Thermal Heat Flux Research Articles

Thermal spreading characteristics of novel radial pulsating heat pipes with diverging nonuniform channels

The heat-spreading performance of a pulsating heat pipe (PHP) can be enhanced by increasing the driving force using a novel channel structure. The objective of this study is to investigate the thermal characteristics of novel radial PHPs with diverging channels under horizontal operation. The heat spreading characteristics of radial PHPs with diverging uniform channels (PHP1) and nonuniform channels (PHP2) were measured and analyzed under various working fluids, filling ratios, and heat inputs. HFE-7100, HFE-7200, and ethanol were used as the working fluids. Furthermore, the flow patterns and pressure variations in the PHPs within a short time frame were analyzed. Based on the measured data for both PHPs, the optimum filling ratio for each working fluid was determined to achieve the maximum performance. In addition, the maximum thermal performances of PHP1 and PHP2 were evaluated, aiming to achieve the lowest thermal resistance and maximum heat flux. Overall, the thermal resistance and heat flux of PHP2 were 5.9–11.7% lower and 20–37.5% higher than those of PHP1, respectively.

Thermo‐solutal Marangoni convective assisting/resisting flow of a nanofluid with radiative heat flux: A model with heat transfer optimization

AbstractThe mixed Marangoni assisting/resisting flow of a nanofluid with thermal radiative heat flux is analyzed when thermal and solutal buoyant forces are significant. The heat and mass transfer rates are simultaneously optimized by utilizing the Response Surface Methodology (RSM). The face‐centered Central Composite Design (fc‐CCD) is used for the numerical experimental design involved in RSM. The sensitivities of the heat and mass transfer rates are evaluated to compare the impact of the thermal and solutal buoyant forces. Appropriate scaling and similarity transformations are utilized to simplify the problem and then numerical solutions are obtained. The nanoliquid flow, temperature, and concentration profiles are plotted for the buoyancy assisting and opposing Marangoni cases. The Marangoni flow with opposite buoyancy is found to have a greater magnitude of velocity while the flows assisted by the buoyancy have a greater magnitude of temperature and concentration profiles. Thermal buoyancy force has a predominant (0.6%) impact on both heat and mass transfer rates compared to solutal buoyancy force. Buoyancy forces are positively sensitive to heat and mass transfer rates. The thermal radiation aspect augments the temperature profile throughout the domain. The optimized mass and heat transfer rates ( and ) is achieved at the highest level of the buoyancy forces and ratio of Marangoni numbers.

Transportation of heat and mass in chemically reacted flow of third-grade model in the presence of heat generation/absorption and activation energy effects

Numerous industrial and technical dynamic applications of non-Newtonian liquid flow research in thermal and process engineering are increasing every day, owing to their multifunctional relevance. The viscometric flow, heat and mass transfer of an incompressible third-grade liquid model across an exponentially inclined plate according to all of these potential implications are studied in this paper. The inclusion of elements such as mixed convection, heat sink/source, activation energy, thermal heat flux and chemical reaction improves the flow model’s novelty. Using the appropriate similarity transformations, the existing governing expressions are transmuted into nonlinear ordinary differential equations (ODEs). The resulting nonlinear ODEs are numerically solved via the Runge–Kutta (RK) technique in conjunction with a shooting strategy. The dimensionless parameters are graphically illustrated and discussed for the involved profiles. The viscosity of the liquid drops for increased fluid variable, which enhances the velocity field. The velocity profile is declined continuously throughout the boundary layer with increasing buoyancy ratio parameter. The thermal profile inclines for growing values of the radiation and heat source/sink parameters.

Significance of Convection and Internal Heat Generation on the Thermal Distribution of a Porous Dovetail Fin with Radiative Heat Transfer by Spectral Collocation Method.

A variety of methodologies have been used to explore heat transport enhancement, and the fin approach to inspect heat transfer characteristics is one such effective method. In a broad range of industrial applications, including heat exchangers and microchannel heat sinks, fins are often employed to improve heat transfer. Encouraged by this feature, the present research is concerned with the temperature distribution caused by convective and radiative mechanisms in an internal heat-generating porous longitudinal dovetail fin (DF). The Darcy formulation is considered for analyzing the velocity of the fluid passing through the fin, and the Rosseland approximation determines the radiation heat flux. The heat transfer problem of an inverted trapezoidal (dovetail) fin is governed by a second-order ordinary differential equation (ODE), and to simplify it to a dimensionless form, nondimensional terms are utilized. The generated ODE is numerically solved using the spectral collocation method (SCM) via a local linearization approach. The effect of different physical attributes on the dimensionless thermal field and heat flux is graphically illustrated. As a result, the temperature in the dovetail fin transmits in a decreasing manner for growing values of the porosity parameter. For elevated values of heat generation and the radiation-conduction parameter, the thermal profile of the fin displays increasing behavior, whereas an increment in the convection-conduction parameter downsizes the thermal dispersal. It is found that the SCM technique is very effective and more conveniently handles the nonlinear heat transfer equation. Furthermore, the temperature field results from the SCM-based solution are in very close accordance with the outcomes published in the literature.

A regularization method for inverse heat transfer problems using dynamic Bayesian networks with variable structure

In this paper, dynamic Bayesian networks (DBNs) were employed to solve one-dimensional inverse heat transfer problems (IHTPs) with temperature history data. Temperature-dependent conductivities and surface heat flux histories were discretized into a finite number of parameters and used as parent nodes in the DBN. Parameter sensitivity analyses were adopted to identify the dominant parameters at each time step. Non-dominant parameters were removed from the corresponding frames for the sparsification of the DBN, which reduces the number of parameters to be identified simultaneously. Thus, the structure of the DBN was dynamically optimized for the regularization of inverse problems. Numerical and experimental tests for IHTPs were conducted to validate the proposed method. Both thermal conductivities and surface heat flux were identified with relatively small error, even if considering the measurement error. Sensitivities of the remaining parameters increased significantly with the parameter identification process, and insensitive parameters in the initial DBN frames were also effectively identified in the subsequent frames. The accuracy of parameter identification can be improved, and the cost of the parameter sampling combination can be reduced. The proposed method is not subject to heat transfer problems and can be used for a wide range of applications.

Evaporation Characteristics of Lubricant/Gasoline Blending Oil Film Under Different Thermal Radiations

Abstract The evaporation and pro-ignition characteristics of the lubricating oil blending in the cylinder can bring a super knock for the high-efficiency gasoline engine. The evaporation characteristics of the lubricant/gasoline blending oil film were investigated experimentally under different thermal radiative heat flux, film thickness, and carrier material in a radiation device. The blending ratios of lubricant/gasoline oil film changed from 0% to 15%. Three stages of the blending oil film evaporation process were observed according to the different evaporation rates, namely, transient heating, equilibrium evaporation, and evaporation gel. During the transient heating stage, with the increase of gasoline blending ratio, oil film thickness, and radiative heat flux, the evaporation rate increases, while the evaporation rate decreases in the equilibrium evaporation stage. The evaporation rates in transient heating stage and equilibrium evaporation stages are reasonably predicted by using the proposed relationship model.

Effects of the Conjugate Heat Transfer and Heat Flux Strength on the Thermal Characteristics of Impinging Jets

A numerical study using the conjugate heat transfer approach has been performed to investigate the effects of boundary heat flux, conduction effect, and working fluid on the thermal characteristics due to the jet impingement process. Air and water are used in this study as working fluids. For the water jet, the volume of fluid method is used to capture and track the interface in the multiphase flow. It is found that the wall conduction may change the fluid-solid interfacial thermal characteristics compared with no conduction or pure convection process. The amount of influence depends on the working fluid, nozzle size, metal thermal conductivity, metal thickness, and boundary heat flux. The conduction inside the solid wall tends to reorganize the uniform heat flux distribution at the boundary to a non-uniform heat flux distribution at the fluid-solid interface. This is mainly attributed to the conjugate effect of the solid. For a given jet Reynolds number and boundary heat flux, the conjugate heat transfer results divulge that the convective heat flux removed from the stagnation point is higher for the air jet than for the water jet. Contrary to the air jet, the effect of thermal boundary on the stagnation Nusselt number profile is negligible for the water jet. The disc material and thickness have no obvious effect on the stagnation Nusselt number profile for both air and water fluids.

Interface dynamics and flow fields’ structure under thermal heat flux, thermal conductivity, destabilizing acceleration and inertial stabilization

Interfaces and interfacial mixing are omnipresent in fluids, plasmas, materials in vastly different environments. A thorough understanding of their fundamentals is essential in many areas of science, mathematics, and technology. This work focuses on the classical problem of stability of a phase boundary that is a subject to fluxes of heat and mass across it for non-ideal thermally conducting fluids. We develop a rigorous theory resolving challenges not addressed before, including boundary conditions for thermal heat flux, structure of perturbation waves, and dependence of waves coupling on system parameters in a broad range of conditions. We discover the novel class of fluid instabilities in the three regimes—advection, diffusion, and low Mach—with properties that were never earlier discussed and that are defined by the interplay of the thermal heat flux, thermal conductivity and destabilizing acceleration with the inertial stabilization. We reveal the parameter controlling transitions between the regimes through varying the initial conditions. We find that the interface stability is set primarily by the macroscopic inertial mechanism balancing the destabilizing acceleration. The thermal heat flux and the microscopic thermodynamics create vortical fields in the bulk. By linking micro to macro scales, the interface is the place where balances are achieved.Article highlightsThis work yields the general theory of interface dynamics in a broad range of conditions.The interplay is explored of inertial stabilization, destabilizing acceleration, thermal conductivity and heat flux.We discover that interface is the place where balances are achieved through linking micro to macro scales.

Vibration Analysis and Experimental Testing of Existing 3-Wheeler Automotive Muffler Using Modal and FFT Analyzer

A muffler is a device used to reduce the noise and vibration of gas emitted by internal combustion engine. So, it become a necessary equipment in automobile to have a proper emission of gases to surrounding. Due to improper design some muffler decreases the mass flow rate due to which there is increase in fuel consumption, large pressure drops across its cross section and higher knock sensitivity. In present project existing 3-wheeler vehicle muffler is experimentally tested with FFT analyser (Impact Hammer Test) technique to determine the mode shapes, natural frequencies and thermal heat flux analysis and FEA analysis is performed in ANSYS software to validate the experimental results.

Impacts of inclined Lorentz forces on hybrid CNTs over an exponentially stretching sheet with slip flow

ABSTRACT A mathematical model is proposed to analyze the impacts of an inclined magnetic field and velocity slip on a hybrid nanoliquid over an exponentially elongated sheet in the presence of thermal heat flux. In this study, single wall and multiwall carbon nanotubes (SWCNT and MWCNT’s) are considered as nanoparticles with water as a base fluid due to their distinctive nanostructures and excellent thermal conductivity in many industrial and engineering applications. The governing equations are converted into ordinary differential equations by employing appropriate similarity transformations and are then solved by utilizing the bvp4c technique with the help of MATLAB software. The influence of various parameters such as magnetic field (), velocity slip parameter (), angle of inclination (), thermal radiation (), Prandtl number (), the volume fraction of the nanoparticles () on fluid velocity and dimensionless temperature are discussed graphically. The fluid momentum and dimensionless temperature are dominant for hybrid nanoliquid against a single wall or multi-wall carbon tubes/water. Also, the heat transfer rate decelerates by increasing the slip parameter and the magnetic parameter.

Thermal and diffusion Cattaneo-Christov heat flux models on Walter’s-B Buongiorno nanofluid over an electromagnetic surface with second order velocity slip

The intension of the current study is to explore optimization in heat transfer using Cattaneo-Christovs thermal and the solutal diffusions along with heat source/sink which are non-uniform on a stagnation points flow of nanoWalter’s B fluid over an electromagnetic sheet subjected to the multiple slip mechanisms. This study also scrutinizes the role of electromagnetic fields. The flow equations are modified via incorporating suitable transformations into a self-similarity equalities. Further numerically solved by employing Runge–Kutta method of shooting technique. The acquired results shows good agreement with the previous published works. The noteworthy findings are- Walter’s B nanofluid which flow parallel to the electromagnetic sheet is assisted by the Lorentz force. Electromagnetic sheet can be used for better cooling since improvement in Hartmann declines thermal boundary layer. Augmentation in thermal, velocity, and the solutal slip parameter shrink the hydrodynamic, solutal and thermal boundary layer.

Comparative Study on the Damage Effects in the Deflagration Process of Typical Liquid Propellants

AbstractTo study the damage effects caused by accidental deflagration of liquid propellants during production, storage, transportation and use, the information of the deflagration processes and the shock wave hazards of three typical liquid propellants under external flame stimulation were obtained by a high‐speed camera and a shock wave pressure acquisition system. Additionally, in the same situation, the highest temperature of the surface fireball and the law of fireball of the thermal radiation were also studied by an infrared thermal imager and heat flux test system. High‐speed video results showed that the fireball of DT‐3 developed most violently of the three liquid propellants; anhydrous hydrazine took the second place and metallized gelled MMH was the weakest. The average TNT equivalents of 18 kg anhydrous hydrazine, 18 kg DT‐3, 120 kg anhydrous hydrazine and 120 kg DT‐3 were 0.724, 0.629, 0.000375 and 0.0293 respectively. The peak values of thermal radiation flux were in the order of DT‐3>anhydrous hydrazine>metallized gelled methylhydrazine. The corresponding death radius in the accident was supposed to be 20–30 m. Experimental results indicated that package design pressure of liquid propellant had a significant effect on the intensity of the reaction response to the action of flame stimulation. Within a certain range, the package design pressure of liquid propellant should be appropriately reduced to improve its security in storage and use. The study provided a theoretical guidance for the explosion protection of liquid propellant in case of accidental deflagration.

The dynamic thermal properties of aerogel-incorporated concretes

This study characterizes the dynamic thermal properties of aerogel-incorporated cement composites and other lightweight concretes. The tested specimens were prepared based on three types of aggregates: expanded clay, sintered fly ash aggregate and natural stone aggregate as a reference. The primary method of increasing the overall composite porosity was to prepare specimens by adding aerogel particles. A second method of increasing the cement matrix porosity was obtained using an air-entraining agent. The microstructure of the tested concretes was examined by mercury porosimetry. The novelty of the manuscript is that it presents the comparison of dynamic properties of concretes with the addition of aerogel and other types of lightweight concretes. Thermal properties tests were performed utilizing a non-stationary method. Based on experimentally obtained thermal properties, the values of dynamic thermal characteristics of the tested composites were calculated. The essential part of the experimental research were the tests carried out in non-stationary heat flow conditions in the analyzed composites. The aim of this research was to assess the influence of the thermal properties of a given composite on its behavior in changing temperature conditions. Having the data of the temperature change in specimens and the thermal properties of the tested composites, the total temperature increase, change of the accumulated thermal energy, heat flux, and densities were determined. Based on the experimental data, relationships between physical properties and dynamic thermal characteristics were evaluated.

FEM Analysis: A Review of the Most Common Thermal Bridges and Their Mitigation

The necessity to improve the energy saving potential of buildings is now a duty. European and national policies are being implemented to address the important decisions being made on this subject. For these reasons, several studies focus on this relevant topic. This paper review not only focusses on it but studies it in-depth. A commercial 3D simulation software was used to design a building sited in Palermo estimating the thermal losses before and after external envelope insulation. In particular, all the thermal bridges (TBs) were analysed with the finite element method (FEM) and mitigated with rock wool insulation. The paper shows the linear thermal transmittance difference and heat flux loss before and after TB mitigation. The results confirm the importance of installing an external insulation layer in the old building envelope. The linear thermal transmittance of TBs and the associated heat flux loss often decrease by more than 50%.

Inverse Compton scattering of the ITG turbulence by energetic ions

Linearly stable toroidal Alfvén eigenmodes (TAEs) can be non-linearly excited by the ion temperature gradient mode turbulence having frequencies an order of magnitude lower than TAE. An excitation mechanism is the inverse Compton scattering by energetic ions, i.e., the inverse non-linear Landau damping accompanied by a frequency increase in the scattered waves. This effect can be responsible for excitation of the stable TAE by turbulence observed in numerical simulations [Di Siena et al., Nucl. Fusion 59, 124001 (2019)]. Such non-linear coupling to stable TAE via energetic ions provides an efficient energy sink for turbulence and can explain strong reduction of the thermal ion heat flux in the presence of fast ions observed in gyro-kinetic modeling [Citrin et al., Phys. Rev. Lett. 111, 155001 (2013)].

Heat transfer simulation through textile porous media

Over the last decade, modelling of heat and mass transfer through textile materials has become a constant focus of researchers, the research being directly influenced by the development of computer systems. The importance of the heat transfer properties of clothing is particularly crucial in high-risk professions, such as firefighters and military, or in sportswear and healthcare. While some analytical and numerical models have been developed regarding these materials, most approaches are at the macroscopic level, where microscopic details are filtered out to reduce numerical and physical complexity. When the unsteady transfer occurs, the results can have significant errors. On the other hand, simulation is a cheaper method to obtain the static or dynamic characteristics of porous materials. This paper aims to model a simple textile structure and to perform a heat transfer simulation using Comsol Multiphysics®. Comsol Multiphysics® is a software that allows the simulation of physical phenomena using geometric models. By applying the standard boundary conditions, a comparison between the simulated and experimental values was made. To have a significant result for the entire system, the dimension of the sample was chosen so that it becomes a Representative Elementary Volume. Starting from the characteristics of the yarns and a geometric model of the textile structure, by simulation has been achieved the global characteristics of the material such as thermal resistance, porosity, heat flux and relative times for which the transfer becomes stationary. Global values were obtained by the volumetric average method using predefined functions in Comsol Multiphysics®.

Entropy analysis in an unsteady MHD flow of a radiating fluid through a vertical channel filled with a porous medium.

This paper investigates the blended effects of thermal buoyancy, magnetic field and radiative heat flux on the unsteady flow of an electrically conducting fluid through a permeable walled passageway filled with a penetrable medium. The model non-linear partial differential equations are obtained and solved analytically using separation of variable techniques and numerical for fluid velocity and fluid temperature. The two functions are then used to obtain entropy generation rate, skin friction, Nusselt number and the Bejan number. The effects of manifold novel parameters on the overall flow structure and thermal putrefaction are displayed graphically and discussed. One of the crucial findings of the current model is that entropy generation rate diminished temporally and with an upsurge in a magnetic field but amplified with a soar in porous medium permeability, thermal buoyancy and fluid Prandtl number.

Optimal number of thermal hotspots selection on motorized milling spindle to predict its thermal deformation

Two primary heat-generation sources in motorized machine tool spindles are (i) friction in spindle bearings, and (ii) losses in the motor components. The difference in heat generation and heat dissipation rate from the high-speed motorized milling machine tool spindle cause structural deformation, resulting in part inaccuracy. Several research groups used thermo-mechanical and data-based modelling of high-speed motorized spindles to predict and compensate thermal deformation and improve machining accuracy. In real-time thermal compensation, selection of optimal number of thermal hotspots to place the temperature sensors on the spindle is crucial. The present work proposes an approach to select the optimal number of temperature sensors that can be employed to predict the thermal deformation while maintaining required prediction accuracy. For this purpose, the experiments were conducted to evaluate the thermal heat flux across the spindles at different rotational speeds. Furthermore, a finite element analysis (FEA) was performed to simulate the thermal deformation at the tool center point (TCP). The input parameters considered for predicting the simulated deformation were different temperature sensor data on the motorized spindle and the ambient temperature. This work uses the thermal deformation results obtained from FEA to build an improved second-order polynomial regression model. The model reduces the requirement of temperature sensors from three to one to predict the TCP deflection. Results show that the proposed model accuracy was 86.72% with two temperature sensors and 85.99 % with one temperature sensor. It indicates that one temperature sensor is sufficient to predict the TCP deflection with a compromise of 0.73% prediction accuracy level.

Thermal and Structural Analysis of Different Piston Geometries of Compression Ignition Engine

Improvement in performance of the diesel engines is carried out by focusing on several parameters. One among these is piston which undergoes higher thermal loads and thermal stresses during its entire working cycle and duration. Therefore, it is necessary to analyse the stresses that the piston can be able to withstand and give its contribution to maximize the engine performance. In this study, four different piston shapes were considered namely, flat, dome, cup and bowl type pistons. 3D models were developed for these pistons and simulations was carried out in the ANSYS at steady state conditions using finite element method (FEM). Based on the investigations, it was observed that the maximum temperature distributed was nearly same in all the types of pistons as 1133K which appeared near the combustion area. The thermal stress and total deformation values of the piston was found to be lesser for the flat and dome types of pistons. Based on the data obtained for thermal stress, temperature distribution, heat flux and total deformation, it can be suggested that flat or dome type pistons can be considered for use in the IC engine to maximize the performance of diesel engine.

Finite element modeling of railway wheel gauge change during braking: Effect of lateral shift of brake block

Finite element analysis is used to investigate the wheel gauge change in a new railway wheel under regular braking conditions and shifted brake block away from the flange. The FEM model used here accounts for residual stress development during manufacturing, thermal heat flux partitioning during braking, and heat dissipation to rail and ambient. The wheel gauge decreases while braking and increases once the wheel cools down in normal braking conditions. When the brake blocks are moved away from the wheel flange, a similar pattern emerges; however, the wheel gauge change is greater than in the previous case. The lateral displacement of brake blocks away from the flange side of the railway wheel during braking may result in a larger wheel gauge drop during braking and a larger wheel gauge increase after cooling.