Transient Temperature Behavior Research Articles

A study on the impact of using a subchannel resolution for modeling of large break loss of coolant accidents

The nuclear industry is investigating the feasibility of transitioning from 18- to 24-month fuel cycles because of the positive impact it would have on the operational costs for the current fleet of light-water reactors. A challenge to making this change is the increased risk of fuel fragmentation, relocation, and dispersal (FFRD) due to the known potential for ceramic fuel to pulverize into fine particles at the higher discharge burnups. Previous work has been performed by the Nuclear Energy Advanced Modeling and Simulation program to assess FFRD risk in high-burnup cores using the BISON fuel performance code and a coarse mesh thermal hydraulics (T/H) solution for a loss-of-coolant accident (LOCA) using the TRACE system T/H code. Because of the importance of the T/H solution for FFRD assessment, this study seeks to investigate the impact of using higher-fidelity subchannel techniques for modeling of the LOCA transient. CTF was used to model a subregion of a high-burnup core that was depleted by the Virtual Environment for Reactor Applications (VERA) multiphysics core simulator. Both coarse-mesh and pin-resolved models were created in CTF, and a consistent coarse-mesh TRACE model was also developed to allow for benchmarking the code results. A large-break loss-of-coolant accident (LBLOCA) reflood transient was simulated using these three models, and results were compared. Results showed some consistent differences between the CTF and TRACE coarse models, including a higher peak cladding temperature (PCT) prediction in CTF and later quenching in CTF; however, the transient clad temperature behavior was similar, and these differences are likely due to post-critical heat flux heat transfer modeling differences and minimum film boiling temperature model differences. The pin-resolved results indicate that the PCT in the lumped model is often under-predicted by as much as 70 °C and that PCT occurs at a different location than the high-power pin in the assembly. The lumped model predicts a difference of 10 °C or less between the average and hot pins in the assembly, whereas the pin-resolved model predicts a range of over 100 °C. These results indicate that higher-fidelity T/H results may have an impact on predicted core behavior during LOCA, which may be important to consider when assessing FFRD risk.

RELAP5-3D validation studies based on the High Temperature Test facility

In the spring and summer of 2019, experiments were conducted at the High Temperature Test Facility (HTTF) that form the basis of an upcoming high-temperature gas-cooled reactor (HTGR) thermal hydraulics (T/H) benchmark. HTTF is an integral effects test facility for HTGR T/H modeling validation. This paper presents RELAP5-3D models of two of those experiments: PG-27, a pressurized conduction cooldown (PCC); and PG-29, a depressurized conduction cooldown (DCC). These models used the RELAP5-3D model of HTTF originally developed by Paul Bayless as a starting point. The sensitivity analysis and uncertainty quantification code, RAVEN was used to perform calibration studies for the steady-state portion of PG-27. We developed four PG-27 calibrations based on steady-state conditions. These calibrations all used an effective thermal conductivity equal to 36 % of the measured thermal conductivity, but they differed with respect to the frictional pressure drops and radial conduction models. These models all captured the trends in steady-state temperature distributions and transient temperature behavior well. All four calibrations show room for improvement in predicting the transient temperature rise. The smallest error in temperature rise during the transient was a 21 % underprediction, and the largest was a 48 % underprediction. The errors in transient temperature rise are largely a result of a mismatch in power density between the RELAP5-3D model and the experiment due to the location of active heater rods along the boundary between heat structures in the model. The best of these calibrations was applied to PG-29 to model the DCC. Once again, temperatures during the transient were underpredicted but trends in temperature were captured. The RELAP5-3D model captured trends in the data but could not reproduce measured temperatures exactly. This result is not attributed to deficiencies in the experimental data or to RELAP5–3D itself. Rather, this result likely arises due to the some of the assumptions and decisions made when the RELAP5-3D model was first developed, prior to the execution of HTTF experiments. An agreement in prediction of temperature trends but challenges reproducing HTTF temperatures within measurement uncertainty is consistent with previous analyses of HTTF in the literature. Future RELAP5-3D validation activities centered around HTTF may be able to provide greater insight into the code’s capabilities for HTGR modeling with a more finely nodalized model.

NUMERICAL ANALYSIS OF TRANSIENT SOIL TEMPERATURE VARIATION DURING WILDFIRES

In this study, transient behavior of soil temperature during large forest fires is analyzed using the Comsol© software package. The increase in soil temperature during large wildfires can be very critical, especially when oil or gas pipelines have been laid at a certain depth in the soil in or near forests. During forest fires, the temperature of the soil surface can reach extreme levels that penetrate deep into the ground if the fire is not extinguished within a short period of time. This increase in temperature on the soil surface can lead to extremely dangerous situations if the laying depth of the pipeline is not sufficient, since the heat conducted through the soil causes the surface temperature of the pipeline and therefore that of the fluid inside to also reach very high values. This can lead to a sudden rupture of the pipeline and ultimately lead to catastrophic consequences. Although the present study is conservative due to the assumptions made in structuring the numerical model, it is believed to provide invaluable information about the considerations in selecting gas pipeline locations and pipeline laying depths, while also taking into account extreme temperatures due to wildfires, seismic impacts and traffic loads. Future research could include extensive study on the energy content of different species of forest trees, considering their time-dependent heat release rates (HRR) during a forest fire, as well as experimental work if a realistic setup could be designed.

Experimental investigation of time-dependent electrical load effects through multipoints in-situ measurement of temperature and relative humidity of PEMFC bipolar plate under transient operation

In this study, multiple micro-relative humidity and temperature (RH/T) sensors were installed in the anode and cathode channels of a proton exchange membrane fuel cell (PEMFC) bipolar plate to simultaneously observe and analyze the variation in RH/T behaviors during transient operation. In order to simulate the acceleration and deceleration process, the electrical load was ramped from 10 to 40 A and then back to 10 A, with time intervals of 0, 2, and 5 s. The data corresponding to different acceleration/deceleration time intervals were compared and analyzed to assess the time-dependent effects of load changes. The analyzed data provide visual information, including the transient voltage response, transient behavior of temperature and water distribution, and evolution of RH/T within PEMFC. The results indicate that the acceleration and deceleration interval times significantly influence the temperature and water distribution within PEMFC during transient operation. Shorter acceleration times lead to more rapid changes in temperature and humidity within the PEMFC active area, resulting in higher transient temperature and water concentration. This finding explains why the output voltage decreases more when the load changes with a short time interval. This research enhances our understanding of transient temperature and water behavior, providing a foundation for further research and development of effective operational strategies and vehicle PEMFC designs.

Modeling Approach Estimates Temperatures in Growing High-Temperature Wells

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 214836, “Downhole Temperature Estimation of a Growing High-Temperature Wellbore Using a Modified Drift-Flux Modeling Approach,” by Ningyu Wang, SPE, Mohamed S. Khaled, and Anthony Luu, The University of Texas at Austin, et al. The paper has not been peer reviewed. _ Downhole temperature (DHT) estimation is very important for heat management while drilling high-pressure/high-temperature (HP/HT) and geothermal wells. Existing transient models neglect the effect of wellbore growth or deepening on the downhole temperature. The complete paper provides a new modeling tool to estimate and manage the DHT in higher-temperature oil, gas, and geothermal wells. The model, which has the potential to run in real time and thereby digitally twin the drilling operation, may contribute to preventing premature temperature-related failures of bits and downhole tools while drilling future wells in high-temperature environments. Introduction Analytical and numerical modeling are the two main approaches discussed in the literature to estimate the mud temperature inside the drillstring and the annulus. Although these models provide valuable insights on selecting optimal heat-management techniques during circulation, none consider the effect of drilling rate of penetration (ROP) on downhole temperature, and all consider the wellbore as having fixed and static dimensions. On the other hand, the effect of ROP in an arbitrarily growing wellbore on other aspects of drilling has been modeled and studied. In this work, the authors present a validated thermohydraulic model based on the drift-flux approach to simulate the transient behavior of downhole temperature during drilling. This model can predict the effect of different cooling-strategy techniques based on real-time operational changes and can predict temperature-sensor measurements. It thereby establishes a foundation for active managed-temperature drilling of HP/HT and geothermal wells. Methodology The drift-flux model is a well-studied model for 1D flow in a flow channel with static geometry. Conservation equations, and their discretization, are detailed in the complete paper, as are equations regarding heat transfer in the solid. Assumptions. To lay the foundation for a thermohydraulics model that considers the effect of the growth of the wellbore, the following key assumptions are made: - The ROP is much slower than the mud-flow velocity. - The cuttings are assumed to be perfectly integrated into the mud and to share the physical properties of the drilling mud. Therefore, the added mud volume equals the volume of the cuttings. The complete paper focuses on laying the foundation for a solver that accounts for the wellbore growth. - The transient temperature distribution in the drillstring is neglected because the authors are primarily interested in temperature behavior on larger time scales. - The growth of the wellbore trajectory is an external input and is to be updated in a timely manner if the solver is run in real-time mode. - The drillpipe entering the well has constant cross-sectional geometry. - The formation temperature ahead of the bit is considered to not yet be disturbed as drilling proceeds.

Field Stop (FS) Type IGBT Transient Temperature Characteristics: E-Thermal Simulation Approach

This research presents an electro-thermal simulation method for analyzing the transient temperature characteristics of Field Stop (FS) type Insulated Gate Bipolar Transistors (IGBTs). The method combines IGBT working principles and semiconductor physical principles to investigate the influence of internal excess carrier lifetime on the IGBT's transient temperature behavior. By conducting actual tests on an FS type IGBT switching transient working process, the research establishes an electro-thermal simulation method with improved accuracy and simplified parameter calculation.

Transient multi-physics behavior of an insert high temperature superconducting no-insulation coil in hybrid superconducting magnets with inductive coupling

Transient multi-physics behavior of an insert high temperature superconducting no-insulation coil in hybrid superconducting magnets with inductive coupling

Real Time Power Control in a High Voltage Power Supply for Dielectric Barrier Discharge Reactors: Implementation Strategy and Load Thermal Analysis

Atmospheric-pressure plasma treatments for industrial and biomedical applications are often performed using Dielectric Barrier Discharge reactors. Dedicated power supplies are needed to provide the high voltage frequency waveforms to operate these nonlinear and time-dependent loads. Moreover, there is a growing technical need for reliable and reproducible treatments, which require the discharge parameters to be actively controlled. In this work, we illustrate a low-cost power supply topology based on a push–pull converter. We perform experimental measurements on two different reactor topologies (surface and volumetric), showing that open loop operation of the power supply leads to a temperature and average power increase over time. The temperature increases by ΔTvol~120 °C and ΔTsup~70 °C, while the power increases by ΔPvol~78% and ΔPsup~60% for the volumetric (40 s) and superficial reactors (120 s), respectively. We discuss how these changes are often unwanted in practical applications. A simplified circuital model of the power supply–reactor system is used to infer the physical relation between the observed reactor thermal behavior and its electrical characteristics. We then show a control strategy for the power supply voltage to ensure constant average power operation of the device based on real-time power measurements on the high voltage side of the power supply and an empirical expression relating the delivered power to the power supply output voltage. These are performed with an Arduino Due microcontroller unit, also used to control the power supply. In a controlled operation the measured power stays within 5% of the reference value for both configurations, reducing the temperature increments to ΔTvol~80 °C and ΔTsup~44 °C, respectively. The obtained results show that the proposed novel control strategy is capable of following the transient temperature behavior, achieving a constant average power operation and subsequently limiting the reactor thermal stress.

Interpretation of temperature transient data from coupled reservoir and wellbore model for single phase fluids

This paper presents a non-isothermal, transient coupled reservoir/wellbore model that accounts for the Joule-Thomson (J-T), isentropic expansion, conduction and convection effects for predicting the transient temperature behavior and computing the wellbore temperature at different gauge depths. In this study, single phase fluid flow of oil or geothermal brine from a fully penetrating vertical or inclined well in an infinite-acting homogeneous single layer reservoir is modeled. The coupled simulator solves mass, momentum and energy conservation equations simultaneously for both reservoir and wellbore. We improve solutions by the functional iteration procedure that updates fluid properties based on available correlations as a function of pressure and temperature at a given time step. A comparison of the developed model with a commercial simulator is provided. To understand and identify diagnostic characteristics of temperature transients at gauge locations at the sandface and above the sandface that may arise during a well test, we examine the sensitivity of the model parameters appearing in the coupled non-isothermal reservoir/wellbore model through a synthetically generated test data sets and history matched field application. The drawdown and buildup sandface transient temperature data are obtained from the coupled model and used to interpret and analyze temperature transients. In addition to the J-T coefficient of fluid, history matching transient temperature data provides estimates for the skin zone radius and permeability when analyzed jointly with the conventional pressure test analysis (PTA). An investigation on the effect of gauge location on temperature data shows that the early-time response is influenced by the wellbore phenomena while the J-T effects are clearly identified at later times at typical gauge locations up to 100 m above the top of the producing horizon. Logarithmic derivative of temperature transients are found as a useful diagnostic tool to differentiate the wellbore phenomena from the reservoir response. It is also shown that the temperature transient is more reflective of the properties of the near wellbore region (e.g., skin zone) than the pressure transient. For this reason, analyzing temperature transients together with the pressure transients could add more value to the analysis to better examine near wellbore characteristics. • A fully implicit transient single phase coupled wellbore/reservoir non-isothermal simulator is presented. • New diagnostic plots for temperature transient analysis are provided. • For typical gauge locations (usually up to 100 m above the producing horizon), reservoir response is acquired through drawdown wellbore temperature data. • An effective well radius is introduced for history matching due to the placement of many tools in wellbore during temperature transient analysis. • Reservoir and skin zone parameters are estimated reliably by history matching pressure and temperature field data together.

EXPERIMENTAL STUDY OF PCM BASED HYBRID HEAT SINK FOR ELECTRONIC COOLING

The present experimental study reports the thermal performance analysis of a phase change material (PCM)-basedfinned heat sink placed on a silicone rubber heater which mimics the CPU chip and is cooled by natural and forced convection. The heat sink is subjected to constant and cyclic loading for five input power values (4, 6, 8, 10, and 12 W). Paraffin wax and 1-hexadecanol are selected as PCM for this study, which have melting points in the ranges of 58°C−60°C and 48°C−50°C, respectively. The steady-state and transient base temperature behavior of the heat sink indicated that the heat sink with PCM performed better than the heat sink without PCM under natural convection subjected to a constant load. With the increase in input power, the melting time of the PCM is reduced. Between the two PCMs, the heat sink filled with 1-hexadecanol performed better in transient operation. It was observed that cyclic loading offers better insight into the thermal behavior of the heat sinks at different power inputs. The total operation time of heat sink filled with 1-hexadecanol takes less time than paraffin-filled heat sink during cyclic loading when subjected to natural convection. For cyclic loading, the total operation time of the heat sink is reduced by a factor of 0.41 and 0.43 times when cooled by forced convection as compared to natural convection for heat sink filled with paraffin wax and 1-hexadecanol, respectively.

Transient Temperature Impact on Deep Reservoir Fracturing

Hydraulic fracturing enables the commercial development of unconventional resources in shales and tight formations. The conductivity and complexity of created fractures are critically dependent on the rheology of fracking fluid and the mechanics properties of rocks. Literatures show that both the rheology of fracturing fluid and fracture propagation dynamics are affected by the temperature of fracturing fluid. Neglecting the temperature transient behaviour may defeat the purpose of fracturing optimization during fracture initiation, propagation, and sand packing. The objective of this paper is to investigate the impact of temperature on fracturing design by studying the transient temperature behaviour across a complex wellbore using numerical modelling by coupling a finite difference heat transfer model with a dynamic fracture propagation model. The study results show that with the injection of cold fracturing fluid, hydraulic fracture propagation is decelerated, and production prediction is thus lessened compared with the case ignoring temperature effect. For multistage fractured wells, fracture geometry enlarges along the fluid flow direction in a horizontal segment. This potentially lowers the cost of hydraulic fracturing designs.

Analysis of The 2-D Transient Heat Conduction in a Composite Finite Cylinder with Heat Generation.(Dept.M)

The objective of this paper is to study the 2-D transient temperature behavior in a composite finite cylinder with internal heat generation. For this purpose, a new dimensionless 2-D finite difference technique in the axial and radial directions is developed. The developed technique is then applied to obtain the time development of temperature profiles in a complex composite cylinder.

An Enhanced Numerical One-Dimensional Transient Fuel Rod Code for Light Water Reactors.(Dept.M)

In this paper a new enhanced simple numerical fuel rod code is developed, which is used to calculate the transient one-dimensional fuel temperature behavior in Light Water Reactors. The proposed code is then applied to determine the transient temperature behavior of fuel due to sudden rise in heat generation rate. The obtained results are then compared with that obtained from an analytical transient solution. The steady state values obtained from both solutions are then compared with that obtained from the corresponding closed form solution of this problem. It is proved that the numerical code is more powerful and accurate.

Investigation of the thermal behavior and energy consumption of refrigeration systems

The object of this research study is to develop a thermal simulation model that can be used to investigate the thermal parameters of the refrigerant systems (with ON/OFF and PID control) used in cooling chambers. Moreover, the model was further developed which takes into account also the types of compressors, feeder, and control units used commonly in practice for energetic investigations. Using the measured energy consumption data obtained by experimental tests during the previous phase of this research work, the validation of the developed energy simulation model by MATLAB R2016a could be also achieved with good agreement. The MATLAB software seemed to be the most appropriate tool for numerical investigations on the energy consumption of refrigeration systems used in commercial cold stores and transient behavior of the indoor air temperature of the cold store, cooling energy performance and consumed energy to the goods stored in cold store.

Temperature dynamics and its effects on gas influx handling during managed pressure drilling operations

With Managed Pressure Drilling (MPD) becoming increasingly important to oil and gas well construction, there has been a growing demand for comprehensive models that can accurately describe the well hydraulic dynamics, especially for complex well geometries, High-Pressure High-Temperature (HPHT) conditions, during well control events, etc. To meet this demand, new multi-phase hydraulic models have been developed. However, despite their improvement over the traditional lumped parameter models, these models typically do not consider detailed temperature effects, which markedly influence well hydraulics and need to be explicitly considered for accurate MPD control.The development of a new integrated multi-phase thermal and hydraulic modeling framework is presented in this paper. This integrated model can estimate the mud temperature in the drillstring and the annulus, as well as the temperature variations of the formation during complex well control situations. The model uses a semi-implicit finite volume approach and solves the mixture energy equation for the wellbore fluids, assuming that all the phases are in thermal equilibrium. Heat transfer between the drillstring and wellbore fluids, and between the wellbore fluids and the formation is calculated using thermal resistance networks.The steady-state and transient temperature behaviors during mud circulation are compared to the steady-state analytical model by Hasan and Kabir and commercial software. These comparisons show good agreement for both steady-state and transient cases. To demonstrate the importance of accurate temperature estimation of the drillstring and annulus fluids in HPHT conditions, offshore kick scenarios for non-aqueous drilling fluids and dynamic kick control methods are simulated. Simulation results indicate that the model enables real-time estimation of crucial parameters during well control, such as the wellbore pressure and temperature profiles, increased outflow and pit gain during kicks, gas thermodynamic behavior including solubility and unloading behavior at low pressure conditions, gas rising velocity, and temperature-dependent formation strength.

Particle-based simulation, dimensional analysis and experimental validation of laser absorption and thermo-viscous flow during sintering of polymers

Smoothed Particle Hydrodynamics simulations are used to study the thermo-viscous flow on the powder particle length scale. The effects of laser absorption, latent heat, thermal diffusion, melting and re-solidification, viscous diffusion, surface tension, Marangoni currents and gravity are considered in the model. Influences of varied laser scanning parameters are analyzed. The strongly different time scales of laser absorption, heat conduction and viscous flow as well as the transient behavior of temperature and strain rate observed in the simulations are predicted with good accuracy by a dimensional analysis. The simulation results for the transient surface temperature are validated by infrared camera measurements.

Advantage in Friction Control in the Automotive Press Shop by Prelube 2nd Generation

Prelubes of the 2nd generation are the lubricant solution to the important challenges for the production in the automotive press shop during the last two decades. These challenges are increasing flexibility, reduction of scrap, smaller production batches, multiple parts and high strength steels. Tools to manage this rising complexity are standardization, better process control and simulation of process chains. The demands for a modern forming lubricant in the automotive press shop have to be aligned to the process chain of the body in white process. Tribology is only one part along the chain of application, corrosion protection, compatibility with welding, adhesives and the E-coating process of the body in white. Two main factors for unstable tribological conditions in the press shop are the uneven distribution of the oiling coming from the steel mill and the transient temperature behavior of the tool during the production cycle. Both can be controlled more easily by reduction of the oil amount with an advanced Prelube 2nd generation. The verification comes by strip drawing experiments and press shop trials. The reduction of the lubricant amount gives additionally benefits e.g. compatibility for the welding, adhesive process and finally the environment.

Transient behaviors of friction, temperature and fatigue in different contact trajectories for spiral bevel gears

Abstract The dramatic changes in contact geometry, load, entraining and sliding velocity vectors along contact trajectories of spiral bevel gears may cause significant squeezing action. It suggests that the steady-state analysis at each discrete engaging point cannot effectively describe the tribological behavior in spiral bevel gears. The present study aims to systematically study the transient friction, temperature and contact fatigue behaviors in different contact trajectories for spiral bevel gears based on a newly developed transient mixed EHL model. It shows that the obtained transient friction coefficient is much higher than the steady-state when the gears mesh in the first half of the engagement period. During the entire engagement period, the predicted transient fatigue life is significantly longer than the predicted steady-state fatigue life, which is of importance to the integrated and economical design of spiral bevel gears. The comparison with single half-sine waveform asperity demonstrated that the transient asperity contact pressure is much lower than that in quasi-steady state. The variation of flash temperature appears to be insignificant. Moreover, in different contact trajectories, the weakest point in one engagement period always occurs at a certain point when one teeth pair just finished the engaging-in and another pair of teeth completed engaging-out, and the toe contact exhibits the maximum frictional energy consumption and shortest fatigue life among them.

A Coupled Model of Two-Phase Fluid Flow and Heat Transfer to Transient Temperature Distribution and Seepage Characteristics for Water-Flooding Production Well with Multiple Pay Zones

Temperature is one of the most prominent factors affecting production operations, predicting the accurate wellbore-formation temperature in a water-flooding production well is of great importance for multiple applications. In this paper, an improved coupled model of oil–water two-phase fluid flow and heat transfer was developed to investigate the transient temperature behavior for a producing well with multiple pay zones. Firstly, a novel method was derived to simulate the water saturation and the water breakthrough time (WBT) for tubing, which are key monitoring parameters in the process of water flooding. Then, we incorporated water saturation and an equation set for immiscible displacement to calculate the seepage velocity and the pressure of the two-phase fluid in the pay zones. Next, the upward seepage velocity of the tubing fluid change with depth was focused on, and the proper coupled initial and boundary conditions are presented at the interfaces, therewith the implicit finite difference method was used to compute the transient temperature with the input of the seepage characteristics for the reservoirs. Meanwhile, the validity of the proposed model has been verified by the typical model. Finally, a sensitivity analysis delineated that the production rate and the production time had a significant impact on the tubing fluid temperature. The overburden was hotter with a lower volumetric heat capacity or a higher thermal conductivity. In addition, the sensitivity of the porosity and the irreducible water saturation to formation temperature was significantly different before and after the WBT. The coupled model presented herein helps to advance the transient seepage characteristics analysis of pay zones, the precise temperature prediction is very useful for reservoir characterization and production analysis purposes and provides insight for designing the exploitation scheme in deep reservoirs and geothermal resources.

Radiation field analysis of a photoconductive antenna using an improved carrier dynamics

Photoconductive antennae are one of the most common sources of terahertz radiation. Although extensive experimental and simulation work has been done to analyze the radiated fields, very limited theoretical analysis has been done to build elegant and compact models. This work presents the derivation of the radiated fields from a photoconductive antenna incorporating the effect of the semiconductor substrate. Additionally, an improved model of the semiconductor carrier dynamics has been proposed to analyze the radiation characteristics of the photoconductive antenna. The proposed carrier dynamics includes a novel analysis of the transient behavior of the substrate temperature and its effect on the parameters of the substrate material. It also incorporates the effect of the lifetime, polarization and velocities of the carriers as well as the effects of the radiated near zone fields and antenna geometry. The derived formulae and the proposed carrier dynamics model have been validated by comparing the results with the available experimental results in the literature. It has been found that the analytically calculated results closely follow the experimental results reported in the literature.