Thermal Analysis System Research Articles

The thermal analysis of the heat dissipation system of the charging module integrated with ultra-thin heat pipes

• A hybrid heat dissipation system of charging module is performed. • An application of ultra-thin heat pipes (UTHPs) in charging module. • Effects of heat dissipation factors are compared quantitatively. • The HTUPs greatly improve the temperature uniformity. Electric vehicles (EV) played an important role fighting greenhouse gas emissions that contributed to global warming. The construction of the charging pile, which was called as the "gas station" of EV, developed rapidly. The charging speed of the charging piles was shorted rapidly, which was a challenge for the heat dissipation system of the charging pile. In order to reduce the operation temperature of the charging pile, this paper proposed a fin and ultra-thin heat pipes (UTHPs) hybrid heat dissipation system for the direct-current (DC) charging pile. The L-shaped ultra-thin flattened heat pipe with ultra-high thermal conductivity was adopted to reduce the spreading thermal resistance. ICEPAK software was used to simulate the temperature and flow profiles of the new design. And various factors that affected the heat dissipation performance of the system were explored. Simulation results showed that the system had excellent heat dissipation capacity and achieved good temperature uniformity. Rather than solely relied on the fans, this new design efficiently dissipated heat with a lower fan load and less energy consumption.

Flowability and Strength Characteristics of Binary Cementitious Systems Containing Silica Fume, Fly Ash, Metakaolin, and Glass Cullet Powder.

The present study examines the effects of supplementary cementitious materials (SCMs) on the flowability and strength development of binary mixes. This study was primarily motivated by the need to bridge the knowledge gap regarding paste and mortar mixes containing binary cement from a variety of performance perspectives. This study examined the flowability and strength development of binary mixes in their pastes and mortars when they contain various doses of silica fume (SF), fly ash (FA), metakaolin (MK), and glass cullet powder (GP) compared with the control mix. While the presence of SF and MK reduced workability because of the nature of their particles, the addition of FA and GP improved it to a certain extent because of the spherical and glassy nature of their particles, respectively. In addition, GP was used to compare its performance against SF, MK, and FA as an alternative cementitious material. In this study, the GP performed comparably to the other SCMs investigated and was found to be satisfactory. An investigation of the rheological properties, heat of hydration, thermal analysis, and pore systems of these mixes was conducted. Compared to the control mix, the presence of 5% GP improved the rheological properties and reduced the heat of hydration by 10%. The reduced workability in SF and MK mixes resulted in a lower content of pore water, while GP and FA incorporation enhanced it, owing to improved workability. The pore area is related to the pore water, which is directly related to improved workability. According to the following order, SF > MK > GP > FA, the strength was highest for mixes containing SF and MK, whereas, with GP and FA, there was a gradual reduction in the strength proportional to replacement level and improved workability. SF, GP, and FA can be identified as performance enhancers when formulating ternary and quaternary cementitious systems for low-carbon cement.

Performance analysis of CO2 thermal management system for electric vehicles in winter

CO2 is well-suited for thermal management systems (TMSs) in electric vehicles, particularly in winter when both the cabin air and the battery require heating. However, due to the distinct heat exchange boundary conditions of these two heated components, traditional theories of optimal operation of CO2 cycle are not applicable. In this paper, the system characteristics of a CO2 TMS in the cabin-and-battery mixed heating mode are comprehensively investigated. The results show that there is a pseudo-optimal discharge pressure that maximizes the COPTMS, regardless of whether the system is operating in a transcritical or subcritical mode. In addition, besides the global optimal COPTMS, there may still be other local maximum points, which are determined by the CO2 flow distribution in both gas coolers and the COP rise rate of the battery cycle. Furthermore, this work offers a thorough investigation of the impact of essential factors on the pseudo-optimal discharge pressure and proposes an accurate prediction approach for the best control of the CO2 TMS. The CO2 TMS can still ensure a COPTMS above 2.0 to meet the thermal demands of both the cabin and the battery even under the challenging operating circumstances of −20 °C, proving the technology's great competitiveness.

High-temperature interaction mechanisms of typical igniting pyrotechnics with cellulose as the packing material

In order to study the effect of cellulose shell on the thermal behavior including pyrolysis gaseous products, ignition and combustion characteristics of typical pyrotechnics, three composites of pyrotechnics/cellulose were prepared in this paper. Various characterization techniques were used to investigate the prepared composites and their combustion condensed products (CCPs), including scanning electron microscopy (SEM), simultaneous thermal analysis (DSC-TG-FTIR), X-ray diffraction (XRD), bomb calorimetry, and home-made combustion diagnostic system. The results showed that the overall heat release of the black powder and Mg/PTFE decreased from 3108 J·g−1 and 1157.4 J·g−1 to 1045.4 J·g−1 and 810.4 J·g−1 in the presence of 33.3% cellulose, respectively. Moreover, the FTIR spectra showed that the cellulose did not change the reaction pathways of black powder and Mg/PTFE, which mainly include H2O, CO2, NO2 for the black powder, and HF, H2O, CO2, CF2 for Mg/PTFE. However, the condensed products of cellulose would interact with B/KNO3 at a higher temperature, so that the heat release was largely increased by 339%. The cellulose has obviously impact on the energy release rate of Mg/PTFE in comparison to the other two composites. Moreover, the negative impact on ignition of Mg/PTFE composite is significant, when the content of cellulose reaches over 33.3%, resulting in difficult self-sustainable combustion at ambient pressure. The cellulose can largely reduce the maximum flame temperature of the black powder and Mg/PTFE, whereas it has little effect on B/KNO3. The CCPs of the involved igniting pyrotechnics and their cellulose-based composites have different phases due to their strong thermal interactions with cellulose.

Thermal Loss Analysis, Design, and Test of a Novel HTS Magnet System for the Double-Stator Field-Modulation HTS Electrical Machine

A novel double-stator field-modulation high temperature superconducting electrical machine (DSFM-HTSM) has been proposed, in which the armature windings and the HTS magnets are mounted on the outer and inner stator respectively, realizing stationary seal of the coolant and brushless transfer of the excitation current. The HTS magnet system is the core component of the DSFM-HTSM, consisting of the HTS magnets and the cryogenic refrigeration system, the design and safe operation of which are a key issue. Therefore, this paper focuses on the thermal loss analysis, design and test methods of the new HTS magnet system for the DSFM-HTSM. An atypical HTS magnet with small dimensions is proposed to suit the topology of the DSFM-HTSM. The different thermal loss sources are carefully analyzed and theoretically calculated, considering the characteristics of each source. The detailed design process of the HTS magnet system is presented. Moreover, an experimental platform is built and tested to verify the validity of the thermal loss analysis and design method. The corresponding research results can lay the foundation for the development and application of the large scale DSFM-HTSM, and can provide some reference for the analysis and design of similar HTS magnet systems.

A categorized and decomposed algorithm for thermal system simulation based on generalized benders decomposition

Accurate and efficient analysis of thermal systems is increasingly difficult with the increasing system scale and complexity. Many studies have to sacrifice the accuracy for calculation efficiency by simplifications. This work proposes a categorized and decomposed (C&D) algorithm to simulate thermal systems efficiently and robustly without introducing any simplification. It converts the system simulation into an equivalent optimization problem, which categorizes system constraints according to whether they are linear, and decomposes the optimization problem into a subproblem and a master problem to handle nonlinearity. Besides, variables’ gradient information is used to accelerate the convergence and enhance the stability. The proposed algorithm is applied to a supercritical carbon dioxide (sCO2) recompression Brayton cycle, and results show that it consumes about 8.84% calculation time compared with sequential modular method and requires much fewer initial values (about two orders of magnitude) compared with simultaneous equations method. Compared with the hierarchical and categorized algorithm, the proposed algorithm has a 48% larger convergence range regarding the deviation of initial values, and is more efficient when the initial value deviation is small. The proposed C&D algorithm owns a much higher efficiency and robustness and is a promising tool for complex thermal system simulation.

The applicability study and validation of TULIP code for full energy range spectrum

NECP-SARAX is a neutronics analysis code system for advanced reactor developed by Nuclear Engineering Computational Physics Laboratory of Xi'an Jiaotong University. In past few years, improvements have been implemented in TULIP code which is the cross-section generation module of NECP-SARAX, including the treatment of resonance interface, considering the self-shielding effect in non-resonance energy range, hyperfine group method and nuclear library with thermal scattering law. Previous studies show that NECP-SARAX has high performance in both fast and thermal spectrum system analysis. The accuracy of TULIP code in fast and thermal spectrum system analysis is demonstrated preliminarily. However, a systematic verification and validation is still necessary. In order to validate the applicability of TULIP code for full energy range, 147 fast spectrum critical experiment benchmarks and 170 thermal spectrum critical experiment benchmarks were selected from ICSBEP and used for analysis. The keff bias between TULIP code and reference value is less than 300 pcm for all fast spectrum benchmarks. And that bias keeps within 200 pcm for thermal spectrum benchmarks with neutron-moderating materials such as polyethylene, beryllium oxide, etc. The numerical results indicate that TULIP code has good performance for the analysis of fast and thermal spectrum system.

Thermal Analysis and Phase Equilibria of the Molten System Na3AlF6-NdF3-Nd2O3

Phase diagrams of the systems Na3AlF6-NdF3 and (Na3AlF6-NdF3)eut-Nd2O3 were experimentally determined by thermal analysis up to 60 mol.% NdF3 and 45 mol.% Nd2O3, respectively. The Na3AlF6-NdF3 system was found to be a simple eutectic system with the eutectic point with the following approximate coordinates: 49 mol.% NdF3 and 905°C. This eutectic composition was then used for the thermal analysis of the (Na3AlF6-NdF3)eut-Nd2O3 system. The coordinates of the eutectic point of the (Na3AlF6-NdF3)eut-Nd2O3 system were found to be approximately 46 mol.% Nd2O3 and 733°C. After the thermal analysis, the x-ray diffraction analysis of the solidified samples of both systems was performed. The XRD analysis of the Na3AlF6-NdF3 system has shown the formation of two new compounds; NaNdF4 and NdOF. The formation of NdOF is probably the product of the high-temperature hydrolysis between the moisture in the atmosphere and NdF3. The XRD analysis of the solidified samples of the (Na3AlF6-NdF3)eut-Nd2O3 system has shown the formation of the following new compounds: NaNdF4, NdOF, NdAlO3, and NaF.

Thermal economy analysis and multi-objective optimization of a small CO2 transcritical pumped thermal electricity storage system

With expansion of application scale of distributed renewable energy, importance of researching small electricity storage system is increasing. Thermal economic performance of a small CO2 transcritical pumped thermal electricity storage system (SCT-PTES) is studied in this paper. NSGA-II optimization method and TOPSIS decision method are used to optimize system performance. This paper also proposes a small CO2 transcritical pumped thermal electricity storage coupled building heating system (STC-PTES-H) scheme. The system performance is also studied. Results show that: (a) When round-trip efficiency and LCOS of SCT-PTES are 26.93% and 0.3862 $/(kW·h), respectively, thermal economic performance is optimal. (b) When amount of electricity produced by renewable energy sources is 10 MW, LCOS of SCT-PTES is 0.2002$/(kW·h). (c) Correlation between thermodynamic performance and economic performance of system is fitted, and optimization time is reduced. It provides a theoretical basis for optimization of thermal economic performance of system. (d) Energy utilization of SCT-PTES-H can reach 97.66%. It makes better use of energy. This research provides technical support for application of SCT-PTES in distributed renewable energy power plants.

Optical and thermal analysis of solar parabolic dish cavity receiver system for hydrogen production using deep learning

The solar thermochemical cycle, responsible for converting solar energy to chemical fuel, is an emerging clean hydrogen production technique. The distribution of the concentrated heat flux and temperature on the receiver is crucial in deciding solar-to-fuel conversion efficiency. Thus, the optimum configuration of a solar parabolic dish collector (PDC) is necessary for providing efficient thermal energy. The dish diameter, rim angle, and distance of the receiver aperture from the focal point of the dish characterize the optimization of the PDC. The non-uniform heat flux captured is coupled with a heat transfer model of a solar thermochemical reactor for a thermal dissociation of ZnO involved in a ZnO/Zn thermochemical cycle for hydrogen production. The directly irradiated rotating reactor comprises a cylindrical cavity packed with insulation layers and a quartz glass window. The rotating cavity is loaded with ZnO granular particles held by a centrifugal force. A 3D CFD numerical model is analyzed by coupling the Eulerian multiphase model for ZnO particle dynamics, fluid flow of gaseous mixture, RNG k-ԑ turbulence model, Energy and Discrete Ordinates (DO) radiation model, and Arrhenius reaction rate chemical reaction of ZnO dissociation. A numerical model with non-uniform heat flux input is validated for a cavity temperature, mass fraction of zinc and oxygen, and oxygen molar flow rate at the reactor outlet. An artificial neural network model is adopted to predict the heat flux and uniformity factor values of PDC. Correlation Coefficient (R2), Root Mean Square Error (RMSE), and Mean Absolute Percentage Error (MAPE) error metrices were used to evaluate the model's performance having the receiver diameter (d), the dish diameter (D), the rim angle (φ), and the distance between the focus and receiver (h) as input variables.

Computational design and analysis of LiFePO4 battery thermal management system (BTMS) using thermoelectric cooling/thermoelectric generator (TEC–TEG) in electric vehicles (EVs)

The best option for addressing the issue of rising carbon dioxide levels, which is the primary cause of global warming, currently involves using electric vehicles (EVs). The successful production of EVs can be attributed to batteries. However, one major issue lies in the rise in temperatures for the battery system of EVs. Therefore, a good battery thermal management system (BTMS) is necessary. Several traditional and non-traditional types of these systems are available. BTMSs for EVs have utilized thermoelectric cooling (TEC) and thermoelectric generator (TEG). The current research introduces a hybrid BTMS that combines thermoelectric materials with forced air. While the use of thermoelectric materials in BTMS is not a new concept, this approach offers a novel solution. In the current study, the thermoelectric cooler (TEC) and thermoelectric generator (TEG) are combined into a single unit. While TECs have long been used in BTMS, the new addition of TEGs allows for the conversion of lost heat from the TEC's hot surface into a reverse voltage that powers both the TEC and TEG. Additionally, the TEG helps to reduce the overall temperature of the battery container by converting heat into a potential difference, as previously mentioned. Simulation of the single battery cell and the full BTMS is realized using the ANSYS 2021R1 software. A single battery cell and BTMS utilize 6,197,879 and 12,697,173 numbers of mesh, respectively. The introduced BTMS was utilized in the current study to decrease the maximum surface temperature of a single battery cell by approximately 7 °C.

A modified IHB method for nonlinear dynamic and thermal coupling analysis of rotor-bearing systems

This paper presents a modified incremental harmonic balance (IHB) method to analyze the nonlinear dynamic and thermal coupling characteristics of rotor-bearing systems after thermal balance. The IHB method is modified by tensor contraction and fast Fourier transform (FFT) to efficiently calculate the residual vector and Jacobian matrix. Nonlinear dynamic and thermal full coupling is implemented through the nonlinear part of the Jacobian matrix. The presented method achieves the simultaneous and efficient calculation of the motion and heat balance equations in the frequency domain according to the improvement measures. The effectiveness of the presented method is tested using the vibration response and temperature variation analysis for the coupled thermo-mechanical model of a rotor-ball bearing system. Furthermore, the performance comparisons show the good consistency of results between the presented method and the step-by-step (S-S) method, which is a partitioned iterative solution method for dealing with fully coupled problems in the time domain. The presented method has greater computational efficiency, more accurate temperature prediction, and better recognition of nonlinear phenomena in the system rather than the S-S method. Consequently, the presented method has a broad application prospect in solving fully coupled thermo-mechanical problems of more complex and higher dimensional rotor-bearing systems.

A novel transfer matrix-based method for steady-state modeling and analysis of thermal systems

Performance analysis and optimization of thermal systems are unprecedentedly crucial in pursuing higher energy efficiency. However, the precise modeling and high-efficiency calculation of modern, complex thermal systems are still challenging. Here we present a transfer matrix-based system modeling method to tackle these challenges. The transfer matrix of heat exchangers is defined to describe the temperature mapping relation between inlet and outlet nodes. Heat-work conversion devices are described by the working fluid temperature variation. The system modeling follows a three-step procedure: (1) building system transfer matrix by aggregating component models; (2) separate given and unknown node temperatures by removing redundant rows and columns in the system transfer matrix; (3) rearrange the reduced system transfer matrix to calculate internal and outlet node temperatures. The constructed system model does not introduce unnecessary simplifications and describes the system’s nonlinearity accurately. The proposed modeling method is first presented and validated on a parallel-series and a multi-loop heat exchanger network. Numerical results with both constant and varying fluid properties confirm the method’s validity. Case studies on three thermodynamic systems further validate the method’s capability and efficiency. The proposed method is finally compared with conventional modeling methods and heat current method to highlight its features and advantages.

A comparison between two kinetic models for the pyrolysis and gasification of woody wastes under a carbon dioxide atmosphere

A pine forest residue, a pine wood industrial waste and their mixture were pyrolyzed and subsequently gasified under a carbon dioxide atmosphere up to 1000 °C in a thermal analysis system. Thermal decomposition parameters, such as reactivity, reaction rate and syngas yield, were determined and the influence of CaO catalyst was examined. Two kinetic models, independent parallel reactions model (IPR) and distributed activation energy model (DAEM), were developed in Matlab® code for the kinetic analysis of the processes. Three first order reactions were found to accurately describe the pyrolysis process by both models, with deviation values between 1.3 % and 2.9 %. Activation energy values varied between 26 kJ/mol and 201 kJ/mol. One pseudo-component was necessary to describe successfully the gasification process by application of both models, with deviation values 2.4–6.5 %. Activation energy values ranged between 192 kJ/mol and 345 kJ.mol. The IPR model was found to be more practical to employ.

Optimal structure design and heat transfer characteristic analysis of X-type air-cooled battery thermal management system

This paper develops an X-type double inlet and outlet symmetrical air-cooled battery thermal management system (BTMS) that overcomes the high temperature, large temperature difference, and high power dissipation problems. The proposed method extends previous symmetrical BTMSs, i.e., single inlet and outlet BTMS, single inlet and double outlet BTMS, and double inlet and single outlet BTMS. However, compared with the existing symmetrical BTMS, the suggested X-type BTMS improves performance and reduces the maximum temperature, maximum temperature difference, and maximum power dissipation by 4.33 K, 74 %, and 62.9 %, respectively. Additionally, the inlet and outlet parameters of the X-type BTMS are optimized with orthogonal analysis, and the optimum settings defined as 71 mm near the outlet, 135 mm near the inlet, 90° for the outlet angle, and 150° for the inlet angle, among which the outlet position and inlet angle significantly affect the performance of the BTMS. The original X-type BTMS is optimized to reduce the maximum temperature and maximum temperature difference by 4 K and 76.5 %, respectively. Furthermore, the heat transfer correlation expression for the X-type BTMS is obtained through theoretical analysis within an 8 % deviation, providing a reference for the design of BTMS.

Numerical analysis of cylindrical lithium-ion battery thermal management system based on bionic flow channel structure

To improve the thermal and flow performance of the battery thermal management system (BTMS), a heat exchanger with a bionic flow channel structure was designed and applied to a cylindrical lithium-ion battery module in this work. To accurately reflect the transient thermal behavior of the battery, a battery thermal model was obtained by experimentally collecting thermodynamic parameters. A computational fluid dynamics model of the BTMS was established. The influences of different bionic flow channel structure parameters on the thermal performance of the BTMS were investigated by a multi-factor optimization analysis. In addition, the thermal performance was also compared with that of a heat exchanger with a bionic honeycomb-like structure and a traditional helical structure. The results show that at the optimum structural parameters, the maximum temperature, maximum temperature difference, and pressure drop of the BTMS were calculated as 302.656 K, 3.726 K and 29.69 Pa respectively. For the same volume fraction and geometrical parameters, the heat exchangers with a spider web-like structure has better thermal and flow characteristics than honeycomb-like and traditional helical structures.

Parameter optimization and sensitivity analysis of a Lithium-ion battery thermal management system integrated with composite phase change material

In order to ensure the performance and to extend the life cycle of power battery module within electric vehicle, a battery thermal management system (BTMS) integrated with composite phase change materials (PCM) was proposed. The heat dissipation performance of BTMS using paraffin/expanded graphite (EG) composite PCM with different mass fraction was investigated. The results showed the optimal heat dissipation performance was observed using composite PCM with 20 wt% EG. The combined effect of liquid volume fraction and thermophysical parameters of composite PCM on heat dissipation performance of battery module was revealed. The phase transition temperature of composite PCM was found to have the largest impact on the maximum temperature and temperature uniformity of battery module, followed by latent heat and thermal conductivity of composite PCM. A 10 % decrease in the phase transition temperature led to a 7.9 % in the maximum temperature of battery module. Both the thermal conductivity and latent heat growth contributed to the reduction in the maximum temperature of battery module. Composite PCM with the thermal conductivity of 3 W m−1 K−1, phase change temperature of 38 °C, and latent heat of 220 J g−1, was found to achieve the optimal heat dissipation performance of BTMS and a high utilization rate of 97.3 % for composite PCM. The findings of this work could be beneficial for future development of highly-efficient and economical composite PCM for BTMS.

Energy saving control and operation strategy analysis of thermal coupling system of fuel cell and metal hydride tank

The thermal coupling system (TCS), where the heat generated by proton exchange membrane fuel cell (PEMFC) is transferred to the metal hydride (MH) tank, has been investigated extensively and proved beneficial to system compactness as well as capital cost. However, there is a lack of attention to the regulation of hydrogen desorption to increase the efficiency of hydrogen-to-power/heat (ηh−p), especially when the TCS is used in a distributed energy system (DES) combining power and heat. In this study, an energy saving control strategy for a TCS applied in DES is proposed to increase the ηh−p on the premise of the satisfaction of cosine-form hydrogen demand. The threshold temperature is introduced to characterize the maximum of ηh−p, and a prediction framework of threshold temperature for arbitrary signal is proposed based on its functional relationship with five operation parameters and Fourier decomposition method (FDM). The operation strategy of two-tank TCS is also discussed. The results indicate that up to 7.26 × 103 kJ more heat could be utilized by energy saving control strategy compared with the reference case. The relative error of predicted threshold temperature within 0.14% is obtained for a square wave and aperiodic signal, verifying the generalization capability of the proposed framework. Besides, the operation strategy that the rated hydrogen demand is supplied by both MH tanks, is suggested in a two-tank TCS to increase the hydrogen utilization and extend the supply duration.

Characteristic analysis and optimisation of seasonal solar thermal storage heating system

This study considers the seasonal solar thermal storage and heating system in the Jilin region of China, and a system model is established by using the TRNSYS software under heat storage and heating modes. The operating characteristics of the system are analysed during the complete heat storage and heating seasons, and the economic cost of the system is minimised by optimising the ratio of the collector area to the water tank volume. The results show that the most heat is stored in the system during May, and the maximum heat loss from the tank occurs during October. The maximum solar fraction is 47.85%, the maximum heat loss rate of the water tank is 29.82% and the energy efficiency ratio of the system is 1.70. The optimised ratio of the heat storage tank volume to solar collector area is 4.5, energy efficiency ratio of the system is 1.67 and the annual cost about ¥440 000 (£52 860).

Developing criteria for advanced exergoeconomic performance analysis of thermal energy systems: Application to a marine steam power plant

Developing criteria for advanced exergoeconomic performance analysis of thermal energy systems: Application to a marine steam power plant