Mathematical modeling heat transfer in closed two-phase thermosyphon

Проведен численный анализ теплопереноса в замкнутом двухфазном термосифоне цилиндрической формы в условии подвода теплоты на нижней крышке. Для описания исследуемого процесса предложена упрощенная математическая модель, отличающаяся от известной описанием только процессов теплопроводности в системе "корпус термосифона - паровой канал - пленка конденсата". Сформулированная краевая задача решена методом конечных разностей. Получены поля температур в термосифоне для типичных тепловых нагрузок и режимов работы

The Opportunity Analyses of Using Thermosyphons in Cooling Systems of Power Transformers on Thermal Stations

The opportunity analyses of using the thermosyphons as the main elements in the systems of thermal regime supplying has been conducted under the conditions of their usage in power transformers on thermal stations. Mathematical modeling of jointly proceeding processes of conduction, forced convection and phase transitions (evaporation and condensation) of coolant in the thermosyphon of rectangular cross section has been carried out. The problem of conjugated conductive-convective heat transfer was formulated in dimensionless variables "vorticity/stream function/temperature" and solved by finite difference method. The effect of the heat flux density supplied to the bottom cover of the thermosyphon from a transformer tank on the temperature drop in the steam channel was shown based on the analysis of numerical simulation results (temperature fields and velocities of steam). The parameters of energy-saturated equipment of thermal stations were found to be controlled by an intensification of heat removal from the top cover surface of the thermosyphon

Numerical analyses of the effect of a biphasic thermosyphon vapor channel sizes on the heat transfer intensity when heat removing from a power transformer of combined heat and power station

Numerical analyses of the effect of a biphasic thermosyphon vapor channel sizes on the heat transfer intensity was conducted when heat removing from an oil tank of a power transformer of combined heat and power station (CHP). The power transformer cooling system by the closed biphasic thermosyphon was proposed. The mathematical modeling of heat transfer and phase transitions of coolant in the thermosyphon was performed. The problem of heat transfer is formulated in dimensionless variables "velocity vorticity vector - current function - temperature" and solved by finite difference method. As a result of numerical simulation it is found that an increase in the vapor channel length from 0.15m to 1m leads to increasing the temperature difference by 3.5 K

Peculiarities of temperature fields formation in vapor channels of thermosyphons with heat carriers boiling at low temperatures

We conducted experiments on specially developed setup consisting of evaporation, transport and condensation parts. Heat was supplied to the evaporation part by the heating element which was supplied with voltage and alternating current from a single-phase transformer. Temperatures in the characteristic sections of each part were recorded by thermocouples. Junctions of thermocouples were mounted on the axis of symmetry in the liquid layer, at the lower boundary, in the middle part, and at the upper boundary of the vapor channel. To minimize the influence of the random factors (ambient air movement, operation of ventilation system, room temperature, etc.), we placed thermosyphon in a glass box. We used N-pentane as a heat carrier, and the filling ratio of the thermosyphon is equal to 4%

Critical heat flux density in diphasic thermosyphons

The paper presents an analysis of known dependencies for determining the critical heat flux density in diphasic thermosyphons. The critical heat flux density for the created experimental model of thermosyphon were calculated on the basis of the theoretical contributions of 1) the occurrence of a “flooding” regime in a thermosyphon characterized by a disturbance of the hydrodynamic stability of the phase interface and the entrainment of the liquid phase by the gas flow; 2) the mutual influence of gravitational forces and surface tension; 3) S.S. Kutateladze hydrodynamic theory of the heat transfer crisis during boiling. It is found that the existing theoretical contributions which can be used to calculate the critical heat flux density and subsequently determine the minimum filling ratio of a thermosyphon are conditionally applicable

Experimental Research of Thermophysical Processes in A Closed Two-Phase Thermosyphon

The temperature distribution in a thermosyphon was studied experimentally. To conduct the research, a closed two-phase thermosyphon was developed, which differs from the known by simple construction. The method of studying the rapid processes of conduction, convection and phase transitions was also developed. It will allow to highlight the operational modes of the thermosyphon, considering the load, cooling conditions of the condensation section, value of the heat supply. According to obtained results the instabilities of the temperature fields over the cross-section of the two-phase closed thermosyphon were observed by means of using the modern measuring equipment. It has been suggested that the instabilities can be caused by different modes of thermosyphon operation

An experimental study of the influence of a thermosyphon filling ratio on a temperature distribution in characteristic points along the vapor channel height

Results of experimental studies of heat transfer in a thermosyphon illustrating the influence of the filling ratio and the heat load on the temperature distribution in the vapor channel, evaporation and condensation zones are presented. The thermosyphon was made of copper and was 161 mm high with side walls 1.5 mm thick, bottom cover 2 mm thick, an internal dimmer of the evaporation part of 54 mm and an internal diameter of the vapor channel of 39.2 mm. Based on the results of experimental studies, temperature dependences were established in the characteristic cross sections of the thermosyphon on the heat flux value supplied to the bottom cover. In addition, a well-appearing thermosyphon self-regulation property has been found – the growth of the heat load in the evaporation zone in the range from 1940 to 7685 W/m{2} does not lead to a decrease in the heat removal intensity from the heat-release region

Critical heat flux density in diphasic thermosyphons

The paper presents an analysis of known dependencies for determining the critical heat flux density in diphasic thermosyphons. The critical heat flux density for the created experimental model of thermosyphon were calculated on the basis of the theoretical contributions of 1) the occurrence of a “flooding” regime in a thermosyphon characterized by a disturbance of the hydrodynamic stability of the phase interface and the entrainment of the liquid phase by the gas flow; 2) the mutual influence of gravitational forces and surface tension; 3) S.S. Kutateladze hydrodynamic theory of the heat transfer crisis during boiling. It is found that the existing theoretical contributions which can be used to calculate the critical heat flux density and subsequently determine the minimum filling ratio of a thermosyphon are conditionally applicable

Experimental study of temperatures in characteristic sections of the working zone of a closed two-phase thermosyphon under the condition of a heat removal by external periphery

We present the results of the experimental study of temperature fields in a closed two-phase thermosyphon. Operational modes of a thermosyphon with different heat supply conditions are studied experimentally using setup consisting of the copper case, systems of heat supply and removal in evaporation and condensation zones, and temperature recording facilities. The height of the heat exchanger is 161 mm, thickness of the side walls and bottom wall are 1.5 mm and 2 mm, respectively, inner diameter is 39 mm. Heat is supplied to the bottom wall by heating element. The heat carrier is distilled water. We obtained thermograms when heat fluxes to the bottom wall of the thermosyphon are 695 - 2136 W/m{2}

Analysis of potential method of geothermal energy application

Проведено численное моделирование процессов теплопереноса в каскаде термосифонов, представляющих собой систему извлечения геотермальной энергии с больших глубин. Предложена математическая модель теплопереноса в слое теплоносителя на нижней крышке термосифона и паровом канале, отличающихся от известных упрощенным описанием комплекса теплофизических процессов, протекающих в зонах испарения, транспорта и конденсации термосифона. Целью исследования является разработка упрощенного метода расчета температурных полей в каскаде термосифонов, обеспечивающего возможность проведения опытно-конструкторских работ по созданию систем извлечения геотермальной энергии на основе каскада термосифонов. Краевая задача математической физики решалась методом конечных разностей. Показана возможность анализа основных характеристик – температур – в рамках модели «эффективной» теплопроводности, коэффициенты переноса которой могут быть определены экспериментально. Установлена возможность переноса теплоты с больших глубин с «эффективностью», достаточной для достижения в системе теплоснабжения температур около 330 К в условиях полной теплоизоляции внешнего контура (поверхностей термосифона). Полученные результаты являются базой для дальнейшего развития моделей и методов анализа процессов извлечения геотермальной энергии с больших глубин с использованием каскада последовательно работающих термосифонов. По результатам полученных теоретических следствий сформулированы основные направления экспериментальных исследований с целью обоснования сделанных по результатам численного анализа выводов. Результаты численного моделирования дают основания для вывода о перспективности дальнейшей (экспериментальной и теоретической) разработки метода извлечения геотермальной энергии с больших глубин залегания грунтовых вод с использованием каскада термосифонов большой высоты.The numerical simulation of heat transfer was conducted in a cascade of thermosyphons representing a system for extracting geother- mal energy from great depths. We proposed a mathematical model of heat transfer in the coolant layer on the bottom cover of a ther- mosyphon and in the vapor channel differing from the well- plified method for calculating temperature fields in a cascade of thermosyphons, which makes it possible to conduct design and expe- rimental work to create the systems for extracting geothermal energy based on a cascade of thermosyphons. The boundary problem of mathematical physics was solved by the method of finite differences. We showed the possibility to analyze the main characteristics - temperatures - within the framework of the model of «effective» thermal conductivity. The transfer coefficients of this model can be determined experimentally. We found the possibility of heat transfer from large depths with «efficiency» sufficient to achieve tempe- ratures of about 330 K in the heat supply system when the external contour (thermosyphon surfaces) is completely thermally insulated. The results obtained are the basis for the further development of models and methods for analyzing geothermal energy extraction from great depths using a cascade of sequentially operating thermosyphons. According to the obtained theoretical results, the main directions of experimental studies were formulated to justify the conclusions made by the results of a numerical analysis. The results of numerical simulation provide grounds for concluding that the future (experimental and theoretical) development of a method for extracting geothermal energy from large depths of groundwater using a cascade of thermosyphons is promising