Transient Temperature Prediction Research Articles

Design and control intended low-order model for transient investigation of an electric oven: Static mode

In general, electric ovens represent a low-efficiency class among home appliances, contributing to overall environmental changes in buildings and apartments. To improve their low efficiency, which is typically between 10% to 12%, industries are increasingly focused on developing effective technologies. One suitable strategy is to design and control the oven's center temperature, as specified by the EN 60350-1 European standard, which regulates the energy efficiency index (EEI) test. The present simulation study explains the transient thermo-fluid behavior of a domestic electric oven subjected to free convection, i.e., static mode. For this purpose, appropriate dynamic models are employed, intended for design and control. A lumped-parameter based methodology is considered to develop a low-order dynamic model, resulting in reduced computational cost and run time. A finite level of discretization is introduced into the model, enabling the capture of limited insights, such as temperature, heat flux, mass flow rate, pressure drop, etc., particularly at the cavity center, internal and external cavity wall surfaces, and at suction and exit openings. The electric oven is mainly divided into four sub-systems: door, cavity, ventilation, and cabinet. Each sub-system has a suitable level of discretization signifying a lumped mass parameter to reproduce the transient behavior within the electric oven. Heaters are considered as individual lumped masses and are integrated within the cavity sub-system. The above sub-systems employ both the first principle equations and correlations based on experimental data, giving a low-order grey-box identity to the system. In addition to conduction and convection, a non-linear form of radiation is considered to increase model accuracy. The developed model is further calibrated with available physical data. Once calibrated, the model is then compared with the remaining physical data produced at different heat loads to understand the accuracy in terms of transient temperature prediction at various temperature set points.

A one-dimensional transient temperature prediction model for Chinese assembled solar greenhouses

The prediction of the thermal environment of greenhouses has always been an essential component of greenhouse development. In this paper, a one-dimensional transient temperature prediction model is constructed based on the principle of energy balance for Chinese assembled solar greenhouses (CASG). The daily temperature trends for each surface in the greenhouse were obtained by solving the model using MATLAB. The performance of the model was assessed by comparing the measured and predicted values. The mean absolute errors for the temperature of air, back roof, front roof, heat collector plate, north wall, ground and water storage tank were computed to be 1.4 °C, 1.89 °C, 1.98 °C, 2.07 °C, 2.26 °C, 1.44 °C and 0.68 °C, respectively. The results demonstrate a high level of concurrence between the simulated and measured values, indicating that the model is proficient in predicting the thermal environment of CASG. Based on this, predictions were made regarding the internal environment of CASG on both sunny and cloudy days, which contributes to a comprehensive understanding of the thermal environment. The research provides theoretical support for regulating environmental conditions of CASG.

Prediction of transient temperature at bit-rock interface using numerical modelling approach and optimization

Prediction of transient temperature at bit-rock interface using numerical modelling approach and optimization

A Reduced-Order Decoupling Method Applied to Efficient Junction Temperature Simulation Model in Multichip Devices

As the power density of power modules increases, the cross-heating effects in multichip modules become severe, which intensifies the local overheating stress. To accurately predict the dynamic thermal characteristics of the multichip modules, this paper establishes the mathematical relationship between the resistance-capacitance (RC) parameters and the thermal diffusion angle to obtain accurate RC parameters. The decoupling of the self-heating and cross-heating effects is realized according to the dynamic power flow in the RC thermal network, reducing the transient thermal impedance matrix to the steady-state thermal resistance matrix. In this way, the 3-D cross-heating effect on the junction temperature is characterized by the 1-D RC thermal network. Then, an efficient junction temperature simulation model based on the reduced-order decoupling method is proposed. This article also identifies the variation law of RC parameters with boundary conditions. Compared with existing models that need transient information, the model parameter extraction process requires only the steady-state information of the finite element method (FEM) and fewer RC parameters, which improves the parameter extraction efficiency by more than 87 times. In addition, compared with the FEM model, the transient junction temperature prediction efficiency is improved by more than 994 times. Finally, based on a 1200V/50A half-bridge module, an electrothermal coupling model is constructed and applied to a three-phase two-stage inverter circuit. The results verify the accuracy and effectiveness of the proposed model, demonstrating that the junction temperature error between the proposed model and the experimental result is less than 5%.

A multi-criterion optimization of mechanical properties and sustainability performance in friction stir welding of 6061-T6 AA

Nowadays, the transportation industry is curious about fabricating lightweight vehicles under a sustainable manufacturing process to minimize fuel consumption costs and environmental footprints. Assessing the sustainability performance metrics of the friction stir welding (FSW) process reduces the sawing costs and environmental impacts. However, the evaluation and assessment of the sustainability performance metrics integrated with the mechanical properties of the weld joint have not been sufficiently studied. Thus, this study investigates the multi-criterion process parameter optimization of friction stir welding (FSW) to attain an optimum parameter to enhance the mechanical properties of the weld joint and decrease energy consumption and carbon dioxide emission. Experimentations are conducted using a vertical CNC milling machine on a 5 mm 6061-T6 AA material with a butt joint orientation. Tool rotational speed, traverse speed, and tool profile were used as processing parameters. Response of the study, such as transient temperature and energy consumption, was measured during the joining process, whereas hardness, tensile strength, and CO2 emission were examined post-processing. The multi-criterion optimization was done using the Taguchi-based grey relational analysis method. In addition, the transient temperature was predicted by an auto-regressive moving average (ARIMA) and Ansys simulation. The finding showed that higher rotational and minimum welding speeds had imparted a sound weld. Besides, the analysis of variance results showed that welding speed has a significant parameter at a 95% confidence interval. The proposed ARIMA model's result showed that the transient temperature prediction accuracy reached 99.922%, and the error percentage between the FEA simulation and experimental work reached 2.067%.

A dynamic prediction method of transient temperature in friction stir welding process

Establishing an accurate heat source model is the primary work in analyzing welding temperature field. We propose a novel transient temperature prediction method for friction stir welding by analyzing the material movement process to build an accurate heat source model. For verifying the present method, several groups of friction stir welding experiments were carried out, and the computed results obtained by the present method are compared with the experimental results. The effects of rotational speed, tilting angle, welding speed and normal force on the calculation results are analyzed. It is found that the peak temperature in the welding temperature field increases with the increase in rotating speed, tilting angle and normal force, and decreases with the increase of welding speed. The peak time decreases with the increase of rotational speed, tilting angle and welding speed, and almost does not change with the normal force.

Numerical Study on Transient Annular Pressure Caused by Hydration Heat during Well Cementing

Annular pressure has been recognized as one of the most challenging problems in the petroleum industry, posing a series of threats to wellbore integrity. Annular pressure caused by thermal expansion during the cement hydration process is rarely studied by researchers. In light of the hydration heat generation process, a kinetics model for cement hydration under different curing temperatures is demonstrated in this paper. Considering interactions between temperature and cement hydration, a transient temperature prediction model during well cementing is built. On the basis of these assumptions, the prediction model of annular pressure is established, considering the change in cement temperature and the change in annulus volume. Using the models illustrated in this paper, a series of numerical simulations are performed. The changing roles of transient cement hydration degree and temperature in wellbores are analyzed thoroughly. The annular pressure during well cementing shows a rapid increase and then a decrease, which is similar to that of the temperature. In addition, a sensitive analysis of annular pressure is conducted. The analysis shows that the annular pressure increases with the geothermal gradient, the cement hydration heat, and the wellbore diameter. Suggestions and conclusions can provide safety guidance for the management of annular pressure during well cementing.

Experimental characterization of a novel configuration of thermoelectric refrigerator with integrated finned heat pipes

• A thermoelectric refrigerator is constructed and characterized in this work. • A performance analysis is performed including energy consumption, cooling time, temperatures and COP. • A mathematical model is developed to predict transient temperatures and cooling limit time. • Empirical equation for transient temperature prediction is settled. Thermoelectric refrigerating systems (TER) are environment-friendly technologies. They have several advantages such as low maintenance costs, are less cumbersome and long lifetime. However, these systems have low coefficient of performance and are limited in achieving low temperature levels. This study investigates a new configuration of TE refrigerator employing a novel arrangement of heat sinks with integrated flat and finned heat pipes. A mathematical model is firstly developed to predict transient temperatures and cooling limit time. An experimental characterization is then performed and it includes optimization of energy consumption, cooling time, temperature levels and TE refrigerator related COP. TE module coefficient of performance (COP TEC ) is evaluated at 0.74 while the hot and cold sides temperature difference ΔT is equal to 32.7 °C. The coefficient of performance of the TE refrigerator (COP TER ) is evaluated at 0.297 with an inside/outside temperature difference ΔT i/ o = 13 °C and an energy consumption rate of 42.7 Wh. Multiple experiment's results lead to a specific characterized chart adapted for this TE refrigerator. An empirical equation for transient temperature prediction is established and presents a novel contribution in this work.

Digital Twin for the Transient Temperature Prediction During Coaxial One-Side Resistance Spot Welding of Al5052/CFRP

Abstract In the present research, a digital twin of coaxial one-side resistance spot welding (COS-RSW) was established for the real-time prediction of transient temperature field. A three-dimensional (3D) model of COS-RSW joint was developed based on the in-house finite element (FE) code JWRIAN-SPOT. The experimental verified FE model was employed to generate the big data of temperature of COS-RSW process. Multiple dimension interpolation was applied to process database and output prediction. The FE model can predict the thermal cycle on COS-RSW joints under different parameter couples. The interpolation effect of individual welding parameters was discussed, and a power weight judgement for welding time was essential to ensure accuracy. With the support of big data, the digital twin can provide visualization prediction of COS-RSW within 10 s, whereas numerical modeling needs at least 1 h. The proposed application of digital twin has potential to improve the efficiency of process optimization in engineering.

A gray-box model for real-time transient temperature predictions in data centers

In response to the need to improve the energy efficiency of data centers (DCs), system designers now incorporate solutions such as continuous performance monitoring, automated diagnostics, and optimal control. While these solutions must ideally be able to predict transient conditions, in particular real time DC temperatures, existing forecasting methods are inadequate because they (1) make restrictive assumptions about system configurations, (2) are extremely time-consuming for real time applications, (3) are accurate only over limited time horizons, (4) fail to accurately model the effects of operating conditions, such as cooling unit operation conditions and server workloads, or (5) ignore important facets of the flow physics and heat transfer that can lead to large prediction errors in extrapolative predictions. To address these deficiencies, we develop a gray-box model that combines machine learning with the thermofluid transport equations relevant for a row-based cooled DC to predict transient temperatures in server CPUs and cold air inlet to the servers. An artificial neural network (ANN) embedded in the gray-box model predicts pressures, which provide inputs for the thermofluid transport equations that predict the spatio-temporal temperature distributions. The model is validated with experimental measurements for different (1) server workload distributions, (2) cooling unit set-point temperatures and (3) the airflow of the cooling units. This gray-box model exhibits superior performance compared to a conventional zonal temperature prediction model and an advanced black-box model that is based on a nonlinear autoregressive exogenous model. An application of the gray-box model involves a case study to detect cooling unit fan failure in a row-based DC cooling system.

Comprehensive Assessment of Avalanche Operating Boundary of SiC Planar/Trench MOSFET in Cryogenic Applications

The avalanche ruggedness of power devices becomes a crucial issue to ensure the safe operation of the power conversion systems, particularly under the extreme temperature conditions. In this article, the avalanche capability of SiC planar/trench MOSFETs is systematically evaluated and analyzed over the temperature range of 90 to 340 K. Importantly, the essential mechanisms and temperature dependence of avalanche failure under cryogenic conditions are further explored by combining many analysis methods such as TCAD simulations, the unclamped inductive switching characterizations, and the transient junction temperature prediction. The highest avalanche energy density of 171.24 mJ/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 90K indicates the great application potential of SiC plannar mosfet in cryogenic electronics. Moreover, the safe avalanche operation boundary (AOB) model is established over the cryogenic temperature range. The relevant analysis method and AOB model can be used to accurately evaluate and quantitatively predict the avalanche capability of SiC planar/trench mosfets for the cryogenic converter design.

Study of Heat Transfer and Freezing Time-Temperature Behavior of Individual Pea Grains by Numerical and Experimental Methods

Abstract The present research demonstrates an accurate and simple numerical model for heat transfer analysis within spherical peas when exposed to the cold air stream in a rectangular duct. The transient heat conduction equation (THCE) is solved for spherical shaped pea grains. A detailed numerical and experimental study of freezing time-temperature history for peas has been carried out. Thermal conductivity and volumetric heat capacity are measured experimentally. Temperature-dependent thermophysical properties are used in the transient temperature prediction of peas throughout the phase change process. Crank–Nicolson method has been used for the formulation of the numerical model. The effect of important parameters, viz., the initial temperature of peas, cooling air temperature, and cooling air velocity over pea samples has been studied both numerically as well as experimentally and it has been found that there is good agreement between numerical and experimental results. The correlation coefficient of linear regression, R2, between numerically predicted and experimental results, is found to be 0.987.

Dynamical well-killing simulation of a vertical H2S-containing natural gas well

This work aims to explore the dynamical well-killing process of a vertical H2S-containing natural gas well. A dynamical well-killing model considering an H2S solubility was established to simulate the overflow and well-killing process of a vertical H2S-containing natural gas well. The mass and momentum equations of the coupled model were solved using finite difference method, while the transient temperature prediction model was solved using finite volume method. The coupled model was validated by reproducing experimental data and field data of Well Tiandong #5. The effect of H2S content, mud displacement, drilling fluid density, and initial overflow volume on the dynamical well-killing process of an H2S-containing natural gas well were obtained and analyzed in this work. Results showed that H2S will gasify near wellhead during well killing when casing pressure decreases. To balance the bottom hole pressure, when H2S releases, the casing pressure increases as H2S content increases. As initial overflow volume increases, the annular temperature, annular pressure and the casing pressure increase significantly. When H2S gasifies, the casing pressure applied at wellhead should be higher at lower initial overflow volume to balance bottom hole pressure. In the well-killing process, the annular pressure and temperature decrease as drilling fluid density increases and a lower casing pressure is needed for balancing bottom hole pressure. The casing pressure is lower at a higher displacement for higher friction resistance. Besides, as well-killing displacement increases H2S will gasify at an earlier time. When drilling for H2S-containing natural gas well, early detection of gas kick should be more frequent to avoid severe overflow. Besides, higher displacement and density of drilling fluid should be considered to avoid stratum fracturing and prevent leakage accidents under the premise of meeting drilling requirements.

Research on dynamical overflow characteristics of a vertical H2S‐containing natural gas well

AbstractThis work aims to explore the overflow characteristics of a vertical H2S‐containing natural gas well. A two‐phase flow model for H2S‐containing natural gas well combining with a transient temperature prediction model was established to simulate the overflow process of a vertical H2S‐containing natural gas well. The model was validated by reproducing the field data of Well Longhui #2. The effects of H2S content, mud displacement, drilling fluid density, geothermal gradient, and reservoir permeability on the overflow characteristics of a vertical H2S‐containing natural gas well were studied and analyzed in this work. Results indicate that bubble, slug, and churn flows constitute the main flow patterns in the whole overflow process. The higher the H2S content is, the more obviously the gas void fraction increases. The phase change position of H2S is closer to the wellhead at lower H2S content. An increase in mud displacement indicates the decreases in overflow time. As drilling fluid density increases, the release position of H2S moves up, and the overflow time and shut‐in casing pressure increase. The initial gas void fraction is higher and the gas invasion volume will be larger in gas reservoirs with higher permeability. As the reservoir permeability increases, the shut‐in casing pressure rises while the overflow time declines. With higher geothermal gradient, the wellbore temperature tends to be higher at the same depth, leading to an increase in the H2S solubility. The gasification starting position is further away from the wellhead at higher geothermal gradient. The results of this work could provide important theoretical basis and technical guidance for drilling engineers to reduce a blowout risk during drilling of H2S‐containing natural gas well.

On the comparison between computational fluid dynamics (CFD) and lumped capacitance modeling for the simulation of transient heat transfer in solar dryers

In this paper transient heat transfer in a solar food drier is modeled by using both computational fluid dynamics (CFD) and lumped capacitance modeling techniques. The CFD model is used to simulate the air flow and transient heat transfer within the dryer. A lumped capacitance model, developed from energy exchanges between various components of the drying chamber, is extensively compared with the results of the CFD model. The two models predict both a 40 °C rise in steady-state temperature within the drying chamber. Before reaching this temperature, there is about 8 °C RMS deviation between the transient temperature prediction of the two models. This deviation is mainly caused by the heat transfer coefficient around the food rack shelfs. Fitting these coefficients give rise to a minimal RMS deviation between the two models of 1.8 °C and 0.9 °C on the lower and upper rack shelfs respectively. The transient heat transfer phenomenon from CFD modeling also showed that the spatial distribution of temperature after 30 min is uniform thus validating the very assumption of lumped capacitance modeling. This demonstrates that the lumped capacitance model can supplant the computationally demanding CFD modeling technique in predicting transient heat transfer phenomenon in solar food dryers.

Large-Area Electron Beam Melting: Frequency Analysis and Critical Frequency Prediction

During large-area electron beam irradiation, high energy flux pulses of electrons melt a thin layer of material. The objective of this work is to analyze the spatial frequencies of a turned, S7 tool steel surface before and after electron beam melting. It was observed that high frequency features are significantly reduced following melting, but lower frequency features were created and increased the unfiltered areal average roughness. Previous work on laser remelting-based polishing derived a critical frequency that defines the frequency above which higher frequency features are dampened. As the critical frequency depends on the melt duration that the surface experiences, a one-dimensional, transient temperature prediction model was created for this work to estimate the melt time for a single electron beam pulse. This model allowed for the calculation of a critical frequency that showed good ability to predict the frequencies that are dampened.

Transient temperature prediction models of wellbore and formation in well-kick condition during circulation stage

In the exploration and development of deep reservoir resources, well kick often occurs during drilling. The occurrence of well kick can change the flowing state and the various properties of the drilling fluid, which can have a very important impact on the wellbore temperature distribution. Based on the actual situation in the drilling process, the wellbore and formation heat transfer model in the case of normal circulation and in the case of well kick in the open-hole formation was established. The model was discretized by using the finite volume method and solved with under-relaxation iterative method. By comparing with previous research results, the validity of the model was established. Compared with the condition of normal circulation, the occurrence of well kick significantly changes the wellbore temperature distribution and has an important influence on the temperature difference profile and formation radial temperature distribution. Sensitivity factors that affected the wellbore temperature distribution were analyzed. Based on the difference in wellbore temperature distribution under normal circulation conditions and well kick conditions, this paper proposes a new method to detect the occurrence of well kick by monitoring the annulus temperature change. The new method can provide guidance for the well control operations and drilling operations.

Modeling temperature behavior of multistage fractured horizontal well with two-phase flow in low-permeability gas reservoirs

This study aims to study the temperature behaviors and quantitatively diagnose water exits for multi-fractured horizontal wells (MFHWs) in low-permeability gas reservoirs (LPGRs) with two-phase flow. Firstly, a transient temperature prediction model is developed on the basis of mass, momentum and energy conservation with consideration of a variety of subtle heat effects (e.g. Joule–Thomson effect, thermal expansion etc.). Subsequently, synthetic cases are simulated to illustrate the temperature behaviors of a two-phase MFHW with identical/non-identical fractures. The sensitivity analysis indicates that the existing of Non-Darcy flow and gas-phase slippage effect reduces the wellbore temperature. The wellbore temperature shows significant sensitivity to reservoir permeability and fracture half-length. Then, by simulating the temperature profile of MFHWs with different water/gas ratio (WGR) of each fracture, the unique characteristics of wellbore temperature variation under each WGR situation are observed. That provides the potential to diagnose the water exits of MFHWs from temperature measurement. Finally, we apply the model to a field case and the results validated the feasibility of the developed model to simulate the temperature behavior of MFHWs in LPGRs.

Transient temperature prediction model of horizontal wells during drilling shale gas and geothermal energy

A transient temperature prediction model was established to analyze wellbore temperature distribution of horizontal wells during drilling shale gas and geothermal energy based on unsteady two-dimensional convection-diffusion equation and the model was discretized with finite volume methods and solved by owe relaxation iteration method. The validity of the model has been verified by field temperature data. The influence of drilling parameters on temperature distribution of drilling fluid were discussed. Results indicated that the closer to the bottom of the well, the smaller the rate of change of the drilling fluid temperature with depth. The temperature of the drilling fluid at the same well depth increases with the increasing horizontal section length, drilling fluid density, geothermal gradient and vertical depth. The temperature of the upper part of the wellbore increases with the increasing circulation time and drilling displacement, and the lower part of the wellbore decreases with the increasing circulation time and drilling displacement. Drilling fluid temperature inside the drilling string decreases with the increase in viscosity. However, drilling fluid temperature inside the annulus of the upper part of the wellbore increases with the increase of the viscosity while the drilling fluid temperature of the lower part of the wellbore decreases with the increasing viscosity.

Analysis of Wellbore Temperature Distribution and Influencing Factors During Drilling Horizontal Wells

Horizontal well drilling technology is widely used in the exploitation of petroleum and natural gas, shale gas, and geothermal resources. The temperature distribution of wellbore and surrounding formation has a significant influence on safe and fast drilling. This study aims to investigate the temperature distribution of horizontal wellbores during circulation by using transient temperature model. The transient temperature prediction model was established by the energy conservation law and solved by the relaxation iterative method. The validity of the model has been verified by the field data from the Tarim Oilfield. The calculation results showed that the highest temperature of the drilling fluid inside the drill string was at the bottomhole and the highest temperature of annulus drilling fluid was at some depth away from the bottomhole. Sensitivity analysis of various factors that affect the temperature distribution of annulus drilling fluid were carried out, including the circulation time, the flow rate, the density of drilling fluid, the inlet temperature, the vertical depth, the horizontal section length, and the geothermal gradient. It can be found that the vertical depth and the geothermal gradient have a significant influence on the bottomhole temperature, and inlet temperature plays a decisive influence on the outlet temperature. These findings can supply theoretical bases for the horizontal wellbore temperature distribution during drilling.