• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.25 no.1
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• pp.57-81
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• 1997

Numerical prediction of nocturnal thermal high in summer of the 1995 near Taegu city located in a basin has been carried out by a non-hydrostatic numerical model over complex terrain through one-way double nesting technique in the Z following coordinate system. Under the prevailing westerly winds, vertical turbulent fluxes of momentum and heat over mountains for daytime hours are quite strong with a large magnitude of more than $120W/\textrm{m}^2$, but a small one of $5W/\textrm{m}^2$ at the surface of the basin. Convective boundary layer (CBL) is developed with a thickness of about 600m over the ground in the lee side of Mt. Hyungje, and extends to the edge of inland at the interface of land sea in the east. Sensible heat flux near the surface of the top of the mountain is $50W/\textrm{m}^2$, but its flux in the basin is almost zero. Convergence of sensible heat flux occurs from the ground surface toward the atmosphere in the lower layer, causing the layer over the mountain to be warmed up, but no convergance of the flux over the basin results from the significant mixing of air within the CBL. As horizontal transport of sensible heat flux from the top of the mountain toward over the basin results in the continuous accumulation of heat with time, enhancing air temperature at the surface of the basin, especially Taegu city to be higher than $39.3^{\circ}C$. Since latent heat fluxes are $270W/\textrm{m}^2$ near the top of the mountain and $300W/\textrm{m}^2$ along the slope of the mountain and the basin, evaporation of water vapor from the surface of the basin is much higher than one from the mountain and then, horizontal transport of latent heat flux is from the basin toward the mountain, showing relative humidity of 65 to 75% over the mountain to be much greater than 50% to 55% in the basin. At night, sensible heat fluxes have negative values of $-120W/\textrm{m}^2$ along the slope near the top of the mountain and $-50W/\textrm{m}^2$ at the surface of the basin, which indicate gain of heat from the lower atmosphere. Nighttime radiative cooling produces a shallow nocturnal surface inversion layer with a thickness of about 100m, which is much lower than common surface inversion layer, and lifts extremely heated air masses for daytime hours, namely, a warm pool of $34^{\circ}C$ to be isolated over the ground surface in the basin. As heat transfer from the warm pool in the lower atmosphere toward the ground of the basin occurs, the air near the surface of the basin does not much cool down, resulting in the persistence of high temperature at night, called nocturnal thermal high or tropical night. High relative humidity of 75% is found at the surface of the basin under the moderate wind, while slightly low relative humidity of 60% is along the eastern slope of the high mountain, due to adiabatic heating by the srong downslope wind. Air temperature near the surface of the basin with high moisture in the evening does not get lower than that during the day and the high temperature produces nocturnal warming situation.

• Journal of the Korean Geophysical Society
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• v.8 no.4
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• pp.201-205
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• 2005

Turbulent fluxes of heat, water vapor, and CO2 have been measured since August, 2003 at Dasan Station (78o 55’ N, 11o50’E) in the Arctic. These data can allow us to better understand the interactions between the Polar ecosystems and the atmosphere together with those at King Sejong Station in the Antarctic. Due to the buildings and measurement platforms around the flux tower, it is required to evaluate how they influence measured flux data. By using one-year turbulence statistics data and footprint model, flux footprint climatology was analyzed together with data availability. The upwind distance of source area ranged from 150 to 300 m, where the buildings and measurement platforms existed. However, flow distortion due to them may be not a major factor to reduce the data availability significantly. Based on, the dominant wind direction of SW and footprint climatology, the location of flux tower is considered suitable for flux measurement.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.9
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• pp.923-932
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• 2011

Because of the instability of a flow pattern in the inlet transition square duct (hereinafter referred to as "transition duct") of a heat recovery steam generator (hereinafter referred to as "HRSG") in a combined cycle power plant, the Reynolds number in the first row of a tube bank is differs sharply from that in the sectional area of the transition duct. This causes differences in the heat flux in each tube in the tube bank. The computational fluid dynamics (CFD) predictions provide three-dimensional results for velocity, temperature, and other flow parameters over the entire domain of the duct and HRSG. A renormalization group theory (RNG) based k-${\epsilon}$�� turbulent model is used for obtaining the results cited in this study. A porous media option is used for modeling the tube banks and the number of transfer units method is used for determining the heat transfer characteristics. This study describes a comparison between the numerical simulation results and actual design output.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.3
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• pp.29-35
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• 2000

The present numerical study investigates heat transfer enhancement mechanism for suspensions of polystyrene particles in water. Numerical simulations were done for turbulent hydrodynamic fully developed flows in a circular duct with constant wall heat flux. The experimental result of microparticle suspensions show 25∼45% heat transfer enhancement over those of water. The present numerical results show the main parameter for the heat transfer enhancement of microparticle suspension in a circular duct is the change of velocity profile by the non-Newtonian fluid behavior.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.1
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• pp.78-85
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• 1991

An experimental result for heat transfer of pulsating turbulent pipe flow was presented under the condition of fully developed dynamic regime and uniform wall heat flux. Experiments were performed at following conditions ; Inlet time-averaged Reynolds number varied from 5000 to 11000; The peak pressure fluctuation were 1.3, 2.3 and 3.5 percent of the mean pressure; Pulsating frequency ranged from 53 Hz to 320 Hz The measurements showed that the effect of pulsation on local heat transfer is greater at downstream, in which pulsating source exists, than upstream and the heat transfer rate, averaged over the pipe length, was higher or lower than in an equivalent non-pulsating flow according to the pulsating conditions. In addition, the significant change of heat transfer rate was observed in acoustically resonant conditions, when the pulsating frequency of the flow corresponded to the pipe natural frequency.

• Journal of computational fluids engineering
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• v.8 no.3
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• pp.56-65
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• 2003

A numerical procedure for analyzing the heat transfer in a regenerative cooling passage of liquid rocket has been developed. The thermal analysis is based on the numerical model of Naraghi〔1〕. The thermodynamic and transport properties of the combustion gases are evaluated using the chemical equilibrium composition. The pressure and heat flux obtained by the isentropic relation are in good agreement with the result of Navier-Stokes equations. The effect of design parameters on heat transfer is addressed for the pressure loss and temperature variation. Also, their constraints in designing the cooling passage are recommended. Finally, in a heated rectangular duct, the effects of secondary flow on heat transfer are scrutinized by the nonlinear k- e -fu of Park et at.〔2〕.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.118-123
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• 2000

This experimental study was conducted to figure out the characteristics of convective heat transfer in non boiling vertical downward flow with polymer additives. This experiment was studied in 26mm diameter, 800mm heating length and $1{\times}10^5W/m^2$ heat flux. The polymer concentration ranged from 0PPM to 500PPM with corresponding from Reynolds number $3.3{\times}10^4$ to $6.8{\times}10^4$ in non boiling vertical downward flow. Experimental results show that the characteristics of convective heat transfer was a strong function of polymer concentration and it has decreased with increasing the polymer concentration in non boiling vertical downward flow.

• Aerospace Engineering and Technology
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• v.2 no.2
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• pp.142-150
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• 2003

Turbulent flows and related heat transfer in a square heated duct is investigated by a turbulence model and a large eddy simulation. The cooling channel of calorimeter is modeled to the square duct. The nonlinear k-ε-fμ model of Park et al. [3] is slightly modified and their explicit heat flux model is employed. The Reynolds number is varied in the range 4000≤Reｂ≤20000. The heat transfer is closely linked to the secondary flows which driven by the turbulent motion. Its magnitude is 1~3% of the mean streamwise velocity. The relation of Nu~Re0.8Pr0.34 is validated by comparing with the predicted Nu of k-ε-fμ model. Finally, the coherent structures and thermal fluctuations are scrutinized.

• 한국전산유체공학회:학술대회논문집
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• 2001.10a
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• pp.91-97
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• 2001

The thin-layer Navier-Stokes equations are solved for the hypersonic flow over blunt cone configurations with applications to laminar as well as turbulent flows. The equations are expressed in the forms of flux-vector splitting and explicit algorithm. The upwind schemes of Steger-Warming and van Leer are investigated in their ability to accurately predict the heating loads along the surface of the body. A comparison with the second order extensions of these schemes is made and a hybrid scheme incorporating a combination of central differencing and flux-vector-splitting is presented. This scheme is also investigated in its ability to accurately predict heat transfer distributions.

• 한국해양학회지
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• v.30 no.2
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• pp.91-115
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• 1995

Air-sea heat fluxes in the East Sea were estimated from the various ship's data observed from 1961 to 1990 and the JMA buoy #6 data from 1976 to 1985. The oceanic heat transport in the sea was also determined from the fluxes above and the heat storage rate of the upper layer of 200m from the sea surface. In winter, The incoming solar radiation is almost balanced with the outgoing longwave radiation. but the sea loses her heat through the sea surface mainly due to the latent and sensible heat fluxes. The spatial variation of the net surface heat flux is about 100 Wm/SUP -2/, and the maximum loss of heat is occurred near the Tsugaru Strait. There are also lots of heat losses in the southern part of the East Sea, Korea Strait and Ulleung Basin. Particularly, the heat strong loss in the south-western part of the sea might be concerned with the formation of her Intermediate Homogeneous Water. In summer, the sea is heated up to about 120∼140 Wm/SUP -2/ sue to strong incoming solar radiation and weak turbulent heat fluxes and her spatial variation is only about 20 Wm/SUP -2/. The oceanic heat flux is positive in the southeasten part f the sea and the magnitude of the flux is larger than that of the net surface heat flux. This shows the importance of the area. In the southwestern part of the sea, however, the oceanic heat flux is negative. This fact implies cold water inflow, the North Korean Cold Water. The sigh of net surface heat flux is changed from negative to positive in March and from positive to negative in September. The heat content in the upper surface 200 m from the sea surface reaches its minimum in March and maximum in October. The annual variation of the net surface heat flux is 580 Wm/SUP -2/ in southwestern part of the sea. The annual mean values of net surface heat fluxes are negative, which mean the net heat transfer from the sea to the atmosphere. The magnitude of the flux is about 130 Wm/SUP -2/ near the Tsugaru Strait. The net surface fluxes in the Korea Strait and the Ulleung Basin are relatively larger than those of the rest areas. The spatial mean values of surface heat fluxes from 35$^{\circ}C$ to 39$^{\circ}$N are 129, -90, -58, and -32 Wm/SUP -2/ for the incoming solar radiation, latent hear flux, outgoing longwave radiation, and sensible heat flux, respectively.