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• The full-morphology simulation of the large-scale automobile PEM fuel cell is proposed. • All components, the realistic morphology of distribution area and the coolant flow is fully considered. • The advantages and disadvantages and its influence on physical and chemical processes of double-cell structure are deeply analyzed. • Novel double-cell structure can significantly improve power density (almost 20%) under actual operating conditions. The structural design of PEM fuel cell is crucial to improving its power density, and the cell structure largely depends on the bipolar plate (BP). This study compares the conventional single-cell structure and double-cell structure through three-dimensional (3D) large-scale (cell area: 312 cm2) full-morphology simulation. As for the double-cell structure, the channels are arranged in a dislocation manner and there is one cooling flow field per two cells. For the structure of the BP, we also fully considered the realistic morphology of distribution area and the coolant flow. It is found that the heat dissipation effect of double-cell structure is worse but the performance is very close compared to single-cell structure. Moreover, its volumetric power density is significantly improved (∼ 20%) due to the reduction in height. It is also found that increasing the velocity of coolant in the double-cell structure increases the performance first and then decreases. [ABSTRACT FROM AUTHOR]

Ultrahigh power density is of primary importance to next-generation polymer electrolyte membrane fuel cell (PEMFC) for commercialization, which demands an in-depth insight into the intricate multi-physics transports, particularly for large-size PEMFCs in automobile application. In this study, a three-dimensional two-phase model is extended to study an automobile fuel cell with the active area of 366.6 cm2, including full morphologies of metallic bipolar plate, flow field, and distribution zones for hydrogen, air and coolant flow. It is found that the cross flow inside membrane electrode assembly under the rib between two adjacent channels promoted by the distribution zone can effectively mitigate local oxygen starvation and water flooding, increasing PEMFC performance at high current density, in comparison with conventional single-channel or no-dot-matrix models. Theoretical analysis indicates that the dot matrix distribution zone induces a larger pressure gradient and hence the cross flow than the commonly-used channel & rib distribution zones. Additionally, the counter-flow configuration has a higher cell performance and more uniform current density than the co-flow one due to internal humidification. When the internal humidification effect is weak, for example, in anode/cathode gas co-flow configuration, coolant flow direction becomes more important for the temperature profile and prevent severe dehydration. • A full-scale 366.6 cm2 automobile PEMFC model with full morphologies is presented. • Cross flow inside MEA effectively mitigates oxygen starvation and water flooding. • Dot matrix enables a stronger cross flow than that of channel & rib structure. • Counter-flow achieves uniform multi-physics transfer by internal humidification. [ABSTRACT FROM AUTHOR]

In the high-speed cutting process, coolant is applied to ensure the cutting tools temperature stable. In the current study, scholars mainly studied the characteristics of the tool surface temperature during the cutting process. However, the cooling and heat transfer characteristics of the cooling fluid were ignored during the cutting process in their study. By analyzed the motion state of the coolant around the cutting tool, a heat transfer model of the coolant fluid is proposed in this paper based on the fluid boundary layer theory. In the heat transfer model, the solution of the temperature gradient of the coolant is obtained by solving the Brahzyus similarity solution. Moreover, the relationship between the temperature of the cutting tool in the coolant environment and the natural convection environment was analyzed by simulation experiment. Then the temperature trend of different Pr for coolant was obtained. In addition, the effect of coolant flow on the cooling effect of the system was discussed in this paper, and the expression of Nu number was obtained. The heat transfer model about the coolant boundary layer proposed in this paper is of great significance for the study of the coolant's cooling characteristics during high speed cutting. [ABSTRACT FROM AUTHOR]

This paper concerns with numerical modeling of fluid flow through a zigzag-shaped channel to be used as the cooling plate for polymer electrolyte membrane fuel cells. In general, large scale PEM fuel cells are cooled by liquid water flows through coolant flow channels, and the shape of these channels has a key role in the cooling performance. We perform a three-dimensional numerical simulation to obtain the flow field and heat transfer rate in square area cooling plates. The performance of zigzag flow channels is evaluated in terms of maximum surface temperature, temperature uniformity and pressure drop. The results indicate that in the zigzag channels model, maximum surface temperature, surface temperature difference and temperature uniformity index, respectively, reduce about 5%, 23%, and 8% with respect to straight channels model. Hence, the cooling performance of fuel cells can be improved by implementing the zigzag channels model as the coolant fluid distributors, although the coolant pressure drop is higher than straight channels in this model. [ABSTRACT FROM AUTHOR]

Effective coolant application in deep hole gundrilling is crucial to prevent rapid degradation and failure of drills through high performance cooling, lubrication and chip evacuation. This paper presents a novel methodology to increase effectiveness of coolant application through strategic optimization of gun drill designs that leads to appreciable tool life improvement, based on computational fluid dynamics (CFD) analysis. Through the analyses of coolant flow characteristics and rheological properties, conventional designs of critical drill geometries like nose grind contour, coolant hole configuration and shoulder dub-off angle, which are detrimental to coolant application and hence tool life are determined. A new, optimized gun drill design for the drilling of deep holes on Ni-based alloys is proposed. All findings are experimentally substantiated. [ABSTRACT FROM AUTHOR]

Grinding is one of the most important manufacturing processes, especially when high surface qualities have to be realized or if hard or brittle materials have to be machined. Often the grinding performance is limited by workpiece failure due to a high thermal load in the contact zone. Therefore structured or patterned grinding wheels are frequently used to reduce the thermal load in the contact zone. In this paper a new patterning method will be introduced by using a fly-cutting kinematic for the structuring process. In face grinding experiments the patterned grinding wheels showed great potential to enhance the overall grinding performance by significantly decreasing process forces and grinding burn. The reduction of the thermal load in the contact zone can be explained by an improved coolant flow through the contact zone, which was measured with a specially designed coolant collecting bin. [ABSTRACT FROM AUTHOR]

The beam dump of the LIPAc consists of a long and thin copper cone where the ions are stopped, cooled by water flowing along its outer surface. The high water velocity (between 4 and 8 m/s) and the turbulent regimes involved may compromise the mechanical stability of the slender beam dump structure and cause damages due to flow induced vibrations. Since the system is too complex to be studied theoretically, some tests have been carried out to evaluate its behavior in normal operating conditions. These tests, performed on a model built at 1:1 scale and replicating exactly the final version, have been focused on finding experimentally the main vibration modes and the responses to the different working flow rates. This modal analysis, together with the results of the measurements of the vibration characteristics obtained at several positions of the cone, is presented here. With amplitudes not greater than 500 mg rms in any case, the structure has proved its practical immunity to flow induced vibrations, thus validating its design and construction methodology. [ABSTRACT FROM AUTHOR]

Abstract: Engine cooling system plays an important role to maintain the operating temperature of engine. The coolant circuit initiates by picking up heat at water jackets. With the pressure gradient exists in coolant circuit, hot coolant flows out from engine to radiator or to bypass circuit (during cold start). The under hood air flow carries heat away at radiator after the air flows through numerous hood components. The coolant flow circuit and air flow circuit meet each other and exchange heat at radiator. Extensive researches are carried out to study vehicles’ cooling system extensively either numerically or experimentally. The research covers many individual topics which include numerical modelling of engine cooling system, under hood air flow, heat transfer at water jacket, heat transfer at radiator and coolants’ after-boiling phenomenon. [Copyright &y& Elsevier]