Accurate Thermal Analysis Research Articles

New application of a calorimetric sensor: Measurement of the heat capacity of heat-conducting small parts

This study explores a novel application of a calorimetric sensor to measure the heat capacity of small heat-conducting parts under varying environmental conditions. The sensor, a hybrid of a heat conduction calorimeter and a differential scanning calorimeter (DSC), has been adapted from its original use on living skin to measure conductive materials. We present a detailed description of the sensor's instrumentation, its operating model, and the experimental procedure. The sensor's accuracy is evaluated through experimental measurements on aluminum and brass samples, showing a maximum deviation of 5 % and a mean deviation of 2.35 % from the theoretical values. Additionally, finite element method (FEM) simulations are employed to further investigate the sensor's performance, confirming that both measurement time and sample size significantly influence the results. This research demonstrates the potential of this calorimetric sensor for rapid and accurate thermal analysis of small heat conducting parts, with potential applications in various scientific and industrial fields.

An efficient 3D tube-level flux-thermal model of external tubular receivers in solar power tower systems

Accurate and efficient radiative flux simulation and thermal analysis of liquid tubular receivers are essential for safe and stable operations of solar power tower systems. However, the complicated structure and photothermal processes on these receivers pose significant challenges for simulation. Although existing models have made great simplifications, the simulation results are still inefficient and inaccurate. To address these issues, a novel and universal 3D flux-thermal model is proposed. Firstly, a flux model is proposed via a tube-level Monte Carlo ray tracing method based on GPU parallel computing, enabling real-time and accurate radiative flux density distribution simulation for each absorber tube. Secondly, a high-resolution multi-tube thermal model is proposed, providing accurate 3D thermal analysis for each absorber tube. Through pre-factorization and highly parallelized designs, the proposed thermal model achieves a 600 times acceleration in efficiency, even with tens of millions of discrete elements. Finally, the novel flux-thermal model is validated against publicly published measured data from Solar Two, indicating a mean deviation of only 0.1% and a root mean square error of 0.006, demonstrating its high accuracy. Furthermore, the proposed flux-thermal model reveals complex and asymmetrical flux and temperature distributions on the absorber tube, in contrast to the symmetrical distributions obtained by the simplified models. Such inaccuracies in the simplified simulations may cause operational misjudgements and affect system safety potentially. Therefore, the proposed 3D tube-level flux-thermal model provides an accurate and efficient solution to radiative flux simulation and thermal analysis, enhancing the safe and stable operation of solar power tower systems.

Building thermal energy efficiency modeling based on light image inspection and super resolution algorithm in interior landscape design

With the intensification of global climate change and energy crisis, the thermal efficiency of buildings has become increasingly important. Interior landscape design not only affects living comfort, but also plays a key role in building energy efficiency. Therefore, it is of great practical significance to explore the modeling method of building thermal energy efficiency based on optical image inspection and super resolution algorithm. The light image inspection technique is used to obtain the data of light and temperature distribution inside the building. The super-resolution algorithm of deep learning is used to process the acquired low-resolution image to improve the clarity and detail of the image. Combined with the physical characteristics of the building, the thermal efficiency model of the building is constructed and multi-dimensional analysis is carried out. The experimental results show that the combination of optical image inspection and super resolution algorithm can effectively improve the accuracy of building thermal efficiency modeling. Compared with traditional methods, the prediction error of the model is reduced, and the recommended optimization scheme performs better in terms of energy consumption in different interior landscape design schemes. Therefore, the building thermal efficiency modeling method based on optical image inspection and super resolution algorithm provides a new idea for interior landscape design. Through accurate thermal efficiency analysis, it can provide more scientific decision-making basis for architectural designers, so as to realize the sustainable development of buildings and maximize the energy efficiency.

Enhancing thermal modelling of electric machines: steady-state verification of a novel methodology

The increasing power density of electric machines for electric vehicles necessitates accurate thermal analysis in design through simulations with computation times not exceeding one minute. Existing thermal models are either accurate and complex while requiring large computation times or they are fast but lack accuracy. To address these challenges, a novel hybrid modelling methodology is proposed, combining 3D lumped parameter thermal networks with thermal resistances extracted from 2D finite element models (FEM) to reduce computation demands while preserving accuracy. Verification of the modelling methodology against 3D FEM in OpenFOAM shows key component temperature deviations of less than 0.67 °C comparable to the 3D FEM uncertainty of 0.39 °C. The computation time is 18.3 s compared to 44 h for 3D FEM. This highlights the time-efficiency of the proposed methodology while maintaining accuracy for key component temperatures.

Thermal analysis of permanent magnet synchronous linear motor accounting for three-phase current unbalance

Three-phase current unbalance is a common winding fault of the motor, which will bring local overheating, cause security risks and economic losses, accurate temperature rise calculation and thermal flux characteristics analysis of the motor working in three-phase current unbalance are necessary and challenging. However, little research has been conducted on the thermal characteristics and analysis methods for the permanent magnet synchronous linear motor (PMSLM) working in three-phase current unbalance. To address this problem, a multilayer composite flat wall model contained heat source of the primary is proposed firstly to analysis the heat transfer characteristics of the PMSLM caused by three-phase current unbalance qualitatively. Then, the heat transfer and temperature distribution characteristics of the PMSLM are obtained by calculating the fluid-thermal coupling model of the PMSLM directly. What's more, the effect of current grade on heat transfer is analyzed by comparing the heat transfer characteristics of the PMSLM working in four different three-phase current balance cases. Finally, the qualitative analysis and fluid-thermal analysis results are verified experimentally with a PMSLM adopting four different three-phase current unbalance conditions. Thermal analysis of the PMSLM working in three-phase current unbalance makes it is possible to prevent local heat accumulation and avoid unexpected interruptions for the redundant motor system and the fault tolerant motor system.

Accurate Time-Efficient Thermal Modeling and Discretization Methodology Applied to Electric Machines

The increasing power density of electric machines for electric vehicles necessitates accurate thermal analysis in design and real-time condition monitoring through simulations with computation times not exceeding one minute. Existing thermal models are either accurate and complex while requiring large computation times or they are fast but lack accuracy. To address these challenges, a novel hybrid modeling methodology is proposed, combining 3D lumped parameter thermal networks with thermal resistances extracted from 2D finite element models (FEM) to reduce computation demands while preserving accuracy. Further, a methodology is introduced to define the thermal network discretization for a desired threshold accuracy while minimizing computation time. Analysis of this discretization methodology demonstrates that the desired accuracy can be reliably achieved with limited computational effort. Verification of the modeling methodology against 3D FEM in OpenFOAM shows key component temperature deviations of less than 0.67 °C in steady-state simulations and 0.75 °C in transient simulations, comparable to the 3D FEM uncertainty of 0.39 °C. The computation times for steady-state and transient simulations are 18.3 s and 43.5 s respectively compared to 44 h and 175 h for 3D FEM. This highlights the time efficiency of the proposed methodology while maintaining accuracy for key component temperatures.

Accurate and nonuniform CFD-based thermal behavior analysis of distribution transformers: voltage imbalance effect

Accurate and nonuniform CFD-based thermal behavior analysis of distribution transformers: voltage imbalance effect

Thermal camera for System-in-Package (SiP) technology: Transient thermal analysis based on FPGA and Finite Element Method (FEM)

Accurate thermal analysis is essential for the design of reliable of system-in-package (SiP). This paper proposes a transient thermal analysis of the SiP technology based on four chips to study the effect of the underlying layers on the thermal model and to know the optimization scenario of the chips based on the thermal aspect that should be considered for the best possible accuracy. The finite element method (FEM) using the COMSOL Multiphysics® tool is proposed to achieve this goal. The temperature variation in the numerical simulation shows that the underlying layers are very important to decrease the maximum value of the SiP temperature. This work is performed with a field-programmable gate array (FPGA), which acts as a packaged system, and the detected heat source is validated with a thermal camera. A maximum error of 2.4% is reported between the thermal camera measurements and the numerical simulations.

Electromagnetic-Thermal Analysis of a Hybrid-Excited Flux Switching Permanent Magnet Generator for Wind Turbine Application

An accurate thermal analysis needs to be performed on the machines with new structures to ensure that their electromagnetic performance is not negatively affected. In this regard, this paper details an investigation into the electromagnetic-thermal analysis of an outer rotor hybrid-excited flux switching permanent magnet generator that gains from ferrite PMs in stator yoke and neodymium PMs in rotor segments. Incorporating ferrite PMs and barriers in the stator core enhances the power density of the proposed generator compared to the basic topology. Also, the temperature of the stator and windings of the HEFSG decreases due to the presence of barriers. As a result, the HEFSG can be a potential candidate for DDWT applications. In this study, the thermal modeling started with a 3-D FEM electromagnetic analysis to calculate the losses as heat sources. Afterward, an accurate thermal network was plotted to elucidate the thermal behaviors between various parts of the generator, where the heat sources, heat transfer coefficients, thermal resistances, and heat capacitances form the thermal characteristics of the network, which was then followed by the 3-D FEM thermal analysis. Finally, the experimental test results from the prototyped generator confirmed the accuracy of the simulation results.

Heat transfer theory research and multi-physical field simulation optimization of high-speed motorized spindle

The thermal error generated by the high-speed motorized spindle during machining is the main reason for the exactness of the machine tool, so accurate thermal characteristics analysis is essential. In this paper, the experimental platform of motorized spindle was set up to measure the temperature and thermal displacement data at 10000r/min. Secondly, the simulation parameters of A02 high-speed motorized spindle are obtained through theoretical calculation, and the multiphysics simulation model is established. After calculation, the exactness of the temperature field model can reach about 95%, and the exactness of the displacement field can reach 85%, it shows that the simulation model can accurately predict the state of motorized spindle. Finally, a new cooling jacket structure is proposed, and it is found that the optimized temperature is reduced by 32.11% and the thermal displacement of the front surface is reduced by 32.63%. indicating that the improved cooling water jacket has better cooling performance than the traditional cooling water jacket.

Integrated use of CFD and field data for accurate thermal analyses of oil/gas boilers

In the present study we develop a complete Computational Fluid Dynamics (CFD) modeling procedure suitable for accurate simulations of industrial boilers fed alternatively with gaseous and liquid fuels. The model is developed and validated by means of data from on-site testing.Two different boilers are considered: a 6-burner steam generator of a refinery for the model definition, and a 32-burner thermal power plant boiler for validation, fed by flare-gas/natural-gas or Heavy-Fuel-Oil (HFO). Selected reliable experimental data coming from performance testing are used for both the set-up of the CFD simulations as well as to compute the Flue Exit Gas Temperatures (FEGTs) employed as validation criteria. The flare-gas testing on the 6-burner boiler allows us to accurately determine that a membrane wall emissivity around 0.60 is appropriate as a boundary condition for radiation. By a sensitivity analysis, the relevance of wall emissivity with respect to fouling thermal resistance on the overall heat transfer inside the furnace is established. For boilers alternatively operating with gaseous fuel and HFO a value of 2.8 kW/(m2·K) has been found appropriate. HFO testing on the 6-burner boiler provides data to develop the additional soot modeling, crucial to properly catch oil flame emissivity, based on the model of Khan and Greeves. This allows the matching of a mean soot mass fraction of 1%–3% in the flame zone, a range found by in-flame measurements in the literature and confirmed in the present study by overall heat exchange data in the whole furnace coming from HFO boiler testing. Finally, the 32-burner boiler is considered for validation: using the same procedure and parameters, excellent agreement is found between experimental and CFD results, both on a 100% load natural gas and on a 107% load HFO performance testing.The study demonstrates how field data can be used to validate CFD simulations and confirms that the use of physically meaningful parameters and models exempts from repeated tuning: no change is needed for emissivity and fouling thermal resistance between gaseous and liquid fuel operation, and even a simple soot modeling can be used, just ensuring physically consistent particulate concentration in the oil flame.

The Modeling and Simplification of a Thermal Model of a Planar Transformer Based on Internal Power Loss

With the development of high-performance wide-band-gap devices and increasing converter frequency, planar transformers are widely used in high-frequency and high-power-density power conversions. Due to the skin effect and proximity effect, accurate thermal analysis and a simplified thermal model of planar transformers are needed for quick thermal verification as well as system design. This paper proposes two thermal simplification models based on the planar transformer’s thermal impedance network. The internal power loss and thermal coupling between each component are first analyzed. Then, based on thermal radiation theory, the simplified thermal model of the planar transformer is presented. It only requires the input of the total power loss of the planar transformer to calculate the temperature rise, and it does not need the power loss of each component. Finally, the simulation and experimental verification are carried out on a MHz prototype.

Thermal Model Approach to the YASA Machine for In-Wheel Traction Applications

The axial-flux permanent magnet (AFPM) machines with yokeless and segmented armature (YASA) topology are suitable for in-wheel traction systems due to the high power density and efficiency. To guarantee the reliable operation of the YASA machines, an accurate thermal analysis should be undertaken in detail during the electrical machine design phase. The technical contribution of this paper is to establish a detailed thermal analysis model of the YASA machine by the lumped parameter thermal network (LPTN) method. Compared with the computational fluid dynamics (CFD) method and the finite element (FE) method, the LPTN method can obtain an accurate temperature distribution with low time consumption. Firstly, the LPTN model of each component of the YASA machine is constructed with technical details. Secondly, the losses of the YASA machine are obtained by the electromagnetic FE analysis. Then, the temperature distribution of the machine can be calculated by the LPTN model and loss information. Finally, a prototype of the YASA machine is manufactured and its temperature distribution under different operating conditions is tested by TT-K-30 thermocouple temperature sensors. The experimental data matches the LPTN results well.

An accurate thermoelastic model and thermal output error analysis of a hemispherical resonator gyroscope under varying temperatures

This paper proposes an accurate thermoelastic model of a hemispherical shell resonator (TM-HSR) taking into consideration thermal stress and reveals the effect of its thermal deformation on the hemispherical resonator gyroscope (HRG) output error for the first time. First, a set of thermoelastic dynamic equations of the TM-HSR are derived by leveraging the thermoelastic shell theory, and the relationship between temperature and the equivalent thermal load is determined. Next, an approximate analytical solution of thermal deformation of HSRs is derived using Bubnov-Galerkin method and its accuracy is evaluated by comparing its result with ANSYS simulation results of HSRs with different structures. The approximate analytical solution is found to be very accurate, which is important for temperature testing of HRGs and application to various vibratory sensors with hemispherical shell structures. Subsequently, the effects of thermal deformations under uniform and nonuniform temperature distributions on the HRG output error are revealed by using a thermal output error model. Comparative simulation and experimental results demonstrate the effectiveness and practicability of the proposed model. The proposed model can be used for accurate error analysis and developing a compensation scheme for the thermal output error of HRGs.

Development of dynamic battery thermal model integrated with driving cycles for EV applications

Accurate thermal analysis of batteries for realistic operating conditions is a key requirement to develop an effective battery thermal management system of electric vehicles (EV), which ensures battery safety. In this context, a dynamic battery thermal model is developed to investigate the thermal characteristics of the battery module under dynamic EV operating conditions. The comprehensive modeling on EV dynamics is firstly conducted to determine the power demands with driving cycle applications. The efficiencies of components within the EV powertrain are closely considered, and the power consumed or regenerated in traction or brake mode is estimated. The battery thermal model considering both the joule and entropic heats is developed to predict the heat generation rates and temperature profiles following the dynamic battery loads. The developed models are validated within 3.98% for the EV dynamics model and 0.76% for the battery thermal model in relative error, respectively, allowing precise power and thermal simulation under the realistic operating conditions of the EV battery. A comparative analysis between the dynamic and steady modes for the same power loads to confirm the effects of the dynamic patterns is conducted for ten continuous cycles. As a result, the maximum differences between steady and dynamic modes are discovered about 3.57 times in heat generation, and 4.58 °C in temperature. These differences remain significant even with the thermal management, turning out more active cooling is required for normal operation under dynamic operating conditions.

A rapid heating and high magnetic field thermal analysis technique

A new thermal analysis technique is described that allows measurements to be performed on bulk samples at extreme heating and cooling rates and in high magnetic fields. High heating rates, up to 1000 °C min−1, are achieved through electromagnetic induction heating of a custom-built apparatus fitted with commercial thermal analysis heads and sensor. Rapid cooling rates, up to 100 °C min−1, are enabled by gas quenching and the small thermal mass of the induction furnace. The custom apparatus is designed to fit inside a superconducting magnet capable of fields up to 9 Tesla. This study demonstrates that the instrument is capable of collecting accurate thermal analysis data in high magnetic fields and rapidly acquiring data for dynamic processes. While the full potential of the technique is still unrealized, currently, it can provide insight into phenomena at time scales relevant to heat treatment in many industrial processes and into little understood effects of high magnetic field processing.

Thermal-Flow Network Modeling for Virtual Prototyping of Power Electronics

Fast and accurate thermal analysis is critical in designing power electronics converters through virtual prototyping to achieve high power density, efficiency, etc. Virtual prototyping can save cost and time in comparison to hardware prototyping and experimental test and can lead to an overall optimized design. For removing the heat in power converters effectively, forced convection, such as air cooling or liquid cooling, is usually adopted. To estimate the temperature distribution and assist the layout optimization without building physical prototypes, fast and accurate thermal prediction is required, which is an essential area in virtual prototyping of power electronics. In this article, a thermal-flow network (TFN) modeling method is proposed to solve the flow and temperature distribution in a power converter. The flow distribution is calculated by flow network consisting of flow resistances, flow branches, and sources. The temperature distribution is then estimated by the thermal network, where the related boundary conditions (heat transfer coefficient and local fluid temperature) are assigned using empirical equations. The fundamental and basic circuit elements for the TFN modeling method have been implemented in software, which helps to build the TFN modularly. The comparison between the proposed method, computational fluid dynamics (CFD), and experiment is provided to show the effectiveness of the TFN modeling method. The proposed modeling and analysis process can also be adapted for other forced cooling methods.

Absolute calibration of the latent heat of transition using differential thermal analysis.

We describe a simple and accurate differential thermal analysis setup to measure the latent heat of solid state materials undergoing abrupt phase transitions in the temperature range from 77K to above room temperature. We report a numerical technique for the absolute calibration of the latent heat of transition without the need for a reference sample. The technique is applied to three different samples-vanadium sesquioxide undergoing the Mott transition, bismuth barium ruthenate undergoing a magnetoelastic transition, and an intermetallic Heusler compound. In each case, the inferred latent heat value agrees with the literature value within its error margins. To further demonstrate the importance of absolute calibration, we show that the changes in the latent heat of the Mott transition in vanadium sesquioxide (V2O3) remain constant to within 2% even as the depth of supersaturation changes by about 10K in non-equilibrium dynamic hysteresis measurements. We also apply this technique for the measurement of the temperature-dependent specific heat.

A spectrally-resolved method for evaluating the solar effect on user thermal comfort in the near-window zone

The effects of solar radiation play an important role in human thermal comfort. When predicting the shortwave solar thermal effect through windows on indoor occupants, the spectra of solar irradiance, window transmittance, and skin absorptance must be considered. This work proposes a spectrally-resolved method for predicting this effect on occupants facing windows in the near-window zone. The vertical and horizontal penetration of direct solar irradiance is also characterized. In this work, we quantify the differences in resultant thermal comfort estimations between the spectrally-resolved and conventional constant-value methods through a series of simulated conditions on different days of the year and at different times of day, as well as with various window orientations and sky conditions. Through numerical analysis, we investigate the effects of and interactions among the various parameters and demonstrate situations in which the spectrally-resolved method is necessary. By understanding the necessity of the spectrally-resolved method and the influence of variations in spectral and energy intensities, we are able to make preliminary judgments regarding when the spectrally-resolved method is essential to making relatively accurate predictions of indoor thermal comfort in the near-window zone. This research provides a new and fundamental numerical method that can be used to take the spectral characteristics of solar energy, windows, and human skin into account for more accurate user thermal comfort analyses in the near-window zone.

Thermal analysis for fundamental power coupler of HALF 499.8 MHz superconducting cavity

The preliminary research work of Hefei Advanced Light Facility (HALF), a fourth generation diffraction limit storage ring, is in progress. Two 499.8 MHz superconducting cavities may be used in the HALF RF system. RF power will be feed into each cavity through a coaxial fundamental power coupler (FPC). Thermal design of the coupler is very important because of the large power losses on the coupler will cause overheating. Accurate and fast thermal analysis is a challenge in the thermal design. In this paper, two thermal analysis methods for evaluating the cooling effect of the coupler were compared. Computational Fluid Dynamics (CFD) code is used to perform thermal-fluid coupled analysis for the coupler in the first method, which is quite accurate but time-consuming. In the second method, average convective heat transfer coefficient calculated by correlation equations based on experimental results is used to evaluate the heat transfer between the fluid and the cooling pipe wall. The calculation time of the first method is about four times that of the second method. The simulation results of the two methods are consistent well at high flow rate, especially for turbulent flow. Therefore, the second method was used to perform thermal simulation under different cooling conditions and RF power levels. The influence of thermal radiation on the heat load to the cryogenic environment was also given in this paper. Simulation results show that thermal radiation has a slight impact on the heat load. When the copper emissivity equal to 0.02, the total static and dynamic heat load to 4.5 K are 0.833 W and 2.614 W at the power level of 200 kW, and the heat load to 4.5 K cryogenic environment caused by thermal radiation is 0.065 W.