Heat Source Temperature Research Articles

Parametric analysis and comprehensive multi-criteria evaluation of double-stage organic Rankine cycle

Double-stage organic Rankine cycle (DORC) is a more effective mechanism of circulation for recovering heat released from industrial wastewater. It is crucial to determine the optimum operating circumstances for the DORC system, and its effectiveness cannot be effectively assessed by applying a single objective evaluation approach. The AHP-entropy analysis method is utilized to establish a three-level assessment system, taking into account several indicators, in order to execute a thorough study of the DORC system. Eight organic fluids, including R113, R124, R1233zd(E), etc, are chosen as the working mediums of the DORC system. The results demonstrate that the heat source temperature exists maximum value that match the working fluids under the impact of the pinch point temperature difference and the critical temperature of the working medium. When the evaporation pressure increases, the whole system performance improves, according to the AHP-entropy analysis of the operating state that corresponds to the single goal optimum value. When the critical temperature of the working medium is approximately 50 °C above the hot water temperature for a given heat source, the system performs more effectively. Additionally, when the heat source temperature is close to the critical temperature of the eight organic fluids, the DORC system operates more effectively.

Multi-stage humidification–dehumidification system integrated with a crystallizer for zero liquid discharge of desalination brine

Desalination plants discharge a massive volume of brine every day, which negatively affects the ecosystem, particularly the subsurface ecology and marine life. To mitigate the brines' detrimental effects on the environment and facilitate the recovery of salt crystals and freshwater, the Zero Liquid Discharge (ZLD) approach was proposed. This study proposes four different configurations of multistage humidification dehumidification systems integrated with a crystallizer, exploring their energy and economic implications. Key findings from the study include the higher Gained Output Ratio (GOR) in series configurations due to lower temperature differences, resulting in lower heater energy consumption. The crystallizer significantly enhances water productivity, but it is a major consumer of both electricity (85%) and thermal energy (50.45–57.7%) in the system. Increasing the heat source temperature reduces the Specific Electrical Energy Consumption (SEEC) and the specific area while slightly increasing the Specific Thermal Energy Consumption (STEC). Elevated cooling water temperature raises SEEC and specific area but has negligible effects on STEC. Higher feed water flow rates increase SEEC but lower both STEC and specific area. Feed salinity elevation decreases productivity, SEEC, STEC, and specific area. The crystallizer constitutes 15.43–26.44% of the total capital cost, with series configurations incurring higher costs. Unit freshwater production costs, considering salt selling, range from 1.733 to 4.821 $.m−3. In a waste heat scenario, parallel configurations become profitable, where freshwater can be distributed at zero cost, while the produced salt crystals can be sold at an even lower price of $58.09 per tonne and $57.04 per tonne, respectively.

Optimal discharging of solar driven sorption thermal battery for building cooling applications

In this study, optimal discharge conditions of sorption thermal battery (STB) are determined for stable supply of the building cooling load based on different load patterns. Parametric analysis is conducted to ascertain the influence of heat source temperature and the mass flow rate ratio between the solution and the heat transfer fluid on the performance of the STB. The maximum values of energy storage density (ESD) and coefficient of performance (COP) are estimated as 207.73 kWh/m3 and 0.74, respectively. The daily transient behaviors of STB are examined in detail, and the optimal solution charge and the solution flow rate are quantified based on the building types (residential, hospital, hotel, and office). For a building with an air conditioning floor area of 181.63 m2, the most suitable cooling load response is observed in the hotel scenario. The minimum deviated cooling output from the building load is 8.69%. Concurrently, COP and ESD are estimated of 0.69 and 101.99 kWh/m3. This paper demonstrates the cooling load responsiveness and optimal operating point of STB based on building load pattern. Additionally, a dimensionless number is defined to generate the discharge trend and enable to predict COP and ESD.

A novel finite element model for thermally induced machining of Ti6Al4V

Titanium alloys, including Ti6Al4V, are considered hard to cut materials due to their low thermal conductivity, low elastic modules and high chemical reactivity. This leads to high cutting forces and high surface roughness. Thermal assisted machining is used to improve the machinability of Ti6Al4V. To improve the performance of thermal assisted machining, this study investigates how are the cutting force, cutting zones temperatures, chip morphology, shear plane angle and strain rate are affected by the cutting speed and the heating element characteristics during thermally assisted machining of Ti6Al4V. A 2D numerical model simulating orthogonal cutting process was created using ABAQUS/Explicit software. In this model, Johnson Cook constitutive model was used to describe the material behavior during cutting process. Also, Johnson Cook damage model was used to simulate chip separation mechanism. After the verification of the model by comparison with results found in the literature, a number of simulations were run at different levels of four factors: cutting speed (40, 60, 80, 100, 120 and 140 m/min), heat source temperature (200, 400 and 600 °C), heating source distance from the cutting tool (0.3, 0.6 and 0.9 mm) and heating source size/diameter (0.6, 0.8 and 1 mm). Taguchi L18 orthogonal mixed level design was used to plan for simulation runs using Minitab software. ANOVA analysis was used to investigate the significance of the four factors. The response table of means and the main effect of means are used to compare between the four factors and find their ranking. Based on 95% confidence Interval (CI), the results show that cutting speed has a significant effect on cutting force, strain rate, chip compression ratio, cutting tool nose temperature, cutting tool and chip temperature in the secondary deformation zone, average chip thickness at peaks and average chip thickness at valleys and average pitch. This conclusion is based on the P-values which are << 0.05 and the contribution which reaches 99.01%. Similarly, based on P-values (< 0.05) and contributions (up to 12.16%), the heating source temperature has a significant effect on average chip thickness at valleys, chip compression ratio and strain rate. The cutting speed has Rank 1 among the four factors affecting cutting force, cutting zones temperatures, chip morphology, shear plane angel and stain rate. The effect of instantaneous heating directly before cutting process is negligible compared to the effect of plastic deformation and fracture mechanism in the cutting zone.

Multi-objective optimization of the dual-pressure organic Rankine cycle system based on the orthogonal design method under different external conditions

The dual-pressure organic Rankine cycle (DPORC) system can obtain a better temperature match between the heat source and working fluid due to the existence of two evaporation processes, which can significantly improve the utilization rate of the heat source and reduce the irreversible loss. Firstly, single-objective optimization of the DPORC system is conducted based on the orthogonal design method with thermal efficiency, exergy efficiency, electricity production cost (EPC) and annual emission reduction (AER) as the performance indicators, respectively. Then, multi-objective optimization of all performance indicators is carried out based on the comprehensive scoring method. Finally, the contribution rates of the operation parameters and the optimal working conditions under different external conditions are investigated. The results show that condensation temperature, high-pressure evaporation temperature and turbine isentropic efficiency are the most critical parameters for system comprehensive performance. When heat source temperature is 170 °C, thermal efficiency, exergy efficiency, EPC and AER under the optimal working conditions are 11.91%, 48.46%, 2.71 × 10−2$/kWh and 11.17 × 105kg, respectively. With the increase of heat source temperature, condensation temperature and turbine isentropic efficiency always have an important influence on system comprehensive performance. The contribution rates of high-pressure evaporation temperature and low-pressure evaporation temperature increase and decrease, respectively. Better comprehensive performance can be obtained by using HC working fluid.

Thermodynamic analysis of La and Mm based metal hydride pairs for solar energy-driven cold storage applications

Cold storage plays a vital role in many applications such as agricultural and food processing units. Metal hydride-based sorption cold storage systems are environmentally friendly as they use hydrogen. In the present study, La and Mm metal hydrides based cooling system is proposed for cold storage application which can work using solar energy. Ten metal hydride (AB5) pairs were selected for the thermodynamic analysis of the cold storage module. The minimum cooling temperature and maximum heat source temperature required for each pair are calculated. Hydrogen storage and thermodynamic properties of La0.95Ce0.05Ni5, La0.85Ce0.15Ni5, and MmNi4.5Al0.5 are obtained by measuring pressure concentration isotherms at different temperatures. The effect of source temperature and cooling temperature on COP, Exergy COP, and specific cooling load (SCL) are studied. MmNi4.6Fe0.4/MmNi4.6Al0.4 pair has attained a theoretical maximum COP and exergy COP of 0.784 and 0.89 respectively at a heat source temperature of 60 °C and cooling temperature of 2 °C. However, at higher heat source temperature La0.95Ce0.05Ni5/MmNi4.5Fe0.5 has better performance than MmNi4.6Fe0.4/MmNi4.6Al0.4. In addition, the effect of cooling load on the size of the system for cold storage of 10 kg apples is also studied. For cold storage of 10 kg apples at 2 ℃, La0.95Ce0.05Ni5/ LaNi4.7Al0.3 has the best performance with a COP of 0.693 and minimum total weight of 18.35 kg.

Performance simulation study of multi-stage compression-throttle water working medium high-temperature heat pump system

In order to meet the demands of industrial high temperature heat and waste heat recovery in an economical and low-carbon manner, there has been a growing interest in the high-temperature heat pump using water as working medium. The study aims to address the issue of higher exhaust temperature in water working medium heat pumps resulting from a substantial increase in temperature, especially for the large temperature difference system which needs to adopt multi-stage compression. This will be accomplished by proposing a new and energy-efficient high-temperature heat pump system that utilizes water as the working medium. The optimized system combining with self-circulating water spraying and multi-stage compression, which can significantly reduce exhaust superheat and steadily improve system performance. A thermodynamic analysis was conducted on both two-stage and three-stage high-temperature heat pumps, taking into account the improved structure. The results indicate that the three-stage compression-throttle type can achieve the highest maximum water spraying ratio and the lowest exergy loss. This can effectively decrease the superheat of the compressor exhaust and enhance the overall system performance. Furthermore, in the three-stage compression-throttle system, when the evaporation temperature is set at 100 °C with a temperature increase of 40 °C, a mere 0.01 % augmentation in the water spraying ratio results in approximately a 0.0776 uplift in the COP of the water working medium system. This notable observation suggests that the implementation of self-circulating water spraying considerably enhances the system’s overall performance. Subsequently, an analysis of the corresponding design and operating parameters was conducted. It is important to note that the temperature of the waste heat source and the rotational speed of the compressor are the two key parameters that significantly impact the operation of the system. By this study, it provides some theoretical guidance for practical engineering applications.

Self-cleaning, energy-saving aerogel composites possessed sandwich structure: Improving indoor comfort with excellent thermal insulation and acoustic performance

In the context of “carbon neutrality and emission peak”, aerogel that can meet national energy saving and emission reduction requirements while achieving efficient noise reduction has become a hot research topic. However, the development of multifunctional applications is greatly limited by the fact that pure aerogel usually exhibits relatively homogeneous properties. In this paper, SA@UGFW sandwich aerogel composites with functional silanes for structural strengthening were developed. SA@UGFW not only demonstrates ultra-lightweight (58 kg/m3) and high-strength properties (0.1 MPa) but also highly efficient self-cleaning capability (water contact angle ≈ 152.4°). The sandwich aerogel created super-efficient thermal insulation (0.015–0.017 W/(m·K)) and sound absorption performances (αmax = 0.93, NRC = 0.51, 9.77 mm). SA@UGFW exhibited a cold surface temperature of 54.2 ℃ and a ΔT of 145.8 ℃ when the heat source temperature was 200 ℃, despite the sample thickness of only 9.77 mm. At this point, ΔT was higher than 70 % of the heat source temperature. The thermal conductivity of SA@UGFW was as low as 0.00975 W/(m·K), even in −40 ℃ environment. In addition, the sandwich aerogel also showed 0.0204 W/(m·K) of low thermal conductivity following ultra-low temperature (-196 ℃) treatment for 168 h. Simulation results show that aerogel building insulation reduces heating energy savings by 31.00 % and cooling energy savings by 27.34 % compared to traditional insulation. Therefore, the sandwich aerogel with multiple functions reported in this paper achieved the enhancement of indoor comfort and was expected to be widely applied in the construction field.

Energetic performance of a solar driven absorption refrigeration system integrated with humidification dehumidification desalination system

Integrating cooling and desalination systems with a single heat source is a shortcut technique to meet the shortage of fresh water and energy as well as enhancing the efficiency of energy utilization. In this paper, the energetic performance of a double effect vapor absorption refrigeration system integrated with humidification-dehumidification desalination system has been optimized·H2O–LiCl achieves higher system primary energy ratio and needs lower heat source temperature by 5 °C and 11 °C at evaporation temperature of 10 °C and 4 °C, respectively as compared with H2O–LiBr. Therefore, a parametric study has been performed to get the optimum operating conditions for the integrated system using H2O–LiCl as working pair by varying generation, condensation, and evaporation temperatures. The optimum system conditions are generation, condensation, and evaporation temperatures of 103 °C, 103 °C and 7 °C, respectively. The corresponding system COP, GOR and EUF are 1.471, 2.391 and 3.863, respectively. Finally, the transient performance of the proposed integrated system assisted by solar energy has been evaluated for Marsa-Matrouh city in Egypt. The proposed integrated system could save 71.2 % of the input energy without solar assistance and 88.5 % with solar assistance as compared with separated systems.

Investigating maximum temperature lift potential of the adsorption heat transformer cycle using IUPAC classified isotherms

Adsorption heat transformer (AHT) cycle is capable of upgrading the low-grade waste heat to a higher temperature. The maximum temperature lift of the AHT cycle can represent its theoretical performance limit. However, such a metric is currently absent from the literature due to the scarcity of fundamental studies on the heat upgrading sorption cycles. Therefore, in the present study, three models are proposed to derive the ‘maximum temperature lift’ of a typical AHT cycle: (i) heat engine heat pump representation, (ii) the 2nd law of thermodynamic formulation, and (iii) complete preheating. The first two models are developed based on the reversible cycle approach, whereas the 3rd model incorporates adsorbed phase properties. Thus, the first two models might be considered as the formulations for the thermodynamic temperature limit (lift) of an AHT cycle while the 3rd model is specific to the nature of a particular adsorbent + adsorbate pair which might be close to practical applications. The reversible models predict a maximum temperature lift of 22∘C to 58∘C for heat source temperatures between 50∘C to 80∘C. The 3rd model exhibits lower values of maximum temperature lift compared to the reversible models, owing to the inclusion of material properties in its formulation. The performance of the models is demonstrated by determining the maximum temperature lift of four water-based adsorption working pairs, each featuring distinct IUPAC (International Union of Pure and Applied Chemistry) isotherm types. This study will help propel the working pair selection and the thermodynamic modeling of sorption cycles to achieve its near maximum capability.

Exploration and optimization on thermoelectric conversion of waste heat of blast furnace slag

The iron and steel industry involves processes that generate abundant waste heat resources. The energy utilization rate can be improved by using thermoelectric conversion technology to directly convert waste heat into electric energy through the Seebeck effect. In this study, a special waste heat recovery device, designed according to the production environment characteristics of blast furnace (BF) slag, is proposed. The heat transfer process between the BF slag and thermoelectric generator (TEG) is analyzed, and the heat source temperature field model is constructed. Based on the temperature distribution, the size of the TEG is determined. The heat transfer behavior of the thermoelectric module (TEM) is optimized using a non-contact heat collection mode and a water-cooling device, which improves the temperature gradient. A thermal conductive silicone grease is introduced as the thermal conductive layer to achieve uniform distribution of the hot end temperature and improve the heat transfer capacity of the collector plate. After design optimization, the temperature gradient of the TEM increased by 15.3 °C and 38 % on average. The experimental results show that a single TEM can generate about 3.084 J of electric energy. Using 70 kg of BF slag with an initial temperature of 600 °C, the TEG per unit installed area can generate about 1.23 kJ of electric energy in 1 h. This study provides an important foundation for research in thermoelectric conversion, utilization of BF slag waste heat and sustainable development of the iron and steel industry.

Thermodynamic analysis of novel mixtures including siloxanes and cyclic hydrocarbons for high-temperature heat pumps

This paper presents the investigation of zeotropic binary fluid mixtures containing cyclohexane (critical temperature above 200 °C) as the base fluid with R600, R600a, R601, R601a, R1336mzz(Z), R1234ze(Z), R1233zd(E) and cyclopropane (critical temperatures between 100 °C and 200 °C). For pure components and their mixtures, the performance of the vapor compression system with an internal heat exchanger was analysed at 50 °C and 80 °C heat source and sink inlet, respectively. Variation of the heat source temperature difference and the internal heat exchanger pinch point temperature difference at supply temperatures (140–170 °C) were also investigated. A pinch point temperature difference of 5 K was maintained for the evaporator and condenser. An increase of 6.59 % in COP was obtained with the zeotropic mixture of cyclohexane/cyclopropane compared to that of pure cyclopropane. The design point analysis showed that increasing the heat source temperature difference and internal heat exchanger pinch point temperature difference reduces the COP. The adopted mixture criteria increased the performance between 3.23 % and 3.91 % with respect to standard working fluids like R1233zd(E) and R601, for a 170 °C supply temperature. With this promising thermodynamic analysis in a subcritical operation, the cyclohexane/cyclopropane mixture has prospect of full integration heat pump design.

Preparation, Microstructure and Thermal Properties of Aligned Mesophase Pitch-Based Carbon Fiber Interface Materials by an Electrostatic Flocking Method.

The mesophase pitch-based carbon fiber interface material (TIM) with a vertical array was prepared by using mesophase pitch-based short-cut fibers (MPCFs) and 3016 epoxy resin as raw materials and carbon nanotubes (CNTs) as additives through electrostatic flocking and resin pouring molding process. The microstructure and thermal properties of the interface were analyzed by using a scanning electron microscope (SEM), laser thermal conductivity and thermal infrared imaging methods. The results indicate that the plate spacing and fusing voltage have a significant impact on the orientation of the arrays formed by mesophase pitch-based carbon fibers. While the orientation of the carbon fiber array has a minimal impact on the shore hardness of TIM, it does have a direct influence on its thermal conductivity. At a flocking voltage of 20 kV and plate spacing of 12 cm, the interface material exhibited an optimal thermal conductivity of 24.47 W/(m·K), shore hardness of 42 A and carbon fiber filling rate of 6.30 wt%. By incorporating 2% carbon nanotubes (CNTs) into the epoxy matrix, the interface material achieves a thermal conductivity of 28.97 W/(m·K) at a flocking voltage of 30 kV and plate spacing of 10 cm. This represents a 52.1% increase in thermal conductivity compared to the material without TIM. The material achieves temperature uniformity within 10 s at the same heat source temperatures, which indicates a good application prospect in IC packaging and electronic heat dissipation.

Structural Study of the Thermoelectric Work Units Encapsulated with Cement Paste for Building Energy Harvesting.

Cement-based material encapsulation is a method of encapsulating electronic devices in highly thermally conductive cement-based materials to improve the heat dissipation performance of electronic components. In the field of construction, a thermoelectric generator (TEG) encapsulated with cement-based materials used in the building envelope has significant potential for waste heat energy recovery. The purpose of this study was to investigate the effect of cement-based materials integrated with aluminum heatsinks on the heat dissipation of the TEG composite structure. In this work, three types of thermoelectric work units encapsulated with cement paste were proposed. Moreover, we explored the effect of encapsulated structure, heat dissipation area, the height of thermoelectric single leg, and heat input temperature on maintaining the temperature difference between the two sides of the thermoelectric single leg with COMSOL Multiphysics. The numerical simulation results showed that under the conditions of a heat source temperature of 313.15 K and ambient temperature of 298.15 K, the temperature difference between the two sides of the internal thermoelectric single leg of Type-III can maintain a stable temperature difference of 7.77 K, which is 32.14% higher than that of Type-I and Type-II (5.88 K), and increased by 26.82% in the actual experiment. This work provides a reference for the selection and application of TEG composite structures of cement-based materials combined with aluminum heatsinks.

Experimental and numerical analysis of variable cross-section channel liquid cooling plate for server chips thermal management

Utilizing high-performance chips results in increased heat generation, necessitating more effective heat dissipation method. To address challenges in microchannel liquid cooling plates for server chips cooling the study presents the variable cross-section channel liquid cooling plate designs. To investigate the effect of channel structure on the performance of liquid cooling plate, two types of samples, one featuring side wall ribs and bottom cavities (SC) and the other featuring side wall ribs and bottom waves (SW), are evaluated through experimental analyses under various heating power and flow rate conditions. Comparing their performance to a conventional rectangular channel (RC) liquid cooling plate, their heat transfer and flow attributes were assessed. Finally numerical analysis was conducted to investigate the flow behavior inside the channel and extreme performance prediction were made using the numerical study. Results demonstrate that the SC and SW designs outperform the RC in terms of heat transfer capabilities, despite having the weaker flow characteristics. Under 300 W heat source power, the SW variants enable the heat source surface temperature to stay below 77.8 °C with a 194 mL/min flow rate. Notably, the SW variant showcases lower average heat source surface temperature and demonstrates lower pressure drop compared to the SC variant. As the flow rate increases, the heat transfer efficiency of the SW variant is further amplified while simultaneously highlighting the relatively suboptimal flow behavior of the SC variant. Predictive numerical models underscore that the SW variants offers improved thermal performance when subjected to high heat source power scenarios. Remarkably, under the heat source power of 500 W, a mere augmentation in flow rate proves sufficient to reduce the heat source temperature below the prescribed threshold value. The combination design of side wall ribs and bottom waves should enable a low cost, simple and high efficiency electronics cooling.

Waste Heat Conversion to Power via Organic Rankine Cycle

several studies have been carried out on how to recover waste heat using Organic Rankine cycle. Each study applied different working conditions, power scale and cycle configuration, hence an assessment of working fluids is given for specific case. As a result, no single working fluid have been identified that would meet an entire heat source temperature levels. This motivated us to examine various substances for use as working fluids for subcritical ORC systems operating in the temperature range (543 - 633K). In this study, with a given finite thermal source, performance of working fluid candidates are evaluated and assessed using four criteria: thermal efficiency, exergy efficiency, total exergy destruction and net power output. Results of the study indicate that from a performance point of view, the linear alkanes such as nonane seem to be a suitable fluid in the temperature range (543-573K). Beyond aforementioned temperature range it appears that aromatic hydrocarbons such as toluene, ethylbenzene, P-xylene, O-xylene, propylbenzene preformed better. Under this condition, they represent comparably similar proposed screening criteria parameters and comparably high evaporating pressure, with only occasional slight differences between them.

Low-temperature ammonia absorption refrigeration system based on the temperature difference uniformity principle: Optimization analysis

AARS (ammonia absorption refrigeration system) is one of the effective ways to utilize low-temperature waste heat below 100 °C for industrial applications. This novel system of LT-AARS is designed based on the principle of temperature difference uniformity for improving the overall COP. The partial condenser at the distillation section is adopted to achieve the purity of ammonia to more than 99.9 % with a small reflux ratio. A thermodynamic model is established to analyze the influence of the optimized distillation process on system performance and exergy loss. These modifications reduce the temperature difference uniformity factor from 1.12 to 1.025 and improve the COP from 0.414 to 065. Meanwhile, it is proved that the LT-AARS protocol is reasonable and effective by comparing the experimental values with the theoretical model. The exergy loss of the absorber and distiller accounts for about 55 % of the total exergy losses of LT-AARS. With the increases in refrigeration temperature from −15 to 5 °C and heat source temperature from 80 to 100 ℃, the COP can reach a maximum of 0.77. ECOP first increases sharply and then decreases slowly with the increase of refrigeration and heat source temperature, and ECOP has a maximum value. The optimal range of △x for LT-AARS varies from 5 % to 10 %. The COP and ECOP of the LT-AARS are more than 0.6 and 0.3, respectively.

Heat and Mass Transfer Characteristics of Oily Sludge Thermal Desorption

Oily sludge is a loose material containing solid and multiple liquid components. Thermal desorption is an efficient method of disposing of liquids from oily sludge. Most existing studies have mainly discussed the effect of some external process parameters on thermal desorption, with little discussion on the heat transfer characteristics and the variation in the wet component mass of oily sludge under heating. Small-scale experiments have been performed to measure the rise in temperature and liquid phase content change of the sludge during heating. The temperature rise rate increases with material density and increases faster during the initial heating stage, while it slows down as the liquid phase evaporates. The adhesive shear stress is determined by measuring the pulling force of the test rod, which decreases with decreasing water content and increases significantly with decreasing oil phase content. Heat transfer and energy distribution models have been developed to calculate the rise in the temperature of materials and the evaporation of contained liquids. The heat and mass transfer processes are obtained from simulation calculations by taking the initial material with a mass content of 25% water and 10% oil under a heating temperature of 500 °C. When the heating time reaches 135 min, the drying region reaches the boundary of the test container, at which the material temperature exceeds 350 °C. During the evaporation of different liquid-phase components, there are multiple segments in the corresponding temperature curves. The processing time and heat source temperature can be reasonably determined by analyzing the temperature rise of the material, and the effect of the disposal of liquids from oily sludge can be predicted by analyzing the changes in liquid content. The results may guide the formulation of process parameters for engineering project schemes for oily sludge disposal.

Ignition behavior of a mixture of brown coal and biomass during the movement of fine particles in a hot air flow

The combustion of brown coal, biomass and their mixtures was studied experimentally and analytically. The experimental research was conducted using a laboratory setup that reproduced the conditions of combustion of pulverized solid fuel in a boiler furnace. Thermogravimetric analysis was employed as part of the analytical study to determine the key characteristics of combustion of solid fuels, such as temperatures at which the ignition and burnout occur, as well as the combustion index. Scanning electron microscopy was utilized to analyze the surfaces of coal and wood particles to detect pores, cracks and channels. To determine the tendency of the solid fuel mixture to slag heat exchangers in boiler furnaces, the ash residue characteristics (iron oxide deposits, active alkali, calcium sulfate compounds) were obtained. Biomass is more reactive than brown coal. Its ignition delay times at 500 °C and 750 °C are 57 % and 25 % lower, respectively, than those for coal. The higher the biomass content in the solid fuel mixture, the lower the ignition delay time. The heating source temperature at which the coal/biomass fuel mixture ignites corresponds to the temperature at which biomass ignites. With a larger proportion of biomass, the temperature during the fuel mixture combustion goes down, while the combustion index increases. On the basis of the findings of the conducted research, optimal proportions of solid fuel components were found (80 % brown coal, 20 % biomass). Also, fuel preparation and feeding systems for pulverized fuel combustion and fluidized bed combustion of optimal fuel mixtures in a coal-fired boiler furnace were proposed.

Waste heat recovery from the biomass engine for effective power generation using a new array-based system

Thermoelectric generator (TEG)-thermosyphon-based heat recovery system (HRS) for harvesting the heat from the high temperature sources is a well-known technology for power generation. However, various thermal resistances (a total of nine) are involved in the thermosyphon-based HRS between the heat sources and TEGs which generate irreversibility that ultimately reduces its performance. In this work, a new design of HRS i.e. TEG-array-based is proposed for effective power generation even at low temperatures of sustainable heat source by minimizing the thermal resistances. This TEG-array-based HRS is driven by a salt gradient thermal storage device (SGTSD) which is used for efficiently recovering and storing of sustainable waste heat generated from a biomass(renewable energy)-based engine-generator. The proposed system is experimentally studied to analyse the temperature variations in SGTSD, characteristics of sustainable waste heat temperature, and performance features of TEGs in terms of obtained electrical parameters, output power and conversion efficiency. The experimental results showed that the maximum open circuit voltage, output power and conversion efficiency of TEG are obtained as 81.62V, 7.438W and 4.63\\% respectively. With this proposed system, seven thermal resistances (out of total nine) are totally eliminated while the others two are lowered that leads to effectively transfer the energy from sustainable heat source to TEGs via minor equivalent thermal resistance of 0.01198oC/W. The proposed system is found to be capable of charging a 12 V, 80 Ah heavy-duty battery for real life applications.