Non-uniform Heat Research Articles

Study of multi-frequency heating based on the nonlinear response characteristics of magnetron to improve uniformity

The majority of microwave ovens on the market are powered by magnetrons, which can only produce a narrow-band frequency that has a large peak, resulting in poor uniformity. A method is proposed to improve nonuniform heating based on nonlinear response characteristics of the magnetron to produce multi-frequency. First, a multi-physics model of microwave heating is established to realize the calculation of multi-frequency heating. Second, a multi-frequency heating experimental system based on the characteristics of the magnetron is built and verified with the calculated results. The results show that the calculated results are in good agreement with the experimental results. Finally, based on the multi-physics model, the influences of different parameters, such as frequency intervals, cavity size, location of the object to be heated and material properties, on microwave heating uniformity have also been discussed. The results show that the method adopted in this paper is feasible, and the heating uniformity of microwaves is improved.

Numerical Analysis of Heating Technique in Corium Melt Pool Convection Flow Field & Thermal Interaction in a Volumetrically Heated Molten Pool

In-Vessel Retention (IVR) is one of the existing strategies of severe accident management of LWR, which intends to stabilize and isolate corium & fission products inside the reactor pressure vessel (RPV) and primary containment structure. Since it has become an important safety objective for nuclear reactors, it is therefore needed to model and evaluate relevant phenomena of IVR strategy in assessing safety of nuclear power reactors. One of the relevant phenomena during accident progression in the oxidic pool is non-uniform high heat generation occurring at large scale. Consequently, direct experimental studies at these scales are not possible. The role computer codes and models are therefore important in order to transpose experimental results to reactor safety applications. In this paper, the state-of-the-art ANSYS FLUENT CFD code is used to simulate Non-uniform heat generation in the lower plenum by the application of Cartridge heating under severe accident conditions to derive the basic accident scenario. However, very few studies have been performed to simulate non-uniform decay heat generation by Cartridge heaters in a pool corresponding lower plenum of power reactor. The current investigation focuses on non-uniform heating in the fluid domain by Cartridge heaters, which has been done using ANSYS FLUENT CFD code by K-epsilon model. The computed results are based on qualitative assessment in the form of temperature and velocity contour and quantitative assessment in terms of temperature and heat flux distribution to assess the impact of heating method on natural convective fluid flow and heat transfer.

DARCY-FORCHHEIMER TANGENT HYPERBOLIC NANOFLUID FLOW THROUGH A VERTICAL CONE WITH NON-UNIFORM HEAT GENERATION

The convective flows through different geometries have numerous applications in high-speed aerodynamics, nuclear cooling systems, fiber technology, and polymer engineering. In the present paper, we investigate the non-linear, mixed convective, boundary-driven, tangent hyperbolic nanofluid flow through a cone. The flow takes place under nonuniform heat sink/source. Darcy-Forchheimer effects have also been taken into account in mathematical modeling and analysis. The Buongiorno model is implemented to examine the effects of thermophoresis and Brownian motion parameters. The governing equations are constructed through the laws of conservation. The modeled flow problem is converted into a set of ordinary differential equations with the help of proposed similarity transformations. To interpret the modified system of equations, the homotopy analysis method (HAM) is applied. The roles of versatile parameters of interest are analyzed and sketched for better understanding. The velocity profile increases by increasing the Darcy number, and converse behavior is found by giving rise to the Forchheimer inertial drag parameter. The rise in temperature profile occurs by increasing a non-uniform heat source variable. The concentration profile enhances when the value of the thermophoresis parameter increases, and shows inverse behavior for the Brownian motion parameter. In the Buongiorno model, nanoparticle concentration has an inverse relation with the Brownian motion parameter. So, the concentration profile declines for greater Brownian motion parameter. To understand the behavior of flow through a cone, the values of Nusselt number and Sherwood numbers are examined.

Numerical study and structural optimization of mid-and-low temperature solar absorber/reactor for methanol decomposition

• A multi-physics coupling numerical model of MLTSAR is established. • The circumferential non-uniform heat flux has a slight effect on the MCR and STE. • The MCR and STE of MSR is higher and lower than that of MD, respectively. • A novel structure can enhance the MCR and STE by 1.47% and 1.49%, respectively. Driving endothermic thermochemical reactions by employing concentrated solar thermal energy is a perspective method for efficient utilization of solar energy, and solar reactor is a key equipment for wider application. In this paper, a multi-physics coupling model of mid-and-low temperature solar absorber/reactor (MLTSAR) for methanol decomposition (MD) reaction is established. The thermochemical performance of MLTSAR and the influencing factors including solar radiation intensity and non-uniform solar heat flux in circumferential direction are studied. The non-uniform solar heat flux in circumferential direction has a slight effect on the methanol conversion rate (MCR) and solar thermochemical efficiency (STE) but it leads to the non-uniform temperature distribution of absorber/reactor. And then, the comparative study of the thermochemical characteristic between MD and methanol steam reforming (MSR) reaction indicates that the MCR of MSR is higher than that of MD, but the STE is lower than that of MD. The MLTSAR structure is optimized by changing the aperture width, to reduce the energy level difference between the concentrated solar heat and the chemical reaction. The results show that compared with the original MLTSAR, the MCR and STE of the novel MLTSAR can be enhanced by 1.47% and 1.49%, respectively, and the outlet temperature is reduced by 15.48 K under the typical working condition. This optimization scheme could guide the design of practical solar reactors.

Mathematical Modeling of MHD Flow of CNTs/Ag Nanoparticles Past a Heated Stretchy Surface with Nonuniform Heat Sink/Source and Thermal Radiation Impacts

This research communication intends to evaluate the impact of time‐dependent MHD Darcy–Forchheimer flow of CNTs/Ag nanoparticles on a heated stretchy surface. Water is employed as a base fluid, and two types of CNTs such as single‐ and multiwall carbon nanotubes are considered. The significance of nonlinear radiation and heat sink/source is added to our analysis. To accommodate the suitable variables, the governing nonlinear partial differential models are transformed into a set of ordinary differential models. These resulting models are solved analytically and numerically by utilizing the homotopy analysis technique and the bvp4c procedure in MATLAB. The distinctive behavior of pertinent physical parameters on the dimensionless profiles are displayed and discussed through diagrams, tables, and charts. It is discovered that the velocity profile decrepitude whenever there is a change in the unsteady, porosity, and injection/suction parameters. The space and temperature‐dependent heat sink/source parameter cause to elevate the thermal profile. The Ag nanoparticles have a lesser surface shear stress compared to both CNTs. The heat transfer gradient develops for larger quantities of radiation and temperature ratio parameters. This research has significant applications in many industrial sectors, such as thermal exchangers, chemical reactors, microelectronics, biomedical engineering, aerodynamics, and industrial production processes.

MHD Casson nanofluid boundary layer flow in presence of radiation and non-uniform heat source/sink

<abstract><p>On stretched magnetic surfaces, we present a numerical study of Casson nanofluids moving through porous materials. The Casson liquid model explains how non-Newtonian liquids behave. Numerical techniques are utilized to solve the nonlinear partial differential equations produced by similarity transformations. Results are gathered for the Nusselt number, skin friction coefficient, temperature and velocity. The impacts of physical variables on the flow and heat transfer characteristics of nanofluids are depicted in graphs. They include the Prandtl number, magnetic parameter, radiation parameter, porosity parameter and Casson parameter. Findings indicate that as the Casson nanofluid parameters are increased, the temperature profile rises but the velocity field decreases. With increasing magnetic parameters alone, it is possible to see a decrease in the thickness of the pulse boundary layer and an increase in the thickness of the thermal boundary layer. All the results are depicted in graphical representations.</p></abstract>

Evaluating the Mechanism of Tropical Expansion Using Idealized Numerical Experiments

A wide range of evidence reveals that the tropical belt is expanding. Several mechanisms have been proposed to contribute to this expansion, some of which even contradict each other. The study of Yang et al. suggests that the poleward advancing mid-latitude meridional temperature gradient (MTG), originating from enhanced subtropical ocean warming, plays a leading role in driving tropical expansion. However, the abrupt4xCO2 experiment indicates that tropical expansion occurs at a faster rate than is indicated by changes related to ocean temperature rise. The idealized amip4K experiment illustrates that without introducing any ocean warming pattern, uniform ocean surface warming also drives tropical expansion. The results based on these idealized experiments seem to contradict the hypothesis proposed by Yang et al. In this study, we revisit these 2 experiments and show that both experiments actually support the hypothesis that MTG migration is driving tropical expansion. More specifically, in the abrupt4xCO2 experiment, although the rate of ocean warming is relatively slow, the poleward shift of the MTG is as rapid as tropical expansion. In the amip4K experiment, although ocean surface warming is uniform, the heating effect of the ocean on the atmosphere is nonuniform because of the nonlinear relationship between temperature, evaporation, and thermal radiation. The nonuniform oceanic heating to the atmosphere introduces a poleward shift of the MTG within the upper troposphere and drives a shift in the jet streams. By conducting an additional idealized experiment in which tropical expansion occurs under both a migrating MTG and a cooling climate, we argue that the migration of the MTG, rather than global warming, is the key mechanism in driving tropical expansion.

Erratum to: LES Simulation of Mixed Convection for Downward Mercury Flow in a Nonuniformly Heated Vertical Pipe Using Conjugate Problem Statement

Erratum to: LES Simulation of Mixed Convection for Downward Mercury Flow in a Nonuniformly Heated Vertical Pipe Using Conjugate Problem Statement

Thermo-mechanical Analysis of Railway Brake Disc with the Consideration of Contact Pressure Distribution and Non-uniform Heat Flux Density

Thermo-mechanical Analysis of Railway Brake Disc with the Consideration of Contact Pressure Distribution and Non-uniform Heat Flux Density

Research progress on heat dissipation technology of vapor chamber

Vapor chamber is a new type of two-phase flow heat dissipation technology. It offers the benefits of excellent thermal conductivity, uniform and consistent temperature, and the ability to reverse heat flow direction. It addresses the limitations of conventional heat pipes, such as limited contact area, high thermal resistance, and non-uniform heat flow. In the future, it will be an effective solution for cooling high heat flux electron devices in the electronic industry. This paper summarizes three types of wicks: micro-channel, sintered powder, and sintered screen. This article contrasts the benefits and drawbacks. This brief overview illustrates the latest advancements in heat and mass transfer theory related to vapor chamber, both domestically and internationally. Scholars employ the boiling theory of transport modelling to capture the gas-liquid interface, ascertain the critical heat flux, and analyze the flow and heat transfer laws of the working fluid in the uniform temperature plate. This paper analyzes several factors that affect the performance of the uniform temperature plate, including the selection of fluid, filling rate of liquid, size and distribution position of heat source input power, and working angle. Finally, this study analyzes and forecasts the practical applications of vapor chamber, taking into account the surrounding environmental factors.

An approach to thermal modeling of power cables installed in ducts

The power cables laying in the urban areas require utilization of the protective ducts, mainly to facilitate the faulty section replacement. However, the use of cable ducts results in reduced capacity to dissipate generated heat to the surroundings. Thus, the thermal analysis of cables placed in ducts is very important for proper power cable operation. The thermal response of cables laid in mutual and in separate ducts, respectively, is considered at two values of current load. The full-scale field measurement setup is utilized to carry out the analysis of both steady-state and dynamic power cable heating under actual field conditions for the two backfill configurations. The measurement results provide the insight into the power cable heating dynamics related to the situations of a short-term over-loads and fault drive-through responses and also the opportunity to verify the proposed numerical approach based on the use of finite element method and the boundary conditions on the interior duct surface. The approach could be considered as a compromise between the standardized procedure and the tedious procedure involving the computational fluid dynamics simulations due to straightforward implementation and very good accuracy. The results obtained suggest that cables laid in mutual duct lead to a less favorable thermal situation when compared to cables laid in separate ducts. Also, the numerical results suggest that the use of non-uniform heat flux around the inner duct surface results in a significantly better agreement with measurements, compared to the purely numerical approach utilizing the concept of the effective thermal conductivity to model heat transfer in the air gap between cable and duct. Finally, the sensitivity analysis has been carried out to assess the effects of various backfill thermal conductivities and the ground surface temperature on the resulting thermal field. • Full scale field measurements. • Simplified approach for thermal field estimation when cabled are placed in ducts. • Nonuniform heat flux distribution along the cable duct is implemented. • Better agreement with measurements when non-uniform heat flux distribution is used. • Use of effective thermal conductivity results in notable temperature underestimation.

Heat transfer and mechanical characteristics of the absorber in solar photo-thermal power generation system

In order to solve the problems of thermal fatigue, high temperature gasification and low temperature solidification of the heat receiver, a numerical calculation model for the heat transfer function of the tower type solar thermal power gener?ation high temperature receiver is proposed. A perfect analysis method is used for the simulation, and a thermal simulation program for predicting the heat gain of the solar thermal energy tower is compiled. In this paper, considering the various field connection characteristics, numerical value and distribution of convective heat transfer coefficient of the heat absorption medium, the temperature of the outer wall of the heat pipe absorption, and the thermal image conversion work in a non-uniform heat flow boundary area of a model of heat receiver was studied. The experiments show that when the flow rate of molten salt in the tube increases from 1 m/s to 2 m/s, the heat collection efficiency of the heat collection increases rapid?ly, while the flow time is more 3 m/s, the heat collection efficiency increases more gradually. The efficiency of heat absorption of the heat receiver is in the middle of the heat receiver, which can achieve 88 of the thermal image conversion. In the same large enough value, the heat collected at the inlet and outlet of the heat sink is about 82. It is clear that the numerical simulation provides a reliable basis for the design engineering, and provide guidance for the design of a full control model of tower solar photovoltaic power generation.

Numerical study on heat transfer characteristics of a pin–fin staggered manifold microchannel heat sink

• A pin-fin staggered manifold microchannel (PFSMMC) heat sink was designed. • The heat transfer characteristics of PFSMMC in single-phase flow were studied. • The staggered divider length-width ratio of PFSMMC was optimized. • The heat transfer characteristics of PFSMMC with different non-uniform heat sources were studied. Manifold microchannel(MMC) heat sink is an efficient thermal management solution for high heat flux electronic devices. A pin-fin staggered manifold microchannel(PFSMMC) heat sink is proposed to enhance the heat dissipation performance of the MMC heat sink in this paper. The heat transfer performance of the PFSMMC heat sink, the rectangular manifold microchannel(RMMC) and the pin-fin manifold microchannel(PFMMC) are compared by single-phase flow numerical simulation. The results show that the PFSMMC heat sink has better heat transfer capability and more uniform heating surface temperature. The effect of staggered divider length-width ratio on the heat transfer characteristics of PFSMMC heat sink is analyzed. The maximum heating surface temperature of PFSMMC heat sink has a valley with the increase of length-width ratio. The length-width ratio corresponding to the valley value of the maximum heating surface temperature is about 0.32. In addition, the heat characteristics of PFSMMC with different non-uniform heat sources are studied. The results show that the heating surface temperature uniformity deteriorates with the increase of length-width ratio, but the maximum heating surface temperature is lower at the length-width ratio of 0.32.

Design optimization of the gallium nitride high electron mobility transistor with graphene and boron nitride heat-spreading elements

The self-heating effect has long been a persistent issue for high electron mobility transistors based on gallium nitride due to their inherently poor heat dissipation capability. Although a wide variety of thermal management solutions has to date been proposed, the problem of the extremely non-uniform heat dissipation at the micrometer scale is still challenging. It has recently been demonstrated, however, that the performance of gallium nitride high electron mobility transistors can be substantially improved by the introduction of various heat-spreading elements based on graphene, boron nitride or diamond. In this paper, using numerical simulation, we carried out a design optimization procedure for a normally-off gallium nitride high electron mobility transistor containing both graphene and cubic boron nitride layers. First, a screening experiment based on a very economical Plackett-Burman design was performed in order to find the most critical geometric parameters that influence the dc characteristics. After that, a full two-level factorial experiment consisting of three factors was implemented and an optimized parameter set was yielded. By applying this set, the output power was increased by 11.35%. The combination of the most significant parameters does not include any factors related to the heat-spreading layers. Keywords: gallium nitride, high electron mobility transistor, optimization, Plackett-Burman design, screening experiment, self-heating.

Topology optimization of regenerative cooling channel in non-uniform thermal environment of hypersonic engine

Regenerative cooling technology is widely used in the active thermal protection system of hypersonic airbreathing engine. However, the overall efficiency of active cooling with limited total coolant quantity needs to be improved due to flow non-uniformity, hydrocarbon fuel pyrolysis and other factors. This paper presents a fluid–structure coupled topology optimization design of the regenerative cooling channel to improve heat transfer efficiency. To further verify the advantages of topology-optimized cooling channels under real operating conditions, detailed three-dimensional numerical simulations were conducted to investigate the supercritical flow and heat transfer processes of hydrocarbon fuel in the topology-optimized channels. Results reveal that compared to the traditional straight cooling channel, the topology-optimized channel has improved the heat transfer efficiency and flow distribution significantly. Many micro-channels perpendicular to the mainstream direction which can be termed as “capillary-like” zone in the optimized channel distribute the inlet fuel to the adiabatic walls, thus significantly improving the overall heat transfer. Remarkable cooling capacity robustness of the topology-optimized cooling channels has been found under different non-uniform heat flux conditions. Comparing to the straight channels, the averaged temperature of the heated wall in the optimized channels can be decreased up to 5.8% and the pressure drop can be decreased up to 20.6%. The uniformity of the fuel temperature distribution is about 2 times better than that of the straight channel. However, although overall heat transfer efficiency is high, complex flow and heat transfer phenomenon occurs in the topology-optimized cooling channel, such as the reverse flow phenomenon induced by adverse pressure gradient near the entrance and the stagnated flow in the “capillary-like” zone near the exit, which impair the local heat transfer and cause the existence of high temperature regions.

Optimized method for thermal through silicon via placement with non-uniform heat sources in 3-D-IC

In the past few years, thermal through silicon via (TTSV) has been experimentally investigated as an effective heat dissipation path. Although a lot of heat dissipation-related issues have been solved in 3-D integrated circuit (3-D-IC), there are neglections in TTSV placement with non-uniform heat sources so far. In this study, a unique optimization is proposed to locate TTSV while effectively alleviating hot spots in 3-D-IC. The thermal dissipation of non-uniform heat sources are studied using the finite element method. The simulation results show that the minimum temperature is reduced by 2.1% compared with peak temperature in the single-layer chip, and by 1.9% in the three-layer chip.

Significance of Chemical Processes and Non-uniform Heat Sink/source Aspects for Time-dependent Polymer Liquid Carrying Nanoparticles

Owing to extensive application developments of nanofluid, the engineers and scientists have concentrated their attention in regions of thermal and engineering processes. Additionally, nanofluids have wide-ranging returns as compared to traditional fluids. Keeping aforementioned logicality of nanofluid in observation, we deliberated a time-varying mathematical model to formulate the non-uniform heat sink-source assume Sutterby liquid over Brownian movements and thermophoretic. Thermal- solutal stratification phenomenon in addition with heat sink-source and activation energy aspects are scrutinized. Characteristics of random motion and thermophoresis diffusion properties for Sutterby fluid are examined. Similarity variable techniques are used to reduce partial differential equations into ordinary differential equations and solved numerically by using bvp4c method. The physical aspects of fluid flow, temperature, concentration for variation of involved parameters have been explained through graphs. Velocity of Sutterby nanofluid has contrary performances against unsteady and mixed convection parameters. Augmented values of Brownian moment, thermophoresis and heat source parameters exaggerate the temperature of nanofluid. Concentration of Sutterby nanofluid deteriorates for greater Schmidt number. Moreover, transportation rate of heat dwindles against Pr while it rises against NSUBt/SUB.

증기 자가방출 스마트 전자레인지 포장재 적용을 위한 복합필름 특성연구

The demands for Home Meal Replacement (HMR) products are continuously increasing owing to the convenience of instant food and online food delivery. Ready-to-heat (RTH) products have received massive attention in the HMR industry because these products can be easily warmed using a microwave oven. However, the conventional microwave packaging should be opened before microwave heating to prevent bursting or food loss owing to the steam-pressure build-up inside the package. Open packaging might lead to non-uniform food heating and cross-contamination. Therefore, packaging materials that are able to release steam without opening are of interest to the HMR industry. In this study, polylactic acid(PLA)/polyethylene glycol(PEG)/nanoclay composite films were manufactured using an extrusion method as packaging materials with a smart steam-releasing function. The introduction of PEG to the PLA imparted a steam selfreleasing feature to the composite films owing to the morphology change of composite films during microwave heating. Further, PEG increased the ductility of PLA, which in turn prevented bursting caused due to the steam-pressure build-up. The uniform dispersion of nanoclay obtained by a twin-screw extrusion led to stronger mechanical properties. Therefore, the smart composite films developed here can be applied as microwave packaging materials with a self-releasing function.

Numerical Solution of Two-Phase Radiated Unsteady Flow Over a Horizontal Stretching Sheet with Simultaneous Effect of Electrification, Radiation and Non-Uniform Internal Heat Source/Sink

A parametric study to investigate the impact of electrification and radiation inside a thermal particulate boundary layer, where the flow is due to an unsteady stretching sheet in presence of non-uniform heat source/sink. Both the fluid as well as the particles are assumed to be gray, emitting and absorbing radiation. Again, neither the fluid is considered in electric medium nor supplied by an external electric force. But, due to the random motion of the particles i.e., the interaction between particle-particle, particle-fluid and particle-wall, a tribo-electrification occurred. As on impact, both the fluid and particles are electrified though the flow has been considered in a neutral medium. Hence, a balanced mathematical model of highly non-linear partial differential equations has been formulated for two-phase unsteady boundary layer considering the above parameters/impacts on both the phases. An appropriate similarity transformation has been employed to transfer the governing equations into ordinary differential equations and solved numerically by built in solver Bvp4c of MATLAB. An excellent agreement between the present and previous literature has been made to validate the result. Moreover, the influence of Electrification parameter, Radiation parameter, Internal heat source/sink parameter on the rate of heat transfer and other flow characteristics has been analyzed.

Analysis and Simulation of Hydromagnetic Nano-Fluid Flow Passing an Inclined Heated Sheet

The examination of nano-fluid in recent time has been encouraging just as its research interest cuts across some disciplines such as mathematics, mechanical, chemical, civil engineering, physics, earth and natural sciences. Its applicability in the industrial and technological advancement helps in controlling the rate at which heat is conducted and diffuses in a given medium, as well as improving thermal transportation through convection, radiation and conduction. In this work, the analysis of hydromagnetic nano-fluid flow past an inclined heated surface with temperature dependent non-uniform heat source/sink and thermal radiation under heat and mass transmission perspective is considered. Adequate similarity variables are employed in recovering the nonlinear coupled ordinary differential equations (ODEs) from the partial differential equations (PDEs) which describe the equation of the boundary layer. The transformed equations (ODEs) are addressed both analytically and numerically with the aid of regular series approximation technique and Wolfram Mathematica package. The numerically simulated obtained results are graphically presented with legends. The computations opined that velocity declines while energy increases as the magnetic field number enhances. Similarly, improvement on angle of inclination, breeds velocity deceleration. Furthermore, the rate of energy transfer increases as the temperature dependent non-uniform parameters due to thermal generation enhances. In addition, the nanoparticle concentration decreases with increasing values of Schmidt and thermal radiation factors.