Results 1 - 10 of 94
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[en] The investigation purpose an experimental study of the natural convection flow. This study simulates the fires evolving in a free and unlimited environment then in interaction with their material surrounding. The fires met such as in the forests in the oil fields and in the tower blocks create a thermal plume which extends in space. The pollutants transported by the fires flows threaten the inhabitants health and cause a natural imbalance of the environment. In reality the thermal plume generated by these fires undergone the influence of the neighbouring walls. Indeed, the walls which surround it are heated by thermal radiation thus creating a thermosyphon flow which interacts with the plume. According to former work, the researchers [16, 20] noticed that the fires can be simulated by a hot source heated by Joule effect. For that, we studied the thermal plume flow generated by a hot rectangular source placed in a free then in a semi-confined environment. To better understand the development mechanisms of the free fire flow and in interaction with surrounding, we simulated these phenomena at the laboratory. In a first time we studied a thermal plume generated by a rectangular source heated uniformly by Joule effect. In a second time the same source is placed at the entry of a vertical canal which its the two Duralumin walls are heated at a constant temperature. The visualization by laser plane enables us to follow the vertical evolution of the flow for two studied configurations. Using hot wire anemometry, we explored the thermal and dynamic field of the flow. In order to better describe the fine structure of the flow, we analyzed the spectra of temperature fluctuations
[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] Solar energy is one of the promising resources of renewable energy. It is of particular interest due to the energy shortage and environment pollution problems. Water heating by solar energy for domestic use is one of the most successful and feasible applications of solar energy. The thermosyphon SDHWS and the loop type thermosyphon systems are widely used for domestic hot water system. The loop type thermosyphon is a circulation device for transferring the heat produced at the evaporator area to the condenser area in the loop by a working fluid. The system has the advantage of high heat transfer rate. A phase change of the working fluid occurs at the evaporator section and the vapor is transported to the condenser by the density gradient. The loop type thermosyphon collector can be made of smaller area and has higher efficiency than the present thermosyphon SDHWS. In this study, the operating characteristics of various working fluids being used have been identified. The working fluids employed in the study were ethanol, water and a binary mixture of ethanol and water. The volume of working fluid used in this study were 30%, 40%, 50%, 60% and 70% of evaporator volume. An increased heat was applied with the increased volume of working fluid. It is observed that, in the thermosyphon with low volume of working fluid, such as 30% or 40%, the fluid was dried out. The average efficiency of the loop type thermosyphon was 46% with high solar irradiation and 43% with low irradiation. The flow pattern and mechanism of the heat transfer were identified through this study. Flow patterns of the binary mixture working fluid were also investigated, and the patterns were recorded in the camera. The system parameters were calculated using the thermal performance data. Modelling of the system was carried out using PSTAR method and TRNSYS program
[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.
[en] An effective algorithm for the numerical simulation of thermocapillary convection with non-planner fluid interfaces is described. Thermocapillary effects include convection away from an interface as well as distortion of the interface, including possible rupture of the interface. As a result, the algorithm must solve the complete moving boundary problem for the Navier-Stokes equations and must predict the onset of processes leading to the rupture of the interface. The algorithm is based on the stream function - vorticity formulation and finite-difference discretization coupled with domain transformation required for regularization of the computational domain. The algorithm is tested on a model problem consisting of a cavity filled initially with a certain amount of liquid resulting in a non-planar interface and then subjected to a concentrated external heating applied directly to the interface. The numerical simulation is used to determine the convection pattern, the interface shape, and the limits of existence of continuous interface (limit point of the system). Detailed results are presented for the large Biot and zero Marangoni number limits. (author)