Variation Of Heat Generation Research Articles

Simulation of Friction Stir Welding of AZ31 Mg Alloys.

Friction stir welding has been extensively applied for the high-quality bonding of Mg alloys. The welding temperature caused by friction and plastic deformation is essential for determining the joint characteristics, especially the residual stress and weld microstructure. In this work, a modified moving heat source model was proposed by considering the variations in heat generation caused by friction shear stress at both the side and bottom surfaces of the tool. The application of this model was further extended to the entire welding process, especially in the plunging stage. The relative errors between the experimental and simulated peak temperatures at characteristic points were small, with a maximum of 10%, thereby validating the model for accurate temperature prediction. Furthermore, the influence of welding and rotational speed on temperature fields was systematically investigated. At relatively low welding and rotational speeds, the welding temperature increased significantly with either an increase in rotational speed or a decrease in welding speed. However, this effect gradually diminished at higher welding and rotational speeds. These results provide some valuable guidelines for controlling heat generation to improve the quality of Mg alloy welds.

Elucidating the in-process interfacial friction regime and thermal responses during inertia friction welding of dissimilar superalloys

Inertia friction welding (IFW) is a robust joining technique, particularly for hybrid structures composed of similar or dissimilar alloys. The highly transient thermal responses during friction heating produce variations in heat generation and temperature distribution, which are crucial for designing and controlling the IFW process. This study establishes a finite element (FE) model of the IFW process for dissimilar superalloys and investigates the transition of the interfacial friction regime and its impact on the transient thermal responses. The in-process state variables, including the frictional stress and heat flux, along with their spatial distributions at the welding interface, are obtained through FE simulations. The predicted results indicate that the transient transition of the friction regime produces two Coulomb friction zones accompanied by a shear friction zone. To capture the transient evolution of the friction regime, a novel phenomenological formula is developed. This model accurately predicts the shrinkage and disappearance of the two Coulomb friction zones and the enhancement of the shear friction zone from the initial 0.42 R0–0.87 R0 (where R0 is the workpiece radius) to the entire interface during the IFW process. The variations in interfacial heat flux, frictional stress, and temperature caused by the transition of the friction regime are comprehensively analyzed. Our results reveal that the transition from the Coulomb friction regime to shear friction regime at the interface is beneficial for temperature homogenization at the welding interface. The FE simulation results are validated against published experimental measurements, which confirms the accuracy and reliability of the FE model.

On the Relations between Lithium-Ion Battery Reaction Entropy, Surface Temperatures and Degradation

Understanding and mitigating the degradation of batteries is important for financial as well as environmental reasons. Many studies look at cell degradation in terms of capacity losses and the mechanisms causing them. However, in this study, we take a closer look at how degradation affects heat sources in batteries, thereby requiring dynamic cooling strategies for battery systems throughout the battery life. In this work, we have studied and compared reversible (entropy-related) and non-reversible heat sources in a commercial LCO-graphite lithium-ion battery (LIB) alongside measuring the surface temperature as a function of the State of Health (SoH). In addition, we studied the effect of different thermal management strategies on both degradation and cooling efficiency. We found that entropic heating plays a major role in overall heat generation. This causes large variations in heat generation and battery temperature over both State of Charge (SoC) and charge versus discharge. The maximum battery temperature increases when the cell degrades as irreversible heat generation increases. Temperature variations over the cell thickness are substantial and increase drastically when the cell degrades. In addition, significant increases in thickness were observed as a result of cell degradation. Furthermore, cycling at elevated temperatures resulted in a larger thickness increase with significant gas production.

Thermal-hydraulic analysis of fuel rod of a TRIGA Mark II research reactor

In this work, the feasibility of employing “Single Flow Channel Analysis” technique for obtaining the thermal-hydraulic behavior of a TRIGA Mark II research reactor has been studied. Two different simulation methods have been investigated for this purpose; one in which there is no variation in volumetric heat generation along the fuel axis and the other in which there is variation. A hot rod factor of 1.70 has been taken. Results obtained from simulation methods have been compared with both theoretical results and experimental data provided by the manufacturers. Results show that data generated from both simulation methods are more accurate compared to theoretical calculations. Also, the simulation method exempting variation of heat generation has predicted maximum temperature of the fuel centerline just above 750 oC, which is sufficiently accurate. However, temperatures obtained at different axial and radial locations are not close to the experimental values. On the other hand, the simulation technique in which variation of heat generation exists has been able to provide temperature profiles inside the fuel rod and cladding surface almost identical to the experimental values. However, temperature profile of the fuel outer surface is found to be quite different from experimental values. Â

Exact Method for Annular Disc Fins with Heat Generation and Nonlinear Heating

An annular disc fin is a common choice to enhance heat from a cylindrical primary surface. In nuclear applications, heat transfer from the fin surface is due to convection and radiation and heat also generated in the fin. With radiation and heat generation, an analysis is presented. A closed-form analysis based on the differential transform method was established for fin heat transfer. As heat is generated, it is suggested to determine the fin heat transfer by an integral approach, and an integrodifferential formulation to the differential transform function was implemented newly and is the only way for calculating the heat transfer rate for the internal heat generation in the fin. This method is introduced in the literature for the first time for annular disc fins. The effects of heat generation on the fin performance parameters were studied under a design condition. A new scheme for the optimization study with variation of heat generation was carried out to provide a superior aspect of the thermal design of annular fins. For the simplification of analysis to a designer, approximate methods were also established for a design condition taken in the analysis.

Role of Threaded Tool Pin Profile and Rotational Speed on Generation of Defect Free Friction Stir AA 2014 Aluminium Alloy Welds

<p class="abstract">Influence of threads on tool pin and rotational speeds on defect occurrence in friction stir welding (FSW) of aluminum alloy AA 2014 T6 plates has been studied. The effect of FSW forces on the evolution of mechanistic defects, caused in turn through a variation in heat generation during the process has also been examined. In case of conical tool pin, relatively lower rotational speeds resulted in unbounded zones and micro defects while high speeds caused excessive flash, thereby resulting in surface defects and voids inside the weld. The FSW joints were defect-free at moderate speeds, hinting an optimum heat generation and flow. Reaction forces on the tool pin, in the welding direction, were correlated with the defect formation. Tools equipped with a threaded conical pin profile resulted in sound welds, irrespective of the tool rotational speeds in the entire range of 400 rpm - 2400 rpm. The threaded conical pin, with a relatively larger frictional area, may be contributing to higher levels of heat generation compared to a plain conical pin. Further, positive displacement of the hot plasticised material by the threads will carry away excess heat from the advancing-to-the-retracting side and simultaneously downwards, thus confining all heat within the weld zone.</p><p class="abstract"><strong>Defence Science Journal, Vol. 66, No. 1, January 2016, pp. 57-63, DOI: http://dx.doi.org/10.14429/dsj.66.8566</strong></p>

Thermal–electrochemical model for passive thermal management of a spiral-wound lithium-ion battery

Safe and reliable operation of a Li-ion battery requires control and often management of the thermal envelope. In this context, a two-dimensional, transient mathematical model comprising conservation of charges, species, and energy together with electroneutrality, constitutive relations and relevant initial and boundary conditions for a spiral-wound cylindrical Li-ion battery is derived and solved numerically for passive thermal management with and without a phase change material (PCM) at various galvanostatic discharge rates. Two-way coupling of the electrochemical and thermal equations of change is attained through heat generation terms and temperature-dependent physical properties. Within this framework, the electrochemical and thermal behavior is discussed in terms of edge effects arising from the design of the spiral-wound structure and variations in heat generation in the functional layers. In addition, the cell performance with passive thermal management through a PCM is shown to lower the overall temperature of the cell at discharge rates around 5 C-rates, provided the PCM layer is thick enough to provide cooling during the entire discharge. The model can be employed for wide-ranging parameter studies as well as multi-objective optimization of not only design parameters pertaining to the spirals but also, for example, for design of the thickness of the PCM layer.

CFD-Assisted Optimization of Chimneylike Flows to Cool an Electronic Device

Natural convection cooling provides a reliable, cost-effective, energy-efficient and noise-free method to cool electronic equipment. However, the heat transfer coefficient associated with natural convection mode is usually insufficient for electronic cooling and it requires enhancement. Chimneylike flows developed within the cabinets of electronic devices can provide better mass flow and heat transfer rates and can lead to greater cooling efficiency. Constraints in the design of natural convection cooling systems include efficiency of packing, aesthetics, and concerns of material reduction. In this paper, methods based on computational fluid dynamics are used to study the effects of parameters such as (1) vertical alignment of the slots, (2) horizontal alignment of slots, (3) area of slots, (4) differential slot opening, and (5) zonal variation in heat generation on natural convection cooling within such design constraints. Insights thus derived are found useful for designing an energy-efficient and ecofriendly cooling system for electronic devices.

Thermal Management of Electronic Chips in a Channel Using Input Power to Control Flow Velocity

In this research, thermal management of an electronic device using the input power is investigated numerically using the finite element method. The considered geometry consists of a horizontal channel with three volumetrically heated chips mounted on the bottom wall of the channel. The magnitude of the channel’s inlet velocity is varied with the variation of heat generation in the chips. The thermal characteristics of the system are presented, and compared with thermal characteristics of a system at a steady state condition. The effect of the Reynolds number and the oscillating period of the heat generation on the chips’ average temperature and Nusselt number is presented. The pressure drop in the channel is also calculated. The results indicated that the transient operating condition causes temperature to be higher than steady state by more than 45%, and difference between the transient and steady operations is reduced if the frequency is high. However, flow frequency has nearly no effect on the pressure drop in the channel.

Synchronization between temporal variation in heat generation, floral scents and pollinator arrival in the beetle‐pollinated tropical Araceae Homalomena propinqua

AbstractInflorescences of beetle‐pollinated plants, such as Araceae, show temporal heat generation, the role of which varies among plants. Homalomena propinqua is a common understory herb in the lowland dipterocarp forests of Borneo. Two species of beetle, Parastasia bimaculata Guerin (Scarabaeidae) and Dercetina sp. (Chrysomelidae), are known to visit inflorescences of this species and subsequently transfer its pollen. In this study, to examine the role of heat generation by inflorescences of H. propinqua, especially as an attractant of pollinators, measurements of the temperature of spadices, behavioral experiments with beetles and chemical analyses of floral scents were carried out. As a result, spadices of H. propinqua exhibited heat generation from 06:30 hours (dawn) until 09:30 hours on both the first and second days of flowering, and this paralleled the arrival of the beetle pollinators. Behavioral tests showed that both beetle pollinators were attracted to spadices significantly more than spathes. Floral scents of H. propinqua were composed of 18 compounds, the main one being 2‐butanol, a highly volatile low molecule compound. The amount of floral scents increased temporally between 07:00 hours and 08:00 hours on the first day of flowering, which was consistent with the arrival of pollinators and heat generation by the spadices. These results indicate that the heat generated by spadices may promote temporal volatilization of floral scents, especially highly volatile compounds such as 2‐butanol, and as a result temporally attracting beetle pollinators.

Are Cold Light Sources Really Cold?

A fiber optic light source is the central part of endoscopic surgery. However, the light generation process causes heat transmission from a source to tip of a scope. In this study, we measured the amount of heating and pathologic effects of direct contact with the tip of scopes on the small bowel in an experimental set-up. Temperature measurements were performed at the tip of 4 different scopes (Aesculap, Olympus, Karl Storz, and Richard Wolf), which were connected to either of 3 different xenon light sources (Olympus, Richard Wolf, Karl Storz). Temperatures at the outlet of light sources and the tip of fiber optic cables were measured as well. Tissue samples from the small bowel of a pig were obtained after exposing them to direct contact with the tip of the scopes or the fiber optic cable. The temperature measurements at the tip of the scopes varied between 60 degrees C and 100 degrees C (Celsius). The temperatures showed a wide variation according to the type of light source and fiber optic cable the scopes were connected to. The average temperature at the outlet of the light sources and the tip of fiber optic cables was 750 degrees C and 250 degrees C, respectively. The microscopic scores of the small bowel injury induced by exposition to the heat at the tip of the scopes were significantly high after 5 seconds of contact. Direct contact of the tip of the fiber optic cable caused total carbonization in the wall of the small bowel. Direct contact of the tip of the scope with small bowel may cause functional and cytologic injury even after short durations of exposure. Therefore, we do not recommend direct contact of scopes with the intra-abdominal organs to avoid heat injuries. In addition, this study also emphasizes the variation in heat generation at the tip of the scopes when used with a mismatching light source and fiber optic cable.

Genetic Algorithm Based Resistive Susceptor Design for Uniform Heating During the Induction Bonding Process

In this research work, cut mesh design optimization for the induction bonding process using genetic algorithms (GAs) is investigated to solve the problem of nonuniform heating, which leads to nonuniform temperature fields and temperature gradients exceeding the process window required for bonding. Cut patterns in the metal mesh can redirect the magnetically induced electric currents generated thus changing the temperature distribution. In this work, the heat generation model for determining current and heat generation distribution for a given coil and mesh size, coded as a Mathematica function, was coupled with a simple genetic algorithm. The cost function to be minimized by the GA was the ratio of the maximum heat generation in the mesh to the minimum heat generation. Two studies were performed with the GA-based design optimization: the first with a six sided square mesh and the second using a ten sided square mesh. The best cut mesh designs obtained from the GA were compared with the globally optimal designs, where available, and with the baseline mesh. The GA could not reach the global optima due to the complex nature of the design search space. However, it was determined that the GA was able to reduce the variations in heat generation in the mesh for all cases and delivered significant improvements over the baseline case in reasonable computational time, evaluating less than 2% of the possible cut mesh patterns. Thus the genetic algorithm based design optimization was proven to be a computationally efficient tool in the generation of good cut mesh designs for the induction bonding process.

Hydrological distortion of heat flow in sedimentary basins

Heat flow in sedimentary basins shows major variations both laterally and vertically, whereas, in contrast, measurements in crystalline rocks usually show no vertical variation and only lateral variations that are appropriate to thermal refraction and variations in heat generation. The thermal characteristics of basins vary widely. Some, such as the Paris Basin, show no evidence of anomalous variation in heat flow, but others, such as the North Sea Basin and the Western Canada Basin, show major variations that seem to be explainable only by widespread lateral movement of water in permeable aquifers. The drive for such water migration may be derived from contrasts in surface elevation, such as the Rocky Mountains, but such contrast does not provide hydraulic potential in a sub-sea environment. Simple models of wedge-shaped basins show that the flow of water in inclined aquifers is capable of producing anomalies on the scale of those observed. Because of the potential for distortion of heat flow in the sediments, it is more important, for tectonic and crustal interpretation, to measure the heat flow from the relatively impermeable basement.

Variation of heat generation, density and seismic velocity with rock type in the continental lithosphere : Rybach, L; Buntebarth, G TectonophysicsV103, N1–4, 20 March 1984, P335–344

Variation of heat generation, density and seismic velocity with rock type in the continental lithosphere : Rybach, L; Buntebarth, G TectonophysicsV103, N1–4, 20 March 1984, P335–344

The variation of heat generation, density and seismic velocity with rock type in the continental lithosphere

The petrophysical properties radioactive heat generation, compressional wave velocity and density are related to rock type in crystalline rocks. The cation fraction in the rock-forming minerals is applied to determine the relationships quantitatively. Heat generation exhibits considerable variation with rock type as well as with the geologic age of the rocks. Therefore, the relation between heat generation and rock type has been split into a relation for Phanerozoic rocks and another for Precambrian rocks which exhibit significantly lower heat generation (only 1 3 of that of Phanerozoic rocks). The interrelations between the petrophysical properties are applied to Fennoscandia (Precambrian terrane) and southern Bavaria, northern Alpine Foreland (Phanerozoic rocks) to estimate the heat generation by radioactivity in the crust and the heat flow density from the upper mantle.