• Title/Summary/Keyword: Transfer resistance

Search Result 1,288, Processing Time 0.023 seconds

An analysis on the solidification process of alloy casting with a contact resistance (접촉 열저항을 고려한 합금주조의 응고과정 해석)

  • Kim, W.S.;Lee, K.S.;Im, I.T.;Kim, K.S.
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.21 no.1
    • /
    • pp.57-67
    • /
    • 1997
  • The solidification process of Al 4.5%Cu alloy is numerically studied in the presence of contact resistance between mold and cast. Natural convection is considered in the liquid and mushy regions. The porosity approach is applied to the mushy zone modeling and linear variation of the solid fraction on the temperature is assumed. Results show that the mushy region is wider in the case with a contact resistance compared to the perfect contact condition. The temperature of the cast with a temporal variation in the contact heat transfer coefficient changes very rapidly in the early stage of the casting process compared to that with constant contact heat transfer coefficient.

The Heat Transfer Characteristics of Rotating Heat Pipe with Tapered Condensers in the both Sides of Evaporator (증발부 양단에 테이퍼 응축기를 가진 회전형 히트파이프의 전열 특성)

  • 이기우;이영수;장기창;장영석
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.8 no.1
    • /
    • pp.13-25
    • /
    • 1996
  • The purpose of this paper is to study heat transfer characteristics of rotating heat pipe with tapered condensers by numerical analysis and experimental method. An experimental investigation has been carried out on thermal resistance between condenser wall and vapor region fo the rotating heat pipe with various taper 0, 1/11.4, 1/38. Heat transfer characteristics by analytical study were applied to describe various Nu numbers on the base of dimensionless condensate film, Re and Pr numbers in both condensers. Comparison between calculated results and experimental data showed qualitatively good agreement and the numerical analysis of this study can be utilized to predict the performance of a rotating heat pipe. The thermal resistance can be decreased by increasing the revolution per minute. Regardless of various dimensionless condensate film, Nu number was largely influenced by saturation temperatures of working fluid.

  • PDF

A Study on the Characteristics of Heat Transfer in Heat Pipe with Composition Wick of Screwed Groove - Metallic Mesh (나선형그루브-금망의 복합윅을 갖는 히이트파이프의 전열특성에 관한 연구)

  • Chang, Young-Suk;Lee, Young-Soo;Seoh, Jeong-Il
    • The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
    • /
    • v.15 no.3
    • /
    • pp.273-282
    • /
    • 1986
  • The purpose of this research was to study the characteristics of heat transfer in Heat Pipe which used the composition wick of screened groove - metallic mesh by ADI method and experimental results. As the results, the more than number of metallic mesh screen layers in a heat pipe increased, the fewer the effect of heat recovery decreased. In case of 1 - layer metallic mesh screen wick, the response of the effect in heat recovery was more rapidly showed than in case of other layers and in spite of high load, the evaporation section of Heat pipe with 1 - layer metallic mesh screen wick showed the stable response and did not show excessive super heat. There was a interrelation between thermal resistance and the variable layers, between thermal resistance and the variable gaps of metallic meshes, the heat transfer characteristics of Heat pipe were depended on the thermal resistance of composition wick.

  • PDF

Public Health Risks: Antibiotic Resistance - Review -

  • Barton, Mary D;Hart, Wendy S
    • Asian-Australasian Journal of Animal Sciences
    • /
    • v.14 no.3
    • /
    • pp.414-422
    • /
    • 2001
  • Antibiotic resistance in human pathogens is a major public health issue. Some of the resistance problem can be attributed to the transfer of resistant bacteria from animals to people and the transfer of resistance genes from animal pathogens and commensal bacteria to human pathogens. Control measures include improvements in food hygiene to reduce the spread of zoonotic bacteria to people via the food chain. However, to specifically address the issue, the medical profession must control misuse and overuse of antibiotics in hospitals and community practice. In addition, the livestock industries and their advisors must reduce and refine the use of antibiotics in animal production and replace antibiotics with alternative disease control measures as much as possible.

Mixed Convection Transport from a Module on the Bottom Surface of Three Dimensional Channel (3차원 채널 밑면에 탑재된 모듈로부터의 혼합대류열전달)

  • Lee, Jin-Ho;Park, Sang-Hee;Riu, Kap-Jong;Bang, Chang-Hoon
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.24 no.5
    • /
    • pp.632-639
    • /
    • 2000
  • Conjugate heat transfer from a heat generating module ($31{\times}31{\times}7mm^3$) bonded through the module support on the floor of a parallel-plate channel(20mm high, 400mm wide, and 800mm long) to mixed convective air flow(0.2${\sim}$0.9m/s) is studied experimentally. The input power to the module is changed in a range 1.0${\sim}$4.5W, the floor thickness 0.2${\sim}$5mm, and the thermal resistance of module support, Rc:=0.06, 1.03 and 82.0K/W. Thermal conductance(Uc) of the board and convective thermal conductance($U_A$) from the module were derived, and the effect of V; Rc and t on Uc was investigated. It is found that the conjugate conductance (Uc) and the conductive heat transfer ratio ($Q_B$/Q) depend on the thermal resistance of the module support, the air velocity and the board thickness. The change of the module support resistance and the board thickness helps to elucidate the relative significance of heat transfer paths through the module support, the board, and from the board surface to the air. Additional information is investigated about the dependence of the heat transfer rate on the mixed convection parameter.

Evaluation on Sensitivity and Approximate Modeling of Fire-Resistance Performance for A60 Class Deck Penetration Piece Using Heat-Transfer Analysis and Fire Test

  • Park, Woo Chang;Song, Chang Yong
    • Journal of Ocean Engineering and Technology
    • /
    • v.35 no.2
    • /
    • pp.141-149
    • /
    • 2021
  • The A60 class deck penetration piece is a fire-resistance apparatus installed on the deck compartment to protect lives and to prevent flame diffusion in the case of a fire accident in a ship or offshore plant. In this study, the sensitivity of the fire-resistance performance and approximation characteristics for the A60 class penetration piece was evaluated by conducting a transient heat-transfer analysis and fire test. The transient heat-transfer analysis was conducted to evaluate the fire-resistance design of the A60 class deck penetration piece, and the analysis results were verified via the fire test. The penetration-piece length, diameter, material type, and insulation density were used as the design factors (DFs), and the output responses were the weight, temperature, cost, and productivity. The quantitative effects of each DF on the output responses were evaluated using the design-of-experiments method. Additionally, an optimum design case was identified to minimize the weight of the A60 class deck penetration piece while satisfying the allowable limits of the output responses. According to the design-of-experiments results, various approximate models, e.g., a Kriging model, the response surface method, and a radial basis function-based neural network (RBFN), were generated. The design-of-experiments results were verified by the approximation results. It was concluded that among the approximate models, the RBFN was able to explore the design space of the A60 class deck penetration piece with the highest accuracy.

Distribution of thermophilic Campylobacters in animals and transfer of drug resistance factor of isolates to related bacteria II. Plasmid profile and transfer of drug resistance of isolated Campylobacter (동물(動物)에서의 thermophilic Campylobacter의 분포(分布) 및 분리세균(分離細菌)의 약제내성(藥劑耐性) 전달(傳達)에 관(關)한 연구(硏究) II. Campylobacter의 plasmid profile 및 약제내성(藥劑耐性) 전달(傳達))

  • Kim, Yong-hwan;Mah, Jum-sool
    • Korean Journal of Veterinary Research
    • /
    • v.29 no.3
    • /
    • pp.303-313
    • /
    • 1989
  • To investigate the epidemiological trait of intestinal diseases of animals caused by thermophilic Campyllobacter spp., isolation of etiological agent was carried out and the profiles of plasmids and the transfer of resistance plasmid in the isolated Campylobacter spp. were examined. The results were as follows. 1. A total of 110 isolates of C jejuni and C coli were subjected to the test for the presence of plasmid DNA. Of the isolates examined, 60% of the isolates were noted to harbor plasmid DNA. Plasmid occurrencer ate from pigs, chickens and cattle were 76.2%, 61.7% and 37.7%, respectively. The plasmids of a large molecular weight, ranging from 36 Md to 86Md, were identified with the strains of tetracycline resistant. 2. Transfer frequency of tetracycline resistant plasmids was higher in the case of the filter mating method than in the broth mating method by the factor of 10~1,000. 3. Tetracycline resistant plasmids of C jejuni were transferrable to C jejuni and C coli by conjugation. In a low frequency, the transfer of tetracycline plasmid was also possible to Vibrio parahemolyticus. However, it was impossible to transfer to Streptococcus fecalis, E coli and Vibrio cholerae. 4. Tetracycline resistant plasmids of C jejuni were impossible to transfer to Campylobacter spp. and related bacteria by transformation.

  • PDF

Heat ,rind Moisture Transfer Properties of Fabrics for Korean Folk Clothes (시판 한복지의 열.수분이동 특성)

  • 성수광;성은정
    • Journal of the Korean Society of Clothing and Textiles
    • /
    • v.20 no.6
    • /
    • pp.1071-1083
    • /
    • 1996
  • This study was carried out to obtain some fundamental data for designing thermally comfortable Korean folk clothes (KFC) which were classified into 4 groups according to seasons and materials. It was conducted to find the relationship among structural, thermal, and moisture transfer properties, and then the properties of heat and mositure transfer while changing thickness of air layer of selected similar fabrics with various thickness were examined. The summarized results of this study were as follows ; 1. The relationship between the structrual and thermal properties showed high positive correlation with thickness SE thermal insulation value (TIV), porosity & TIV. 2. The relationship between the structural and mositure transfer properties showed high negative correlation with thickness & moisture vapor permeability (Mp), porosity & Mp respectively. 3. The relationship between the heat and moisture transfer properites showed high negative correlation with qmax, air permeability (Ap), Mp & TIV while showed high positive with Ap & Mp respectively. 4. Resistance to dry heat transfer according to thickness of air layer for KFC was increassed rapidly up to 2 mm and above this increasing rate was reduced. Resistance to evaporative heat transfer was remarkable changes in 6∼8 mm but slowly in 6∼8 man. 5. Mioisture permeability index (i) according to thickness of air layer for KFC showed the greatest value at 2 mm but had not difference between groups according to thickness.

  • PDF

A Study on the Formation of Fouling in a Heat Exchanging System for River Water (하천수를 이용하는 열교환 시스템 내 파울링 형성에 관한 연구)

  • Sung, Sun-Kyung;Suh, Sang-Ho;Roh, Hyung-Woon
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.28 no.6
    • /
    • pp.646-651
    • /
    • 2004
  • When the water flowing inside of the heat transfer equipments such as heat exchangers, condensers, and boilers is heated, calcium, magnesium sulfate, and other minerals in the water are deposited and built up for scales on the heat transfer surfaces. When those scales accumulate on the heat transfer surfaces, their performance of the heat transfer become progressively reduced due to the increase of the heat transfer resistance. The mechanism of this reduced heat transfer is called fouling. This study investigated the formation of the fouling in a heat exchanger with river and tap water flowed inside of it as a coolant. In order to visualize the formation of the fouling and to measure the fouling coefficients, a lab-scale heat exchanging system was used. Based on the experimental results, it was found that the formation of fouling for river water was quite different with the formation for tap water.

Experimental Study on Condensation Heat Transfer Characteristics of Special Heat Transfer Tubes (응축용 특수 전열관의 열전달 특성에 관한 연구)

  • 한규일;박종운;권영철;조동현
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.13 no.9
    • /
    • pp.827-835
    • /
    • 2001
  • In this study, condensation heat transfer characteristics were conducted with special heat transfer tubes of SH-C type. Experiments were carried out the saturated vapor temperature of 334K and the wall subcooling of 1.5-4.5K. The refrigerant was R-113 and the enhanced tubes used in the present study were SH-CDR, SH-CYR and SH-CHR. The experimental results showed that the condensation heat transfer coefficients of SH-C type tubes were about 23-66% higher than those of a low integral-fin tube. It was visualized that the condensed liquid on the outer surface of SH-C type tubes flowed continuously down unlike a low integral-fin tube and a plain tube, due to a 3-D extending fin on the outer surface of SH-C type tubes. As a result, the thermal resistance of the condensed liquid decreased and the heat transfer coefficient increased. Also, the enhancement ratio of SH-CDR tube was the highest, and it was about 9-11 times as compared to that of a plain tube.

  • PDF