On the effects of surface waviness upon catalytic steam reforming of methane in micro-structured reactors - a computational study

The effects of wavy channels upon steam methane reforming in catalytic micro-structured reactors, using Nickle as the catalyst, are investigated numerically. Laminar, three-dimensional models of reacting flows, with heterogeneous chemistry, are developed and applied to micro-structured reactors with different wave patterns on their internal walls. It is observed that introduction of surface waves on the walls of reactor, can significantly alter production and consumption of H2 and CH4. This is shown to be due to large fluctuations in convective mass and heat transfer, induced by the surface waviness. In particular, it is shown that separation and reattachment of concentration and thermal boundary layers and the subsequent modifications in Sherwood and Nusselt number can significantly affect the catalytic processes over the walls of reactor. A major local intensification of catalytic processes is observed where Sherwood and Nusselt number are maximised. Similarly, the catalytic process becomes highly inefficient in places with minimal Sherwood (and Nusselt) number. The analyses further reveal that a strategic discrete coating of wavy walls with the catalyst can substantially improve the performance of microstructure. For example, by coating only 25% of the surface area of wavy walls, CH4 conversion rate and selectivity per coated surface area increase by 459% and 308% compared to those of an equivalent fully coated straight channel. This implies the possibility of developing highly efficient and cost-effective catalytic micro-reactors for production of hydrogen from methane

Recent progress on flat plate solar collectors equipped with nanofluid and turbulator: state of the art.

This paper reviews the impacts of employing inserts, nanofluids, and their combinations on the thermal performance of flat plate solar collectors. The present work outlines the new studies on this specific kind of solar collector. In particular, the influential factors upon operation of flat plate solar collectors with nanofluids are investigated. These include the type of nanoparticle, kind of base fluid, volume fraction of nanoparticles, and thermal efficiency. According to the reports, most of the employed nanofluids in the flat plate solar collectors include Al2O3, CuO, and TiO2. Moreover, 62.34%, 16.88%, and 11.26% of the utilized nanofluids have volume fractions between 0 and 0.5%, 0.5 and 1%, and 1 and 2%, respectively. The twisted tape is the most widely employed of various inserts, with a share of about one-third. Furthermore, the highest achieved flat plate solar collectors' thermal efficiency with turbulator is about 86.5%. The review is closed with a discussion about the recent analyses on the simultaneous use of nanofluids and various inserts in flat plate solar collectors. According to the review of works containing nanofluid and turbulator, it has been determined that the maximum efficiency of about 84.85% can be obtained from a flat plate solar collector. It has also been observed that very few works have been done on the combination of two methods of employing nanofluid and turbulator in the flat plate solar collector, and more detailed work can still be done, using more diverse nanofluids (both single and hybrid types) and turbulators with more efficient geometries

Transient cooling of a lithium-ion battery module during high-performance driving cycles using distributed pipes - A numerical investigation

Transient effects are often excluded from the design and analysis of battery thermal management systems (BTMS). However, electric vehicles are subjected to significant dynamic loads causing transient battery heating that is not encountered in a steady state. To evaluate the significance of such effects, this paper presents a time-dependent analysis of the battery cooling process, based on an existing cooling system that satisfactorily operates in steady conditions. To resemble realistic conditions, the temporal variations in the battery power withdrawal are inferred from different standard driving cycles. Computational fluid dynamics is then utilized to predict the coolant and battery temperatures inside a battery module for a period of 900 s. It is shown that, for air cooling, the batteries temperature can exceed the safe limit. For example, in a high-performance driving cycle, after 200 s, the battery temperature goes beyond the critical value of 308 K. Nonetheless, the temperatures are always within the safe region when liquid is used to cool the battery module. Also, during a high-performance cycle where the flow rate is 1.230 g/s, the battery temperature decreased below the critical threshold and reached 304 K. In addition, to maintain the temperature of the batteries below the critical threshold during NYCC traffic and US06 driving cycles, a maximum coolant pressure inlet of 1.52 and 0.848 g/s, equivalent to 100 Pa and 50 Pa, respectively, are required. The temporal changes in Nusselt number distribution over the battery module, induced by the acceleration of the vehicle during the driving cycles, are also discussed. It is concluded that the assumption of a steady state might lead to the non-optimal design of BTMSs

Transient cooling of a lithium-ion battery module during high-performance driving cycles using distributed pipes - A numerical investigation

Transient effects are often excluded from the design and analysis of battery thermal management systems (BTMS). However, electric vehicles are subjected to significant dynamic loads causing transient battery heating that is not encountered in a steady state. To evaluate the significance of such effects, this paper presents a time-dependent analysis of the battery cooling process, based on an existing cooling system that satisfactorily operates in steady conditions. To resemble realistic conditions, the temporal variations in the battery power withdrawal are inferred from different standard driving cycles. Computational fluid dynamics is then utilized to predict the coolant and battery temperatures inside a battery module for a period of 900 s. It is shown that, for air cooling, the batteries temperature can exceed the safe limit. For example, in a high-performance driving cycle, after 200 s, the battery temperature goes beyond the critical value of 308 K. Nonetheless, the temperatures are always within the safe region when liquid is used to cool the battery module. Also, during a high-performance cycle where the flow rate is 1.230 g/s, the battery temperature decreased below the critical threshold and reached 304 K. In addition, to maintain the temperature of the batteries below the critical threshold during NYCC traffic and US06 driving cycles, a maximum coolant pressure inlet of 1.52 and 0.848 g/s, equivalent to 100 Pa and 50 Pa, respectively, are required. The temporal changes in Nusselt number distribution over the battery module, induced by the acceleration of the vehicle during the driving cycles, are also discussed. It is concluded that the assumption of a steady state might lead to the non-optimal design of BTMSs

Nieliniowe rozwiązanie problemu niefourierowskiego przewodzenia ciepła w płycie nagrzewanej źródłem laserowym

The effect of laser, as a heat source, on a one-dimensional finite body was studied in this paper. The Cattaneo-Vernotte non-Fourier heat conduction model was used for thermal analysis. The thermal conductivity was assumed temperature-dependent which resulted in a non-linear equation. The obtained equations were solved using the approximate-analytical Adomian Decomposition Method (ADM). It was concluded that the non-linear analysis is important in non-Fourier heat conduction problems. Significant differences were observed between the Fourier and non-Fourier solutions which stresses the importance of non-Fourier solutions in the similar problems.W artykule badano działanie laserowego źródła ciepła na ciało jednowymiarowe o skończonych wymiarach. Do analizy rozkładu temperatury zastosowano niefourierowski model przewodnictwa ciepła Cattaneo-Vernotte. Założono, że przewodność cieplna jest zależna od temperatury, w wyniku czego otrzymano równania nieliniowe. Do rozwiązania równań zastosowano przybliżoną analityczną metodę dekompozycji Adomiana (ADM). Stwierdzono, że analiza nieliniowa ma istotne znaczenie w problemach przewodnictwa ciepła typu niefourierowskiego. Zaobserwowano istotne różnice między rozwiązaniami fourierowskimi i niefourierowskimi, co podkreśla celowość stosowania tych ostatnich w podobnych problemach