Heat Transfer Method Research Articles

Assessment of various Full-Spectrum Correlated K-distribution methods in radiative heat transfer in oxy-fuel sooting flames

Thermal radiation plays an important role in heat transfer process in oxy-fuel sooting flame (OFS). The accuracy of Full-Spectrum Correlated K-distribution (FSCK) methods with the original scheme (Modest and Zhang, 2002), the improved one (Cai and Modest, 2014), and the rank correlated one (Solovjov and Webb, 2018) is evaluated in two OFSs. As a comparison, two oxy-fuel non-sooting flames (OFNSs) are constructed as well. The performance of these three schemes in OFSs is basically consistent with that in OFNSs except for the original scheme in the high-soot-concentration regions. The original scheme displays larger errors than the other two schemes in the high-temperature regions, especially in the high-soot-concentration regions, though the error is quite small. The improved scheme provides excellent accuracy in the high-temperature regions, but significant errors in the low-temperature regions, which results in an overestimation of temperature by 38.8 K. The rank correlated scheme displays the best accuracy in both OFSs and OFNSs. Furthermore, the reference (or Planck) temperature has obvious impacts on the accuracy of original scheme, but has much weaker effects on the improved and rank correlated schemes.

Heat transfer and flow structure characteristics of film-cooled leading edge model with sweeping and normal jets

The heat transfer and flow structure characteristics of a film-cooled leading edge model with sweeping and normal jets were numerically investigated using the conjugate heat transfer method. The leading edge model is a simplified obtuse body model that has three rows of traditional cylindrical film holes, each with three holes inclined at 25° with respect to the surface and three angles oriented at 0° and ± 30° with respect to the axial direction. A normal jet has one row of cylindrical impingement nozzles, and a sweeping jet has only one fluidic oscillator. Three blowing ratios (M = 1.05, 2.07, and 4.11) and three temperature ratios (TR = 0.5, 0.625, and 0.75) are considered in the study. The shear stress transport k–ω turbulence model and an extremely fine structured grid were validated and applied to all simulations. The results indicate that the total pressure loss coefficient and heat transfer performance increase internally and externally, respectively, with the blowing ratio. However, they are insensitive to the temperature ratio in all cooling configurations. The sweeping jet and film (SJF) composite cooling exhibits 1.6162, 2.1195, and 2.1766 times the total pressure loss coefficient of the normal jet and film composite cooling when the blowing ratio increases from 1.05 to 4.11. However, the SJF offers the advantages of uniform Nusselt number distribution on the impinging surface and high overall cooling effectiveness on the external surface.

Discontinuous finite element method for transient conductive heat transfer in layered media with thermal contact resistance

Research on accurately solving the transient conductive heat transfer problem in layered media has both scientific and engineering significance. Numerical algorithms up to date usually suffer from additional dubious treatments when dealing with the temperature discontinuity induced by the thermal contact resistance (TCR) between the inner interface. In this paper, we extend the discontinuous finite element method (DFEM) to solve the problem of transient conductive heat transfer in a layered slab with TCR interfaces. The correctness of the DFEM for handling the TCR-induced temperature discontinuity is verified at first. Then we utilize the DFEM to solve the transient conductive heat transfer problem in a three-layered medium subjected to Dirichlet, Neumann, and Robin boundary conditions, respectively. The time-dependent temperature along the slab and the temperature discontinuity across the TCR interfaces are captured and analyzed. Results indicate the present DFEM can naturally capture the TCR interface-induced temperature discontinuities accurately. The time-dependent temperature and temperature discontinuities across the TCR interfaces presented in this work can serve as benchmarks for later research on conductive heat transfer in layered media.

An improved blocked-off method for radiative heat transfer in complex enclosures with structured grids

The blocked-off based finite volume method for the radiation heat transfer problem has an obvious shortcoming that yields oscillating radiative heat flux on complex walls when using structured grids. This work aims to improve the accuracy of the blocked-off model by using a boundary radiation intensity interpolation method. The new method is validated for inclined and curved walls, and the predicted radiative heat flux has almost no fluctuations with great accuracy. This improved method works well for optically thin, moderate and thickness conditions. The deviation in radiative heat flux decreases from about 10% to less than 1% compared to previous schemes.

Study on Thermodynamic Characteristics and Heat Transfer Method of Uncontrolled Fire in Coal Mine Gangue Mountain Spontaneous Combustion Based on System Dynamics.

Coal fire disaster caused by the spontaneous combustion of coal has always been one of the serious problems that threaten the safety of coal mining. In our study, we first solved the dynamic parameters and mechanical functions of coal gangue using the Achar differential method and Coats-Redfern integral method. Then, based on the flow and heat transfer mechanism of hot rod vapor-liquid two-phase flow, combined with coal spontaneous ignition conditions, influencing factors, coal pile spontaneous combustion temperature field structure distribution, etc., the heat transfer process of the hot rod in the coal pile (coal gangue mountain) was analyzed. Results show the average activation energies of the second stage of different types of coal mine gangue. Upon comparing the characteristic parameters of coal gangue in different regions and ages, it is found that 8# coal gangue has better combustion and burn-out characteristics, and its comprehensive combustion characteristics are second only to those of the coal gangue in Datong and higher than those in Panzhihua, Pingdingshan, and Hancheng. The higher the content of volatile matter and fixed carbon in coal gangue, the lower the ash content, and the better the comprehensive combustion performance of the coal gangue. Under the condition of sufficient oxygen supply combustion, the larger the fuel ratio, the better the burnout performance of the coal gangue. The test of the influence of the hot rod on the temperature field distribution inside the coal pile shows that the maximum cooling rate of a single hot rod to the coal pile during the test period is 33.4°C, and the maximum cooling rate reaches 39.6%. The calculated heat dissipation of the 80 h hot rod is 1.0865, 2.1680, and 3.3649 MJ, respectively.

Exploring print setting tradeoffs to improve part quality using a visual thermal process simulation

While desktop 3D printer manufacturers continually work to increase the usefulness of their machines, a successful first print of a part is still a significant challenge for many users. Many of the manufacturers provide software offerings to help users choose print settings to reduce errors, and the corresponding number of times a part must be printed. However, these offerings often present a myriad of settings to adjust without a clear indication of the outcomes. These settings, combined with environmental effects must be simulated, and presented so a user can understand and avoid common print failures. This paper presents research into one of the most prevalent of these, thermal issues, in 3D desktop printing. An extrusion process was simulated by displaying a printed road shape during and after a G-code print command and accurately represents the position, size, and shape of a 3D printed part's roads, based on changes in nozzle position, orifice diameter, and layer thickness. The Lumped Capacitance heat transfer method was used to determine each road's temperature with a corresponding color legend. A thermal imaging camera attached to the print head of an actual 3D printer monitored temperature for simulation validation. This simulation, in conjunction with a usable 3D software interface, provides a prototype visual tool for users to explore setting tradeoffs and view resultant outcomes with any combination of 3D printer and 3D printing software without requiring extensive 3D printing experience.

Enhancing Boiling Heat Transfer on a Superheated Surface by Surfactant-Laden Droplets.

Boiling, one of the most common phase-change heat transfer methods, is widely used in nuclear power plants, spacecraft, integrated circuits, and other situations, where rapid and efficient heat transfer is crucial. However, boiling heat transfer is efficient only in a specific surface temperature range when a droplet impacts a superheated surface. Here, we enhance the boiling heat transfer and extend this temperature range by adding a tiny amount of surfactant. We find that surfactants can weaken the Kelvin effect of boiling bubbles, and thus reduce the onset of boiling driven temperature and significantly enhance the maximum vaporization rate of the droplet effectively. In particular, different from previous studies, we find that the surfactants at lower concentrations can increase the Leidenfrost temperature of the droplets. All the above effects jointly expand the temperature range of effective boiling heat transfer. This study sheds new light on the role of surfactants in the boiling process and offers a new medium to promote heat-transfer applications.

Physical Model of Influence of CaO–FeO–SiO2 Powder Fraction on the Heat Transfer from Torch

Introduction. One of the main ways of heat transfer in metallurgical units is the interaction of the charge with a burning gas torch. The heat is transferred from the torch mainly by radiation. In particular, oxygen converter process under its typical temperature and chemical conditions of oxidation processes is accompanied by combustion reactions with the formation of a torch both in the cavity of the converter (in the so called reaction zone) and above the converter neck as a result of partial post-combustion of exhaust gases leaving the unit.Problem Statement. The processes in metallurgical units are accompanied by significant smoke and dust, which affect the efficiency of heat transfer from the torch of exhaust gases post-combustion to the metal bath that is an additional source of heat in the converter process.Purpose. The purpose of this research is to study the influence of the introduction of solid powder components into the environment around the torch on its heat transfer.Materials and Methods. The research has been carried out on the physical model of a burning torch when CaO-FeO-SiO2 system powders are fed into the torch in air flow. The magnitude of the heat flow density has been estimated on the basis of the registered temperature difference in different parts of the model.Results. It has been established that the feed of air or any solid material at a temperature much lower than the torch temperature has a negative effect on heat transfer from the torch by radiation. However, the total heat flow density is not significantly reduced due to the possible involvement of heated solids in other heat transfer methods. For the CaO-FeO-SiO2 system, the share of silicon dioxide powder as a component with the highest heat capacity has the greatest negative effect on the heat transfer from the torch.Conclusions. The studies based on the physical model have allowed us to qualitatively assess the effect of dustiness of the components of CaO-FeO-SiO2 system of the burning torch environment on its heat transfer and on the contribution of different heat transfer methods from the torch to the total heat flow density in given conditions.

Effects of lateral cooling hole configuration on a swirl-stabilized combustor

It is necessary to cool the combustor liner due to its harsh operating conditions. In the current study, wall temperatures of a swirling combustor with and without cooling holes are compared using a three-dimensional numerical simulation with conjugate heat transfer method. It is shown that the wall temperature can be reduced by 344–501 K by using cooling holes. Two lateral coolant injection designs are then proposed since the laterally injected coolant may interact with the swirling flow. Normal axial injection is also investigated to compare NOx emissions, cooling effectiveness and total pressure loss for various scenarios with different injection angles. The results show that when the incidence angle is 15°, NOx emissions remain low for all incidence configurations. When the lateral incidence is implemented, especially at small incidence angles such as 15° and 30°, the cooling effectiveness is maintained above 0.9. However, when the coolant incidence direction is opposite to the swirling flow and the incidence angle is 15° results in a high total pressure loss. At an incidence angle of 60°, the total pressure loss is about the same for all cases, at 3.2%.

Heat exchange structure design and overall performance analysis of double-concentrator solar thermal thruster

In this paper, the platelet heat exchanger in the thermal propulsion system of micro satellite with liquefied gas as propellant was designed, the complete gasification and stabilization scheme of propellant was proposed. The unsteady conjugate heat transfer (CHT) characteristics between the heat exchanger and gaseous propellant were analyzed, and the cumulative data of error estimation in the numerical simulation process was provided to ensure the credibility of the results. The CHT computational fluid dynamics (CFD) simulation of the platelet 3D model under steady-state conditions was carried out to find the empirical correlation between the average Nusselt number and the average Reynolds number. A simplified unsteady 1D model of heat exchanger was established by using the loose coupling method based on quasi steady flow field. The results show that the platelet structure could heat the working medium to more than 2379 K with the heat transfer efficiency of 86%, the outlet temperature and heat transfer efficiency of the heat exchanger were maintained at 1871 K and 69% in steady state when the mass flow rate was 1.14e-6 kg/s. The 1D model could accurately reflect the real heat transfer situation to a certain extent, the simulation error was less than 8.5% compared with the 3D model, and the calculation time was greatly shortened, making the adjustment of heat transfer strategy more convenient. Intermittent heat transfer method could keep the outlet gas temperature, thrust and specific impulse of the thruster at a high level to improve the performance of the system. Taking the nanosatellite with a total mass of 7.55 kg and a propellant mass of 0.25 kg as an example, when the duration of valve open time was 1.5s, the velocity increment of the satellite reached 72.21 m/s with the specific impulse of over 2400 m/s, which was twice than that of nanosatellites without heat exchange structure.

A variational splitting of high-order linear multistep methods for heat transfer and advection–diffusion parabolic problems

The main result of this paper is the generalization of the concept of variational splitting proposed by Behnoudfar et al. (2018) into higher-order time-stepping schemes. The key novelty of the technique proposed here is the following: when using the isogeometric finite elements, one can factorize the matrix of the linear system and obtain the linear complexity. This matrix has the form M+ηK, where M is the mass matrix, K is the stiffness matrix. Following the technique of Behnoudfar et al. (2018), and factorizing M+ηK one would get the additional error of order η2. We propose the technique to couple the possibility of factorization of M+ηK with the higher-order time-stepping schemes and preserve this higher order. Thus, we introduce a variational splitting for implicit, linear multistep methods of order s for parabolic partial differential equations. Our technique exploits the tensor-product structure of the discretization in space (mesh and basis functions) to derive an update strategy with a linear cost regarding the total number of degrees of freedom for multi-dimensional problems. As an example, we consider two popular methods: Adams–Moulton (AM) and backward differentiation formulae (BDF). We derive the corresponding coefficients for AM and BDF methods. We present a C++ implementation of the time-integration schemes, targeting shared-memory Linux clusters. We present numerical results for the heat transfer problem and advection–diffusion problem. We also discuss the limitations of the method and possible extensions overcoming this limitation by using our method as a preconditioner for an iterative solver.

4E analysis for the implementation of parabolic trough solar collectors in Mexican dairy industry sector: An optimization approach including passive heat transfer methods

This research work strengthens a numerical evaluation of four different types of passive heat transfer methods (nanofluids, flow inserts, selective coating, and receiver geometry modification) in a parabolic trough solar collector array through an energetic, exergetic, environmental, and economic analysis (4E) for the generation of heat for the Mexican dairy industry. For this purpose, eight different scenarios of passive methods were evaluated under four different climatic zones to find the best optimal scenario considering various indicators such as temperature, efficiency, CO2 mitigation potential, and net present value. For each scenario, an annual performance assessment was projected using daily average values. The highest values of fluid temperature, useful heat, thermal efficiency, useful exergy, exergetic efficiency, and amount of CO2 mitigated were 88.50 °C, 81.82 kW, 24.84, 14.28 kW, 4.65 %, and 206.77 tons of CO2, respectively, corresponding to scenario 8 during warm climate. Nevertheless, the maximum net present value was obtained with scenario 7 with a value of 784,286.21 $ USD, while scenario 4 reached the highest internal rate of return of 34.5 % which has indicated that the economic analysis has suggested a different optimum scenario, thus, the current study is relevant for multi-parametric decision-making analysis. In conclusion, the methodology framework of this article can be adapted to other branches of the industrial sector which can yield a performance optimization of solar thermal technology by incorporating different passive heat transfer methods. This can also bring scientific justification to the policymakers for its implementation in the Mexican dairy industry specially to identify the most profitable option for their proliferation in the national market.

Semi-Analytical Method for 3D Transient Heat Transfer in Thermally Interacting Fields of Ground Heat Exchangers

The study of heat transfer in ground heat exchangers (GHEs) considering the fluid advection inside the pipes; the heat transfer between the fluid and the ground through the grout material; and the thermal interaction between GHEs is a challenging task. The present paper presents a new semi-analytical method that takes into account the aforementioned effects to consider both the short- to long-term effects of GHEs. The heat transfer between the fluid and grout was studied by a transient multipole expansion considering time-dependent fluid temperatures and an advection model for the pipes obtained from an energy balance on the heat carrier fluid. Thermal interactions were analyzed using an equivalent borehole method while penalizing the transient multipole expansion to include thermal interaction effects. Validation of the short-term predictions was performed by comparing the proposed model to experimental data found in the literature and to an FEA model. The proposed model was then compared with a FEA model in long-term simulations of a geothermal field comprised of 24 GHEs for multi-annual simulation. The method resulted in substantial reduction in computational time while preserving good accuracy when compared with the FEA model.

Some recent advances in computational heat transfer and fluid flow

• Recent advances in computational heat transfer and fluid flow outlined. • Computational techniques from microscale to macroscale phenomena along with experimental assessment are illustrated. • Applications of new methodologies, such as emerging machine-learning and data-driven modelling, are envisioned. Computational methods in heat transfer and fluid flow have gained significant progresses and stimulated strong interest and continued efforts in academic and industrial communities for a broad range of thermal engineering. The topics included in this special issue cover computational methods from microscopic to macroscopic modellings and related applied researches from single-phase to multi-phase flow phenomena, as well as an introduction of Prof. Wen-Quan Tao’s 50-year academic career in heat transfer. The research efforts documented in the papers clearly reflect the most recent advances in computational heat transfer and fluid flow. The vision of the paper shows some of the key achievements and main challenges which still remain in applied thermal engineering. Finally, some future perspectives in employing modern methods are given to highlight pathways of ongoing researches in understanding and predicting complex physical phenomena and processes in heat transfer and fluid flows.

Numerical study of swirl cooling enhancement by adding mist to air: Effects of droplet diameter and mist concentration

Swirl cooling with air/mist mixture coolant is a promising heat transfer method, for which the combined influence of swirl and mist should be clearly understood. In this work, numerical simulations on the swirl cooling performance of the leading edge of a turbine vane using mist/air mixture and air are implemented for comparative study. The Eulerian-Lagrangian particle tracking method is adopted to investigate the two phase cooling. The coolant air impacts tangentially the inner surface of the circular swirl chamber through two rectangular nozzles, and the mists with different concentrations (5%, 10%, and 20%) and droplet diameters (1 μm, 2.5 μm, 5 μm, 7.5 μm, and 10 μm) are included to explore their effects on the cooling performance. The results demonstrate that the circumferentially-averaged Nusselt number, Nucir, increases with the increase of mist concentration, and this effect becomes prominent when the droplet diameter increases. For droplet diameter of 10 μm and mist concentration of 20%, Nucir can increase by 12.6% to 309.7% as compared to pure air. In addition, the empirical correlations of the global-averaged Nusselt number, and friction coefficient to the mist diameter and mist concentration are given for the first time. It is concluded that the thermal performance factor, which can be used to evaluate comprehensively the cooling characteristics, increases with the increase of mist concentration and droplet diameter. The empirical correlations and thermal performance evaluation provide the basis for further theoretical analysis of the cooling performance using air/mist mixture.

Finite Element Method for Non-Newtonian Radiative Maxwell Nanofluid Flow under the Influence of Heat and Mass Transfer

The recent study was concerned with employing the finite element method for heat and mass transfer of MHD Maxwell nanofluid flow over the stretching sheet under the effects of radiations and chemical reactions. Moreover, the effects of viscous dissipation and porous plate were considered. The mathematical model of the flow was described in the form of a set of partial differential equations (PDEs). Further, these PDEs were transformed into a set of nonlinear ordinary differential equations (ODEs) using similarity transformations. Rather than analytical integrations, numerical integration was used to compute integrals obtained by applying the finite element method. The mesh-free analysis and comparison of the finite element method with the finite difference method are also provided to justify the calculated results. The effect of different parameters on velocity, temperature and concentration profile is shown in graphs, and numerical values for physical quantities of interest are also given in a tabular form. In addition, simulations were carried out by employing software that applies the finite element method for solving PDEs. The calculated results are also portrayed in graphs with varying sheet velocities. The results show that the second-order finite difference method is more accurate than the finite element method with linear interpolation polynomial. However, the finite element method requires less number of iterations than the finite difference method in a considered particular case. We had high hopes that this work would act as a roadmap for future researchers entrusted with resolving outstanding challenges in the realm of enclosures utilized in industry and engineering.

Shape optimization of chilled concrete ceilings – Reduced embodied carbon and enhanced operational performance

The design of lightweight, thermally activated concrete floor systems offers the opportunity to simultaneously tackle two of the most urgent challenges currently faced by the built environment: reducing the use of concrete, responsible for 5–8% of global carbon emissions, and implementing energy-efficient cooling strategies to mitigate the consequences of extreme heat events. This paper introduces a novel chilled concrete ceiling technology integrated into the structural floor slab. This system reduces embodied carbon and enhances operational performance through rigorous structural-thermal shape optimization. As a radiant ceiling with embedded water pipes, the system's cooling capacity improves due to the extended exposed surface provided by the shaping. Additionally, condensation risk decreases as thermal comfort is reached through warmer surface temperatures.Two cooling-dominated climates and five slab geometries are analyzed using a multi-objective optimization approach, achieving Pareto optimal designs that reduce their embodied carbon by up to 52.5% while achieving 12–14% operational savings relative to conventional prismatic floors. The latter can be reduced by as much as 22–32% at the expense of lowering the embodied savings to 30%. Further, this work introduces a novel method for simulating shaped thermally activated surfaces in Building Energy Modeling (BEM) platforms. An equivalent flat slab model is proposed to transfer the complex 3-D heat transfer processes captured by numerical Conjugate Heat Transfer (CHT) methods into annual, climate-specific simulations. This solution offers a flexible and modular framework that allows architects and engineers to replicate the structural-thermal analysis conducted in this work for other locations and geometries of interest.

Numerical Simulation of the Flow and Heat Transfer Characteristics of Sweeping and Direct Jets on a Flat Plate with Film Holes

The internal heat transfer performance and flow structures of a sweeping jet and film composite cooling on a flat plate were numerically studied. Sweeping jet and film composite cooling consists of a fluidic oscillator and 20 cylindrical film holes; the direct jet is formed by removing the feedback from the fluidic oscillator, which is different from the traditional cylindrical nozzle. Four different mass flow rates of coolant were considered, and the inclination angle of the film hole was 30°. The Conjugate Heat Transfer method (CHT) and Unsteady Reynolds Averaged Navier Stokes equation (URANS) were employed. The results indicated that the flow resistance coefficients of the sweeping jet were larger than those of the direct jet, and the Nusselt number monotonously increased with the increase in the mass flow rate. Compared to the direct jet, the sweeping jet had a more spatially uniform heat removal rate, and the area-averaged Nusselt number was slightly lower. Therefore, the sweeping jet and film composite cooling caused the distribution of the flat plate heat transfer to be more uniform. It is worth noting that the novel direct jet nozzle in the present work had considerable area-averaged impingement cooling effectiveness.

Multiscale Modeling of Gas–Solid Surface Interactions Under High-Temperature Gas Effect

The high-temperature gas effect is critical to the design of high-speed aircraft in terms of the thermal protection at their surfaces. However, studies on this topic are challenging for both experiments and numerical simulation. To cope with the breakdown of continuum methods and the extremely high cost of molecular methods, a multiscale model and simulation method for flow, diffusion, adsorption/desorption, reaction, and heat transfer is developed to understand the gas effect based on hard-sphere/pseudo-particle modeling (HS-PPM). The model was first used to describe the catalytic reactions of high-temperature gas without flow on the surface of copper, tungsten, platinum, nickel, silicon dioxide, etcetera. The recombination coefficients of oxygen and nitrogen atoms obtained at different temperatures are in good agreement with the existing simulation and experimental results, which verified the effectiveness and accuracy of the approach. The approach is also capable of simulating the complex physical and chemical processes in the gas flow near the silicon dioxide surface, with the critical flow velocity slip and temperature jump reasonably reproduced. These studies demonstrated that HS-PPM can be a comprehensive virtual experimental tool for the study of surface catalytic characteristics of thermal protection materials in a hypersonic environment and accurate prediction of the aerodynamic thermal behavior there.

An enthalpy-based cascaded lattice Boltzmann method for solid-liquid phase-change heat transfer

• The CLB method is extended to simulate solid-liquid phase-change problems. • The unphysical numerical diffusion can be effectively eliminated by the CLB method. • The CLB method can achieve better numerical stability due to the enhanced Galilean invariance. In this paper, a cascaded lattice Boltzmann (CLB) method for investigating solid-liquid phase-change heat transfer is developed. In the CLB method, the enthalpy methodology is adopted to capture the solid-liquid phase interface implicitly. Mesoscopically, the enthalpy is defined as the basic evolution variable of the CLB equation of the temperature field so as to consider the phase-change effect in simulations without iteration procedure, and to achieve this purpose, the cascaded collision process is artfully designed by modifying the shifting procedure. Numerical results demonstrate that the enthalpy-based CLB method can serve as an accurate and reliable numerical tool for simulating solid-liquid phase-change heat transfer.