Transient Temperature Distribution Research Articles

Analytical solution for transient radial interaction between energy piles and soils: Thermo-elastic cavity expansion analysis

Bearing capacity of energy piles may be affected by the Radial Interaction between Energy Piles and Soils (RIEPS) such as energy pile expansion and transient radial heat conduction. This paper proposes a cavity-expansion-based solution to investigate the thermo-elastic RIEPS. Transient temperature distributions are shown by assuming heat conduction in the radial direction and constant temperature at the pile-soil interface. With the temperature distributions, a thermo-elastic solution is obtained to capture the changes in stresses and displacements around energy piles. It is found that the solution under the combined thermal-mechanical loading pattern is the linear superposition of those under the thermal loading and mechanical loading patterns. Hence, the stresses, strains and displacements in soils are determined by the competitive relationships between thermal and mechanical loading patterns. The expression for radial stress change at the pile-soil interface is discussed by the cavity expansion analysis and comparison with field data. For typical soil and pile parameters, the expression could be quite general considering transient temperature distributions and soil/pile moduli. This paper can benefit to the capacity design of energy piles by taking the RIEPS into account.

In-flight anti-icing simulation of electrothermal ice protection systems with inhomogeneous thermal boundary condition

Conventional anti-icing computational solvers calculate the convective heat transfer coefficient using a homogeneous thermal boundary condition, assuming a constant temperature across the surface. However, this approach can lead to inaccuracies in regions with significant temperature variations. To address this limitation, the present study proposes a novel approach that utilizes an inhomogeneous thermal boundary condition, which updates the convective heat transfer coefficient based on the transient wall temperature distribution. We developed a unified finite volume framework that efficiently integrates various in-house solvers, including a compressible Navier-Stokes-Fourier (NSF) airflow solver, a Eulerian droplet impingement solver, a PDE-based ice solver, and a multilayer heat conduction solver. Thermal interaction between the different solvers was modeled using the conjugate heat transfer method. The effects of updating airflow on anti-icing results were investigated by comparing the results obtained by coupled and decoupled solvers. While the decoupled solver computes airflow once and remains unchanged, the coupled solver updates the airflow during the anti-icing simulation. Our findings show that the decoupled solver has the highest deviations from the coupled solver in evaporative anti-icing regimes, where dry regions form within the protection limits. Using coupled solvers in designing ice protection systems in evaporative regimes improves temperature prediction accuracy, enabling designers to reduce safety factors and save energy.

An Experimental Method to Capture the Thermal Conductivity Coefficient of Fine-Grained Concretes during Transition from Liquid to Solid.

During the transition from liquid to solid, the thermal conductivity coefficient λ of concrete decreases. Although λ of hardened concrete is well investigated, there is limited research on the transition from liquid to solid and how it depends on hydration. Currently, only simplified qualitative approaches exist for the liquid state and the transient process. An experimental method is not available. For this purpose, a test rig is designed to experimentally capture the evolution of λ for fine-grain concretes during transition. The performance of the test setup is evaluated on a characteristic high-performance concrete (HPC). The results are compared to theoretical predictions from the literature. The developed test rig is mapped in a digital twin to investigate extended boundary conditions, such as different heat sources and temperatures of the experimental setup. It allows the experiment to be repeated and optimized for different setups with little effort. The test principle is as follows: A liquid concrete sample is heated through a controlled external source, while the transient temperature distribution over the height is measured with a fiber optic sensor. The thermal conductivity is derived from the heat flux induced and the temperature distribution over an evaluation length. Experiments show that λ in the liquid state is approximately 1.4 times greater than in the solid state and exponentially decreases for the transient process. Numerical results on the digital twin indicate that the robustness of the results increases with the temperature of the heat source. Moreover, the derivation in λ turns out to be strongly dependent on the evaluation length. A length of three times the maximum grain diameter is recommended.

CFD Applications to Pressurized Thermal Shock-Related Phenomena

In pressurized water reactor accident scenarios, the injection of water from the emergency core cooling system (ECCS) (ECC injection) might induce a pressurized thermal shock (PTS), affecting the reactor pressure vessel (RPV) integrity. Therefore, PTS is a vital research issue in reactor safety, and its analysis is essential for evaluating the integrity of RPVs, which determines the reactor life. The PTS analysis comprises a coupled analysis between thermal–hydraulic and structural analyses. The thermal–hydraulic approach is particularly crucial, and reliable computational fluid dynamic (CFD) simulations should play a vital role in the future because predicting the temperature gradient of the RPV wall requires data on the transient temperature distribution of the downcomer (DC). Since one-dimensional codes cannot predict the complex three-dimensional flow features during ECC injection, PTS is one reactor safety issue where CFD simulation can benefit from complement evaluations with thermal–hydraulic system analysis codes. This study reviewed from the viewpoint of the turbulence models most affecting PTS analysis based on papers published since 2010 on single- and two-phase flow CFD simulation for the experiment on PTS performed in the Rossendorf coolant mixing model (ROCOM), transient two-phase flow (TOPFLOW), upper plenum test facility (UPTF), and large-scale test facility (LSTF). The results revealed that in single-phase flow CFD simulation, where knowledge and experience are sufficient, various turbulence models have been considered, and many analyses using large eddy simulation (LES) have been reported. For two-phase flow analysis of air–water conditions, interface capturing/tracking methods were used in addition to two-fluid models. The standard k–ε and shear stress transport (SST) k–ω models were still in the validated phase, and various turbulence models have yet to be fully validated. In the two-phase flow analysis of steam–water conditions, many studies have used two-fluid models and Reynolds-averaged Navier-Stoke (RANS), and NEPTUNE_CFD, in particular, has been reported to show excellent prediction performance based on years of accumulated validation.

Dual-tracer laser-induced fluorescence thermometry for understanding bubble growth during nucleate boiling on oriented surfaces

Nucleate boiling is perhaps one of the most efficient cooling methodologies due to its large heat flux with a relatively low superheat. Nucleate boiling often occurs on surfaces oriented at different angles; therefore, understanding the behavior of bubble growth on various surface orientations is of importance. Despite significant advancement, numerous questions remain regarding the fundamentals of bubble growth mechanisms on oriented surfaces, a major source of enhanced heat dissipation. This work aims to accurately measure three-dimensional (3D), space- and time-resolved, local liquid temperature distributions surrounding a growing bubble on oriented surfaces that quantify the heat transfer from the superheated liquid layer during bubble growth. The dual tracer laser-induced fluorescence thermometry technique combined with high-speed imaging captures transient 2D temperature distributions within a 0.3 ºC accuracy at a 30 μm resolution. The results show that the temperature close to the heated surface and bubble interface exhibits an acute transient behavior at the time of bubble departure, and the growing bubble works as a pump to remove heat from the surface with a temperature difference of up to 10 °C during its growth and departure. The experimental results are compared with data available in the literature to validate the accuracy of the technique. It was found that the heat transfer coefficient close to the bubble interface and heater is approximately 1.3 times higher than the heat transfer coefficient in the bulk liquid.

Accurate Temperature Reconstruction in Radiofrequency Ablation for Atherosclerotic Plaques Based on Inverse Heat Transfer Analysis.

Radio frequency ablation has emerged as a widely accepted treatment for atherosclerotic plaques. However, monitoring the temperature field distribution in the blood vessel wall during this procedure presents challenges. This limitation increases the risk of endothelial cell damage and inflammatory responses, potentially leading to lumen restenosis. The aim of this study is to accurately reconstruct the transient temperature distribution by solving a stochastic heat transfer model with uncertain parameters using an inverse heat transfer algorithm and temperature measurement data. The nonlinear least squares optimization method, Levenberg-Marquardt (LM), was employed to solve the inverse heat transfer problem for parameter estimation. Then, to improve the convergence of the algorithm and reduce the computational resources, a method of parameter sensitivity analysis was proposed to select parameters mainly affecting the temperature field. Furthermore, the robustness and accuracy of the algorithm were verified by introducing random noise to the temperature measurements. Despite the high level of temperature measurement noise (ξ = 5%) and larger initial guess deviation, the parameter estimation results remained closely aligned with the actual values, with an overall ERMS consistently below 0.05. The absolute errors between the reconstruction temperature at the measurement points TC1, TC2, and TC3, and the actual temperature, remained within 0.33 °C, 2.4 °C, and 1.17 °C, respectively. The Levenberg-Marquardt algorithm employed in this study proficiently tackled the ill-posed issue of inversion process and obtained a strong consistency between the reconstructed temperature the actual temperature.

Coupled heat and water transfer in heterogeneous and deformable soils: Numerical model using mixed finite element method

We present a generic model framework for coupled heat and water transfer (CHWT) in deformable (non-rigid) soils with spatial variations of soil properties. The model backbone is a mixed finite element method (FEM), which solves the Philip and de Vries (1957) CHWT model and achieves conservation of mass and energy on both local and global scales. Spatial variations occur in soil hydraulic and thermal properties due to transient water content and temperature distributions. Based on the mixed FEM scheme, a gradient measure and a clustering model (“k-means”) are proposed to trace the regions with large spatial variations of soil properties, and an adaptive mesh refinement technique is developed to improve the spatial resolution and simulation accuracy. Deformation perturbates local soil topography and alters transient soil water and temperature regimes in the deformed regions. A quasi-static deformation model is presented, and the deformation effects are incorporated into the mixed FEM scheme. When external load exists, soil deformation is simulated with an updated Lagrangian formulation, and the local water content and temperature variations due to soil volume changes are also updated in the CHWT model. Numerical examples, including thermally induced soil water transfer and water infiltration, illustrate the model ability to provide plausible CHWT results, especially the refined solutions near the wetting fronts and the water content and temperature distributions when the soil is deformable. In conclusion, the proposed model framework provides an effective pipeline to incorporate and process the spatial variations of soil properties and soil deformation in CHWT simulations.

Evaluation by Liquid Crystal Thermography of Transient Surface Temperature Distribution in Radiant Floor Cooling Applications and Assessment of Analytical and Numerical Models

Abstract The purpose of our study is to evaluate the surface temperature distribution on a radiant floor, particularly focusing on space cooling operations, to assess the presence of nonuniformities. In fact, knowing the temperature difference between the average superficial temperature and the coldest spot can be a useful indication for condensation prevention. Primarily, we performed an experimental campaign in test rooms using temperature sensors and liquid crystal thermography. This allowed us to evaluate the floor temperature distribution both on a local scale, influenced by the discontinuous presence of buried water pipes, and on a macroscale, influenced by internal use, objects, and boundary conditions of the surrounding space. Then, the experimental temperature field on the radiant floor surface has been compared with analytical and numerical models in steady-state and transient phases, respectively. The results indicate limited superficial temperature variations that become more significant at larger tube spacings and under transient conditions. In particular, the numerical transient analysis showed that shortly after a step change in the pipe's temperature boundary condition, a larger variation is locally observable on the floor, which then decays to the new steady-state conditions, presenting more uniformity. However, local effects are generally overshadowed by macro-effects, especially for practical scenarios where many objects, furnishings, and different boundary conditions are present. Finally, as a conservative guideline for the cooling system control, we recommend maintaining the average superficial floor temperature at least 1 °C above the dew point, to account for the described nonuniformities.

On material removal analysis in ECSM process during micro-channelling with rough tool: Experimental investigation and numerical simulation

The prevailing ECSM investigation using rough tools exhibits its superior performance, especially during micro-channelling. However, the critical aspects related to microchannel quality, such as straightness error, depth/width ratio, MRR and surface quality, have not been thoroughly explored in the existing literature. This research endeavours to fill this gap by addressing these pertinent issues. It also introduces a finite element-based model to analyze the transient temperature distribution and material removal rate, considering the influence of multiple spark discharges generated by rough tools during micro-channelling. The research encompasses theoretical analysis, simulations accounting for partition energy, and experimental assessment of various ECSM parameters for fabricating microchannels with better MRR, depth/width ratio and straightness without compromising the machined surface quality. Theoretical and simulation analyses emphasize the superior performance of rough tools in achieving efficient micro-channel fabrication compared to smooth tools, attributed to a substantial 245 % higher electric field distribution over the entire rough tool surface. Particularly, under low-energy interactions (70 V, 20 % electrolyte concentration, 6 mm/min tool feed, and 3 ms pulse on time), the close alignment between experimental, simulation and regression model results validates the accuracy of the FEM model in capturing the performance of the rough tool in ECSM micro-channelling. This comprehensive investigation provides valuable insights into the benefits of employing rough tools and the factors influencing the quality and efficiency of ECSM for microchannel fabrication.

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.

Transient Thermal Exchange Analysis of an External Rotor Hub Motor for Electrified Defense Vehicles Applications Based on FVM and TNM

This paper investigates the transient temperature distribution law of a 75kW external rotor hub motor for electrified defense vehicles (EDV) using the finite volume method (FVM) and the thermal network method (TNM). Based on thermal exchange and fluid flow theories, both a transient fluid-solid coupled thermal exchange model and a lumped parameter thermal network model (LPTNM) with transient thermal capacity parameters are established. An iterative algorithm for the heat transfer coefficient is proposed to improve the accuracy of LPTNM. Compared with existing methods, this algorithm exhibits higher accuracy and stronger practicality. In addition, an experimental platform of the hub motor temperature rise is built for measuring the end winding temperature. The calculated results are in good agreement with the experimental results, verifying the rationality of the 3D transient fluid-solid coupled thermal exchange model and the LPTNM. The axial parallel water channel structure was adopted to improve the cooling performance of the end winding, taking into account the structural characteristics and assembly mode of the hub motor. This paper provides theoretical references for the transient thermal analysis and cooling structure design of the EDV hub motor.

Quantification of geometrical errors and thermal effects during wire EDM of thin wall structures—A numerical study

Machining thin-walled structures with a high aspect ratio using Wire EDM can lead to geometrical errors, primarily of two types; overcut error due to kerf formation and thermal deformation of the entire wall section. To understand the driving mechanisms behind these errors three distinct numerical models were developed. Initially, a model based on a moving heat source was created, employing the apparent heat capacity approach to predict kerf width and the associated overcut error. These insights were then utilized to formulate a transient temperature distribution model with a redesigned geometry, considering time-dependent evolution of the kerf and corresponding changes in the material properties of the sub-domains. Finally, a thermo-mechanical coupled model was developed to predict geometrical errors caused by the deflection of the wall, considering the varying stiffness of the part. A series of experiments were conducted to gain insight into the effect of the designed wall thickness on wall deflection. For the selected design profile and machine parameters, the model predicts a 62.4% reduction in thickness and a corresponding over-cut error of 188μm. Similarly, the model predicts wall deformation in the range of 6μm to 312μm for various wall thickness levels and these findings were validated with experimental observations.

Thermal shock fracture in a cracked strip: Incorporating convective heat transfer between lateral surfaces and ambient environment

This paper presents a comprehensive analysis of transient temperature and thermal stress around a thermal insulated crack in a finite thermoelastic strip subjected to thermal shock based on the dual-phase-lag (DPL) heat conduction. A detailed investigation of the effect of convective heat exchange between the lateral surfaces of the strip and the ambient environment is conducted. By employing integral transform technique, the thermoelastic crack problem is reduced to a set of singular integral equations, and solutions for the transient temperature distribution and dynamic stress intensity factors (SIFs) at the crack tips are then obtained. Numerical results reveal a considerable temperature gradient near the heating surface when both the high convective heat transfer coefficient and thin strip are involved. Consequently, the SIFs in such scenarios where cracks are located close to the heating surface are significantly larger compared to those calculated by neglecting the convective heat loss. Furthermore, during the initial period following a thermal shock, the SIFs may exhibit higher magnitudes than the steady-state values. These findings emphasize the importance of accounting for the influence of convective heat exchange with the ambient environment in material design and optimization to enhance fracture resistance under transient thermal loading.

Heat transfer near a growing bubble during nucleate boiling using dual-tracer laser-induced fluorescence thermometry

Boiling heat transfer associated with bubble growth is perhaps one of the most efficient cooling methodologies due to its large latent heat during phase change. Despite the significant advancements, numerous questions remain regarding the fundamentals of bubble growth mechanisms, which is a major source of enhanced heat dissipation. This work aims to accurately measure three-dimensional (3D), space and time-resolved, local liquid temperature distributions surrounding a growing bubble to quantify the heat transfer in the superheated liquid layer during bubble growth. The dual tracer laser-induced fluorescence thermometry technique combined with high-speed imaging captures transient 2D temperature distributions, that will render 3D temperature distributions by combining multiple 2D layers, within a 0.3 °C accuracy at a 30 μm resolution. Two fluorescent dyes, fluorescein and sulforhodamine B, were used to measure transient temperatures, by account of their temperature-sensitive emissions. The results show that the temperature close to the heated surface and bubble interface exhibits an acute transient behavior at the time of bubble departure. The growing bubble works as a pump to remove heat from the surface with a peak temperature difference of up to 10 °C during its growth and departure. The experimental results were compared with previously reported studies to validate the accuracy of the technique. It was found that the heat transfer coefficient close to the bubble interface and heater is approximately 1.3 times higher than the heat transfer coefficient in the bulk liquid.

Optimisation of the cooling of pressurised thick-walled components operating with fluid at saturation temperature

Determining the optimum heating or cooling times for thick-walled pressure elements allows a steam boiler to reduce start-up or shutdown times. A new method has been developed to determine the optimum fluid temperature change to shorten the steam boiler start-up and shutdown. The fluid temperature curve is designated so that the total circumferential stress at the hole edge does not exceed the allowable stress. The total stress at the hole edge where it is concentrated consists of thermal and pressure stress. The example of the optimum cooling of the steam boiler drum illustrated the method used. A three-dimensional finite element method (FEM) analysis was carried out for the connection between the drum and the downcomer to determine the transient temperature and stress distributions. It was shown that the total circumferential stress due to pressure and thermal loading at the hole edge did not exceed the allowable stress when optimal fluid temperature changes were used. The method shown in this paper was compared with the boiler standard EN 12952-3, which permits the determination of allowable heating and cooling rates of boiler pressure components as a function of pressure. The comparison shows that the cooling/heating time determined by the new method can be significantly shorter than that determined by the method in EN 12952-3. By using the new method for designating the optimum fluid temperature, the flexibility of the boiler and the power unit can be improved as the heating or cooling of critical pressure elements can be more rapid. It can also be used to accidently cool PWRs (Pressurised Water Reactors) and BWRs (Boiling Water Reactors) pressure vessels.

Transient Computational Fluid Dynamics Analysis of Passive Cooling in a Building with Diurnal Radiative Cooling Material Coated onto Its Rooftop

Building cooling loads, which continue to increase with increasing global temperatures, are responsible for large quantities of greenhouse gas emissions. Radiative cooling (RC), whereby structures are cooled by emitting radiation in the atmospheric window, from 8–13 μm, to outer space, is a promising clean technology that can be used to meet ever‐increasing building cooling demands. However, the effects of using RC on the airflow velocity and temperature distributions within the occupied zone of buildings are yet to be investigated. Herein, computational fluid dynamics simulations are performed to study the transient airflow velocity and temperature distributions in buildings that are cooled using RC material on their rooftops. For idealized conditions when the thermal mass of the house is neglected, the results show that when the cooling power provided by the RC material is , and the average temperature of the occupied zone in the building is reduced from 295 K to about 293 and 289.7 K after two minutes, respectively. These rapid cooling rates were attained without exceeding head‐to‐ankle temperature differences of about 2.7 °C and with air flow velocities maintained below 19.0 cm s−1, which is consistent with a comfortable environment.

Inverse analysis method of molten shape by deep learning

Most structural damage occurs in welds, and transient stress analysis corresponding to the welding procedure is performed to investigate the cause. To accurately reproduce the stress generated in the welds, it is necessary to accurately reproduce the transient heat input in the welding procedure. Thus, traditionally, inverse analysis on the transient heat input is conducted by focusing on the molten shape of the actual components; i.e., try and error work performing transient temperature distribution analysis assuming heat input until the molten shape is reproduced. Goldak's double-ellipsoidal heat source model was used by most of the researchers. In this case, heat source parameters from experience are assumed, and transient temperature distribution analysis is repeated by changing the parameters until the obtained region above the melting point matches the target molten shape. Recently, machine learning methods have been become effective to improve inverse analysis in structural integrity issues to straight-forward analysis. In this work, a model using the deep learning has been developed that can directly determine the parameters of the heat source model from the welding records and the molten shape, which can omit the inverse analysis of the heat source parameters, which has been a bottleneck in the past. This deep learning model can reduce the time required determining parameters used in FEA for failure analysis of welded components.

Transient heat transfer studies of aluminium graphene nanocomposite heat spreaders using digital interferometry

The thermal runaway caused by poor thermal management of batteries is one of the main challenges being faced by electric vehicles (EVs). An energy-saving, passive method for efficient thermal management of two and three wheeler battery packs is the use of aluminum (Al) heat spreaders with superior thermal conductivity, in conjunction with natural air cooling. Thermal conductivity of the (Al) heat spreaders can be enhanced by incorporation of graphene flakes. The present work focuses on extensive heat transfer studies of Al graphene nanocomposite (AGNC) heat spreaders with enhanced heat transfer capability. Few layered graphene (FLG) was synthesized by the liquid phase exfoliation method and characterized by X-Ray diffraction (XRD) analysis, Transmission electron microscopy (TEM), and Confocal Raman spectroscopy. AGNC heat spreaders were made by powder metallurgy. Mach-Zehnder interferometric (MZI) technique was employed to analyse the heat dissipation characteristics of AGNC heat spreaders, which infact is the novelty here. The slope of the local heat flux curve obtained by MZI was found to be less in the case of AGNC heat spreaders as compared to Al heat spreader indicating more uniform heat dissipation for AGNC heat spreaders. Transient heat transfer studies showed 63 % enhancement in the heat dissipation for AGNC heat spreader as compared to pure Al heat spreader. The transient temperature distribution was also visualized using Infrared (IR) thermography and the results show more uniform temperature distribution in the case of AGNC heat spreaders. The better phonon transport across the grain boundaries loaded with FLGs could be the reason for faster heat transport in AGNC heat spreaders.

Transient thermal analysis of the rotary compressor during startup process

The transient temperature distribution and heat transfer characteristics of the rotary compressor are crucial to its reliability and efficiency of the compressor. In this paper, a transient mathematical model on predicting the temperature in the compressor during startup is proposed. Control volumes are divided including the fluid and solid domains. The convective heat transfer coefficient of each surface is discussed. A coupled solution method and its Fortran calculation program are developed. This mathematical model is experimentally validated by comparing the measured and calculated temperatures of the compressor. The results shows that calculated temperatures are consistent with the measured results during the startup process. The maximum error of the steady-state temperature is within 2 °C. The refrigerant in the compression unit mainly absorbs heat from the refrigerant in the lower chamber. Measures should be taken to reduce the heating of the upper bearing surface by the refrigerant in the lower chamber to improve the volume and indicated efficiencies.

Study on thermal effect and electro-optically Q-switching of Cr, Tm, Ho: YAG laser

The thermal effect and Q-switching of flashlamp-pumped Cr, Tm, Ho: YAG (CTH: YAG) laser were investigated systematically. The fraction of pump power dissipated as heat in flashlamp-pumped CTH: YAG laser system was evaluated for the first time by measurements and calculations on thermal lens effect. The quasi-steady state and transient temperature distributions of laser rod were numerical simulated. In addition, Electro-optically Q-switching was studied by design of thermal effect compensation resonator. An unusual phenomenon that the optimal delay time of Q-switch in CTH: YAG was shorter than the pump duration was reported for the first time as far as we know. According to the experimental and theoretical calculation results, the main cause of the phenomenon is the long lifetime of lower laser level, followed by up-conversion and fluorescence quenching at high temperature. The mechanism proposed in this paper is of great significance for the design of highly efficient Q-switched CTH: YAG lasers.