Convert Heat Energy Research Articles

Thermophysical Analysis of Microconfined Turbulent Flow Regimes at Supercritical Fluid Conditions in Heat Transfer Applications

Abstract The technological opportunities enabled by understanding and controlling microscale systems have not yet been capitalized to disruptively improve energy processes, especially heat transfer and power generation. The main limitation corresponds to the laminar flows typically encountered in microdevices, which result in small mixing and transfer rates. This is a central unsolved problem in the thermal–fluid sciences. Therefore, this work focuses on analyzing the potential of supercritical fluids to achieve turbulence in microconfined systems by studying their thermophysical properties. In particular, a real-gas thermodynamic model, combined with high-pressure transport coefficients, is utilized to characterize the Reynolds number achieved as a function of supercritical pressures and temperatures. The results indicate that fully turbulent flows can be attained for a wide range of working fluids related to heat transfer applications, power cycles and energy conversion systems, and presenting increment ratios of O(100) with respect to atmospheric (subcritical) thermodynamic conditions. The underlying physical mechanism to achieve relatively high Reynolds numbers is based on operating within supercritical thermodynamic states (close to the critical point and pseudo-boiling region) in which density is relatively large while dynamic viscosity is similar to that of a gas. In addition, based on the Reynolds numbers achieved and the thermophysical properties of the fluids studied, an assessment of heat transfer at turbulent microfluidic conditions is presented to demonstrate the potential of supercritical fluids to enhance the performances of standard microfluidic systems by factors up to approximately 50×.

Study of the Thermoelectric Properties of Bi2Te3/Sb2Te3 Core-Shell Heterojunction Nanostructures.

Thermoelectric materials convert heat energy into electricity, hold promising capabilities for energy waste harvesting, and may be the future of sustainable energy utilization. In this work, we successfully synthesized core-shell Bi2Te3/Sb2Te3 (BTST) nanostructured heterojunctions via a two-step solution route. Samples with different Bi2Te3 core to Sb2Te3 shell ratios could be synthesized by controlling the reaction precursors. Scanning electron microscopy images show well-defined hexagonal nanoplates and the distinct interfaces between Bi2Te3 and Sb2Te3. The similarity of the area ratios with the precursor ratios indicates that the growth of the Sb2Te3 shell mostly took place on the lateral direction rather than the vertical. Transmission electron microscopy revealed the crystalline nature of the as-synthesized Bi2Te3 core and Sb2Te3 shell. Energy-dispersive X-ray spectroscopy verified the lateral growth of a Sb2Te3 shell on the Bi2Te3 core. Thermoelectric properties were measured on pellets obtained from powders via spark plasma sintering with two different directions, in-plane and out-of-plane, showing anisotropic properties due to the nanostructure alignment in the pellets. All samples showed a degenerate semiconducting character with the electrical resistivity increasing with the temperature. Starting from Sb2Te3, the electrical resistivity increases with the increase in amounts of Bi2Te3. Thermal conductivity is lowered due to the increase in interfaces and additional phonon scattering. We show that the out-of-plane direction of the BTST 1-3 sample (where 1-3 indicates the ratio of BT to ST) demonstrates a high Seebeck value of 145 μV/K at 500 K which may be attributed to an energy filtering effect across the heterojunction interfaces. The highest overall zT is observed for the BTST 1-3 sample in the out-of-plane direction at 500 K. The zT values increase continuously over the measured temperature range, indicating a probable higher value at increased temperatures.

Directional combustion induced by 3D aligned carbon channel arrays for combustion chamber-free micro-thruster

Micro-solid propellant thrusters are widely used in propulsion and attitude adjustment of micro-spacecraft, and nano-satellites prospect. However, they suffer from low specific impulse owing to the existence of the conventional structural parts (combustion chamber and nozzle) that account for a large weight ratio. Herein, we report a combustion chamber-free micro-thruster consisting of balsa wood-derived carbon aerogel as well as ammonium perchlorate (AP) and Ti3C2 MXene supported on carbon aerogel. The microstructure engineering design of carbon aerogel give it 3D aligned channel arrays structure and defect rich carbon framework. The 3D aligned channel could guide the burning fluid in the channel to form directional flame, thus converting heat energy into kinetic energy with absence of the additional combustion chamber and nozzle. The defect-rich carbon aerogel with high reactivity could participate in the combustion reaction as fuel. To further promote the combustion performance of the chamber-free micro-thruster, Ti3C2 MXene is applied as reactive combustion catalyst to accelerate the thermal decomposition of AP. Coupled with the advantageous of chamber-free, high combustion efficiency, and efficient heat and mass transfer in the channel structure, the Ti/CA/AP composite can be directly applied as a micro-thruster and generates a high specific impulse of 2044.0 N·s/kg.

Energy and environmental analysis of a solar evacuated tube heat pipe integrated thermoelectric generator using IoT.

This paper investigates the solar evacuated tube heat pipe system (SETHP) coupled with a thermoelectric generator (TEG) using the internet of things (IoT). The TEGs convert heat energy into electricity through the Seebeck effect that finds application in the waste heat recovery process for the generation of power. The present work deals with the theoretical study on solar evacuated tube heat pipe integrated TEG and it is validated experimentally using with and without parabolic trough concentrating collector. However, it is found that the maximum power output due to the influence of the parabolic trough concentrator results in increased efficiency when compared with the non-concentrating SETHP-TEG system. Thus, the thermoelectric generator's electrical energy efficiency for the concentrating system was 0.151% greater than the latter one. A power electronic boost converter may enhance the acquired TEG output power to a maximum of 5.98 V. This would be directly used for both mobile charging and lighting applications in distant places and military camps where the community lacks sufficient electrical access. And the carbon credit of the TEG system is determined to find its potential in the environmental aspects of carbon emission per watt, carbon mitigation, and carbon credit and its results are 2.34 × 10-3 g/W, 0.027 tonnes, and 0.681 dollars respectively for a TEG module. Besides, the recorded real sensor data with Arduino is implemented in the experimental process for automatic remote monitoring of the temperature.

Pengujian Boiler untuk Pembangkit Listrik Tenaga Panas Laut

Energy needs are one of the reasons why research on renewable energy is the choice. One of the renewable energies is OTEC (ocean thermal energy conversion) with sea surface heat being an energy source and boilers being a medium for converting heat energy into motion energy so that in the end it becomes electrical energy. Boilers are a vital part of a generator, so boiler testing is a requirement for a generator. The research was carried out by experiment by testing the boiler with various temperatures and pressures so as to produce output power. The results show that temperature and pressure are highly correlated with output power. The application of OTEC shows that temperature and pressure are things that must be considered, the higher the surface temperature, the greater the output power.

Effects of different piston combustion chamber heights on heat transfer and energy conversion performance enhancement of a heavy-duty truck diesel engine

The heat transfer and energy conversion characteristics of 3 kinds of pistons are studied based on the heat load prediction model of diesel engine piston. Thermal energy conversion effects of pistons for heavy-duty truck engine performance are investigated which involve air-fuel ratio, intake flow, exhaust temperature and fuel consumption. The research results illustrate the whole temperatures and heat flux of piston rise with increase of piston combustion chamber height. The maximum and the minimum temperature difference are 18.34 K and 3.07 K of piston-12, piston-15 and piston-18 with the piston wall surface temperature change dramatically. Maximum heat flux (1 203 500 W/m2, 1 488 500 W/m2, 1 523 200 W/m2) and the minimum heat flux (761.37 W/m2, 990.41 W/m2, 1325.2 W/m2) of piston-12, piston-15 and piston-18 are conspicuously conspicuously different with piston wall surface heat flux significant change. Piston-18 has the characteristics of large air-fuel ratio (27.3) and intake flow (844.33 kg/h), low fuel consumption (217.3 g/kW·h) and exhaust temperature (776.8 K), which shows that it is more efficient and the heat energy conversion capability is improved remarkably. The appropriate piston chamber height can improve heat transfer and energy conversion performance.

Optimal Operation for Regional IES Considering the Demand- and Supply-Side Characteristics

A regional integrated energy system (RIES) is an electricity-centric multi-energy system that can realize the mutual conversion of electricity, heat, cold, and other energy. Through multi-flexible resource interaction and the transaction of multi-investment entities, the efficiency of energy utilization can be improved. To systematize energy-consuming entities and scale photovoltaic-based renewable energy in a distribution network, the energy-consuming behavior, energy-producing schedule, and trading strategy can be coupled. Considering the interaction between the energy-consuming behavior and the uncertainty of distributed photovoltaic output, an optimal operation method for RIES is proposed on the basis of social network theory and an uncertain evolutionary game method in this paper. From the perspective of the operator, the overall profits of RIES are maximized considering the entity characteristics of both the demand and the supply side. A case study shows that the proposed method can ensure the reasonable distribution of profit among the investment entities. A closer social relationship between energy-consuming entities or a lower transaction risk cost of energy-producing entities can increase the overall energy transaction profit.

Zinc-Guided 3D Graphene for Thermally Chargeable Supercapacitors to Harvest Low-Grade Heat.

Low-grade heat energy recycling is the key technology of waste-heat utilization, which needs to be improved. Here, we use a zinc-assisted solid-state pyrolysis route to prepare zinc-guided 3D graphene (ZnG), a 3D porous graphene with the interconnected structure. The obtained ZnG, with a high specific surface area of 1817 m2·g−1 and abundant micropores and mesopores, gives a specific capacitance of 139 F·g−1 in a neutral electrolyte when used as electrode material for supercapacitors. At a high current density of 8 A·g−1, the capacitance retention is 93% after 10,000 cycles. When ZnG is used for thermally chargeable supercapacitors, the thermoelectric conversion of the low-grade heat energy is successfully realized. This work thus provides a demonstration for low-grade heat energy conversion.

Hot-carrier infrared detection in PbS with ultrafast and highly sensitive responses

Traditional infrared semiconductors with direct narrow bandgaps, such as HgCdTe, InGaAs, and lead salts (PbS, PbSe, and PbTe), have been commercialized for decades in various infrared technologies, such as night vision, military communication, and health monitoring. However, traditional infrared (specifically middle- and long-wave infrared) semiconductors suffer from serious noise generation via thermal excitation and external current bias. Although thermal infrared detectors can operate at room temperature, their response speed is very slow, typically on the order of milliseconds or worse, which limits their applications. Herein, we reinvent a classical lead salt semiconductor (PbS) as a room temperature, high speed, and high-detectivity infrared detector. The detection is operated via the self-driven (no bias voltage necessary) photothermoelectric (PTE) effect with a response time reaching 500 ns (limited by the measurement setup)—three orders of magnitude faster than commercial PTE and photoconductive PbS detectors. Furthermore, the physical principle of hot-carrier-dominated heat energy conversion is proposed to understand the unconventional ultrafast response behavior. Combined with high sensitivity at room temperature (noise equivalent power 0.3 pW Hz−1/2) and broadband detection range (0.4–2.3 μm), this hot carrier makes the traditional commercial semiconductor PbS applicable to a class of infrared detection applications.

PUP PUMP: PROCESSING OF HUMAN FECES AS A ALTERNATIVE BIOENERGY POWER PLANT ZERO WASTE

OPEC (Organization of the Petroleum Exporting Countries), predicts world oil and gas consumption to increase from year to year (Sebayang, 2018). In 1999, Indonesia was one of the 2nd largest oil producers in the Asia Pacific (Dzulfaroh, 2020). However, now the situation has reversed, Indonesia's oil reserves are very depleted and it is predicted that they will only be able to last for less than 10 years (RI, 2021). Meanwhile, the demand for oil and natural gas is still high, especially for power generation. Therefore, a new alternative that is environmentally friendly is needed (Kholiq, 2015). One of them is by utilizing biogas. Biogas is a gas produced by methanogenic bacteria, by degrading (decomposing) organic compounds under anaerobic conditions. One of the compounds that can be used as a source of biogas is feces. Usually human feces will only accumulate and settle at the bottom of the septic tank. This fecal sediment must be drained for 2-5 years (Sudarmadji, 2013). If this waste is managed properly, it has the potential as an alternative power plant, through the biogas it produces. Furthermore, this biogas is connected to the gas storage box. In the box is also equipped with a pressure detector. If the pressure is appropriate, then the gas will be released to the generator that has been assembled coupled with a biodigester. The generator converts heat energy into kinetic energy, then into mechanical energy, and finally into electrical energy (Biogas, 2018). 1 m3 of biogas is able to produce electricity equivalent to 1.25 Kwh or the equivalent of turning on a light for 6 hours (Talakua, 2019). Meanwhile, biogas processed waste (slurry) contains organic material with complete nutrition (Muanah, 2019), so it can be used as fertilizer. In addition, slurry can also be used as raw material for bricks (Syaifuddin, 2018).

Potensi Tempurung Kelapa Sebagai Pembangkit Listrik Dengan Menggunakan Termoelektrik Generator

Around 35% of the total utilization of coconuts at this time is still not fully utilized. Thermoelectric is a technology that converts heat energy directly into electrical energy or converts electrical energy into heating and cooling energy. Data retrieval using two multimeters and an electric thermometer, data collection was carried out for 2 minutes. From the test results, this tool can produce an average voltage of 10.05 Volt for 200gram coconut shells, an average current of 0.99 Ampere and an average power of 13.84 Watts and can fully charge the battery up to 3 hours 33 minutes, while for 300 grams produces an average voltage of 10.59 Volts for 300gram coconut shells, an average current of 0.995 Ampere and an average power of 13.56 Watts and the battery can be fully charged in about 3 hours 36 minutes, while a coconut shell weighing 400 grams can produces an average voltage of 10.94 Volts, an average current of 1 Ampere and an average power of 13.70 Watts and the battery can be fully charged in about 3 hours 30 minutes. The more coconut shells used for combustion, the hotter the temperature and the faster the voltage and current are obtained, but with a note that the maximum temperature limit of the thermoelectric is T not more than 200o C.
 Keywords: Coconut Shell, Thermoelectric, Electrical Energy.

Thermoelectric properties of Zn- and Ce-alloyed In2O3 and the effect of SiO2 nanoparticle additives

Thermoelectric materials are considered promising candidates for thermal energy conversion. This study presents the fabrication of Zn- and Ce-alloyed In2O3 with a porous structure. The electrical conductivity was improved by the alloying effect and an ultra-low thermal conductivity was observed owing to the porous structure, which concomitantly provide a distinct enhancement of ZT. However, SiO2 nanoparticle additives react with the matrix to form a third-phase impurity, which weakens the electrical conductivity and increases the thermal conductivity. A thermoelectric module was constructed for the purpose of thermal heat energy conversion. Our experimental results proved that both an enhancement in electrical conductivity and a suppression in thermal conductivity could be achieved through nano-engineering. This approach presents a feasible route to synthesize porous thermoelectric oxides, and provides insight into the effect of additives; moreover, this approach is a cost-effective method for the fabrication of thermoelectric oxides without traditional hot-pressing and spark-plasma-sintering processes.

Integracija toplotnih pumpi u postojeći energetski sistem u malim i srednjim preduzećima

Industry processes are characterized by large amounts of energy losses dissipated as waste heat to the ambient. In industry sectors analysed in the US, China and EU28 lowtemperature waste heat below 230ºC makes up from 33% up to 60% of waste heat. The recovery of low-temperature waste heat is usually complex, affected by the user demand, mismatches between the waste heat source and the user demand, limited space for heat recovery facilities, the heat-power conversion is not efficient for low-temperature waste heat, payback period, etc. The purpose of this paper is to present a methodology for technical and economic analysis of waste heat recovery. To address the issue of sensible criterion, methodology appropriate for small and medium enterprises is developed and in this paper, the user-friendly optimization integrating the heat exchange, energy conversion and heat storage is presented. A case study of waste heat recovery from an induction machine cooling system is used to demonstrate the applicability of the proposed methodology. The introduced methodology can simplify the heat pump integration process, and the proposed method can be further extended to other industrial processes for low-grade waste heat recovery.

Thermal properties of single-layer MoS2-WS2 alloys enabled by machine-learned interatomic potentials.

Two-dimensional (2D) quantum materials are poised to transform conventional electronics for a wide spectrum of applications that will encompass chemical sciences. For the study of thermal transport in single-layer (1L) or multi-layer transition metal dichalcogenides (TMDs), this work explores the combination of density functional theory (DFT) and algorithmic training for the generation of a moment tensor potential (MTP) that models 1L-MoS2, 1L-WS2 and their alloys, and demonstrates a synergy of theoretical techniques that is anticipated to play an important role in the field. From a high-performance computing perspective, these yield very convenient inter-atomic (or inter-molecular in other contexts) potentials that are useful to predict the response of quantum materials to thermal perturbations, or other driving forces. We show that our trained MTP functions successfully describe vibrational properties of the systems, and their thermal conductivities. The trained potential displays consistent agreement with DFT calculations, as well as the Stillinger-Weber (SW) potential. We also find that the thermal conductivity of the 2D alloys is little affected by sulfur vacancies. This is a behavior that may aid the fine-tuning of material's thermal properties for heat management and energy storage and conversion applications.

A comprehensive review on small-scale thermal energy harvesters: Advancements and applications

During energy conversion, energy is dissipated and wasted in the form of heat. This energy if recovered reduces the cost per unit of power generation and also ensures higher efficiency of the system. There are multiple systems that can directly convert heat energy into electricity namely, Thermoelectric generator(TEG), Pyroelectric energy harvester(PYEH), Thermomagnetic energy harvester(TMH), Thermoelastic energy harvester (TEH), and Thermionic energy conversion (TIC) systems. The entire transformation of these systems throughout the ages are presented in this work. And also reviews the performance and recent progress of these systems along with their applications in heat recovery. Also, heat energy recovery sources and their matching heat energy conversion systems are discussed. Each model application in converting different energy recovery sources into electrical energy is enumerated along with its research gaps. All system’s current and potential future applications in commercial, industrial and other related fields are briefly explained.

Effect of NiCo2O4-modified expanded graphite on heat transfer and storage improvement of CaCl2⋅6H2O

The efficient heat energy storage and conversion can be achieved by form-stable composite phase change material (CPCM) to cope with energy supply and demand imbalances in time and space. The modification of expanded graphite (EG) is important in promoting the phase change behavior of inorganic CPCM. The NiCo2O4 with spinel structure has an excellent thermal conduction channel and great hydrophilia. In this study, the in-situ NiCo2O4 was adopted to optimize the thermal conductivity and improve the thermal reliability of CaCl2⋅6H2O (CCH)-based CPCM. It was found that the obtained CPCM exhibited the enhanced thermal conductivity (4.652 W⋅m − 1⋅K − 1), which was nearly 8.25 times that of CCH (0.564 W⋅m − 1⋅K − 1). The thermal reliability increased, which was ascribable to the improvement of hydrophilicity. Moreover, the CCH-based CPCM showed great chemical compatibility, good energy storage density (149.32 J⋅g − 1), and optimized apparent activation energy (363.62 kJ⋅mol−1). This work will provide new insights into enhanced thermal conductivity and reliability for form-stabilized CPCM by establishing three-dimensional bimetallic oxide channels.

Pengaruh konduktivitas thermal pada hot cylinder mesin stirling menggunakan energi surya terkonsentrasi

Renewable energy is one of the businesses sector that will develop rapidly after the changing economic order due to the corona outbreak. The characteristics of Indonesia's tropical climate by getting good sunlight throughout the year can be used as alternative and renewable energy. The Stirling engine is one type of external combustion engine, because combustion is carried out outside the engine using a closed regenerative cycle in which the working fluid is compressed or expanded in a separate reservoir and then distributed to drive the power piston reciprocatingly. The method developed is the use of solar energy which is concentrated by a parabolic reflector to the hot cylinder of the Stirling engine to convert heat energy into motion energy. The purpose of this study was to determine the effect of the thermal conductivity of several material specimens used in the hot cylinder of the Stirling engine including copper, stainless steel, & glass. This study uses an experimental method to describe the performance of a stirling engine prototype using various types of hot cylinder material specimens. The results showed that the gamma stirling engine using hot cylinder glass material had the best performance because with a heat conductivity of 0.78 W/m˚C it was able to drive a stirling engine with a speed of 132 rpm and a torque of 0.57 N.mm at the temperature difference between hot cylinder and cold cylinder of 88˚C and with a thermal efficiency of 20.39%.

Design and research of a low-noise pyrotechnic separation device

To solve the problem of large operating noise of existing pyrotechnic separation devices, a new low-noise pyrotechnic separation device is designed by changing the utilisation mode of pyrotechnic separation, using micro gas pyrotechnic as heat sources, and shape memory alloy material to convert heat energy into mechanical energy. The results showed that the separation time was 1.526 s when the preload was 20 kN, and the maximum shock response was 319 G (2268 Hz) for 100 Hz–100 kHz. When used underwater, the maximum sound pressure level is 106.9 dB at 12,698 Hz and 98.5 dB from 10 Hz–5 kHz. Compared with a conventional separation nut, the frequency band sound pressure level can be reduced by more than 70 dB, realising underwater low-noise separation.

Numerical investigation of transient thermo-fluid processes in a Ranque-Hilsch vortex tube

A 2D numerical investigation is performed to better understand the transient thermo-fluid processes in a vortex tube for a cold mass fraction equal to0.44. The results along the Ranque-Hilsch vortex tube reveal a close agreement with past numerical and experimental data. The distribution of axial, radial, and tangential velocities as well as the stagnation pressure and temperature are examined at different positions for different time steps. The results indicate that the tangential velocity is the most significant velocity component and dominates the heat transfer and energy conversion processes. In addition, it is evident that the core of the cold end experiences the highest pressure gradient along with almost zero tangential and radial velocities. The maximum axial velocity appears close to the inlet and its value increases with higher cold mass fractions due to higher pressure gradient which may lead to the enlargement of the inner vortex. The impact of different cold mass fractions in the range of 0.22−0.82 at tube length ratios x/L equal to 0.05, 0.5, and 0.9 for different time steps are examined. The results indicate that there is relatively no vortex decomposition near the cold outlet.

Development of Thermal Energy Conversion Devices into Electrical Energy as Physics Learning Teaching Aids

This research aimed to produce a device for converting heat energy into electrical energy as a teaching aid for physics. This research process is development research, which refers to the Research and Development (R&D) model. The instrument used was a questionnaire with a five Likert scale, which addressed media experts, material experts, physics teachers in SMA Negeri 2 Sigi, and class XII MIA SMA Negeri 2 Sigi students. The product quality data obtained were analyzed using descriptive analysis. Based on the analysis of the media expert’s assessment, the quality of the product obtained a percentage value of 87.69% with the interpretation of “Very Good”. Based on the analysis of the assessment by material experts, the quality of the product obtained a percentage value of 84.44% with the interpretation “Very Good”. For the results of the physics teacher’s response, a percentage value of 86.00% was obtained with the interpretation “Strongly Agree”. For the results of the responses of class XII MIA students in the limited test, a percentage value of 83.56% was obtained with the interpretation “Strongly Agree”. The test results and questionnaire analysis showed that the heat energy conversion device developed into electrical energy was feasible to use.