Variable Thermal Loading Research Articles

Experimental study on dynamic flow and heat transfer performance of silicon-based microchannel under variable thermal load

The issue of high power density in chips has become one of the bottlenecks restricting the improvement of chip performance. Silicon-based microchannel heat sinks (Si-MCHS) can guide the cooling fluid close to the chip junction, significantly enhancing the cooling capability. Due to the rapid changes in chip power consumption, understanding the flow and heat transfer performance of Si-MCHS, especially their dynamic heat transfer performance, is crucial. This paper introduces the fabrication of Si-MCHS and experimentally tests its static and dynamic performance. The microchannels can handle a maximum thermal flux of 71.3 W/cm2. It was found that the temperature response process of Si-MCHS mirrors that of a first-order system’s step response or zero-input response. Upon a sudden change in power consumption, the thermal response can reach 90 % of the steady-state temperature difference (ΔT) within 4 s and 50 % ΔT within 1 s. Increasing the pump speed significantly reduces the response time, while different power step changes have minimal impact on the response time. Consequently, we have formulated a graded flow rate control strategy based on the flow and heat transfer performance of Si-MCHS, which achieves effective flow rate control.

The Role of Thermal Analysis in Engine Fin Design: Insights and Perspectives

Objective: The study aims to address the significance of fins in enhancing the heat transfer rate of engine cylinders and highlight their applications and advancements in various fields. Methods: Thermal analysis of fins using ANSYS Workbench is an invaluable tool for engineers and researchers in determining and optimizing the heat transfer characteristics of finned structures. ANSYS Workbench provides a comprehensive platform for evaluating the performance of fins in various applications using simulations of computational fluid dynamics (CFD) and finite element analysis (FEA). With ANSYS Workbench, it is possible to assess the thermal behaviour of fins under a variety of conditions, such as variable boundary conditions and thermal loads. Some significant recent patents on Engine fin are also discussed in this review article. Results: Fins are designed to maximize contact with the surrounding air or coolant, thereby facilitating engine heat transfer to the surrounding environment. Engineers can enhance heat dissipation capabilities by considering parameters such as fin geometry, density, material selection, and manufacturing techniques while minimizing associated drawbacks. Conclusion: The numerous applications of fins highlighted in this review article will encourage researchers to find novel strategies to improve heat transfer by employing fins for use in a variety of sectors.

Thermomechanical interaction in a living tissue due to variable thermal loading with memory

AbstractIn order to address various clinical applications within living tissue, the aim of this work is to analytically study the thermomechanical interaction for a living tissue which is subjected to variable thermal loadings. Human tissues undergoing regional hyperthermia treatment for cancer therapy is based on graded changes of the cells, and as a consequences, the constitutive equations have been formulated using the nonlocal elasticity theory. The heat transport equation for the present problem is formulated in the context of Moore‐Gibson‐Thompson theory of generalized thermoelasticity assimilating the memory‐dependent derivative within a slipping interval. Both the boundaries of the tissue is maintaining the condition of zero traction. The lower boundary of the tissue is subjected to prescribed thermal loading while, the upper boundary is kept at zero temperature. Utilizing the Laplace transform mechanism, the governing equations have been solved and the general solutions have been obtained in the transformed domain. In order to arrive at the solutions in the real space‐time domain, suitable inversion of the Laplace transform has been carried out numerically using the method of Zakian. Numerical findings suggest that thermomechanical waves propagate through skin tissue over finite distances, which helps mitigate the unrealistic predictions made by the Pennes' model. Significant effect due to different effective parameter such as nonlocal parameter and the time‐delay parameter is reported. Also, how a nonlinear kernel function can be more effective in bio‐heat transfer, is outlined in the study also.

2D thermo-fluidynamic rotary model of an elastocaloric cooling device: The energy performances

Elastocaloric cooling has been considered a promising solid-state technology for cooling and heat pumping among the alternatives to vapor compression, at room temperature range. The technology is based on elastocaloric effect that is a thermophysical phenomenon occurring in materials like Shape Memory Alloys (SMA). The effect is detectable as a temperature change in the material if adiabatically subjected to a forcing field of mechanical nature. The latter provokes to the materials a stress that can derive from tension, compression, bending, torsion solicitations. As a result, the SMA experiments a structural phase change from austenite to martensite (coupled with heat addition) and temperature rise. Dually when the stress is removed, the SMA releases heat with a temperature decrease. In this paper the SUSSTAIN-EL rotary elastocaloric heat pump has been deeply investigated to test the energy performances while it works on open loop and closed loop, through a 2D numerical model based on the finite element method, for cooling and heating operation modes. The device employs a binary NiTi SMA as elastocaloric refrigerant and air as heat transfer medium. A wide set of working conditions has been considered like variable inlet mass flow rate, rotation frequency and thermal loads. The acquired results demonstrate that, both in open and closed loop, the prototype’s energy performances are promising and highly favourable for the intended macroscale collocation of the device.

A bio-inspired shape memory alloy-based smart fin system for adaptive thermal management

Thermal management systems utilizing fixed-area extended surfaces for thermal enhancement have been extensively investigated. Unlike these systems, in nature, few creatures display the ability to control heat dissipation in adaptation to changes in environmental conditions by controlling their exposed surface area of the body. Motivated by this, the primary objective of this research is the design, development, numerical and experimental evaluation of an adaptive variable area smart fin system for intelligent thermal management using a high-strain SMA spring actuator. Unlike most thermal management devices and techniques that involve a fixed surface area, a smart fin controlled by Pennate structure-based SMA (PeSMA) actuator is proposed for large actuation and compact arrangement. The capabilities of the smart fin to adaptively enhance heat transfer are experimentally demonstrated and numerically modeled. The proposed fin design can deliver improved thermal performance in terms of reduced operating temperature and pressure drop, which is an indicator of operational cost when the application involves variable and uncertain thermal load conditions. We envisage one of the future applications of this technology in the battery thermal management of Electric Vehicles (EVs) where deployable compact heat transfer system is highly desirable.

CONTROL OF A HEAT PUMP COMPRESSOR WITH VARIABLE FREQUENCY DEVICE DRIVEN BY PID

Integrating advanced control technologies to enhance energy efficiency and environmental sustainability in heat pump systems is of growing significance. This article offers a comprehensive review on the utilization of Proportional-Integral-Derivative (PID) control and Variable Frequency Drive (VFD) technology to govern the compressor's operation in a heat pump. The primary objective is to optimize energy consumption and thermal output under varying loads and environmental conditions, thus enhancing the heat pump's performance.
 
 The article delves into the fundamental principles of heat pump operations, emphasizing the compressor's pivotal role in maintaining the delicate balance between energy consumption and desired thermal output across applications, spanning residential HVAC to industrial processes. The PID control algorithm is introduced to adapt the compressor's speed and power consumption dynamically. The VFD is incorporated into the control system, enabling variable speed compressor operation for a responsive reaction to load fluctuations. Combining PID and VFD control is explored to achieve peak system performance and energy efficiency.
 
 Through practical experiments and simulations, the research investigates the influence of PID and VFD control on energy efficiency, stability, and performance. The results underscore substantial energy savings and environmental impact reduction potential, particularly in scenarios with variable thermal loads and fluctuating environmental conditions.
 
 This study advances our understanding of advanced control strategies in heat pump technology and underscores the pivotal role PID and VFD control play in creating energy-efficient heating and cooling solutions. The findings offer practical implications for diverse applications, from residential settings to industrial processes, and provide insights into sustainable heat pump technology use in the context of energy conservation and climate change challenges.

Maximizing cooling/heating performance of thermoelectric modules across variable thermal loads via optimal control based on COP curves

The thermoelectric module has high potential as a compact electrothermal actuator in the generation of cooling/heating effects without any moving part. However, one difficulty of the design is that the fundamental principles of optimal cooling/heating performance of thermoelectric modules are not yet fully understood and implemented. The purpose of this paper is to propose a mathematical optimization to gain insight and implement the most effective usages. In the proposed analysis, it is found that the coefficients of performance (COP) are dependent on the driving voltage and the ceramic-substrate temperatures of the thermoelectric module at both the cold and hot sides. The thermoelectric properties of a 91.2W thermoelectric module are used to simulate the proposed performance analysis to find the optimal driving voltage at desired operating temperatures at both sides on COP curves. The coefficient of determination R2 of 0.9832 indicates strong agreement on the coefficients of performance between the analysis and the experiments under one hundred thirty-seven operating conditions. With the proposed methodology, the 91.2W thermoelectric module can be operated at the maximum coefficient of performance across variable thermal loads of airflow where the optimal driving voltage is determined from desired operating temperatures at both sides.

Energy, economic, and carbon emission analysis of a residential building with an energy pile system

This paper investigated the combined energy, economic and carbon performances of energy piles used for heating and cooling buildings, an issue that has received limited interest in the past. To address this knowledge gap, a 30-year numerical simulation, calibrated using field data, was conducted for variable building thermal loads, pile spacing, pile length and number of energy piles for a six-storey residential building in Melbourne, Australia. The energy pile system in the annual heating-only mode demonstrated a 75 % reduction in energy consumption and a 5 % reduction in energy costs compared to a natural gas boiler. The energy piles performances in the annual heating-and-cooling mode were significantly higher than in the heating-only mode, demonstrating a 39 % reduction in energy consumption, carbon emissions and energy costs compared to an air-source heat pump. Increasing the pile spacing from 2.05 m to 6.4 m, pile length from 10 m to 20 m, and number of energy piles from 38 to 114 increased the energy, economic and carbon benefits of energy piles by 76 %, 77 % and 119 %, respectively. The results highlight the importance of building thermal loads and pile configuration on assessing the energy, economic and carbon performances of energy piles during early design stages.

Thermomechanical loads of powerful turbogenerator stator winding insulation in the presence of water cooling defects

Introduction. An analysis of incidents linked to power units’ emergency disconnecting from network as a result of turbogenerators’ malfunction on the NPP of Ukraine is conducted. It is identified, that the reason of the majority of incidents is an insufficient reliability of the stator winding’s direct cooling system. Problem. The most problematic point in winding for today is the frontal parts, where, while cooling is reduced, there are not only thermal, but also thermomechanical loadings on an insulation appearing. The level of these loading depends on structural design of frontal parts and a character of violation of coolant agent circulation in a bar. In some cases they can exceed limit values. The spread and the quality of research on this issue for today are insufficient. Goal. The aim of the completed research is to determine the thermomechanical loading of insulation of stator winding bar in a powerful turbogenerator with a direct liquid cooling under condition when coolant circulation is malfunctioned. Methodology. A complex mathematical model of thermomechanical processes in an insulation of stator winding bar of a powerful turbogenerator is developed. It takes into account the real geometry of the winding bar, variable thermal loading of core elements in radial and axial directions, as well as ways of fixation of slot and frontal winding parts. Studies of thermomechanical processes in an insulation of stator winding bar of turbogenerator are conducted. Results. Values of mechanical displacement and stress for the different modes of malfunction are obtained. Areas of bar, where mechanical loading may exceed the boundaries of mechanical durability of material of insulation of stator winding are identified. With decline of coolant liquid consumption the radial displacement and stress in the winding insulation bar in the area, where the bar exits from the slot are increasing along with that the values of radial stress of insulation of the winding bar in places of frontal parts’ fixation exceed limit values. Practical significance. The offered mathematical models allow to realize calculation experiments and can be used in practice for development and validation of diagnostic systems, analysis, design and investigation of emergency situations during exploitation of turbogenerators on power stations of Ukraine.

Experimental validation and numerical assessment of a temperature-controlled thermoelectric generator concept aimed at maximizing performance under highly variable thermal load driving cycles

Although the internal combustion engine (ICE) dominance in mobility is being challenged, ICE R&D enables a non-disruptive transition towards sustainable transportation through hybridization and carbon neutral fuels. The efficiency improvement of ICE-based mobility through Waste Heat Recovery (WHR) is thus a priority, especially in the area of hybrid, plugin hybrid and long-haul transportation, where the recovery potential is high, and ICEs will still be used for a long time. Thermoelectric (TE) Generators (TEGs) have been assessed as a possible low maintenance WHR solution for long. However, viable market solutions are still not a reality. While material costs are steadily being overcome with novel affordable TE materials, there is still the issue of low average conversion efficiency under realistic driving conditions. This is caused by the fact that the efficiency of TEGs is further deprecated by the big challenge of thermally optimizing the TEGs under highly variable conditions of exhaust flow rate and exhaust temperature during real-world driving. This thermal optimization mainly means that the hot side temperature should be as close as possible to the maximum allowable temperature of the modules, but not higher.The authors have been exploring exhaust heat exchanger (HX) concepts that allow achieving this thermal optimization under highly variable thermal loads by using phase change. The strategy used incorporates the spreading of excess heat along the HX by variable conductance heat pipes (VCHPs) embedded in it, thus enabling to maximize the energy conversion without thermal dilution under low thermal loads or overheating risk under high thermal loads. This was done by pre-regulating the pressure of the non-condensable gas (NCG) present inside the VCHPs so that these devices would start performing the spreading of excess heat from over-heated to under-heated regions of the HX at a precise phase change temperature, optimized to the optimal thermal level of the thermoelectric generators.The merit of the aforementioned strategy was confirmed through modelling and illustrated in previous work. The scientific novelty of present study relatively to previous work by the authors or other researchers is that it finally provides a full experimental validation of this concept with two different prototypes attached to a light duty engine. The experimental proof-of-concept results were successfully compared against predictions. Finally, theoretical performance analysis of the impact of the application on a light duty vehicle in terms of fuel economy and GHG emissions during the WLTC class 3 b was assessed with the help of driving cycle and engine simulations performed with AVL Suite software.The unique heat spreading and temperature control features of the concept were confirmed experimentally. In addition, predictions made by the model were far beyond the current state of the art for light duty automotive TEG generators. Namely, maximum output powers exceeding 2 kW and 1.2 kW were predicted during the WLTC cycle when using commercial bismuth telluride and the silicide-Tetrahedrite modules explored by the authors, respectively. Average fuel/CO2 savings of 4% were predicted for the WLTC cycle, with these savings raising to 12% during the highway portion of the cycle. This unparalleled performance is explained by the possibility of achieving both an optimized hot face temperature and a high heat exchanger effectiveness even under highly variable thermal loads.

Designing a professional burnout correction program based on life-purpose orientations in wartime conditions

The work is devoted to substantiation of possibility of reduction of failure rate of thermal mode support system when operating with variable load by control of reliability indicators of thermoelectric cooler. A mathematical model for evaluating the effect of variable thermal load on reliability indicators of a single-cascade thermoelectric cooler at a given temperature level of cooling, medium temperature, geometry of thermocouple branches for various current modes of operation is considered. The relationship between the cooler steady-state operation time and mass and heat capacity of the structure, relative operating current and temperature difference is presented. The results of thermal load relation with operating current, refrigerating factor, time to steady-state mode, energy input, heat dissipation capacity of the radiator, and relative failure rate are presented. Calculations have been made at a given cooling temperature level, medium temperature, temperature differential, and thermocouple branch geometry for various characteristic current operating modes. It is shown that with decreasing thermal load at a given design of thermoelectric cooler, the value of operating current decreases, thus increasing the probability of no-failure operation. The obtained relationship of thermal load with operating current and relative failure rate serves as primary information for design of thermoelectric system for providing thermal modes of thermally loaded elements with variable thermal load. Using the rate of change of temperature difference between the thermally loaded element and the cold electrode of the cooler as a control feature, it is possible to reduce the failure rate when the thermal load decreases, which contributes to increasing the average probability of no-failure operation

Controlling the reliability performance of a thermoelectric cooler under variable heat load

The work is devoted to substantiation of possibility of reduction of failure rate of thermal mode support system when operating with variable load by control of reliability indicators of thermoelectric cooler. A mathematical model for evaluating the effect of variable thermal load on reliability indicators of a single-cascade thermoelectric cooler at a given temperature level of cooling, medium temperature, geometry of thermocouple branches for various current modes of operation is considered. The relationship between the cooler steady-state operation time and mass and heat capacity of the structure, relative operating current and temperature difference is presented. The results of thermal load relation with operating current, refrigerating factor, time to steady-state mode, energy input, heat dissipation capacity of the radiator, and relative failure rate are presented. Calculations have been made at a given cooling temperature level, medium temperature, temperature differential, and thermocouple branch geometry for various characteristic current operating modes. It is shown that with decreasing thermal load at a given design of thermoelectric cooler, the value of operating current decreases, thus increasing the probability of no-failure operation. The obtained relationship of thermal load with operating current and relative failure rate serves as primary information for design of thermoelectric system for providing thermal modes of thermally loaded elements with variable thermal load. Using the rate of change of temperature difference between the thermally loaded element and the cold electrode of the cooler as a control feature, it is possible to reduce the failure rate when the thermal load decreases, which contributes to increasing the average probability of no-failure operation

An investigation on the crack growth in aluminum alloy 7075-T6 under cyclic mechanical and thermal loads

This study evaluates the consequences of mechanical load frequencies and thermal fluctuations on the fatigue crack growth in CT samples made by AA7075-T6. A controllable electrical resistance heating furnace/cooling fan setup was built for applying constant and variable thermal loads. In the first step, fatigue crack growth behavior was studied under different constant temperatures and a maximum load as 12 kN with R = 0. This evaluation indicated that the fatigue lives of the samples were reduced by increasing the constant temperature. Numerical simulations were performed by using the concept of the contour integral in evaluation of the stress intensity factors (SIFs) and crack growth based on Walker's Equation. Applying cyclic temperatures on the samples and altering the mechanical load frequencies revealed that reducing the load frequency from 30 to 10 Hz hasn’t considerable effects on the fatigue crack propagation behavior. On the other hand, lowering the frequency to 5 Hz resulted in a minor decrease in the fatigue lives, while more reduction to 0.5 or 0.1 Hz, severely reduced the failure cycles.

Modelling and real-data validation of a logistic centre using TRNSYS®: Influences of the envelope, infiltrations and stored goods

In this paper, the authors aim to support users when modelling scenarios with complex processes entailing thermal loads and infiltrations. The large building analysed is a logistics centre for the replenishment and distribution of perishable foodstuffs where cold chains must be maintained. The logistics centre, with 96 loading/unloading docks, handles large turnovers of different goods. This produces heat inside the facility. Due to continuous loading/unloading, the infiltrations in the building, and the fixed and variable thermal loads, this facility consumes a large amount of energy.Aiming to optimise the centre and contribute to sustainable development goal SDG7, this building has been modelled with a classical non-D envelope using TRNBuild® and also with the more sophisticated 3D software, SketchUp®, to compare and validate their results over a year with real consumption, as well as to assess the main sources of energy consumption. To obtain reliable results, the authors provide some methodology models to identify the sources of the building's thermal losses and quantify the different sources of consumption. These models are useful tools to support decision-makers (to improve insulation and arrange loads, among other things) when trying to reduce energy use in large buildings with intense operating processes.The results indicate that by modelling the entire facility with 3D software, the model estimation differs from real consumption by around 7.22%, while using a non-D model increases the difference to 26%. Additionally, the results show that around 47% of the energy consumption in the building is due to air infiltrations during loading/unloading, 18% is due to perishable products, and around 30% is due to building insulation. The methodology and models presented here, including the possibility of modifying the thermal load profiles, have demonstrated their capacity to reduce and optimise the load demand of refrigeration for warehouses if reliable data records are available.

Experimental Thermal Response Study of Multilayered, Encapsulated, PCM-Integrated Building Construction Materials

Thermal energy storage integration using phase change materials (PCMs) in buildings has great potential for energy conservation and greenhouse gas (GHG) emission reduction. Cutting-edge research and innovative ideas are required when using multilayered PCMs within typical construction materials to take advantage of their heat storage capability over a wide temperature range within buildings. This current study was carried out to experimentally test the efficacy of using dual PCMs RT28HC and RT21HC with different melting temperature ranges (28 °C and 21 °C) under variable thermal loading. The transient thermal response of various PCM-based configurations of concrete and cement blocks at different temperature inputs was obtained to determine the effectiveness of dual PCMs and their optimized configuration under experimental laboratory conditions. The range of the temperature input was varied from 22 °C to 50 °C, suitable for hot climatic conditions such as those in Pakistan. Laboratory ambient temperatures remained at ~17 °C for all experimental tests. Moreover, the results were compared using two parameters, i.e., decrement factor (DF) and time lag (TL). With DF and TL values of 0.10 and 5.72, respectively, in the high-temperature heating (HTH) regime and a low DF value of 0.08 and high TL of 5.17 in the moderate-temperature heating (MTH) regime, the RT28HC–RT21HC combination proved to be the most effective. The application of the RT28HC–RT21HC combination provided up to a 54.3% reduction in indoor temperatures in the HTH regime. This research contributes through experimental validation that these novel configurations are capable of providing substantial improvement in indoor thermal comfort.

Group Performance of Energy Piles under Cyclic and Variable Thermal Loading

Energy piles, a new type of heat exchanger that serves dual purposes, have gained increasing attention due to the growing energy demand and corresponding carbon emissions. Depending on intended operational requirements or by accident, energy pile groups may be subjected to cyclic and variable thermal loadings. This study presents the results from a series of full-scale field tests of a 2×2 energy pile foundation. The energy pile group was operated partially or fully during the tests to investigate the potential effects of cyclic nonuniform thermal loadings. The results indicated that the cyclic thermal loadings could induce an increase in compressive stress of piles at the end of the experiments. Further comparative analysis showed that the residual compressive stress was attributed mainly to the drag-down effects of the surrounding soil. The compressive stress induced by drag-down effects will overlap with the thermally induced stress, and thus lead to a more significant effect on the energy piles. If the drag-down effects are presented, the stress change may exceed the theoretical upper bound of thermal stress and may be underestimated. In addition, cyclic nonsymmetrical thermal loadings could induce accumulation of differential settlement and group tilt in the energy pile group. It was shown that the group tilt caused by cyclic and variable thermal loadings can be acceptable for general engineering structures. The group tilt will not accumulate further when subjected to symmetrical thermal loadings. A reasonable arrangement of operational piles still can be used to avoid unwanted group tilt generation.

Assessment of an Exhaust Thermoelectric Generator Incorporating Thermal Control Applied to a Heavy Duty Vehicle

The road transport industry faces the need to develop its fleet for lower energy consumption, pollutants and CO2 emissions. Waste heat recovery systems with Thermoelectric Generators (TEGs) can directly convert the exhaust heat into electric energy, aiding the electrical needs of the vehicle, thus reducing its dependency on fuel energy. The present work assesses the optimisation and evaluation of a temperature-controlled thermoelectric generator (TCTG) concept to be used in a commercial heavy-duty vehicle (HDV). The system consists of a heat exchanger with wavy fins (WFs) embedded in an aluminium matrix along with vapour chambers (VCs), machined directly into the matrix, that grant the thermal control based on the spreading of local excess heat by phase change, as proposed by the authors in previous publications and patents. The TCTG concept behaviour was analysed under realistic driving conditions. An HDV with a 16 L Diesel engine was simulated in AVL Cruise to obtain the exhaust gas temperature and mass flow rate for each point of two cycle runs. A model proposed in previous publications was adapted to the new fin geometry and vapour chamber configuration and used the AVL Cruise data as input. It was possible to predict the thermal and thermoelectric performance of the TCTG along the corresponding driving cycles. The developed system proved to have a good capacity for applications with highly variable thermal loads since it was able to uncouple the maximisation of heat absorption from the regulation of the thermal level at the hot face of the TEG modules, avoiding both thermal dilution and overheating. This was achieved by the controlled phase change temperature of the heat spreader, that would ensure the spreading of the excess heat from overheated to underheated areas of the generator instead of wasting excess heat. A maximum average electrical production of 2.4 kW was predicted, which resulted in fuel savings of about 2% and CO2 emissions reduction of around 37 g/km.

Experimental characterization of a small-scale solar Organic Rankine Cycle (ORC) based unit for domestic microcogeneration

The integration of a Micro-Organic Rankine Cycle (ORC) power unit with conventional solar flat plate collectors ensures the simultaneous fulfillment of electricity and domestic hot water (DHW) demands. Due to the variability of the solar source, despite the introduction of a thermal storage unit, the plant is subject to severe off design operating conditions. A small-scale ORC-based was designed, built and fully tested, to experimentally assess the performance and operating robustness of the plant in steady and dynamic off-design condition. The unit is fed by hot water from a 135 L reservoir. Dedicated electric heaters (12 kW each one) reproduce the thermal availability from 15 m2 of standard solar thermal collectors for domestic applications. The test bench underwent an extensive experimental assessment in both stationary conditions of the hot source and in presence of a variable thermal load at the evaporator. Due to the plant architecture and components, the control of the unit is based on the variation of the mass flow rate of the working fluid (R245fa) matching the thermal equilibrium at the evaporator in each operating condition of the system. The variation of the flow rate, in fact, must fit with thermal power available. The off-design steady state assessment allows the understanding of the wide operability of the plant (17–62 g/s), with power and efficiency varying between 150 and 500 W and 2.4–4%, respectively. The dynamic testing of the pilot unit points out the plant consistency and robustness to severe off-design operation, mostly due to the 1 kW scroll expander, very suitable for time-varying operating conditions. Both the option of a full discharge of the thermal energy of the reservoir and the option of a split discharge to the evaporator were investigated and provided a clear indication on the CHP feasibility when no addition of thermal energy takes place at the reservoir. It was observed that during a complete reservoir thermal discharge, the plant works for 3000–3300 s continuously, with a slow power decrease from 500 W to 100 W. Considering the thermal energy recharging time, the plant could be averagely operated up to 7 times during the day if a partial discharge was performed. Each plant activation lasts 900 s producing a power ranging from 500 W to 200 W. This operating strategy allows to cover up to 11.2% of the whole electric energy yearly required by an average European household.

Experimental Investigation of Performance Characteristics of PZT-5A with Application to Fault Diagnosis

In the previous couple of decades, techniques to reap energy and empower low voltage electronic devices have received outstanding attention. Most of the methods based on the piezoelectric effect to harvest the energy from ambient vibrations have been revolutionized. There’s an absence of experiment-based investigation which incorporates the microstructure analysis and crystal morphology of those energy harvest home materials. Moreover, the impact of variable mechanical and thermal load conditions has seldom been studied within the previous literature to utilize the effectiveness of those materials in several practical applications like structural health monitoring (SHM), etc. In the proposed research work, scanning electron microscope (SEM) and energy dispersive x-ray (EDX) analysis are performed to examine the inside crystal morphology of PZT-5A and ensure the quality of the piezoelectric ceramic. Further, the performance of piezoelectric vibration-based energy harvester has been investigated in the second phase of current research work under the variable mechanical and thermal load conditions through a regular series of experiments. It’s been found that the output voltage of piezoelectric sensors will increase by increasing the applied load, whereas a decreasing trend in output voltage is noticed by increasing the applied temperature, resistance and frequency. Within the third part, a measuring setup is developed in the laboratory to further investigate the effectiveness of PZT-5A in practical applications such as electromechanical impedance (EMI) based structural health monitoring under the controlled heating environment. Therefore, this analysis not only evaluates the performance of PZT sensors under the variable operating conditions but also encourages developing a temperature compensation approach in EMI-based SHM.

Scheduling Delays and Curtailment for Household Appliances With Deterministic Load Profiles Using MPC

Smart home appliances can time-shift and curtail their power demand to assist demand side management or allow operation with limited power, as in an off-grid application. This paper proposes a scheduling process to start appliances with time-varying deterministic load profiles. Self-triggered model predictive control is used to limit the household net power demand below a given threshold. Meanwhile, deterministic load profiles are more difficult to schedule compared to variable charging or thermal loads because system failure will occur once power demand is not satisfied. The proposed scheme formulates the decision of the load shifting time as a continuous optimization problem, and an inhomogeneous time grid system is introduced to handle the optimization of different appliances and their consensus at this resolution. The efficacy of the proposed scheme is studied by numerical comparison with a mixed-integer MPC controller and by a case study of three home appliances and an interruptible washing machine.