Detailed Thermal Model Research Articles

Thermal modelling and reliability analysis of recently introduced high gain converters for PV application

High step-up DC-DC converter (HSDDC) topologies are getting more attention in hybridisation of energy sources especially for renewable energy integration. In the last decade, several high gain converters have been proposed; however, application-orientated development, and its thermal modelling and comparative analysis associated with it, has been unnoticed. Thus, intensive investigation in terms of thermal performance attributes is crucial for the selection of application orientated HSDDC topologies. A detailed analytical thermal model of the recently reported HSDDC is presented in this article. In addition, detailed comparison of performance are carried out based on different parameters. The thermal models of HSDDC are built in PLECS simulation environment to ensure the appropriate selection device to handle the normal and abnormal situations in the topology. Finally, peak thermal stress on semiconductors is measured and presented to validate the efficacy of each converters.

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.

Non-Isolated DC-DC Converters in Fuel Cell Applications: Thermal Analysis and Reliability Comparison

An alternative energy source that has appeared beyond expectations and has seen a lot of progress is the fuel cell. A proton exchange membrane (PEM) fuel cell is chosen for analysis and requires a DC-DC boost converter as an interface between the fuel cell and the load to provide a high-gain regulated voltage. Although great effort towards developing different converter topologies has been made during recent decades, less attention has been devoted to the reliability and thermal performance assessment of the present converters. In this paper, five non-isolated DC-DC converters are analyzed in terms of both thermal behavior and reliability. The temperature estimation of semiconductor devices as a critical part of the thermal analysis has been made via a detailed thermal model and the reliability is evaluated by means of a power cycling test. Finally, a performance score has been attributed using the TOPSIS ranking methodology and considering all the criteria (e.g., the number of components and cost) at the same time. The results indicated that the floating interleaved boost converter is always at the top of the list, even if the weight of the indicators is changed. When the weight of the cost criterion is higher than the reliability criterion, the multi-switch boost converter will be in second place. If the weight of the reliability criterion is greater than cost, the interleaved and multi-switch converter are ranked second and third, respectively. Additionally, the Cuk converter with a closeness coefficient of zero is always associated with the most unfavorable performance.

Coordinated Voltage Control Strategy by Optimizing the Limited Regulation Capacity of Air Conditioners

The high penetration of distributed renewable energy and the popularization of electric vehicles has led to voltage quality problems in distribution networks. Voltage problems, such as over-voltage, under-voltage, and voltage fluctuations, are increasingly becoming severe. Voltage regulation services play an essential role in improving the power supply quality of the distribution network. The development of information and communication technologies has promoted the upgrading of remote control technology. Air conditioners (ACs) can be easily remote controlled to change the power consumption for voltage regulation services. This study proposes a voltage control strategy by optimizing the limited regulation capacity of ACs. Firstly, a detailed thermal model is developed to analyze the room temperature and the regulation capacity of the ACs. Secondly, a successive voltage regulation algorithm is proposed to solve the voltage problems of the limited regulation capacity of ACs. In addition, the control strategy is developed to exploit the potential of voltage regulation. The control strategy formulates the participation priority of the ACs according to room temperature, which makes the ACs have a long regulation time and prevent the ACs switching working states in the process of voltage regulation. The case studies show that the proposed coordinated voltage regulation strategy can make node voltage restore to a permissible range and make full use of the limited regulation capacity of ACs for voltage control.

A Novel Approach to Predict Transformer Temperature Rise under Harmonic Load Current Conditions

In South Africa, distribution transformers (DTs) facilitating solar photovoltaic applications represent the highest percentage of total ownership cost investment for independent power producers (IPPs). One of the most indispensable variables that regulate DTs’ operational life span is the hotspot temperature. The prevailing analytical approaches designated to guesstimate the transformer thermal necessities were fathered in accordance with the conservative foundation that an electrical transformer is prone to uniform mean daily and monthly peak loads. In order to appropriately puzzle out the transformer thermal necessities, the formation of a more detailed thermal model that operates with real-time contorted cyclic loading, ambient air temperature, and the intrinsic characteristics of the transformer in-service losses is required. In the current work, various regression models are proposed for the modification of the top-oil formula and the hotspot temperature formula in the IEEE loading guide standard to replicate the real harmonic load currents (HLCs) and the fluctuating ambient air temperature (AT) on an hourly and daily basis. The proposed thermal model is examined in various transformers case studies, in which the computed outcomes produce an error margin of no more than 3% throughout all test cases when compared to the measured data.

Boundary Condition Independent Thermal Network Modeling of High-Frequency Power Transformers

With increasing global power demands and the trend of miniaturization of power converters, electronic components are being pushed toward their thermal limits. This has accentuated the need for accurate and low-cost thermal models of electronic components. Lumped Parameter Thermal Network Modeling (LPTNM) is commonly used to evaluate the thermal performance of electronic components, but unlike semiconductors, transformer LPTNM is not standardized in the academic community. Due to this lack of standardization, most proposed transformer thermal models have not been evaluated for Boundary Condition Independence (BCI). This study presents a BCI thermal modeling approach for power transformers based on LPTNM. A thermal network model is developed by discretizing the transformer geometry into smaller volumes and evaluating the thermal resistances by approximating the three-dimensional heat transfer problem as a piecewise one-dimensional model. The network model/geometry discretization is iteratively improved for a set of different boundary conditions, resulting in a BCI model. The modeling approach is experimentally and numerically validated on a PQ40/30 transformer operating in a 3.3 kW switch mode power supply. The BCI transformer thermal model closely matches both numerical and experimental results with a fraction of the computational cost of the numerical model. The proposed BCI modeling approach provides a low-cost alternative to detailed thermal models and can predict transformer thermal performance for varied applications.

Liquid-cooled structure design and heat dissipation characteristics analysis of cross-flow channels for lithium batteries

A detailed three-dimensional thermal model is developed to examine the thermal behaviour of a lithium-ion battery. This model is a cross-flow liquid cooling model, which can make the heat dissipation of lithium-ion battery pack achieve higher safety. Two kinds of fluids are used for cooling, and the polynomial fitting function is used as the heat source term of lithium battery pack. The battery temperature distribution under the conditions of different Reynolds numbers, different numbers of micro-channel and different micro-channel radii are studied for this model. The simulation results show that the maximum battery temperature is 295.84 K, the minimum battery temperature is 293.14 K, and the maximum temperature difference of the battery pack is 2.7 K. The maximum temperature and temperature difference of the battery under the model are in line with the reasonable operating temperature range of lithium-ion battery pack. The maximum temperature of battery pack decreases with the increase of Reynolds number, but the effect of Reynolds number on heat dissipation of lithium-ion battery pack has a critical value. As the number of micro-channels increases, the maximum temperature of the battery string decreases. However, when the number of micro-channels increases to a certain value, the maximum temperature of the battery pack decreases slowly. The maximum temperature of the battery pack does not decrease monotonically as the radius of the micro-channel increases. Orthogonal analysis results show that the Reynolds number has the greatest influence on the cooling effect of the model, followed by the size of the micro-channel radius, and the number of micro-channels has the least influence. The optimized liquid cooling model can effectively reduce the maximum temperature of lithium-ion battery in theory, and the maximum temperature of lithium-ion battery decreases by 26.24 K in comparison with that of single battery at 2C discharge rate. The reliability of the cross-flow channel model is proved by numerical analysis, and it is also proved that the cross-flow channel has an equilibrium point between the perturbation gain and the flow retarding effect. The heat dissipation effect of lithium- ion battery pack is correlated with the number and radius of micro-channels, but not a single positive correlation. Reasonably increasing the number and size of micro-channels can effectively enhance the heat dissipation effect of battery pack.

Heat and mass transfer performance and exergy performance evaluation of seawater cooling tower considering different inlet parameters

Cooling towers are important components within re-circulating cooling water systems. Due to a shortage of freshwater resources, seawater cooling towers are widely used both in manufacturing and everyday life. This paper researches the mechanical draft counterflow wet seawater cooling tower, and establishes and verifies a detailed thermal performance calculation model. Referring to the Second law of thermodynamics, the heat and mass transfer performance and exergy performance of the seawater cooling tower were studied. The effects of salinity, inlet air speed, and air wet-bulb temperature on the cooling efficiency, thermal efficiency, and exergy efficiency were analyzed. The results show that compared to the air wet-bulb temperature, changes in air speed have more influence on cooling and thermal efficiency under the study conditions. Moreover, the air wet-bulb temperature is the significant parameter affecting exergy efficiency. With an increase in salinity, the cooling, thermal, and exergy efficiency are about 2.40-8.25%, 1.06-3.09%, and 2.47-7.73% lower than that of freshwater, respectively, within an air speed of 3.1-3.6 m/s. With an increase in salinity, the cooling, thermal, and exergy efficiency are about 2.28-8.47%, 1.03-3.37%, and 2.44-7.99% lower than that of freshwater, respectively, within an air wet-bulb temperature of 25-27?. Through the exergy analysis of the seawater cooling tower, it is obvious that the heat and mass transfer performance and exergy performance can be improved by selecting the optimum operating conditions and appropriate packing specifications.

Bi-level energy management and pricing for community energy retailer incorporating smart buildings based on chance-constrained programming

To explore the interaction between community energy retailers and smart building (SB) consumers in the energy market, this paper proposes a bi-level energy management and pricing method for the community energy retailer incorporating SBs based on chance-constrained programming. Aiming at maximizing the profits of both retailers and consumers, a Stackelberg game model is established. At the upper level, the community energy retailer maximizes its profit by optimizing offering prices while ensuring the secure operation of the community distribution system. At the lower level, based on the detailed thermal dynamic model of buildings, consumers flexibly adjust the air conditioning’s energy consumption according to the offering price provided by the retailer to minimize the operational cost of SBs. Then, the chance-constrained programming is exploited to consider uncertainties of market prices, and the proposed bi-level optimization model is transformed into a mixed-integer linear programming problem using Karush-Kuhn-Tucker conditions, strong duality theorem, linearization, and deterministic transformations of chance constraints for solving. Numerical results show that the proposed approach can combine the flexibility of both supply and demand to benefit both retailers and customers. In addition, the economic impact of different confidence levels on the retailer and consumers is analyzed.

Small Satellite Operational Phase Thermal Analysis and Design: A Comparative Study

This paper is about the modeling and design of the passive thermal control system for the European Student Earth Orbiter (ESEO) satellite. A detailed thermal model was created in Thermal Desktop software. The model was running for the operative phase which includes cycles of 28 orbits. During these 28 orbits, there are several modes (10 modes). Each mode has a specific duration, attitude (Sun-nadir), and certain internal heat dissipation. The design of the passive thermal control system was based on controlling the conductive and radiative heat exchange between the internal components and the mounting panels, between panels themselves, and controlling external radiation exchange to achieve the desired components temperature ranges. The temperature results from simulations were presented to show the expected component temperatures and to demonstrate that the passive thermal control system met the requirements of the temperature limits. The final passive thermal control design shows that the satellite components temperatures were always maintained within their required limits during the operational phase

Comfort and efficiency-based improvements to the control of residential Venetian blinds

This study focuses on the control of movable Venetian blinds. Multiple improvements to an existing on/off open-loop control strategy in a case-study apartment have been simulated in TRNSYS 18, thanks to the detailed optical and thermal modelling allowed by the Bidirectional Scattering Distribution Function (BSDF) used as input to the Type56_CFS. The control strategy improvements include the combination of rule-based, closed-loop and discrete state control, in addition to four control strategy activation methods (three use a schedule, and one measures the external temperature). Simulated control inputs include internal temperature, external temperature and vertical irradiance. The results show reductions in overheating, achieved without completely blocking natural illumination or compromising heating demand. While on/off control in winter often leads to increased heating energy consumption, the space sees regular overheating when on/off control is inactive over winter. Conversely, discrete state control is able to more precisely control solar gains in winter to maintain an adequate temperature without utilising the heating system, all the while allowing some level of natural illumination. Ultimately, it is concluded that the choice of the control strategy depends on which objective (minimisation of heating energy consumption, maximisation of daylight harvesting, reduction of overheating risk, etc.) is prioritised.

A Model for Temperature-Dependent Degradation in Lithium-Ion Batteries: Correlating Electrochemical Phenomena with Cell-Level Performance Parameters

Significant progress has been made in developing lithium-ion battery models that incorporate transport phenomena, electrochemical kinetics, and thermodynamics. While these models have been used to produce reliable results for initial performance, they lack the ability to predict capacity degradation during cycling. The prediction of key performance parameters like battery lifetime and capacity is vital for the design and thermal management of the batteries. There is often a complex interplay of simultaneous degradation mechanisms with the electrochemical dynamics of the cell. These phenomena in turn influence trends in cell-level parameters of interest, namely cell capacity and voltage response. Degradation modeling is an active research area where several works have attempted to augment state-of-the-art electrochemical models with those of various degradation mechanisms.1 In this work, we aim to develop a detailed and efficient physics-based model which couples temperature gradients within the battery with the standard models for electrochemical SEI formation.2 The model inputs for temperature can be obtained experimentally or using a detailed thermal model for the battery. There have been past attempts to combine one or multiple degradation mechanisms.3 While these works provide valuable insight, a more comprehensive picture requires consideration of electrolyte dynamics and temperature variations within the battery. The poor predictions for battery degradation are related to spatial non-uniformities and difficulties in uniform thermal management, whether due to cost or performance constraints. There is also a significant variation in parameters, mechanisms, and predictive capability of the models in the literature. The present model will consider simultaneous battery degradation due to the SEI layer growth with temperature effects and will be integrated into state-of-the-art electrochemical models like the classic pseudo-two-dimensional (p2D) model4 to be able to present a comprehensive analysis of the battery performance parameters. In order to check for the computational challenges, the integration of fade and thermal models will be performed in two different solver environments to ensure accuracy and mitigate any convergence issues.The ultimate goal is a simple and efficient numerical framework for fast and robust simulations such that the developed model would be able to generate cell-level signatures of degradation over a wide range of operating conditions and temperatures. This tailor-made model can also be combined with available experimental data for an improved qualitative understanding, as well as quantitative prediction of the different stages of battery degradation. References Edge, J. S., O'Kane, S., Prosser, R., Kirkaldy, N. D., Patel, A. N., Hales, A., Ghosh, A., Ai, W., Chen, J., Jiang, J. and Li, S., Chem. Chem. Phys. (2021) DOI: 10.1039/D1CP00359C.Safari, M., Morcrette, M., Teyssot, A., and Delacourt, C., Electrochem. Soc., 156, A145 (2009).Reniers, J. M., Mulder, G. and Howey, D. A., Electrochem. Soc, 166(14), A3189 (2019).Fuller, T. F., Doyle, M., and Newman, J., J. Electrochem. Soc., 141, 1 (1994).

Improving Cracking Severity in an Ethane Thermal Cracker Based on Dynamic Optimization Considering Process Limitations

The main goal of this research is to improve cracking severity in an industrial ethane thermal cracker in a domestic plant. In the first step, the considered cracker is modeled based on the mass and energy balance equations considering a molecular kinetic model. To develop an accurate model, a detailed thermal model is adopted to predict the tube skin temperature. To prove the accuracy of the developed model and considered assumptions, the simulation results are compared with the available plant data. In the next step, a sensitivity analysis is performed to investigate the effects of coil outlet temperature and steam to ethane ratio on the cracking severity factors including ethane conversion and production rate. Based on the results of sensitivity analysis although increasing steam to ethane ratio decreases ethane conversion, it improves ethylene yield. Then, a dynamic optimization problem is formulated to maximize ethylene production and minimize production decay during the process run time considering feed temperature, furnace temperature, and steam to ethane ratio as decision variables. The results show that applying the optimal condition to the system improves ethylene production by about 9.44%.

A Preliminary Thermal Model of the LHe-Based SCAPE Cryostat

The SCAPE (SuperConducting Arbitrarily Polarizing Emitter) undulator is under development at the Advanced Photon Source (APS). This new undulator requires a cryostat that will be designed based on expected heat loads. For instance, the expected heating of the beam chamber by electron beam is estimated to be at a level of 182 W - much higher than in planar SCUs. This and other challenges require careful thermal analysis of the LHe-based SCAPE cryostat. A detailed thermal model of the LHe-based SCAPE cryostat has been created in ANSYS. This paper presents calculated cooling capacity and temperatures of the SCAPE cryostat for the static and dynamic heat loads.

A Preliminary Thermal Model of the Conduction-Cooled SCAPE Cryostat

The SCAPE (Superconducting Arbitrarily Polarizing Emitter) undulator is under development at the Advanced Photon Source (APS) as a part of the APS upgrade at Argonne National Laboratory. This new undulator requires a cryostat to handle the heat load on the beam chamber at a level of 182 W - much higher than in APS planar superconducting undulators. These challenges require careful thermal analysis of the SCAPE cryostat. Despite relatively large heat loads, a cryostat that does not contain any cryogen is a desirable option. Based on the experience on demo scale tests on SCAPE, a cryocooler-based cryogen-free cryostat is proposed. A detailed thermal model of such a cryostat has been created in Thermal Desktop. This paper presents the calculated heat load and temperatures profile of this cryostat under the static and dynamic heat loads

A multiphysics model of large-scale compact PV–CSP hybrid plants

Do compact Photovoltaic–Concentrated Solar Power hybrid systems offer the opportunity for the expansion of the global solar market? Despite the inherent potential of this technology to provide both affordable and dispatchable solar electricity, it is still unclear how the combination of Photovoltaic and Concentrated Solar Power may offer a net advantage over conventional solar plants. Herein, large-scale compact Photovoltaic–Concentrated Solar Power hybrid plants are modeled considering two different hybrid approaches, over a whole year operation, and compared with a conventional Concentrated Solar Power plant. A detailed optical, electrical and thermal model is developed to analyse the temporal output characteristics of the hybrid plants, based on realistic input parameters and representative meteorological data in Targassonne, France. Results show that both hybrid systems may deliver significantly higher energy output over the conventional Concentrated Solar Power plant, provided that several key parameters are optimized. Furthermore, the sensitivity of the two-hybrid strategies investigated to the operating conditions, and to the characteristics of the solar cells used, are analyzed. In the light of these results, the main scientific and technological issues one should address to ensure optimal operation of these compact hybrid plants are finally discussed.

3-D Global Thermal Analysis of DSEM Considering the Temperature Difference Between Excitation and Armature Coils

The complexity of winding distribution of doubly salient electro-magnetic machine (DSEM) results in its uneven temperature distribution, and its temperature rise characteristics under different working conditions need to be further studied. Different from the thermal analysis method of uniformly distributed electrical machine, this article proposes a time-saving thermal analysis method for the new topology of DSEM. In view of the sensitive change of DSEM excitation loss with temperature, the magnetic-thermal bidirectional coupling method is adopted. Considering the temperature difference between excitation and armature coils, a detailed thermal model is established for the armature-excitation slot. The number of bidirectional coupling iterations of finite-element method is reduced by steady-state temperature prediction. Then the temperature distribution of DSEM is analyzed in detail, and the variation of the temperature distribution under different operating conditions is studied. The temperature rise characteristics of a three-phase 12/8-pole prototype are tested to verify the correctness of the proposed method. The research results can provide reference for the temperature evaluation of DSEM and its electromagnetic and cooling design.

Thermal Characterization of SiC Modules for Variable Frequency Drives

Silicon carbide (SiC) devices can exhibit simultaneously high electro-thermal conductivity and extremely fast switching. To perform optimal designs showing the benefits of SiC in achieving efficiency, size, weight, and cost objectives for electric converters design, it is necessary to establish better models for calculating device losses and an efficient thermal model that can be calibrated to consider the nuances of measurement based thermal equivalent circuits. This work's outputs can be used in a power converter multi-objective optimization process or real-time temperature prediction of drives to improve reliability and maximize performance. The proposed modified loss calculation and thermal model demonstrate the SiC power module's advantages to reduce peak junction temperature and power cycling effects. A detailed power loss calculation and thermal model is developed and tested on a 480 V, 186 A, 150 HP variable frequency drive (VFD) with SiC modules. A comparison between the SiC module and an equivalent rated Si module demonstrates the reduction in power cycling effects, particularly at low-speed operation. Infrared (IR) imaging results and analytical explanations of the phenomenon is provided. Power cycle tests show that higher thermal conductivity is not the only reason contributing to the lower temperature ripple in low-speed operation.

A solar regenerated liquid desiccant evaporative cooling system for office building application in hot and humid climate

In this paper, we provide the thermal analysis and design methodology of a liquid desiccant assisted dew point indirect evaporative cooling system. The purpose of the system is to serve as an alternative for conventional vapour-compression based building air conditioning systems in providing satisfactory human thermal comfort conditions in the hot and humid climatic regions. The main features of the study are the following: i) novel incorporation of a forced parallel flow direct solar regenerator and a dew point indirect evaporative cooler within the same air conditioning unit; ii) detailed thermal modelling of each of the system components with fewer simplifying assumptions compared to earlier works; iii) large cooling capacity (~18.8 TR) under harsh climate; and, iv) a comprehensive year-round case study for system operation in a hot and humid location (Kolkata, India). Our thermal model is validated with a reference model study. The maximum room air temperature predicted by the current system for year-long analysis is 26.7 °C. The thermal COP of the system for diurnal operation in the most humid month of a calendar year (July) varied between 0.40 and 0.96. The cooling system can prevent overheating of the conditioned space, as specified by ASHRAE Standard 55–2017, throughout the year.

Numerical modeling and performance assessment of elongated compound parabolic concentrator based LCPVT system

In this work, a non-imaging low concentrating 2.5X Compound Parabolic Concentrator (CPC) truncated to 1.7X has been explored. CPCs inherently form non-uniform distribution of flux on the PVT module which has been mitigated by the integration of optimized homogenizer referred to as Elongated CPC (ECPC). The study involves detailed optical, thermal, and electrical modeling of the ECPC based Low Concentrating Photovoltaic Thermal (LCPVT) system. Optical simulations provide insight into the flux distribution on the PVT panel surface, which is further coupled with a thermal and electrical model for precise prediction of the performance of the system. These models are validated experimentally with a 315 Wp solar panel integrated with ECPC based LCPVT system. Performance evaluation of the system has shown peak thermal efficiency of ∼40% at ΔT of 16 °C, peak electrical efficiency of 12%, and an overall peak exergy efficiency of 15% at 38 Liters per hour (LPH) flow rate. A comparison of outlet water temperature results obtained from the numerical model and experiments has shown an excellent match with a relative error of 4%. Results also show that the increase in mass flow rate from 22 LPH to 38 LPH improves the electrical efficiency by 3% however a drop in ΔT of 2–3 °C is observed.