Industrial Heating Applications Research Articles

Fuel Pellets from a Mixture of Rice Husk and Wood Particles

The physical and mechanical properties were studied for fuel pellets made from a mixture of rice husk and Gmelina arborea wood particles. Pellet density, compressive strength, and abrasion resistance were used to evaluate pellet quality at various densification pressures and proportions of rice husk to wood particles. Pellet density and compressive strength increased from 850 to 1070 kg/m3 and 0.61 to 1.2 MPa, respectively, when densification pressure increased from 80 to 120 MPa. The abrasion resistance for all pellet samples in this study was < 2.0%. Proximate analyses of the fuel pellets showed that volatile matter, fixed carbon, and heating value were relatively high and increased with a higher proportion of wood particles. Ash levels were also high (1.3 to 17.8%), which could cause problems with emission and deposition during thermal conversion. In general, except for the ash content, the physical and mechanical properties of pellets made from rice husk and G. arborea wood particles in this study were within the acceptable limits to be used as fuel pellets for industrial heat applications.

A hybrid PV/T collector using spectrally selective absorbing nanofluids

Nanotechnology is a rapidly developing field with a wide range of potential applications. One such application is using nanoparticles to selectively absorb and transmit light. By controlling the material, size and shape of nanoparticles it is possible to achieve spectrally selective optical properties. This phenomena can be exploited in solar energy applications where selective absorption of the solar spectrum enables high efficient hybrid photovoltaic/thermal (PV/T) collectors. In this study, we suspend core-shell Ag-SiO2 nanoparticles in water to filter out the ideal spectrum for creating electricity from Si PV cells. A detailed optical and heat transfer model for this approach was developed and validated using the electric and thermal outputs from a prototype system operating in real outdoor conditions. The results of this experimental work indicates that 12% more value (weighted energy output) can be achieved from this PV/T prototype compared with a stand-alone PV system under the same illumination. Since the proposed system inherently decouples the thermal receiver from the PV cells, it is possible to extend this technology to industrial combined heat and power applications.

EXPERIMENTAL INVESTIGATIONS OF A SOLAR PARABOLIC TROUGH COLLECTOR FOR CIRCULAR AND ELLIPTICAL ABSORBER

            Solar parabolic trough collector is one of the most efficient and an effective technology to deal with environmental pollution and it has gained much attention due to the recent energy demand. The solar parabolic trough collector is one of the most promising techniques for absorbing the heat from the sun. This heat is utilized for electricity generation and other industrial heating applications. This paper describes the theoretical and experimental assessment of performance of the circular and elliptical absorbers used in solar parabolic trough collector. The absorber tube of parabolic trough collector is used to transfer the heat to the working fluid. The working fluid considered over here is water which is the best operating medium in direct steam generation. The mass flow rate of water in absorber tube is analyzed in 3 stages as 0.016, 0.024 and 0.030 kg/s respectively. The experimental test is done in Chennai-Tamilnadu, Southern part of India which experiences a superior temperature throughout the year. The experiment is conducted for the period of one year from June 2015 to May 2016. The performance improvement focuses on collector efficiency, useful heat transfer rate, outlet temperature of working fluid, temperature gradient, overall heat transfer rate and the thermal losses.

(Invited) Practical Considerations of Si Vs SiC Technology in High POWER, High Frequency Inverters for Industrial Induction Heating Applications

Introduction The paper aims to give practical technical considerations for choosing Si vs SiC technology in practical high frequency, high power inverters for industrial induction heating applications. Actual inverters, for this application, are resonant inverters, in a current of in a voltage–fed configuration. For current–fed inverters, the basic switch is a turn-on or turn-off controlled device (IGBT of MOS) in series with a diode, while in voltage–fed inverters the basic switch is a turn-on or turn-off controlled device with a diode in antiparallel. Si vs SiC diodes in high power inverters High power converters, both current-fed or voltage fed, require paralleling high frequency diodes. With Si technology, diodes have to be matched due to their negative thermal coefficient, making in this case, the use of SiC diodes a much more robust solution due to its positive thermal coefficient. Manufacturing as well as maintenance costs compensate the over cost of SiC technology. But on the other hand, many of the hardening application require a large number of power cycles and considering power cycling (PC) capabilities, the use of SiC diodes offers worst PC capabilities as the higher increase of the junction Temperature ΔTj due to higher body resistance of the SiC diode in comparison with the Si counterpart. For that reason, long term reliability has to be when using SiC diodes instead Si ones. The following figure shows the increase of the die temperature of SiC and Si diodes under the same conditions (1). Figure 1 Another aspect influencing the PC capacity is related the different material properties of both materials. Figure 2 shows that under the same junction temperature increase ΔTj, the power cycling capacity of SiC diodes is about one third of the equivalent Si Diodes (2). Figure 2 As a conclusion the use of Si or SiC diodes is a trade-off between paralleling and power cycling capabilities and the decision on the optimal diode technology is dependent on the application. Si IGBT vs SiC MOSFET in high power inverters SiC MOSFETs are specially adapted to high frequency applications as per their lower switching losses. The following figure shows the required number of semiconductor devices of a 240 kW/400 kHz induction welder as well as the better overall efficiency of the inverter (3). Figure 3 Figure 4 shows the 200 kW/ 400 kHz the developed all SiC inverter prototype for testing SiC technology capacity vs IGBT technology. Figure 4 Based on the experimental results from the above prototype, the curves for the optimal technology, depending the frequency in voltage-fed inverters for induction heating are shown in the next figure. Figure 5 Consequently, the above experimental results show that up to 100 kHz, IGBT is the optimal technology for induction heating inverters, while from 150 kHz until 500 kHz SiC technology offers better power capability. The range from 100 to 150 kHz can be optimal covered with IGBT technology and advanced control techniques (interleaved Pulse Density Modulation-PDM ) or with SiC technology with actual PDM controllers. Conclusions The replacement of Si diodes by SiC diodes improves robustness of high power inverters for industrial induction heating applications due to their ability to be paralleled, but in applications, as hardening, with a large number of Power Cycles, the direct replacement is questionable due to the lower Power Cycling capacity of SiC diodes vs Si ones. The use of SiC MOSFETs is specially encouraged in very high frequency induction, high power induction heating inverters, as in the case of welders operating at frequencies above 150 kHz. On the opposite, SiC technology does not give an optimal solution at lower frequencies than 100 kHz, being in that case SI-IGBT technology the optimal one. In the final paper a much more deeper view on the above considerations, based on our experimental results, will be described for the optimal use of Si vs SiC technology in high frequency, high power resonant inverters for industrial induction heating applications. Bibliography 1.- Ortiz González, J., Alatise O., Nobee N., Hu J., Mawby P., “ Electrothermal Considerations for Power Cycling in SiC Technologies” CIPS 2016 Proc.- Nürnberg. 2.- Herold Ch, Schaeffer M., Sauerland F.,Poller T., Lutz J., Schilling O., “ Power Cycling Capability of Modules with SiC Diodes” Proc. CIPS 2014 Conference. Nürnberg 3.- Dede, E. “A 100kW Full SiC Inverter for Induction Heating Applications”, Proc. ISiCPEAW 2015 Workshop. Stockholm 2015. Figure 1

Capacitor‐sharing two‐output series‐resonant inverter for induction cooking application

Induction heating (IH) technique has been widely used in industrial and domestic heating applications. In IH cooking applications, multi-output IH systems are increasing in demand. In this study, an inverter configuration is proposed for two-output IH cooking applications. The objective of this proposal is to reduce the component count and thereby the size of the circuit and cost. In this proposed configuration, two IH loads are connected to a full-bridge inverter output and these loads are sharing a common resonant capacitor. The output power is controlled using on–off control. Switching losses are reduced due to zero voltage switching operation. The two loads are independently controlled with high efficiency. The control logic of the proposed system is described in detail and prototype is designed, implemented and the validity is verified through experimental and simulation results.

An investigation of thermal stability of carbon nanofluids for solar thermal applications

Carbon nanofluids are engineered materials with controllable thermal and optical properties. Stable, high temperature operation (>20) of these fluids would enable them to improve upon – and eventually replace – pure fluids in many important commercial and industrial applications including applications in solar thermal collectors. To date, however, much of the nanofluids research focuses on low temperature (<100°C) applications and testing. For solar thermal collector applications, carbon nanofluids are uniquely well-suited due to their high absorptivity over the entire solar spectral range. This study pushes well beyond the 100°C mark by conducting a range of experiments to identify appropriate base fluids and functionalization methods to produce stable carbon nanotube (CNT)-based nanofluid dispersions at temperatures of up to 250°C to ensure their suitability for industrial heating applications (typically 100–250°C). Different forms of CNTs including, single-walled carbon nanotubes, double-walled carbon nanotubes and multi-walled carbon nanotubes were chemically functionalized to obtain stable dispersions in water, glycol and Therminol (a synthetic heat transfer oil). The stability of chemically functionalized carbon nanotube dispersions at different temperatures, 20, 80, 100, 150, 200 and 250°C, was investigated. The results of broadband UV–VIS–NIR spectroscopy showed no agglomeration in mildly oxidized multi-walled carbon nanotubes dispersed in Therminol when heated to 250°C, highlighting this low-cost composite medium as a potential candidate for use in high temperature nanofluid-based solar thermal collectors.

Experimental and numerical investigation of volumetric versus surface solar absorbers for a concentrated solar thermal collector

A low-profile concentrated solar thermal collector (<15cm in height) was proposed and investigated to demonstrate its potential to deliver heat energy in the range of 100–250°C. We use both experimental and numerical methods to investigate of the effect of modifying the absorber in this collector. As such, a volumetric absorber (consisting of a multi-walled carbon nanotube nanofluid contained within a glass tube) was compared against a conventional surface absorber (consisting of a black chrome-coated copper tube). The experimental and computational fluid dynamics (CFD) results were found to be in good agreement for the thermal efficiency of these two receivers.The analysis revealed that the vacuum-packaged volumetric receiver had an efficiency of 54% and 26% operating at 80°C and 200°C, respectively. This lower than a vacuum-packaged black chrome-coated receiver, which had an efficiency of 68% and 47% in the same concentrator, operating at the same temperatures, respectively. [Note that commercial linear concentration systems typically have efficiency in the range 44–57% at 200°C.] The inferior performance of the volumetric receiver was found to be due to higher reflective optical and radiative heat loss from the surface of glass tube. Overall, this study reveals that the proposed low-profile collector design is suitable for utilisation in industrial and commercial heating applications, but that volumetric absorbers will require anti-reflective and good selective coatings to be competitive with surface absorbers. If these challenges can be overcome, nanofluid receivers may have a cost/manufacturing advantage since glass-to-glass vacuum sealing is easier to achieve than metal-to-glass.

Influence of thermal losses on the incidence angle modifier factorization approach

Solar thermal applications for industries must be designed to operate at high temperature levels; however, the thermal dependency of the accuracy of the incidence angle modifier factorization has not been sufficiently analyzed. In this study, the annually delivered energy based on both factorized and non-factorized incidence angle modifier values were compared with each other. The integration was conducted for a typical meteorological year in Seville and Stockholm. Four collector types were considered: evacuated tube collector, MaReCo collector, Fresnel collector, and CCStaR collector. Thermal process parameters were shown to have an influence on the error made by the factorization approach; however, within the economically viable temperature range of an industrial heat application, this influence is not significant.

&lt;b&gt;Pulse Mask Controlled HFAC Resonant Converter for high efficiency Industrial Induction Heating with less harmonic distortion

This paper discusses about the fixed frequency pulse mask control based high frequency AC conversion circuit for industrial induction heating applications. Conventionally, for induction heating load, the output power control is achieved using the pulse with modulation based converters. The conventional converters do not guarantee the zero voltage switching condition required for the minimization of the switching losses. In this paper, pulse mask control scheme for the power control of induction heating load is proposed. This power control strategy allows the inverter to operate closer to the resonant frequency, to obtain zero voltage switching condition. The proposed high frequency AC power conversion circuit has lesser total harmonic distortion in the supply side. Modeling of the IH load, design of conversion circuit and principle of the control scheme and its implementation using low cost PIC controller are briefly discussed. Simulation results obtained using the Matlab environment are presented to illustrate the effectiveness of the pulse mask scheme. The obtained results indicate the reduction in losses, improvement in the output power and lesser harmonic distortion in the supply side by the proposed converter. The hardware results are in good agreement with the simulation results.

Investigations for performance enhancement of dual pressure HRSG in gas/steam combined cycle power plants

ABSTRACTA heat recovery steam generator (HRSG) is the vital equipment in a gas/steam combined cycle power plant (CCPP) which plays an important role in enhancing the overall performance of the plant. An HRSG is designed on the basis of the size of the gas and steam turbines used in the power plant. Therefore, the HRSG directly affects the performance of the CCPP and its optimisation based on physical design can improve the plant performance. In the present study, the plant data of the CCPP of NTPC Ltd. at Auraiya (U.P.), India, has been considered for study. A segmented finned model has been chosen as it is the preferred arrangement [Ganapathy, V. 2003. Industrial Boiler and Heat Recovery Steam Generator Design, Application and Calculation. New York: Marcel Dekker Inc.] and thermodynamic investigations have been carried out upon a dual pressure HRSG in a gas/steam CCPP from the perspective of maximum heat recovery and minimum pressure loss. The performance investigations of varying physical parameters of a dual pressure HRSG with segmented fins are useful for CCPP designers and for all those who are engaged in the area of heat recovery.

Physico-chemical properties of wood pellets from coppice of short rotation tropical hardwoods

The study investigated the physical and chemical properties of wood pellets from coppice of intensively cultured tropical hardwoods viz., Gmelina arborea, Acacia mangium and Paraserianthes falcataria. Proximate, ultimate and elemental analyses were performed to assess fuel properties of pellets from coppice feedstock. In general, physical and chemical properties of pellets from coppice biomass were within recommended limits for class A2 pellets under EN 14961-2. Pellets from coppice of tree species used in this study showed good potential for compressed solid fuel for industrial and residential heating applications.

Exergy and energy analyses of liquid food in an Ohmic heating process: A case study of tomato production

Abstract Six different voltage gradients ranging from 6 to 16 V/cm were used to evaporate water from tomato samples of 9.3 (kg water/kg dry matter) to a safer level of 2.3 (kg water/kg dry matter). Energy efficiency decreased from 100 to 55.53% with decreasing moisture content and increasing voltage gradient, while, exergy efficiency increased from 3 to 83.51% with decrease in moisture content (P Industrial relevance Due to the ability of the ohmic heating technologies to achieve rapid and reasonably uniform heating of electrically conductive materials its impact on food quality is of interest. Based on literature review, in ohmic heating process it could be possible to obtain efficiencies greater than 90% in an industrial process in which these losses were controlled by the wall insulation. However there is limited information on the exergy analysis of ohmic processes and systems, to the best of the authors’ knowledge. Exergy analysis becomes more crucial, especially for the industrial (large-scale) high temperature heating applications, and it can reveal whether or not and by how much it is possible to design more efficient thermal systems by reducing the sources of existing inefficiencies. This paper deals with the performance evaluation of ohmic heating process by applying exergy analysis.

Control Optimization through Simulations of Large Scale Solar Plants for Industrial Heat Applications

Abstract The European FP7 Project InSun; which started in April 2012; aims to demonstrate the reliability and efficiency of three different collector technologies suitable for heat production employed in diverse industrial processes in different climatic regions. These collectors are installed and will be monitored in detail over a period of almost two years. One of the plants is installed at Fleischwaren Berger GmbH located in Sieghartskirchen, Austria, a company which produces meat and sausage products. The second solar plant is installed at the company Laterizi Gambettola SRL (SOLTIGUA) located in Gambettola, Italy, which produces highly insulating hollow brick blocks for external walls of buildings. The control optimization and commissioning of the two solar plants has been carried out as a part of the InSun project. Considering measurements and results of simulations developed with dynamic models, potential improvements of the low-level control algorithms are presented for the two solar plants.

An experimental and numerical investigation of heat transfer distribution of perforated plate burner flames impinging on a flat plate

Heat transfer from perforated plate burner flame impinging on a flat plate finds importance in industrial (gas fired boiler) and domestic heating (household gas burner and commercial hotel gas burners) applications. A limited study on heat transfer distribution of this kind of burner plate is found in the literature. In the present work, high resolution heat flux is estimated by the inverse heat conduction (IHCP) technique based on use of analytical solution for semi-infinite medium for the impingement plate. Inline, star and staggered holes patterns with three different inter-hole distances (pitch) are considered in the present study. Methane–air premixed flame of Reynolds number varying from 50 to 600 and an equivalence ratio varying from 0.6 to 1.2 is considered. The hole to impingement plate distance is varied from 3 to 7. From the experimental results, it is found that the inline and staggered patterns have the same heat flux averaged over an area of 50 mm × 50 mm for different Reynolds number. The intermediate pitch of 7 mm is the optimal pitch over the entire mixture flow range considered in the present study. The specific fuel consumption for the star pattern is less by 40–60% as compared with the inline pattern for p/d = 1.67, Re = 50–300 and z/d = 3–7. A numerical simulation is carried out using CFD software to explain the shift in the peak heat flux away from the geometric intended location.

Capacity modulation of a cascade heat pump with the variation of compressor speed and electronic expansion valve opening

With the increased awareness on excessive energy consumption, increasing fuel cost and negative environmental impact (ozone depletion and global warming) of the major heat generation systems and processes, the ability of heat pumps to generate high temperature with very efficient use of energy and minimal environmental impact has gained lots of awareness over the years. Some domestic and most industrial heating and refrigeration applications demand very high temperature lifts. Single-stage cycles do not practically support these applications since their performance and reliability decrease greatly. High temperature generation can be successfully executed through the use of cascade heat pump. This study analyzes the effects of compressor speed and electronic expansion valve (EEV) opening on the performance of the cascade heat pump in heating mode. The rate of increase of capacity with high-stage (HS) EEV opening at higher HS compressor speed is larger than it at high low-stage (LS) compressor speed. The slope of the capacity with the HS EEV opening was much steeper at small opening range than that at large opening range. When the LS compressor speed increased, the maximum Coefficient of Performance (COP) occurred at larger HS EEV opening than the standard opening. The COP variation at the range of low HS compressor speed had smaller dependency on the LS EEV opening than that at the range of high HS compressor speed.

Heat transfer distribution for impinging methane–air premixed flame jets

Heat transfer by flame jet impingement is extensively used in industrial and domestic heating applications. The present experimental study proposes the application of an inverse heat conduction (IHCP) technique to obtain the heat flux distribution for methane–air premixed flame jet impinging on a flat plate. The heat flux distribution is studied for burner tubes of circular shape (d = 10 mm and 8.75 mm), square shape (width = 10 mm and 7.65 mm) and rectangular shape (19 mm × 9 mm). Methane–air premixed flame jet of Reynolds number varying from 600 to 2200 and an equivalence ratio of 1 is considered. The nozzle to burner tip distance is varied from 2 to 6. Axis switching is observed for non-circular shaped burner flame jets. Correlations for local Nusselt number and effectiveness distribution are proposed for circular and square burners by direct measurement of the adiabatic wall temperature. The heat transfer coefficients and adiabatic wall temperatures are validated with the experimental heat flux data available in the literature. The non-dimensional flame premixed cone height (ratio of flame premixed cone height to the distance of the burner tip from the impingement wall) alone governs the Nusselt number and effectiveness.

A novel method of estimation of adiabatic wall temperature for impinging premixed flame jets

Impinging flame jets are widely used in industrial and domestic heating applications. Most of the studies in literature report heat flux and the wall temperature which are dimensional parameters. The proper way of presenting this data is in the form of Nusselt number and effectiveness which are non-dimensional parameters. In order to determine the Nusselt number (heat transfer coefficient), the knowledge of adiabatic wall temperature is essential. In the present work, a hybrid analytical–numerical method is proposed to evaluate the adiabatic wall temperature by computing the steady state adiabatic wall heat flux. Circular burner of 11.5mm diameter is used for impingement on a flat quartz plate. The Reynolds number range is 600–2400, ratio of distance from tube burner tip to impingement plate to tube burner diameter is 2–6 and the equivalence ratio is 1. The adiabatic wall temperature estimated by the present hybrid analytical–numerical method is in good agreement (within 3–5%) with the experimentally measured adiabatic wall temperature. Radial distribution of Nusselt number and effectiveness for circular tube burner are presented based on the adiabatic wall temperature estimated by the present hybrid analytical–numerical method.

Improving the Reliability of Series Resonant Inverters for Induction Heating Applications

This paper analyzes a high-power (100-kW) high-frequency (50-kHz) voltage-fed inverter with a series resonant load circuit for industrial induction heating applications which is characterized by a full-bridge inverter composed of isolated-gate bipolar transistors and a new power control based on phase-shift (PS) control. This power control circuit incorporates a load-adaptive variable-frequency controller and automated blanking time management in order to allow the inverter to work in zero-voltage switching for all output power levels and load conditions. An important improvement of the inverter reliability is achieved by choosing an appropriate and novel switching sequence for the PS inverter. The results are verified experimentally using a prototype for induction hardening applications. A comparative study between the proposed and standard PS power control will be made.

Levelized Cost of Heat for Linear Fresnel Concentrated Solar Systems

In this paper, a deep investigation upon levelized cost of heat (LCOH) produced by small-scale solar linear concentrating Fresnel collectors (CSLFC) is proposed. Solar industrial process heat applications have temperature requirements from about 60°C to 260°C. CSLFCs can effectively integrate conventional fossil fuel thermal systems. The study is addressed to assess technology cost projection needed to achieve competitive LCOH. So, on the basis of a framework specifically developed for these economic assessments, the best investment scenarios, in terms of industrial application, geographical location and technical design solutions, where to effectively apply the technology of CSLFC, are highlighted.The analysis has been focused on specific cost of several existing CSLFCs associated with declared performances at different operating temperatures. Two main classes of CSLFC with different total efficiency (optical and thermal) corresponding to various design solutions and specific cost were selected. The expected performances in the whole application temperature range have been evaluated through Glayx Tech proprietary simulation code, including optical and thermal unsteady analysis.A huge database coming from full CSLFC simulation varying latitude, yearly DNI, operating fluid, outlet temperature, thermal storage options, has been collected. CLSFC design and performance requirements are the key-choice to achieve competitive LCOH: the use of high efficiency – high cost components is not always rewarding in terms of final LCOH and must be attentively decided basing on site, irradiation, heat quality and LCOH target. In this perspective, CLSFCs are the most promising for industrial small scale heat applications since they show the greatest potential to reduce manufacturing costs.

Formulation Techniques for Nanofluids

Fluids with suspended nanoparticles, commonly known as nanofluids, may be formulated to improve the thermal performance of industrial heat transfer systems and applications. Nanofluids may show enhanced thermal and electrical properties such as thermal conductivity, viscosity, heat transfer coefficient, dielectric strength, etc. However, stability problems may arise as nanoparticles usually have the tendency to agglomerate and sediment producing deterioration in the increment of these properties. In this review, we discuss patents that report advances in the formulation of nanofluids including: production methods, selection of components (nanoparticles, base fluid and surfactants), their chemical compositions and morphologies, and characterization techniques. Finally, current and future directions in the development of nanofluid formulation are discussed.