• Proceedings of the KSME Conference
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• 2001.06d
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• pp.408-413
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• 2001

Numerical analysis on the three-dimensional laminar flows (Re=1000) and heat transfer in a rectangular channel with punched longitudinal vortex generator have been conducted to explore the heat transfer enhancement and the combined effect of the angle of attack ${\alpha}$ and the lovour angle ${\beta}$. Rectangular winglets have been used as vortex generators. Velocity and temperature fields and spanwise averaged Nu and friction factor were presented. Enhancement of heat transfer and flow loss penalty are evidenced. The results show performance characteristics allowing a reduction in heat transfer surface area of 62% for fixed heat duty and for fixed pumping power compared with that of channel flow without vortex generator. However, adding lovour angle to the vortex generator shows no positive effect on the heat transfer enhancement.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.2
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• pp.165-172
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• 2005

Heat transfer enhancement of three types of brazed plate heat exchangers has been evaluated experimentally. The effects of flow resonance in a plate heat exchanger on the heat transfer rate and pressure drop have been investigated in a wide range of mass flow rates in detail. The problem is of particular interest in the innovative design of a plate heat exchanger by flow resonance. The results obtained indicate that both heat transfer coefficient and pressure drop are increased as mass flow rate is increased, as expected. It is also found that the heat transfer enhancement is increased with an increase in the plate pitch, while the heat transfer is decreased with a decrease in the chevron angle. Pressure drop also increased with an increase in the plate pitch and with a decrease in the chevron angle. Heat transfer enhancement in the plate heat exchangers is maximized by flow resonance and the resonance frequency of the present plate heat exchangers is found to be in the range of $10~15\;Hz$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.2
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• pp.199-206
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• 2004

The heat transfer enhancement by pulsating flow in a plate heat exchanger has been experimentally investigated in this study. The effect of the pulsating flow, such as pulsating frequency and flow rate on the heat transfer as well as pressure drop in a plate heat exchanger has been studied in detail. Reynolds number in cold side of a plate heat exchanger is varied 100∼530 while that of hot side is fixed at 620. The pulsating frequency is considered in the range of 5∼30 Hz. The results of the pulsating flow are also compared with those of steady flow. It is found that the average heat transfer rate as well as pressure drop is increased as flow rate is increased for both steady flow and pulsating flow cases. When pulsating flow is applied to the plate heat exchanger, heat transfer could be substantially increased in particular ranges of pulsating frequency or Strouhal number; St=0.36∼0.60 and pressure drop is also increased, compared with those of steady flow. However, in the region of low pulsating frequency or high pulsating frequency, heat transfer enhancement is in meager. Heat transfer enhancement map is suggested based on Strouhal number and Reynolds number of pulsating flow.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.591-596
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• 2005

The objectives in the present study are to investigate that the enhancement heat transfer was experimentally measured and was compared with the acoustic pressure obtained by numerical analysis. From the results of the present study, a strong Fluid motion initiated by ultrasonic vibrations can affect heat and mass transfer. This phenomenon. called acoustic streaming, clearly observed by PIV measurement leads to increase in velocity of a Fluid which is a crucial physical concept to explain the enhancement heat transfer. The heat transfer coefficient is increased with increase in the ultrasonic intensities. The largest enhancement heat transfer (about 26%) is measured at the ultrasonic intensity of 300W. Acoustic streaming results from sudden acoustic pressure variations in the liquid. The results of numerical analysis reveal that acoustic pressure is increased by 59.5% at the ultrasonic intensity of 300W. The higher acoustic pressure near four ultrasonic transducers develops more intensive flow destroying the flow instability. Also, the profiles of acoustic pressure variation are consistent with those of enhancement heat transfer.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1447-1452
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• 2003

Vortex is very interesting flow phenomena on the heat transfer enhancement. In the present study, naphthalene sublimation technique is used to determine the average and local mass transfer coefficients on the flat plate with vortex generator. A parametric study with Reynolds number and angle of attack is carried out to investigate the heat transfer enhancement. The heat transfer coefficients on the flat plate with rectangular type and delta type vortex generator are compared with those of the flat plate without the vortex generator. Comparing heat transfer coefficients between rectangular type and delta type vortex generator, rectangular type vortex generator has much higher value than delta type vortex generator at the same condition.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.7
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• pp.602-611
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• 2001

Experiments on the condensation heat transfer characteristics inside a smooth and a microfin tube with R410A/R22 are performed in this study. The test tubes 7/9.52 mm in outside diameters and 3m in length are used. Varying the mass flux of the refrigerant and the condensation temperatures, the average heat transfer coefficients and pressure drop are investigated. Most flows in this study are in the annular and/or wavy flow regime. It is shown that the heat transfer is enhanced and the pressure drops are larger in the microfin tube than the smooth tube. From the heat transfer enhancement coefficients and the pressure drops, it is found that the high heat transfer enhancement factors are obtained in the range of small mass flux while the penalty factors are almost equal. Experiments results show that average heat transfer coefficients of R410A is larger than that of R22 and pressure drop of R410A is less than R22.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.1
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• pp.48-56
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• 1992

The purpose of this study was to investigate the enhancement of heat transfer without additional external power in the case of rectangular air jet impinging vertically on the flat heating surface. In an attempt to enhance the heat transfer rate in two-dimensional impinging jet, the technique used in the present study was placement of square rod bundles as a turbluence promoter in front of the heat transfer surface. The effects of the clearance between the flat plate and square rod, and the nozzle exit velocity on the heat transfer characteristics have been investigated experimentally. The results obtained through this study were summerized as follows. High heat transfer enhancement was achived by means of flow acceleration and thinning of boundary layer by inserting rods in front of the heating flat plate. The smaller the clearance between rod and heating plate was, the larger heat transfer effect became. Average Nusselt number reached maximum at $Re=5.76{\times}10^4$ and C＝1㎜ and the enhancement rate of heat transfer became maxium at this condition with the enhancement ratio as high as about 1.427 when normalized by the flat plate value. The correlating equation of average Nusselt number and Reynolds number was obtained, which is $\bar{N}uo=1.324{\cdot}Re^{0.459}{\cdot}(C/A)^{-0.034}$.

• Journal of Mechanical Science and Technology
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• v.14 no.12
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• pp.1421-1428
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• 2000

The characteristics of heat transfer and pressure drop for fully developed turbulent flow in a tube with circumferential fins and circular were experimentally studied. The various spacing and sizes of circumferential fins and circular disks were selected as design parameters, while the effects of these parameters on heat transfer enhancement and pressure drop were investigated. In order to quantify the effect of heat transfer enhancement and the increase of pressure drop due to the fins and disks in a tube, the Nusselt numbers and the friction factors for various configurations and operating conditions were compared to those for a corresponding smooth tube. The results showed that the heat transfer rate was significantly enhanced by increasing the height of circumferential fins and decreasing the pitch of circumferential fins. On the other hand, the influence of the disk size and the fin-disk spacing were not significant. Based on the experimental results, a correlation for estimating the Nusselt number was suggested.

• 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.

• Journal of Mechanical Science and Technology
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• v.20 no.5
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• pp.681-691
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• 2006

Nucleate boiling heat transfer for refrigerants, R113, and R113+wt4% ethanol mixture, an azeotropic mixture under electric field was investigated experimentally in a single-tube shell/ tube heat exchanger. A special electrode configuration which provides a more uniform electric field that produces more higher voltage limit against the dielectric breakdown was used in this study. Experimental study has revealed that the electrical charge relaxation time is an important parameter for the boiling heat transfer enhancement under electric field. Up to 1210% enhancement of boiling heat transfer was obtained for R113+wt4% ethanol mixture which has the electrical charge relaxation time of 0.0053 sec whereas only 280% enhancement obtained for R113 which has relaxation time of 0.97 sec. With artificially machined boiling surface, more enhancement in the heat transfer coefficient in the azeotropic mixture was obtained.