• Journal of Mechanical Science and Technology
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• v.14 no.9
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• pp.997-1004
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• 2000

The experiments were conducted by using water and paraffin slurry to investigate the effect of a chip spacing in the multichip module on the cooling characteristics from an in-line $4{\times}3$ array of discrete heat sources which were flush mounted on the top wall of a channel. The experimental parameters were chip spacing in a multichip module, heat flux of simulated VLSI chip, mass fraction of paraffin slurry, and channel Reynolds number. The removable heat flux at the same chip surface temperature decreased as the chip spacing decreased at the first and fourth rows. The local heat transfer coefficients for the paraffin slurry were larger than those for water, and the chip spacing on the local heat transfer coefficients for paraffin slurry influenced less than that for water. The enhancement factor for paraffin slurry showed the largest value at a mass fraction of 5% regardless of the chip spacing, and the enhancement factors increased as the chip spacing decreased. This means that the paraffin slurry is more effective than water for cooling of the highly integrated multichip module.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.61-66
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• 2003

Fouling is very serious problem in heat exchanger because it rapidly deteriorates the performance of heat exchanger. Cross-flow heat exchanger with vortex generators is developed, which enhance heat transfer and reduce fouling. In the present heat exchanger, shell and baffle are removed from the conventional shell-and-tube heat exchanger. The naphthalene sublimation technique is employed to measure the local heat transfer coefficients. The experiments are performed for single circular tube, staggered array tube bank and in-line array tube bank with and without vortex generators. Local and average Nusselt numbers of single tube and tube bank with vortex generator are investigated and compared to those of without vortex generator.

• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.85-90
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• 2005

The heat transfer enhancement by pulsatile flow in plate heat exchanger has been investigated numerically in the present study. The numerical study was performed ill the range of the Strouhal number from 0.04 to 2 and the Reynolds number from 370 to 730. The results showed that the pulsatile flow produces resonating vortex shedding at the groove sharp edges and a strong transient vortex rotation within the grooved channels. As a result, the mixing between the trapped volume in the grooved cavity and the main stream was enhanced. Good agreements between the predictions and measured data are obtained for the optimum frequency of pulsation and corresponding heat transfer enhancement

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.4
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• pp.495-503
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• 2000

The present numerical study investigates flow characteristics and heat transfer enhancement of the viscoelastic non-Newtonian fluid in a 2:1 rectangular duct. The combined effect of temperature-dependent viscosity, buoyancy and secondary flow caused by second normal stress difference are all considered. The Reiner-Rivlin model is used as a viscoelastic fluid model to simulate the secondary flow and temperature-dependent viscosity model is adopted. Three types of thermal boundary conditions involving different combinations of heated walls and adiabatic walls are considered in this study. Calculated Nusselt numbers are in good agreement with experimental results in both the thermal developing and thermally developed regions. The heat transfer enhancement can be explained by the combined viscoelasticity-driven secondary flow, buoyancy-induced secondary flow and temperature-dependent viscosity.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.8
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• pp.683-689
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• 2002

This paper is to present the results of a comprehensive study on heat transfer in annuli with spirally corrugated inner tubes in the turbulent regime. Tube surface-temperature measurements were used to explain the enhancement phenomena in the annuli with several different corrugated tubes. Nusselt numbers were between 1.1 and 2 times the smooth annulus values. These enhancement values can be used to determine the appropriate range of applicability for spirally corrugated annuli.

• Journal of the Korean Society of Safety
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• v.21 no.2 s.74
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• pp.7-14
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• 2006

A Problem of low-velocity forced convection in a channel flow with heated wall is of practical importance and widely considered in the design of devices such as heat exchangers, and electronic equipments. Therefore, there is an urgent need for improving heat transfer performance of heated wall in the channel. In the present study, an oscillating vortex generator method is proposed to enhance the heat transfer in a channel. In this method, a rectangular bars are set in the upstream of heated region of the channel. The bars are forced to oscillate normal to the inflow, and then actively and largely generates transverse vortices behind the bars. As a result, this apparatus can enhance the heat transfer rates remarkably. Because of the interaction between the flow and oscillating bars, the variations of the flow and thermal fields become time-dependent state.

• Journal of computational fluids engineering
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• v.18 no.2
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• pp.85-92
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• 2013

In this study, we consider heat transfer enhancement in laminar channel flow by means of an infinite streamwise array of equispaced identical circular cylinders. This flow configuration can be regarded as a model representing a micro channel or an internal heat exchanger with cylindrical vortex generators. A numerical parametric study has been carried out by varying Reynolds number based on the bulk mean velocity and the cylinder diameter, and the gap between the cylinders and the channel wall. An immersed boundary method was employed to facilitate to implement the cylinders on a Cartesian grid system. No-slip condition is employed at all solid boundaries including the cylinders, and the flow is assumed to be periodic in the streamwise direction. Also, the Prandtl number is fixed as 0.7. For thermal boundary conditions on the solid surfaces, it is assumed that heat flux is constant on the channel walls, while the cylinder surfaces remain adiabatic. The presence of the circular cylinders arranged periodically in the streamwise direction causes a significant topological change of the flow, leading to heat transfer enhancement on the channel walls. The Nusselt number averaged on the channel wall is presented for the wide ranges of Reynolds number and the gap. A significant heat transfer enhancement is noticed when the gap is larger than 0.8, while the opposite is the case for smaller gaps. More quantitative results as well as qualitative physical explanations are presented to justify the effectiveness of varying the gap to enhance heat transfer from the channel walls.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.8
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• pp.710-719
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• 2001

Pool boiling heat transfer coefficients (HTCs) of HCFC123, HFC134a, HCFC22, HFC407C, HFC410A and HFC32 wre measured on a horizontal smooth tube, 26 fpi low fin tube, Turbo-B and Thermoexcel-E enhanced tubes. AN experimental apparatus was designed such that all tubes heated by cartridge heaters could be installed at the same time to save the refrigerant. Data were taken in the pool of $7^{\circ}C$ with the heat flux decreasing from 80 kW/$m^2\;to\;5kW/m^2$. Test results showed that HTCs of pure refrigerants and those of a azeotrope were greatly influenced by reduced pressure. HTCs of HFC407C were 21~25% lower than those of HCFC22 due to mass transfer resistance. For all refrigerants, enhanced tubes with sub-surface and sub-tunnels showed the largest heat transfer enhancement. Especially the largest heat enhancement was obtained for HCFC123 whose reduced pressure is the lowest among al the refrigerants tested. This indicates that either Turbo-B or Thermoexcel-E enhanced tube would be the best choice when used with a low vapor pressure refrigerant.

• Korea-Australia Rheology Journal
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• v.19 no.3
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• pp.99-107
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• 2007

A nanofluid is a mixture of solid nanoparticles and a common base fluid. Nanofluids have shown great potential in improving the heat transfer properties of liquids. However, previous studies on the characteristics of nanofluids did not adequately explain the enhancement of heat transfer. This study examined the distribution of particles in a fluid and compared the mechanism for the enhancement of heat transfer in a nanofluid with that in a general microparticle suspension. A theoretical model was formulated with shear-induced particle migration, viscosity-induced particle migration, particle migration by Brownian motion, as well as the inertial migration of particles. The results of the simulation showed that there was no significant particle migration, with no change in particle concentration in the radial direction. A uniform particle concentration is very important in the heat transfer of a nanofluid. As the particle concentration and effective thermal conductivity at the wall region is lower than that of the bulk fluid, due to particle migration to the center of a microfluid, the addition of microparticles in a fluid does not affect the heat transfer properties of that fluid. However, in a nanofluid, particle migration to the center occurs quite slowly, and the particle migration flux is very small. Therefore, the effective thermal conductivity at the wall region increases with increasing addition of nanoparticles. This may be one reason why a nanofluid shows a good convective heat transfer performance.

• Journal of Power System Engineering
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• v.5 no.4
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• pp.18-23
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• 2001

This paper is to present the results of a comprehensive study on heat transfer in annuli with spirally corrugated inner tubes in the turbulent regime. Tube surface-temperature measurements were used to explain the enhancement phenomena in the annuli with several different corrugated tubes. Nusselt numbers were between 1.1 and 2 times the smooth annulus values. These enhancement values can be used to determine the appropriate range of applicability for spirally corrugated annuli.