Preparation of composite adsorbent with high performance of heat and mass transfer

2013 ◽  
Vol 58 (3) ◽  
pp. 280-285
Author(s):  
ZhenNeng LU ◽  
LingBao WANG ◽  
XianBiao BU
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
High Performance ◽  
Composite Adsorbent

Heat Transfer Design in Adsorption Refrigeration Systems for Efficient Use of Low Grade Thermal Energy

2010 ◽  
Author(s):  
R. Z. Wang ◽  
Z. Z. Xia ◽  
L. W. Wang ◽  
Z. S. Lu ◽  
S. L. Li ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Exchanger ◽  
Heat And Mass Transfer ◽  
Thermal Energy ◽  
High Performance ◽  
Low Grade ◽  
Adsorption Refrigeration ◽  
High Efficient ◽  
Sorption Systems

Adsorption refrigeration and heat pump systems have been considered as very important means for the efficient use of low grade thermal energy in the temperature range of 60–150°C. Sorption systems are merely heat exchanger based thermodynamic systems, and therefore a good design to optimize heat and mass transfer with reaction or sorption processes is very important for high performance of the systems. Studies on heat and mass transfer enhancement in adsorption beds have been done extensively. Notable techniques is whereby the adsorbent bed is fitted with finned heat exchanger embedded with adsorbent particles, or the adsorbent particles may be compressed and solidified and then coupled with finned tube or plate heat exchangers. The use of expanded graphite seems to be an effective method to improve both heat and mass transfer in the reaction bed. Studies have also shows the need to enhance the heat transfer in adsorption bed to match with the heat transfer of thermal fluids. Use of heat pipes and good thermal loop design could yield higher thermal performances of a sorption system, when coupled with adsorption beds to provide heating and cooling to the beds. A novel design with passive evaporation, known as rising film evaporation coupled with a gravity heat pipe was introduced for high cooling output. It has also been shown that heat and mass recovery in the internal sorption systems is critical, and novel arrangement of thermal fluid and refrigerant may result in high performance sorption systems. Based upon the above researches, various sorption systems have been developed, and high efficient performances have been reached. Typical sorption systems include (1) A silica gel-water adsorption water chillier with a COP about 0.55 when powered with 80°C hot water, (2) A CaCl2-ammonia adsorption refrigerator with a COP over 0.3 at −20 °C when powered with 120 °C water vapor, which has a specific cooling power about 600 W/kg-adsorbent. The above mentioned systems have shown that solid sorption systems have become market potential products, and low grade thermal energy, which is usually considered as waste heat, could be utilized to provide high grade cooling. This paper gives details of high efficient solid sorption systems recently developed, their heat transfer design, thermodynamic system coupling, and performance test results. Some examples of low grade thermal powered cooling systems are also presented.

Heat and Mass Transfer in Loop Heat Pipes

2003 ◽  
Author(s):  
Triem T. Hoang ◽  
Jentung Ku
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
High Performance ◽  
Heat Pipes ◽  
Thermal Control ◽  
Complete Understanding ◽  
Loop Heat Pipes ◽  
Transfer Processes ◽  
Mass Transfer Processes ◽  
Control Concept

Loop Heat Pipes (LHPs) have gained acceptance among spacecraft engineers in recent years as high performance heat transport devices for thermal control systems (TCS). However, the most common criticism from people who use LHPs is that their behavior is difficult to predict. Complex interaction of thermodynamics and fluid flow dynamics inside a LHP poses a challenge for the analytical modeling of its performance. The need for a complete understanding of mechanisms involving the heat and mass transfer in a LHP cannot be overstated. During the initial spacecraft TCS design phase, trade studies are usually carried out to select an appropriate thermal control concept for the design. The inability to accurately predict the LHP response in the actual operating environment often leads to the dismissal of LHPs for lack of certainty. This paper attempts to present a simplistic explanation of LHP operation in terms of heat and mass transfer processes, in hope that it will help the potential end-users to understand the technology better. Most of the observed phenomena described herein are based on available test data of various LHP systems. Nevertheless, a few anomalies especially during operational transients are still not well understood. For that, research ideas will also be proposed.

Experimental Study of the Heat and Mass Transfer in a Packed Bed Liquid Desiccant Air Dehumidifier

1998 ◽  
Vol 120 (4) ◽  
pp. 289-297 ◽  
Author(s):  
V. O¨berg ◽  
D. Y. Goswami
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
High Performance ◽  
Energy Requirement ◽  
Experimental Studies ◽  
Triethylene Glycol ◽  
Electrical Energy ◽  
Packed Bed ◽  
Liquid Desiccant ◽  
Flow Rates

Desiccant cooling systems have the ability to provide efficient humidity and temperature control while reducing the electrical energy requirement for air conditioning as compared to a conventional system. Naturally, the desiccant air dehumidification process greatly influences the overall performance of the desiccant system. Therefore, the effects of variables such as air and desiccant flow rates, air temperature and humidity, desiccant temperature and concentration, and the area available for heat and mass transfer are of great interest. Due to the complexity of the dehumidification process, theoretical modeling relies heavily upon experimental studies. However, a limited number of experimental studies are reported in the literature. This paper presents results from a detailed experimental investigation of the heat and mass transfer between a liquid desiccant (triethylene glycol) and air in a packed bed absorption tower using high liquid flow rates. A high performance packing that combines good heat and mass transfer characteristics with low pressure drop is used. The rate of dehumidification, as well as the effectiveness of the dehumidification process are assessed based on the variables listed above. Good agreement is shown to exist between the experimental findings and predictions from finite difference modeling. In addition, a comparison between the findings in the present study and findings previously reported in the literature is made. The results obtained from this study make it possible to characterize the important variables which impact the system design.

scholarly journals Combining Baffles and Secondary Porous Layers for Performance Enhancement of Proton Exchange Membrane Fuel Cells

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3675
Author(s):  
Luka Mihanović ◽  
Željko Penga ◽  
Lei Xing ◽  
Viktor Hacker
Keyword(s):  
Mass Transfer ◽  
Flow Field ◽  
Heat And Mass Transfer ◽  
High Performance ◽  
Proton Exchange Membrane ◽  
Proton Exchange ◽  
Cell Performance ◽  
Manufacturing Cost ◽  
Water Removal ◽  
Exchange Membrane

A numerical study is conducted to compare the current most popular flow field configurations, porous, biporous, porous with baffles, Toyota 3D fine-mesh, and traditional rectangular flow field. Operation at high current densities is considered to elucidate the effect of the flow field designs on the overall heat transfer and liquid water removal. A comprehensive 3D, multiphase, nonisothermal computational fluid dynamics model is developed based on up-to-date heat and mass transfer sub-models, incorporating the complete formulation of the Forchheimer inertial effect and the permeability ratio of the biporous layers. The porous and baffled flow field improves the cell performance by minimizing mass transport losses, enhancing the water removal from the diffusion layers. The baffled flow field is chosen for optimization owing to the simple design and low manufacturing cost. A total of 49 configurations were mutually compared in the design of experiments to show the quantitative effect of each parameter on the performance of the baffled flow field. The results elucidate the significant influence of small geometry modifications on the overall heat and mass transfer. The results of different cases have shown that water saturation can be decreased by up to 33.59% and maximal temperature by 7.91 °C when compared to the reference case which is already characterized by very high performance. The most influencing geometry parameters of the baffles on the cell performance are revealed. The best case of the 49 studied cases is further optimized by introducing a linear scaling factor. Additional geometry modifications demonstrate that the gain in performance can be increased, but at a cost of higher pressure drop and increased design complexity. The conclusions of this work aids in the development of compact and high-performance proton exchange membrane fuel cell stacks.

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