scholarly journals Thermal effects of high energy and ultrafast lasers

2015 ◽  
Author(s):  
◽  
Nazia Afrin
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Heat Transport ◽  
Phonon Scattering ◽  
Heated Surface ◽  
High Energy ◽  
Electron Interaction ◽  
Energy Laser ◽  
High Energy Laser

Heat transfer describes the exchange of thermal energy, between physical systems depending on the temperature and pressure, by dissipating heat. The fundamental modes of heat transfer are conduction or diffusion, convection and radiation. Heat and mass transfer are kinetic processes that may occur and be studied separately or jointly. Studying them apart is simpler, but both processes are modeled by similar mathematical equation in the case of diffusion and convection. There are complex problems where heat and mass transfer processes are combined with chemical reactions, as in combustion. The resulting behavior of heat transport in microscale will be very different from macroscale heat transfer based on the averages taken over hundreds of thousands of grains (in space) and collision (in time). From the microscopic point of view, the process of heat transport is governed by phonon-electron interaction in metallic films and by phonon scattering in dielectric films, insulators and semi-conductors. For extremely heated surfaces by high energy laser pulse, it is very difficult to measure temperature of flux at the heated surface because of the unendurable capacity of the conventional sensors. Laser is the tool of choice when drill holes ranging in diameter from several millimeters to less than one micro-meter. Instead of having advanced melting and resolidification modeling process recently, the inherent uncertainties of the input parameters can directly cause unstable characteristics of the output results which means the parametric uncertainties may influence the characteristics of the phase change processes (melting and resolidification) which will affect the predictions of interfacial properties i.e., temperature, velocity and mainly the location of solid-liquid interface. All of those processes can be considered under high energy laser interaction with materials.

scholarly journals A novel internal heat recycling concept for reducing energy consumption and increasing flux through three-stage air-gap–water-gap membrane distillation system

2020 ◽  
Vol 20 (7) ◽  
pp. 2858-2874
Author(s):  
Mostafa Abd El-Rady Abu-Zeid ◽  
Xiaolong Lu ◽  
Shaozhe Zhang
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Energy Consumption ◽  
Heat And Mass Transfer ◽  
Waste Heat ◽  
Internal Heat ◽  
High Energy ◽  
Membrane Distillation ◽  
Air Gap ◽  
Air Gap Membrane Distillation

Abstract The low flux and high energy consumption problems of the conventional three-stage air-gap membrane distillation (AG-AG-AG)MD system caused by the low temperature difference between hot and cold feed at both sides of the membrane and high boundary layer thickness were solved successfully by replacing one of the three stages of air gaps by a water gap. The novel three-stage air-gap–water-gap membrane distillation (AG-AG-WG)MD system reduced energy consumption and increased flux due to efficient internal heat recycling by virtue of a water-gap module. Heat and mass transfer in novel and conventional three-stage systems were analyzed theoretically. Under a feed temperature of 45 °C, flow rate of 20 l/h, cooling temperature of 20 °C, and concentration of 340 ppm, the (AG-AG-WG)MD promoted flux by 17.59% and 211.69%, and gained output ratio (GOR) by 60.57% and 204.33% compared with two-stage (AG-WG)MD and one-stage AGMD, respectively. This work demonstrated the important role of a water gap in changing the heat and mass transfer where convection heat transfer across the water gap is faster by 24.17 times than conduction heat transfer through the air gap. The increase in flux and GOR economized the heating energy and decreased waste heat input into the system. Additionally, the number of MD stages could increase the achieving of a high flux with operation stability.

3-D Inverse Heat Transfer in a Composite Target Subject to High-Energy Laser Irradiation

2011 ◽  
Author(s):  
Jianhua Zhou ◽  
Yuwen Zhang ◽  
J. K. Chen ◽  
Z. C. Feng
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Heat Conduction Problem ◽  
High Energy ◽  
Inverse Heat Conduction Problem ◽  
Back Surface ◽  
Composite Target ◽  
Inverse Heat Transfer ◽  
Energy Laser ◽  
High Energy Laser

A new numerical model is developed to simulate the 3-D inverse heat transfer in a composite target with pyrolysis and outgassing effects. The gas flow channel size and gas addition velocity are determined by the rate equation of decomposition chemical reaction. The thermophysical properties of the composite considered are temperature-dependent. A nonlinear conjugate gradient method (CGM) is applied to solve the inverse heat conduction problem for high-energy laser-irradiated composite targets. It is shown that the front-surface temperature can be recovered with satisfactory accuracy based on the temperature/heat flux measurements on the back surface and the temperature measurement at an interior plane.

scholarly journals Characteristics of supercritical heat transfer during filmboiling of nanofluids on a vertical heated wall

2018 ◽  
pp. 29-35
Author(s):  
А. Avramenko ◽  
M. Kovetskaya ◽  
A. Tyrinov ◽  
Yu. Kovetska
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Mathematical Model ◽  
Mass Transfer ◽  
Heat Flux ◽  
High Temperature ◽  
Heat And Mass Transfer ◽  
Heated Surface ◽  
Heated Wall ◽  
Film Boiling

Nanofluid using for intensification of heat transfer during boiling are analyzed. The using boiling nanofluids for cooling high-temperature surfaces allows significantly intensify heat transfer process by increasing the heat transfer coefficient of a nanofluid in comparison with a pure liquid. The properties of nanoparticles, their concentration in the liquid, the underheating of the liquid to the saturation temperature have significant effect on the rate of heat transfer during boiling of the nanofluid. Increasing critical heat flux during boiling of nanofluids is associated with the formation of deposition layer of nanoparticles on heated surface, which contributes changing in the microcharacteristics of heat exchange surface. An increase in the critical heat flux during boiling of nanofluids is associated with the formation of a layer of deposition of nanoparticles on the surface, which contributes to a change in the microcharacteristics of the heat transfer of the surface. Mathematical model and results of calculation of film boiling characteristics of nanofluid on vertical heated wall are presented. It is shown that the greatest influence on the processes of heat and mass transfer during film boiling of the nanofluid is exerted by wall overheating, the ratio of temperature and Brownian diffusion and the concentration of nanoparticles in the liquid. The mathematical model does not take into account the effect changing structure of the heated surface on heat transfer processes but it allows to evaluate the effect of various thermophysical parameters on intensity of deposition of nanoparticles on heated wall. The obtained results allow to evaluate the effect of nanofluid physical properties on heat and mass transfer at cooling of high-temperature surfaces. The using nanofluids as cooling liquids for heat transfer equipment in the regime of supercritical heat transfer promotes an increase in heat transfer and accelerates the cooling process of high-temperature surfaces. Because of low thermal conductivity of vapor in comparison with the thermal conductivity of the liquid, an increase in the concentration of nanoparticles in the vapor contributes to greater growth in heat transfer in the case of supercritical heat transfer.

Three-Dimensional Inverse Heat Transfer in a Composite Target Subject to High-Energy Laser Irradiation

2012 ◽  
Vol 134 (11) ◽  
Author(s):  
Jianhua Zhou ◽  
Yuwen Zhang ◽  
J. K. Chen ◽  
Z. C. Feng
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Heat Conduction Problem ◽  
High Energy ◽  
Inverse Heat Conduction Problem ◽  
Back Surface ◽  
Composite Target ◽  
Inverse Heat Transfer ◽  
Energy Laser ◽  
High Energy Laser

A new numerical model is developed to simulate the 3D inverse heat transfer in a composite target with pyrolysis and outgassing effects. The gas flow channel size and gas addition velocity are determined by the rate equation of decomposition chemical reaction. The thermophysical properties of the composite considered are temperature-dependent. A nonlinear conjugate gradient method (CGM) is applied to solve the inverse heat conduction problem for high-energy laser-irradiated composite targets. It is shown that the front-surface temperature can be recovered with satisfactory accuracy based on the temperature/heat flux measurements on the back surface and the temperature measurement at an interior plane.

Study of Heat and Mass Transfer in MgCl2/NH3 Thermo-Chemical Batteries

2016 ◽  
Author(s):  
Seyyed Ali Hedayat Mofidi ◽  
Kent S. Udell
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Energy Storage ◽  
Phase Change ◽  
Heat And Mass Transfer ◽  
Waste Heat ◽  
Reaction Rates ◽  
High Energy ◽  
Solid Matrix ◽  
Dominant Factor

Intermittency of sustainable energy or waste heat availability calls for energy storage systems such as thermal batteries. Thermo-chemical batteries are particularly appealing for energy storage applications due to their high energy densities and ability to store thermal energy as chemical energy for long periods of time without any energy loss. Thermo-chemical batteries based on a reversible solid-gas (MgCl2 - NH3) reactions and NH3 liquid-gas phase change are of specific interest since the kinetics of absorption are fast and the heat transfer rates for liquid — vapor phase change are high. Thus, a thermo-chemical battery based on reversible reaction between magnesium chloride and ammonia was studied. Experimental studies were conducted on a reactor in which temperature profiles within the solid matrix and pressure and flow rates of gas were obtained during charging processes. A numerical model based on heat and mass transfer within the salt and salt-gas reactions was developed to simulate the absorption processes within the solid matrix and the results were compared with experimental data. The studies were used to determine dominant heat and mass transfer processes within the salt. It is shown that for high permeability materials, heat transfer is the dominant factor in determining reaction rates. However increasing thermal conductivity might decrease permeability and reduce reaction rates. The effect of constraining mass flow rate on the temperature and reaction propagation is also studied. These results show that optimized heat and mass transfer within the solid-gas reactor will lead to improved performance for heating and air conditioning applications.

Mechanisms of Heat Transfer to Liquid Films in the Manifold of Port-Injected Petrol Engines

1993 ◽  
Vol 207 (3) ◽  
pp. 211-222 ◽  
Author(s):  
N Ladommatos
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Heated Surface ◽  
Air Flow ◽  
Liquid Films ◽  
Inlet Valve ◽  
Automotive Engine ◽  
Air Stream ◽  
Transfer Mechanisms

Results are presented from flow-rig tests in which water from an automotive engine injector was sprayed on to a small heated surface in the presence of both steady and pulsative air flow. The injection was intermittent and synchronized with the pulsating air flow. The aim of the tests was to improve understanding of some of the basic heat and mass transfer mechanisms that occur in port-injected sparkignition engines where fuel is usually sprayed on to the back of the inlet valve. The main observations focused on the heat transfer to the film and the entrainment of the spray and film by the air stream.

scholarly journals An Experimental Study of Heat and Mass Transfer in a Falling Liquid Film Evaporation into a Crossflow of Neutral Gas

2020 ◽  
Vol 7 (1) ◽  
pp. F30-F38
Author(s):  
V. K. Lukashov ◽  
Y. V. Kostiuchenko ◽  
S. V. Timofeev ◽  
M. Ochowiak
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Flow Rate ◽  
Liquid Flow Rate ◽  
Heated Surface ◽  
Mass Transfer Process ◽  
Transfer Coefficients ◽  
Average Heat ◽  
Neutral Gas

The work is devoted to the study of heat and mass transfer in a liquid film flowing down on a heated surface under conditions of evaporation into a crossflow of a gas neutral with respect to the liquid. The work aimed to experimentally determine the average heat transfer coefficients from a heated surface to the film, heat transfer and mass transfer from the film to the gas flow and to establish their dependence on the input parameters of the heat and mass transfer process. To achieve this goal, an experimental setup was created, and a research technique was developed based on the proposed mathematical model of the heat and mass transfer process. The results of the study showed that the dependences of the average heat and mass transfer coefficients on the initial liquid flow rate are extreme with the minimum values of these coefficients at the liquid flow rate, which corresponds to the critical value of the Reynolds criterion Re l cr ≈ 500, which indicates a transition from the laminar falling films to turbulent mode under the considered conditions. The dependences of the heat and mass transfer coefficients on other process parameters for both modes of film falling are established. A generalization of the experimental data made it possible to obtain empirical equations for calculating these coefficients. Keywords: heat and mass transfer, cross flow, film apparatus, heat and mass return coefficient, neutral gas.

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