Experimental approaches for probing heat transfer and energy conversion at the atomic and molecular scales

2020 ◽  
pp. 8-1-8-18
Author(s):  
Longji Cui ◽  
Edgar Meyhofer ◽  
Pramod Reddy
Keyword(s):  
Heat Transfer ◽  
Energy Conversion ◽  
Experimental Approaches

Atomic-level, Energy-conversion Heat Transfer

2021 ◽  
Author(s):  
Massoud Kaviany
Keyword(s):  
Heat Transfer ◽  
Energy Conversion ◽  
Optical Phonon ◽  
Atomic Level ◽  
Atomic Scale ◽  
Energy Conditions ◽  
Spectral Energy ◽  
Level Energy ◽  
High Entropy ◽  
Low Entropy

Abstract Heat is stored in quanta of kinetic and potential energies in matter. The temperature represents the equilibrium and exciting occupation (boson) of these energy conditions. Temporal and spatial temperature variations and heat transfer are associated with the kinetics of these equilibrium excitations. During energy-conversion (between electron and phonon systems), the occupancies deviate from equilibria, while holding atomic-scale, inelastic spectral energy transfer kinetics. Heat transfer physics reaches nonequilibrium energy excitations and kinetics among the principal carriers, phonon, electron (and holes and ions), fluid particle, and photon. This allows atomic-level tailoring of energetic materials and energy-conversion processes and their efficiencies. For example, modern thermal-electric harvesters have transformed broad-spectrum, high-entropy heat into a narrow spectrum of low-entropy emissions to efficiently generate thermal electricity. Phonoelectricity, in contrast, intervenes before a low-entropy population of nonequilibrium optical phonons becomes a high-entropy heat. In particular, the suggested phonovoltaic cell generates phonoelectricity by employing the nonequilibrium, low-entropy, and elevated temperature optical-phonon produced population–for example, by relaxing electrons, excited by an electric field. A phonovoltaic material has an ultra-narrow electronic bandgap, such that the hot optical-phonon population can relax by producing electron-hole pairs (and power) instead of multiple acoustic phonons (and entropy). Examples of these quanta and spectral heat transfer are reviewed, contemplating a prospect for education and research in this field.

The Thermodynamic Evaluation and Optimization of Fuel Cell Systems

2006 ◽  
Vol 3 (2) ◽  
pp. 155-164 ◽  
Author(s):  
N. Woudstra ◽  
T. P. van der Stelt ◽  
K. Hemmes
Keyword(s):  
Heat Transfer ◽  
Fuel Cells ◽  
High Temperature ◽  
Fuel Cell ◽  
Energy Conversion ◽  
System Optimization ◽  
Fuel Conversion ◽  
Cell Systems ◽  
Electrochemical Conversion ◽  
Conversion Efficiencies

Energy conversion today is subject to high thermodynamic losses. About 50% to 90% of the exergy of primary fuels is lost during conversion into power or heat. The fast increasing world energy demand makes a further increase of conversion efficiencies inevitable. The substantial thermodynamic losses (exergy losses of 20% to 30%) of thermal fuel conversion will limit future improvements of power plant efficiencies. Electrochemical conversion of fuel enables fuel conversion with minimum losses. Various fuel cell systems have been investigated at the Delft University of Technology during the past 20 years. It appeared that exergy analyses can be very helpful in understanding the extent and causes of thermodynamic losses in fuel cell systems. More than 50% of the losses in high temperature fuel cell (molten carbonate fuel cell and solid oxide fuel cell) systems can be caused by heat transfer. Therefore system optimization must focus on reducing the need for heat transfer as well as improving the conditions for the unavoidable heat transfer. Various options for reducing the need for heat transfer are discussed in this paper. High temperature fuel cells, eventually integrated into gas turbine processes, can replace the combustion process in future power plants. High temperature fuel cells will be necessary to obtain conversion efficiencies up to 80% in the case of large scale electricity production in the future. The introduction of fuel cells is considered to be a first step in the integration of electrochemical conversion in future energy conversion systems.

Numerical Modeling for the Energy Conversion and Thermal Transmission Accompanying the Process of Oily Cuttings Agitation

2016 ◽  
Author(s):  
Zhipeng Sun ◽  
Hongwu Zhu ◽  
Jian Hua
Keyword(s):  
Heat Transfer ◽  
Energy Conversion ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Solid Phase ◽  
Conductive Heat ◽  
Heat Transmission ◽  
Gas Reservoirs ◽  
Coupling Approach ◽  
Solid Motion

As a kind of unconventional gas reservoirs, shale gas reservoirs are full of potential to develop and have attracted global attention. Accompanying the exploiting of shale gas, a large amount of drilling cuttings contaminated by the oil-based drilling fluid are generated inevitably. How to deal with the drilling cuttings in a environmental-friendly way is tough especially for offshore oilfield. So it is important to investigate this aspect deeply and develop methods to clean the contaminated drilling cuttings. As is known to all, the thermal desorption technology has outstanding performance in oily cuttings cleaning. This paper bases on a kind of mechanical-thermal cuttings cleaning apparatus where the contaminated drilling cuttings are heated up by friction heat produced by the friction between the cuttings and the agitating vanes. And the harmful substance is separated from the cuttings in the agitated and high temperature flow field. This thesis investigates the fundamental of the energy conversion in the frictional process, infer formulas analyzing the thermo-physical phenomena and quantitatively model the energy conversion and thermal transmission accompanying the friction. Firstly, the principle of heat transfer and the law of conservation of energy are employed to investigate the natural law of the energy conversion in the frictional process. Based on the investigation, taking the liquid bridge between the oily cuttings and the agitating vane into account, this paper deduces the physical equations and the frictional energy model to calculate the total frictional heat, heat density and temperature distribution. Following up the frictional model, in the Eulerian-Lagrangian coupling framework, this paper develops a parallel numerical platform of computational fluid dynamics combined with discrete element method (CFD-DEM). In the coupling approach, the gas motion is solved at the computational grid level while the solid motion is resolved at the particle-scale level. Furthermore, the coupling approach is extended with the frictional energy model. The numerical platform can calculate the dense gas-solid motion in the fluidizing apparatus, the convective heat transfer between gas and solid phase, and the conductive heat transfer between particles. Based on the platform, the mechanical-thermal energy conversion and the convective heat transfer between gas and oily cuttings, and the conductive heat transfer between cuttings and the agitating vanes are investigated. Meanwhile an experiment is conducted. By comparing the numerical results with the experiment data, the paper can come to the conclusion that how to dispose the nonlinear parameters such as the friction contact area, the friction coefficient and the normal pressure is the key to accurately model the energy conversion and the heat transmission. What’s more, it can be understood that the convective heat transfer between gas and solid phase play an important role in the heat transmission.

Improved Heat Transfer Using Micro-Structures in Trifold Solar Energy Conversion Systems

2014 ◽  
Vol 659 ◽  
pp. 417-420
Author(s):  
Aristotel Popescu ◽  
David Pfund ◽  
Abel Hernandez-Guerrero ◽  
Ema Carmen Panaite ◽  
Ana Georgiana Lupu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Solar Energy ◽  
Energy Conversion ◽  
Renewable Energy Sources ◽  
Solar Energy Conversion ◽  
Thermal Systems ◽  
Heat Transfer Augmentation ◽  
Flow And Heat Transfer ◽  
Energy Conversion Systems ◽  
Micro Structures

The worldwide renewable energy sources harvesting grew recently at rates of 10–60% annually for many technologies, due to improvements made in all areas. In solar energy conversion, an improvement recently presented in literature is the hybrid system that provides both electricity and thermal energy for domestic applications. For the trifold PV-TE-DHW system, the electrical conversion efficiency is increased by using a thermoelectric (TE) module. This paper proposes the use of micro-channeled heat exchangers at both hot and cold sides of the TE module to improve the heat exchange from the working fluids. The authors developed prior works and published papers in the area of fluid flow and heat transfer in microstructures, heat transfer augmentation, and in solar thermal systems. Results obtained show an improved efficiency energy transfer.

scholarly journals Parametric study on hydrothermal properties of condensing flow in microtube heat exchangers using numerical and experimental approaches

2021 ◽  
Author(s):  
Abdolali K Sadaghiani
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Bubble Dynamics ◽  
Heat Transfer Fluid ◽  
Interface Shear ◽  
Improve Energy Efficiency ◽  
Experimental Approaches ◽  
Flow Heat ◽  
Flow Condensation ◽  
Flow Map

Microchannels have increasingly been used to miniaturize heat transfer equipment, improve energy efficiency, and minimize heat transfer fluid inventory. A fundamental understanding of condensation in microscale will yield far-reaching benefits for the different areas of industry. In this study, microtubes with inner diameters of 250, 500, 600, and 900 µm were used to investigate the effect of microtube diameter, inlet quality, and mass flux on the liquid/vapor interface near the wall boundaries in condensing flow. After validation with the experimental results, a transient numerical model (based on the volume of fluid approach) was developed to investigate the hydrothermal properties of condensing such as bubble dynamics, flow map transitions, transient interface shear force, and temperature on flow condensation performance in terms of heat transfer coefficient and pressure drop. The liquid film thickness, slug velocity, and location of transition from annular flow to slug flow inside the microtube were characterized for different microtubes, and the resultant alteration in condensation flow heat transfer and pressure drop is discussed in detail. The obtained results indicated that the interfacial characteristics of condensing flow in microtubes with hydraulic diameters lower than 500µm are majorly different from those with D>500µm.

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