Model Of Thermal System Research Articles

Modeling and simulation of wind turbine heat recycling system

The paper aims to discuss the power supply and heat supply system of wind turbine, promote the development of wind energy in heat recycling, and expand the application of renewable energy resources in replacing fossil energy. Starting from the construction of wind power heat storage system model, first, molten salt was selected as the fluid heat storage material. Based on the realization process of two-pot molten salt electrothermal transformation, the model of two-pot molten salt heat storage (MSHS) system was established. Second, based on the model of heat storage system, the high temperature MSHS wind power heating system was simulated by using the numerical simulation analysis method. The results showed that the simulation results of the thermal storage system model were highly consistent with the actual results, and the model was accurate and reliable, which was suitable for the simulation analysis of the thermal storage system. After a day of operation, the utilization rate of wind energy of the MSHS wind power heating system could reach more than 94%. The combination of the MSHS wind power system and regional heating had obvious effect on absorbing wind power, saving resources, and solving the problems of wind curtailment. In the MSHS wind power supply heating system, the configuration of MSHS significantly improved the utilization ratio of wind energy in the wind power generation system, even up to 100% at maximum. To sum up, the configuration of MSHS can absorb most of the wind energy generated on that day, thus improving the energy utilization ratio of the wind power generation system.

Dynamic Prediction of the Thermal Nonlinear Process Based on Deep Hybrid Neural Network

Nonlinear system prediction plays an important role in the practical thermal process, and deep learning algorithm is now popular in nonlinear dynamic system modeling because of its powerful learning ability. In this paper, the dynamic artificial neural networks (DANNs), which can be divided into two different types with external dynamic characteristics and internal dynamic characteristics, are analyzed. The mathematical formulations of feedforward deep neural network (DNN), traditional recurrent neural network (RNN) and Long-Short Term Memory network (LSTM) models are given. Furthermore, the structure of deep Hybrid Neural Network (DHNN) is described. Finally, the applicability of the above models in the thermal nonlinear process with different structural features is discussed. Simulation experiments reveal that DANNs with internal dynamic characteristics more suitable for solving thermal nonlinear system modeling problems with unknown order, and DHNN based on LSTM model has performed much better in approximating the dynamics of the thermal process with state parameters.

Numerical study on the heat release capacity of the active-passive phase change wall affected by ventilation velocity

The north wall of Chinese solar greenhouses (CSGs) plays an important role in maintaining their indoor thermal environment without additional heating during the wintertime. To enhance the heat storage/release capacity of the CSG wall and further improve the indoor thermal environment, an active-passive phase change thermal storage wall system has been developed in this study. The system was composed of 5 concentrating solar air collectors (CSACs), 6 tanks that were embedded in the north wall of the CSG and filled by phase change material (PCM), tubes linking the tanks and the CSACs and a centrifugal fan with variable-frequency drive (VFD). During the daytime, the solar energy was collected by the CSACs and stored in the tanks, whereas during the nighttime, the stored energy was released into the indoor environment of the CSG through a passive heat mode of the north wall or an active heat mode of the system. Then, a numerical model of the active-passive phase change thermal storage wall system has been developed. The simulation results were validated by the experimental data with the maximum relative error and average relative error being 5.6% and 3.9%, respectively. Furthermore, the heat release capacity characteristics in three cases with the air velocities of 2 m/s (Case A), 3 m/s (Case B) and 4 m/s (Case C) at indoor outlet for the active heat mode and a passive heating case (Case D) were chosen as the control groups for study. In the proposed wall, the heat release capacity of ventilation increased and that of inner surface of the wall declined with an increasing ventilation velocity. The total heat release capacities of the cases A, B and C were 38.12 MJ, 40.26 MJ, 42.00 MJ, respectively, higher than that of the case D (33.76 MJ). On the other hand, the calculated temperature distribution indicated that there was no thermal-stable layer within depth of the 360 mm in the wall due to an apparent temperature variation of the PCM layer by ventilation. These results suggested that the proposed system could effectively promote the heat storage/release capacity of the middle layer of the wall.

Heat Generation and Failure in Padmount Transformers Due to Zero Sequence Saturation

After a transformer failed following a double-phase fault, there was an interest in understanding how the fault mechanism led to the failure. This paper investigates this fault condition in detail and demonstrates the underlying challenges in correcting the failure. The electrical and thermal system models were developed and simulated to analyze the transformer response under double-phase fault conditions. Experimental measurements validated the simulation results on a real three-phase distribution transformer. This paper presents the results from simulated and experimental analysis from double-phase fault on a Yg–Yg distribution transformer.

Impact of ultra‐capacitor on automatic generation control of electric energy systems using an optimal FFOID controller

Automatic generation control (AGC) acts as a significant part in alleviating dynamic oscillations and sustaining constancy in frequency and scheduled tie-line power to establish the reliable, secure, and stable operation of electric energy systems under dynamic conditions. AGC needs energy storage system (ESS) and elevated expert, intelligent, and flexible control strategies to ensure generation-demand balance in modern complex structured energy systems following inconsistent load demands. Hence, this paper utilizes a new fuzzy fractional order integral derivative (FFOID) controller along with ultra-capacitor (UC) ESS to solve AGC issue in energy systems effectively. The imperialist competitive algorithm is employed to tune the output scaling factors like integral, derivative, and noninteger order of integrator/derivative of FFOID controller using ISE performance index. Initially, the technique is applied on a one-area nonreheat thermal system. Then, to demonstrate its competency and scalability, the study is boosted to prevalent two-area nonreheat thermal, two-area multisource multi-unit hydrothermal, and three-area reheat thermal energy system models. The advantage of the proposed controller is demonstrated by juxtaposing the outcomes with those offered by various best claimed intelligent control approaches expressed in the contemporary literature and fuzzy proportional integral (FPI)/fuzzy FO PI (FFOPI) controller. The UC with the FFOID controller outperforms other methods. The robustness analysis proves that parameters of the utilized controller acquired at nominal situation are healthy enough and necessarily not needed to retune under broad alterations in the system loading/parameters, size/position of load perturbation, and under the appearance of system constraints and random load pattern with/without noise.

A review study on the modeling of high-temperature solar thermal collector systems

Concentrated solar power technologies are gaining more attention in the last two decades in order to replace the conventional power technologies and reduce their environmental impact. Among the developed concentrating technologies, parabolic trough solar collector and solar tower are the most mature and dominant technologies. As part of the continuous development of these technologies, significant efforts have been deployed to predict and improve their performance, and therefore reduce their cost and make them more competitive. In this context, numerous analytical and numerical studies have been developed and presented in the literature. This review aims to summarize the state-of-the-art modeling approaches used to simulate, predict and evaluate the optical, thermal and dynamic performance of high-temperature solar thermal collectors. The review includes the different analytical and ray tracing models used to determine the non-uniform flux on the receiver aperture. Energy balance models are also presented as simple and easy computational models suitable to predict the thermal performance at a reasonable time and computational cost, whereas Computational Fluid Dynamic models are more convenient to study the details of the coupled fluid flow and heat transfer in the internal and external flow. The review also includes dynamic models such as the lumped capacitance models which are used to simulate the dynamic characteristics of the heat transfer fluid and interaction with the solar receiver under transient conditions. The dynamic behavior of the whole solar plant using different codes is examined. Furthermore, different features and capabilities of those approaches are also analyzed and compared. Finally, the use of numerical modeling in the development of new designs and assessment of the use of nanofluids is discussed. In summary, this work presents a comprehensive review of the existing numerical models and could serve as a guideline to develop new models for future trends in concentrating solar technologies.

Peak shaving performance of coal-fired power generating unit integrated with multi-effect distillation seawater desalination

The peak-load regulation of a coal-fired power plant is critical to promote renewable energy power generation in grid systems. A low-temperature multi-effect distillation (LT-MED) was proposed to improve the dispatchability of a 600 MW coal-fired power generating unit; here, an unsteady thermal system model was established using the Ebsilon software to study peak shaving capacities. The results show that the increased extraction amount and pressure will reduce the power generation and increase the coal consumption. The peak shaving capacity curve was obtained based on the extraction amount. It is indicated that the peak shaving capacity can reach a maximum of 477 MW when the amount of steam extraction is less than 238 ton/h. When the amount of extraction is sufficiently large, the exhaust steam from the low-pressure turbine attains the minimum allowable value, the peak shaving capacity of the unit then sharply decreases. The dynamic response of an LT-MED system to the step variation of the output load of the power generating unit was also revealed. Moreover, the power generation and coal consumption are slightly influenced by the steam consumption in a single LT-MED system. The maximum extraction of the unit can afford a maximum of 19 LT-MED systems. The results of this study will provide a useful reference for the peak shaving of coal-fired power generating units.

Utilisation of plug‐in electric vehicles for frequency regulation of multi‐area thermal interconnected power system

The application of plug-in electric vehicles (PEVs) is assumed to be wide in power system in regulating the system frequency in the near future. This paper provides an aggregate model of an interconnected multi-area thermal system with the incorporation of PEVs for frequency control in each of the three areas. Two degree of freedom proportional–integral–derivative (2DOF-PID) controller has been utilised for robust secondary control in all the three control areas. An optimisation technique inspired by nature named as wind-driven optimisation (WDO) technique is employed to decide the optimal values of the controller gains. The effectiveness of WDO optimised 2DOF-PID controller is verified by performing various comparative analysis with conventional PID controller under nominal system condition and random loading condition. An analysis has also been carried out to evaluate the system performance with variation in state of the integrated PEVs. The impact of introducing PEVs in the system in frequency regulation has been vigorously studied under different system conditions such as nominal, random loading condition, and simultaneous perturbation in two and three areas to testify their advantages. The comparisons reveal that with the integration of PEVs in the system, the system dynamics gets enhanced to a large extent.

Development of a dairy multi-objective optimization (DAIRYMOO) method for economic and environmental optimization of dairy farms

The aim of this paper was to develop a Dairy Multi-Objective Optimization (DAIRYMOO) method to carry out multi-objective optimization of dairy farm equipment, management practices and electricity tariffs, optimizing based on a user specified economic and environmental weighting factor. Models of both solar thermal water heating and heat recovery systems were developed, validated, and used as part of a test case for DAIRYMOO. Optimizing dairy farm equipment, management practices and electricity tariffs both economically and environmentally is necessary because of the competing goals of increasing farm milk production and the necessity to reduce agricultural related greenhouse gas emissions. Models of solar thermal water heating and heat recovery systems were created using experimental data to evaluate the economic and environmental performance of these technologies. Multi-objective optimization was used to obtain the optimal selection of equipment, management practices and electricity tariffs which impact electricity related costs and CO2 emissions, based on a user specified economic and environmental weighting factor. A Genetic Algorithm was employed to maximize a combined objective function based on this weighting factor. For a test case with a 195 cow farm, over a ten year time horizon the optimal equipment, management and electricity tariff combination was found using 11 different weighting factor values ranging from 0 to 1. The combined objective function was gradually weighted towards the environmental criterion and away from the economic criterion. It was found that the optimal equipment combination changed incrementally relative to the change in the weighting factor. Furthermore, an analysis was carried out which performed the same multi-objective optimization on the same 195 cow farm, but with a mandatory real time pricing tariff in place. The optimal configurations using the mandatory real time pricing tariff showed that gas water heating was selected regardless of the weighting factor employed. This differed from the results with no mandatory tariff in which a day/night tariff was optimal for all weighting factor values, and electric water heating was optimal for weighting factor values of 0.9 or higher i.e. when the combined objective function was weighted heavily towards the economic criterion. For both analyses, heat recovery systems were not included in the optimal farm configuration unless the weighting factor was 0.2 or less, indicating that the economic performance of these systems was poor. Solar thermal water heating systems were not included in the optimal farm configuration regardless of the weighting factor value. The DAIRYMOO method described in this study will provide useful advice to farmers and policy makers relating to economic and environmental optimization around equipment, management and electricity tariff choices on dairy farms.

Numerical investigation and parametric analysis of a photovoltaic thermal system integrated with phase change material

In this paper, a comprehensive three-dimensional model of photovoltaic thermal system integrated with phase change material (PVT/PCM) is developed and simulated. The effect of some key parameters using parametric analysis on performance of PVT/PCM system with water as working fluid is investigated. Parameters considered in this study include the properties of PCM (i.e. melting temperature, enthalpy of fusion and thermal conductivity), solar radiation and mass flow rate. The parametric analysis ranges are selected according to the properties of the most of available PCMs on the market, which shows the practical application of the numerical research. Furthermore, a three-dimensional model of PVT system is simulated as well to compare its performance with PVT/PCM system. An enthalpy-porosity method is used to simulate the solidification and melting of PCM. To solve the governing equations, the pressure-based finite volume method using transient solver in ANSYS Fluent 16.2 is employed. Moreover, the SIMPLE algorithm is selected to provide the coupling between the pressure and velocity components. The results present that the PVT/PCM system has lower surface temperature and coolant outlet temperature compared to the PVT only system. The results also shows that enhancing the melting temperature of PCM from 40 °C to 65 °C increases the surface temperature from 51.53 °C to 58.78 °C, while it reduces the percentage of melted PCM from 82.7% to 9.6%. It is also concluded that as the thermal conductivity of PCM enhances, both electrical and thermal energy efficiency of PVT/PCM system increase.

Comparison of operational performance and analytical model of high concentrator photovoltaic thermal system at 2000 concentration ratio

This paper presents the development of a model based on efficiency equations to evaluate the performance of an HCPV/T system and compares its outputs with data of an operational case-study system installed in Palermo, Italy. The model is validated with data of the operational system to show real performance. The model can evaluate (a) the electric efficiency of the InGaP/InGaAs/Ge TJ solar cell and (b) electrical and thermal power/energy production potential of one module. The model predictions are compared with experimental electric and thermal data by obtaining linear regression plots of experimental results vs. analytical results; the R2 for experimental electrical and thermal results are 0.91 and 0.87 respectively. Using the model, the evaluated average daily analytical and experimental InGaP/InGaAs/Ge TJ solar cell efficiencies are 33 % and 25 % respectively; with a maximum daily experimental value of 30 %. It was found that the annual analytical and potential (based on derived equations from experimental data) electric energy produced by one module are 158 kWh/m2/year and 144 kWh/m2/year respectively, while the annual analytical and potential thermal energy are 375 kWh/m2/year and 390 kWh/m2/year respectively.

Cooling water mass flow optimization for indirect dry cooling system of thermal power unit under variable output load

The analysis was conducted for the optimal operation under off-design conditions of the indirect dry cooling thermal power generating unit. The numerical model of natural draft dry cooling tower (NDDCT), as well as the off-design performance model of whole thermal system of a supercritical power generating unit, including that of turbine, condenser and regenerative system, were combined together. An iterative procedure was adopted so that the operating parameters of dry cooling system with cooling water mass flow rate and output power load were obtained. The total coal consumption of power generation, which considered both effects of back pressure of turbine and power consumption of circulating pump, was taken as the optimization object. The results indicated that the pump power consumption increased, while the back pressure decreased with circulating cooling water mass flow rate. There was the optimum cooling water mass flow rate corresponding to the lowest coal consumption of power generation. For the objective power generating unit, 4.83 ton standard coal per hour at most can be saved by adjusting the circulating cooling water flow rate to the optimum value.

A Novel Optimal Combined Fuzzy PID Controller Employing Dragonfly Algorithm for Solving Automatic Generation Control Problem

In this paper, a novel optimal combined fuzzy PID controller employing Dragonfly Algorithm (DA) was proposed for solving Automatic Generation Control (AGC) problem in interconnected power systems. The DA algorithm was employed in this work to optimize the controller parameters including the scaling factors of fuzzy logic and the PID gains. To show the potential of the proposed approach, initially, a two equal areas non-reheat thermal power system was investigated, and then the proposed approach was extended to a typical AC/DC two-area multisource power system connected via an AC tie-line as well as High Voltage Direct Current (HVDC) transmission link. The superiority of the proposed controller was proven by comparing the obtained results with the previous AGC techniques reported in the literature. Moreover, sensitivity analysis was done. Further, the proposed control strategy was also extended to a nonlinear three-area thermal power system model by considering the effect of appropriate Generation Rate Constraint (GRC) with nonlinearity in each area. Finally, the results were tabulated in terms of settling time and peak overshoot. The comparative study demonstrates the effectiveness of the proposed control strategy and shows its robustness to enhance frequency regulation loop of linear and nonlinear interconnected power systems.

Multidimensional Finite Volume Fully Implicit Ablation and Thermal Response Code

A finite volume, fully implicit ablation and thermal response code that simulates the pyrolysis gas flow, thermochemical ablation, and shape change of thermal protection materials and systems in multiple dimensions is developed. Both structured and unstructured grid approaches are implemented. The governing equations (which include energy conservation, pyrolysis gas mass conservation with Darcy’s law, a multicomponent decomposition model, and a surface energy balance) are solved with a moving grid system to simulate the response of charring ablators in aerothermal heating environments. This work demonstrates and validates new capabilities that are added to the code. These expanded capabilities include fully implicit time integration, pyrolysis gas flow due to Darcy’s law, an unstructured grid option, and parallel computing. Three groups of test cases that consider three different charring ablators are presented. In the first group, three-dimensional iso-q-shaped phenolic-impregnated carbon ablator test models with various throughthickness conductivity directions are studied. In the second group, axisymmetric flat-faced dual-layer woven carbon phenolic models are examined. Finally, in the third group, axisymmetric iso-q-shaped three-dimensional multifunctional ablative thermal protection system models are analyzed. For all cases, predictions are compared with available temperature data.

Solar heating and hot water supply of high-rise buildings

Southern Russia, the Far East and Siberia regions have a lot of solar sources. These climate conditions are appropriate for using such combined power systems. Combined power systems are capable of providing building with heat in winter partially. In summertime the same system satisfies hot water demands.Numerical modeling is carried out to prove the utility of the combined power systems . One of the calculations is based on the Black Sea coast climate conditions. The input data was seventeen-storeyed public building with 3 columns of 68 solar thermal panels Vitosol 100 SH1on the southern side of its facades. Each panel is installed with a 90-degree tilt towards the horizon and connected with the next by series connection.Automatic control system supplies air temperature set at 18 degrees Celsius in the daytime and 12 degrees in the nighttime (standby conditions). In view of the above, the solar thermal system completely covers heating systems energy requirements. In the summertime solar thermal system covers about 60% of hot water demand.Numerical modeling also showed that in low temperature conditions of Far East climate the described system covers only 30% of heating systems energy requirements. But it covers almost 90% of hot water demand. This difference between working data (60% and 90%) for summertime is related to higher number of sunny days in the Far East than in the Black Sea coast region.The numerical modeling of solar thermal combined systems with big solar collectors area showed some advantages. It is possible to use the produced energy all year round. Also the system proved its universality: it supports both heat and hot water systems. The system ensures high level of efficiency in many climate zones. Another important advantage is that such system produces non-polluting energy. However, some of the described issues are not shown in climate conditions of other regions, i.e. Central and Northwestern Russia.

Research on Thermal Characteristics of Spindle System With Tilting Pad Bearing

Spindles with tilting pad bearings have been widely applied in machine tools due to their high running precision. However, friction power loss will increase dramatically when the bearing runs at a higher speed. So far, little research on the thermal modeling of spindle systems with tilting pad bearings can be found in literature. In this paper, based on the Newtonian law of viscosity, formula that describes the friction power loss of the tilting pad bearing has been derived. The thermodynamic equilibrium equation for the spindle lubrication system has been established. Thermal boundary condition of the spindle system has been obtained using the heat transfer theory. Thermal model of the spindle system with tilting pad bearing has been built with the finite element method in order to calculate its temperature and thermal displacement distribution. Effects of the eccentricity ratio and the lubricant flow rate on thermodynamic behavior of the spindle system have been studied systematically. Finally, experiments have been conducted to verify the proposed thermal model for the spindle system with tilting pad bearing.

Heat Transfer Operability Limits for an Actively and Passively Cooled Hypersonic Vehicle

For a trimmed hypersonic waverider vehicle, computations were performed to investigate the operability limits that occur due to excessive heating of the external surface, including the nose region and combustor wall region, and the heating of the liquid hydrogen fuel, which is used as coolant. The operability limits computed include the maximum values of flight Mach number, dynamic pressure, and the flight time before one of several temperature limits is exceeded. To compute operability limits, efficient aerodynamic heating and thermal protection system models were added to the reduced-order model MASIV, which contains an advanced combustion analysis and a trim code. Results show the effects of varying the thickness of the three-layer thermal protection system that consists of a radiation shield, an insulation layer, and the vehicle wall. Results also show the effect of varying the fraction of fuel in the active cooling system that is recirculated back into the fuel tank. Recirculating the heated fuel raises the fuel tank temperature and decreases the fuel density (increasing the volume); the analysis computes the maximum flight time before the fuel tank temperature and fuel volume exceed acceptable limits. By extending the active cooling system to a small region of the inlet (instead of just around the combustor), the operability limits are increased from a flight Mach number of 7.3 to 8.6.

Non-linear thermal simulation at system level: Compact modelling and experimental validation

In this work, a general methodology to extract compact, non-linear transient thermal models of complex thermal systems is presented and validated. The focus of the work is to show a robust method to develop compact and accurate non-linear thermal models in the general case of systems with multiple heat sources. A real example of such a system is manufactured and its thermal behaviour is analyzed by means of Infra-Red thermography measurements. A transient, non-linear Finite-Element-Method based model is therefore built and tuned on the measured thermal responses. From this model, the transient thermal responses of the system are calculated in the locations of interest. From these transient responses, non-linear compact transient thermal models are derived. These models are based on Foster network topology and they can capture the effect of thermal non-linearities present in any real thermal system, accounting for mutual interaction between different power sources. The followed methodology is described, verification of the model against measurements is performed and limitations of the approach are therefore discussed. The developed methodology shows that it is possible to capture strongly non-linear effects in multiple-heat source systems with very good accuracy, enabling fast and accurate thermal simulations in electrical solvers.

Dynamical Graph Models of Aircraft Electrical, Thermal, and Turbomachinery Components

The current trend of electrification in modern aircraft has driven a need to design and control onboard power systems that are capable of meeting strict performance requirements while maximizing overall system efficiency. Model-based control provides the opportunity to meet the increased demands on system performance, but the development of a suitable model can be a difficult and time-consuming task. Due to the strong coupling between systems, control-oriented models should capture the underlying physical behavior regardless of energy domain or time-scale. This paper seeks to simplify the process of identifying a suitable control-oriented model by defining a scalable and broadly applicable approach to generating graph-based models of thermal, electrical, and turbomachinery aircraft components and systems. Subsequently, the process of assembling component graphs into a dynamical system graph that integrates multiple energy domains is shown. A sample electrical and thermal management system is used to demonstrate the capability of a graph model at matching the complex dynamics exhibited by nonlinear and empirically based simulation models.

Thermal protection study of bladder compensatory suit using a heat transfer model.

The bladder compensatory suit (BCS) is important individual protective equipment for pilots' activities in a high-flying environment. The layout and thermal diffusion ability of the bladder directly affects the thermal comfort of pilots in flight. (1) Established and verified a human-compensatory suit-environment heat transfer model; (2) Used the model to study the human thermal variation of each segment in hot conditions and clothing. To verify the two-dimensional heat transfer model, simulated data of body temperature were compared with experimental results under the same conditions (AT: 40/45°C, ordinary clothing). The model could be used to calculate the temperature variation of each body segment in three environments temperature (28°C, 35°C and 40°C) and three types of clothing (naked, ordinary clothing, BCS). The results showed that: (1) the bladder significantly affected sweating speed and skin temperature, as well as core temperature; (2) the skin temperature of the area covered by the bladder was difficult to reduce by the thermal regulation system. It was because sweat secretion was inhibited, thus, to limit evaporation. The model could be used as a reference for the thermal protection design of bladder compensatory suit. The bladder compensatory suit (BCS) is important individual protective equipment for pilots activities in a high-flying environment, and its layout directly affects the thermal comfort. Based on a two-dimensional thermal regulation system model, a body-clothing-environment heat transfer model was established. The model was used to calculate the temperature and sweat variation of each body segment in different environments and clothing.