Heating Applications Research Articles

Recent advances in electrostatic precipitation of particles from flue gases generated by domestic heating appliances. A brief outlook

Winter season is the time of increased emission of exhaust gases from household heating appliances containing particulate matter (PM) and other noxious contaminants. Many old buildings and single houses, particularly at rural and small town regions, still use stoves, fireplaces or ovens to flat heating. Besides qualified fuels like coal or biomass pellets, all kinds of wastes are also burned in many cases, producing not only mineral particles but also toxic volatile organic compounds or other carcinogenic species. To solve the problem of high level of emission of solid particles and organic-compound molecules different constructions of electrostatic precipitators, which can remove such particles, have been developed in last two decades, which were designed to operate downstream of small domestic boilers. Such electrostatic precipitator must comply with the ECODESIGN emission limits, which set the emission level at 20 mg/m3, for biomass. The mass collection efficiency should be higher than 95 % to obtain this emission level. This brief review presents different constructions of electrostatic precipitators designed to be used for the removal of fly ash particles from domestic heating appliances.

Modeling of gas sensor based on zinc oxide thin films by feedback loop using operational amplifier

Nanostructured Zincoxide thin-film is widely used as a sensing material because of its tunable surface microstructure and wide optical bandgap but synthesizing a film with desired value of resistance and reproducibility of film is challenging, particularly by chemical method. In this work, we showed how a ZnO film of arbitrary resistance can be used as a sensor without application of heat using operational amplifier. Zinc oxide thin film was synthesized by using the Sol-gel method (Spin coating) and was characterized by XRD and SEM which revealed wurtzite polycrystalline nature of Zinc oxide film with average grain size 17–25 nm. In this report, we designed a noble electronic circuit capable of detecting analyte gas molecule even if very small change in film resistance occurs due to the influence of gas molecule. In recently available sensors, the quality of the film degrades over time due to repeated heating and cooling, resulting in a reduced lifetime for the sensor. To address this issue and achieve higher sensitivity, as well as to fabricate an affordable, portable, precise, energy-efficient and durable device, this electronic model offers advantages over classical temperature-dependent sensors.

Study on spray characteristics of a compact pressure swirl nozzle integrating tangential inlet flow channel and swirl chamber

Pressure swirl nozzles are widely applied in various heat and mass transfer applications due to advantages of reliable performance, simple structure, and easy processing. However, the complex design of the nozzle structure makes it difficult to miniaturize the pressure swirl nozzle, which restricts its use in limited spaces. In this study, a compact pressure swirl nozzle is proposed by merging a swirl chamber with the tangential inlet flow channel, addressing the issue of liquid atomization in limited spaces. The key geometric parameters are determined based on the internal flow properties by swirl chamber simulation. A spray test bench utilizing a phase Doppler particle analyzer and a high-speed camera was built to study the effect of pressure drop, geometric size, and nozzle inlet shape on spray characteristics. The simulation results show that the nozzle diameter and inlet shape are the main factors affecting flow in the swirl chamber. The experimental results further demonstrate that increasing nozzle diameter increases flow rate and spray cone angle, causing the droplets to move to the spray edge. The spray characteristics are affected by the inlet shape of the nozzle hole: radial velocity and particle size show a wider range of change with a funnel-shaped inlet. Axial velocity and pressure drop are obviously affected by a cylindrical-shaped inlet. This study provided a new design approach for pressure swirl nozzles and achieved flow rate of 5–35 l/h and Sauter mean diameter below 40 μm with an overall weight of 12 g. This compact nozzle construction is a reference for the design of atomizing nozzles in limited spaces.

CFD modeling of a tubular three-pass solar air heater with phase change material: Investigating heat transfer enhancement and energy efficiency

The present study introduces a novel solar air heater design featuring a tubular surface with three passes arranged in a counter-flow configuration, aimed at improving compactness and enhancing heat transfer characteristics. The research involved the development and validation of a computational fluid dynamics (CFD) model, which was utilized to accurately depict the distribution of solar flux through the system components by comparing the model results with experimental data. The study involved conducting a comparative analysis between the tubular three-pass solar air heater with phase change material (TTPSAH_PCM) and conventional flat plate solar air heaters (FPSAH) to ascertain the superior design characteristics. A thorough investigation was carried out, encompassing evaluations of energy, exergy, outlet temperature, convection heat transfer coefficient, and useful heat gain. The findings indicate that the TTPSAH_PCM outperforms alternative geometries. For instance, when operating at a mass flow rate of 0.006 kg/s, the TTPSAH_PCM demonstrates substantial enhancements in several key metrics, including an 11.4 % increase in the system's daily thermal efficiency, a 17 % improvement in exergy efficiency, and a 4 % rise in outlet air temperature. The convection heat transfer coefficient of TTPSAH_PCM exhibited a 155.6 % increase compared to the FPSAH type. Moreover, the system being investigated demonstrates an 8.5 % rise in useful heat gain. The results underscore the enhanced efficacy of the TTPSAH_PCM system in contrast to alternative solar air heater arrangements, and its applicability for both drying operations and indoor heating applications.

Investigation on Residual Mechanical Properties of Galvanized Iron Cold-Formed Steel Sections Exposed to Elevated Temperatures

Cold-formed steel (CFS) sections are used to construct medium and low-rise structures designed to carry small-scale loads. CFS sections are manufactured without the application of heat. Therefore, it is crucial to comprehend the properties of CFS sections which are exposed to fire or elevated temperatures. To simulate the real- time fire exposure, an ISO Standard fire curve was used to heat the CFS sections. The objective of the study is to assess the residual mechanical strength of exposed sections after the elevated temperature test. The study aims to compile data for forecasting the degeneration of elements and to ascertain whether the structural components can be reused or replaced. The CFS sections were subjected to different temperatures, and after heating, two cooling methods were used to bring down to room temperature. The characteristics of the retrieved specimens, taken from exposed CFS sections were assessed using a tensile coupon test. The residual properties such as ultimate strength, yield strength, and elastic modulus were examined and reported. The influence of heating and cooling is more pronounced from the test results. A reduction in the yield and ultimate strength was noticed, and it was found to decrease as the heating intensity increases for air and water cooling respectively. In the case of yield and ultimate strength, the strength reduction is critical beyond 60 minutes. The elastic modulus was also found to be reducing with a similar trend. Based on the test results, reduction factors are proposed for ultimate strength, yield strength and elastic modulus. Reduction factors obtained for yield strength under 60 minutes of heating for air and water cooling is 0.575 and 0.557 respectively. In 120 minutes, the values are 0.400 and 0.329. Reduction factors obtained for ultimate strength under 60 minutes of heating for air and water cooling is 0.586 and 0.566 respectively. For 120 minutes, the values are 0.331 and 0.313.

AC-Duino Kit: Enhancing the Teaching and Learning Experience of Root-Mean-Square Current in Alternating Current through Arduino Microcontroller Application

Root-mean-square current in alternating current is an abstract concept that appears challenging to students in the absence of any hands-on experimental tool. Therefore, the AC-Duino Kit, utilising an Arduino Uno microcontroller and ACS712 current sensor, is developed and used in an experiential learning activity involving real-life household electrical appliances to enhance this topic's teaching and learning experience. Two-cycle action research was conducted on forty-six students undertaking a one-year matriculation program with data collected from document analysis, interview, and observation. The result shows that the students could relate root-mean-square current to power consumption, differentiate between heat and motor appliances, and relate peak current to electrical safety. The study confirmed that this activity could bridge the theoretical concept to real-life applications.

Development of an iot-based humidity, temperature, and air quality monitoring system

Monitoring the environment has become of great importance as it helps individuals keep tabs on their environment. Air pollution is very dangerous to human health and it is known to cause deadly health conditions. This research presents an IoT-based design that will effectively monitor the humidity, temperature, and air quality of a given environment. NodeMCU humidity, temperature, and gas sensors were deployed in the design of the system. The output interface was designed using the Blynk IoT platform. The system was tested in two stages using application of gas pollutants and heat on one hand, whilereadings were taken from a cool evening and sunny afternoon on the other hand. After testing all the functions of the system under various conditions, it revealed 76% humidity, 26.8oC temperature, and 461ppm on the application of gaseous air pollutants, 43.1% humidity, 45.6OC temperature, and 199ppm of air quality on the application of heat, 51.1 humidity, 20.4% temperature, 198ppm of air quality on a cool evening and 70.7% humidity, 29.5OC of temperature and 206ppm of air quality on a sunny afternoon. The system showed improved performance in terms of monitoring of humidity, temperature and air quality and can be deployed suitably in homes, schools, and industries.

Utilization of wood pellet for industrial use

The use of wood pellets for industrial uses has grown significantly in recent years due to their sustainability, cost-effectiveness, and environmental advantages. Wood pellets have a wide range of industrial applications, including energy generation, heating, and manufacturing processes. They made from compacted sawdust and wood waste provide a renewable alternative to traditional fossil fuels, helping to cut greenhouse gas emissions and combat climate change. In the energy industry, wood pellets are a feasible substitute for coal in power plants, allowing for the transition to greener energy sources. Their stable quality and high energy density make them an appealing option for power generation, especially in areas trying to meet renewable energy requirements. Furthermore, wood pellets are rapidly being used in industrial heating applications such as boilers and furnaces across a wide range of industries, including manufacturing, food processing, and agriculture. Their efficient combustion properties and dependable supply chain make them an affordable option for enterprises looking to save operating expenses and carbon footprints. Technological developments in the pellet production process, along with governmental frameworks that encourage sustainable practices and renewable energy, are anticipated to propel market expansion. In summary, the use of wood pellets in industry presents a strong way to satisfy the rising need for environmentally friendly heating and energy sources. Wood pellets have the potential to be a key player in the shift towards a more sustainable industrial landscape by utilizing its renewable nature and environmental advantages.

Acute Effect of Passive Hyperthermia on Lactate Concentrations

Background: Knowledge on the effect of heat on recovery is still incomplete. The present study aimed to evaluate the effect of a passive acute hyperthermic stimulus before and after a lactic anaerobic test on the production and oxidation of lactate blood concentrations. In addition, the purpose was to evaluate the effect that the application of this previous hyperthermic stimulus may have on the athletic performance in the test. Methods: For this purpose, a cross-over design through an anaerobic treadmill test in three different situations (normothermia, pre-test hyperthermia, and post-test hyperthermia) was performed. Twelve male subjects participated (age: 21.25 ± 1.64 years; height: 1.76 m ± 0.08; weight: 72.59 ± 9.44 kg). An anthropometric assessment was carried out with weight, height, skinfolds, body perimeters and diameters, and external and internal body temperatures in each of the tests. A nutritional survey was also carried out 48 h prior to each test. Results: The results of the study showed a decrease in blood lactate concentrations when the hyperthermic effect was applied as passive recovery just after the end of the test (p < 0.05). A decrease in lactate concentrations was also achieved when applying the hyperthermic effect just before the start of the test (p < 0.05). However, no significant improvements were obtained from this application of heat on test performance. Conclusions: The results suggest that the application of passive acute hyperthermia has a favourable effect in terms of decreasing blood lactate concentrations in a 5 min recovery period after lactic anaerobic activity.

Recent Research in Solar-Driven Hydrogen Production

Climate concerns require immediate actions to reduce the global average temperature increase. Renewable electricity and renewable energy-based fuels and chemicals are crucial for progressive de-fossilization. Hydrogen will be part of the solution. The main issues to be considered are the growing market for H2 and the “green” feedstock and energy that should be used to produce H2. The electrolysis of water using surplus renewable energy is considered an important development. Alternative H2 production routes should be using “green” feedstock to replace fossil fuels. We firstly investigated these alternative routes through using bio-based methanol or ethanol or ammonia from digesting agro-industrial or domestic waste. The catalytic conversion of CH4 to C and H2 was examined as a possible option for decarbonizing the natural gas grid. Secondly, water splitting by reversible redox reactions was examined, but using a renewable energy supply was deemed necessary. The application of renewable heat or power was therefore investigated, with a special focus on using concentrated solar tower (CST) technology. We finally assessed valorization data to provide a tentative view of the scale-up potential and economic aspects of the systems and determine the needs for future research and developments.

Carbon Sequestration Potential of Manure-Derived Hydrochar Aided by Secondary Stabilization.

Hydrothermal carbonization (HTC) is a process that produces a carbon-rich solid from wet organic materials through the application of heat and pressure. Carbonized solids, previously correlated to long-term soil stability, may be considered for carbon sequestration through incorporation into soil. Chars produced by pyrolysis are known for exceptional stability in soil, but pyrolysis is expensive when applied to wet biomass, such as manure. Chars produced from manure by HTC show considerably improved potential for carbon sequestration relative to untreated manure, although not as great as that of chars produced by pyrolysis. This study focuses on producing and evaluating chars by HTC paired with pyrolysis and different methods of chemical oxidation for long-term carbon sequestration in soil. It is shown that a two-step process of pyrolysis following HTC produces a char that outperforms those produced by either individual process (HTC or pyrolysis) in carbon yield, carbon content, and, more importantly, soil carbon sequestration potential. It was found that acid-catalyzed HTC followed by pyrolysis resulted in a char with a 13% increase in carbon yield, a 51% increase in carbon content, and an atomic O/C ratio 64% smaller than the char produced by conventional pyrolysis.

CFD analysis of artificially roughened solar air heater: a comparative study of C-Shape, reverse C-Shape, and reverse R-Shape roughness element

Solar Air Heater (SAH) serves as a pivotal device for converting solar radiation into heat applications. This study focuses on enhancing the performance of SAH through modifications to the absorber surface by introducing ribs as artificial roughness. A two-dimensional CFD analysis investigates the impact of C-shape, reverse C-shape, and reverse R-shape ribs on thermal and hydraulic performance within the SAH channel. RNG (k-ϵ) turbulence model is employed for numerical simulation and model accuracy is validated against established correlations and literature results. The numerical analysis involves the designing and modelling of the SAH using a constant pitch ratio (P/e) of 14.285 and a height ratio (e/D) of 0.021. The Reynolds number (Re) from 4000 to 18000 was considered for the present study. The result reveals that the present rib geometries significantly enhance heat transfer and fluid mixing, leading to substantial improvements in Nusselt number (Nu) and friction factor (f) by 2.5 to 3.3 times and 2.8 to 5.05 times respectively over smooth duct SAH. The C-shape rib configuration attains the highest Thermohydraulic Performance Factor (THPF) at approximately 2.0078 for a Re of 4000 over reverse C-shape, and reverse R-shape ribs.

Symbolic Aggregate Approximation-Based Clustering of Monthly Natural Gas Consumption

Natural gas is an indispensable non-renewable energy source for many countries. It is used in many different areas such as heating and kitchen appliances in homes, and heat treatment and electricity generation in industry. Natural gas is an essential component of the transportation sector, providing a cleaner alternative to traditional fuels in vehicles and fleets. Moreover, natural gas plays a vital role in boosting energy efficiency through the development of combined heat and power systems. These systems produce electricity and useful heat concurrently. As nations move towards more sustainable energy solutions, natural gas has gained prominence as a transitional fuel. This is due to its lower carbon emissions when compared to coal and oil, thus making it an essential component of the global energy framework. In this study, monthly natural gas consumption data of 28 different European countries between 2014 and 2022 are used. Symbolic Aggregate Approximation method is used to analyse the data. Analyses are made with different numbers of segments and numbers of alphabet sizes, and alphabet vectors of each country are created. These letter vectors are used in hierarchical clustering and dendrogram graphs are created. Furthermore, the elbow method is used to determine the appropriate number of clusters. Clusters of countries are created according to the determined number of clusters. In addition, it is interpreted according to the consumption trends of the countries in the determined clusters.

Sodium acetate-based thermochemical energy storage with low charging temperature and enhanced power density

The electrification of heat necessitates the development of innovative domestic heat batteries to effectively balance energy demand with renewable power supply. Thermochemical heat storage systems show great promise in supporting the electrification of heating, thanks to their high thermal energy storage density and minimal thermal losses. Among these systems, salt hydrate-based thermochemical systems are particularly appealing. However, they do suffer from slow hydration kinetics in the presence of steam, which limits the achievable power density. Additionally, their relatively high dehydration temperature hinders their application in supporting heating systems. Furthermore, there are still challenges regarding the appropriate thermodynamic, physical, kinetic, chemical, and economic requirements for implementing these systems in heating applications. This study analyzes a proposal for thermochemical energy storage based on the direct hydration of sodium acetate with liquid water. The proposed scheme satisfies numerous requirements for heating applications. By directly adding liquid water to the salt, an unprecedented power density of 5.96 W/g is achieved, nearly two orders of magnitude higher than previously reported for other salt-based systems that utilize steam. Albeit the reactivity drops as a consequence of deliquescence and particle aggregation, it has been shown that this deactivation can be effectively mitigated by incorporating 10 % silica, achieving lower but stable energy and power density values. Furthermore, unlike other salts studied previously, sodium acetate can be fully dehydrated at temperatures within the ideal range for electrified heating systems such as heat pumps (40 °C – 60 °C). The performance of the proposed scheme in terms of dehydration, hydration, and multicyclic behavior is determined through experimental analysis.

Experimental comparison and seasonal performance evaluation of different scroll compressor capacity modulation methods in an R410A water to water system

Rising cooling needs for the residential and commercial air conditioning sectors and the demand for higher SEER require HVAC&R to handle cooling loads below the design condition. Although several studies exist focusing on a particular capacity modulation strategy, there is no extensive study that explores all these available modulation strategies in the same experimental facility. This study experimentally compared a single speed, a two-stage compressor, tandem combinations of two single speed compressors, a single speed and two-stage compressor, and a variable speed compressor using the same R410A water ethylene glycol (WEG) system for cooling application. These modulation strategies were tested according to AHRI Standard 551/591 (2020), and their seasonal performance is given by Integrated Part Load Value (IPLV.SI). A two-stage compressor with lower LMTD at the heat exchangers and a single speed compressor with higher isentropic efficiency have the same performance at one of the part load conditions. Additionally, a single speed compressor with an improved compressor motor has a 3% higher IPLV.SI than a two-stage compressor with the baseline motor. Different methods of interpolation that are available when the capacity is in between two compressor stages of operation were discussed. The tandem combinations with different number of stages have the same seasonal performance, showing that not all the stages available might be useful. The variable speed compressor with the best IPLV.SI was selected to further study the performance under heating application using EU 14825 (2013) standard with constant and variable condenser outlet conditions. For heating application, variable speed compressor with a wider range of modulation is recommended when selecting the compressor for variable condenser outlet temperature conditions while it might not be the best option due to compressor operating envelope limitation when operating with constant condenser temperature outlet.

Improved solar-thermal heat exchanger for space heating with surface roughness: A numerical parametric investigation and its optimization

The heat exists in solar radiation can be extracted and utilized in drying and heating applications. In the present study, an attempt is made to improve the performance of a solar-thermal heat exchanger consisting of a flat-plate collector by producing roughness on the heat-absorbing surface. A repeated pattern of staggered arc roughness is introduced along the streamlines and the roughness is characterized using height ratio, relative pitch, number of gaps, etc. The influence of the roughness characteristics is studied on the thermal performance by computational fluid dynamics. The developed model is validated with well-established relations before predicting the results for the proposed design. The effective mixing of the viscous sublayer and free stream results in a significant enhancement in the thermal performance and it is predicted that the proposed model improves heat transfer up to 5.57 times that obtained in the conventional one. The comparative heat transfer over continuous arc-shaped roughness is increased from 32.72% to 62.46% and 44.62%–62.46% with the variation of number of gap and, gap with ratio from 1 to 3, and 0.5 to 1.0, respectively However, the disturbance in the streamlined pattern in the flowfield resulted in a pressure loss/pumping power increment of 4.46 times in the system. The results are summarized in correlation for heat augmentation and pressure loss which estimate results with the accuracy of 12% and 10%, respectively.

Ohmic heating application with different electric fields on inactivation of Listeria monocytogenes in protein-enriched cow milk.

The aim of this study was to determine the effects of an ohmic heating (OH) process with different electric field intensities on Listeria monocytogenes inactivation in protein-enriched cow milk. Protein powder was added at rates of 2.5%, 5% and 7.5% in 1.5% fat content milk, and L. monocytogenes (ATCC 13932) strain was then inoculated into the samples. The OH process was carried out in a laboratory-type pilot unit created using stainless steel electrodes, a K-type thermocouple, a datalogger and power supply providing AC current at 0-250 V, 10 A. The inoculated milk samples were heated to 63°C by applying an electric field intensity of 10V/cm and 20V/cm. L. monocytogenes counts, pH, color measurement and hydroxymethylfurfurol levels were then determined. OH applied with an electric field intensity of 10 V/cm caused an average decrease of 5 logs in L. monocytogenes level in the samples containing 2.5% protein and decreased below the detection limit (<1 log) at the 9th minute (p<0.05). Similarly, application of an electric field intensity of 20 V/cm in milk containing 2.5% and 5% protein caused the L.monocytogenes level to decrease below the detection limit (<1 log) at 2 minutes 30 seconds (p<0.05). No change was observed in the L* (brightness) values of the samples but it was determined that there was a slight increase in pH, a* (redness) and b* (yellowness) values compared to the control group. It was observed that the inactivation of L. monocytogenes by OH depends on the duration of the OH process, protein concentration in the milk and the applied voltage gradient.

Impact of Culinary Techniques on Nutritional Profiling: Unraveling the Transformation of Proteins and Vegetables in Cooking

This paper explores the impact of cooking technique and vegetable nutritional components. As a crucial provider of nutrients, food goes through profound changes when cooked, hence its effect on macro- and micronutrients. Protein denaturation, which may lead to the breakdown of the tertiary structure resulted from the effect of heat, acid, alkali, or ultraviolet radiation, is a process that disrupts the original characteristics of proteins. Proteins basically remain more secure than vitamins while cooking, but they risk denaturation after overcooking or exposure to high heat. Although micronutrients like vitamins and minerals needed for growth are stable in their content and behavior, they can change their content and behavior during cooking process as they cannot withstand heat. The paper underlines the multiple impacts of cooking techniques on vegetables by pointing out that some techniques of heat application might result in inferior nutritional quality. Bioactive compounds that are in vegetables undergo changes in the physical attributes, the sensory properties and bioactive content based on the techniques such as boiling, steaming or microwaving. Besides, during food preparation such as washing, peeling and cutting almost everything like flavor, texture or final nutritional values is already determined. The cooking method chosen in a wide range including microwave, pressure cooker, open pan or steaming has a great impact on the nutrient composition. Bacterial contamination in eggs, which is a health safety concern that can cause nutrients losing and even harm consumer health, stresses the need for cooking to preserve nutrients and protect consumers. The modern consumer who cares about the nutritional values and benefits of home cooked meals must be aware of the magnitude of method of cooking on the content of nutrients. Being a fact that more and more consumers after minimally processed and additive free snacks and nutrition information about cooking method is critical. The study concludes by suggesting that additional research is needed so as to develop the guidelines for the best cooking methods that promote nutrient conservation, safety, and palatability. Keywords: Cooking technologies, Nutrient value, Protein denaturation, Vitamins and minerals, Vegetables processing, Food processing, and Consumers trends

Application of ohmic heating in cooking mixtures of brown rice and whole grains: total phenolic content, antioxidant activities, vitamin B1, some minerals, and energy consumption

ABSTRACT Brown rice and whole grains are vital nutrient sources for humans; however, they usually require a long cooking period and are difficult to cook uniformly. This study investigated electrical conductivities of brown rice (KDML 105, Riceberry, and red cargo rice) and whole grains (lotus seed, red kidney bean, and Job’s tear) under various conditions. Furthermore, ohmic heating was applied in cooking the mixtures of brown rice and whole grains and the results were compared with conventional heating. The key objective was to apply ohmic heating in cooking the mixtures of brown rice and whole grains to improve the retention of nutrients in cooked products and to improve process efficiency. It appeared that electrical conductivities of all samples were sufficiently high for applying ohmic heating. Electrical conductivities of lotus seed mixed with water were between 0.061 and 0.402 S/m at 30–100°C that were higher than red kidney bean (0.016–0.256 S/m) and Job’s tears (0.018–0.148 S/m). Brown rice of Riceberry variety had the highest electrical conductivities (0.067–0.204 S/m) followed by red cargo rice (0.067–0.173 S/m) and KDML 105 (0.048–0.130 S/m). Sample mixtures cooked using ohmic method had significantly higher antioxidant activities and the calcium, phosphorus, and potassium contents than those cooked using conventional method. Precooking steps for lotus seed, red kidney bean, and Job’s tears were needed with the conventional cooking approach; however, these were unnecessary with ohmic cooking. Ohmic cooking apparatus in this study consumed approximately 2% more energy than electric rice cooker.

A Self Tuning Fuzzy Control Based Dual Input Nine-Level Self Balancing Switched-Capacitor Inverter for Induction Heating Applications

A Self Tuning Fuzzy Control Based Dual Input Nine-Level Self Balancing Switched-Capacitor Inverter for Induction Heating Applications