• Journal of Advanced Marine Engineering and Technology
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• v.15 no.3
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• pp.57-65
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• 1991

The quenching of steels by water is one of the important problems in engineering for the applications of heat treatment or continuous casting process, but the fundamental researches by the theoretical approaches have not been satisfactorily improved yet. The very rapid cooling problems by the thermal conduction including the latent heat of phase transformation in steel and the transient boiling heat transfer of water on the surface of the steel covering from $850^{\circ}C$ to $20^{\circ}C$ are the key problems of heat treatment. The present quenching experiments are performed for the cylindrical specimens of carbon steel, S45C of diameters (12-30). Nonlinear transient heat conduction and transient boiling heat transfer problem of water on the surface of specimens is analyzed by the numerical method of inverse heat conduction problem. The conditions for the calculation are that the initial temperature of specimens is $820^{\circ}C$ and the cooling water in bath are $20^{\circ}C$,$40^{\circ}C$,$60^{\circ}C$,$80^{\circ}C$,$95^{\circ}C$ with no agitation.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.419-424
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• 2001

This paper deals with the development of a new method that can obtain heat transfer coefficient and reference tree stream temperature simultaneously. The method is based on transient heat transfer experiments using two narrow-band TLCs. The method is validated through error analysis in terms of the random uncertainties in the measured temperatures. It is shown how the uncertainties in heat transfer coefficient and tree stream temperature can be reduced. The general method described in this paper is applicable to many heat transfer models with unknown free stream temperature.

• The KSFM Journal of Fluid Machinery
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• v.14 no.6
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• pp.76-84
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• 2011

The effect of inlet velocity profile on the heat transfer coefficient in a rotating smooth channel was investigated experimentally. Three simulated inlet flow conditions of fully developed, uniform, and distorted inlet conditions were tested. The Reynolds number based on the channel hydraulic diameter was ranged from 10,000 to 30,000 and the transient liquid crystal technique was used to measure the distribution of the heat transfer coefficient in the rotating channel. Results showed that the overall heat transfer coefficient increased as the Reynolds number increased. Also, the distribution of the heat transfer coefficient was strongly affected by the inlet flow condition. Generally, the fully developed flow simulated condition showed the highest heat transfer coefficient.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2352-2356
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• 2008

Heat transfer and performance characteristics have been investigated for a rectangular wavy duct with dimple or protrusion arrays. The test duct was 15mm in height and 105mm wide. The print diameter of the dimple/protrusion wall was 12.99mm and the depth/height of the dimple/protrusion was 3.75mm. Local heat transfer coefficients on the dimple/protrusion wall were measured using a transient TLC technique. The Reynolds number was varied from 3,000 to 10,000. For the wavy duct tested in this study, adverse static pressure characteristics occurred at turning region of the wavy duct due to secondary flows. For the wavy duct with protrusion array, higher heat transfer enhancement level of 7.4 times than smooth straight case in maximum was obtained at low Reynolds number due to the high heat transfer enhancement by vortex flows. Also, the protrusion array increased the performance level of 3.0 at low Reynolds number of 3,000.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.3
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• pp.422-432
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• 2001

An analytical characterization is presented on the transient heat transfer by an oscillating flow through a porous slab. Based on a two-equation model, analytic solutions are obtained for both the fluid and solid temperature variations. Two parameters are identified as the Stanton number for the internal heat exchange and the ratio of the thermal capacities between the solid and fluid phases. The heat transfer characteristics are shown to be classified into four regimes according to the two parameters and physical interpretation is presented on the particular heat transfer processes within each regime. In addition, the condition for the local thermal equilibrium between the phases is examined and the relevant criterion is suggested.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.1
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• pp.68-78
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• 1997

A numerical study on the transient vapor flow and heat transfer is performed to investigate the ideal switching operation of heat source in a high temperature heat pipe. The cylindrical 2-dimensional compressible laminar vapor flow is assumed for the vapor space and the conjugate heat transfer for the heat pipe wall, wick and vapor space is calculated. The different boundary conditions such as constant heat flux, convective or radiative boundary at the outer wall are used respectively to compare the influence of boundary conditions on the transient operation. The transient temperature profile and the internal flow of the entire pipe for the switching operation are described as a result. The results show that the transient time is not significantly affected by the boundary conditions at the outer wall in present study. During the transition, two independent flows are observed temporarily on the right side and left side of the heat pipe. It is also found that the trend of temperature variation in the vapor region is different from the variation in the wick and wall region.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.1
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• pp.60-67
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• 2000

An experimental investigation on transient heat transfer phenomena of impinging diesel-spray on a flat plate in a pressurized chamber is carried out. A diesel spray is injected from a single-hole nozzle and impinges to a heated flat plate in the chamber. A fast-response thermocouple installed in the top surface of the plate measures the transient variation of surface temperature of the plate under various conditions of the chamber pressures. Utilizing the semi-infinite model, the temporal variation of the heat flux on the plate is determined. Effects of various parameters, such as vertical distances between the nozzle and the plate, radial distances from the injection-axis, and the chamber pressures, on the heat flux characteristics of impinging diesel-spray are studied.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.3
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• pp.37-43
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• 2002

There have been numerous experimental studies for heat transfer measurement technique. This study investigates optical methods for measuring local heat transfer coefficient using thermochromic liquid crystal. Transient and steady methods have been utilized to measure local heat transfer coefficient on a cylinder with a cross flow. The steady method is based on the heat-coating technique and two transient methods adopt by-pass technique and insertion technique, respectively. Both techniques of transient method employ heating technique in which the flow is heated by using the electric heater and cooling technique which cools the preheated cylinder. Experimental results indicate that each methods have nearly similar results. Detailed discussions have been made for its own advantages and disadvantages.

• Journal of the korean Society of Automotive Engineers
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• v.9 no.4
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• pp.69-76
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• 1987

A conjugate conduction-convection analysis has been made for a plate fin which exchanges heat with its fluid environment by forced convection. The analysis is based on a one- dimensional model for the plate fin whereby the transient heat conduction equation for the fin is solved simultaneously with the conservation equations for mass, momentum, and energy in the fluid boundary layer adjacent to the fin. The forced convection heat transfer coefficient is not specified in advance but is one the results of the numerical solutions. Numerical results of the overall heat transfer rate, the local heat transfer coefficient, the local heat flux, the fin efficiency and the fin surface temperature distribution for Pr=0.7 are presented for a wide range of operating conditions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.5
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• pp.337-345
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• 2003

In the case of heat exchangers operating under frosting condition, the growth of frost layer causes the heat exchanger to increase the thermal resistance and pressure loss of the air flow. In this paper, a transient characteristic prediction model of the heat transfer for multi inverter heat pump with frosting on its surface was presented taking into account the change of the fin efficiency due to the growth of the frost layer. In this dynamic simulation program, which was peformed for a basic air conditioning system model, such as evaporator, condenser, compressor, linear electronic expansion valve (LEV) and bypass circuit. The theoretical model was driven from the obtained heat transfer coefficient and mass transfer coefficient, independently. And we consider heat transfer performance was only affected by a decrease of the wind flow area. The calculated results were compared with some cases of experiments for frosting conditions.