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Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
In general, heat pipes have advantages over many traditional heat-exchange devices when: Heat needs to be transferred nearly isothermally over relatively long distances.Low weight and passive operation are essential.Fast thermal-response times are required.Low maintenance is mandatory. Further advances in the heat pipe field include the development of the loop heat pipe by Maydanik and colleagues at the Russian Academy of Sciences. The loop heat pipe can transport even greater amounts of heat than standard heat pipes do as it separates the vapor passage from the liquid passage and reduces the overall size of the wick in the heat pipes. This optimizes the balance of small pores for capillary pumping and low frictional losses. Ochterbeck [2003] has further information on loop heat pipes.
Liquid Metals as Heat Transfer Fluids for Science and Technology
Published in Alina Adriana Minea, Advances in New Heat Transfer Fluids, 2017
Alexandru Onea, Sara Perez-Martin, Wadim Jäger, Wolfgang Hering, Robert Stieglitz
Recently, for a dish/AMTEC system, a loop-type heat pipe made from SS 304 and using sodium as working fluid has been proposed by Boo et al. (2015). Compared to the traditional heat pipe, which has a single-container geometry, the loop heat pipe separates the liquid/vapor lines and thus enhances the thermal capabilities and reduces the fluidic resistances occurring at the liquid/vapor interface, while the capillary structure on the vapor line is eliminated. However, the liquid/vapor lines were placed close to each other to reduce the start-up time, since sodium could be heated faster. The heat pipes tested have dimensions 12.7 × 738 × 1 mm3 (diameter × length × wall thickness) for vapor and 9.5 × 582 × 1 mm3 for liquid. At steady state, the loop heat pipe was capable of transporting a 800 W thermal load, corresponding to about 730°C on the evaporator (solar receiver side), and reached a heat discharge temperature at the condenser (AMTEC side) just a few degrees lower. The working fluid charge ratio was identified to significantly affect the heat pipe performances.
Experimental study on steam side vacuum capillary concentrated ethylene glycol aqueous solution
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Liangwei Hao, Hao Wu, Hong Xu, Jun Cao
Metal powder sintered porous capillary wick has advantages of lightweight, large specific surface area, large capillary force, high heat transfer efficiency, and corrosion resistance, and has been widely used in loop heat pipe (Rosenfeld and North 1995). The loop heat pipe is an effective heat transfer device that exchanges heat through the phase change of the liquid working fluid, which has achieved excellent heat dissipation applications in areas such as heat dissipation of electronic components and aerospace. Its main work principle is to achieve the circulation of the working fluid and the exchange of heat by capillary force. The working medium is vaporized into steam in the evaporation section of the loop heat pipe, condensed into liquid in the condensation section, and then pumped back to the evaporation section by the capillary force.
The Two-Phase Spreading of High Heat Fluxes Density Dissipative Components for Space and Non-Space Applications
Published in Heat Transfer Engineering, 2019
Mikaël Mohaupt, Stéphane Van Oost, Laurent Barremaecker
If miniaturization allows the increase of operating modes and functions of a module, associated waste heat from electronics becomes one of the most stringent limits to overpass. Dissipating a high amount of power over a very small surface, in other terms dissipating a high power surface density (denoted q, in W/m²), necessitates to implement very effective cooling devices. Indeed these cooling devices shall have to provide very high heat exchange coefficients (denoted h, in W/m²/°C) to limit the thermal gradient between the cold source and the electronic to cool down. As a function of exchange surface, the spreading of the heat over a larger surface is investigated to reduce constraints on the cooling device and allows the use of classical techniques such as liquid forced convection and air natural or forced convection. Obviously classical heat pipe networks or two-phase loops (Loop Heat Pipe or LHP and Capillary Pumped Loop or CPL) can also be used as very efficient cooling devices to transport heat to a remote cold source with reduced thermal gradient.
Characterization of flat miniature loop heat pipe using water and methanol at different inclinations
Published in Experimental Heat Transfer, 2021
Sireesha Veeramachaneni, Srinivas Kishore Pisipaty, Dharma Rao Vedula, A. Brusly Solomon
A loop heat pipe is an improved design of heat pipe in that the condenser section is separated from the evaporator. Condensation is facilitated more effectively in an external heat exchanger, and the condensate is sent to a compensator (or reservoir), which supplies the working liquid to the evaporator through a wick as per the requirement. Kaya et al. [1] developed a mathematical model to calculate the steady-state performance of an LHP for different sink temperatures and elevations. Maydanik [2] presented a review based on the experiments and theoretical analyses carried out at Institution of Thermal Physics and in certain other organizations that the loop heat pipes have high efficiency and can operate through large distances in any orientations. Riehl and Dutra [3] built an experimental LHP with acetone as working fluid, which was designed to manage up to 70 W and startups were observed even at low heat inputs such as 2 W. The review presented by Launay et al. [4] on LHP showed that the operation of an LHP is affected by the boiling and capillary limitations, the fill charge ratio, the porous wick geometry and thermal properties, the sink and ambient temperature levels, the design of the evaporator and compensation chamber, the elevation and tilt, the presence of non-condensable gases, and the pressure drops of fluid along the loop. Singh et al. [5] conducted an experimental investigation on copper miniature loop heat pipe (mLHP) with a flat disk-shaped evaporator for temperature control of a computer microprocessor and obtained a thermal resistance of 0.17°C/W at a maximum load of 70 W with an evaporator temperature of 99.6°C. The influence of the conductance between compensation chamber and heater plate on operating temperatures was found by Adoni et al. [6] who tested an ammonia LHP with flat evaporator and nickel wick encased in an aluminum-stainless steel casing.