Steady Heat Source Research Articles

Enhancement of material properties of SS 316 L base metal by TIG cladding process

The Tungsten Inert Gas (TIG) welding process was utilized to apply stainless steel (SS) 304 filler cladding onto the stainless steel (SS) 316 L base metal. This cladding resulted in an enhancement of the base metal's properties. An optical study and scanning electron microscope (SEM) analysis conducted to investigate the metallurgical properties revealed refined grain structures, indicating improved deposition of the SS 304 filler. The optical survey classified the different zones as base metal, weld metal, and transition line, with the transition line distinguishing the deposition of the filler metal through the cladding process. The refined grain structures, optimal process parameter selection (current, gas flow rate, and travel speed at a minimal level), and double-pass cladding have significantly influenced microhardness and tensile test values. The cladding of SS 304 fillers on SS 316 L alloys demonstrated improvement in the microhardness and tensile properties by 42.5 % and 13.2 %, respectively. Further investigation into the nozzle gun's heat input, current, and travel speed showed that maintaining a consistent travel speed with a steady heat source had a substantial impact on the material properties of the base metal.

Evaluating crown scorch predictions from a computational fluid dynamics wildland fire simulator

BackgroundCrown scorch—the heating of live leaves, needles, and buds in the vegetative canopy to lethal temperatures without widespread combustion—is one of the most common fire effects shaping post-fire canopies. Despite the ability of computational fluid dynamic models to finely resolve fire activity and buoyant plume dynamics including heterogenous 3D distributions of forest canopy heating, these models have had only limited use in simulating fire effects and have not been used to evaluate crown scorch. Here, we demonstrate a method of evaluating crown scorch using a computational fluid dynamics model, FIRETEC, and validate this approach by simulating the experiments that were used to develop Van Wagner’s 1973 crown scorch model.ResultsThe average scorch height prediction from FIRETEC compares well with the empirical model derived by Van Wagner, which is the most widely used empirical model for crown scorch. We further find that the 3D buoyant plume dynamics from a steady and homogeneous idealized heat source on the ground results in a spatially heterogenous crown scorch pattern reflecting complex heating dynamics that are best represented by percent scorch rather than height of scorch.ConclusionsThe ability of the computational fluid dynamics model to capture variation in crown scorch due to 3D buoyant plume dynamics provides direct links between forest structure, fire behavior, and fire effects that can be used by forest managers and researchers to better understand how fires result in crown damage under various environmental and management scenarios.

Experimental and numerical analysis of cosine wave heat source on thermal storage performance of a conical spiral shell-tube energy storage system

Solar radiation is the main driving force for the energy source of solar collectors, and its intensity determines the amount of energy that solar collectors can absorb. Therefore, the periodicity of radiation intensity will lead to periodic fluctuations in the outlet water temperature of solar collectors. This study numerically investigates the effects of the heat source period, amplitude, inlet flow rate, and steady state heat source temperature on the thermal storage performance of conical spiral shell-tube energy storage systems when the inlet temperature varies periodically as a cosine function using fluent software. The results show that when heat source periods are between 5 and 300 min, compared to the constant heat source, the total energy storage capacity can be increased by a maximum of 7.32 %. The melting time can be shortened by a maximum of 16.31 %. The average energy storage rate and energy storage efficiency can be increased by a maximum of 4.08 % and 0.17 %, respectively. When amplitudes are increased from 0 to 20 K, the melting time, total energy storage capacity, and energy storage efficiency are reduced by 30.21 %, 1.19 %, and 1.64 %, respectively. The average energy storage rate increases by 41.59 %. Furthermore, compared to the constant heat source, increasing the inlet flow rate and steady state heat source temperature has more significant effects on the thermal storage performance under cosine wave heat sources. The results can provide some reference for the optimization of phase change thermal storage systems under unsteady state conditions.

Dynamical Tests of a Deep Learning Weather Prediction Model

Abstract Global deep learning weather prediction models have recently been shown to produce forecasts that rival those from physics-based models run at operational centers. It is unclear whether these models have encoded atmospheric dynamics or simply pattern matching that produces the smallest forecast error. Answering this question is crucial to establishing the utility of these models as tools for basic science. Here, we subject one such model, Pangu-Weather, to a set of four classical dynamical experiments that do not resemble the model training data. Localized perturbations to the model output and the initial conditions are added to steady time-averaged conditions, to assess the propagation speed and structural evolution of signals away from the local source. Perturbing the model physics by adding a steady tropical heat source results in a classical Matsuno–Gill response near the heating and planetary waves that radiate into the extratropics. A localized disturbance on the winter-averaged North Pacific jet stream produces realistic extratropical cyclones and fronts, including the spontaneous emergence of polar lows. Perturbing the 500-hPa height field alone yields adjustment from a state of rest to one of wind–pressure balance over ∼6 h. Localized subtropical low pressure systems produce Atlantic hurricanes, provided the initial amplitude exceeds about 4 hPa, and setting the initial humidity to zero eliminates hurricane development. We conclude that the model encodes realistic physics in all experiments and suggest that it can be used as a tool for rapidly testing a wide range of hypotheses.

Effect of entropy waves on the thermoacoustic instability of choked outlet combustion chambers

Thermoacoustic instability is a major issue in aero-engine and gas turbine combustion chambers, especially for the case of lean premixed combustion. The instability is caused by the interaction of acoustic waves with unsteady heat release. As considering the accelerated entropy waves in the system, the entropy effect on the acoustic waves cannot be ignored, which will further modify the thermoacoustic instability. Recent researches have shown that the entropy waves can be generated by the steady heat sources or temperature gradients, which can exclude the interference of unsteady heat release factors in instability analysis. In this study, the effect of entropy waves on the thermoacoustic instability of the combustion chamber model with choked outlets is investigated by constructing a low-order acoustic network model. New modes introduced by entropy waves, called as the entropy acoustic modes (EA modes), are investigated by a steady heat source. Then the unsteady heat release is considered, and the effect of entropy waves on different modes and the coupling behavior of these modes are analyzed comprehensively. It is found that some modes are jointly affected by the flame, entropy waves as well as the acoustic waves, which are called as the entropy thermoacoustic modes (ETA modes). Moreover, the modal frequencies of the intrinsic thermoacoustic instabilities modes (ITA modes) are changed remarkably due to the introduction of entropy waves. In addition, the entropy wave dispersion and dissipation show a non-negligible effect on the thermoacoustic instability.

Triple diffusive Marangoni convection in a fluid-porous structure: Effects of a vertical magnetic field and temperature profiles

In this study, the triple diffusive Marangoni convection (TDMC) problem when a steady heat source is present in both layers and a vertical uniform magnetic field in a fluid-porous structure is investigated in closed form. The horizontally infinite fluid-porous structure, which is horizontally surrounded by adiabatic boundaries and subjected to basic uniform and non-uniform temperature profiles. For all three temperature profiles (TP), linear, parabolic and inverted parabolic, the eigenvalues, the thermal Marangoni numbers (TMNs) are determined in closed form for lower rigid and upper free boundaries with surface tension, depending on both temperature and concentrations. The effects of relevant parameters on the eigenvalues, hence on TDMC, against depth ratio are attempted for all TPs. It is noticed that, the inverted parabolic TP on TDMC in a composite layer is the most stable of all the three TPs, the linear TP is the most unstable one and the parabolic TP is the moderate one. The relevant physical parameters considered in the study are effective for porous layer dominant fluid-porous structures.

Energy and exergy study of the integrated adsorption-absorption system driven by transient heat sources for cooling and desalination

The scarcity of clean water and the lack of sustainable cooling systems are continuously pressing. Although many technologies are well-established, such as vapour compression for refrigeration and reverse osmosis for desalination, they are energy-intensive and conventional refrigeration technology utilising working fluids of long-lasting ozone-depleting and greenhouse effects. Alternatively, adsorption and absorption technologies can meet such demands, and they are the most feasible to utilise the waste and renewable heat abundant in many locations. Therefore, this paper computationally studies the emerging integrated adsorption-absorption system for cooling cum desalination employing transient waste heat sources of various waveform characteristics. A previously validated computational model for the adsorption subsystem was coupled with a thermodynamic model for the absorption subsystem and experimental heat profiles obtained from an internal combustion engine. The energy and exergy analysis of the integrated system utilising the actual heat source from an internal combustion engine and predefined waveforms were undertaken and benchmarked against that operated under steady heat sources. The integrated system operated with a relatively low exergy efficiency in the absorption cycle of up to 15.33%. The adsorption bottoming cycle successfully utilised the heat from the absorption subsystem at a relatively higher exergy efficiency of up to 42.69%. The execution of a transient heat source of sinusoidal waveform enhanced the water production by up to 30% and the cooling of absorption and adsorption subsystems by 24% and 15%, respectively. However, admitting realistic waveforms of an internal combustion engine showed marginal differences compared to the steady heat sources owing to their high frequencies and small amplitudes.

An integrated smart thermo-chemical energy network

Managing the intermittency of renewable sources together with transient (hourly to daily to seasonal) energy demands is one of the principal challenges of delivering a net-zero energy system. Smart multifunctional thermo-chemical energy networks represent an alternative energy network and storage system, a solution based on the distribution of energy via thermo-chemical material rather than thermal energy, gas, fuels or electricity– an option that has scope for integrated short- and long-term energy storage. This is the first research work to realise such a system and demonstrate how it might operate using smart control strategies and how thermo-chemical fluids (TCFs) can be used as a medium for timely energy storage and distribution. The experimental study also describes the effect of steady and variable heat sources on TCF regeneration performance and estimates the potential of thermo-chemical energy networks, which would be particularly beneficial in buildings with high energy consumption for humidity control. This research proves the practicality of the design idea for such a network, which would be governed by centralised control, regenerated by steady or transient heat loads and capable of supplying a variety of demands in an experimental setting. The energy and economic potential of the network were also assessed, identifying temperature and humidity control application scenarios with energy savings of more than 60% compared to conventional operation and payback periods of 6.6–9.7 years.

Theoretical analysis of sound propagation and entropy generation across a distributed steady heat source

Acoustic and entropy waves interacting in a duct with a steady heat source and mean flow are analysed using an asymptotic expansion (AE) for low frequencies. The analytical AE solutions are obtained by taking advantage of flow invariants and applying a multi-step strategy. The proposed solutions provide first-order corrections to the compact model in the form of integrals of mean flow variables. An eigenvalue system is then built to predict the thermoacoustic modes of a duct containing a distributed heat source or sink. Predictions from the AE solutions agree well with the numerical results of the linearised Euler equations for both frequencies and growth rates, as long as the low-frequency condition is satisfied. The AE solutions are able to accurately reconstruct the acoustic and entropy waves and correct the significant errors in the predicted entropy wave associated with the compact model. The analysis illustrates that the thermoacoustic system needs to account for the entropy wave generated by the interaction of acoustic wave and the distributed steady heat source, especially when density- or entropy-dependent boundary conditions are prescribed at the duct ends. Furthermore, a combination of the AE method and the modified WKB approximation method is discussed for a cooling case. The AE solutions remedy the disadvantage of the WKB solution in the low and very low-frequency domain and facilitate full-frequency theoretical analyses of sound propagation and entropy generation in inhomogeneous duct flow fields.

Electron Heat Source Driven Heat Transport in GaN at Nanoscale: Electron-Phonon Monte Carlo Simulations and a Two Temperature Model.

The thermal energy transport in semiconductors is mostly determined by phonon transport. However in polar semiconductors like GaN electronic contribution to the thermal transport is non-negligible. In this paper, we use an electron–phonon Monte Carlo (MC) method to study temperature distribution and thermal properties in a two-dimensional GaN computational domain with a localized, steady and continuous electron heat source at one end. Overall, the domain mimics the two-dimensional electron gas (2DEG) channel of a typical GaN high electron mobility transistor (HEMT). High energy electrons entering the domain from the source interact with the phonons, and drift under the influence of an external electric field. Cases of the electric field being uniform and non-uniform are investigated separately. A two step/temperature analytical model is proposed to describe the electron as well as phonon temperature profiles and solved using the finite difference method (FDM). The FDM results are compared with the MC results and found to be in good agreement.

Investigation of effective thermal conductivity of SiC foam ceramics with various pore densities

Abstract SiC foam ceramics are extensively used in numerous industrial applications that require high-temperature conditions. They can be used as thermal insulation, structural catalyst supports and energy storage materials. In this article, effective thermal conductivity of SiC foam ceramics at high temperature is studied by steady plane heat source method. This research aims to investigate the variations of effective thermal conductivity with pore density, stacking thickness, heat source temperature, and pore arrangement structure of foam ceramics. By a comparison of effective thermal conductivities of various pore density ceramic sheets, the experimental results show that the effective thermal conductivity of foam ceramics decreases with the increase of the pore density and stacking thickness. The effective thermal conductivity of the foam ceramics increases significantly when the heat source temperature is more than 200°C. For modular SiC foam ceramics, increasing the average pore density and sudden change of the pore density between ceramic sheets are not conducive to the increase of the effective thermal conductivity.

Experimental investigation on the thermal performance of a heat sink filled with PCM

Electronic devices and technologies have been revolutionized to meet future needs and users demands in terms of size, cost, and performance. Therefore, miniaturized devices have been of great interest and under investigation for the last decade. This demand requires attaining no less performance than achieved with large scale devices and designs. Hence, it becomes crucial to improve performance through changing physical design and/or utilized materials such as using composites or phase change material (PCM). In this study, two designs for heat sinks in the form of plates were created. The first was solid, whereas the second was hollow and contained PCM. Both of them were subjected to the same experiment conditions. The goal of the research is to figure out the overall temperature accomplished of both samples and to determine the impact of adding PCM to heat sinks thermal performance. The general design methodology for the heat sink is as follow: a steady heat source is applied to the plate fin heat sink's base. The plate heat sink's thermal efficiency was compared with and without the use of PCM. The results revealed that including PCM into the heat sink plate improves cooling and maintains the target temperature. Furthermore, the heat sink with a PCM outperformed by 30% compared to heat sink without PCM.

Effects evaluation of fin layouts on charging performance of shell-and-tube LTES under fluctuating heat sources

The previous studies focus on the heat storage process of shell-and-tube latent thermal energy storage (LTES) under steady heat sources, without considering the fluctuating and intermittent characteristics of the most available heat sources in real applications. The effect of different fin sizes and locations on the charging performance of shell-and-tube LTES still keeps unclear under fluctuating heat source, and it is critical to improve the heat storage rate and density due to the low thermal conductivity of phase change materials (PCM). Consequently, this study aims to investigate the charging performance of a shell-and-tube LTES considering different fin layouts. Firstly, the effects of different fin number and configurations on heat storage process are performed under fluctuating heat sources. The case with comprehensive performance of high melting rate and large heat storage capacity is obtained. Then the effects of critical parameters on the charging process, including the fin angle, fin thickness, fin height and deviation distance of tube under fluctuating heat sources are further analyzed based on this case, and the results are compared with that of steady heat source. Results indicate that the fin height is the dominant factor influencing the heat storage rate and density under both steady and fluctuating heat source conditions, while the total melting time is shorter and the heat storage capacity is smaller, and the heat storage capacity is less obvious with the variation of fin parameters under the fluctuating heat source. In addition, the effect of downward deviation distance of tube on heat storage capacity is much obvious under fluctuating heat source than that of steady heat source.

Sensitivity analysis of thermophysical properties on PCM selection under steady and fluctuating heat sources: A comparative study

Previous studies on phase change material (PCM) selection for latent thermal energy storage (LTES) mainly focused on steady heat source conditions without considering the effects of thermal fluctuation of real heat sources, and how fluctuating heat sources will affect the charging performance of LTES and material selection is still unclear. This study aims to compare the difference in material selection for a shell-and-tube LTES under steady and fluctuating heat sources, which comprehensively considers the effects of PCM thermophysical properties including the melting temperature, density, specific heat capacity, thermal conductivity and latent heat, as well as their interaction effects. By taking heat storage capacity and charging rate as objectives, orthogonal experiment design and stepwise regression analysis have been conducted to specify the significant factors among these parameters under steady and fluctuating heat source conditions. To further investigate the difference in the ranking of candidate PCMs under two conditions, fourteen pre-screened PCMs are ranked under steady and fluctuating heat sources. The results show that the order of prominent factors for heat storage capacity is ρ·Cp, followed by ρ·L under both conditions. However, when considering the charging rate, temperature fluctuation will weaken the effect of melting temperature, and strengthen the effect of specific heat capacity and latent heat. The order of prominent factors for charging rate is λ·Cp and Cp·L under fluctuating heat source. According to the ranking results, LiNO3-NaNO2 within the melting temperature of 100–200 °C has an excellent comprehensive charging performance under both conditions.

Transient analysis of layered beams subjected to steady heat supply and mechanical load

In this study, an analytical model is developed for the analysis of transient temperature, displacements, and stresses in simply supported layered beams. The beam is suddenly heated from the top and bottom surfaces by external steady heat sources and is subjected to a mechanical load. The temperature in each layer is variable along the thickness and follows the one-dimensional (1-D) transient heat transfer equation. The Laplace transform approach is used to obtain the transient temperature field in the beam. The thermoelastic constants of the beam are temperature-dependent. Dividing every layer into a series of thin slices, the temperature and the thermoelastic constants for each slice can be considered uniform. The two-dimensional (2-D) thermoelasticity theory is adopted to derive the governing equations of displacements and stresses in each slice. The transfer matrix method is applied to obtain the displacement and stress solutions for the beam. As an example, the distributions of transient temperature, displacements, and stresses in a three-layer beam are studied. The effects of the temperature dependent thermoelastic constants on the mechanical behavior of the beam are discussed in detail.

Thermodynamic analysis and improvement of cascaded latent heat storage system using temperature-enthalpy diagram

In order to analyze and improve the cascaded latent heat storage (CLHS) system under the steady heat source, a novel method based on the temperature-enthalpy (T-H) diagram was developed. The heat storage and release processes can be intuitively described by the T-H diagram when the minimum temperature difference ΔTmin related to heat transfer capacity is defined, which is helpful to evaluate the CLHS performance and find heat transfer bottlenecks. The implementation steps of the proposed method were specified in detail, and three typical cases were presented to verify its feasibility. Moreover, an optimization model for the CLHS system was proposed. The optimal melting temperatures of PCMs can be obtained by solving the multivariate linear equations, and meanwhile, a general expression of the optimal melting temperature was derived. Furthermore, the main and interaction effects of the three model parameters were investigated. The results show that a larger stage number Ns, a smaller minimum temperature difference ΔTmin, and a heat capacity flow rate ratio R with a value slightly greater than 1 are recommended. In short, the novel method is primarily graphical and heuristic-based, which provides the benefits of being easy to understand and ready to be used in practice.

Effects of fluctuating thermal sources on a shell-and-tube latent thermal energy storage during charging process

The fluctuating and intermittent nature of industrial heat sources is a crucial technical barrier limiting the implementation of heat recovery energy systems. Latent Thermal Energy Storage (LTES) has the potential to overcome these issues by maintaining a Waste Heat Recovery (WHR) system within designed operation conditions to achieve effective and efficient operation. However, the dynamic heat transfer characteristics of LTES under fluctuating heat sources need to be studied further to better understand the effects of thermal fluctuation. In this work, the charging performance of a shell-and-tube LTES under fluctuating and steady heat source has been investigated and analysed. The effects of period and amplitude for the fluctuating heat source, as well as the Stefan number, are investigated in detail. Results indicate that large-period fluctuating heat sources can considerably reduce the total melting time but also reduce the energy storage capacity, whilst small-period fluctuating heat sources have almost no effect on the melting process of LTES. For the effects of fluctuating amplitude, both the total melting time and energy storage capacity decline at a decreasing rate with an increase of fluctuating amplitude. These results can bridge the knowledge gap needed for future designs of shell-and-tube LTES for fluctuating heat sources used with heat recovery applications.

Characterization of MILD Combustion of a Premixed CH4/Air Jet Flame versus Its Conventional Counterpart.

This study is performed to characterize moderate or intense low-oxygen dilution (MILD) combustion (MC) versus conventional combustion (CC) of a premixed CH4/air jet flame in a hot coflow under identical inlet and ambient conditions. The present CC and MC correspond to the cases using a bluff-body (BB) and a no bluff-body (NBB), respectively. It is demonstrated that the NBB combustion develops by entraining ambient hot low-oxygen gas so as to dilute the reactant mixture and simultaneously heat up beyond the minimum autoignition temperature (Tai), leading to the MC. By contrast, in the BB case, the conventional flame is established and stabilized by a steady heat source of the recirculation zone (RZ) behind the BB with highly intense mixing and rapid ignition. A large reaction zone with uniform temperature distribution (i.e., low temperature rise) is found in the MC mode, while the CC has a much smaller size of the intense reaction zone with the concentrated high temperature and species distributions. Significantly, it has been first revealed that, in the BB case, there is a secondary combustion in the MC mode formed far downstream from the BB flame under the environmental condition of a high-temperature hot coflow.

Development of a robust, field-deployable loop-mediated isothermal amplification (LAMP) assay for specific detection of potato pathogen Dickeya dianthicola targeting a unique genomic region.

Destructive maceration, a wide host range, and longevity in non-plant substrates has established Dickeya dianthicola (blackleg of potato) as a significant threat to potato industries worldwide. To protect these businesses, a specific and sensitive point-of-care D. dianthicola detection tool is necessary. We have developed a loop-mediated isothermal amplification (LAMP) assay for specific, sensitive, and rapid detection of D. dianthicola, which can be streamlined for point-of-care use. The developed LAMP assay targets a unique gene, alcohol dehydrogenase, of D. dianthicola. Assay specificity was assessed using strains present in inclusivity (16 D. dianthicola strains) and exclusivity panels (56 closely related, potato pathogenic, and other bacterial strains). Amplification with strains of inclusivity panel occurred, and cross-reactivity with non-target DNA was not observed. The limit of detection (LOD) was 10 CFU/ml when dilutions were made before isolating the genomic DNA; however, LOD was determined as 1 pg using 10-fold serially diluted D. dianthicola genomic DNA. Similar LOD of 1 pg was observed when serially diluted target genomic DNA was mixed with host genomic DNA. LOD (1 pg) was also calculated with 10-fold serially diluted synthetic DNA fragments containing primer target sites. Naturally and artificially inoculated plant samples were used for field adaptability tests with the field-deployable Optigene Plant Material Lysis Kit and a heat block (65°C); the results were obtained within 20 minutes. Despite the lack of method precision, no false positives or false negatives were observed. Therefore, with prepared reactions and a steady heat source, this assay can be used for rapid point-of-care detection, which is imperative for quarantine, eradication, disease management, and border protection.

一维稳定热源对纯水加热温度场的模拟研究

一维稳定热源对纯水加热温度场的模拟研究