• Journal of Energy Engineering
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• v.10 no.3
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• pp.272-277
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• 2001

An experimental study of jet impinging the non-isothermal heating surface with linear temperature gradient is conducted with the presentation of the turbulent flow characteristics and the heat transfer rate, represented by the Nusselt number. The jet Reynolds number ranges from 15,000 to 30,000, the temperature gradient of the plate is 2~4.2$^{\circ}C$/cm and the dimensionless nozzle to plate distance (H/D) is from 2 to 10. The results show that the peak of heat transfer rate occurs at the stagnation point, and the heat transfer rate decreases as the radial distance from the stagnation point increases. A remarkable feature of the heat transfer rate is the existence of the second peak. This is due to the turbulent development of the wall jet. Maximum heat transfer rate occurs when the axial distance from the nozzle to nozzle diameter (H/D) is 6 or 8. The heat transfer rate can be correlated as a power function of Prandtl number, Reynolds number, the dimensionless nozzle to plate distance (H/D) and temperature gradient (dT/dr). It has been found that the heat transfer rate increases with increasing turbulent intensity. The wall jet is influenced by temperature gradient and the effect becomes more important at higher radii.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.150-155
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• 2006

Falling liquid plays a role in a wide variety of naturally occurring phenomena as well as in the operation of industrial process equipment where heat and mass transfer take place. In such cases, it is required that the falling film should spread widely on the surface forming thin liquid film to enlarge contact surface. An addition of surface active agent to a falling liquid film affects the flow characteristics of the falling film. In this study the heat transfer characteristics for a falling liquid film has been investigated by an addition of the surface active agents. The falling liquid film was formed on a vertical flat plate. As the mass flow rate of liquid falling film is increased, the wetted area is a little increased while the heat transfer rate as well as heat transfer coefficient is significantly increased. It is also found that both wetted area and heat transfer rate is substantially increased while heat transfer coefficient is a little increased with an increase in the surfactant concentration at a given mass flow rate.

• International Journal of Fluid Machinery and Systems
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• v.5 no.1
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• pp.10-17
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• 2012

The objective of this study was to investigate the oxygen transfer characteristics of an ejector aeration system. In order to evaluate the oxygen transfer performance of the ejector aeration system, a comparative experiment was conducted on a conventional blower aeration system. The effect of entrained air flow rate and aerating water temperature on the oxygen transfer efficiency was investigated. The dissolved oxygen concentration increased with increasing entrained air flow rate, but decreased with increasing aerating water temperature for two aeration systems. The volumetric mass transfer coefficient increased with increasing entrained air flow rate and with increasing aerating water temperature for both aeration systems. The average mass transfer coefficient for the ejector aeration system was about 20% and 42% higher than that of the blower aeration system within the experimental range of entrained air flow rates and aerating water temperatures.

• Journal of Welding and Joining
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• v.16 no.4
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• pp.63-72
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• 1998

In this study, the effects of the current pulsing conditions, on the spatter generation rate during the $CO_2$ gas metal arc welding (GMAW) were investigated. Normally using the inverter type power supply, of which the welding current waveform was regulated to reduce the spatter generation rate, but in this study pulsing was imposed on the welding current. Observation of the metal transfer phenomena during the pulsed current GMAS indicated that the droplet transfer from the electrode via the short circuit transfer and the repelling transfer mode could be minimized by selecting optimum combinations of pulsing parameters, which include base and peak current, base and pak duration. It was also demonstrated in this study that proper combinations of the pulsing parameters led to reduce generation of spatters during GMAW shielded by $CO_2$ gas.

• Journal of Embryo Transfer
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• v.12 no.1
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• pp.75-90
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• 1997

This study was carried out to establish the techniques for producing the calves of genetically superior Korean Native cattle by transfer of frozen-thawed embryos. The effects of some factors related to embryo recovery following superovulation and pregnancy rate following transfer of frozen-thawed embryos were evaluated. Also calving state was investigated. The results obtained were as follows ; The mean number of total and transferrable embryos recovered per superovulated cow was 8.72 and 4.90, respectively, from a total of 72 superovulations using 34 donor cows. There were no significant differences in the number of total or transferrable embryos recovered per superovulated cow between products of follicle stimulating hormone (FSH), years, seasons, and collection numbers. The pregnancy rate was found 44.44% following transfer of frozen-thawed embryos of Korean Native cattle to a total of 180 recipient cows including 82 Angus, 27 Charolais, 62 Hereford and 9 Korean Native cows. The pregnancy rate was significantly (P<0.05) higher in the transfer of excellent (42.99) and good embryos (40.17%), compared with fair (5.90%) grade embryos. And the pregnancy rate was significantly (P<0.05) higher in the transfer of embryos of morula stage (43.86%) than blastocyst stage (15.51%). But there were no significant differences in pregnancy rates between natural and induced estrus estrus asynchrony of 1 days, breeds, and parities of recipient cows. The normal calving rate of 80 pregnant cows following transfer of frozen4hawed em-bryos was 87.5% and the other 10 pregnant cows showed abortion during the period from pregnancy diagnosis at 50~60 days to calving. The average gestation length of normally delivered recipients was 288.50 days and the average birth weight of 70 calves born was 24.22 kg. The gestation length was significantly (P<0.05) shorter in the recipients delivering female calves (286.70 days) than males (289.39 days). But there were no significant differences in gestation tength and birth weight of calves born between the recipient breeds.

• 한국전산유체공학회:학술대회논문집
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• 2000.05a
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• pp.172-177
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• 2000

In this numerical work, three dimensional supersonic laminar flow and heat transfer of a blunt body(sphere-cone) at Mach 5 is simulated. The effects of angle of attack and the spin rate on the now and heat transfer are analysed. To solve the three dimensional compressible Wavier-Stokes equation, a finite volume method with the modified LDFSS scheme is employed for spatial discretization, and a point SGS implicit method is used for time integration. It is found that the heat transfer rate increases at the windward side and decreases at the leeward side with the angle of attack. The heat transfer rate at all surfaces slightly increases with the spin rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.6
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• pp.773-778
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• 1997

The present study investigates the effect of the shear rate-dependent thermal conductivity of non-newtonian fluids on the heat transfer enhancement in a 2:1 rectangular duct flow. An axially-constant heat flux and a peripherally-constant temperature boundary conditions(H1) was adopted for a top-wall-heated configuration. The present numerical results of Nusselt numbers for SRDC(Separan) show heat transfer enhancement over those of SRIC. The Nusselt numbers increased linearly as Reynolds numbers increased. The heat transfer enhancement is due to an increased thermal conductivity near the wall, which is attributed to the shear rate-dependence.

• Solar Energy
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• v.9 no.1
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• pp.43-52
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• 1989

Heat transfer rate and heat flux from the condenser with internally triangular fins rotating heat pipe has been numerically studied by finite element method. The results of numerical and P.J. Martos' experimental showed good agreement and it was able to predict to the performance of a rotating heat pipe. By increasing fin half angle or fin height, heat transfer rate from condenser was increased slightly but heat flux was decreased. By increasing condenser radius or r.p.m. of rotating heat pipe, heat transfer rate and heat flux was increased rapidly. Heat transfer rate was rapidly increased with increasing fin numbers in case of few fm numbers but slowly increased at many fin numbers. So the optimum fin numbers were a half of maximum fin numbers which was able to install in the condenser of a rotating heat pipe.

• Journal of Fisheries and Marine Sciences Education
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• v.26 no.4
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• pp.894-901
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• 2014

This study concerns the performance of condensation heat transfer in two-phase loop thermosyphons. In the present work, R134a has been used as the working fluid. Liquid fill charge ratio defined by the ratio of working fluid volume to total internal volume of thermosyphon, heat flux and wind speed of condensation have been used as the experimental parameters. The results show that the filling rate of working fluid and heat flux are very important factors for the operation of two-phase loop thermosyphons. The optimum liquid fill charge ratio for the best condensation heat transfer rate was 80%.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.144-149
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• 2006

In this study ice making characteristics are experimentally investigated for the ice slurry generating system which is pneumatically operated. The experimentations are conducted under the various test conditions such as chilled water inlet temperature, aqueous solution concentration, flow rate of cooling water, scraper pitch and frequency of cylinder stroke. For the above experimental conditions, ice making characteristics of the slurry ice generating system are evaluated in terms of the overall heat transfer coefficient, heat transfer rate and the amount of slurry ice generation. And the experimental results show that the heat transfer rate of the system increases as the flow rate of cooling water solution increases and the concentration of ethylene glycol and inlet temperature of chilled water decreases.