• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.16 no.2
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• pp.1-6
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• 2020

This work experimentally explored the influence of nano-fouling on CHF, flow boiling heat transfer coefficient, contact angle, and surface roughness. In this study, the flow velocity conditions are established at 0.5, 1.0, and 1.5 m/s. Also, the nanoparticles of oxidized MWCNT were deposited on a heat transfer surface for 0, 120, 180, and 240 sec. As the results, it was found that CHF and superheated temperature were increased in case of nano fouling on the heat transfer surface in oxidized MWCNT fluid. Also, the contact angle and surface roughness decreased when flow velocity and nano coating increased.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.141-143
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• 2006

It is well known that there are three mechanisms in the nozzle surface regression, namely ablation, mechanical erosion and chemical corrosion. There are Analogies among these three mechanisms. In order to compare the order of the magnitude of these mechanism, the analogy was adapted and the Mach number of the gas flow was expressed by the nozzle shape(location).

• Journal of Energy Engineering
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• v.10 no.3
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• pp.266-271
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• 2001

Buoyancy-driven natural convection is analysed by employing a linear stability theory in hori-zontal porous media with net through flow. Darcy's law is used to model the flow characteristics in porous media. Bated on the results of linear stability analysis, a heat transfer correlation was obtained by employing weakly nonlinear analysis. As the net through flow increases, the system becomes more stable and the effect of the Darcy-Rayleigh number on the Nusselt number decreases.

• Journal of Advanced Marine Engineering and Technology
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• v.20 no.4
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• pp.59-69
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• 1996

냉동.공조 및 각종 화학공업에 널리 사용되는 열교환기인 응축기의 고성능화 및 합리적인 설계를 위해서는 냉매의 정확한 응축열전달률 예측과 그 메카니즘 규명이 필수 요건이다. 본 연구에서는 내경 9.7mm, 외경 12.7mm, 길이 1200mm의 수직 이중관 응축기의 압력강하 및 응축열전달특성을 실험적으로 밝혔다. 실험으로부터 Lockart-Martinelli의 상관 관계식을 이용한 수직 응축관내 압력강하 특성을 종래의 실험식들과 비교.검토하고 새로운 압력강하식을 제안하였다. 그리고 종래의 해석방법과는 달리 비환상류 모델을 가정한 해석결과로부터 전 유동양식에 걸쳐 적용할 수 있는 새로운 응축열전달 예측식을 제안하였다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.1
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• pp.26-36
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• 1996

Many researches were carried out to estimate heat transfer rate on a circular cylinder in a uniform flow. Various empirical correlations were suggested in the past through experimental studies, however there are considerable discrepancies in the estimated values of heat transfer coefficient. The effect of fluid physical properties on the forced convective heat transfer between a circular cylinder and the external flow was numerically investigated in the present study, The flow and temperature fields were solved using a Finite Volume Method over a wider range of Prandtl number(0.7-40,000) than existing correlations. The cold as well as the hot cylinders in the uniform liquid flow of constant temperature were investigated. A unified correlation was obtainde for both cases.

• Clean Technology
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• v.14 no.1
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• pp.53-60
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• 2008

The condensation heat transfer coefficients and pressure drops of hydrocarbon refrigerants (R-290 and R-600a) and hydrochlorofluorocarbon (HCFC) refrigerants were measured in the two horizontal double pipe heat exchangers with inner diameters of 10.07 mm and 5.80 mm at a mass flux of $35.5{\sim}210.4\;kg/m^2s$ and the condensation temperature of $40^{\circ}C$. The average condensation heat transfer coefficients of hydrocarbon refrigerants were higher than that of HCFC refrigerant(R-22). The pressure drop had a magnitude in the order of R-600a > R-290 > R-22. The pressure drops in the tubes with inner diameter of 10.07 mm were approximately $6{\sim}15%$, $9.8{\sim}12.5%$ and $2.1{\sim}4.6%$ higher for R-600a, R-290 and R-22, respectively, than those with inner diameter of 5.80 mm. The condensation heat transfer coefficients were compared with the published experimental data, and showed the best agreement with Haraguchi et al.'s correlation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.6
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• pp.529-535
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• 2005

This study experimentally examines the air-side performance of spiral finned tube heat exchangers. The effects of fin spacing, fin height, and tube alignment were investigated. Reduction of fin spacing decreased the Colburn j factor. However, the effect of fin height on the Colburn j factor was negligible. An increase of tube row decreased the Nusselt number for both staggered and in-line tube alignments. However, the decrease of the Nusselt number for the in-line tube alignment was much more significant than that of the staggered tube alignment. The average Nusselt number of the staggered tube alignment was larger than that of the in-line tube alignment by $10\%$ when the Reynolds number ranged from 300 to 1700. An empirical correlation of the Nusselt number was developed by using geometric parameters of heat exchanger and correction factors. The correction factor considered the effects of tube alignment and number of tube rows on the heat transfer. The proposed correlation yielded a mean deviation of $4\%$ from the present data.

• Applied Chemistry for Engineering
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• v.7 no.2
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• pp.308-314
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• 1996

The crystal growth rate of benzene from benzene-cyclohexane mixtures at a cylindrical layer crystallizer was determined from the slope of the line of correlation between operating time and layer thickness. The thickness of crystal layer was obtained from the amount of crystal deposited on the cooled wall surface of the crystallizer. The crystal growth rate was related with the degree of subcooling, which was defined as the difference between temperature of melt and that of growing crystal surface. The linear crystal growth rate for binary mixtures was proportional to the second power of the degree of subcooling. Equation model which was obtained from data through the rate of heat and mass transfer in the crystallizer and thus can tell crystal thickness and surface temperature of crystal layer according to the elapsed time was presented and successfully correlated to the experimental data. For the benzene-cyclohexane mixtures contains 5wt% and 10wt% of cyclohexane, the comparison of experimental data with calculation using model equation was done for crystal thickness corresponding to the various cooling temperatures.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.1
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• pp.1-8
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• 2012

Numerical analysis has been carried out to investigate the fully developed flow and heat transfer characteristics of a plate heat exchanger. Multi-cell models with an inlet part and outlet part are used to perform the numerical simulation. The plate heat exchanger is characterized by a chevron angle of $20^{\circ}$ and a P/H ratio of 2.0~4.0. The working fluid is water and the Reynolds numbers range from 300 to 1,500. The correlation is given in the form of $f=CRe^m$ for the friction factor and $j=CRe^m$ for the Colburn factor. It is found that the fully developed flow starts from the third cell and the Nusselt number increases with decreasing P/H ratios.

• Solar Energy
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• v.14 no.2
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• pp.51-60
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• 1994

The fluidization characteristics of the furan foundry sand fluidized bed and the heat transfer characteristics on a single spiral coil tube in the bed have been investigated. In the paper, the heat transfer coefficients for a single spiral coil tube are measured in the furan foundry sand bed as a function of the ratio of heated coil tube pitch to diameter(p/Do) and the ratio of heated coil tube pitch to particle size(p/dp). The experimental results are as follows. 1) Mean heat transfer coefficients increases according to the increasing ratio of heated coil tube pitch to diameter(p/Do). 2) The Increasing rates of mean Nusselt numbers are more greater in the case of p/Do=1.58 than p/Do=4.75. 3) Mean Nusselt number can be expressed by the following equation, $Nu_{mean}=C\;Re^m\;Pr_g^{0.4}(p/dp)^n$.