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Chen Q.,Key Laboratory for Thermal Science and Power Engineering of Ministry of Education | Chen Q.,University of California at Davis | Zhu H.,Tsinghua University | Pan N.,University of California at Davis | Guo Z.-Y.,Key Laboratory for Thermal Science and Power Engineering of Ministry of Education
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2011

Entropy generation is recognized as a common measurement of the irreversibility in diverse processes, and entropy generation minimization has thus been used as the criterion for optimizing various heat transfer cases. To examine the validity of such entropy-based irreversibility measurement and its use as the optimization criterion in heat transfer, both the conserved and non-conservative quantities during a heat transfer process are analysed. A couple of irreversibility measurements, including the newly defined concept entransy, in heat transfer process are discussed according to different objectives. It is demonstrated that although thermal energy is conserved, the accompanied system entransy and entropy in heat transfer process are non-conserved quantities. When the objective of a heat transfer is for heating or cooling, the irreversibility should be measured by the entransy dissipation, whereas for heat-work conversion, the irreversibility should be described by the entropy generation. Next, in Fourier's Law derivation using the principle of minimum entropy production, the thermal conductivity turns out to be inversely proportional to the square of temperature. Whereas, by using the minimum entransy dissipation principle, Fourier's Law with a constant thermal conductivity as expected is derived, suggesting that the entransy dissipation is a preferable irreversibility measurement for heat transfer.

Li B.,University of Southern California | Liu N.,University of Southern California | Zhao R.,University of Southern California | Egolfopoulos F.N.,University of Southern California | And 2 more authors.
Journal of Propulsion and Power | Year: 2013

Extinction strain rates of premixed and non-premixed flames of n-C 14H30, n-C16H34, a petroleum-derived JP-5 jet fuel, a camelina-derived hydrotreated renewable JP-5 jet fuel, a petroleum-derived F-76 diesel fuel, and an algaederived hydrotreated renewable F-76 diesel fuel were measured in the counterflow configuration at atmospheric pressure and a fuel-containing stream temperature of 443 K. Recently developed kinetic models were used to simulate the experimental data for n-C 14H30 and n-C16H34 flames. The computed results are in close agreement with the data for premixed flames, whereas the data are over-predicted for non-premixed flames. Furthermore, the extinction strain rates of premixed n-C14H30 and n-C 16H34 flames are similar, while compared to n-C 16H34, n-C14H30 nonpremixed flames exhibit greater extinction resistance. Regarding the practical fuels, the extinction propensity of flames of petroleum-derived fuels is higher compared to bio-derived fuels. The extinction strain rates of flames of 80% n-C 16H34 + 20% toluene mixtures were computed also to evaluate the effects of addition of aromatics on extinction. The results confirmed that the addition of toluene increases the extinction propensity compared to neat n-C16H34 flames under both premixed and non-premixed conditions, which explains partially the experimental results for petroleum- and bio-derived practical fuels. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc.

Zhi Q.,Central University of Finance and Economics | Sun H.,Tsinghua University | Sun H.,Key Laboratory for Thermal Science and Power Engineering of Ministry of Education | Li Y.,Tsinghua University | And 2 more authors.
Applied Energy | Year: 2014

In the last decade, China's photovoltaic (PV) industry has developed rapidly, with the joint promotion of the world market and domestic policies, and China has now become the largest PV manufacturer in the world. Meanwhile, the international market has responded to China's rapid development, in light of the Chinese government's industrial policies, and "anti-dumping and anti-bribery investigation", focusing on China's solar industry policies, has been proposed. This paper examines the development history of China's PV industry policy system from the perspective of industrial policies and compares China with United States, Germany and Japan from the perspective of both the supply and demand-side policies. The study finds that, unlike the international practice, which attaches importance to subsidies for the market demand-side, China's policies focus on government regulation, concentrating mainly on the product popularization and application stages, with insufficient investment in research and development in the early stage. On the other hand, however, China's PV policies are gradually changing from production supply prioritization to demand-side policy domination. This paper suggests that, while simultaneously increasing investment in research and development, China's PV policies should continue to reinforce the market demand-side policies and gradually exit the production supply-side policies. © 2014 Elsevier Ltd.

Li Z.,Key Laboratory for Thermal Science and Power Engineering of Ministry of Education | Li Z.,Beijing Municipal Key Laboratory for CO Utilization and Reduction | Li Z.,Tsinghua University | Liu Y.,Key Laboratory for Thermal Science and Power Engineering of Ministry of Education | And 5 more authors.
Chemical Engineering Science | Year: 2013

The decay of sorbent reactivity in multiple carbonation/calcination cycles is a critical problem for calcium looping. By introducing inert support materials into CaO particles, the cyclic reactivity of calcium based sorbent could be drastically improved. However, there is a lack of understanding of the interaction between the CaO grain and the support material; thus, much of studies of synthesizing calcium based sorbents are by trial-and-error. In order to understand the possible mechanism of synthetic calcium based sorbent, the widely accepted Zener pinning theory in the field of metallurgy was used here to describe the inhibition of CaO grain sintering due to the addition of inert support. A simple model of CaO grain growth for synthetic calcium-based sorbents was developed to analyze the effect of inert support on the stabilization of cyclic reactivity of CaO. The mechanism of sintering resistant in the synthetic calcium-based sorbents was the pinning force exerted by the dispersed support particles. The inhibition effect of inert support on CaO grain growth is related with the grain migration due to surface energy (γ), support size (r) and volume fraction (f), and the interaction (Finteract) between the support and CaO. The model was validated with the published data and can predict reasonably the experimental results, and the relative importance of some elementary steps was discussed. This study will provide a theoretical understanding for the further development and reactivity improvement of synthetic calcium-based sorbents. © 2012 Elsevier Ltd.

Jiang P.,Tsinghua University | Jiang P.,Key Laboratory for Thermal Science and Power Engineering of Ministry of Education | Li X.,Tsinghua University | Li X.,Key Laboratory for Thermal Science and Power Engineering of Ministry of Education | And 7 more authors.
International Journal of Greenhouse Gas Control | Year: 2014

Carbon dioxide capture and storage is a new technology that can realize low-carbon utilization of fossil fuels in a large scale. The China Shenhua Group has built a 100,000tons/year integrated CCS demonstration project in Ordos, China. This paper chose Ordos basin as the simulation site and developed a full-field model of a coupled injection well and reservoir to simulate the CO2 behavior during CO2 injection through the wellbore and reservoir, taking into account thermal exchanges with rocks and natural convection of water in the annulus. Information for CO2 temperature and pressure distributions in the wellbore and the reservoir, and their variation with time, were obtained. The simulation results for the temperature and pressure profiles of CO2 in the wellbore were consistent with the well data log within 8.5%. The three factors leading to CO2 temperature increase from the wellhead to bottomhole, heat extraction from rocks, compressibility and potential energy loss were analyzed both qualitatively and quantitatively. Comparison between the bottomhole temperature in our full-field model and the simplified model with a heat flux to substitute for the rock was conducted. Finally, the wellbore transient shut-in effect was simulated to predict the potential pressure drop and cooling at the wellhead. © 2014 Elsevier Ltd.

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