• Journal of the Korean GEO-environmental Society
• /
• v.18 no.12
• /
• pp.59-63
• /
• 2017

In the cold region, road surface is frequently frozen, resulting in property/facility damage as well as people's death. In order to prevent the road surface from being frozen, conventional deicing methods such as salt, geothermal, and electric wires have been widely used. However, theses methods have some problems such as anti-environment, high-construction and -maintenance cost and so on. To improve the drawbacks of aforementioned methods, carbon nanotube (CNT) was used as an heating material in the laboratory test. Through the test, heat transferring effect of CNT on the concrete slab was investigated and maximum interval of CNT installation was determined.

• Journal of Energy Engineering
• /
• v.23 no.3
• /
• pp.191-197
• /
• 2014

To increase the heat transfer rate of the air pre-heating heat exchanger used for the condensing boiler, We investigated condensation heat transfer coefficients through plasma surface treatment. The hydrophilic surface showed about 10% increase in heat transfer rate than original plate. It shows that Shah correlation can be used to predict the condensation heat transfer coefficient on the original surface within 10% error range after the compatison between Shah correlation and the condensation heat transfer coefficients measured on the hydrophilic surface and original surface. Therefore, we have shown that Shah correlation is available when designing the air pre-heating heat exchanger using the original surface in this study.

• KIEAE Journal
• /
• v.16 no.1
• /
• pp.81-87
• /
• 2016

Purpose: Heat transfers phenomena are described by the second order partial differential equation and its boundary conditions. In a three-dimensional structure of a building, the heat transfer phenomena generally include more than one material, and thus, become complicate. The analytic solutions are useful to understand heat transfer phenomena, but they can hardly be applied in engineering or design problems. Engineers and designers have generally been forced to use numerical methods providing reliable results. Finite volume methods with the unstructured grid system is only the suitable means of the analysis for the complex and arbitrary domains. Method: To obtain an numerical solution, a discretization method, which approximates the differential equations, and the interpolation methods for temperature and heat flux between two or more materials are required. The discretization methods are applied to small domains in space and time, and these numerical solutions form the descretized equations provide approximated solutions in both space and time. The accuracy of numerical solutions is dependent on the quality of discretizations and size of cells used. The higher accuracy, the higher numerical resources are required. The balance between the accuracy and difficulty of the numerical methods is critical for the success of the numerical analysis. A simple and easy interpolation methods among multiple materials are developed. The linear equations are solved with the BiCGSTAB being a effective matrix solver. Result: This study provides an overview of discretization methods, boundary interface, and matrix solver for the 3-dimensional numerical heat transfer including two materials.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.40 no.10
• /
• pp.653-658
• /
• 2016

A study on the measurement of critical heat flux using the transient inverse heat conduction method in spray cooling was performed. The inverse heat conduction method estimates the surface heat flux or temperature using a measured interior temperature history. The effects of the measuring time interval and location of temperature measurement on the measurement of critical heat flux were primarily investigated. The following results were obtained. The estimated critical heat flux decreased as the time interval of temperature measurement increased. Meanwhile, the effect of measurement location on critical heat flux was not significant. It was also found, from the experimental results, that the critical superheat increased as the measurement location of thermocouple neared the heat transfer surface.

• Plant Journal
• /
• v.4 no.3
• /
• pp.54-59
• /
• 2008

The resonance of boiler is caused by exciting force in the gas path and it generates the vibration by the harmony of boiler's dimensional factor. According to trending toward the boiler of increasing capacity and a bigger size, it has a problem of the vibration at back-pass heating surfaces. We can predict such vibrations as comparison between vortex frequency and gas column's natural frequency. We can't rely on the method for the past decades because of changing parameters, such as an allowable error, gas temperature, gas velocity, Strouhal number. We can reduce the vibration to use the seasoning effect and change the operating condition in coal fired boiler but it's not essential solution. When the vibration occurred in the model boiler, we must measures the acoustic pressure and frequency of places for considering the means. So far, we confirmed the problem from field measures and theoretical analysis about the acoustic vibration of boiler. We installed anti-acoustic baffle in a existing boiler to change the acoustic natural frequency at the cavity, which results in reducing the acoustic vibration. The first, we prove that the acoustic resonance is caused by harmonizing vortex shedding frequency of tube heat surface with acoustic natural frequency of cavity in the range of 650~750 MW loads. The second, the acoustic resonance at the back-pass heating surface has the third order of acoustic natural frequency at the second economizer. We install five anti-acoustic baffles at the second economizer to reducing the resonance. We confirm considerably reducing the acoustic vibration of boiler during the commercial boiler.

• Solar Energy
• /
• v.18 no.3
• /
• pp.217-228
• /
• 1998

The purpose of this research is to investigate the characteristics of static and total pressure distribution in the upward free water jet system impinged on a downward flat plate. The rectangular nozzle was used and its contraction and aspect ratio was five and about seven respectively. Experimental conditions considered were jet velocity, distance between nozzle and flat plate, height of supplementary water. It was founded that pressure distribution on the flat plate had the Gaussian curve when the pressure at stagnation point and impinging half width were chosen as the scaling parameters. The maximum pressure was shown at the stagnation point. The central impingement velocity decreased with the increment of distance between nozzle and flat plate, and its slop of decay was similar to that of chracteristics decay region in the three-dimensional free jet.

• Solar Energy
• /
• v.15 no.1
• /
• pp.53-71
• /
• 1995

Experiments have been conducted on a planar, free surface jet of water to investigate the effects of aspect ratios(AR=6.67, 15, 26.67), average nozzle velocity($V_0=3.3m/s{\sim}78m/s$) and nozzle-to-plate spacings($Z/W=6{\sim}40$) on the characteristics of heat transfer, when 3 rectangular waterjets impinging on a flat plate which has the uniform heat flux. the scondary peaks which produced by circular jets also produced by rectangular water jets. The position of the scondary peaks depends upon the aspect ratio of nozzle. The heat transfer coefficient was subjected to the influence of aspect ratio. The heat transfer correlations and best position of nozzles which produced maximum heat transfer coefficient at stagnation point are provided.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.12 no.1
• /
• pp.59-66
• /
• 2000

In a previous paper, we have examined the effects of nozzle configuration and jet to jet spacing on the heat transfer of 1 row of circular water jets. In this paper, experiments have been conducted to obtain the effects of nozzle to target plate distances on the heat transfer of 1 row of 3 jets and 1 row of 5 jets. The nozzle configurations are Cone type, Reverse cone type and Vertical circular type. Nozzle to target plate distance H was varied from 16 mm(H/D=2) to 80mm(H/D=10). For fixed value of mass flow rate and nozzle to target plate distance, larger values of average Nusselt number were obtained for the smaller jet to jet spacing. For the array of water jets, the average heat transfer was decreased slightly with increasing nozzle to target plate distance at low jet velocity of $\textrm{V}_{o}$=3 m/s. However, except for $\textrm{V}_{o}$=8 m/s of 1 row of 5 jets, it was increased with increasing nozzle to target plate distance at high jet velocity of $\textrm{V}_{o}$$\geq$6m/s. We proposed to apply the nozzle configuration of maximum average heat transfer to each nozzle to target plate distance for 1 row of 3 jets, and, it was Reverse cone type nozzle for 1 row of 5 jets(Reynolds number$\geq$36000).

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.8 no.3
• /
• pp.131-150
• /
• 1979

Recently only a few correlations between various factors due to the different grades of surface roughness for the nucleate pool boiling have been proposed. The main purpose of this work is to test the validity of these types of correlations between related factors to nucleate pool boiling phenomena. The boiling experiments using distilled water were carried out at the heat flux ranging from $7.4\times10^4\;to\;2.4\times10^5kcal/m^2h$ on the sintered porous metal surface with the cavity diameter of 10, n, 40, 70, $100{\mu}$, respectively, at the atmospheric pressure, To determine the bubble sizes, number of nucleation sites, delay and growth time, frequency of bubble emission and rising velocities of bubbles, the high speed motion picture technique was employed. In the correlation $f{\propto}D_b^n$, where f denotes frequency of bubble emission and $D_b$ departure diameter, n, the power factor of $D_b$, have been found to be from -2 to -10/3. The correlation C in the correlation between heat flux q and density of nucleation sites $\frac{N}{A}$, $q=C(\frac{N}{A})^n$, was appeared to be more crucial than the power factor n. The correlation of the heat flux q to the temperature difference ${\Delta}T$ and the density of nucleation sites$\frac{N}{A}$, was proposed to be $$q-460{\Delta}T^{\frac{5}{4}}=K{\Delta}T{\frac{5}{3}}(\frac{N}{A})^{\frac{2}{3}}$$. The values of heat transfer coefficient obtained in this experiments for the porous sintered metal surface appeared to be very high in comparison with the formerly obtained results for the other surfaces.

• Journal of the KSME
• /
• v.35 no.9
• /
• pp.836-847
• /
• 1995

파울링은 열교환기에 형성되는 열저항으로 에너지 손실에 많은 영향을 미친다. 그러나 파울링은 그 예측이나 감소 또는 제거가 매우 어려운 것으로 인식되어 왔다. 작동유체자체를 철결하게 유지함으로써 파울링을 감소할 수도 있으나 작동유체 자체의 특성 때문에 본질적으로 작동유체를 청결하게 유지할 수 없는 경우가 대부분이다. 즉, 폐열 회수의 대상이 되는 액체가 하천수나 생 활하수인 경우 작동액체를 청결하게 유지함으로써 파을링을 저감시피는 방법은 타당치 않다.일 본의 폐얼회수 프로젝트와 담수화 프로젝트에서 특이한 점은 두 가지 프로젝트에서 열교환기면의 파울링 문제 해경을 전열 촉진의 내용과 거의 비슷한 비중으로 다루고 있다는 점이다. 파울링은 오래 전부터 열시스템설계자의 주요 관심사였으나 큰 진전은 없었다. 그러나 현재는 주변기술이 발달로 더 이상 연구 불가능 영역은 아닐 듯 싶다.