China 
Africa 
Explore chapters and articles related to this topic
Numerical Investigation of Heat Flow and Fluid Flow in a Solar Water Heater with an Evacuated-Tube Collector
Published in Hemen Dutta, Mathematical Methods in Engineering and Applied Sciences, 2020
K.D.N. Kumari, J.K. Wijerathna
This study is specially focused on the passive direct solar water heater system. The thermosiphon effect is used in this type of solar water heaters for the heat transfer process. A thermosiphon effect relies on warm water rising, a phenomenon known as natural convection, to circulate water through the collector and in the storage tank (shown in Figures 5.1a and 5.1b).
Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
During the last 100 years, a wide variety of evaporator types has evolved, each offering advantages for certain specific applications. The forced-circulation crystallizer shown in Figure 62.2 is utilized for many applications where no crystallization occurs, but the liquids being handled are viscous, and use of the circulation system is needed to promote heat transfer. A number of evaporator types have been developed that require no external circulating system. For the most part, these rely upon thermo-syphon effects to promote movement of liquid through the tubes as an aid to heat transfer. The calandria evaporator (or Roberts type) shown in Figure 62.8 is a design that has been widely used since the 19 th century for both crystallization and evaporation applications. It relies on natural circulation in relatively short tubes (1 to 2m) to maintain heat transfer rates; a relatively large amount of recirculation occurs through the tubes. Since there is no recirculation pump or piping, this type of equipment is relatively simple to operate and requires a minimum of instrumentation. The volume of liquid retained in this vessel is much larger than in some of the rising or falling film designs and, therefore, in dealing with heat-sensitive materials where concentration must proceed at relatively short retention times, the calandria would be
Domestic Water Heating
Published in William C. Dickinson, Paul N. Cheremisinoff, Solar Energy Technology Handbook, 2018
It is inconvenient to freezeproof thermosiphon systems. The system shown can be drained manually only by closing the collector isolation valves V and opening the draincocks D. It is also possible to employ a heat exchanger inside the preheat tank and to use antifreeze in the collectors to permanently freezeproof the system.
Heat Transport Augmentation Using Vibration Material Excited by Boiling Bubbles for Heat Removal from Divertor
Published in Fusion Science and Technology, 2021
Noriyuki Unno, Kazuhisa Yuki, Jun Taniguchi, Shin-ichi Satake
An advantage of thermosiphon is its use of water as the working fluid, which is more eco-friendly than liquid metals. Water has been used for a long time in thermosiphons and heat pipes for the cooling of electric devices. However, the maximum heat flux in the evaporation unit of the thermosiphon [namely, boiling heat transfer (BHT)] should be improved to remove heat at heat fluxes over 10 MW/m2. The critical heat flux (CHF) of water in saturated pool boiling is only approximately 1.1 MW/m2 at atmospheric pressure.7 Therefore, the CHF must be improved to remove heat at high heat flux. Subcooled boiling is a simple technique for improving the CHF. For example, the CHF in subcooled pool boiling is expected to be above 4 MW/m2 at the liquid subcooling of 60 K with water at atmospheric pressure (Fig. 1). However, chillers are necessary to decrease the temperature of water to below 30°C, resulting in high power consumption. Therefore, it is difficult to further improve the CHF by increasing the liquid subcooling.
Numerical study on vapor–liquid phase change in an enclosed narrow space
Published in Numerical Heat Transfer, Part A: Applications, 2020
Chengbin Zhang, Suchen Wu, Feng Yao, Dongke Sun
When a moderate heat load is imposed to the evaporator section, the fully developed nucleate boiling occurs, and the local heat transfer coefficient variates frequently with irregular amplitude and period. As mentioned, the faster frequency of bubble nucleation, coalescence and detachment contribute to this fluctuation. Accompanied by the induced liquid motion, the heat transfer performance on the evaporator section of the thermosiphon gets enhanced. For the high heat load (q = 0.0025), the occurrence of film boiling results in the vapor film always covering the evaporator wall surface. Without bubble nucleation, the heat transfer capability keeps at a low level with a small fluctuation, which corresponds to the bubble rise induced by the interface instability. During the fully developed nucleate boiling, the bubble dynamics including nucleation, coalescence, detachment and break up always take place near sequentially or even simultaneously around point (I). The variation of h is no longer solely affected by the bubble nucleation. Then the transient heat transfer coefficient at point (I) shows frequent fluctuation with a relatively lower amplitude.