• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.1
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• pp.55-60
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• 2010

Vortex tube is the device that can separate small particles from the compressed gas, as well as compressed gas into hot and cold flow. Due to energy separation ability, a vortex tube can substitute for an EGR cooler of the automotive engine. In this study, experimental approach has been performed to analyze the energy separation characteristics of the vortex tube. Energy separation characteristics of the vortex tube has been tested for supply pressure, cold-out pressure, and hot-out pressure. As increasing supply pressure, energy separation effect increased. Maximum temperature exists about 0.85 of the cold-out-flow-ratio, and minimum exists about 0.35. Hot-out temperature of the vortex tube is affected by the hot-out and cold-out pressure. However, for the given conditions, cold-out temperature is independent of exit pressure change. The results from this study can be used for the basic design parameter of the EGR cooler substitute of an automotive engine.

• Nuclear Engineering and Technology
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• v.27 no.5
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• pp.775-783
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• 1995

This study is to assess the effects of increasing wall thickness on the safety margin of pressure tube in operating and of lowering initial hydrogen concentration on the DHC growth in respect to the improvement of the reliability of pressure tube in CANDU reactors. The pressure tube with thicker wall of 5.2 mm shows much higher safety margin for flaw tolerance by 25％ than the current 4.2mmm tube. The thicker pressure tubes have a great benefit in LBB assessment including the initial crack depth at which DHC occurs, the crack length at onset of leaking and the available time for action. The resistance for the pressure tube ballooning at LOCA accident is also increased with the thicker tube. The calculations for Heq concentration after 20 years of operation as a function of wall thickness and initial hydrogen concentration show that the 5.2 mm nil thickness tube with 5 ppm initial hydrogen concentration is the most resistant to DHC. with the lower initial hydrogen concentration, TSS temperature for the precipitation or hydride decreases and the crack growth during cooldown reduces.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.5
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• pp.235-241
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• 2002

The process of energy separation in a low pressure vortex tube with air as a working medium is studied In detail. Experimental data of the temperature of the cold and hot air leaving the vortex tube are presented. The variation of the maximum wall temperature along the inner surface of the vortex tube and the temperature distribution in the vortex tube provides useful information about the location of the stagnation point of the flow field at the axis of the vortex tube. In this study Outer tube is used for the application of Diesel engine exhaust. The hot gas flow is fumed 180° and passes the outside of the vortex tube a second time heating it. From this geometric setup of a vortex tube the effects of energy separation and the prediction of the ignition of Diesel Soot is presented by experimental data.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.6
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• pp.47-55
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• 2011

The present paper deals with numerical analysis to investigate the effect of rounded tube on the pressure drop and heat transfer in a compact tubular heat exchanger designed for high temperature and high pressure system. The pressure drop and heat transfer in the tubular heat exchanger greatly depend on the location of rounded tubes. The effect of locations of the rounded tubes was also analyzed. Three different locations which were tube inlet, tube outlet, and inlet&outlet were considered. In this paper, the tube with a rounded inlet&outlet showed the minimum pressure drop with decreased heat transfer while the tube with a rounded outlet showed better characteristics of pressure drop and heat transfer compared with the results of original model.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.353-358
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• 2005

The heat transfer and pressure drop of supercritical $CO_2$ cooled in a helically coiled tube was investigated experimentally. The experiments were conducted without oil in the refrigerant loop. The experimental apparatus of the refrigerant loop consist of receiver, a variable speed pump, a mass flowmeter, a pre-heater, a gas cooler(test section) and an isothermal tank. The test section is a helically coiled tube in tube counter flow heat exchanger with $CO_2$ flowed inside the inner tube and coolant( water) flowed along the outside annular passage, It was made of it copper tube with the inner diameter of 4.55[mm]. the outer diameter of 6.35 [mm] and length of 10000 [mm]. The refrigerant mass fluxes were $200^{\sim}600$ [kg/m2s] and the inlet pressure of gas cooler varied from 7.5 [MPa] to 10.0 [MPa]. The main results are summarized as follows : The heat transfer coefficient of supercritical $CO_2$ increases, as the cooling pressure of gas cooler decreases. And the heat transfer coefficient increases with the increase of the refrigerant mass flux. The pressure drop decreases in increase of the gas cooler pressure and increases with increase the refrigerant mass flux.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.93-96
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• 2012

The spontaneous ignition mechanism of high pressure hydrogen gas released into tube is well-deduced from previous studies. However, those results have a limit because the studies have been conducted at low burst pressure of about 10 MPa. In this study, the process or ignition feature are investigated with higher burst pressure of up to 30 MPa through numerical analysis. The results show that the trend of ignition became to be different with a burst pressure. While two reaction regions is important to initiate the ignition when burst pressure is about 10 MPa, the reaction of the core region does not play a role in ignition inside the tube when a burst pressure is above 20 MPa.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.2
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• pp.63-68
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• 2015

The fin and tube type heat exchangers widely used in air conditioners have been developed to improve on the heat transfer performance and compactness. This study presents the new type of tube for the heat exchanger to improve the heat transfer performance by increasing the heat transfer area per unit volume in the air-conditioner heat exchanger. The new type tube can be used for mechanical expansion facility, due to the two-port copper tube. Numerical calculation shows that the heat exchanger using the two-port copper tube outperforms the conventional heat-exchanger using a circular copper tube, in terms of the increased heat transfer coefficient and higher pressure drop. The calculation results were experimentally validated and are in agreement with the experimental results. Compared to the heat exchanger using a conventional circular tube, the heat exchanger with a two-port tube increased the heat transfer coefficient up to 21%, and the pressure dropped up to 16%.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.4
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• pp.463-473
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• 2006

The effect of tube diameter on heat and mass transfer characteristics of absorber in absorption chiller/heater using LiBr solution as a working fluid has been investigated by both of numerical and experimental study to develop a high performance and compact absorber. The diameter of the heat exchanger tube inside absorber was changed from 15.88mm to 12.70mm and 9.52mm. In numerical study a model of vapor pressure drop inside tube absorber based on a commercial 20RT absorption chiller/heater was performed. The effect of tube diameter, longitudinal pitch, vapor Reynolds number, longitudinal pitch to diameter ratio on vapor pressure drop across the heat exchanger tube banks inside absorber have been investigated and found that vapor pressure drop decreases as tube diameter increases, longitudinal pitch increases, vapor Reynolds number decreases and longitudinal pitch to diameter ratio increases. In experimental study, a system includes a tube absorber, a generator, solution distribution system and cooling water system was set up. The experimental results shown that the overall heat transfer coefficient, mass transfer coefficient. Nusselt number and Sherwood number increase as solution flow rate increases. In both of study cases, the heat and mass transfer performance increases as tube diameter decreases. Among three different tube diameters the smallest tube diameter 9.52mm has highest heat and mass transfer performance.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.4
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• pp.215-221
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• 2009

The objectives of this paper are to measure the heat transfer and pressure drop of the heat transfer tube for an evaporator of absorption system applications. Five types of heat transfer tubes with different shape and heat transfer area are tested in the present experiment. Heat transfer and pressure drop performance of heat transfer tubes are measured in various operating conditions, and compared each other. The results show that the heat transfer coefficient of thermoexcel notch tube increases about 79.6% and 45.3% at the film Reynolds number 69.7 compared with that of bare tube and low fin tube, respectively. The thermoexcel notch tube is show the best performance considering pressure drop and heat transfer coefficient.

• Journal of Mechanical Science and Technology
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• v.17 no.7
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• pp.947-957
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• 2003

The pressure tube is a major component of the CANDU reactor, which supports nuclear fuel bundle. In order to complete the integrity evaluation of pressure tube, expert knowledge, iterative calculation procedures and a lot of input data are required. More over, results of integrity assessment may be different according to the evaluation method. For this reason, an integrity evaluation system, which provides efficient way of evaluation with the help of attached database, was developed. The present system was built on the basis of 3D FEM results, ASME Sec. XI, and Fitness For Service Guidelines for CANDU pressure tubes issued by the AECL (Atomic Energy Canada Limited). The present system also covers the delayed hydride cracking and the blister evaluation, which are the characteristics of pressure tube integrity evaluation. In order to verify the present system, several case studies have been performed and the results were compared with those from AECL. A good agreement was observed between those two results.