• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.5
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• pp.523-534
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• 1998

The convection heat transfer on horizontal circular tube is studied as a conjugated heat transfer problem. With uniform heat generation in a cylindrical heater placed in a cross flow boundary condition, heat flow that is conducted along the wall of the heater creates a non-isothermal surface temperature and non-uniform heat flux distribution. In the present investigation, the effects of circumferential wall heat conduction on convection heat transfer are investigated for the case of forced convection around horizontal circular tube in cross flow of air and water. Non-dimensional conjugation parameter $ K^*$ which can be deduced from the governing energy differential equation should be used to express the effect of circumferential wall heat conduction. Two-dimensional temperature distribution$ T({\gamma,\theta})$ is presented. The influence of circumferential wall heat conduction is demonstrated on graph of local Nusselt number.

• Journal of the korean Society of Automotive Engineers
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• v.11 no.1
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• pp.20-30
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• 1989

The unsteady conjugate forced convection-conduction heat transfer from a plate fin is numerically studied. The external forced flow is steady but the temperature of the fin base is an exponential change with time. Therefore, the unsteady energy equations of the fluid and the fin are solved simultaneously under the conditions of equality in heat flux and temperature at the fluid-fin interface at every instant of time. Numerical results are given for various quantities of interest including the local heat transfer coefficient, the local heat flux, the total heat transfer rate and the temperature distribution of fin under the effects of the convection-conduction parameter and the ratio of thermal diffusivities. The results of the present numerical solution have been compared with those of the conventional fin theory.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.11 no.6
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• pp.60-67
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• 2002

A precise measurement of field test was performed to estimate the thermal performance of the forced convection electric air heater by experiment. Air temperature, flow rate and electrical power input were measured with the related measurement sensors, and acquisition methods for the measured data were studied to estimate the thermal performance of the tested air heater effectively. To determine the mean air temperature at the flow cross-section, measuring positions were chosen by considering the flow velocity profile and the equally divided cross-sectional area. From the experimental results, thermal efficiency was obtained accurately as an indication of the tested heating system performance.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.6
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• pp.117-123
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• 2018

Automotive headlamps have been continuously developed as one of the most important devices for securing the driver's view, and the LED lamps are getting popular in recent years. However, in case of the LED lamps, because the heat generated by the LED lamps are too high, it shorten the product life and lower the LED efficiency. Therefore, this study was investigated the cooling characteristics of the LED lamp heat sink for automobile by forced convection for LED heat generation control. In order to analyze the cooling characteristics of the heat sink, the temperature distribution results were investigated through the experiment and computational analysis under the increase of the air flow velocity, and the convective heat transfer coefficient was obtained. Also, convective heat transfer coefficient was calculated by the theoretical formula under the same condition and compared with experimental and computational results. From the result of this study, as the air flow velocity around the heat sink fins increased, the convective heat transfer coefficient significantly increased, confirming the improvement in the cooling effect.

• Korean Journal of Materials Research
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• v.14 no.7
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• pp.522-528
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• 2004

Heat analysis of the plate type and wave type heat sink were carried out by using computational simulation. The heat resistance and air flow of two heat sink models were analysed according to natural and forced convection condition and positions of fan. When a fan was at the position of z-axis and y-axis in forced convection, the heat resistances of plate type heat sink were $0.17^{\circ}C/W$, and $0.28^{\circ}C/W$ respectively. In the case of wave type heat sink, they were $0.18^{\circ}C/W$ and $0.53^{\circ}C/W$. As the air flow velocities were averagely $0.386\;m/s\~3.269\;m/s$, air flow velocity of plate type heat sink was faster than that of wave type. In this experiment, it was observed that the plate type heat sink showed a good ability of heat radiation comparing with wave type one.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.314-322
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• 2003

Pipe cooling method is widely used for reduction of hydration heat and control of cracking in mass concrete structures. However, in order to effectively apply pipe cooling systems to concrete structures, the coefficient of flow convection relating the thermal transfer between inner stream of pipe and concrete must be estimated. In this study, a device measuring the coefficient of flow convection was developed. Since a variation of thermal distribution caused by pipe cooling has a direct effect on internal forced flows, the developed testing device is based on the internal forced flow concept. Influencing factors on the coefficient of flow convection are mainly flow velocity, pipe diameter and thickness, and pipe material. Using experimental results from the developed device, the coefficient of flow convection was calculated. Finally, a general prediction model was proposed by theoretical procedures. The proposed prediction model is able to estimate the coefficient of flow convection with flow velocity and material properties of pipe. From comparison with experimental results, the coefficient of flow convection by this model was well agreed with those by experimental results.

• Journal of Ocean Engineering and Technology
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• v.15 no.2
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• pp.39-45
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• 2001

With uniform heat generation from the inner surface of the cylindrical heater placed in a cross flow boundary condition, heat flow that is conducted along the wall of the heater creates a non-isothermal surface temperature and non-uniform heat flux distribution. In the present investigation, the effects of circumferential wall heat conduction on convection heat transfer is investigated for the case of forced convection around horizontal circular tube in cross flow of air. The wall conduction number which can be deduced from the governing energy equation should be used to express the effect of circumferential wall heat conduction. It is demonstrated that the circumferential wall heat conduction influences local Nusselt numbers of one-dimensional and two-dimensional solutions.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.4
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• pp.580-584
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• 2012

The insulating oils perform a cooling and insulation action in electric power transformer. The mineral oil has immanent fire dangerousness and environmental contamination problem. Vegetable insulating oil has higher ignition point, flash point and more excellent biodegradability than conventional mineral oil. In a real oil-filled transformers, some of the power is dissipated in the form of heat. And transformer require the heat to be removed from the winding and insulator by forced convection of the insulating oil. The flow electrification occurs when insulating oil was forced to be circulated. In this paper, influence of temperature, velocity of flow, and insulating pipe and diameter on streaming electrification of vegetable insulating oil was investigated using forced circulation apparatus. Temperature effects were most significant, and it showed a peak in the temperature $30^{\circ}C$ to $35^{\circ}C$ at insulating and copper pipe. The change of flow electrification according to area variety could be checked by change of diameter.

• Journal of the Korean Society of Safety
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• v.14 no.3
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• pp.33-39
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• 1999

In a compartment fire with openings, convective heat transfer consists of natural convection from the hot bodies and forced convection by airflow through the openings. The same finite volume method that was applied to pure natural convection in part I was utilized without modification to the square cavity with two openings. The objective of this study is to investigate effects of the openings on temperature distribution. Flow patterns, temperature distribution and heat transfer were compared for different Rayleigh numbers and with and without the openings.

• Journal of Energy Engineering
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• v.13 no.4
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• pp.275-280
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• 2004

Augmentation of heat transfer by ultrasonic vibration in pipes are investigated. Measurements of convective heat transfer coefficients on circular pipe walls are made with and without ultrasonic vibration applied to water. These data are compared with each other to quantify the effects of ultrasonic vibration on heat transfer enhancement. Numerical analysis has been also performed in order to extend the ranges of examined temperature and flow rate. FLUENT Ver.6.1 is used to simulate velocity and temperature fields and evaluate heat transfer coefficient with and without ultrasonic vibration. The results show that the ultra- sonic vibration enhances the Nusselt number of forced convection flow and the increase rate strongly depends on flow rate.