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Chen Q.,Key Laboratory for Thermal Science and Power Engineering | Chen Q.,University of California at Davis | Yang K.,Key Laboratory for Thermal Science and Power Engineering | Wang M.,Los Alamos National Laboratory | And 2 more authors.
Energy | Year: 2010

Using the analogy between heat and mass transfer processes, the recently developed entransy theory is extended in this paper to tackle the coupled heat and mass transfer processes so as to analyze and optimize the performance of evaporative cooling systems. We first introduce a few new concepts including the moisture entransy, moisture entransy dissipation, and the thermal resistance in terms of the moisture entransy dissipation. Thereinafter, the moisture entransy is employed to describe the endothermic ability of a moist air. The moisture entransy dissipation on the other hand is used to measure the loss of the endothermic ability, i.e. the irreversibility, in the coupled heat and mass transfer processes - this total loss is shown to consist of three parts: (1) the sensible heat entransy dissipation, (2) the latent heat entransy dissipation, and (3) the entransy dissipation induced by a temperature potential. Finally the new thermal resistance, defined as the moisture entransy dissipation rate divided by the squared refrigerating effect output rate, is recommended as an index to effectively reflect the performance of the evaporative cooling system. In the end, two typical evaporative cooling processes are analyzed to illustrate the applications of the proposed concepts. © 2010 Elsevier Ltd. All rights reserved.

Zhang F.-Z.,Beijing Key Laboratory for CO2 Utilization and Reduction Technology | Zhang F.-Z.,Key Laboratory for Thermal Science and Power Engineering | Zhang F.-Z.,Tsinghua University | Xu R.-N.,Beijing Key Laboratory for CO2 Utilization and Reduction Technology | And 5 more authors.
Applied Thermal Engineering | Year: 2016

Numerical simulations have indicated that pure CO2 is superior to water for wellbore hydraulics and for recovering heat from hot fractured rock. However, CO2 captured from power plants may contain impurities such as nitrogen, oxygen and particles. Rather than treating CO2 as merely a waste fluid to be stored in the deep subsurface, impure CO2 may also be used as a geofluid in EGS to extract heat energy from the hot dry rock while permanently storing the CO2 in the rock. Thus, the system performance with impure CO2 must be evaluated for large-scale CO2 utilization. This paper presents an entire cycle model for the flow in the wellbore, the heat extraction and the flow in the reservoir to model the system based on the reservoir parameters and ambient temperatures. The pressure and temperature profiles of the impure CO2 in the injection well and the production well, the power output and the thermal efficiency for an impure CO2-EGS were simulated by a FORTRAN code. The result clarifies the basic principles for the system optimization and the ORC working fluid selection for the impure CO2-EGS. © 2016 Published by Elsevier Ltd.

Wang W.,Key Laboratory for Thermal Science and Power Engineering | Zhu C.,Tianjin University | Cao Y.,Tianjin Normal University
International Journal of Hydrogen Energy | Year: 2010

Density functional theory has been used to study the thermodynamics associated with steam reforming of ethanol under cold plasma conditions. The calculation results showed that the only thermodynamic obstacle of the production of hydrogen, carbon monoxide, methane and acetaldehyde was the dissociation of ethanol and steam molecules, which was easy to be overcome under cold plasma conditions. The formation of hydrogen and carbon monoxide was through a multi-step pathway via the methoxy radical conversion and dissociation of formaldehyde, while the recombination of H{radical dot} generated extra hydrogen. The syntheses of ethane and butane are from the recombination of CH3{radical dot} and CH3CH2{radical dot}, which could be primarily generated through ethanol dissociation. The structure of ethanol anion were also studied in this work. Theoretical calculation showed that the ethanol anion was less stable than the neutral molecule. The route for the formation of CH3{radical dot} and CH2OH{radical dot} from ethanol anion is thermodynamically favorable. © 2009 Professor T. Nejat Veziroglu.

Yang Z.,Key Laboratory for Thermal Science and Power Engineering | Lee D.-J.,National Taiwan University | Liu T.,National Science Foundation
Journal of Colloid and Interface Science | Year: 2010

Advective flow of a permeable sphere in an electrical field is comprehensively studied. The sphere has a uniform permeability and is subject to an incoming Newtonian flow. The electrical field generates an electro-osmotic flow inside the sphere, which markedly affects sphere flow dynamics. A numerical model elucidates the effects of flow dynamic parameters on the drag coefficient and ratio of drag forces to a permeable and solid sphere. The model solves the Navier-Stokes equations both inside and outside the porous sphere. The unique flow field and pressure patterns of the permeable sphere flow are characterized in detail, and utilized to interpret the distinguishing flow behaviors of spheres induced by electro-osmotic flow. Drag force decreases and or reverses in direction when the intensity of the electro-osmotic flow in the sphere increases. When the electro-osmotic flow is counter to the incoming flow, drag force increases significantly, and vortices form near the sphere. As the sphere becomes highly permeable, the influence of the electro-osmotic flow and incoming flow velocity are reduced markedly. © 2009 Elsevier Inc. All rights reserved.

Fu T.,Key Laboratory for Thermal Science and Power Engineering | Yang Z.,Hefei University of Technology | Wang L.,Hefei University of Technology | Cheng X.,Hefei University of Technology | And 2 more authors.
Optics and Laser Technology | Year: 2010

The measurement performance of a CCD-based pyrometer system using a three-color method was evaluated for scientific and engineering metrology. The relationships between the system parameters (exposure time and sensor gain) and the intensity measurements in an integrating sphere experiment were determined for a specific CCD sensor. The pyrometer system uses the three-color method based on the intensity ratio without geometry calibrations. The field measurement characteristics and the effectiveness of coupling the three-color channels were investigated in terms of the temperature measurement uniformity, temperature sensitivity and temperature range of the pyrometer system in standard blackbody tests. The results showed that the temperature non-uniformity is not proportional to the intensity non-uniformity and is in the range of 0.13-2.14%. The relative temperature sensitivities of intensity ratios for different channel combinations are different, which may provide a way to improve the measurement results. The temperature range bandwidth for object with a non-uniform temperature distribution varies from 190 to 270 K for this specific CCD-based pyrometer. The performance evaluation conclusions for the system with this specific CCD sensor are general and applicable for pyrometer systems using other CCD sensors. © 2009 Elsevier Ltd. All rights reserved.

Liu G.Q.,Key Laboratory for Thermal Science and Power Engineering | Liu G.Q.,University of Vermont | Marshall J.S.,University of Vermont
Journal of Electrostatics | Year: 2010

A discrete-element/boundary-element method is developed for simulation of adhesive particle transport by traveling waves on an electric curtain. The study shows that both wall adhesion and particle-particle collisions have an important influence on particle transport on electric curtains at different wave frequencies. The most significant effect of particle collisions occurs for cases with medium frequencies in which particles with large negative-charge collect in high-concentration bands and move in a synchronous surfing mode, pushing forward particles with lower charge. Cases with higher and lower frequencies exhibited hopping motion, for which adhesion determines the range of non-transported particles. © 2009 Elsevier B.V. All rights reserved.

Li C.,Key laboratory for Thermal Science and Power Engineering | Shi Y.,Tsinghua University | Cai N.,Key laboratory for Thermal Science and Power Engineering
Journal of Power Sources | Year: 2010

In this paper, a detailed one-dimension transient elementary reaction kinetic model of an anode-supported solid oxide fuel cell (SOFC) operating with syngas based on button cell geometry is developed. The model, which incorporates anodic elementary heterogeneous reactions, electrochemical kinetics, electrodes microstructure and complex transport phenomena (momentum, mass and charge transport) in positive electrode|electrolyte|negative electrode (PEN), is validated with experimental performance for various syngas compositions at 750, 800 and 850 °C. The comparisons show that the simulation results agree reasonably well with the experimental data. Then the model is applied to analyze the effects of temperature and operation voltage on polarizations in each component of PEN, electronic current density in both electrodes and species concentrations distributions in anode. The numerical results of carbon deposition simulation indicate that higher temperature and lower operation voltage are helpful to reduce the possibility of carbon deposition on Ni surfaces by Bouduard reactions. Furthermore, a sensitivity analysis of cell performance on syngas composition is performed for the typical syngas from entrained-flow coal gasifier and natural methane thermochemical reforming processes. The cell performance increases with the increasing of effective compositions (e.g. H2 and CO) in syngas and the large N2 content introduced by using air as oxidant leads to significant deterioration of performance. © 2009 Elsevier B.V. All rights reserved.

Yao Z.,Tsinghua University | Yao Z.,Key Laboratory for Thermal Science and Power Engineering | Gao Y.,Tsinghua University | Gao Y.,Key Laboratory for Thermal Science and Power Engineering | And 4 more authors.
Journal of Propulsion and Power | Year: 2012

The pressure oscillation within combustion chambers of aeroengines and industrial gas turbines is a major technical challenge to the development of high-performance and low-emission propulsion systems. In this paper, an approach integrating computational fluid dynamics and one-dimensional linear stability analysis is developed to predict the modes of oscillation in a combustor and their frequencies and growth rates. Linear acoustic theory was used to describe the acoustic waves propagating upstream and downstream of the combustion zone, which enables the computational fluid dynamics calculation to be efficiently concentrated on the combustion zone. A combustion oscillation was found to occur with its predicted frequency in agreement with experimental measurements. Furthermore, results from the computational fluid dynamics calculation provide the flame transfer function to describe unsteady heat release rate. Departures from ideal one-dimensional flows are described by shape factors. Combined with this information, low-order models can work out the possible oscillation modes and their initial growth rates. The approach developed here can be used in more general situations for the analysis of combustion oscillations. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Wang H.-D.,Key Laboratory for Thermal Science and Power Engineering | Cao B.-Y.,Key Laboratory for Thermal Science and Power Engineering | Guo Z.-Y.,Key Laboratory for Thermal Science and Power Engineering
International Journal of Heat and Mass Transfer | Year: 2010

Based on Einstein's mass-energy relation, the equivalent mass of thermal energy or heat is identified and referred to as thermomass. Hence, heat conduction in carbon nanotubes (CNTs) can be regarded as the motion of the weighty phonon gas governed by its mass and momentum conservation equations. The momentum conservation equation of phonon gas is a damped wave equation, which is essentially the general heat conduction law since it reduces to Fourier's heat conduction law as the heat flux is not very high and the consequent inertial force of phonon gas is negligible. The ratio of the phonon gas velocity to the thermal sound speed (the propagation speed of thermal wave) can be defined as the thermal Mach number. For a CNT electrically heated by high-bias current flows, the phonon gas velocity increases along the heat flow direction, just like the gas flow in a converging nozzle. The heat flow in the CNT is governed by the electrode temperature until the thermal Mach numbers of phonon gas at the tube ends reach unity, and the further reduction of the electrode temperature has no effect on the heat flow in the CNT. Under this condition, the heat flow is said to be choked and temperature jumps will be observed at the tube ends. In this case the predicted temperature profile of the CNT based on Fourier's law is much lower than that based on the general heat conduction law. The thermal conductivity which is determined by the measured heat flux over the temperature gradient of the CNT will be underestimated, and this thermal conductivity is actually the apparent thermal conductivity. In addition, the heat flow choking should be avoided in engineering situations to prevent the thermal failure of materials. © 2010 Elsevier Ltd. All rights reserved.

Liu Y.-Q.,Key Laboratory for Thermal Science and Power Engineering | Liu Y.-Q.,Tsinghua University | Liu Y.-Q.,China Aerospace Science and Technology Corporation | Xiong Y.-B.,Key Laboratory for Thermal Science and Power Engineering | And 6 more authors.
International Journal of Heat and Mass Transfer | Year: 2013

The influences of the thermal conductivity and porosity of the porous wall and locally extraordinarily high heat fluxes on the hot surface and the location of a low porosity region within one and two layer porous walls on the temperature field were analyzed numerically. The local thermal non-equilibrium model was used to predict the temperature distributions in the solid and phases within a 2-D computational domain. The predicted results show that the porosity and thermal conductivity of the top layer significantly influence the temperature distribution of the solid matrix when the hot surface is subjected to uniform or locally extraordinarily high heat flux boundary conditions. In addition, the study shows that the location of the low porosity region also significantly affects the temperature field in the two layer model consisting of a bronze matrix and a ceramic coating. © 2013 Elsevier Ltd. All rights reserved.

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