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The convective heat transfer characteristics of end-winding for a 10 kW external rotor PMSM with open end cap are studied in this paper. A coupling iterative method of CFD and thermal network (TN) is proposed to solve the motor temperatures and convective heat transfer coefficients (CHTC). The variation laws of the CHTCs and heat dissipation proportions of 10 kW motor walls with speed are analyzed. The heat dissipation capacities of the end-winding for motors with open and closed end cap are compared. Based on the CFD results, a fitting formula of end-winding CHTC for external rotor motor with open end cap is constructed, in which the Nusselt number is calculated by the dimensionless parameters composed of the geometric features of the open end cap. The validities of the proposed coupling iterative method and the fitting formula are verified by the temperature rise experiment of the 10 kW prototype. [ABSTRACT FROM AUTHOR]

The positioning precision of the ball screw system in machine tools is primarily affected by the thermal deformation of the screw. Hence, the adaptive prediction method must be established to calculate thermal errors of the ball screw system. First, based on heat transfer theory, a new adaptive moving thermal network model of the screw system with moving thermal excitation and varying operating conditions is proposed. The time-serial data of kinematic-pair representative temperatures and the time-serial position data of the moving nut are used as inputs. This adaptive model is used to determine the temperatures of the key elements in the supporting bearings and those of the moving nut and key points of the screw shaft. Further, the heat generation rate of each kinematic pair can be obtained simultaneously. Furthermore, a real-time prediction method of thermal errors of the screw system with moving thermal excitation under various operating conditions is presented. The effectiveness and robustness of the real-time prediction method of thermal errors was verified experimentally. This method is suitable for the rapid prediction of thermal errors of screw systems by monitoring the real-time kinematic-pair representative temperatures and real-time position of the moving nut. • A new adaptive moving thermal network model for a screw system is proposed. • Based on the moving network model, the real-time thermal error model is proposed. • The heat generation rates of the heat sources are simultaneously identified in real-time. • The presented model can be used for the multiple varying working conditions. • This model has self-adaptive ability and robustness. [ABSTRACT FROM AUTHOR]

This paper presents theoretical analysis and experimental validation on the behavior of a proposed thermoelectric power generation system using a solar parabolic dish collector. A low-cost solar thermoelectric generator (TEG) has been designed and fabricated for people in rural areas in India where electric power is still short in supply. Thermodynamics and a heat transfer approach are employed in the theoretical model developed to predict the performance of the solar TEG. A model of the TEG is useful to find the temperature of each junction at different operating parameters. The performance of the designed solar TEG was experimentally tested and verified by an analytical method. Maximum power outputs of 16.43 W and 15.35 W were obtained from theoretical analysis and experimental results, respectively. The average error and standard deviation between theoretical and experimental results are 11.12% and 0.869, respectively. The uncertainty of the TEG electrical power is 2.07%. The proposed TEG model can be used to predict the performance of a TEG at any location. [ABSTRACT FROM AUTHOR]

Rolling element bearing is an essential component in mechanical transmission because it reduces friction between two rotating parts. Two main approaches to evaluate power losses are proposed in literature: (i) global engineering models using few input data; (ii) local models which are more accurate but need much more information on rolling element bearing geometry. Based on thermal network approach, an intermediate model is developed in this study. This new model allows obtaining lumped information (temperature of rings) with a minimum of input data (external geometry only) and by using global power loss models. This intermediate model is developed for angular contact ball bearing under oil jet lubrication for high speed application. Thermal network results are compared with experimental findings. [ABSTRACT FROM AUTHOR]

An important trend of Building Integrated Solar Thermal (BIST) system is to improve the aesthetic aspect of the solar collector to meet the requirement of architectural style and energy collection. Painting on the glass cover in an appropriate method is a simple and practical way. In this study, a halftone coating was used to print a red brick wall pattern on the glass cover. A series of comparative experiments were carried out to test the effect of the coating on the thermal behavior of the solar collector. In heat collection processes, compared with the solar collector with blank cover plate, the one with coated cover plate has lower absorber plate temperature and higher cover plate temperature. The lower the solar irradiance, the smaller the effect of color coating on the solar collector. Compared with the uncoated surface, the coated surface is more sensitive to solar irradiation. In the same heat collection process, compared with the solar collector coated on the outer surface of the cover plate, the one coated on the inner surface has 0.8 °C higher heat absorber plate temperature and 5% lower top heat loss.

Highlights • Models to relate the surrounding and food temperatures was developed and verified. • Multilayers model was used to consider the spatial temperature distribution. • Spatial distribution of heat transfer coefficient was analyzed using simulation. Abstract Multilayer food temperature models considering the spatial temperature distribution in the food were developed to predict temporal temperature changes experienced by food during distribution considering the surrounding temperature, initial food temperature, and the predetermined surface heat transfer coefficient. Parameters used in the models were determined using the results of unsteady three-dimensional computational fluid dynamics simulations for the conjugated heat transfer problem between the food and surroundings. Models were validated by comparing model predictions with the food temperature experimentally measured under fluctuating temperature conditions with a mean absolute deviation of less than 1°C. The developed food temperature model was integrated with a freshness monitoring model to complete the real-time food quality monitoring system. Food quality prediction using the integrated food quality monitoring system was validated for eggs and milk. Quality predictions using the food temperature model showed better accuracy than when using a single point measurement of food temperature. [ABSTRACT FROM AUTHOR]

This paper presents a totally enclosed self-circulation (TESC) axial ventilation system (AVS) for large direct-drive permanent magnet synchronous machines (PMSMs). The configuration and the cooling air circulation process of the cooling system are described in detail. Then, the lumped parameter (LP) based airflow analysis and thermal analysis applicable to large PMSMs with the presented TESC AVS are proposed. The airflow network model and thermal network model are set up, respectively, and both of them are programmed. In order to verify the feasibility of the ventilation system and the accuracy of the LP models, a 1.65-MW PMSM prototype with the proposed ventilation system is developed and manufactured, and the temperature rise of the prototype is tested under generator operation mode. The accuracies of the developed airflow network model and thermal network model are verified by comparing the calculation results of the temperature rise with the test results. The LP models can be used to investigate the effects of different geometrical and operational conditions on the distributions of the airflow rate and the temperature of PMSMs with the TESC AVS. [ABSTRACT FROM AUTHOR]

Traditional overload protection depends on pre-set values and cannot reflect the current tolerance capability of the line. If the current of a line exceeds the setting value of its overload protection, then it will be subsequently tripped off and cause power flow transferring, which may trigger the cascade tripping of power grid. So it is of significant importance for the overload protection to accurately evaluate the real-time safety status of transmission line and coordinate with power system control to eliminate the overload. In this article, starting from the mechanism analysis of conductor heat transfer, a thermal network model is established by focusing on radial and circumferential heat transfer paths. The temperature rise response of the network node is obtained through nonlinear iteration. The calculation model, which is verified by a test platform, is better than standard models. Then, the current tolerance capability calculation model of the whole line is constructed on the basis of the thermal network and applied to improve the overload protection. The proposed multi-parameter overload protection can effectively prevent unnecessary tripping to avoid the expansion of accidents. Finally, the validity of the proposed protection is verified by the New England 10-machine 39-bus test system. [ABSTRACT FROM AUTHOR]

A ventilated wall module is an outdoor air-intake device that can clean the drawn air, reduce heat loss or gain, and insulate outdoor noises. It contains a solar board, air cavities, and an air filter. This investigation proposes a zonal network model to efficiently predict temperature profiles in a ventilated wall module. The thermal network is established by applying an energy balance to each network node. The outdoor temperature, indoor temperature, and solar irradiation intensity are specified as boundary parameters. The proposed model is validated by the measured temperatures in a prototype model. The results show that the proposed model provides reasonably accurate temperatures with a maximum gap of 3°C between the prediction and the measurement. The temperature profiles approach straight lines when the mass flow rate significantly increases. A similar trend is observed when the solar irradiation intensity, the solar board absorptivity, or the glass transmitivity dramatically decreases. [ABSTRACT FROM AUTHOR]

In the present study, a new thermal resistance capacity circuit for the heat transfer modeling in borehole heat exchanger with low computation time is developed. Generally, the thermal circuit models result in sets of ordinary differential equations which are solved numerically. The system of equations derived from the traditional thermal resistance capacity model (TRCM) are usually stiff and lead to unstable results unless for a very small time steps which can increase the computation time significantly. Meanwhile, the system of ordinary differential equations derived from the present model is non-stiff and there is no time step limitation for the stability of the results. It is shown that the present model yields accurate and stable results even for large time steps. Finally, the two-dimensional model is extended to the three-dimensional model. The results of the three-dimensional solution of the present model are in good agreement with the numerical results and experimental measurements reported in the literature. [ABSTRACT FROM AUTHOR]

Simulation and optimisation of district heating and cooling networks requires efficient and realistic models of the individual network elements in order to correctly represent heat losses or gains, temperature propagation and pressure drops. Due to more recent thermal networks incorporating meshing decentralised heat and cold sources, the system often has to deal with variable temperatures and mass flow rates, with flow reversal occurring more frequently. This paper presents the mathematical derivation and software implementation in Modelica of a thermo-hydraulic model for thermal networks that meets the above requirements and compares it to both experimental data and a commonly used model. Good correspondence between experimental data from a controlled test set-up and simulations using the presented model was found. Compared to measurement data from a real district heating network, the simulation results led to a larger error than in the controlled test set-up, but the general trend is still approximated closely and the model yields results similar to a pipe model from the Modelica Standard Library. However, the presented model simulates 1.7 (for low number of volumes) to 68 (for highly discretized pipes) times faster than a conventional model for a realistic test case. A working implementation of the presented model is made openly available within the IBPSA Modelica Library. The model is robust in the sense that grid size and time step do not need to be adapted to the flow rate, as is the case in finite volume models. [ABSTRACT FROM AUTHOR]

Optimal design and operation of district heating networks require accurate, but simple models to allow fast simulation. This paper describes the analytical derivation of such a model based on existing work regarding heat loss and dynamic temperature profile calculations in literature. The most important addition from this work is the incorporation and investigation of heat transfer from supply to return side in double pipes, something which is often (over)simplified in more commonly used models. The paper presents the mathematical derivations and the assumptions made in detail for the case of steady-state heat losses in double pipes. The resulting model is carefully examined in a parameter study, from which a number of interesting conclusions can be drawn. Firstly, the heat losses are found to be nearly independent of the mass flow rate in the range of mass flow rates usually encountered in thermal network pipes. The remaining heat loss calculation is simply based on temperature levels and thermal resistance factors, determined by the pipe dimensions and materials. Furthermore, it is found that heat losses from supply to return side should be incorporated in the analysis for better accuracy of the results, even more so with the increasing popularity of twin pipes with common insulation. [ABSTRACT FROM AUTHOR]

In order to master the thermal characters of tank armor,the tank armor is divided into many units based on lumped parameter method. Thermal balance equations are established and the thermal networks of the armor are constructed. Then a computing method of thermal balance is also determined. The temperature of a certain type of tank armor is computed in design,the high temperature areas with distinct thermal features are reached,and influence reason is analyzed. The temperature of a certain type of tank armor is measured through experiments,and then it is compared with computing temperature. The maximum deviation between them is 6. 92%,which proves that the model is reasonable. [ABSTRACT FROM AUTHOR]

• Importance of contact orientation to anisotropic thermal conductivity is analysed. • Directed weighted thermal network is used to identify shortest heat transfer paths. • A directed thermal resistance is extracted from the new directed thermal network. • Directed resistance involves particle connectivity, contact quality and orientation. • Directed thermal resistance is well related to anisotropic thermal conductivity. The effective thermal conductivity of a granular material varies with the predominant heat transfers direction. The anisotropic effective thermal conductivity is known to be dominated by the microstructure in a dry material. However, no microstructural parameters that are well related to thermal anisotropy have been proposed. After analysing the heat transfer mechanisms at the particle scale, this work constructs new directed weighted thermal networks for both lattice and randomly distributed sphere packings, by considering particles as nodes and local heat transfer paths with thermal resistance as directed edges. With the implementation of graph theory to the directed weighted thermal networks, the shortest preferential heat transfer paths between nodes paired at opposite faces of a sample across the driving temperature gradient direction are identified. Based on the shortest heat transfer paths, a new sample-scale feature named " directed network thermal resistance " is computed for each sample. This new parameter accounts for particle connectivity, interparticle contact orientation and contact quality simultaneously. After computing the effective thermal conductivity of each sample in different directions using a weighted thermal network model, it is found that directed network thermal resistance is inversely proportional to anisotropic effective thermal conductivity. [ABSTRACT FROM AUTHOR]

Highlights: [•] Investigation of temperature profiles and thermal transients in Si power MOSFET. [•] New Cauer thermal network to predict longitudinal temperature profile as a function of time. [•] Thermal RC elements calculated assuming cylindrical heat propagation. [•] Thermal transient predicted compared with numerical electro-thermal simulations. [•] Accuracy of the thermal network increases by increasing the number of RC elements. [ABSTRACT FROM AUTHOR]

Abstract: Domed roofs have been used in Iran and many other countries to cover large buildings such as mosques, shrines, churches, schools. They have been also employed in other buildings like bazaars or market places in Iran due to their favorable thermal performance. The aim of this research is to study about domed roofs thermal performance in order to determine how they can be helpful in reducing the maximum air temperature of inside buildings during the warm seasons considering all parameters like air flow around them, solar radiation, radiation heat transfer with the sky and the ground as well as some openings on the building. The results of the study show that the thermal performance of the investigated domed roof is better than the building with flat roof, particularly when the dome is covered with glazed tiles. In addition to their aesthetic values, domes covered with glazed tiles have thermal benefits of keeping the inside air of these buildings relatively cool during the summer. Moreover, openings cause passive air flow inside building, which is helpful for human comfort. [Copyright &y& Elsevier]

Abstract: Thermal actuators are extensively used in microelectromechanical systems (MEMS). Heat transfer through and around these microstructures are very complex. Knowing and controlling them in order to improve the performance of the micro-actuator, is currently a great challenge. This paper deals with this topic and proposes a dynamic thermal modelling of thermal micro-actuators. Thermal problems may be modelled using electrical analogy. However, current equivalent electrical models (thermal networks) are generally obtained considering only heat transfers through the thickness of structures having considerable height and length in relation to width (walls). These models cannot be directly applied to micro-actuators. In fact, micro-actuator configurations are based on 3D beam structures, and heat transfers occur through and around length. New dynamic and static thermal networks are then proposed in this paper. The validities of both types of thermal networks have been studied. They are successfully validated by comparison with finite elements simulation and analytical calculations. [Copyright &y& Elsevier]

Abstract: A two dimensional lumped parameter model (LPM) which provides the steady state solution of temperatures within axisymmetric single-sided, slotted axial flux generators is presented in this paper. The two dimensional model refers to the heat modelling in the radial and axial directions. The heat flow in the circumferential direction is neglected. In this modelling method, the solid components and the internal air flow domain of the axial flux machine are split into a number of interacting control volumes. Subsequently, each of these control volumes is represented by thermal resistances and capacitances to form a two dimensional axisymmetric LPM thermal circuit. Both conductive and convective heat transfers are taken into consideration in the LPM thermal circuit by using annular conductive and convective thermal circuits respectively. In addition, the thermal circuit is formulated out of purely dimensional information and constant thermal coefficients. Thus, it can be easily adapted to a range of machine sizes. CFD thermal modelling and experimental testing are conducted to validate the temperatures predicted from the LPM thermal circuit. It is shown that the LPM thermal circuit is capable of predicting the surface temperature accurately and potentially replacing the CFD modelling in the axial flux machine rapid design process. [Copyright &y& Elsevier]

Abstract: A new improved solution, Detached Variables-Parameters Coefficient (DVPC) method and Monte Carlo Ray Tracing (MCRT) method, is proposed to solve a thermal network problem in heat-transfer analysis of spacecraft. DVPC method emphasized directly on correcting the key Solar Absorption Coefficient (SAC) material parameter rather than the network conduction and radiation coefficients generally. MCRT method is contributed to reducing computation assumption and clarifying physical concepts and used to solve solar direct incidence area and network radiation transfer coefficient with different round circular angles and zenith angles of solar incidence radiation. Numerical simulation is carried out for temperature distribution of satellite. In steady stage, maximum temperature difference reaches up to 200 K and increasing the radio of absorptivity to emissivity will lead to temperature rise rapidly. In unsteady stage, maximum temperature value of satellite main body is lager than that of solar array. To begin with, cooling velocity increased rapidly and got to maximum value, then descended slowly and reached up to steady stage with 17 K discrepancy. Meanwhile, increasing SAC is better than that of decreasing to true value. [Copyright &y& Elsevier]

A model is developed using a thermal network analysis approach. An experimental setup is designed and built to validate the model. The model is based on an inverse thermal network analysis using a singular value decomposition algorithm. The data from the experiments are used to determine the thermal conductances using inverse model's unsteady- and steady-state forms. The model development and experimental results are presented together with possible sources of error and how to avoid or decrease their influence. Good agreement between the thermal network model predictions and experiments was found. [ABSTRACT FROM AUTHOR]

• Heat pipe cooling system allows for passive molten salt reactor cooling. • System allows significant reduction in the plant's overall auxiliary load. • Thermal network model shows highly efficient heat transfer form reactor to steam cycle. A Molten Salt Reactor (MSR) cooling concept is presented, using passive Multiple Evaporator and Condenser Loop Thermosyphons (MECLTS) to transfer heat from the reactor core to the steam cycle. This concept allows for the intermediary coolant salt system to be eliminated, reducing the associated auxiliary power load. Heat transfer using the MECLTS cooling method is investigated using a thermal network approach, and results are compared to a conventional active MSR cooling concept. In a conceptual 450 MW th MSR power plant the passive MECLTS cooled MSR improved net power output from 200 to 206.8 MW e compared to the conventional active cooling system. [ABSTRACT FROM AUTHOR]

An important trend of Building Integrated Solar Thermal (BIST) system is to improve the aesthetic aspect of the solar collector to meet the requirement of architectural style and energy collection. Painting on the glass cover in an appropriate method is a simple and practical way. In this study, a halftone coating was used to print a red brick wall pattern on the glass cover. A series of comparative experiments were carried out to test the effect of the coating on the thermal behavior of the solar collector. In heat collection processes, compared with the solar collector with blank cover plate, the one with coated cover plate has lower absorber plate temperature and higher cover plate temperature. The lower the solar irradiance, the smaller the effect of color coating on the solar collector. Compared with the uncoated surface, the coated surface is more sensitive to solar irradiation. In the same heat collection process, compared with the solar collector coated on the outer surface of the cover plate, the one coated on the inner surface has 0.8 °C higher heat absorber plate temperature and 5% lower top heat loss. [ABSTRACT FROM AUTHOR]