Numerical investigations of small diameter two-phase closed thermosyphon

Abstract: A heat pipe, which contains evaporator, adiabatic, and condenser, is a simple device with proper heat transfer rate and a little heat loss, without any moving parts. In this study, the effects of length of the three mentioned sections of heat pipe were investigated through introducing the ratio of adiabatic length to the condenser length or evaporator length as aspect ratio (AR), filling ratio of working fluid, and heat load on the thermal performance of a thermosyphon heat pipe by combining computational fluid dynamics (CFD) and design of experiment (DOE). Optimum conditions were obtained using DOE. Prior to determining the optimum conditions, the heat pipe was simulated using volume of fluid model through solving the governing equations of mass, momentum, and energy for evaporation and condensation phenomena by finite volume method. The results were confirmed by comparing the 2D CFD simulation results with the experimental data. The purpose of this research was to find the optimal lengths of different parts. The results showed that the averaged optimum values for the above mentioned parameters (AR, heat load, and filling ratio) were 0.8325, 246 W, and 85%, respectively. In total, thermal performance of the heat pipe was improved for lower adiabatic zone length and higher values of heat load and filling ratio.

Abstract: Thermodynamics: An Engineering Approach 3rd edition by Cengel and Boles; Heat Transfer: A. Practical Approach by Cengel; Thermodynamics. 6th edition by Thermodynamics: An Engineering Approach, 6th Edition, McGraw Hill, 2007. Yunus A. Cengel and Michael A. Boles Thermodynamics: An Engineering . Thermodynamics: An Engineering Approach, 7th Edition Explain the basic concepts of thermodynamics such . solution of engineering problems and it. OBJECTIVES: 1. To develop a conceptual understanding of the fundamental elements of "Thermodynamics, An Engineering Approach", 7th Edition. . "Fundamentals of Engineering Thermodynamics, 6th Edition, Copyright 2008; Michael J..

Abstract: An experimental investigation of the performance of thermosyphons charged with water as well as the dielectric heat transfer liquids FC-84, FC-77 and FC-3283 has been carried out. The copper thermosyphon was 200 mm long with an inner diameter of 6 mm, which can be considered quite small compared with the vast majority of thermosyphons reported in the open literature. The evaporator length was 40 mm and the condenser length was 60 mm which corresponds with what might be expected in compact heat exchangers. With water as the working fluid two fluid loadings were investigated, that being 0.6 ml and 1.8 ml, corresponding to approximately half filled and overfilled evaporator section in order to ensure combined pool boiling and thin film evaporation/boiling and pool boiling only conditions, respectively. For the Fluorinert™ liquids, only the higher fill volume was tested as the aim was to investigate pool boiling opposed to thin film evaporation. Generally, the water-charged thermosyphon evaporator and condenser heat transfer characteristics compared well with available predictive correlations and theories. The thermal performance of the water-charged thermosyphon also outperformed the other three working fluids in both the effective thermal resistance as well as maximum heat transport capabilities. Even so, FC-84, the lowest saturation temperature fluid tested, shows marginal improvement in the heat transfer at low operating temperatures. All of the tested Fluorinert™ liquids offer the advantage of being dielectric fluids, which may be better suited for sensitive electronics cooling applications and were all found to provide adequate thermal performance up to approximately 30–50 W after which liquid entrainment compromised their performance.

Abstract: The Saudi Cultural Bureau in London, the Ministry of Higher Education and the Mechanical Engineering Department, Umm Al-Qura University

Abstract: The heat transfer characteristics of a two-phase closed thermosyphon are studied experimentally and a simple mathematical model is developed to predict the performance of such thermosyphons. Water, ethanol and Freon 113 are used as the working fluids. The effects of the amount of the working fluid, the operating temperature, the heat flux and the working fluid, are investigated experimentally. Heat transfer coefficients at the condenser and the evaporator are estimated from experimental results. From these experimental results, a simple mathematical model is developed. In the present model, film condendation along the inside surface of the condenser, and evaporation from a liquid film above the pool and boiling of the liquid pool in the evaporator are considered for the heat transfer mechanism of the thermosyphon and the effects of the amount of the working fluid, the operating pressure, the heat flux and the working fluid are brought into consideration. A good agreement between the overall thermal resistance of the thermosyphon estimated from experimental results and the predictions from the present mathematical model is obtained.