• Journal of Advanced Marine Engineering and Technology
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• v.34 no.2
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• pp.235-242
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• 2010

An experimental investigation has been conducted to clarify roughness effects of geothermal water scale deposited onto a heating surface upon its forced convection heat transfer characteristics. Examined was a circular cylinder, on which particles of silica scale having five different sizes are uniformly distributed. The Reynolds number was varied from 13000 through 50000. Local and mean heat transfer characteristics were measured as functions of particle size and Reynolds number. Subsequently the mean fouling resistance was estimated from those results, and its characteristics are clarified. It was found that the heat transfer of cylinders greatly varies with the fouling of geothermal water scale, especially its scale height. Further, the local and average Nusselt numbers strongly depend upon the cylinder spacing and the Reynolds number.

• Journal of the Korean Institute of Gas
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• v.23 no.3
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• pp.27-32
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• 2019

In this study, the vorticity distribution and the temperature distribution change around a circular cylinder were compared and analyzed with time for constant inlet velocity and periodic inlet velocity. Also, the frequency characteristics of the flow were analyzed by analyzing the time variation of lift and drag and their PSD(power spectral density). In the case of constant inlet velocity, the well known Karman vorticity distribution was shown, and vortices were alternately generated at the upper and lower sides of the circular cylinder. In case of periodic inlet velocity, it was observed that vortex occurred simultaneously in the upper and lower sides of the circular cylinder. In both cases, it was confirmed that the time dependent temperature distribution changes almost the same behavior as the vorticity distribution. For the constant inlet velocity, the vortex flow frequency is 31.15 Hz, and for the periodic inlet velocity, the vortex flow frequency is equal to the preriodic inlet velocity at 15.57 Hz. The mean surface Nusselt number was 99.6 for the constant inlet velocity and 110.7 for the periodic inlet velocity, which showed 11.1% increase in surface heat transfer.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.2
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• pp.122-128
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• 2006

In this paper, frosting experiments were conducted with variations of frosting parameters in order to obtain the correlations of frost properties. As a result, the local thickness, density, and surface temperature of the frost layer were presented. The dimensionless correlations for the frost thickness, frost density, frost surface temperature and heat transfer coefficient were derived as functions of dimensionless frosting parameters by using a dimensional analysis.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1603-1612
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• 1990

An experimental study is conducted to investigate the fluid flow and heat transfer around tubes arranged in line. All measurements are performed at Reynolds number 1.58*10$^{4}$ with varing tube spacings from the small pitch ratio(L/D=1.25) to the large pitch ratio(L/D=3.0). Mean static pressures and mean temperatures of the surface of tubes and mean velocities and turbulent intensities in tube banks are measured. The flow patterns and the characteristics of heat transfer are strongly influenced by the tube spacings. Especially, in the case of very small spacings(L/D=1.25), the flow between neighboring tubes becomes very stagnant and the heat transfer decreases. In the case of each tube spacing, the characteristics of heat transfer around the 3rd, the 4th and the 5th tubes are nearly similar to one another, because the flow around tubes becomes stable at the 3rd tubes. The local heat transfer has the peak value near the reattachment point which has the peak value of pressure, but the local heat transfer for the 2nd tube of L/D=1.25 without reattaching has the peak value at .theta.=75.deg.. For each pitch ratio, the mean heat transfer increases gradually toward the downstream tubes, because the oncoming flow through neighboring tubes comes closer to the forward and rear surfaces of the tube and the turbulent intensity becomes larger in the downstream direction.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1540-1545
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• 2004

This paper presents a semi-empirical model to predict the frost growth formed on the cold cylinder surface. The model is composed of the correlations for frost properties including the various frosting parameters and local heat transfer coefficient. The effects of varying the correlations for local heat transfer coefficient on the frost growth are examined to establish the model. The numerical results are compared with experimental data obtained by the previous researchers. The results agree well with the experimental data within a maximum error of 13%. As the results, the frost thickness decreases with changing angular position from front stagnation to separation point. Also the effects of air velocity on the frost growth are negligible, as compared to the other frosting parameters.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2415-2423
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• 2015

Experiments were conducted on sine wave fin-and-tube heat exchangers having oval tubes under wet condition. Oval tubes having an aspect ratio of 0.6 were made, by deforming 12.7mm round tubes. Twelve samples, having different fin pitch and tube row, were tested. Results showed that, for oval tube samples, the effect of fin pitch on j and f factor was not significant. As for the effect of tube row, the lowest j factor was obtained for one row configuration(81% of two row configuration), which is clear contrast to round tube samples, where the highest j factor was obtained for one row configuration. Possible reasoning is provided considering the flow and heat transfer characteristics of sine wave channel combined with connecting oval tubes. Comparison of $j/f^{1/3}$ with plain fin-and-tube heat exchanger having 15.9mm O.D. round tube reveals that present oval fin-and-tube heat exchanger shows superior thermal performance except for one row configuration. In other words, $j/f^{1/3}$ of the two row oval tube heat exchanger was 1.6~2.5 times larger than those of round tube heat exchanger, 1.4~2.4 times larger for three row configuration and 1.2~2.8 times for four row configuration.

• Solar Energy
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• v.13 no.2_3
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• pp.53-64
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• 1993

This study investigated heat transfer phenomena during the freezing of an initially superheated or non-superheated liquid in a cooled cylinder tube. Numerical and experimental method were performed to obtatin the temperature and velocity distribution, the shape of interface. Natural convection effects in the superheated liquid were confined and moderated a short freezing time. After natural convection ceases, heat conduction dominated in the whole paraffin, so Crystal and much-zone were found out in PCM. Initial superheating of liquid tended to morderatly diminish the frozen layer thickness at short freezing times but little effect on the these quantities at longer times. On the amount of frozen mass, Iintial liquid superheating is less affected than tube wall subcooling.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.8 s.227
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• pp.989-995
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• 2004

This paper presents a semi-empirical model to predict the frost growth formed on the cold cylinder surface. The model is composed of the correlations for frost properties including the various frosting parameters and local heat transfer coefficient. The effects of varying the correlations for local heat transfer coefficient on the frost growth are examined to establish the model. The numerical results are compared with experimental data obtained by the previous researchers. The results agree well with the experimental data within a maximum error of $13\%$. As the results, the frost thickness decreases with changing angular position from front stagnation to separation point. Also, the effects of air velocity on the frost growth are negligible, as compared to the other frosting parameters.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.3
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• pp.155-162
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• 1992

Theoritical Study is performed on heat transfer and fluid flow induced by square-ribbed roughness elements in a concentric annulus. The fluid properties were assumed to be constant, and the radius($r_m$) of the maximum speed point was found by using the principle of equation of Leung and Labib. The Nusselt number and friction factor as a function of the Reynolds number($R_e=10^4$, $5{\times}10^4$, $7{\times}10^4$, $10^5$) in artifical roughness $S/{\epsilon}=5,10,20,30$, $P/{\epsilon}=2,5,8$ and prandtl number = 0.72 have been discussed. In this study, it has been found that the Nusselt number and friction factor of rough wall are larger than those of smooth ones.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1294-1303
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• 1993

The fully developed turbulent momentum and heat transfer induced by the square-ribed roughness elements on the inner wall surface in concentric annuli is studied analytically based on a modified turbulence model. The analytical results of the fluid flow is verified by experiment. The resulting momentum and heat transfer are discussed in terms of various parameters, such as the radius ratio, the relative roughness, the roughness density, fluid Reynolds number and for heat transfer, fluid Prandtl number. The study demonstrates that certain artificial roughness elements may be used to enhance heat transfer rates with advantages from the overall efficiency point of view.