Dynamic Thermal Characteristics Research Articles

Preparation and Characterisation of Natural Rubber Composites Comprising Hybrid Fillers of Activated Carbon / in situ Synthesised Magnetite

The aim of this study was to examine the influence of hybrid fillers based on activated carbon/nanoscale magnetite synthesised in situ on the curing, mechanical and dynamic characteristics, electrical and thermal conductivities, dielectric characteristics and homogeneity of natural rubber based composites. The fillers have been characterised by X-ray diffraction and X-ray photoelectron spectroscopy establishing the influence of the magnetite layer on the texture characteristics. It has been found that magnetite amount changes the texture characteristics of activated carbon. The increasing amount of deposited magnetite hinders the vulcanisation process and loosens the vulcanisation network. The elongation at break and residual elongation increase, while Shore A hardness and the modulus 100 decrease. The storage modulus decreases, while the mechanical loss angle tangent increases together with the dielectric constant and the dielectric loss angle tangent also get higher. The thermal conductivity coefficient and homogeneity increase at higher magnetite amounts.

Investigation of transient thermal dissipation in thinned LSI for advanced packaging

Thinning of LSI is necessary for superior form factor and performance in dense cutting-edge packaging technologies. At the same time, degradation of thermal characteristics caused by the steep thermal gradient on LSIs with thinned base silicon is a concern. To manage a thermal environment in advanced packages, thermal characteristics of the thinned LSIs must be clarified. In this study, static and dynamic thermal dissipations were analyzed before and after thinning silicon to determine variations of thermal characteristics in thinned LSI. Measurement results revealed that silicon thinning affects dynamic thermal characteristics as well as static one. The transient variations of thermal characteristics of thinned LSI are precisely verified by analysis using an equivalent model based on the thermal network method. The results of analysis suggest that transient thermal characteristics can be easily estimated by employing the equivalent model.

Study on dynamic characteristics of the temperature and stress field in induction and laser heating for the semi-infinite body

ABSTRACTThis study analyzed the dynamic characteristics of temperature and stress fields during induction and laser heating of a semi-infinite body. The semi-infinite body was subjected to a distribution heat flux (induction heating) at a particular depth range and then to a surface heat flux (laser heating). Using the Green function method and the Laplace transform, the temperature and stress fields solutions were acquired for both heating methods. The analytical results of the temperature and stress fields are shown graphically in the time domain for a selected position. It was found that under the same input power conditions, the temperature field acquired is identical in both induction and laser heating in the range of more than one skin depth. The peak dynamic thermal stress from both heating methods increases rapidly along the depth, and converges to a fixed value. Meanwhile, the peak thermal shock stress is relatively small, and quickly decays at a certain position in a very short duration. Therefore, the thermal shock dynamic characteristics are negligible in the two highly variant transient heating methods—induction and laser.

Thermal inertia assessment of an experimental extensive green roof in summer conditions

Passive solutions for building envelopes such as green roofs are regarded as promising tools to reduce the energy demand for buildings air-conditioning and to improve the thermal comfort of indoor spaces. It is therefore necessary to quantify and assess properly the summer thermal performance and to determine how a green roof cover can attenuate and delay the temperature and heat flux acting on its surface. The paper deals with an experimental investigation of the dynamic thermal characteristics of a vegetated roof situated on a university building roof in south Italy. An analysis of the daily values of dynamic parameters showed a quite stable trend of the decrement factor with variation in the range 0.0982–0.1920. The time lag exhibited a trend ranging from 7.2 h to 8.5 h. A successive analysis was developed decomposing the trends of temperature into Fourier series to assess the response of the vegetated systems to solicitations of different frequencies and to assess the deviations, in the calculation of the dynamic parameters, arising from considering a sinusoidal variation with a 24 h period of the external forcing, in accordance with the International Standard EN ISO 13786, compared to the experimental values. The green roofs showed a behaviour similar to a high-pass frequency system, and relative errors, by using only the fundamental harmonic under 10% were found for 72.9% of the cases for the decrement factor and for 93.8% of the data for the time lag. Results demonstrated that when climatic conditions of the location are more irregular then the predictions of the dynamic parameters considering only the fundament harmonic instead of the real trend of the forcing can provide more relevant errors.

Influence of TiO2 nanoparticle on the thermal, morphological and molecular characteristics of PHB matrix

PHB/TiO2 nanocomposites were prepared and characterized in terms of thermal, morphological and molecular dynamic characteristics. The TGA analysis revealed that all the PHB systems containing TiO2 presented an increment in thermal stability. From XRD analysis, it was seen that between 30 and 90 °C the systems did not present significant differences regarding their crystalline profiles. On the other hand, presence of TiO2 nanoparticles promoted notable changes, revealing that they can act as nucleating agent for PHB. The systems were also investigated by T1H measurement, combining different experimental NMR techniques. The main NMR results showed that FFC-NMR provided more detailed information about molecular motion in different time and length scales. It was seen that TiO2 addition changed the dynamic molecular behavior of the PHB matrix for chain segments containing more than fifty carbon atoms.

Optimal and Learning-Based Demand Response Mechanism for Electric Water Heater System

This paper investigates how to develop a learning-based demand response approach for electric water heater in a smart home that can minimize the energy cost of the water heater while meeting the comfort requirements of energy consumers. First, a learning-based, data-driven model of an electric water heater is developed by using a nonlinear autoregressive network with external input (NARX) using neural network. The model is updated daily so that it can more accurately capture the actual thermal dynamic characteristics of the water heater especially in real-life conditions. Then, an optimization problem, based on the NARX water heater model, is formulated to optimize energy management of the water heater in a day-ahead, dynamic electricity price framework. A genetic algorithm is proposed in order to solve the optimization problem more efficiently. MATLAB (R2016a) is used to evaluate the proposed learning-based demand response approach through a computational experiment strategy. The proposed approach is compared with conventional method for operation of an electric water heater. Cost saving and benefits of the proposed water heater energy management strategy are explored.

Experimental Research on Catalytic Combustion Characteristics of Inferior Coal and Sludge Mixture

Catalytic effects of metal oxides on combustion characteristics of inferior coal, sludge, and their mixture were investigated by thermogravimetric analysis. Combustion and thermal dynamic characteristics including ignition temperatures, apparent activation energy, and frequency factors of inferior coal, sludge, and their mixture were observed. The catalytic effects and mechanism of combustion were discussed. Results showed that thermal gravity analysis (TG) and derivative thermogravimetric analysis (DTG) curves of coal and sludge shifted to lower temperature side, the weight losses increased, and the ignition performance was improved with the addition of metal oxides CaO, Al2O3, and K2O. The combustion dynamics analysis showed that the apparent activation energy of cocombustion of coal blending sludge decreased by 11–20% and the frequency factors increased by 20–30%. The minimum apparent activation energy and the maximum frequency factors were obtained in the presence of K2O, indicating that the catalytic effect of K2O was most significant.

A dynamic thermal-mechanical model of the spindle-bearing system

Abstract. This paper presents a dynamic thermal-mechanical model to investigate the thermal characteristics in a spindle-bearing system. In this model, transient thermal analysis, static structure analysis and calculation of the boundary conditions are conducted as a solution loop. The transient boundary conditions, such as bearing stiffness, bearing heat generation and thermal contact conductance, are calculated with the appropriate formulas and solution methodology. The thermal feedbacks, which are seldom considered in the previous studies, are calculated in details. In order to validate the prediction accuracy, thermal equilibrium experiment is conducted on a test rig of spindle-bearing system. The predictions of the proposed model, such as bearing preload, temperature and thermal displacements, are in close agreement with the experiment results. The comparisons of the proposed model with two traditional simulations show that, the thermal feedbacks on the boundary conditions and thermal contact conductance are of great importance to the real-time estimation of the thermal characteristics. The proposed model provides a practical method to improve the prediction accuracy. It could also be generalized in other mechanical systems to investigate the dynamic thermal characteristics.

Thermal dynamic simulation of wall for building energy efficiency under varied climate environment

Aiming at different kind of walls in five cities of different zoning for thermal design, using thermal instantaneous response factors method, the author develops software to calculation air conditioning cooling load temperature, thermal response factors, and periodic response factors. On the basis of the data, the author gives the net work analysis about the influence of dynamic thermal of wall on air-conditioning load and thermal environment in building of different zoning for thermal design regional, and put forward the strategy how to design thermal insulation and heat preservation wall base on dynamic thermal characteristic of wall under different zoning for thermal design regional. And then provide the theory basis and the technical references for the further study on the heat preservation with the insulation are in the service of energy saving wall design.All-year thermal dynamic load simulating and energy consumption analysis for new energy-saving building is very important in building environment. This software will provide the referable scientific foundation for all-year new thermal dynamic load simulation, energy consumption analysis, building environment systems control, carrying through farther research on thermal particularity and general particularity evaluation for new energy -saving walls building. Based on which, we will not only expediently design system of building energy, but also analyze building energy consumption and carry through scientific energy management. The study will provide the referable scientific foundation for carrying through farther research on thermal particularity and general particularity evaluation for new energy saving walls building.

A numerical study of building integrated with CaCl2·6H2O/expanded graphite composite phase change material

Integrating phase change material (PCM) into traditional building envelopes can decrease the building energy consumption and improve the indoor thermal comfort by enhancing the heat storage capability. In this work, CaCl2·6H2O/expanded graphite (EG) was employed to fabricate the PCM panels for building envelope as a low-cost PCM. In order to give full play to the role of CaCl2·6H2O/EG, its characteristic in structural insulated panel (SIP) was investigated numerically under different conditions. The enthalpy-porosity technique was used for modeling the solidification/melting process and it was validated by experiment. Temperature time lag, temperature decrement factor and energy saving rate were used to evaluate the dynamic thermal characteristics of the building envelope. The results showed that the density and thermal conductivity of PCM had little effect on the thermal performance of building envelope. However, the change of PCM panel thickness, building orientation, climate region and building construction would affect the phase change process of the PCM panels, which would have a certain influence on the room temperature. By analyzing the effect of CaCl2·6H2O/EG on the thermal performance of the building envelope under different influencing factors, it will provide effective guidance for the selection and use of PCM.

Model Predictive Control Approach for Building Microgrid Considering Dynamic Thermal Characteristics of Building

Abstract A simple dynamic model to simulate heating/cooling energy consumption in a building was proposed in this paper. The model consists of several transient energy balance equations for external walls and internal air, in which the convective heat transfer, conductive heat transfer and heat storage in the heat transfer process are considered. The proposed model has been implemented utilizing the SIMULINK/MATLAB platform. Then, a model predictive control (MPC) approach for the building Microgrid considering the dynamic thermal characteristics of the building was proposed. The MPC approach aims to minimize the total energy consumption of the building Microgrid by combining the model predictive and the short-term control, and guarantees the customer temperature comfort level at the same time. Two comparative cases are presented to verify the effectiveness of the proposed MPC approach.

Ultra-lightweight concrete: Energy and comfort performance evaluation in relation to buildings with low and high thermal mass

Ultra-lightweight concrete (ULWC) was recently introduced as a novel building material that combines moderate thermal insulation properties with load-bearing capacity. Its intended use as monolithic building envelope brings new opportunities in building physics, by merging characteristics of both heavyweight and lightweight construction types. This paper investigates the potential of ULWC building envelopes in terms of energy efficiency and thermal comfort. The dynamic thermal characteristics of a monolithic structure of ULWC were first compared to more conventional constructions using EN-ISO-13786 calculation methods. The main contribution of this article lies in the subsequent development and application of a simulation strategy for predicting the energy and comfort performance of ULWC on the whole-building level. The quality of the simulations in EnergyPlus was first ensured in an analytical validation study, and then applied to assess the performance of ULWC for commercial and residential case studies in the Netherlands. Results show that ULWC constructions are comparable to heavyweight buildings in long-term behaviour, whereas they resemble the performance of lightweight building envelopes for short-term heating periods. ULWC can therefore be a suitable construction type in buildings with intermittent operation, but in other cases it can get outperformed by conventional constructions with low or high thermal mass.

Dynamic Structural and Thermal Characteristics Analysis of Oil-Lubricated Multi-speed Transmission Gearbox: Variation of Load, Rotational Speed and Convection Heat Transfer

The main objective of this research work is to investigate the effects of load, rotational speed and lubrication on gear surface of multi-speed gearbox. Transient structural analysis was performed to evaluate the strength of multi-speed transmission gearbox assembly. Gear oil SAE 85W140 lubricant was used for cooling of gearbox and performance enhancement of medium-duty trucks. To investigate the thermal characteristics of multi-speed transmission gearbox, steady-state thermal analysis was performed with combined varying condition of load and rotational speed of shafts (pinion and gear) with gear oil lubricant. At different operational conditions, the temperature of gearbox surface was measured. An average heat transfer coefficient (h) of the gear surface and tooth flank (100–500 W/m2 K) was varied for steady-state analysis. Solid model of multi-speed transmission gearbox was designed using Solid Edge and Pro-E. Finite element analysis (FEA)-based numerical simulations of multi-speed transmission gearbox were established to find the temperature variations on gear surface. FEA simulation results were validated with the experimental results available in the literature.

Dynamic thermal characteristics analysis of microencapsulated phase change suspensions flowing through rectangular mini-channels for thermal energy storage

A numerical model of laminar forced convection heat transfer for microencapsulated phase change material (MPCM) suspensions with constant heat flux is developed. Phase change process and heat conduction in the microcapsules are solved using the equivalent heat capacity method and finite volume method (FVM). Heat convection of the flowing fluid is solved using FVM with internal heat source induced by the heat transfer resistance between the microcapsules and the working fluid. The influences of various factors are analyzed in detail. The results showed that Stefan number and mass fraction are the most basic factors influencing the heat transfer performance of the MPCM suspension. The maximum modified local Nusselts number enhancement reaches more than 190% for the 20wt% MPCM suspension with Ste=1.5, where the tube wall temperature rises 50% slower than that of water. Sensitivity analyses of several parameters like Reynolds number, particle diameter and particle shell thickness are discussed. Effects of these parameters on heat transfer rate are not as sensitive as that of Stefan number and mass fraction. Evaluation of different aspect ratios of tube cross section with same flow rate is made, and a graphical expression with the tube aspect ratio of 3 is presented to illustrate the working mechanism of this type of heat transfer suspension.

Research of thermal dynamic characteristics for variable load single screw refrigeration compressor with different capacity control mechanism

In the single screw refrigeration compressor (SSRC), the capacity control mechanism is normally employed to meet the actual required cooling capacity under different load conditions. In this paper, theoretical calculation models describing the working process of the SSRC with the single slide valve capacity control mechanism (SVCCM) and SSRC with the frequency conversion regulatingmechanism (FCRM) are established to research the thermal dynamic characteristics for variable load SSRC under part-load conditions. Experimental investigation on a SSRC under part-load conditions is also carried out to verify the theoretical calculation models. By using these validated models, the thermodynamic performances and dynamic characteristics of the SSRC with different capacity control mechanism under part-load conditions have been analyzed and compared. Through the comparison, the economical efficiency andreliability of the SSRC with different capacity control mechanism were obtained. All of these works can provide the basis for the later optimization design for the variable load single screw refrigeration compressor.

Dynamic thermal response characteristics and feasibility analysis of thermoelectric module in impedance measurement

Though the impedance measurement has provided probability for fast characterization of TE devices, the test accuracy and frequency range for various TE modules are rarely investigated. In this paper, a transient three-dimensional numerical TE model has been developed using finite element method. The sinusoidal current with different amplitudes and frequencies was loaded on the TE model to explore its thermal and electrical lumped response. Then the impedance spectrum of the TE model is identified and plotted, which in turn verifies the validity of the simulation procedure. In order to keep the impedance measurement within the frequency range of the equipment, the pole efficiency for TE modules with different material properties and sizes was investigated. The results show that reducing the length of TE module would be an effective way to accomplish the fast measurement. Besides, with consideration of the substrate in TE model, the measurement accuracy and duration are also discussed. It is demonstrated that the substrate would cause certain measurement uncertainty and increase the measurement time. Through the study of the dynamic response characteristics and test feasibility, this work can help to guide the impedance measurement for different TE modules.

ÇOK KATMANLI DUVAR VE ÇATI TİPLERİNİN ISIL VE FİZİKSEL ÖZELLİKLERİNİN DİNAMİK ISIL KARAKTERLERİNE OLAN ETKİSİNİN İNCELENMESİ

Abstract : The growing concern about energy consumption of heating and cooling of buildings has led to a demand for improved thermal performances of building materials. To achieve this goal, in this study, an investigation is performed to analyze the influence of thermophysical properties and thickness of various multilayer building walls or roofs in a building on the dynamic thermal characteristics, such as the decrement factor (DF), time lag (TL) and heat gain. In order to find the thermal performance characteristics of building structures, such as briquette, brick, blockbims and autoclaved aerated concrete (AAC), which are commonly used in Turkey, an analytical solution method was developed in a computer program in MATLAB and results are compared to determine suitable wall or roof material. Calculation method for the heat flow is based on solution of transient heat transfer problem for the multilayer structures. The program is executed to calculate hourly heat gain values for these samples over a period of 24 h during design day for Gaziantep, Turkey. It was found that thermophysical properties of roofs or walls have a very profound effect on the time lag (TL), decrement factor (DF) and also heat gain. Keywords : Building walls, roofs, thermophysical characteristics, heat gain, time lag, decrement factor.

Dynamic thermal characteristics of heat pipe via segmented thermal resistance model for electric vehicle battery cooling

Heat pipe cooling for battery thermal management systems (BTMSs) in electric vehicles (EVs) is growing due to its advantages of high cooling efficiency, compact structure and flexible geometry. Considering the transient conduction, phase change and uncertain thermal conditions in a heat pipe, it is challenging to obtain the dynamic thermal characteristics accurately in such complex heat and mass transfer process. In this paper, a “segmented” thermal resistance model of a heat pipe is proposed based on thermal circuit method. The equivalent conductivities of different segments, viz. the evaporator and condenser of pipe, are used to determine their own thermal parameters and conditions integrated into the thermal model of battery for a complete three-dimensional (3D) computational fluid dynamics (CFD) simulation. The proposed “segmented” model shows more precise than the “non-segmented” model by the comparison of simulated and experimental temperature distribution and variation of an ultra-thin micro heat pipe (UMHP) battery pack, and has less calculation error to obtain dynamic thermal behavior for exact thermal design, management and control of heat pipe BTMSs. Using the “segmented” model, the cooling effect of the UMHP pack with different natural/forced convection and arrangements is predicted, and the results correspond well to the tests.

Study on the morphological, dynamic mechanical and thermal properties of PLA carbon nanofibre composites

Abstract This work explores the dynamic mechanical, morphological and thermal characteristics of melt blended and injection moulded PLA carbon nanofibre (CNF) composites. Composites of neat PLA with 1, 3, 5, 10, and 15 wt% as received VGCNF were evaluated by DMA, MDSC and SEM. SEM images reveal significant fibre pullout. Damping properties were evaluated by isothermal frequency sweeps at different displacement amplitudes performed on the composites in the DMA. At any displacement amplitude, the damping of the composites rises with increase in CNF content – with the highest damping seen in PLA with 10 wt% CNF. Higher displacement amplitudes significantly increase the damping of neat PLA. The tensile modulus shows a rise of almost 50% at 15 wt% CNF content. MDSC reveals that the glass transition is not significantly affected the presence of CNF. Crystallization is seen to be favoured with the presence of CNF and is prominently seen during the cooling cycle.

Stationary and Transient Heat Conduction in Multilayer Non-Homogeneous Stratigraphy

The tendency to speed up the building process and reduce its capital costs is bringing to the increased use of semi-finished products in constructions. One frequent characteristic of those elements is the use of non-homogeneous layers of materials, possibly affecting their thermal properties. In addition to this, the gradual increase in the thickness of insulation layers in buildings is also shifting the focus from the heating loads to the cooling loads, especially for hot climates such as southern Europe, raising the necessity to evaluate the transient properties of construction elements, alongside with the most common stationary properties. The aim of this paper is to correctly evaluate both stationary and transient heat conduction properties of strongly non-homogeneous multi-layered constructions and evaluate the impact of the non-homogeneities. The evaluation of those properties are based on the definitions detailed in the EN ISO 13786 directive, for dynamic thermal characteristics, and in the EN ISO 6946 directive, for stationary thermal characteristics. The stationary thermal transmittance is the parameter considered for the stationary analyses; for transient analyses transient thermal transmittance, time shift and attenuation factor are evaluated. The methodology provided inside the respective directives is applied in order to estimate the parameters. Following, a finite elements model is implemented in the COMSOL Multiphysics software and the same properties are calculated through a finite element analysis performed based on the conditions detailed in the physical definitions of those properties in the respective directives. Each parameter assessed based on the respective directives, EN ISO 13786 and EN ISO 6946, is then compared with the results of the finite elements analyses. Based on those comparisons the impact of the non-homogeneities in the construction for the calculation of its thermal properties are evaluated and conclusions on their relevance in the identification of the thermal properties are given, also the ability of describing non- homogeneous constructions through the directive's methodology is discussed.