Heat Transfer Process Research Articles

Investigating swastika fins to enhance heat transfer and melting process of nano-enhanced phase change materials units

The ability of nano-enhanced phase change materials (NePCM) to store thermal energy has garnered the interest of scientists. An approach to enhancing thermal conductivity involves the implementation of novel fins that facilitate a more rapid PCM melting process. The present investigation assessed the efficacy of eight distinct fin configurations in augmenting the thermal properties of NePCM. Four occurrences featured swastika fins, whereas the remaining instances exhibited a 45-degree tilt angle. The enthalpy-porosity method was implemented to simulate heat transfer and melting process. The present research investigates the effects of fin tilt angles and swastika fins on the NePCM-thermal energy storage (TES) unit's mean temperature, liquid percentage, and thermal energy storage. Compared to the straight fins (Case 1), the long-arm swastika fins (Case 4) decreased the melting time by a factor of 2.3. In addition, Case 4 demonstrated exceptional thermal energy storage capabilities. Case 7 demonstrated that the tilting angle significantly affected the melting time, with a reduction of 34.9 %, compared to the non-tilted swastika fins utilized in Case 2. However, the increase in the fins' length was more substantial. According to the findings of this study, Case 4 is the optimal fin configuration for NePCM-TES.

Reinforcement learning for cooling rate control during quenching

PurposeThe premise of this research is that the coupling of reinforcement learning algorithms and computational dynamics can be used to design efficient control strategies and to improve the cooling of hot components by quenching, a process that is classically carried out based on professional experience and trial-error methods. Feasibility and relevance are assessed on various 2-D numerical experiments involving boiling problems simulated by a phase change model. The purpose of this study is then to integrate reinforcement learning with boiling modeling involving phase change to optimize the cooling process during quenching.Design/methodology/approachThe proposed approach couples two state-of-the-art in-house models: a single-step proximal policy optimization (PPO) deep reinforcement learning (DRL) algorithm (for data-driven selection of control parameters) and an in-house stabilized finite elements environment combining variational multi-scale (VMS) modeling of the governing equations, immerse volume method and multi-component anisotropic mesh adaptation (to compute the numerical reward used by the DRL agent to learn), that simulates boiling after a phase change model formulated after pseudo-compressible Navier–Stokes and heat equations.FindingsRelevance of the proposed methodology is illustrated by controlling natural convection in a closed cavity with aspect ratio 4:1, for which DRL alleviates the flow-induced enhancement of heat transfer by approximately 20%. Regarding quenching applications, the DRL algorithm finds optimal insertion angles that adequately homogenize the temperature distribution in both simple and complex 2-D workpiece geometries, and improve over simpler trial-and-error strategies classically used in the quenching industry.Originality/valueTo the best of the authors’ knowledge, this constitutes the first attempt to achieve DRL-based control of complex heat and mass transfer processes involving boiling. The obtained results have important implications for the quenching cooling flows widely used to achieve the desired microstructure and material properties of steel, and for which differential cooling in various zones of the quenched component will yield irregular residual stresses that can affect the serviceability of critical machinery in sensitive industries.

Effect of the Tesla Valve on the heat transfer performance and the suppression of pressure drop oscillation in a liquid cooling loop

The suppression of pressure drop oscillation within a liquid cooling loop is necessary to maintain the system stability and develop a steady heat transfer performance. The Tesla Valve is proposed as a means of eliminating this instability by suppressing the backward flow, which in turn facilitates a stable heat transfer process. The steady-state analysis is performed to identify the conditions that would induce flow instability. The calculated results indicate that the flow instability will appear when the heat flux (q) reaches a threshold value of 28 W/cm2. Furthermore, the impact of the Tesla Valve on the suppression of instability and the heat transfer coefficient is revealed by comparison with the dynamic features observed in a common liquid cooling loop. Two flow instability regimes, with and without backflow, are observed in the common liquid cooling loop. In the case of the former instability, a violent fluctuation in both the inlet temperature and the heat transfer coefficient is captured. This phenomenon can be effectively eradicated by the Tesla Valve. In the latter instability regime, the hydrodynamic characteristics of pressure drop remain significantly oscillatory, while the heat transfer performance returns stable. Furthermore, this specific form of instability cannot be eliminated by the prototype I of Tesla Valve when q ≥ 30.4 W/cm2. In addition, the liquid cooling loop with prototype III displays a superior heat transfer performance, yet results in an additional pressure drop of 8.1 kPa in comparison to prototype II. To assess the suppression mechanism and efficiency, the Suppression Factor (Fs) and Coefficient of Suppression Performance (Fc) are proposed. It can be found that the pressure drop oscillation instability can be thoroughly suppressed by the Tesla Valve when Fs > 1. Meanwhile, the greater the Fc, the more effective the suppression performance. However, the incorporation of the Tesla Valve shows a negligible effect on the heat transfer performance in the two-phase region.

A critical review on synthesis and application aspect of venturing the thermophysical properties of hybrid nanofluid for enhanced heat transfer processes

Recently, nanofluids (NFs) have gathered significant attention among researchers due to their varied properties, which can be made per the requirements. NFs, created by infusing nanoparticles into a base-fluid, enhance their fundamental properties. A hybrid nanofluid (HNF) is a nanofluid (NF) containing different types of nanoparticles, and it is being studied for its customizable properties. Recently, researchers delved into the applications regarding HNFs, particularly in cases relating to heat transfer (HT). This study analyzes HNFs’ preparation methods and thermophysical properties, giving more importance to their applications in HT, including heat-exchange, solar thermal, and cooling systems. Considering stability, the two-step synthesis method is preferred over the single-step method. Multiple research efforts have led to the development of a fluid that possesses superior HT capabilities compared to the base-fluid. However, while bettering HT, an increase in volume concentration (VC) also raised challenges such as increased viscosity and pressure drop, particularly in porous media, necessitating additional pumping power. The use of turbulators and other configurations, along with HNF in systems like parabolic trough solar collectors (PTSCs), enhances solar thermal systems (STSs) by improving their HT capabilities. An advantageous use of EG-based multiwalled carbon nanotubes (MWCNTs) NF in solar collectors (SCs) is their ability to increase thermal efficiency and decrease carbon dioxide emissions, making them an attractive choice for use in SCs. Researchers face significant challenges in determining the ideal composition and concentration of nanoparticles in HNFs to attain optimal HT without causing excessive viscosity that could impede practical usability. Specifically, this study examines the distinctive thermophysical characteristics of HNFs that substantially improve their efficacy in HT applications.

Performance of an additive-manufactured precooler under high-temperature and negative pressure environment

This paper introduces an original plate-fin precooler designed for potential applications in extreme low-pressure environments. Utilizing additive manufacturing technology, the heat transfer plate thickness is constrained to 2.0 mm, with channel widths inside the plate achieving 0.8 mm. Through experimental methods, this study aims to assess the precooler’s performance and identify critical influencing factors. Experimental results indicate that the hot fluid inlet temperature to the precooler exceeds 1100 K, with static pressures dropping below 30 kPa. Despite these conditions, the precooler demonstrates an impressive pressure recovery coefficient exceeding 97 % and achieves a maximum temperature drop of 731.4 K for the hot fluid. Furthermore, it is observed that the overall performance of the precooler diminishes with increasing mass flow rates of the hot fluid, showing fluctuations of up to 25 % when assessed by the j/f1/3 factor. Additionally, while the hot fluid inlet velocity exceeds 90 m/s, laminar flow predominates during the heat transfer process. Moreover, regardless of whether the cooling fluid experiences a phase change within the precooler, its heat transfer performance show priority than that of the hot fluid. Thus, changes in the mass flow rate of the cooling fluid have minimal impact on the overall precooler performance. Finally, the first-stage heat exchanger plays a critical role in the heat transfer process, accounting for over 2/3 of the total temperature and pressure drop for the hot fluid. This research is expected to contribute to the design of high-efficiency, low-resistance precoolers, particularly those applied for operation under negative pressure conditions.

Numerical investigation of thermal soak within engine bay using lattice Boltzmann method

A large amount of heat accumulates in the engine bay for a short time after the engine runs at high load and shuts down, that will lead to thermal damage and thermal fatigue caused by the temperature rise of some heat sensitive components. This paper uses an aero-thermal coupling approach to study the heat transfer problem in the engine bay of an SUV model under thermal soak conditions. Due to the transient characteristics of the heat transfer process, the natural transient CFD software developed based on the LBM method is used to study the engine bay heat transfer during the 400 s key-off soak process. The analysis reveals that convection and radiation are the main heat transfer modes in the early stage of hot immersion (0–120 s), and conduction only makes a significant contribution in contact with high temperature sources. The radiation and convection are the key contributors to heat transfer processes of engine bay during soak, but the efficiency of radiation heat transfer decreases with the increase of time, whereas the efficiency of convection heat transfer is not always reduced, it will increase and then decrease with the increase of time. The coupling method established can predict the thermal state in the engine bay well, and is in good agreement with the experimental results. The results show that the error in the engine coolant temperature is less than 1 °C, and the error in the temperature of the heat-sensitive components is less than 5 °C. Finally, the potential risks of thermal damage and thermal fatigue states were assessed, providing an important reference for the control design of cooling fan running time after key-off.

Modeling the clogging process of leachate collection systems in municipal solid waste landfills: The role of temperature

The leachate collection system (LCS) is an important component of barrier systems in municipal solid waste (MSW) landfills. LCS Failure due to clogging could lead to leachate accumulation, potential soil and groundwater pollution and slope failure. LCS clogging is generally ascribed to particle deposition, biofilm growth, and calcium carbonate precipitation, while temperature strongly influences microbial activity and thus inevitably affects the clogging process of LCSs. However, the role of temperature in the process of clogging and leachate accumulation in LCSs remains unclear. The main objective of this study was to bridge this research gap by developing reasonable mathematical models and comprehensively analyzing this issue. The mathematical model involved leachate flow, solute migration, physical–chemical-biological clogging, and heat transfer processes. By conducting a series of numerical simulations, the temperature variation, clogging development, and corresponding leachate accumulation inside the system during long-term operation in both the geotextile and gravel layers were numerically analyzed and predicted. The results demonstrated that, in the gravel layer, due to the higher temperature, more thorough microbial substrate consumption led to higher production of carbonate ions and hence faster and more notable calcium carbonate precipitation. Overall, the bioactivity changes due to high temperatures could considerably accelerate the failure of LCS.

Local high temperature phenomena near the complex interfaces of thermal barrier coatings based on non-Fourier model

Thermal barrier coatings (TBCs) consist of a metal substrate (Sub), a bond coat (BC), and a ceramic top coat (TC). The ceramic coating is a porous dielectric layer with a significant relaxation time that cannot be ignored. In high-temperature environments, an irregularly shaped thermally grown oxide layer (TGO) forms between the BC and the TC. Therefore, using non-Fourier model to describe the thermal contact process of TBCs with complex interface can get more accurate results. However, it is difficult to obtain the analytical solution of this model. This paper introduces a finite volume method based on unstructured meshes to address the non-Fourier heat transfer process in the complex interfaces of multilayer TBCs. The gradient reconstruction technique is employed to calculate the cell derivatives on the surface. The method's reliability is confirmed through a comparison with a two-dimensional analytical solution. The results indicate that the thermal wave travels at a limited speed within the TC layer. After passing through the interface, the thermal wave travels very fast within the BC and Sub layers, due to the influence of thermal wave reflection and superposition, obvious local high temperature will be formed near the interface. In addition, the effects of thermal conductivity, relaxation time and interface shapes on the non-Fourier heat conduction process of TBCs are also discussed. The results of this paper are useful for the structural design and failure mechanism research in TBCs.

Thermal distillation of hypersaline waters toward zero liquid discharge via spontaneously siphon-channeling crystallized salt

Membrane distillation of hypersaline solution with low-grade waste heat is particularly outstanding to address the challenge of water-energy nexus. However, the high causticity of hypersaline solution always makes this system complicated and expensive. Here, we design a passive membrane-free thermal distiller for hypersaline desalination with high stability, easy operation and low cost. A siphon channel is constructed with the capillary wick and the crystallized salt, which can self-flush the crystallized salt and assure the stability of this passive system. Together with optimizing heat transfer process to suppress temperature polarization, the integrated distiller system can efficiently collect water and salt, achieving zero liquid discharge. The system can stably desalinate 70 g/L NaCl solution, with the water yield of 1.33 kg m−2h−1 and salt collection of about 0.34 kg m−2h−1 at 60 °C. This passive system is expected to desalinate hypersaline water in large-scale commercial production, for example, integrating with desalination industry.

Increasing the Economic Efficiency of Marine Power Plants Using Waste Heat Boilers with Controlled Flow Separation

Abstract Heat recovery of exhaust gases from main and auxiliary marine diesel engines is an effective way to improve the technical and economic parameters of marine power plants. Improvements in engine efficiency necessitate an increase in the weight-size parameters of the waste heat boilers, which makes it difficult to recover heat. Intensification of the heat transfer process is considered to be an effective way to reduce these indicators. By utilising mathematical modelling, this paper shows the effectiveness of using profiled heating surfaces of waste heat boilers for this purpose. The use of elliptical heating surfaces with a mechanism of controlled flow separation, in the form of a triangular notch, is proposed. This will reduce surface drag and increase the overall thermal-hydraulic efficiency of the heat transfer processes. It is shown that the use of such surfaces in waste heat boilers makes it possible to increase the efficiency of marine power plants in tankers with a deadweight of about 45,500 tons up to 1.5% absolute and container ships with a deadweight of about 122,000 tons up to 2.5% absolute.

Simulation study on heat and mass transfer characteristics within tubular moving bed heat exchangers

In the field of waste heat recovery, tubular moving bed heat exchangers (MBHEs) hold great promise as equipment capable of effectively handling large-sized granular materials with high temperature. To further clarify the heat and mass transfer characteristics within tubular MBHEs, this study firstly conducted detailed investigations on the contributions of different heat transfer mechanisms. The result shows that heat radiation (∼45 %) and gas film heat conduction (∼42 %) control the heat transfer processes involving tube walls, with an inlet particle temperature of 600 °C, tube wall temperature of 50 °C, and particle descent velocity of 2 mm/s. These contributions can be influenced by the inlet particle temperature and the tube wall temperature, rather than the particle descent velocity. Additionally, for a specific particle, its heat transfer state is highly depended on where it is located. Subsequently, the time-varying and space-varying characteristics of the heat transfer processes involving tube walls are studied. The results suggest that the time-varying and space-varying characteristics are inherent in tubular MBHEs due to the difficulty to achieve complete stability. Meanwhile, temporal fluctuations intensify with an increase in the inlet particle temperature, a decrease in wall temperature, or an increase in particle descent velocity. The result of power spectral density (PSD) indicates that the heat transfer processes exhibit a degree of chaotic behavior due to the nonlinear property of sub-models, as well as the randomness in particle feeding and contacts. The space-varying characteristic is mainly determined by the inlet particle temperature and the tube wall temperature, rather than the particle descent velocity. This characteristic can be observed in both the axial and circumferential directions, with the circumferential variation being more pronounced than the axial variation. Furthermore, a double-tube MBHE, a topic that has received scant attention in previous research, is investigated in comparison to a single-tube MBHE to explore the differences in heat and mass transfer between the two configurations. It indicates that under the same boundary conditions, there are differences in heat transfer results, which are attributed to the interactions between two vertically arranged tubes. These interactions are reflected in the reconstruction of particle flow patterns and the effect altering the temperature distribution for the particles or fluid surrounding the tubes. The obtained results provide valuable insights into the mass and heat transfer behaviors of particles and fluids within tubular MBHEs, laying a foundation for advancing the development of efficient tubular MBHEs.

Analysis of the magnetic-thermal response of viscoelastic rotating nanobeams based on nonlocal theory and memory effect

Size-dependent effects in elastic deformation and thermal hysteresis effects in the heat transfer process are significant for small-size structures or devices. As an important component of micro- and nanoelectromechanical systems, the analysis of the thermodynamic properties of rotating nanobeams is crucial for the safe operation of the system. This work aims to construct a new nonlocal thermo-viscoelastic model and use this model to analyze the thermodynamic behavior of rotating nanobeams at the microscale. In this work, fractional order Kelvin-Voigt theory describes the viscoelasticity of materials. Moreover, the theory of continuous medium mechanics is improved by introducing nonlocal parameters to capture the size effect during deformation. Based on the generalized thermoelasticity theory, memory-dependent derivatives predict hysteresis effects during heat transfer. Nanobeams are placed in a longitudinal magnetic field. Graphene strips connected to a power supply are used as the nanobeam heat source. The effects of nonlocal parameters, damping coefficients, and fractional order parameters on the dynamic response of the system are analyzed. In addition, a new comparative study of the effects of voltage and resistance on the system is made in the context of the nonlocal generalized thermoelasticity theory.

Finite element analysis of Cu-water nanofluid flow and heat transfer in a dynamically bulging enclosure

PurposeThe main purpose of this study is to analyze the heat transfer phenomena in a dynamically bulging enclosure filled with Cu-water nanofluid. This study examines the convective heat transfer process induced by a bulging area considered a heat source, with the enclosure's side walls having a low temperature and top and bottom walls being treated as adiabatic. Various factors, such as the Rayleigh number (Ra), nanoparticle volume fraction, Darcy effects, Hartmann number (Ha) and effects of magnetic inclination, are analyzed for their impact on the flow behavior and temperature distribution.Design/methodology/approachThe finite element method (FEM) is employed for simulating variations in flow and temperature after validating the results. Solving the non-linear partial differential equations while incorporating the modified Darcy number (10−3 ≤ Da ≤ 10−1), Ra (103 ≤ Ra ≤ 105) and Ha (0 ≤ Ha ≤ 100) as the dimensionless operational parameters.FindingsThis study demonstrates that in enclosures with dynamically positioned bulges filled with Cu-water nanofluid, heat transfer is significantly influenced by the bulge location and nanoparticle volume fraction, which alter flow and heat patterns. The varying impact of magnetic fields on heat transfer depends on the Rayleigh and Has.Practical implicationsThe geometry configurations employed in this research have broad applications in various engineering disciplines, including heat exchangers, energy storage, biomedical systems and food processing.Originality/valueThis research provides insights into how different shapes of the heated bulging area impact the hydromagnetic convection of Cu-water nanofluid flow in a dynamically bulging-shaped porous system, encompassing curved surfaces and various multi-physical conditions.

Investigating introductory and advanced students’ difficulties with entropy and the second law of thermodynamics using a validated instrument

We use the Survey of Thermodynamic Processes and First and Second Laws-Long (STPFaSL-Long), a research-based survey instrument with 78 items at the level of introductory physics, to investigate introductory and advanced students’ difficulties with entropy and the second law of thermodynamics. We present an analysis of data from 12 different introductory and advanced physics classes at four different higher education public institutions in the United States in which the survey was administered in person to more than 1000 students. We find that a widespread unproductive tendency for introductory students to associate the properties of entropy with those of energy leads to many errors based on an idea of “conservation of entropy,” in which entropy increases are balanced by equal entropy decreases. For many of the more advanced students (calculus based and upper level), we detect a tendency to expect entropy increases even in processes in which the entropy does change. We observed a widespread failure to correctly apply the relationship ΔS=Qreversible/T, either by using it for processes to which it does not apply or by applying it incorrectly or completely neglecting it in reversible processes to which it does apply. We also noted that many introductory students are simply not aware that total entropy must increase in any “spontaneous” heat transfer process. Students at all levels were very frequently found to be confused that while net entropy (system+reservoir) in reversible isothermal processes does not change, the entropy of the working substance itself does indeed increase or decrease depending on whether the process is an expansion or compression. Our findings are broadly consistent with prior research findings in this area, expanding upon them and revealing previously unreported aspects of students’ thinking. Moreover, our results reflect several new problem contexts in addition to those reported in prior research, and our sample population includes large numbers of both introductory and advanced students. Our detailed findings related to common student difficulties with entropy and the second law of thermodynamics before and after traditional instruction in college physics courses can potentially help instructors of these courses improve student understanding of these concepts. These findings can also be valuable for developing effective research-based curricula and pedagogies to reduce student difficulties and help students develop a solid grasp of these fundamental thermodynamic concepts. Published by the American Physical Society 2024

Multi-physics analysis of squeezing fluid flow with rotational, magnetic field, and heat transfer interactions

This research paper presents a comprehensive study on the intricate interplay of rotational, magnetic field and heat transfer effects in squeezing fluid flow, utilizing the foundational framework of Navier–Stokes equations. Fluid flow in confined geometries has significant applications in various industrial processes, including lubrication systems, microfluidics, and heat exchangers. The integration of rotational motion, magnetic fields, and heat transfer phenomena into this context holds immense potential for optimizing performance and efficiency. The study commences with the derivation and analysis of the coupled Navier–Stokes equations, incorporating the Coriolis force due to rotational motion, the Lorentz force arising from magnetic fields, and the energy equation for heat transfer. This comprehensive model accounts for the complex interactions between these physical phenomena, offering a holistic perspective on squeezing fluid flow dynamics. Numerical analysis are conducted to investigate the behavior of fluids under the influence of rotational, magnetic field, and heat transfer effects. The results reveal intricate flow patterns, including vortex formation and heat transfer enhancement. Furthermore, the impact of key parameters such as rotational speed, magnetic field strength, and temperature gradients on flow characteristics is systematically analyzed. The Dufour effect pertains to the transfer of energy resulting from a gradient in mass concentration, occurring as a correlated consequence of irreversible processes. It functions as the inverse of the Soret effect. The temperature changes due to the concentration gradient, amplifying as the Dufour number increases. The most significant temperature rise is observed at the midpoint of the fluid domain. Conversely, the Soret number behaves in a similar but opposite manner. Tables 4–10 has been created to offer a comprehensive analysis of the optimal alignment between Homotopy Analysis Method (HAM) and BVP4c. Specifically, it demonstrates a continuous decrease in skin friction for ξSo, ξRd, and ξR2, while showing an increase for ξSc, ξDo, and ξRem. Meanwhile, the skin friction remains constant for ξPr. The research centers on analyzing heat and mass transfer properties within an incompressible fluid confined between two rotating and stretching disks amidst an unpredictable flow pattern. The study employs a blend of analytical and numerical approaches to solve the governing equations, delving into the intricate fluid dynamics and the intricate processes of heat and mass transfer within this intricate system.

Transient thermal fracture investigation of a cracked functionally graded layer via Guyer-Krumhansl model

Recent experimental evidence proves the Guyer-Krumhansl (G-K) model’s capability of predicting the nonclassical transient heat transfer process in heterogeneous composites. The objective of this article is to explore the dynamic thermal and fracture behaviors of a cracked orthotropic functionally graded material (FGM) layer subject to abrupt thermal shocks via the G-K equation. The thermal and elastic governing equations determined by the G-K model are transformed into the singular integral equations, which are calculated numerically to assess the non-Fourier transient temperatures and the resultant dynamic thermal stress intensity factors. Parametric comparisons are carried out for the effects of the non-Fourier thermal lagging time and thermal nonlocal length on the transient thermoelastic responses. The findings would benefit the applications of unconventional heat conduction theories and shed light on the scientific understanding of FGM’s fracture behaviors.

Nanoengineering Scalephobic Surfaces for Liquid Cooling Enhancement

AbstractCrystallization fouling, a process where mineral scales form on surfaces, is of broad importance in nature and technology, negatively impacting water treatment and electricity production. However, a rational methodology for designing materials with intrinsic resistance to scaling and scale adhesion remains elusive. Here, guided by nucleation physics, this work investigates the effect of coating composition and surface structure on the nucleation and growth mechanism of scale on metallic heat transfer surfaces nanoengineered by large‐area techniques. This work observes that on hydrophilic nanostructured copper, despite its significantly enlarged surface area compared to smooth surfaces, scale formation is substantially suppressed leading to sustained, efficient cooling performance. This work reveals the mechanism through thermofluidic modeling coupled with in situ optical characterization and show that surface bubble formation through degassing is responsible for generating local hot spots enhancing supersaturation. This work then demonstrates a scalephobic nanostructured surface which reduces the accumulated surface scale mass 3.5× and maintains an 82% higher heat transfer coefficient compared to superhydrophobic surfaces with corresponding energy conversion savings. This work not only advances the understanding of fouling mechanisms but also holds promise for practical applications in industries reliant on efficient heat transfer processes.

The study on the coupled influence of water saturation on heat and mass transfer processes within porous media under CW laser irradiation

Continuous wave (CW) laser irradiation induces temperature changes in various phases within porous media, accompanied by phase change and gas transport. Water saturation is a crucial factor influencing this context's moisture and heat transfer process. This paper addresses this issue by establishing a theoretical model for CW laser irradiation on unsaturated porous media. Through experiments and simulations, it studies the effects of different water saturations on heat and mass transfer under laser irradiation. The results indicate that the critical depth reflects the influence of water saturation under laser irradiation on the distribution of solid-phase temperature in both time and space dimensions. Specifically, an increase in water saturation enhances the uniformity of solid-phase temperature distribution, while the gas temperature exhibits a similar distribution pattern. For mass transfer processes, it increases the evaporation rate and Darcy velocity of porous media within the effective range of laser irradiation. Lower water saturation facilitates phase change processes and accelerates gas transport rates. Importantly, this trend remains consistent even with the emergence of dry-saturation zones. Additionally, the decrease in water saturation has a coupled promoting effect on gas temperature and mass transfer processes. Lowering water saturation can increase gas temperature and consequently enhance mass transfer processes. Simultaneously, enhancing mass transfer processes benefits heat exchange between the two phases. In the four sets of experiments, the conformity of the surface temperature rise curves obtained from experiments and simulations is good, indicating that the model can accurately reflect the temperature rise patterns of sand particles. In summary, this work provides valuable research results on the effects of different water saturations on laser irradiation-induced temperature rise, phase change, and gas and moisture transport within porous media. It lays a specific theoretical foundation for laser soil remediation technology.

Prediction of thermal regime and frost heave deformations of subgrade soils during non-stationary heat and moisture transfer

In order to ensure the safe operation of high-speed trains in cold regions, frost heave is one of the basic problems in the research for prediction and control roadbed deformation in such regions. In this paper, based on the classical hydrodynamic model we developed a method of studying thermal regime of soils and predicting frost heave deformations of subgrade soils. Our coupling model takes into account the mutual influence of temperature and soil moisture during non-stationary processes of heat and moisture transfer, calculation of frost heave deformation based on calculated result of the temperature and moisture fields of the roadbed. We have also observed the change of the soil temperatures and frost heave deformation in a freezing-thawing cycle at the geodesic center of PGUPS. The field observation results show that the soil temperature variations amplitude decreases with depth. The simulation verification results and the field observation data show good reproducibility, thus the reliability of the model is confirmed. At last, the paper presents the application of the method in improving high speed railway lines (HSRL) subgrade design in order to reduce frost heave deformations. Based on the results of calculations, it is recommended to lay a thermal insulation layer at the depth of 0.2 m below the subgrade and on the slopes to reduce frost depth and frost heave deformations of subgrade soils.

A novel fault detection and identification method for complex chemical processes based on OSCAE and CNN

The safety and reliability of chemical processes are of paramount importance. However, due to the complicated heat, mass, and momentum transfer processes coupled with chemical reactions, and the interrelated effects among various equipment units, it is difficult to accurately detect and identify faults occurring in the chemical system. This study proposes an innovative fault diagnosis framework specifically designed for chemical systems. A method based on orthogonal self-attention convolutional autoencoder (OSCAE) is constructed for fault detection. The convolutional autoencoder is combined with an orthogonal attention mechanism to extract time-series characteristic information of the operational state, thereby achieving precise detection of fault conditions. Additionally, a convolutional neural network (CNN) model uses both raw signals and data reconstructed by OSCAE to identify different faults, which enhances the features of the input and enables highly accurate fault identification. The effectiveness and robustness of the propose method is validated with simulation data of our self-established chemical distillation system and the publicly available Tennessee Eastman process system. The diagnosis efficacy in fault detection and identification is validated by applying fault detection metrics, high-dimensional feature visualizations, and confusion matrix analyses across two case studies. This paper not only provides an effective diagnostic framework for chemical systems but also offers a usable benchmark dataset for chemical distillation systems to the academic community, with the hope that the research content can enhance the stability and reliability of chemical processes.