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[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] In this study, thermosyphon application is suggested to accomplish the fully passive safety grade system and compactness of components via enhance the heat removal performance. A two-phase evaporating thermosyphon operates when the evaporator is heated, the working fluid start boiling, the vapor that is formed moves to the condenser, where it is condensed on the walls, giving up the heat of phase change to the cooling fluid. Gravity forces cause the condensate to condensed liquid flow to the evaporator again. These processes occur continuously, which causes transfer of heat from evaporator to condenser vice versa. After the thermal design and performance evaluation, the results were compared with the performance of conventional DRACS system. For the same amount of decay heat removal performance of PDRC system of KALIMER-600 mercury thermosyphon system can archive around 30∼50% of compactness. For the detailed design, improved analytical model and experimental data for the validation will be required to specify the new DHR system
[en] In this study, the heat transfer performance of a two-phase single thermosyphon was experimentally measured and compared with respect to the aspect ratio and filling ratio. For the control experiments, we prepared three 1 m-long thermosyphons with the ratio of evaporator and condenser length by 5:5, 4:6 and 3:7. The working fluid, HFE-7100 was selected to consider the evaporator heat source temperature. The experiments were carried out with respect to the filling ratio and cooling air velocity. As a result, the highest heat transfer rate (about 1.0 kW) was obtained at the filling ratio of 40 % with the length ratio of 5:5 and the cooling air velocity of 2.0 m/s. Among the various parameters, we suggest that the filling ratio and the length ratio play a key role in the heat transfer performance. Out of the experimental data, we suggest the Kutateladze number based correlation between the heat transfer and operating parameters in the thermosyphon using HFE-7100 within the error of ±2 %.
[en] Thermosyphon solar water heaters are the best choice to be utilized in residential sector to provide the required hot water in Libya. These systems are autonomy in operation and as a result require less maintenance, and hence low operation and initial costs than active systems. In this paper, GenOpt optimization technique provided in TRNSYS simulation program is used for sizing thermosyphon systems to obtain the optimum size (namely V1/Ac ratio) of thermosyphon systems that suits Libyan families according to the weather and operating conditions of Tripoli. The typical hot water load pattern nd quantity of the Libyan families are taken from a field study conducted on a number of solar systems for a whole year. Whereas, the typical weather data are taken from five year measurements recorded at CSERS weather station. The results showed that the optimum storage tank volume to collector area ratio of thermosyphon systems is between 49-60 Lit/m'2 for the most common collector characteristics ratio (FRUL/FR(τα)=6-8) and the auxility heater set point temperature ranges from (45-60 degree centigrade).(author)
[en] Heat transfer with phase change is an important phenomenon in many industrial processes. Devices such as evaporators, reboilers, condensers and steam generators are examples where phase change through boiling or condensation occurs. For a proper and realistic design of these equipment a thorough understanding of heat transfer and fluid flow aspects of two-phase systems is required. Comparative study of verticle thermosyphon reboiler/evaporator design methods has been carried out. (author). 15 refs., 2 tabs., 6 figs
[en] Experimental studies were carried out for the new thermosyphon type of double tube evaporator. thermosyphons are utilized for transporting large quantities of heat energy. thermosyphons have been widely used in energy and different industrial applications due to their simple construction , small thermal resistance, broad operating limits and low fabrication costs. thermal analysis of thermosyphons performance is experimentally presented in the steady state operation of the closed two-phase thermosyphon of double tube evaporator. the experimental study was performed by inserting an inner pipe into the evaporator of thermosyphon. this study aims to examine the thermosyphons performance against the traditional thermosyphon and analysis of the characteristics of double tube evaporator
[en] The results of experiments with the thermosyphons inclined to horizontal line at angle of 1.5-20 deg are presented. The generalizing equations to determine some thermohydraulic characteristics of thermosyphons are suggested
[ru]Приведены результаты экспериментов с термосифонами, наклоненными к горизонтали под углом 1.5-20 град. Предложены обобщающие уравнения для определения некоторых теплогидравлических характеристик термосифонов
[en] This paper reports on a project carried out by the Centre for Solar Energy Research and Studies (CSERS) to familiarize Libyan people with solar water heating technologies. Around 100 solar water heaters have been installed in the domestic sector and selected systems were equipped with monitoring instruments required to evaluate thermal performance. The paper presents the results of data collected over a one year period from a system installed in a family residence situated in a village located 90 km south of Tripoli (Libyan capital). The results showed that the system solar fraction was 55.8% of the average amount of daily hot water withdrawn (144 liters) at an average withdrawal temperature of 46.6 °. The total energy withdrawn during the whole year was 1557 kWl1. It is concluded that such a system is not adequate in terms of cost effectiveness for the current installed situation. It is recommended that the annual solar fraction for any solar water heating system should be over 70° in order to achieve cost—effectiveness and to help wide spread take—up of this technology.(author)
[en] The issue concerning the dynamic response of closed two-phase thermosyphon with inner tube inserted inside evaporator creating natural circulation system is getting on increasing degree of attention due to its relevance during startup. Thermosyphons transient operation for startup from ambient condition to steady state is considered a stringent necessity for vital applications such as electronic, solar, geothermal and even nuclear reactors safety systems. This typically returns to the need to keep the temperature within certain limits before reaching critical conditions. Also, a greater understanding of the thermosyphon and its transient behavior is needed.Transient thermal-hydraulic analysis of the closed two-phase water/copper thermosyphon with inner tube is theoretically and experimentally presented. The main objective of the current study is to develop a theoretical model that can predict the dynamic behavior of the double-tube evaporator by tracing various transient parameters during operation from start up to steady state condition.The model numerically describes thermosyphon of double tube evaporator (double tube thermosyphon DTT) by seven coupled sub-models. These sub-models are: heater, wall of thermosyphon, fluid in the riser hot channel inside evaporator, vapor core in adiabatic and condenser sections, liquid in the down-comer of thermosyphon, the condensate film in the condenser, and finally the cooling water of the condenser. The mathematical model is derived by applying the energy balance for each section and sub-section in addition to continuity, and momentum equations for the liquid and vapor in different sections of double tube thermosyphon (DTT). The model simulates the thermosyphon by several differential equations which are solved to predict the various parameters. A computer program is designed to solve these differential equations by an explicit finite difference method. To validate the predicted theoretical model results, an experimental investigation has been conducted. An experimental setup is constructed from: thermosyphon main tube of 42 mm inner diameter, 4 mm thickness and 1950 mm long. The evaporator and condenser section lengths are 1100 mm and 400 mm respectively, while the adiabatic section is 450 mm long. An inner tube made of poly propylene is installed inside the evaporator. The inner tube has outer diameter of 34 mm with thickness 3.5 mm and 1100 mm length. This structure forms a hot channel with 4 mm annular gap width, where the natural flowing liquid circulated between inner and outer tubes. The heat source is simulated by 4 electrical coils while the heat sink is directly performed by a cooling process at condenser section, using cooling water of 0.0456 kg /s.
[en] An experimental study is presented for the heat transfer performance of a rectangular, two-phase, natural-circulation loop with water-steam as the working fluid. Local temperature measurements of the core fluid and the wall were made, and the overall heat transfer coefficients of the evaporator, the condenser, and the loop system were obtained and correlated in terms of the fluid properties, heat flux conditions, and the liquid charge level. An overheat phenomenon at very low charge level was also observed. Result of a preliminary analysis shows that if the liquid charge level is below the fractional volume of the connecting tube between the condenser and the evaporator, an overheat phenomenon will occur