Transient Heat Transfer Model Research Articles

Analytical and Computational Investigation of VibroThermoAcoustic Behaviour of Cracks in Aerostructures

Abstract This research investigates the Vibro-thermoacoustic dynamics exhibited by Aerostructures, particularly those harbouring surface cracks. Employing a novel approach, a Thermo-Acoustic field coupled Transient Heat Transfer model is developed to model the interplay among vibrations, heat dissipation, and acoustic behaviour at crack tip interfaces. Local surface flaws proximal to stress concentration sites are investigated via the Newmark Beta Method and Finite Element Analysis, which are applied to displacement and thermal mapping at crack tips through temporal and spatial discretization. Recognizing the implications of flaws in structural integrity and potential lifespan reduction, the study incorporates Analytical, Numerical and Computational analysis of surface cracks into the broader context of Thermoacoustic phenomena. 
The paper explores the application of Elastoplastic Fracture Mechanics (EPFM) to model the impact of plastic deformation on crack growth, local acoustic field and the overarching structural integrity of these components. 
In this study, we also investigate the limitations of the original Ramberg-Osgood equation, particularly in its application to modelling nonlinearities in plastic strain at crack tip interfaces. To address these shortcomings, we propose a novel modified Ramberg-Osgood formulation that incorporates Padé Approximants. This modification enables effective modelling of nonlinear stress-strain variations of high-performance materials while improving computational performance and accuracy. 
Real-world aerostructures experience varying loads, and incorporating these principles in our coupled model allows for accurate modelling of Thermoacoustic Field variations and Instability under dynamic conditions. The research offers valuable perspectives for engineering applications, providing a computational roadmap for thermoacoustic modelling in Aerostructures with cracks.

Heat transfer in large bins during the apples cool-down process

The preservation of apples in cold storage relies deeply on understanding the thermal dynamics governing their environment. Within packaging, apples engage in complex thermal interactions, between themselves and the environment, affecting convective and conductive heat transfer pathways. Challenges escalate in industrial cold storage facilities, manifesting as temperature stratification and non-uniform cooling. Nonetheless, a comprehensive understanding of heat transfer dynamics is vital for optimizing cold storage equipment design and enhancing cooling system operation efficacy. Building upon previous studies validating the use of Peltier elements for detecting and quantifying heat flux in individual apples, this research extends its application to industrial cold rooms. By strategically selecting locations within the apple bin and the storage cold room and comparing changes in total heat content obtained by a conventional method and comparing with the Peltier element for its validation. Results of the convective heat transfer coefficient in an upper-layer bin were in the range of 2.7-5.9 Wm-2 K-1 while in a bin at door level were 5.0-7.0 Wm-2 K-1. The higher values found in the position near the door can be correlated to the faster air speed experienced between the apples in this position. By applying these values in the transient heat transfer model to predict the fruit core temperature during the cooling process, a relatable prediction was found, with apple temperature difference <0.9 °C between predicted by the Peltier element and experimental cooling curves. This study can aid understanding of thermal dynamics in cold storage environments, and support future development for more efficient and sustainable cold storage practices.

The impact of non-isothermal adsorption of dissolved gas on drying of acoustically levitated slurry droplet

In this study, we developed a transient convective heat and mass transfer model of an acoustically levitated slurry droplet evaporating in an atmosphere of air, water vapor, and soluble gas. The advanced model considers the effects of acoustic streaming, forced convection, non-isothermal gas absorption, and adsorption of dissolved gas on the evaporation rate of a liquid droplet containing small active solid particles. Adsorption of dissolved in a droplet soluble gas by solid particles leads to decreased dissolved gas concentration in a liquid droplet. A reduction in dissolved gas concentration in a liquid droplet causes an increase in the mass flux of active soluble gas from a gaseous phase to a slurry droplet, which causes a rise in the heating effect of absorption and an increase in evaporation rate of a droplet. The heat effect of adsorption also intensifies the evaporation rate. It is shown that the time of porous shell formation is essentially shorter when solid particles in slurry droplets are active compared to inert particles.

Temperature prediction of geothermal drilling considering the drilling fluid thermophysical parameters

An increasing number of geothermal wells are being drilled to meet the growing demand for geothermal energy. Given that the harsh environment of geothermal wells exposes drill-following tools to the risk of high-temperature failure, scholars have developed thermo-mathematical models to predict the temperature field distribution in wellbore. To the best of authors' knowledge, most models ignore the interaction between the fluid thermophysical parameters and its temperature. They also overlook the fact that the actual structure of the drilling column causes changes in the convective heat transfer coefficients between the fluid and the well wall, which subsequently affects heat transfer from the wellbore. In this study, we tested the changes of thermal property parameters of drilling fluid with density and temperature. Based on the actual drill string structure and considering the variation in thermophysical parameters during drilling fluids’ circulation, we innovatively established a transient heat transfer model for geothermal horizontal wells with heat–fluid–solid coupling. Subsequently, a drilled geothermal well was used to simulate the temperature during drilling. The effects of the drilling fluid system, density, and displacement, rotary speed, and WOB during drilling on the wellbore temperature distribution were analyzed. Furthermore, suggestions for the selection of drilling fluid and parameters during the drilling process were given. The results of this study can help accurately predict the wellbore temperature of geothermal wells and high-temperature wells, which provides guidance for the rational selection of drilling tools for drilling operations.

Analytical modelling of transient conduction heat transfer in tubes for industrial applications

Analytical modelling of transient conduction heat transfer in tubes for industrial applications

Preliminary study on temperature distribution and pyroelectric current of LiNbO3 heated by nanosecond pulse laser

In order to reduce the volume of compact neutron generators, a lot of investigations are carried out on generating high voltages by heating pyroelectric crystals with external heating. Laser irradiation is an effective non-contact heating method. Different laser parameters determine the crystal's temperature distribution, impacting the accelerating electric field. A preliminary study on the temperature distribution and pyroelectric current response of LiNbO3 heated by nanosecond pulse laser is presented, including both direct heating and heating with Cu and Ti disks adhered to the crystal. A two-dimensional transient heat transfer and circuit model is constructed in COMSOL. To validate the simulation model of temperature field distribution, FLIR thermal camera is utilized to measure the temperature in laser spot center experimentally. The experimental results coincide with simulations, which prove that the simulation model can predict temperature field distribution of the pyroelectric crystal effectively. This study can benefit the optimization of laser parameters for modulating high-quality deuterium ion acceleration fields.

Influence of design parameters on heat production of a multilateral butted closed loop geothermal system

To efficiently develop hot dry rock and other geothermal energy, a multilateral butted closed loop geothermal system (MBCLGS) is presented in this paper to replace the U-shaped closed-loop geothermal system (UCLGS). Besides, a casing-cement-formation transient heat transfer model is established to investigate the influences of key factors on the heat production of MBCLGS. After thermal-fluid-structural coupling analysis, we can find that higher injected rate and lower fluid temperature can improve heat power but reduce output temperature. In addition, the output temperature and heat power do not increase continuously with the increasing of branch well number. There is an optimal value of branch well number. Longer well pair distance can improve both output temperature and heat power. Considering the drilling technology level and design purpose, the recommended injected flow rate of MBCLGS is 90 m3/h, the injected fluid temperature is 42.5 °C, the number of branch wells is 10 and the well pair distance is 200m. Finally, by comparing MBCLGS and UCLGS, it is found that MBCLGS has a lower temperature decline rate and higher output temperature than UCLGS under the same conditions. It works more stable and has better economy. Overall, the proposal of MBCLGS is expected to promote the efficient development of deep geothermal resources.

Modeling Development of a Receiver–Reactor of Type R2Mx for Thermochemical Water Splitting

Abstract This work reports on the development of a transient heat transfer model for a prototype reactor of type R2Mx for thermochemical water splitting by temperature and pressure swing of ceria. Key aspects of the R2Mx concept, which are also incorporated in the prototype design, include a movable monolithic redox structure combined with a linear transport system, a reduction reactor, as well as a dedicated oxidation reactor. With the model, the operation of the prototype is simulated for consecutive water splitting cycles, in which ceria is reduced in a continuously heated reactor, oxidized in a separate oxidation reactor, and transported in between the reaction zones. A 2D axisymmetric numerical model of the prototype reactor was developed in ansys mechanical. The model includes heat transfer calculations in combination with an approximated simulation of the transport of the redox material during cyclic operation. It incorporates the chemical reaction by means of a modified heat capacity for ceria and accounts for internal radiation heat transfer inside the porous redox material by applying effective heat transfer properties. A parametric analysis has been undertaken to evaluate different modes of operation of the oxidation reactor. Model results are used to size the power demand of the reduction reactor and vacuum pump, to define durations of the process steps, as well as to assess operational parameters with respect to achieved temperatures. Findings suggest that suitable operation of the prototype reactor involves reduction durations ranging from 8 to 10 min and oxidations of 6 to 10 min.

Transient thermal management of laser systems using Plate-Fin phase change heat Exchangers: Experimental and computational study

To mitigate transient thermal shocks in lasers and reduce thermal stresses caused by temperature fluctuations, the use of phase change materials (PCMs) in thermal management systems is a viable solution. This study proposes an innovative two-dimensional transient heat transfer model specifically designed for plate-fin phase change heat exchangers (PFPCHEs). The model meticulously simulates the complex heat transfer phenomena within the heat exchanger, including fluid convection, solid thermal conduction, and the phase change processes of PCM. The convective heat transfer coefficient between fluid and plate is calculated using the Wieting correlation. An advanced pulse-mode experimental test platform was constructed to validate the model, dynamically monitoring and recording outlet temperatures and heat exchange performance for stringent experimental comparison. The research explores the impact of key operating parameters such as initial temperature, flow rate, and inlet temperature of the cooling cycle on the performance of the heat exchanger, providing valuable design and control strategies for transient thermal management of laser systems. The experimental results confirm that the model accurately predicts the dynamic response characteristics and temperature distribution of PFPCHEs under multi-cycle pulse loads, with 96% of the predictions within a 10% error margin. A significant finding is that the initial temperature has negligible influence on the heat transfer characteristics when it is below the solid phase temperature of the PCM. Moreover, by meticulously adjusting the flow rate and inlet temperature of cooling cycle, it is possible to effectively maintain the stability of the outlet temperature throughout the entire pulse cycle. This is crucial for minimizing temperature fluctuations within the thermal management system and extending the service life of electronic components.

Simulation and on-line monitoring using optical fiber Bragg grating sensors of temperature history during laser-assisted automated fiber placement

Automated fiber placement (AFP) in situ consolidation (ISC) of thermoplastic composite possess the potential to reduce manufacturing costs and improve manufacturing efficiency. The properties of composite manufactured by the ISC are affected by several mechanisms including polymer degradation, crystallization, intimate contact, polymer healing and void dynamics. All these mechanisms are directly affected by the temperature history. Consequently, the control and accurate measurement of temperature history during ISC are particularly important for improving the properties of composite. In this study, a simplified three-dimensional transient heat transfer model was established. The effect of tool temperature and placement speed on the temperature history and peak temperature were predicted. Simultaneously, an online temperature monitoring system was built and the optical Fiber Bragg Grating sensors (FBGS) was used to measure the temperature history. The results indicated that the predicted results of the model were consistent with the measured results, the error was below 8%. In addition, the temperature history of layers was significantly affected by the tool temperature and placement speed. The temperature of the layers decreased to near the tool temperature after cooling, and a higher tool temperature increasing its peak temperature because of the reduce of the cooling rate. On the contrary, an increase in placement speed will reduce the peak temperature of the layers.

Assessment of evaporative porous clay cooler for Building-Integrated photovoltaic systems via energy, exergy, economic and environmental approaches

A thorough study has been conducted for the energy, exergy, economic and environmental analysis to investigate the feasibility of utilizing an evaporative porous structure cooler for the building-integrated photovoltaic (BIPV) system at different building’s sides and directions. Photovoltaic panels within the BIPV systems dissipate their heat to the building’s sides which contribute to rise the interior building’s temperature. In the proposed system, a water-saturated evaporative porous clay cooler is being installed on the back surface of the PV panels to absorb and dissipate their heat by latent evaporation through an evaporation cooling process. A transient numerical heat and mass transfer model based on energy, exergy, economic and environmental approaches was proposed to assist the feasibility of cooling BIPV system via evaporative porous structure cooler. The model was also validated experimentally in the present study. The results exhibited that, comparing with conventional BIPV systems, the presented BIPV/Clay cooling system achieved a peak photovoltaic temperature reduction of 19.1 °C, with a maximum enhancement in the photovoltaic system’s electrical efficiency, electrical power, and exergy efficiency of 9.8 %, 12.6 % and 11.8 %, respectively. The ultimate reduction in the building’s annual thermal load was around 53.8 % when the clay evaporative cooling approach is applied, while the cost of electricity production reduced ultimately by 7.9 %, (from 0.151 $/kWh to 0.134 $/kWh). Further, the payback period decreased by 2.33 years and the annual amount of CO2 emissions decreased by 10.4 % for the utilized BIPV/Clay cooling system compared with the conventional BIPV system.

A new analytical model for transient heat transfer modeling of geothermal monotube heat exchangers

In this study, we present a new analytical model for the analysis of transient heat transfer (the model is solved after Laplace transformation) in geothermal monotube heat exchangers (GHE). The model accounts for various factors, including the heat exchanger's geometric parameters, the nature of the fluid (air and water), flow characteristics (laminar and turbulent), and heat transfer boundary conditions. Initially, the model's performance is validated by comparing its results with those obtained from computational fluid dynamics simulations using OpenFOAM. This validation process ensures the reliability and accuracy of the model. Additionally, an analysis of the heat transfer mechanisms and key modeling parameters identified from the comparison is provided. In the subsequent section, the analysis is extended by comparing the proposed model to four existing analytical models available in the literature. These reference models employ distinct approaches to simulate heat transfer to the ground. By examining a range of cases, the performance of the model is systematically evaluated against these conventional methods. This work closes by an analysis of the analytical models and the impact on the accuracy of the results highlighting the advantages of the proposed method in geothermal applications.

Evaluating the maximum drilling length of horizontal geothermal wells utilizing temperature constraints

The geothermal industry faces a significant challenge in exploring and developing resources due to elevated temperatures in downhole environments. Successful drilling in high-temperature geothermal wells requires precise thermal management. This research assesses constraints on horizontal section length and temperature during geothermal horizontal well drilling, aiming to formulate effective wellbore temperature management guidelines.The study utilizes thermal resistance analysis to establish a tailored transient heat transfer model for high-temperature horizontal geothermal well drilling. Parameters such as circulation time, horizontal section length, flow rate, drilling fluid properties, formation thermal conductivity, and drill string thermal conductivity are thoroughly investigated. Treating input parameters as triangular distributions, Monte Carlo simulation techniques conduct sensitivity analysis. Tornado diagrams quantitatively determine key parameter impacts on bottom-hole temperature. The research introduces a procedural framework for geothermal well drilling, aiding engineers in swiftly identifying operational parameter combinations for effective wellbore temperature management. This workflow provides practical guidance for geothermal resource development, ensuring drilling safety in diverse conditions.

Investigation on heat transfer performance of flat plate micro-heat pipe phase change heat storage/release device

In the domains of low/zero carbon energy, the ship energy storage system, coupled with phase-change storage and release technology, holds significant importance. The utilization of a flat micro-heat pipe as the primary heat transfer element prompts the development of a test platform and a transient heat transfer model for the heat storage device. This is in response to existing challenges such as a single structure, poor temperature uniformity, and low thermal efficiency in current heat storage technology. The study delves into the impact of varying temperatures and flow rates of heat transfer fluids on the overall performance of heat storage devices and heat transfer efficiency. The findings highlight that the staggered double plate micro-heat pipe structure can enhance total heat storage by 11%, average heat storage power by 19%, and heat storage efficiency by 21% compared to the heat storage device with a single flat micro-heat pipe structure. It becomes evident that the heat storage device with the staggered double heat pipe structure outperforms its counterpart. Additionally, Temperature and flow velocity play pivotal roles in determining the heat transfer performance of phase change materials. As the temperature difference between the heat transfer fluid and the phase change material increases, both the phase transition rate and the equivalent Nusselt number also rise, providing a crucial foundation for examining the heat transfer characteristics of phase change materials during different stages of phase transition.

Exploring energy-saving performance of radiative cooling roofs with a transient heat transfer model

Radiative cooling coatings, serving as building roof exterior surfaces, reflect most solar energy and dissipate heat mainly through the atmospheric window. A roof transient heat transfer model was proposed considering the atmospheric transmittance and spectral properties of radiative cooling coatings within the longwave range by coupling one-dimensional transient heat transfer and a spectral-dependent method. The atmospheric radiation was calculated based on the dew point temperature. Field measurements were conducted to verify the model reliability. The simulation and experimental data matched well. The validated model was employed to analyze the energy-saving performance of radiative cooling coatings in diverse climate zones in China (Guangzhou, Shanghai and Beijing). The results showed that the radiative cooling coatings (solar reflectance β = 0.85 and thermal emissivity ε = 0.95) achieved excellent cooling performance, although they could cause a penalty during the heating period. Compared with conventional exterior surfaces (β = 0.2 and ε = 0.9), the radiative cooling coatings reduced the annual load (the sum of the cooling and heating loads) of roofs by 84.9%, 30.3% and 2.4% in Guangzhou, Shanghai and Beijing, respectively, with roof insulation thicknesses of 40, 80 and 100 mm, respectively. Sensitivity analysis revealed that the solar reflectance determined the roof annual load in Guangzhou, while the insulation thickness determined the roof annual load in Shanghai and Beijing. The numerical model developed herein could be used to analyze the energy-saving potential of radiative cooling roofs with different spectral properties and provide guidance for effectively applying radiative cooling coatings on building roofs.

The role of emissivity of the window surface inside and outside the atmospheric window in the radiative cooling effect

The emissivity design of building surfaces is crucial for radiative cooling (RC) heat dissipation. This work explores regularities of the influence of the emissivity inside and outside the atmospheric window (AW, 8-13 μm) on the window RC effect using a verified transient building heat transfer model. Results show that the RC effect brought by the radiant heat transfer of the window in non-atmospheric window bands (NAW) may exhibit a reversal phenomenon of first improvement and then weakening with the increase of the outer surface emissivity ε‾NAW. The occurrence of this reversal phenomenon is influenced by multiple factors such as meteorological parameters like ambient temperature and solar radiation, as well as architectural features including window orientation and window-to-wall ratio. In addition, as the window-to-wall ratio increases, when no reversal phenomenon occurs, the average RC regulation ability gap between the emissivity inside and outside the AW decreases from 7–40 times, which is observed when the reversal phenomenon occurs, to about 2–5 times, and the relative importance of ε‾NAW greatly increases. Regularities revealed provide more reliable guidance for the performance research and material design of RC windows.

Topography optimisation using a reduced-dimensional model for transient conjugate heat transfer between fluid channels and solid plates with volumetric heat source

Consideration of transient effects is important for industrial applications of heat transfer structure optimisation studies; however, the huge computational cost associated with transient problems is a pressing concern. This paper proposes an extension of a previous reduced-dimensional model to transient conjugate heat transfer between a fluid flow and solid-heated plates in a plate heat exchanger. The extended reduced-dimensional model introduces the temperature field of the plate governed by the heat conduction equation, which is coupled to the temperature field of the fluid, governed by the convection-diffusion equation, through the heat flux balance equation at the contact surface. The model is based on assumptions of fully developed flow and constant temperature profile, reducing the three-dimensional problem to a planar problem and significantly reducing computational costs. The accuracy of the model for the simulation of transient heat transfer is verified by comparison with a three-dimensional model. In this paper, the topography of the heat exchanger plate is optimised for both steady-state and transient conditions by applying the reduced-dimensional model. The effectiveness of the optimised design was demonstrated by the cross-check of both the reduced-dimensional and full three-dimensional models. Furthermore, this work considers the effect of time-independent boundary conditions and time-dependent boundary conditions on transient optimisation. The transient and steady-state optimised designs are analysed and compared for both conditions, and the necessity of transient optimisation is discussed.

Numerical Modeling and Analysis of Transient and Three-Dimensional Heat Transfer in 3D Printing via Fused-Deposition Modeling (FDM)

Fused-Deposition Modeling (FDM) is a commonly used 3D printing method for rapid prototyping and the fabrication of plastic components. The history of temperature variation during the FDM process plays a crucial role in the degree of bonding between layers. This study presents research on the thermal analysis of the 3D printing process using a developed simulation code. The code employs numerical discretization methods with an implicit scheme and an effective heat transfer coefficient for cooling. The computational model is validated by comparing the results with analytical solutions, demonstrating an agreement of more than 99%. The code is then utilized to perform thermal analyses for the 3D printing process. Interlayer and intralayer reheating effects, sensitivity to printing parameters, and realistic printing patterns are investigated. It is shown that concentric and zigzag paths yield similar peaks at different time intervals. Nodal temperatures can fall below the glass transition temperature (Tg) during the printing process, especially at the outer nodes of the domain and under conditions where the cooling period is longer and the printed volume per unit time is smaller. The article suggests future work to calculate welding time at different conditions and locations for the estimation of the degree of bonding.

A new detection method of co-existence of well kick and loss circulation based on thermal behavior of wellbore-formation coupled system

Accurately obtaining wellbore-formation temperature distribution during drilling in fractured carbonate formations is the basis for effectively solving the problem of the well kick and loss circulation coexisting (WK-LC). Therefore, based on the energy conservation law and considering the convective heat transfer and variable mass flow caused by well kick and loss circulation, this paper developed a full transient heat transfer model of wellbore-formation coupled system under the WK-LC. The reliability of model was verified by field measured temperature data. Based on field well, the thermal behavior of wellbore-formation coupled system under normal condition, well kick, loss circulation and WK-LC were compared and studied.The results showed that the bottom-hole temperature of well kick and Case1-2 is higher than that of normal condition, while the bottom-hole temperature of loss circulation and Case3-4 is lower than that of normal condition. The temperature difference between annulus and drill string (TD-AD) shows a “wavy line” trend of increasing-decreasing-increasing-decreasing along the well depth. The TD-AD of wellhead is about 6 °C in normal and WK-LC conditions. The traditional wellhead temperature monitoring method can only distinguish well kick and leakage, and it is difficult to judge whether WK-LC occur.In addition, the influence of the distance and well kick/leakage rate difference between the well kick region and the leakage region on thermal behavior of wellbore-formation coupled system was discussed. Finally, a new auxiliary method is proposed to identify the well kick, the loss circulation and the WK-LC. Which will have a significant implication for well killing and leaking stoppage operations.

Thermal and mechanical investigation of proton exchange membrane fuel cells under combined loading conditions

Mechanical performance of PEM fuel cells under combined loadings is one of critical issues in improving cell performance and reliability. In this study, thermal and mechanical performance of the PEM fuel cell under clamping force and temperature load are investigated by experiments and three-dimensional dynamic simulations. In experiments, pressure distributions between gas diffusion layer and flow field are measured by pressure sensitive films. The experimental results show that the local pressure increases with clamping load, and pressure distribution is much uneven in the midstream. Meanwhile, a three-dimensional model of the cell combined transient heat transfer and mechanical response of components is developed, which is validated by experimental data. The modeling results show that under combined loadings, the porosity of gas diffusion layer under the rib decreases, attributed to compressive deformation caused by thermal gradient and clamping pressure, leading to higher effective thermal conductivity and electrical conductivity. When at a higher temperature, the overall stresses of gas diffusion layer decrease and the minimum stress is located under the center rib, forming a concave stress distribution pattern. Distribution and variation patterns of local deformations and stresses for the membrane are similar to those of gas diffusion layer, but the maximum stress and deformation are much lower. A dimensional stress coefficient is proposed to determine the stress distribution uniformity under the rib. With the increase of clamping torque, dimensionless stress coefficients under lower ambient temperature change slightly. As temperature increases, dimensionless stress coefficients increase significantly and decrease with the clamping torque, indicating the decreasing role of temperature load on mechanical response of the cell.