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

EXPERIMENTAL DETERMINATION OF TEMPERATURES IN CHARACTERISTIC SECTIONS OF THE WORKING ZONE OF A CLOSED TWO-PHASE THERMOSYPHON

In article, presents the results of experimental determination of temperature distributions in characteristic sections of the working zone of a closed two-phase thermosyphon. A thermosyphon made of copper with a constant cross-sectional area is used to study heat transfer. The height of the heat exchanger is 161 mm, the thickness of the side walls is 1.5 mm, the bottom wall is 2 mm, the internal diameter of the evaporative part and the vapor channel is 39 mm. Experimental results give dependences of the change in the characteristic temperatures on the heat flux supplied to the bottom cover of the thermosyphon and the filling ratio. An increase in the heat flow at the bottom cover of the thermosyphon leads to a decrease in the temperature drop along the vapor channel and a reduction in the time to reach the stationary mode of operation. Experiments show that even at high thermal loads (up to 11,2  kW/m2) the temperature drops over the height of the thermosyphon do not exceed 9 K

Numerical analysis of the filling ratio impact on the heat transfer intensityin a two-phase closed thermosyphon

The plane problem of forced convection and conjugate heat exchange in a two-phase closed thermosyphon of rectangular cross-section was solved. Numerical modeling was conducted for three filling ratio variants (10%, 25%, 50%) of the heat transfer device under study. It was established that filling ratio increasing leads to a redistribution of the energy accumulated by liquid and vapor, and, respectively, to the thermal regime change of the heat exchanger under consideration. It was shown that an increase in filling ratio decreases the heat transfer rate from the bottom horizontal boundary to the upper boundary and, as a result, the temperature of thermosyphon bottom lid rises

Evaluating the efficiency of closed two-phase thermosyphons based on experimental determination of temperatures in the characteristic cross sections of the working area

Приведены результаты экспериментального определения температур в рабочем канале замкнутого двухфазного термосифона. Экспериментальные исследования проводились в медном термосифоне с внутренним диметром 39 мм, высотой теплообменника 161 мм, толщиной боковых стенок 1,5 мм и нижней крышки 2 мм. По результатам исследований установлена зависимость температур в характерных сечениях рабочей зоны (при использовании дистиллированной воды и низкокипящей жидкости – н-пентана в качестве основного хладагента) от величины теплового потока (от 0,3 до 9,5 кВт/м2 для дистиллированной воды и от 0,3 до 0,5 кВт/м2 для н-пентана) и коэффициента заполнения (? = 8%). Установлено, что во всем диапазоне изменений тепловых потоков период выхода на стационарный режим характерных температур достаточно длительный (6000-10000 с). Получены зависимости перепадов температур по высоте термосифона. Установлено, что перепады T по высоте двухфазного термосифона для дистиллированной воды не превышают 5 К, для н-пентана – 1,1 К.This article presents the results of the experimental determination of temperatures in the working channel of a closed two-phase thermosyphon. The authors have conducted experimental research using a copper thermosyphon with a height of 161 mm, sidewall thickness of 1.5 mm, and a bottom cover of 2 mm. The internal diameter of the evaporation part and the vapor channel was 39 mm. According to the results, the temperature in characteristic sections of the working area (with distilled water and low-boiling liquid n-pentane as the main coolants) was determined as a function of the heat flux (from 0.3 to 9.5kW/m2 for distilled water and from 0.3 to 0.5kW/m2 for n-pentane) and the filling ratio (? = 8%). The time taken to reach the stationary mode of characteristic temperatures was found to be rather long in the whole range of the heat fluxes. The obtained dependencies of the temperature differences along the thermosyphon height showed that under the maximum thermal loads for the conditions under consideration, the temperature differences in the vapor channel of the thermosyphon do not exceed 5 K for distilled water and 1.1 K for n-pentane

Mathematical Simulation of Temperature Fields in Characteristic Sections of the Working Zone of the Closed Two-Phase Thermosyphon

Приведены результаты численных исследований совместно протекающих процессов теплопроводности и фазовых превращений теплоносителя в термосифоне цилиндрической формы. Решена задача теплопереноса для двух двуслойных пластин. Учитывалось испарение жидкости на нижней крышке и конденсация на верхней крышке термосифона. Численные исследования теплопереноса в закрытом двухфазном термосифоне в условиях отвода энергии от тепловыделяющей поверхности проведены в достаточно типичных диапазонах изменения тепловых потоков к нижней крышке, соответствующих режимам работы энергетического оборудования (от 2 кВт/м2 до 8 кВт/м2). В качестве теплоносителя рассматривалась дистиллированная вода. Коэффициенты заполнения и геометрические параметры термосифона выбирались такими же, как и в проведенных экспериментах (высота – 161 мм, диметр – 42 мм, толщина стенок – 1,5 мм, коэффициент заполнения ? = 4%). Основные результаты математического моделирования представлены в виде полей температур при различных тепловых потоках к нижней крышке термосифона и коэффициента теплоотдачи с поверхности верхней крышки рассматриваемого теплообменника. Установлено, что результаты математического моделирования, полученные численно, достаточно адекватно описывают процессы теплопереноса, протекающие в термосифоне, и лежат в пределах доверительных интервалов экспериментальных данных по температурам в характерных точках теплообменника.The authors present the results of numerical studies of the joint thermal conductivity and coolant phase transformations in a cylindrical thermosyphon. The heat transfer problem for two bilayer plates is solved. The evaporation of liquid on the bottom cover and the condensation on the top cover of the thermosyphon is taken into account. The authors have conducted a numerical study of heat transfer in the closed two-phase thermosyphon with energy removal from a heat-emitting surface in fairly typical ranges of variation of heat flows to the bottom cover, corresponding to the operating modes of power equipment (2-8 kW/m2). Distilled water was considered as coolant. The filling ratios and geometric parameters of the thermosyphon are chosen the same as in the experiments conducted (height 161 mm, diameter 42 mm, wall thickness 1.5 mm, filling ratio ? = 4%). The main results of mathematical simulation are presented in the form of temperature fields for various heat flows to the bottom cover of the thermosyphon and the heat transfer coefficient from the surface of the top cover of the heat exchanger under consideration. The results of mathematical simulation, obtained numerically, describe adequately the heat transfer in the thermosyphon and belong to the confident limits of the experimental data on the temperatures at the characteristic points of the heat exchanger