Gas Heat Research Articles

Analysis of the thermophysical process within the SEOP polarized 3He system

Temperature is a crucial parameter in the spin-exchange optical pumping (SEOP) process of noble gas (3He), but is hard to measure due to its confinement nature. In this paper, we conduct research upon the temperature and gas flow distribution within a sealed SEOP cell through computational fluid dynamics simulation. The simulation result shows that the external heat exchange of the initial heating of the cell becomes a cooling process in the presence of high pumping laser power absorbed by the alkali metal. The heat from the pumping laser would also cause the gas in the cell to reach a much higher temperature than the oven, with the hottest part appearing on the upper side of the cell. These predicted behaviors from the simulation are later confirmed by our experiment measurement, which strongly indicates that a gas flow and heat flow exist within the cell. These results help us to understand the temperature distribution of 3He gas in the cell and provide references for the development and improvement of the future SEOP system.

Computational study of rarefied gas flow and heat transfer in lid-driven cylindrical cavities

The gas flow characteristics in lid-driven cavities are influenced by several factors, such as the cavity geometry, gas properties, and boundary conditions. In this study, the physics of heat and gas flow in cylindrical lid-driven cavities with various cross sections, including fully or partially rounded edges, is investigated through numerical simulations using the direct simulation Monte Carlo (DSMC) and the discrete unified gas kinetic scheme (DUGKS) methods. The thermal and fluid flow fields are systematically studied for both constant and oscillatory lid velocities, for various degrees of gas rarefaction ranging from the slip to the free-molecular regimes. The impact of expansion cooling and viscous dissipation on the thermal and flow fields, as well as the occurrence of counter-gradient heat transfer (also known as anti-Fourier heat transfer) under non-equilibrium conditions, is explained based on the results obtained from numerical simulations. Furthermore, the influence of the incomplete tangential accommodation coefficient on the thermal and fluid flow fields is discussed. A comparison is made between the thermal and fluid flow fields predicted in cylindrical cavities and those in square-shaped cavities. The present work contributes to the advancement of micro-/nano-electromechanical systems by providing valuable insight into rarefied gas flow and heat transfer in lid-driven cavities.

Hot-electron resonant terahertz bolometric detection in the graphene/black-AsP field-effect transistors with a floating gate

We evaluate the terahertz (THz) detectors based on field-effect transistor (FET) with the graphene channel (GC) and a floating metal gate (MG) separated from the GC by a black-phosphorus (b-P) or black-arsenic (b-As) barrier layer. The operation of these GC-FETs is associated with the heating of the two-dimensional electron gas in the GC by impinging THz radiation leading to thermionic emission of the hot electrons from the GC to the MG. This results in the variation of the floating gate potential, which affects the source–drain current. At the THz radiation frequencies close to the plasmonic resonance frequencies in the gated GC, the variation of the source–drain current and, hence, the detector responsivity can be resonantly large.

Numerical Calculation of Wet Exhaust Gas Condensation in the Heat Exchanger

Based on the background of waste heat recovery of gas-fired boiler, this paper studied wet exhaust gas condensation heat transfer using numerical methods. The calculated results indicated that with the exhaust gas Re number increases, heat flux, and Nu number gradually increase, while the Eu number decreases simultaneously. Besides, the variation trend of the Nu and Eu number gradually reduced with Re number increases. With inlet exhaust gas temperature increase, the Nu number increases, and the Eu number decreases. Meanwhile, Nu number and Eu number increases with the increase in wall temperature. On this basis, the empirical correlations for calculating Nu and Eu numbers are obtained, and the deviation between the calculated values and the numerical results is within ±8%. The conclusion of this study provides basis for heat exchanger design in wet exhaust gas waste heat recovery.

Simulation of glow and arc discharges in nitrogen: effects of the cathode emission mechanisms

Experimental evidence in the literature has shown that low-current direct current nitrogen discharges can exist in both glow and arc regimes at atmospheric pressure. However, modelling investigations of the positive column that include the influence of the cathode phenomena are scarce. In this work we developed a 2D axisymmetric model of a plasma discharge in flowing nitrogen gas, studying the influence of the two cathode emission mechanisms—thermionic field emission and secondary electron emission—on the cathode region and the positive column. We show for an inlet gas flow velocity of 1 m s−1 in the current range of 80–160 mA, that the electron emission mechanism from the cathode greatly affects the size and temperature of the cathode region, but does not significantly influence the discharge column at atmospheric pressure. We also demonstrate that in the discharge column the electron density balance is local and the electron production and destruction is dominated by volume processes. With increasing flow velocity, the discharge contraction is enhanced due to the increased convective heat loss. The cross sectional area of the conductive region is strongly dependent on the gas velocity and heat conductivity of the gas.

Feedback in the Extremely Violent Group Merger NGC 6338

The galaxy group NGC 6338 is one of the most violent group–group mergers known to date. While the central dominant galaxies rush at each other at 1400 km s−1 along the line of sight, with dramatic gas heating and shock fronts detected, the central gas in the BCGs remains cool. There are also indications of feedback from active galactic nuclei, and neither subcluster core has been disrupted. With our deep radio uGMRT data at 383 and 650 MHz, we clearly detect a set of large, old lobes in the southern BCG coinciding with the X-ray cavities, while the northern and smaller BCG appears slightly extended in the radio. The southern BCG also hosts a smaller younger set of lobes perpendicular to the larger lobes, but also coinciding with the inner X-ray cavities and matching the jet direction in the parsec-resolution VLBA image. Our spectral analysis confirms the history of two feedback cycles. The high radio frequency analysis classifies the compact source in the southern BCG with a power law, while ruling out a significant contribution from accretion. The radio lightcurve over three decades shows a change about 10 yr ago, which might be related to ongoing feedback in the core. The southern BCG in the NGC 6338 merger remains another prominent case where the direction of jet-mode feedback between two cycles changed dramatically.

A self-condensation supercritical carbon dioxide Rankine cycle system realized by absorption refrigeration

A novel self-condensation supercritical carbon dioxide (sCO2) Rankine cycle system in which a lithium bromide-water absorption refrigeration cycle is used to utilize the waste heat of exhaust gas from the carbon dioxide power cycle and provides a cold source to condense the exhaust gas is proposed. The new system avoids the huge compression power consumption of the sCO2 Brayton cycle system by replacing the compressor with a more efficient pump and the requirement of an extra low-temperature cold source. The power consumption during pressurization, thermal efficiency and levelized cost of electricity (LCOE) of the new integrated system are 26.50% lower, 3.77% higher and 4.32% lower than those of the stand-alone regenerative sCO2 Brayton cycle system, respectively. Parametric analysis is carried out to study the effects of key parameters on the thermodynamic and economic performance of the integrated system. The results show that the generator temperature, maximum system pressure and maximum system temperature have a positive effect on the thermal efficiency and LCOE, while the evaporator temperature and minimum system pressure have a negative effect.

Limited impact of jet-induced feedback in the multi-phase nuclear interstellar medium of 4C12.50

Context. 4C12.50 (IRAS 13451+1232) at z = 0.122 is an ultraluminous infared radio galaxy that has often been proposed as a prime candidate for the link between ultraluminous infared galaxies and young radio galaxies. It is also an interesting target to investigate whether and how radio-induced feedback affects the evolution of galaxies in the early phases of radio activity. Aims. We study, in detail for the first time, the hot (≥1500 K) molecular gas in 4C12.50. The potential impact of the radio jet on this gas phase, as well as on the star formation activity, are investigated. We also study the ionised (including coronal) gas as traced by the near-infrared lines. Methods. Using near-infrared long slit spectroscopy obtained with EMIR on GTC and X-shooter on VLT, we analyse the emission line spectrum of the ionised, coronal, and, specially, the hot molecular gas in the western nucleus hosting the compact radio jet. Based on high spatial resolution ALMA CO(2–1) data, we also revise the location of 4C12.50 in the Kennicutt-Schmidt diagram in order to investigate whether star formation is suppressed. Results. 4C12.50 hosts (2.1 ± 0.4) × 104 M⊙ of hot molecular gas. An unusually high rotational temperature Trot = 3020 ± 160 K is inferred. The molecular gas mass obeys a power-law temperature distribution, dMH2/dT ∝ T−5, from T ∼ 300 K and up to ∼3000 K. Both results support the idea that shocks (probably induced by the radio jet) contribute to the heating and excitation of the hot molecular gas. A molecular outflow is not detected. The coupling of the outflowing ionised and neutral outflows with the hot molecular gas is poor. Contrary to other studies, we claim that there is no evidence for star formation suppression in this object. Conclusions. If radio-induced feedback can regulate the star formation activity in galaxies, 4C12.50 is a promising candidate to reveal this phenomenon in action. However, we find no solid evidence for a current or past impact of this mechanism on the evolution of this system, neither by clearing out the dusty central cocoon efficiently, nor by suppressing the star formation activity.

Mitigating heating of degenerate fermions in a ring-dimple atomic trap

We report on the impact of the extended geometry of a ring-dimple trap on particle-loss heating of a degenerate Fermi gas. When the Fermi level is slightly greater than the depth of the dimple and a broad, low-density ``halo'' is present, the overall heating rate is reduced relative to the case of a bare ring. We find that the experimentally measured heating rates for the overfilled dimple are in good agreement with a model of the hole-induced heating caused by background-gas collisions. This suppression of the heating rate can be helpful for experimental studies of fermionic superfluids in the weak pairing limit, where achieving and maintaining low temperatures over long timescales are essential.

Life cycle assessment of greenhouse gas emissions of typical sewage sludge incineration treatment route based on two case studies in China

The rapidly increasing amount of municipal sewage sludge generated in China necessitates a thorough examination and evaluation of available treatment options. In recent years, thermal-drying and incineration technology has gained popularity, however, it may lead to significant greenhouse gas (GHG) emissions. Nevertheless, the differences in boundary conditions and technological characteristic across various cases may affect emission levels significantly. Therefore, this study utilizes a life cycle assessment to estimate the GHG emissions associated with two typical sludge incineration routes in China: direct thermal-drying combined with coal co-incineration incinerator in Case 1 and indirect thermal-drying and self-sustain combustion in Case 2. The entire treatment processes, containing different functional units, were comprehensively investigated. The results demonstrate that Case 1 and Case 2 produce 1133.33 and 350.89 kg CO2-eq/tDS (sludge dry solid) of GHG emissions, respectively. In Case 1, coal co-incineration produces 828.63 kg CO2-eq/tDS of GHG emissions, accounting for 73.1% of the total GHG emissions. Moreover, the exhaust gas treatment is a significant GHG emission source, accounting for 9.2% and 16.9% of the total GHG emissions in Case 1 and Case 2, respectively. Additionally, the sludge thickening and dewatering unit in Case 2 produces 213.75 kg CO2-eq/tDS of GHG emissions, accounting for 60.9% of the total GHG emissions. Analysis of energy flow and heat balance characteristics indicate that the indirect heat transfer method used in thermal-drying leads to significant heat loss, which limits heat recovery potential and hinders GHG emission reduction. This study proposed a scenario case based on Case 2, addressing the issues with the improvement of heat transfer process and reduction of electricity consumption, potentially reducing GHG emissions by 8.8%. Additionally, applying an exhaust gas heat recovery system could further offset up to 22.8% of the total GHG emission.

Stationary thermal-gas-dynamics of flows in the cylinder and exhaust system of a piston engine

THE PURPOSE. To evaluate the influence of the exhaust manifold design on gas dynamics and heat transfer of stationary, turbulent gas flows in the cylinder and the exhaust system of a reciprocating internal combustion engine for different boundary conditions based on physical and mathematical modeling.METHODS. The study of gas dynamics and heat transfer of flows was carried out using the CFD approach in specialized Russian-made software. The simulation was performed for a pressure drop from 0.15 to 40 kPa (the flow velocity at the outlet of the system was 10-130 m/s). The k-e turbulence model was used for modeling. The computational grid consisted of 610,000 cells. The design change consisted in the use of profiled channels with cross sections in the form of a circle (diameter 30 mm), a square (side 30 mm) and a triangle (side 52 mm).RESULTS. The article describes the mathematical model, the studied geometry of the exhaust system and the analysis of the obtained data. The velocity field, isolines of equal velocities, and tangential velocity vectors were chosen as the gas-dynamic characteristics of the flow. The gas dynamics in the longitudinal section of the exhaust system and the valve, as well as the visualization of the flow structure in 4 control sections along the length of the exhaust system, were analyzed. The heat transfer coefficient in the exhaust system was used to evaluate the heat transfer characteristics of the flow. Qualitative and quantitative differences in gas dynamics and heat transfer processes are shown.CONCLUSION. It has been established that there are common gas-dynamic effects during the flow of gas in different elements of the exhaust system. The evolution of the flow structure along the length of the exhaust system is shown based on the change in the velocity field, isolines of equal velocities, and tangential velocity vectors. The vortex structures formed in the valve assembly and the corners of the profiled channels are revealed. It has been established that the use of profiled channels in the exhaust system leads to a decrease in the heat transfer coefficient by 5 to 12%.

Research on the Carbon Emission Baselines for Different Types of Public Buildings in a Northern Cold Areas City of China

Global excessive CO2 emissions have caused serious environmental and health problems, such as global warming, melting glaciers, droughts, floods, and extreme temperatures, and have become a common challenge for the world. China has set a dual carbon goal, with the peak carbon emissions before 2030. In China, the building sector accounts for 50.9% of the country’s carbon emissions. In particular, public buildings are characterized by a high carbon emission intensity, accounting for 38.6% of carbon emissions in the building sector, which affects the achievement of the dual carbon goal in China’s building sector. Establishing a reasonable baseline of carbon emissions contributes to quota management and trading of carbon emissions for public buildings in Tianjin, China, and will ultimately contribute to the reduction of carbon emissions. This study investigates the operational energy consumption and carbon emissions of 721 public buildings in Tianjin (including electricity, natural gas, and district heating). The applicability of the Quartile method and the K-means clustering algorithm was compared to determine the carbon emission baseline of different types of public buildings, such as constraint value, guiding value, and advanced value, based on which the dynamic baseline from 2022 to 2030 was determined. The results show that the advanced value, guiding value, and constraint value of the Tianjin public building carbon emission baseline obtained using the Quartile method are more reasonable than those obtained by the K-means clustering algorithm. Furthermore, the carbon emission baseline in 2030 will be reduced by 3.4~9.2% compared to 2022. This study can guide the formulation of carbon emission trading schemes, and support Tianjin’s building sector to achieve the “carbon peak”.

Preparation and Analysis of Experimental Findings on the Thermal and Mechanical Characteristics of Pulsating Gas Flows in the Intake System of a Piston Engine for Modelling and Machine Learning

Today, reciprocating internal combustion engines are used in many branches of the economy (power engineering, machine engineering, transportation, and others). In order for piston engines to meet stringent environmental and economic regulations, it is necessary to develop complex and accurate control systems for the physical processes in engine elements based on digital twins, machine learning, and artificial intelligence algorithms. This article is aimed at preparing and analysing experimental data on the gas dynamics and heat transfer of pulsating air flows in a piston engine’s intake system for modelling and machine learning. The key studies were carried out on a full-scale model of a single-cylinder piston engine under dynamic conditions. Some experimental findings on the gas-dynamic and heat-exchange characteristics of the flows were obtained with the thermal anemometry method and a corresponding measuring system. The effects of the inlet channel diameter on the air flow, the intensity of turbulence, and the heat transfer coefficient of pulsating air flows in a piston engine’s inlet system are shown. A mathematical description of the dependences of the turbulence intensity, heat transfer coefficient, and Nusselt number on operation factors (crankshaft speed, air flow velocity, Reynolds number) and the inlet channel’s geometric dimensions are proposed. Based on the mathematical modelling of the thermodynamic cycle, the operational and environmental performance of a piston engine with intake systems containing channels with different diameters were assessed. The presented data could be useful for refining engineering calculations and mathematical models, as well as for developing digital twins and engine control systems.

Simulation and redesigning the methanol production cycle using coil-wound liquefied natural gas heat exchangers

The current research uses Aspen Software to find the best way to run the petrochemical methanol complex. This was done by using pinch technology and arranging the heat exchanger network. First, a process flow diagram of the Kaveh industrial plant was used to simulate different plant parts. Then retrofit the plant’s heat exchanger network to minimize capital costs and improve energy efficiency. Plotting the composite curve of the streams, the type, and the quantity of hot and cold utilities came next., and the most economical minimum temperature difference, etc. The best capital cost decreased by around 70%, while the utilities increased by about 50%, and the payback money lasted for 6 months. The methanol cycle was redesigned using coil-wound heat exchangers to improve operational flexibility because of high-temperature streams.The capital costs decreased by around 10%, and utility costs were saved with the liquefied natural gas heat exchangers.

Mathematical model of indicators determination of quality root crops harvesting and potato energy saving technology in high humidity soil condition

Existing machines for harvesting root crops and potato tubers perform the technological process in conditions of high soil moisture, which negatively affects to the quality of harvesting as a result of a decrease in the completeness of separation of marketable products. To increase the separating capacity of slotted devices for cleaning root crops, it is proposed to improve the method of heating the separating surface with hot exhaust gas from the power plant of a harvesting machine or drive. The FSC VIM has developed a separating system for harvesting root crops and potatoes at high humidity using the heat of the exhaust gases of the power plant. In order to determine the optimal values of the developed separating system, as well as recommendations for subsequent changes in the design and technological parameters of harvesting machines, a mathematical model has been developed for calculating the quality of harvesting root crops and potatoes using energy-saving technology in conditions of high soil moisture. The values of finding the completeness of separation by expression are presented, depending on the heap mass of the root crops and potatoes coming from the digging to the separating working bodies, as well as the coefficient K_С of the change in the structural moisture of the soil.

Low Carbon Economic Dispatch of Integrated Energy System Considering Power-to-Gas Heat Recovery and Carbon Capture

Carbon capture and storage (CCS) is an effective means to achieve the goals of carbon peaking and carbon neutrality. To improve the operating economics and low-carbon emission of an integrated energy system, the strong exothermic property of power-to-gas is utilized for heat recovery and injection into the heat network. This expands the adjustable range of electric output of combined heat and power (CHP) units which will improve wind power accommodation. The CO2 produced by the coal-fired unit is captured using post-combustion carbon capture technology, and then stored and used to manufacture methane, in order to realize the electric–gas–heat integrated energy system coupled with power-to-gas. Based on the ladder-type carbon trading mechanism, a low-carbon economic dispatch model of integrated energy system is proposed, which considers the incorporation of power-to-gas heat recovery and carbon capture and storage. The objective function is to minimize the total operation cost of the system. The model is simulated in the revised IEEE 39-bus power network, Belgium 20-node gas network and 6-node heat network by CPLEX solver and simulation results verify the effectiveness of the proposed model.

Study on the recycling of waste wind turbine blades

The pyrolysis process of waste wind turbine blades in the coal-fired flue gas was studied. The effects of pyrolysis temperature, pyrolysis time, flue gas composition and heating mode on the pyrolysis product were investigated, and the pyrolysis mechanism was also analyzed. Finally, the industrial implementation scheme of pyrolysis process in coal-fired power plants was formulated. The results showed that the matrix resin of wind turbine blades could be carbonized and then oxidized by direct heating with the flue gas. A clean glass fiber was finally obtained to recycle. When the blade was pyrolyzed at 420–450 ℃ for 5–6 h, the purity of recycled fiber was above 99 % and its tensile strength decrease was less than 10 % compared with the original fiber. During the pyrolysis process, the concentration of SO2 in flue gas had little effect on the quality of recycled fiber because of its nonreactivity with SiO2. With the increase of pyrolysis temperature, the purity of recycled fiber increased while its tensile strength decreased. In coal-fired power plants, a small fraction of flue gas was pumped from the tail flue of boiler by a fan. The flue gas after dust removal was sent to a recovery furnace, where the blade was pyrolyzed. The tail gas was transported to the boiler furnace for complete combustion and then purified by the existing pollutant purification devices in the power plant. According to the above scheme, the recycling of waste wind turbine blades in coal-fired power plants could be readily realized by equipping a duster, a recovery furnace and a fan.

Terahertz spin ratchet effect in magnetic metamaterials

We report on spin ratchet currents driven by terahertz radiation electric fields in a Co/Pt magnetic metamaterial formed by triangle-shaped holes forming an antidots lattice and subjected to an external magnetic field applied perpendicularly to the metal film plane. We show that for a radiation wavelength substantially larger than the period of the antidots array the radiation causes a polarization-independent spin-polarized ratchet current. The current is generated by the periodic asymmetric radiation intensity distribution caused by the near-field diffraction at the edges of the antidots, which induces spatially inhomogeneous periodic electron gas heating, and a phase-shifted periodic asymmetric electrostatic force. The developed microscopic theory shows that the magnetization of the Co/Pt film results in a spin ratchet current caused by both the anomalous Hall and the anomalous Nernst effects. Additionally, we observed a polarization-dependent trigonal spin photocurrent, which is caused by the scattering of electrons at the antidot boundaries resulting in a spin-polarized current due to the magnetization. Microscopic theory of these effects reveals that the trigonal photocurrent is generated at the boundaries of the triangle antidots, whereas the spin ratchet is generated due to the spatially periodic temperature gradient over the whole film. This difference causes substantially different hysteresis widths of these two currents.

On the gas heating effect of helium atmospheric pressure plasma jet

Plasma medicine is an emerging research field which has been driven by the development of plasma sources suitable to generate low temperature plasmas. In many cases, such devices can operate without a gas flow, producing a plasma discharge from the ambient air. However, the most common case is the use of a working gas at a given flow rate to produce a plasma jet. Helium (He) is one of the gases commonly used as the carrier gas to generate cold atmospheric pressure plasma jets (CAPPJs) due mainly to the easiness to ignite a gas discharge with it. However, in this work it was observed that most of the heating of a He CAPPJ can come just from the expansion of the He gas. This was found through measurements of gas temperature (T gas ), using fiber optic temperature (FOT) sensors, and thermal output, using both FOT and infrared imaging with the He flow impinging on a copper (Cu) plate. Such findings were achieved through comparisons of T gas and the temperature on the Cu (T Cu ) plate in the conditions with and without discharge ignition, as well as comparing T gas in the free gas/jet mode with and without discharge ignition. It was verified that the T gas values increased as the distance from the gas outlet was enlarged, especially at low He flow rates, even without discharge ignition. Despite the temperature increase with distance, it is possible to produce plasma jets with temperatures lower than 40 °C at low He flow rates.

A comprehensive review of aluminium electrolysis and the waste generated by it.

Aluminium is produced by electrolysis using alumina (Al2O3) as raw material and cryolite (Na3AlF6) as electrolyte. In this Hall-Héroult process, the energy consumption is relatively large, and solid wastes such as spent anodes and spent pot liner, flue gas and waste heat are generated. Therefore, this article discusses from the perspective of high energy consumption and high pollution and summarizes the methods to reduce energy consumption and solve pollution problems. The functions of carbon anode, carbon cathode, refractory material and sidewall in aluminium electrolysis cells are discussed in detail. The process of aluminium electrolysis and the ways to improve the current efficiency of aluminium electrolysis cells and reduce their energy consumption are outlined. The causes and treatment methods of spent anodes, spent cathodes, spent refractories and spent spot liner are reviewed. The research progress of waste heat recovery and aluminium electrolysis flue gas purification are analysed. And the future research directions of aluminium electrolysis flue gas are provided.