Papers by Keyword: Heat Flux

Abstract: Space heating and cooling using geothermal heat exchangers is a promising environmentally friendly green energy solution. Modeling these energy storage systems is crucial for optimizing their design and operation. In this context, the present study consists of numerically investigating the effects of various physical properties, including thermal conductivity, density, and specific heat capacity of each material, as well as flow velocity, on the process of heat transfer in vertical geothermal heat exchangers using coaxial pipes to optimize their energy performance. Numerical simulations were carried out using Gambit-Fluent software. Different materials that make up the coaxial heat exchanger structure studied were tested to highlight their effects on the progress of heat flux and temperature. Thermal and fluid mechanics aspects were also studied. At the end of this study, a comparative analysis was carried out using the U-tube geothermal heat exchanger. The results indicate that the heat exchanger using a coaxial tube demonstrates superior thermal efficiency compared to the U-tube configuration. It has been found that using a low velocity with an appropriate selection of tube, grout, and soil materials results in enhanced dynamic exchanges, thereby enhancing the thermal efficiency of the geothermal exchanger.

Abstract: Self-propagating intermediate temperature synthesis (SIS) is a process that utilizes exothermic reactions to initiate and maintain component combustion so as to produce low porosity values and high hardness. It is necessary to know about the heat transfer phenomenon because SIS has a weakness, namely the high exothermic rate and very fast combustion rate which requires a high level of control. In addition, compression or compaction needs to be done because this method is expected to produce a homogeneous particle density distribution. The phenomenon of heat transfer and pressure that occurs in the SIS process is a simplification of the self-propagating high-temperature synthesis (SHS) process, which can be simulated and analyzed using engineering software based on finite element analysis. Stress simulation that occurs with the addition of weight percent titanium 5%, 10% and 20% using a pressure of 171 MPa and produces a normal stress. The heat transfer simulation that occurs uses a temperature of 750 ^°C, 850 °C, and 950 °C with a processing time of 2 hours with variations in the addition of weight percent titanium 5%, 10%, and 20% which results in an effect on heat flux and temperature distribution. Samples that were given the addition of 20% titanium by weight were given a pressure of 171 MPa to produce a normal stress of-230.44 MPa with the lowest porosity value of 22.63%. Samples processed at 850 °C with the addition of 10% weight percent titanium produced the lowest heat flux value of 0.0027220 W/m².

Abstract: Provides information about the results of the evaluation of anti-icing properties of coatings. It is shown, that the hysteresis of wetting of the superhydrophobic surface based on the developed composition is 3,7 degrees. The critical angle of rolling of a drop of water from an inclined surface is determined. The results of the evaluation of the kinetics of freezing of a water droplet on a superhydrophobic surface are given. It is shown, that in the initial period there is a transfer of heat from the surface to a drop of water. Then there is a movement of the freezing front from the substrate upwards.

Abstract: Non-equilibrium molecular dynamics simulations have been employed to study the explosive boiling phenomena of water over a hot copper plate. The molecular system was comprised of three sections: solid copper wall, liquid water, and water vapor. A few layers of the liquid water were placed on the solid Cu surface. The rest of the simulation box was filled with water vapor. Initially, the water molecules were equilibrated by using Berendsen thermostat at 298 K. Then heat was given to the copper plate at different temperatures so that explosive boiling occurs. After achieving the equilibrium by performing the previous two steps, the liquid water at 298 K is suddenly dropped on the hot plate. NVE ensemble was used in the simulation and the temperature of the copper plate was controlled to different temperatures with phantom atom thermostat. Four temperatures (400K, 500K, 650 K and 1000K) were taken to study the explosive boiling. The simulation results show that, the explosive boiling temperature of water on Cu plate is 500 K temperature. At this point, the energy flux was found 1.79x10⁸ J/m³ which is very promising with the experimental results. Moreover, if the temperature of the surface was increased the explosive boiling occurred at a faster rate. The simulation results also show that explosive boiling occurs earlier for the hydrophilic surface than hydrophobic surface as for the hydrophilic surface the water attracted the Cu plate more than the hydrophobic surface and so the amount of energy transfer is more for the hydrophilic surface.

Abstract: Magnetohydrodynamics (MHD) flow of Casson fluid over a curved stretching surface with the effects of heat and mass flux conditions are studied. Casson fluid is one of the non-Newtonian fluid. Human blood is taken as example of Casson fluid. The flow, heat transfer and the mass transfer characteristics are found by a curved stretching sheet with flux conditions. The governing partial differential equations are converted into nonlinear ordinary differential using similarity transformations and are solved using the Runge-Kutta Fourth order method along with shooting technique. The effects of pertinent governing parameters on the fluid velocity, the temperature and the concentration are shown with help of the graphs. The Skin frication coefficient and the Nusselt number are calculated numerically. The present results have been good agreement when compared with existing results under some special cases.

Abstract: ZrC-20vol.%MoSi₂ (ZM) composite coating was fabricated by vacuum plasma spray and the ablation resistance was assessed using plasma flame under low (1.94 MW/m²) and high (3.01 MW/m²) heat fluxes, respectively. Results showed that the ultimate surface temperatures of ZM coating were about 2100 °C and 2400 °C, respectively. ZM coating exhibited good ablation resistance at low heat flux, which benefited from the low evaporation of SiO₂ and the diffusion of Si derived from MoSi₂ decomposition. However, bubble-burst event took place under high heat flux. The different ablation behaviors of ZrC-MoSi₂ coating were analyzed, which might contribute to the application of ultra-high temperature ceramic coatings.

Abstract: This paper presents the optimal design of vent pipe in a fire station by using design of experiments and analytical method of heat transfer theory. In order to calculate formulation without using tables, equations in terms of temperature are developed for five air properties such as specific heat, thermal conductivity, kinematic viscosity, density and Prandtl number. It is shown that the equations accurately approximate the variations of air properties in terms of temperature. Series of design analysis are performed under considering the process parameters such as inlet temperature, pipe diameter and heat transfer rate. Orthogonal arrays of L₂₇ are used. The signal-to-noise (S/N) and analysis of variance (ANOVA) are utilized to determine the effect of parameters on objective functions, surface temperature and outlet temperature. From the results it is clear that inlet temperature is prominent on objective function.

Abstract: In this paper, a report is given on an experimental study of the combustion characteristics of six bundle lithium-ion batteries in a calorimeter. Several parameters including mass loss, heat release rate, surface temperature and heat flux distribution were measured to evaluate the hazards. The experimental results show that the lithium-ion batteries undergo fierce combustion processes. The total mass loss of six lithium-ion batteries fire is 67.8g, and the effective heat of the fire is 7.06 kJ/g. The highest temperature of the batteries fire is 816.9 °C and the maximum heat flux is 0.68 kW/m².The results provide scientific basis for the development of fire protection measures during the usage, storage and distribution of primary lithium batteries.

Abstract: Experimental studies of concrete in fire or at elevated temperature have traditionally given relatively little scientific attention to quantifying the severity, and to some extent reproducibility, of the thermal boundary conditions imposed on specimens during testing. This paper examines the heat transfer fundamentals of fire testing when controlling the time-history of temperature inside a furnace (or oven), versus controlling the time-history of incident radiant heat flux at a specimen’s exposed surface. The thermal boundary conditions of a concrete specimen during fire testing are fundamentally based on conservation of energy, and thus typically formulated in terms of heat fluxes. While from the standpoint of concrete fire behaviour the aim is typically only to gauge the distribution of temperatures inside concrete; this is rarely explicitly acknowledged or quantified during concrete fire testing. This shows that continued unexamined use of varied heating techniques presents a serious threat to harmonization of the thermal boundary conditions imposed during concrete testing. The current work proposes adopting test control by in-depth temperature distributions or net heat fluxes for a rigorous comparison of the thermal boundary conditions imposed on test specimens when using different heating techniques.

Abstract: Heat flux between molten metal and casting rolls plays a key role in improving the quality of the strip, studying on the interfacial heat flux has very important theoretical significance and practical value. According to the contact form and the heat flux characteristics of molten metal and casting rolls in twin-roll strip casting process, a set of measuring equipments has been developed, which are used to measure the heat flow of the interface between the molten metal and solid, and a relevant software system has been exploited to acquire and analyze the experiment data. Using the method of combining experimental and numerical computation, we analyze the influence of pouring temperature on the contact interface heat flux. The experimental results show that the higher the pouring temperature , the greater the summit of heat flux density and the shorter time to the summit heat flux are, but when the pouring temperature reaches a certain critical value, the summit of heat flux will decrease with the increase of pouring temperature.