이택식;강신형;김진오
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.9 no.1
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    • pp.71-80
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    • 1985
  • The various sizes of wires are attached to the outside of the inner tube in a double pipe heat exchanger to enhance the thermal performance. The diameters of the wires range from 0.5mm to 1.6mm while the pitches are chosen between 5mm and 50mm. Experiments have been performed with the range of Reynolds numbers from 15000 to 30000 in annular space where air flows. The friction factors are increased by 1.5 to 4.5 times depending on the sizes and the pitches of the wires. However, the Nusselt numbers are increased by the factors of 1.8 to 2.8 within this experimental range. It is suggested that there should be an optimum configuration rendered when the weighting values of the heat transfer promotion and the pumping power are given.

Effect of Heat Treatment on the Adhesive Strength of Electoless Nickel Deposits (무전해법으로 Slide Glass 위에 도금된 Ni층의 접착력에 미치는 열처리의 영향)

  • Hyun, Yong-Min;Yu, Sung-Yeol;Yoon, Jung-Yun;Kim, Bo-Young;Kim, Sun-Ji;Tahk, Song-Hee;Kim, Hee-San
    • Journal of Surface Science and Engineering
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    • v.44 no.6
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    • pp.246-249
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    • 2011
  • Surface modification before coating nickel by coupling agents and/or etchant of glass did not provide enough adhesive strength of electroless nickel deposits on glass. Effect of heat treatments on hardness as well as adhesion of nickel deposits was studied by using tape test for adhesion, nanoindenter for hardness and glancing angle x-ray diffractometer (GAXRD) for phase characterization. Heat treatment improved hardness as well as adhesion. XRD results give that the improvements of adhesion and hardness are due to the formation of $NiSiO_4$ around the interface between the nickel deposits and the glass and the precipitation of $Ni_3P$ causing precipitation hardening, respectively. The details in effects of heat treatment on adhesion and hardness are described here.

Measurement of the Surface Heat Transfer Coefficients for Freezing Time Prediction of Foodstuffs (식품의 동결시간 예측을 위한 표면열전달계수 측정)

  • Jeong, Jin-Woong;Kong, Jai-Yul;Kim, Min-Yong
    • Korean Journal of Food Science and Technology
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    • v.21 no.6
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    • pp.735-741
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    • 1989
  • For the accurate prediction of freezing time, probably the most difficult factor to measure and major error source is the surface heat transfer coefficient. In this work, surface heat transfer coefficient were determined for still air freezing and immersion freezing methods by theory of the transient temperature method and confirmed by using a modification of plank's equation to predict the freezing time of ground lean beef. The results showed the cooling rate of immersion freezing was about 11 times faster than that of still air freezing method. A comparison of surface heat transfer coefficient of copper plate and ground lean beef resulted an difference of 25-30% because the food sample surface is not smooth as copper plate. Also, when h-values measured by ground lean beef were applicated to modified model, the accuracy of its results is very high as difference of about 8%.

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Experimental study on the performance improvement of a screw-compressor-type chiller (스크류 압축식 냉동기의 성능향상에 관한 실험적 연구)

  • Lee, D.-Y.;Jung, S.-H.;Kang, B.H.;Hong, H.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.11 no.1
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    • pp.48-60
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    • 1999
  • An experimental study on the performance enhancement of a screw-compressor-type chiller with 100kW of nominal cooling capacity has been carried out. Performance test facility was developed to investigate the effects of a partial modification from the existing chiller on the performance. By replacing the existing shell-and -tube heat exchangers with plate heat exchangers, the cooling capacity is increased by 15~18% and the COP is also increased by 19~21% depending on the operation temperature range. Charging mixed refrigerant R22/R142b(80 : 20) instead of R22 into the chiller with plate heat exchangers improves the cooling capacity by 4% and the COP very largely by 30%. Each contribution of the plate evaporator, plate condenser, and mixed refrigerant to the performance enhancement is examined by analyzing the refrigeration cycle and the heat transfer processes. It is also shown that the chiller performance can be improved by adapting 2-stage-compression cycle using an economizer.

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Enhancement of Condensation Heat Transfer of Anodized Aluminum by Teflon Coating and Oil-Impregnation (테플론 코팅과 오일 담지를 이용한 알루미늄 양극산화피막의 응축 열전달 향상)

  • Kang, Minjoo;Lee, Jonghoon;Cha, Soojin;Shin, Yeaji;Kim, Donghyun;Kim, Kyung-Ja;Lee, Junghoon
    • Journal of Surface Science and Engineering
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    • v.54 no.2
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    • pp.90-95
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    • 2021
  • Surface modification technique enabling the control of condensation provides various benefit in various engineering systems, such as heat transfer, desalination, power plants, and so on. In this study, lubricant oil-impregnation into Teflon-coated nanoporous anodic oxide layer of aluminum to enhance a de-wetting and mobility of water droplet on surface. Due to the surface treatment improving water-repellency, the condensation mode is changed to dropwise, thus the frequency of sliding condensed water droplet on surface is increased. For these reasons, the surface of oil-impregnated Teflon-coated nanoporous anodic aluminum oxide shows significantly enhanced condensation heat transfer compared to bare aluminum surface. In addition, the porosity of anodic aluminum oxide affected the mobility of water droplet even with oil-impregnation and Teflon-coating, indicating that the optimization of porous structure of anodic oxide is required for maximizing the condensation heat transfer.

Numerical Study of Aerodynamics of Turbine Rotor with Leading Edge Modification Near Hub (허브 측 선단 수정에 따른 터빈 로터의 공력 특성에 대한 수치적 연구)

  • Kim, Dae Hyun;Lee, Won Suk;Chung, Jin Taek
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.37 no.8
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    • pp.1007-1013
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    • 2013
  • This study aims to analyze the aerodynamics when the geometry of the turbine rotor is modified. The turbine used in this study is a small engine used in the APU of a helicopter. It is difficult to improve the performance of small engines owing to the structural weakness of the blade tip. Therefore, the improvement of the hub geometry is investigated in many ways. The working fluid of a turbine is a high-temperature and high-pressure gas. The heat transfer rate of the turbine surface should be considered to avoid the destruction of blade owing to the heat load. The SST turbulence model gives an excellent prediction of the aerodynamic behavior and heat transfer characteristics when the numerical simulations are compared with the experimental results. In conclusion, the aerodynamic efficiency is improved when a bulbous design is applied to the leading edge near the hub. The endwall loss is reduced by 15%.

Design Modification of a Thermal Storage Tank of Natural-Circulation Solar Water Heater for a Pressurized System (자연순환형 태양열 온수기 축열조의 압력식 설계 개조)

  • Boo, Joon-Hong;Jung, Eui-Guk
    • Journal of the Korean Solar Energy Society
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    • v.27 no.3
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    • pp.45-54
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    • 2007
  • For a conventional natural-circulation type solar water heater, the pressure head is limited by the height between the storage tank and hot water tap. Therefore, it is difficult to provide sufficient hot water flow rate for general usage. This study deals with a design modification of the storage tank to utilize the tap-water pressure to increase hot-water supply Based on fluid dynamic and heat transfer theories, a series of modeling and simulation is conducted to achieve practical design requirements. An experimental setup is built and tested and the results are compared with theoretical simulation model. The storage tank capacity is 240 l and the outer diameter of piping was 15 mm. Number of tube turns tested are 5, 10, and 15. Starting with initial storage tank temperature of $80^{\circ}C$, the temperature variation of the supply hot water is investigated against time, while maintaining minimum flow rate of 10 1/min. Typical results show that the hot water supply of minimum $30^{\circ}C$ can be maintained for 34 min with tap-water supply pressure of 2.5 atm, The relative errors between modeling and experiments coincide well within 10% in most cases.

A Study on Chemical Modification Effect of Papermaking Fiber by Cyanoethylation (Cyanoethyl화에 의한 제지용 섬유의 화학적 개질효과에 관한 연구)

  • Yoon, Se-Young;Jo, Byoung-Muk;Oh, Jung-Soo
    • Journal of the Korean Wood Science and Technology
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    • v.25 no.1
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    • pp.56-64
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    • 1997
  • Since there are three hydroxyl groups on each anhydroglucose ring of the cellulose, the renewable resources, we can get various functional papers by the chemical modification of cellulose. The reaction involving the introduction of the ${\beta}$-cyanoethyl ($-CH_2-CH_2$-CN) group into organic substances containing reactive hydrogen atoms is known as cyanoethylation. Cellulose reacts with acrylonitrile in the presence of strong alkalis in a typical manner of primary and secondary alcohols to form cyanoethyl ethers. In cyanoethylation, important factors of reaction are temperature, concentration of the NaOH, and addition rate of acrylronitrile. FT-IR spectra of cyanoethyl group was confirmed at $2250cm^{-1}$, which corresponds the introduction of aliphatic nitrile group. Effect of cyanoethyl DS(degree of substitution) on strength properties was resulted that cyanoethylated BKP of DS 0.04 appeared to be the best choice for overall strength properties. Also, excellent thermal stability in aging characteristics was obtained.

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Surface Modification of Poly(tetrafluoroethylene) (PTFE) Membranes (PTFE 막의 표면 개질 방법)

  • Jun Kyu Jang;Chaewon Youn;Ho Bum Park
    • Membrane Journal
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    • v.33 no.1
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    • pp.1-12
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    • 2023
  • In this review, surface modification methods of hydrophobic poly(tetrafluoroethylene) (PTFE) membrane are introduced and their improved hydrophilicity results are discussed. Fluoropolymer based membranes, represented by PTFE membranes have been used in various membrane separation processes, including membrane distillation, oil separation and gas separation. However, despite excellent physical properties such as chemical resistance, heat resistance and high mechanical strength, the strong hydrophobicity of PTFE membrane surface has become a challenging factor in expanding its membrane separation application. To improve the separation performance of PTFE membranes, wet chemical, hydrophilic coating, plasma, irradiation and atomic layer deposition are applied, modifying the surface property of PTFE membranes while maintaining their inherent properties.

The development of UV falme detector (UV 화재감지장치 개발)

  • Gwon, O-Seung;Jeong, Chang-Gi;Lee, Bok-Yeong
    • Fire Protection Technology
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    • s.28
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    • pp.48-54
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    • 2000
  • The technique detects radiant energy form a flaming fire of fuels contained carbonaceous material can be applied to fast growing fires. This technique applied detectors are ultimately effective when early detecting fire alarm system is required or the smoke and heat detectors can not applied. In Korea Fire regulation, a flame detector should be install in case that the installation height is higher than 20[m], chemical plant, hangar refinery. Therefore it is really necessary that a flame detector has to be developed as soon as possible. With foundation technique of flame detector, ideal sensing element and stable circuit design, a trial UV flame detector is manufactured. The stable and reliable technique of flame detector is established through the repeateed perfomance test and modification. An early detecting fire alarm device is developed through the modification, supplement of the structure and circuit. Results of the R & D for the manufacture of an excellent flame detecting device is carried out with the establishment of technique for the mass production and the qualified manufacturing process.

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