Hydraulic and Thermal Performances of a High Temperature Ceramic Plate-Fin Heat Exchanger (PFHE)

Numerical analysis was carried for novel configuration of high temperature PFHE Fluid flow and heat transfer properties were studied for various fin configurations Ripsaw fin design with thickness of 0.05 mm gives maximum heat transfer with less pressure drop and friction factor Validation and parametric study were carried out for all fin configuration

Thermo-hydraulic Characterization of the Smooth Wavy Fin-and-elliptical Tube Heat Exchangers Using New Type Vortex Generators

AbstractIn the present study, 3D computational analysis was performed to investigate heat transfer and pressure drop characteristics of flow in new Smooth Wavy Fin-and-Elliptical Tube (SWFET) heat exchanger model with new vortex generators. Performance results are presented in terms of non-dimensional parameters, friction factor f and Colburn j factor. Four new types of vortex generators were considered; rectangular trapezoidal winglet (RTW), angle rectangular winglet (ARW), curved angle rectangular winglet (CARW) and Wheeler wishbone (WW). Fluid flow and heat transfer are simulated and the results are compared. The SST k–ω turbulence model is used, with steady-state solvers to calculate pressure drop, flow and temperature fields. The influences of the geometrical factors of mounted vortex generators including attack angles of the winglets (αVG = 15°, 30°, 45°, 60° and 75̊) and width/length aspect ratio (w/l = 0.5,1.0) of the Wheeler wishbones in enhancing the heat transfer performance of a smooth wavy fin heat exchanger with a three-row staggered elliptical tube bundle are investigated. The Reynolds number ranges from 500 to 3000 based on the hydraulic diameter. A parametric study on the winglet vortex generators indicated that for the small attack angle, CARW vortex generators gives better thermohydraulic performance under the present conditions. The best thermal performance of the SWFET heat exchanger with winglet VGs in the larger attack angle, was obtained at RTW VGs arrangement. For the SWFET heat exchangers, the WW VGs with width/length aspect ratio of w/l = 0.5 provide the best heat transfer performance

Thermoelectric effect and temperature-gradient-driven electrokinetic flow of electrolyte solutions in charged nanocapillaries

A systematic theoretical study of thermoelectric effect and temperature-gradient-driven electrokinetic flow of electrolyte solutions in charged nanocapillaries is presented. The study is based on a semianalytical model developed by simultaneously solving the non-isothermal Poisson-Nernst-Planck-Navier-Stokes equations with the lubrication theory. Particularly, this paper clarifies the interplay and relative importance of the thermoelectric mechanisms due to (a) the convective transport of ions caused by the fluid flow, (b) the dependence of ion electrophoretic mobility on temperature, (c) the difference in the intrinsic Soret coefficients of cation and anion. Additionally, synergy conditions for the three thermoelectric mechanisms to fully cooperate are proposed for thermo-phobic/philic electrolytes. The temperature-gradient-driven electrokinetic flow is shown to be a nearly unidirectional flow whose axial velocity profiles vary with the axial location. Also, the flow can be regarded as a consequence of the counteraction or cooperation between a thermoelectric-field-driven electroosmotic flow and a thermo-osmotic flow driven by the osmotic pressure gradient and dielectric body force. Moreover, the Seebeck coefficient and the fluid average velocity are demonstrated to be affected by electrolyte-related parameters. The results are beneficial for understanding the temperature-gradient-driven electrokinetic transport in nanocapillaries and also serve as theoretical foundation for the design of low-grade waste heat recovery devices and thermoosmotic pumps.Comment: 17 pages, 11 figures, with some correction

Numerical Study on Mass Transfer Performance of a Spiral-like Interconnector for Planner Solid Oxide Fuel Cells

AbstractIn order to transfer more fuel of a planner SOFC (Solid Oxide Fuel Cell) from gas channel into porous anode, this paper has designed a novel spiral-like SOFC interconnector, a 3-D model is made by COMSOL 3.5a and the cell was operated with the mixture of H2 and H2O as fuel at 1023K. The result shows that, compared with conventional direct channel interconnectors, the new interconnector in this paper could not only improve the gas velocity parallel to the TPB(Triple Phase Boundary), but also with much higher gas velocity perpendicular to it, which has led to the H2 molar fraction close to the TPB in anode is almost two orders of magnitude higher than that of director channel interconnector SOFC, which would be helpful to improve the electrical performance of SOFCs

Numerical modeling of high temperature bayonet heat exchanger and decomposer for decomposition of sulfur trioxide

Motivation Hydrogen is an attractive energy carrier in the future energy technology. Hydrogen is produced from splitting of water through various process namely electrolysis, photo-electrolysis, photo-biological production and thermochemical water-splitting. The aim of this study is to numerically investigate fluid flow, heat transfer and chemical reaction in bayonet high temperature heat exchanger and decomposer. Parametric studies are performed to achieve maximum decomposition with less pressure drop

Novel Analytical and Numerical Methods in Heat Transfer Enhancement and Thermal Management

1Dipartimento di Ingegneria Industriale, Universita degli Studi di Napoli Federico II, 80125 Napoli, Italy 2Laboratoire de Modelisation et Simulation Multi Echelle, Equipe Transferts de Chaleur et de Matiere, Universite PARIS-EST, 77454 Marne-la-Vallee Cedex 2, France 3School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China 4Laboratory of Steam Boilers andThermal Plants, School of Mechanical Engineering, National Technical University of Athens, Zografou, 15780 Athens, Greece 5Mechanical and Aerospace Engineering Department, Rutgers, the State University of New Jersey, Piscataway, NJ 08854-8058, US

Ion steric effect induces giant enhancement of thermoelectric conversion in electrolyte-filled nanochannels

Ionic Seebeck effect has received increasing attention because of its advantages such as high Seebeck coefficient and low cost. However, theoretical study on the ionic Seebeck coefficient is still in its infancy and mainly focuses on diluted simple electrolytes excluding the contributions of ion steric effects and short-range electrostatic correlation. Here, we show that the coupling of the steric effects due to finite ion sizes and ion thermodiffusion in electric double layers can significantly enhance the thermoelectric response in confined electrolytes via both theory and simulation. The Seebeck coefficient can reach 100% or even one order of magnitude enhancement as compared to previous theoretical models depending on the degree of the ion steric effects and the sum of ion Soret coefficients. In addition, we demonstrate that the short-range electrostatic correlation is beneficial to achieving the maximum Seebeck coefficient at weaker confinement or more concentrated electrolytes. These findings can provide a strategy for achieving high Seebeck coefficient and high electric conductivity simultaneously to improve the efficiency of the ionic thermoelectric conversion.Comment: 12 pages, 6 figure

Numerical studies of combined multiple shell-pass shell-and-tube heat exchangers with helical baffles

Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.In order to simplify the manufacture and improve the heat transfer performance, we have invented a combined multiple shell-pass shell-and-tube heat exchanger. The novel combined multiple shell-pass shell-and-tube heat exchanger (CM-STHXs) with continuous helical baffles in the outer shell-pass and other different baffles in the inner shell-pass was compared with conventional STHX with segmental baffles by Computational Fluid Dynamics method. The numerical results show that, under the same mass flow rate M and the same overall heat transfer rate Qm in the shell side, the CM-STHX with discontinuous helical baffles in the inner shell-pass has the lowest overall pressure drop DP, which was 13% lower than that of the segmental baffled STHX; The heat transfer rate Qm of the CM-STHX with discontinuous helical baffles in the inner shell-pass is about 2% and 12% higher than those of the CM-STHX with segmental baffles and disk-and-doughnut baffles in the inner shell-pass. The CM-STHX with discontinuous helical baffles in the inner shell-pass has a much better heat transfer performance and can be used to replace the conventional STHX with segmental baffles in industrial applications to save energy, reduce cost and prolong the service life.vk201

IMECE2011-64425 THEORETICAL ANALYSIS ON FILM THICKNESS OF INTERTUBE FALLING-FILM FLOW WITH A COUNTERCURRENT GAS FLOW

ABSTRACT In falling-film type of heat exchangers, gas/vapor usually exists, and its effect on falling-film mode transitions and heat transfer could not be neglected. It could impact the film thickness, which is an important parameter to determine the thin-film heat transfer performance, or even destroy fallingfilm modes and significantly deteriorate the heat transfer. However, there have been very few studies of countercurrent gas flow effects on the film thickness. In this paper, the fallingfilm film thickness with and without liquid-gas interfacial shear stress due to the countercurrent gas flow was studied. A twophase empirical correlation is used to solve the momentum equation. Calculation results were compared with available experimental data in literatures for validation. Reasonable agreement was achieved. Thus, the two-phase correlation for predicting shear stress of a thin film flow inside a vertical rectangular channel has been extended to a new type of flow. Effects of film Reynolds number, gas velocity, and gas-channel equivalent hydraulic diameter on the film thickness were studied. It is shown that the countercurrent gas flow thickened the falling film. The increased film thickness can shift the mode transitional Reynolds number and reduce the heat transfer coefficient, corroborating the conjecture in our earlier work

Recent Advances in Technology, Strategy and Application of Sustainable Energy Systems

The global COVID-19 pandemic has had strong impacts on national and international freight, construction and tourism industry, supply chains, and has resulted in a rapid decline in the demand for traditional energy sources. In fact, research has outlined that urban areas depend on global supply chains for their day-to-day basic functions, including energy supplies, food and safe access to potable water. The disruption of global supply chains can leave many urban areas in a very vulnerable position, in which their citizens may struggle to obtain their basic supplies, as the COVID-19 crisis has recently shown. Therefore, solutions aiming to enhance local food, water and energy production systems, even in urban environments, have to be pursued. The COVID-19 crisis has also highlighted in the scientific community the problem of people’s exposure to outdoor and indoor pollution, confirmed as a key element for the increase both in the transmission and severity of the contagion, on top of involving health risks on their own. In this context, most nations are going to adopt new preferential policies to stimulate the development of relevant sustainable energy industries, based on the electrification of the systems supplied by renewable energy sources as confirmed by the International Energy Agency (IEA). Thus, while there is ongoing research focusing on a COVID 19 vaccine, there is also a need for researchers to work cooperatively on novel strategies for world economic recovery incorporating renewable energy policy, technology and management. In this framework, the Sustainable Development of Energy, Water and Environment Systems (SDEWES) conference provides a good platform for researchers and other experts to exchange their academic thoughts, promoting the development and improvements on the renewable energy technologies as well as their role in systems and in the transition towards sustainable energy systems. The 14th SDEWES Conference was held in Dubrovnik, Croatia. It brought together around 570 researchers from 55 countries in the field of sustainable development. The present Special Issue of Energies, specifically dedicated to the 14th SDEWES Conference, focuses on four main fields: energy policy for sustainable development, biomass energy application, building energy saving, and power plant and electric systems