Results 1 - 10 of 151
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[en] This paper reviews several R and D activities associated with the subject of passive cooling systems, conducted by the N.R.C.Negev thermohydraulic group. A short introduction considering different types of thermosyphons and their applications is followed by a detailed description of the experimental work, its results and conclusions. An ongoing research project is focused on the evaluation of the external dry air passive containment cooling system (PCCS) in the AP-600 (Westinghouse advanced pressurized water reactor). In this context some preliminary theoretical results and planned experimental research are for the fature described
[en] Single phase natural circulation is of interest in various energy systems, including solar heaters, nuclear reactors, geothermal power production, engine and computer cooling. The present paper deals with an experimental study on the influence of pressure drops on the behavior of a single-phase natural circulation loop. In a simple rectangular loop (MTT-1) located at DITEC, three series of tests have been carried out, with localized pressure drops (orifices of 6 mm, 10 mm and 14 mm diameter in the vertical legs) and different power levels. The experimental data are analyzed and compared with previous results obtained with smooth pipes, demonstrating the stabilizing effect of the pressure drops on the overall behavior of the loop
[en] Mass transfer time relaxation parameters for condensation affect the amount of the mass transfer in the phase change. In the present study, a numerical investigation has been implemented with four different parameters for the condensation process in a thermosyphon, with the parameter of 0.1 for the evaporation process. The numerical results were compared with the experimental results to validate the numerical methods. When the mass transfer time relaxation parameter for the condensation was set to the value considering the density ratio out of the four parameters, the numerical result was in good agreement with the experimental result. This numerical process is expected to be used to predict the temperature distribution in the thermosyphon more accurately.
[en] This book gives descriptions of shell and tube heat exchanger including from, sorts, structure like shell and shell side, channel, and sliding bar, basic design of heat exchanger, flow-induced vibration, shell side condenser, tube side condenser and design of basic structure of condenser by types, selection of reboiler type, kettle type reboiler, internal reboiler, pump through reboiler, design of reboiler like kettle and internal reboiler, and horizontal and vertical thermosyphon reboiler.
[en] The heat transfer characteristics of a thermosyphon designed to passively cool cylindrical heat sources are experimentally studied. The analysis is based on recognizing the physics of the flow within different regions of the thermosyphon to develop empirical heat transfer correlations. The basic system consists of three concentric cylinders, with an outer channel between the outer two cylinders, and an inner channel between the inner two cylinders. Tests were conducted. with two different process material container diameters, representing the inner cylinder, and several different power levels. The experimentally determined local and average Nu numbers for the inner channel are in good agreement with previous work for natural convection between vertical parallel plates, one uniformly heated and the other thermally insulated. The implication is that the heat transfer off of each surface is independent of the adjacent surface for sufficiently high Ra numbers. The heat transfer is independent because of limited interaction between the boundary layers at sufficiently high Ra numbers. As a result of the limited interaction, the maximum temperature within the system remained constant, or decreased slightly when the radii of the inner cylinders increased for the same amount of heat removal
[en] A new experimental facility is being developed for materials irradiation and testing at the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor (HFIR). Details of this facility have been presented before. A prototype of this facility, the Thermosyphon Test Loop (TSTL) has been built, and experimental data have been obtained and analyzed. Pretest calculations for this facility with the RELAP5-3D code have been presented previously as well as other calculations with the TRACE code. The results of both codes were very different. RELAP5-3D predicted much higher pressures and temperatures than TRACE. This paper compares calculated results with the TSTL experimental data. Comparison of calculations with the codes RELAP5-3D and TRACE with experimental data of the new TSTL facility has shown that TRACE results agree well with the data and that RELAP5-3D calculates very high pressures and temperatures. The TRACE code is well suited to model this facility and is being used for future calculations. (authors)
[en] Two-phase closed thermosyphon (TPCT) is vertically oriented wickless heat pipe that has working fluid in the interior. The TPCT transports a large amount of heat from evaporator to condenser by phase change of working fluid, and the working fluid passively returns to evaporator by gravity. Due to these advantages of the TPCT, the TPCT is considered as method of PRHR (Passive Residual Heat Removal) system in nuclear system. Parametric studies have done to investigate the heat transfer characteristics of the TPCT. Different working fluids such as water, ethanol, methanol and acetone were used at various filling ratios and at different operating temperatures to find maximum heat transport capabilities of TPCT. Effect of heat transfer rate, filling ratio and aspect ratio were investigated. Inclined angle effect was investigated at several filling ratios and working fluids. This study is interested in silicon oil effect on the TPCT. To carry out the experiment, experimental apparatus is designed and manufactured. In design process, the TPCT operation limit is considered This study is interested in silicon oil effect on the TPCT. Experiments were carried out at three oil weight percent with three input power. Effect of oil on the TPCT is evaluated by inner wall temperature distribution and thermal resistance. In this study, silicon oil effect on TPCT was investigated. The TPCT was operated with several oil weight percent and input power. From experiment, overall, the silicon oil reduced evaporator thermal performance, but enhanced condenser thermal performance. However, the TPCT total thermal performance was reduced by 100 c St silicon oil
[en] This paper presents an experimental investigation on the heat transfer characteristics of a vertical flat thermosyphon (VFT). Several tests were performed to assess the effects of filling ratios, hydraulic radius, working fluid, and aspect ratio (Le/4HR) at a vertical orientation on the heat transfer characteristics of the VFT. It was found that the filling ratios and hydraulic radius affect heat flux: while the aspect ratios of VFT increased, the heat flux decreased. In addition, the working fluid changed from water and ethanol to R123 as the heat flux increases
[en] This paper presents the results of an experimental study to investigate hoe the effectiveness of a commercial type two-phase thermosyphon coil loop run around air-to-air system using R-11 as its working fluid, will vary when subjected to changes in the temperature difference between hot and cold air streams for various air flow rates and for various amounts of working fluids resident in the evaporator
[en] Carbon steel is a sturdy but inexpensive material and is preferred to copper or stainless steel wherever a lower cost is desirable. However, carbon steel-water combination is known to be incompatible for heat pipes due to generation of non-condensible gases during operation. The life time of the carbon steel-water heat pipe was tested based on the Arrhenius model using accelerated life-test scheme. Mass generation of the non-condensible gas was estimated by measuring axial temperature distribution of the heat pipes. The test was conducted with 8 heat pipes and 2 thermosyphons with 1.2-m length and 2.54-cm outer diameter in an elevated temperature range, 165∼250 .deg. C. From the test results, the heat pipe with a chemical retardant added in the working fluid exhibited about 5 years of life time, which was much longer than the one without the additive.