Thermal Losses Research Articles

Influence of low-density polyethylene addition on nitrogen transformation during sludge protein pyrolysis

Co-pyrolysis of sludge and waste plastics is a long-term strategic approach for producing valuable fuels. However, sludge is characterized by a high protein content, which serves as a significant source of nitrogenous components in bio-oil. To improve the quality of pyrolysis products, the present study investigated the effect of low-density polyethylene (LDPE) on nitrogen transformation during the pyrolysis of sludge protein (SP). The study findings indicated that LDPE addition reduced the amount of solid residue owing to the interaction between SP and H radicals generated by LDPE pyrolysis. The thermal weight loss difference consistently remained below 0 when the SP-to-LDPE mixing ratio was 7:3, indicating that LDPE promotes the pyrolysis of SP. For the analysis of nitrogen-containing products during pyrolysis, LDPE addition significantly reduced the levels of nitrogen-containing compounds in the bio-oils of glutamate (Glu), histidine (His), and tyrosine (Tyr). Specifically, at 600°C, Glu, His, and Tyr in the bio-oils decreased by 31.4%, 33.3%, and 34.38%, respectively. No significant changes were observed in the nitrogen content within the pyrolysis char of Glu and His. However, all three amino acids exhibited a significant increase in the formation of NOx precursors due to the attack on the nitrogen positions of the heterocyclic nitrogen species by the H radicals generated by LDPE. This study contributes to research on the impact of LDPE on nitrogen migration and conversion during the pyrolysis of SP, laying the foundation for subsequent studies on pollutant removal reactions.

Assessing the efficacy of flat-plate solar collectors using nanofluids in the climatic context of Kirkuk city, Iraq

Solar energy is a key renewable energy source. Research and development have focused on enhancing the heat transfer coefficient, heat gain, and practical efficiency of solar systems. The aim of this study is to evaluate the performance of a flat solar panel collector using a nanofluid under conditions in the city of Kirkuk/Iraq, 35° latitude and 45° longitude, in terms of practical calculation of thermal efficiency. The study included making two solar collectors, one traditional and the other improved using a nanofluid (CuO). The CuO/Water nanofluid was prepared with a volumetric concentration of 0.25 % by mechanical mixing and then ultrasonic mixing to homogenise the particles and eliminate the agglomerations that form inside the fluid. Practical testing was conducted for the two solar collectors, one using distilled water and the other using the nanofluid, during four months (January, February, March, and April) of the year 2023. The experiments revealed that the efficiency progressively improves from 9:00 a.m. to 1:00 p.m. This increase is attributed to solar radiation’s decreasing intensity post 12:00 p.m., while thermal storage and minimised thermal losses continue to contribute. After 2:00 p.m., the efficiency dwindles due to the declining solar radiation intensity. The practical efficiency of a 0.25 % nanofluid (CuO) attains its zenith at a mass flow rate of 0.015 ls−1. Higher mass flow rates enhance heat transfer within fluid-filled tubes. The collector efficiency at this flow rate ranges from 31.66 % in January to 44.44 % in April.

An Advanced Propulsion Motor With Enhanced Winding Cooling System for a Solar-Powered Aircraft

Solar-powered aircraft are being upsized and required to carry more payloads, which poses great challenges for propulsion motors, especially for their cooling considering extreme lightweight. Due to remarkable thermal performance, heat pipes (HPs) become one of the most promising solutions for aircraft propulsion motors. However, this may also lead to extra losses, which requires a more intensive study to maximize HP thermal benefits and minimize motor losses. In this paper, a propulsion motor with an HP-based winding cooling system is developed, and the effects of HP insertion on motor performance are investigated. Firstly, a motor topology is proposed, and five HPs of different sizes are selected from the market as candidates, with their thermal properties experimentally measured. Then, an appropriate HP size is determined based on a comprehensive evaluation of the thermal performance and losses of the motors with candidate HPs. Finally, the above results are verified by motor prototyping and testing. Both simulation and test results indicate a significant improvement in cooling capacity, as well as extended motor performance boundaries.

A Predictive PMP Strategy for Plug-In Hybrid Electric Buses Considering Motor Thermal Characteristics and Loss Distribution

Energy management strategy (EMS) is the key to improving the fuel economy of the plug-in hybrid electric bus (PHEB). Some of the current researches mainly concentrate upon reducing fuel consumption, but do not fully consider the influence of thermal dynamics of the vehicle motor. In order to solve the shortage of this research, a predictive EMS considering electromagnetic thermal control is proposed in this paper. First, integrated with the actual working conditions and environment, the distribution of the loss of the main part of the motor under two extreme working conditions, namely, low-speed overload and high speed, is studied. Then the motor thermal model is built to study the maximum temperature variation rule in the actual operating condition. Finally, the motor thermal model is combined with the model prediction control (MPC) strategy based on Pontryagin’s minimum principle (PMP) strategy to ensure fuel economy and avoid motor overheating. The research results have guiding significance for the improvement and design of subsequent EMSs considering the influencing factors of motor temperature rise.

An Improved Design for a Heat Sink of a Power Conversion System Adapted to the High Altitude and Cold Environment of the Plateau

Currently, there are many studies on power conversion system (PCS) in the industry, but there are few studies on high-altitude and plateau application scenarios. This paper takes the extreme environment of plateau and high altitude as the research background, uses PLECS software to establish a thermoelectric simulation of a three-phase LCL grid-connected inverter, and calculates the total heat loss of the power devices IGBT and diodes in the PCS and the power loss of the grid-connected filter. Combining the overall heat generation of IGBTs, diodes and filters and considering the characteristics of high-altitude extreme environments, two liquid-cooled radiators with different structures were designed to measure the thermal resistance and pressure loss of the two radiators (reflecting Flow resistance) and heat dissipation efficiency are quantitatively calculated. The results show that the heat dissipation performance of the liquid cooling radiator designed by the latter is better than that of the former, verifying that by improving the channel structure and size of the liquid cooling radiator, the thermal resistance and flow resistance of the radiator itself can be reduced, and its heat dissipation performance can be improved.

Regulating surface energy and establishing covalent bonds to enhance interface interaction between m‐BN and polyphenylene oxide for 5G applications

AbstractIncorporation of boron nitride (BN) into polymers is a promising method to obtain composites with high thermal conductivity, low dielectric constant (Dk), and dielectric loss (Df), while the practical applications are limited by the poor interface between BN and polymer because of surface energy mismatch and absence of covalent bond connection between them. Herein, polydopamine (PDA) with good adhesion is deposited onto the BN. Then, a different amount of silane coupling agent containing vinyl reactive groups is grafted onto PDA‐coated BN. In this way, the surface energy of modified BN (m‐BN) can be adjusted to ensure BN contacts well with polymers. Moreover, reactive groups were introduced on BN for further reaction. Subsequently, covalent bonds between the m‐BN and the polyphenylene oxide (PPO) were established in situ during the curing process. The effects of the m‐BN surface energy on interface quality and thermal conductivity of composites are investigated. The m‐BN/PPO composite achieves a through‐plane thermal conductivity of 5.87 W/m·K and a low Df value of 1.53 × 10−3, as well as a low coefficient of thermal expansion (CTE) value (7.8 ppm/K) when the m‐BN loading is 32.6 vol%. This research provides a simple and efficient strategy for fabricating high‐performance composites for high‐frequency applications.Highlights Hexagonal boron nitride was modified successfully by combining non‐covalent and covalent modifications. Regulating surface energy and establishing covalent bonds enhances interface interaction between BN and polyphenylene oxide. Modified BN/polyphenylene oxide composites display improvements in thermal conductivity and dimensional stability as well as dielectric loss. Provides a feasible strategy for designing polymer composites with high thermal conductivity, dimensional stability, and low dielectric loss for 5G applications.

Recent advances of spectrally selective absorbers: Materials, nanostructures, and photothermal power generation

With the increasing development of photothermal techniques in various fields, particularly concentrated solar power (CSP) systems and solar thermoelectric generators (STEGs), the demand for high-performance spectrally selective absorbers (SSAs) has grown significantly. These SSAs are essential in achieving high solar absorption and minimal infrared thermal loss, thereby significantly enhancing solar utilization efficiency. This need becomes particularly critical in CSP systems, where high temperatures are pivotal for improved efficiency. However, the necessity for high temperatures imposes stringent requirements on the fabrication of SSAs, given the inherent trade-off between optical performance and thermal stability. SSAs typically require nanoscale thin films, but they are prone to oxidation and diffusion at high temperatures. Recent developments in photothermal materials, including ceramic composites, MXenes, high-entropy materials, and graphene, offer promising solutions to enhance SSAs’ performance. This review article provides a comprehensive evaluation of the latest advancements in these emerging photothermal materials. We summarize the strategies for integrating these advanced materials with already established nanostructures, which is a highly promising approach for the development of advanced SSAs. Additionally, the review explores the application of SSAs in CSP systems and STEGs to boost power generation efficiency. We conclude by summarizing the challenges and opportunities in the field of high-temperature SSAs, offering valuable insights into the development of high-performance SSAs and their role in solar-thermal power generation systems.

A multi-layer fabric for high-efficiency solar-driven seawater desalination

Fiber-based photothermal materials for seawater desalination usage have garnered significant attention owing to their outstanding properties. However, traditional monolayer fabrics are prone to possess inherent inefficiencies such as high thermal dissipation and salt crystallization within the evaporation zone, especially reducing the evaporation efficiency during the long-term seawater desalination. Herein, a novel three-layered three-dimensional (3D) spacer carbon/polyester cotton spacer woven fabric (SWF) evaporator is designed. This SWF material was delineated into three distinct layers: an upper evaporate layer, a foundational water absorption layer, and a central water dedicated to water transition, thermal insulation, and salt crystallization. The rational three-layered 3D architecture guarantees the swift aqueous transition within SWF evaporator, simultaneously curtailing thermal losses from the top layer. The evaporation rate of 3D SWF, with 6 mm interval space, registered at 1.6721 kg · m−2·h−1 under a solar intensity of 1 kW · m−2. Furthermore, under conditions with a solar power of 1 kW · m−2 and a wind velocity of 2 m · s−1, the evaporation efficiency of liquid water from SWF, with a central layer height of 12 mm, culminated at 3.9742 kg · m−2·h−1, which validated its adeptness for the seawater desalination applications. The results of our research are helping to provide for efficient and stable methods of wastewater treatment, desalination, and drinking water collection.

Improving solar still efficiency through integration of cellulose-based water absorbers and Peltier condensation unit

This study involves a series of experiments aimed at assessing the impact of incorporating water-absorbent materials on the productivity of solar stills. It is worth mentioning that the performed experiments examine the effects of both materials and their location inside solar still unit. The solar still used for the experiments comprised a black-painted metal case and a glass layer positioned at a 30° angle relative to the horizontal. To enhance evaporation performance, a Peltier cooling module was integrated into the system. Furthermore, to prevent thermal losses and improve efficiency, the solar still case was insulated using Styrofoam material. From a scientific standpoint, the variations in this context can be ascribed to three primary variables as, integration Peltier condensation unit, use of water absorber materials like hemp and high-absorbent papers, and the incorporation of absorber dark colors. Throughout the experiments, constant test conditions were established using an artificial light source. In the reference setup, a total of 25 g of clean purified water was obtained, whereas in Case 5 (utilizing black high-absorbent papers on a triangle metal frame) and Case 6 (employing high-absorbent papers in the form of upright columns), which yielded the most efficient results, the amounts of purified water obtained were approximately 34 and 40 g, respectively. The results indicated a remarkable enhancement in thermal efficiency for Case 5 and Case 6, with approximately 29% and 45% increases, respectively, compared to the reference setup. Furthermore, a cost assessment has been conducted, demonstrating that the productivity gained through the use of internal materials contributes to improvements in cost efficiency. In comparison to the reference case, Case 6 exhibits a cost reduction for cost per liter exceeding 35%.

Experimental investigation of the external load effect on thermoelectric generator discharge time in a low power energy harvesting system

Thermoelectric generator systems are often evaluated and studied in open circuit and close circuit modes. In the open circuit case, minimum heat flux passes across the thermoelectric module and the module does not have any thermal losses. Moreover, in the close circuit system, the external consumer is connected to the module and higher heat is pumped from its hot side to cold side. Hence, investigating the effect of external load resistance as the consumer connected to the module on its response is a significant issue in thermoelectric systems. In this study, to evaluate the effect of various consumers (4, 8, 10, 15, 20 and 30 Ω) over the module on discharge time, output voltage and temperature on both sides of the module, thermoelectric systems lacking and containing phase change material as the useful means for energy storage and thermal management of thermoelectric system were designed and exposed to constant heat loads. Results of this study show that the power consumption of the internal resistance of the module (connected to the consumer) led to an increase in the temperature of both sides of the module compared to open circuit systems. Therefore, the thermal balance and temperature distribution over the module changes and more affected. The maximum output power and discharge time were obtained at the external resistance of 4 Ω (close to the average internal resistance of the module) in the studied systems. The phase change material prevented excessive temperature on the hot side during the charging process and provided proper thermal management to enhance voltage generation and discharge time. The thermoelectric generator is an effective technology in starting consumers with low resistance, such as light bulbs and remote controls.

Enhancing thermo-hydraulic performance of solar air collectors through three-dimensional airflow using novel artificial roughness designs

BackgroundThe solar air collectors involve exploring their design, efficiency, and performance attributes. Common challenges include addressing issues such as small convective heat transfer coefficients between the air and the absorber, which can result to higher absorber plate temperatures and heightened thermal losses. Through the incorporation of artificial roughness onto the collector plate with a suitable design, it is possible to disrupt the shear layer and improve the convective coefficient. MethodsThis study focuses on hydrodynamic and thermal analyses to identify optimal chicane shapes and arrangements, such as CTPrism, CRRec, and CR, planted on the bottom wall of a solar air collector. Thermo-hydraulic performances are investigated using comprehensive CFD simulations, validated by experimental data and comparing them to smooth ducts. Significant findingsIn this work, a novel hydrodynamic and thermal analysis is introduced, demonstrating that the utilization of (CTPrism) shapes arranged in a staggered configuration leads to a significant enhancement of 68 % in heat transfer and 95 % in turbulent intensity. Consequently, there is an improvement in thermo-hydraulic performance, reaching up to 2.39, while still maintaining moderate friction losses.

Analysis and assessment of electrical and thermal performance of five‐phase voltage source inverter under different modulation strategies: Comparative study under balanced and unbalanced load

SummaryThis paper compares four modulation strategies applied to five‐phase voltage source inverters (5PH‐VSI). The modulation strategies under investigation are sine wave pulse width modulation (S‐PWM), fifth‐harmonic injection PWM (FH‐PWM), space vector‐PWM using two large vectors (2V‐SVPWM), and space vector‐PWM using two medium and two large vectors (4V‐SVPWM). The study utilizes simulations to analyze the results based on four performance criteria: low‐order harmonics (LOH), maximum modulation index (MMI), common mode voltage (CMV), and total harmonic distortion (THD) under balanced and unbalanced load. To validate the simulation results for these criteria, an experimental test‐bench is employed, which includes a 5PH‐VSI feeding an R‐L load, and controlled by a low‐cost STM32F4‐DISCOVERY microcontroller board. Additionally, a mathematical approach is used to calculate the total thermal losses (TTL) then simulations are performed using Piecewise Linear Electrical Circuit Simulation (PLECS) software to assess the modulation schemes based on additional thermal performance criteria: conduction losses (CL), switching losses (SL), TTL, the efficiency, and the maximum permissible heat sink thermal resistance (MPHTR) at the steady‐state regime. The results indicate that the 4V‐SVPWM method demonstrates superior efficiency in terms of THD. Furthermore, it showcases the lowest TTL at high switching frequencies, allowing for the best efficiency and minimizing MPHRT, therefore providing the largest margin for the heat sink thermal resistance design. On the other hand, the 2V‐SVPWM offers the highest MMI, but this comes at the cost of high TTL and some LOHs appearing. In addition, it exhibits the highest CMV for unbalanced load. S‐PWM and FH‐PWM offer the advantage of simpler implementation.

Four‐Terminal Tandem Based on a PM6:L8‐BO Transparent Solar Cell and a 7 nm Ag Layer Intermediate Electrode

To overcome transmission and thermalization losses from single‐junction solar cells, the two‐terminal tandem cell configuration is one of the most widely followed approaches. Unfortunately, the need to match the current from both cells, in addition to the fabrication of an interlayer with excellent optical and electronic performances, makes such two‐terminal configurations a challenging approach. Herein, the fabrication of a four‐terminal tandem incorporating a front transparent cell made using a 7 nm Ag back electrode and a PM6:L8‐BO blend which exhibits a bandgap close to the optimal according to the detailed balance theory is reported. For the opaque back cell in such tandem, a PTB7‐Th:O6T‐4F blend is used. A 16.94% power conversion efficiency is achieved when such two cells are configured in a four‐terminal device separated by a WO3/LiF/WO3 multilayer providing an optimal light absorption distribution among the two cells.

Tuning photovoltaic performance of co-doped graphene quantum dots

The photovoltaic performance of graphene quantum dots (GQDs) faces instability due to structural irregularities. To understand optoelectronic properties, this study employs density functional theory (DFT) to investigate nitrogen-doped GQDs (NGQDs) co-doped with sulfur (N,S) and phosphorous (N,P). Co-doping with N and S or N and P reduces electron-hole pair separation, increasing thermal loss in GQDs with graphitic N functionality. N,S co-doping heightens surface defect likelihood, while N,P co-doping diminishes it. The chemical reactivity of NGQDs is influenced by polar solvent choice, unlike excited-state properties of GQDs doped with other elements. NGQDs with graphitic and pyrrolic N functionalities outperform co-doped GQDs in photovoltaic performance due to enhanced parameters. This study guides rational design of electronic devices using GQD materials.

Dynamic behavior modeling and energy conversion characteristic analysis of a thermoacoustic-piezoelectric generator with the consideration of thermal and viscous losses

The amalgamation of thermoacoustic and piezoelectric principles represents a promising approach to bolster energy harvesting capabilities, offering a viable solution to address the increasingly pressing environmental concerns and energy shortages. This research introduces a thermoacoustic piezoelectric generator, serving as a versatile platform for the efficient interplay of thermal, acoustical, mechanical, and electrical energies. The proposed system comprises distinct components, including a hot buffer, stack, resonators, and piezoelectric transducer. At the left end of the system, a generalized impedance boundary condition is employed. Theoretical models, rooted in the wave equation and thermoacoustic theory, are meticulously developed. These models leverage the smoothed-Fourier series and the Galerkin method, presenting a generalized eigenvalue problem encompassing oscillation frequency and the corresponding coefficients of acoustic pressure. These models are rigorously validated through comparisons with existing literature. Building upon the established model, this study thoroughly investigates the influence of various geometrical and electrical parameters, such as tube length, stack position, external load, and the impact of the general impedance boundary condition, on dynamic behaviors. These dynamic behaviors encompass the onset frequency, and the distributions of acoustic pressure, volume velocity, acoustic impedance, as well as energy conversion characteristics, including captured energy and energy capture efficiency. The theoretical model and analytical framework developed in this study hold significant utility in the design and optimization of thermoacoustic piezoelectric generators. They are poised to advance the field of energy harvesting technology, fostering substantial growth across a multitude of industrial applications.

Quantitative analysis of pyrolysis characteristics and chemical components of tobacco materials based on machine learning.

To investigate the quantitative relationship between the pyrolysis characteristics and chemical components of tobacco materials, various machine learning methods were used to establish a quantitative analysis model of tobacco. The model relates the thermal weight loss rate to 19 chemical components, and identifies the characteristic temperature intervals of the pyrolysis process that significantly relate to the chemical components. The results showed that: 1) Among various machine learning methods, partial least squares (PLS), support vector regression (SVR) and Gaussian process regression (GPR) demonstrated superior regression performance on thermogravimetric data and chemical components. 2) The PLS model showed the best performance on fitting and prediction effects, and has good generalization ability to predict the 19 chemical components. For most components, the determination coefficients R 2 are above 0.85. While the performance of SVR and GPR models was comparable, the R 2 for most chemical components were below 0.75. 3) The significant temperature intervals for various chemical components were different, and most of the affected temperature intervals were within 130°C-400°C. The results can provide a reference for the materials selection of cigarette and reveal the possible interactions of various chemical components of tobacco materials in the pyrolysis process.

Experimental Methods for Measuring the Efficiency of a Molten Salt Central Receiver

In this work, two different methods for measuring the efficiency of central receivers are analyzed by the case of the High Performance Molten Salt II Project (HPMS-II): the continuous power-on method, and the semi-analytical method. The main difference between the two methods is the procedure to calculate the thermal losses of the receiver: on the one hand, the continuous power-on method calculates the thermal losses from the measurement of the absorbed power by the molten salt for different measured incident powers on the receiver. Here, it is assumed that the thermal losses are independent of the incident power if the molten salt temperature is kept constant. On the other hand, the semi-analytical method calculates the thermal losses as the sum of convective and radiative losses, calculated directly from the Newton and Stefan-Boltzmann equations by measuring the temperature of the tube surface, the ambient temperature, and the wind speed. Therefore, the calculation of the thermal losses is independent from one method to another. The procedure of applying these methods during the experimental test campaign of the HPMS-II receiver is detailed in this paper. Additionally, an uncertainty analysis of both methods is conducted to determine the uncertainty expected for the receiver efficiency measurements.

Synthesis and properties of phenolphthalein‐based thermoplastic poly(ether nitrile imide)s via aromatic nucleophilic substitution polymerization

AbstractAromatic nucleophilic substitution polymerization was used to synthesize five poly(ether nitrile imide)s (PENIs) that include benzonitrile and bulky cardo groups from a mixture of phenolphthalein (PP), 4,4′‐bis(4‐fluorophthalimide) diphenyl ether (4,4′‐BFPI), and 2,6‐difluorobenzonitrile (DFBN). The structure and properties relationship of PENIs with different ratios of DFBN and 4,4′‐BFPI was explored. It was found that the glass transition temperature (Tg) of PENIs decreased from 280 to 260°C, while the temperature of 5% thermal weight loss (T5%) in N2 increased from 429 to 453°C as the benzonitrile content in PENI increased. The produced PENI films had good mechanical characteristics, including tensile strengths of 103–112 MPa, elongations at break of 5.6%–8.2%, and tensile moduli of 2.9–3.4 GPa. Furthermore, the solubility and melt processability were also improved with the introduction of the benzonitrile group. Compared with poly(ether ketone imide)s (PEKIs) and poly(ether sulfone imide)s (PESIs), PENIs with benzonitrile displayed higher Tg, tensile modules, and lower complex viscosity.

Experimental investigation of two solar air heaters, with and without employing PCM

AbstractIn the present study, an experimental test was conducted to investigate the energetic performance of a novel designed solar air heaters (SAHs), with, and without phase change material (PCM). Two identical SAHs were fabricated and tested to compare their performance. The first heater is a jacket‐tube solar air heater (SAH 1), while the second heater is similar to the first but filled with PCM (SAH 2). Experimental results showed that increasing air flow rate increases the daily thermal efficiency. Thermal energy during day hours can be stored in the PCM and used after sunset. SAH 2 gave an additional operating time after sunset for 4 hours at 0.01 kg/s, 2.5 hours at 0.035 kg/s, and 1 hour at 0.06 kg/s. Maximum improvement in the daily thermal efficiency was 15% at SAH 2, more than SAH 1 at 0.01 kg/s air flow rate. Employing PCM, as so as increasing air flow rate can reduce the daily thermal losses.

Smart traffic routing and service allocation strategy to reduce water consumption in data centers through power reduction

Due to the growth of communication networks, energy consumption in information and communication technology industries is increasing dramatically. Among these industries, data centers are operating with a large number of processors and other components, which, due to heavy processing and mass data transmission, in addition to consuming high electrical power, also cause high thermal losses. Since water cooling systems are used for cooling different parts of these centers as well as for cooling the electric power generation unit, these centers are among the major consumers of water and electricity resources. In this article, while examining the important factors affecting water consumption in data centers, useful methods are suggested to reduce the consumption of electrical energy and water. Optimizing energy consumption in data centers is possible in three parts: routing, servicing and use of cooling equipment. For all three parts, improvement methods are suggested in this article. For this purpose, an optimization problem is designed and an algorithm is presented to solve it. In the proposed solution, an energy-smart method based on SDN technology is used for routing, virtual machines equipped with the possibility of reducing power consumption in no-load conditions are used for servicing, and two types of water-cooled and air-cooled systems are used for cooling equipment. is used. The simulation results show that depending on the cooling system, the proposed method reduces water consumption between 24% and 32% compared to the case where the proposed solution is not used.