Gas Heat Transfer Research Articles

Investigation of thermal performance in dual‐fuel units

AbstractNumerical studies were carried out to investigate the thermal performance of the muzzle flow with strong shock discontinuities and gas–gas heat transfer mechanism in the base bleed unit (BBU) of an aerodynamic vehicle under the combined effects of muzzle flow and depressurization process. The process was modeled using the Navier–Stokes equations with chemical kinetics and interior ballistic equations. The results show that the muzzle phenomena with large temperature gradients and different wave structures appear after the supersonic vehicle enters into the free‐flight stage. The BBU also experiences a strong depressurization process with the release of high‐temperature propellant gas at 2200 K. However, the igniter combustion gas at a higher temperature of 3050 K in the BBU develops downstream and upstream repeatedly under the combined effects of the base wave and depressurization process, which makes the energy conversion process in the unit more complicated. With the projectile leaving the control of the muzzle flow, the BBU is full of the igniter combustion gas and the energy in the unit is uniformly distributed gradually. The high‐temperature area, at approximately 2750 K, propagates downstream along the axial and radial directions simultaneously until it finally dominates the entire unit. The maximum temperature of the combustion gas acting on the propellant surface is always 2740 K and the maximum heat flux remains approximately 1250 W/cm2 at later periods.

Gas flow and heat transfer in granular energy-releasing materials: Novel computational model and important features

In this paper, the process of flowing the coolant gas through granular or porous media with heat-generating sources is considered. Such process takes place in various ruinous objects with energy release sources formed after natural or man-made disasters, e.g., in destroyed power unit of a nuclear power plant like exploded reactor No. 4 of the Chernobyl NPP. Also, this process is typical for some technologies, e.g., for innovative pebble-bed nuclear reactors. The aim of this work is, firstly, to develop a tool for numerical simulation of 3D processes in porous media with energy release sources, which will allow one to get the proper results quickly, and, secondly, to study some important features of these processes. A computational model and OpenFOAM solver have been developed in the work to simulate the fluid flow and heat transfer in granular or porous energy-releasing materials. The proposed mathematical model is based on the assumption of interacting interpenetrating continua, and the developed numerical method is based on the PIMPLE algorithm adapted for the system of governing equations. The novel OpenFOAM solver has been tested on 1D and 2D problems, which were previously solved by known algorithms based on the finite difference method. The new solver is faster by 1–3 orders of magnitude (depending on the number of cells in the mesh) and makes it possible to carry out calculations of 2D and 3D processes without parallelization within reasonable time, in contrast to the previously used numerical methods. The 3D gas flows through porous energy-releasing object have been studied, and some important features of these processes have been revealed. It has been shown that the temperature dependence of the gas dynamic viscosity leads not only to the fact that the gas tends to flow around the hot zones, but also to an additional increase in temperature in the heated area, caused by a drop of the density and velocity of the gas due to increasing the flow resistance force in this region. It has been revealed that if the total intensity of the energy release in the porous object is known a priori, but the relative location of the energy release sources is unknown, it is impossible to predict the maximum temperature of the object.

Modern Methods for Numerical Simulation of Radiation Heat Transfer in Selective Gases (Review)

Modern Methods for Numerical Simulation of Radiation Heat Transfer in Selective Gases (Review)

Dynamic control method of flue gas heat transfer system in the waste heat recovery process

A new flue gas waste heat recovery system and its control strategy are proposed based on the intelligent control technology and the principle of phase-change heat transfer. It is composed of flue gas heat transfer system (FGHTS) and air heat transfer systems (AHTS). The system pressure and outlet flue gas temperature are adjusted by blower frequency in the AHTS and the concentration of lithium bromide-water in the FGHTS, respectively. For FGHTS, a dynamic control method is proposed based on improved particle swarm optimization (PSO). In this method, the optimization ability and the convergence of PSO algorithm are affected by inertia weight and fitness function. The inertia weight strategy with the inverted S-shaped function (IWS-ISF) can enhance the global search ability in the initial stage and the local search ability in the later stage compared with other inertia weight strategies. Meanwhile, the integral time absolute error (ITAE) fitness function is improved by introducing overshoot into ITAE, and the improved fitness function is defined as IITAE fitness function. The improved PSO algorithm based on IITAE fitness function can reduce the overshoot of FGHTS by 66.23%. This paper can provide a theoretical basis for improving the control performance of the new system.

The influence of central coke charging mode on the burden surface shape and distribution of a blast furnace

Abstract The burden surface shape and distribution in the shaft directly affect the gas distribution, heat transfer and chemical reactions inside the blast furnace. The current study developed a three-dimensional model of bell-less top charging to investigate the influence of the “central coke charging/sub-central coke charging” (CCC/SCCC) mode on the burden surface shape, burden distribution, and mass percentage of ore-to-coke (O/C). The results showed that the burden height of the region between the middle and edge is low by applying the CCC mode, while there is a heap valley in the center and a heap top in the middle region when the SCCC mode was adopted. In radial direction, the mass percentage of bigger size coke in the middle region is largest for the CCC mode, while the largest of the mass percentage was obtained in the center region by applying the SCCC mode. In longitudinal direction, the mass percentages of bigger coke and ore at the top region are largest for both modes. Besides, the mass percentage of O/C increased and then decreased to zero at the center for both modes. And the maximum of the mass percentage of O/C were 7.63 and 7.38, respectively.

The flame mitigation effect of N2 and CO2 on the hydrogen jet fire

Hydrogen has attracted much attention from governments and enterprises around the world due to its zero pollution and recycling use. However, it may bring safety problems such as hydrogen jet fire due to its wide flammability range and low ignition energy. Therefore, the methods of preventing hydrogen jet fire need to be explored urgently. In order to investigate the effect of gaseous fire extinguishing agent on the hydrogen jet fire, a series of experiments were carried out to study the flame behaviors under the effects of nitrogen and carbon dioxide jets. The fire extinguishing agents were released through a jet nozzle with diameter of 3 mm at the pressure of 11 atm. The flame length, thermal radiant flux and total heat flux were analyzed. The results show that the reduction ratio of vertical flame length increases with the decrease of the installation height of the extinguishing agent nozzle. It indicates that when the fire extinguishing agent is injected at the root of hydrogen jet flame, the fire may be extinguished. Due to the reduction of flame size, the thermal radiant flux received by the radiometer decreases, which corresponds to the reduction of flame radiation fraction. The total heat flux received in the downstream region of deflected flame is determined by the joint action of thermal radiation and convection. The convective heat transfer of high-temperature gas may cause the value measured by the heat flux meter on the flow path of the deflected flame to increase. Besides, the extinguishing limit for hydrogen jet flame under the effects of nitrogen and carbon dioxide jets are analyzed.

Influence of Variable-Diameter Structure on Gas–Solid Heat Transfer in Vertical Shaft Cooler

In order to improve the heat transfer between high-temperature sinter and cooling gas in a vertical shaft cooler, a new furnace type with variable-diameter structure was proposed, and the influence of variable-diameter structure on gas–solid heat transfer in vertical-shaft cooler was studied by CFD-DEM coupling method in the current work. The results show that variable-diameter structure can increase the quantity of low-temperature sinter as well as the outlet cooling gas temperature, and can improve the uniformity of sinter and cooling gas temperature along the width, at the cost of significantly increasing the cooling gas pressure. By changing the parameters of the variable-diameter structure, it was found that a smaller width of the vertical section or a larger angle of the contraction section led to a better sinter–gas heat transfer. The influence of vertical section width on cooling gas pressure was more obvious. It is suggested that when designing and using the vertical shaft cooler with variable-diameter structure, consideration should be given to the effect of sinter–gas heat exchange and the pressure of cooling gas. Furthermore, the occurrence of material blockage and excessive equipment height should be avoided.

Influence of surface roughness on the heat transfer coefficient of fluids in an additively manufactured supercharger

The supercharger is intended for heating a fluid (gaseous helium or gaseous nitrogen) used for the pressurization of fuel tanks of oxidizer and propellant of a rocket engine. The fluid is heated with the generator gas downstream the turbine. A supercharger with increased channel surface roughness was made according to an additive technology. High roughness is one of the features of producing parts by selective laser melting. The article presents a method of calculating the heat transfer of generator gas and nitrogen, as well as the results of heat transfer both with and without account of the surface roughness in the channels of the liquid-propellant engines additively manufactured supercharger. Firing tests were carried out at the research base of NPO Energomash JSC. The calculated and experimental values of the temperature of the working medium at the outlet of the supercharger are compared.

Calculation of Heat and Mass Transfer Characteristics and Dust Collection Parameters of a Shock-Vortex Apparatus with a Regular Tubular Packing

Based on the analysis of the gas cleaning equipment operation in the technological schemes of gas purification at chemical enterprises of the Republic of Kazakhstan, the design of a two-stage shock-vortex apparatus with a regular tubular packing was developed. As a result of the studies carried out for the apparatus’ packed zone, graphical dependences of the mass transfer coefficients in the gas phase, heat transfer and dust collection efficiency on the gas velocity and irrigation density have been obtained. Similarly, for the zone of shock interaction of a gas flow with a liquid, graphical dependences of the dust collection efficiency have been obtained with a change in the gas velocity in the inlet fitting and the initial liquid level. Based on the studies carried out, methods for calculating the mass transfer coefficients in the gas phase and heat transfer, the dust collection efficiency in the contact stages and the overall dust collection efficiency have been proposed.

Optimization of thermal barrier coating performance and durability over a drive cycle

A methodology to thermo-mechanically optimize a piston thermal barrier coating over a full drive cycle was established. The optimization objective was to minimize the heat transfer to the engine wall while maintaining structural integrity of the coating. Over 800 candidate materials were investigated and the optimization required more than one million non-road transient drive cycle calculations; real materials were investigated to ensure a realizable result and the existence of thermal and mechanical properties. High computational efficiency was achieved using a recently developed analytical heat transfer technique for multilayer engine walls. An uncoupled approach was utilized for the optimization, wherein the gas temperature and heat transfer coefficient profiles from a fully coupled and calibrated baseline model over the 20-min drive cycle were employed. The coating/piston interface temperature was constrained to be below the maximum piston service temperature limit. The durability was assessed using a recently developed analytical coating delamination framework for engine in-cylinder coatings based on the energy release rate when a crack forms. Results are presented for a mechanically unconstrained optimization and for cases constrained to three fixed levels of drive-cycle maximum energy release rate, and also constrained by the individual material’s toughness. The best-performing coating materials identified were verified using the fully coupled system-level model, which compared well to the uncoupled predictions. A study on the effect of adding a sealing layer to some high-performing, but porous, coatings showed a reduction in fuel consumption benefit and an increased exhaust temperature over the cycle, but the system still outperformed the uncoated case. The results of the study elucidate the importance of including engine performance and mechanical failure considerations in thermal barrier coating design.

Turbulent swirling gas flow around obstacles

Turbulent swirling gas flows in the flow around obstacles in the ventilation system and in the intermachine space are studied. In the development of mathematical decomposition, the effectiveness of developing a spatial decomposition of ventilation for ship and industrial placements and the application of this technology are shown. Keywords: turbulent swirling gas flow, cramped space, obstacle, acoustic characteristics, intensification, heat and mass transfer, Pesochinskiy plan. cascad344@gmail.com

Influences of gas permeation with adsorption effect on the transient thermal insulation performance of silica aerogel at pressure and temperature differences

Silica aerogel is a thermal protective material for an outer space launch under aerodynamic heating, significant temperature difference, and pressure gradient conditions. This paper proposes a gas permeation model by considering the gas adsorption effect for silica aerogel under pressure differences. The gas (N2) adsorption behavior of silica aerogel is simulated by the grand canonical Monte Carlo method. This simulation provides the concentration of the adsorbate gas layer and the average thickness of adsorbate gas in the nanopore. An unsteady-state heat transfer model within silica aerogel, coupling with the acquired gas diffusion effect, heat conduction, and thermal radiation, is developed to study the thermal insulation performance. The gas permeation with the gas adsorption inside silica aerogel exerts a prominent influence on the dynamic temperature response of the hot surface. At the temperature of 77–90 K, the gas adsorption has a remarkable impact on the gas permeation within silica aerogel, which would finally affect the energy migration. The order of the coefficient changes from 10−14 to 10−10 m2. In contrast, the adsorption effect is negligible at the temperature of 298–1300 K. When the gas diffusion and heat transfer directions are opposite, gas diffusion will impede heat transfer, and thus the thermal insulation performance will be improved up to 88.94% and 25.65% at unsteady- and steady-state, respectively.

Numerical investigation of blast furnace gas and coke oven gas combustion under different O2/CO2 environments

AbstractA numerical model of a 75 t/h gas‐fired boiler burning blast furnace gas (BFG) and coke oven gas (COG) was developed to study the effect of O2/CO2 conditions on the combustion characteristics, verified by comparing with the results measured in field experiments. The results showed that the ignition distance of COG was shorter than that of BFG, and COG reached the stable combustion temperature of 1000 K earlier in the condition of O2/CO2 combustion with 31% O2 than in the condition of air combustion. Under different O2/CO2 conditions, the overall temperature of gas‐fired boiler decreased. The maximum temperature of air combustion, O2/CO2 combustion with 26% O2, and O2/CO2 combustion with 31% O2 were 1867, 1678, and 1834 K, respectively. Under the condition of O2/CO2 combustion, the radiation heat transfer of mixed gas was enhanced, and the overall heat flux was obviously improved. Under the O2/CO2 condition, the overall temperature was lower than that of air combustion, but the wall heat flux increased. The NOx production decreased after the change to O2/CO2 combustion, and the NOx generation at the furnace arch decreased from 70.28 mg/m3 to 6.94 mg/m3 under the condition of O2/CO2 combustion with 26% O2. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

A Coupled Multifield Estimation for Temperature Rise in a Gas Insulated Bus Bar Using ANSYS

Gas Insulated Switchgear (GIS) is an integral part of the urban power systems, which have been developed to address the substantial need for making substations more compact and reliable. The gas insulated bus bar is a crucial component of the power equipment in the substations with voltages over 100kV. In general, the ampacity of the bus bar is constrained by the maximum operating temperature, which has to be predicted, according to the demands of the standard IEC 62271. Therefore, thermal analysis of gas insulated bus bar has to be performed in the design of GIS. However, the mechanisms of heat generation and transfer in the SF6 gas and air are so complicated that it is not a simple problem to predict the temperature rise. Joule’s heat due to current in the main conductor and heat due to induced eddy currents in the tank is calculated via Magnetic Analysis. The heat transfer to the tank and atmosphere is done by means of radiation and natural convection. Heat transfer coefficients are not constant and vary on many parameters such as model geometry and material constants, making them difficult to calculate and apply to the boundaries. By considering the factors stated above, Nusselt number is used to analytically compute the temperature dependent heat transfer coefficients on the boundaries. The proposed research work presents a coupled magnetic and thermal field analysis supported by finite element analysis of extra-high voltage GIS bus bar with the help of ANSYS Maxwell and ANSYS Fluent. The results of the coupled finite element approach accord well with the values derived analytically.

Deformation Modeling and Simulation of a Novel Bionic Software Robotics Gripping Terminal Driven by Negative Pressure Based on Classical Differential Algorithm.

A general pneumatic soft gripper is proposed in this paper. Combined with the torque balance theory, the mathematical theoretical model of bending deformation of soft gripper is established based on Yeoh constitutive model and classical differential geometry. Assuming that the pressure in each inner cavity is evenly distributed, the input gas is in an ideal state, which is approximately treated as an isothermal condition, and all orifices experience blocked flow. In addition, compared with the mechanical work of gas, the energy related to gas flow and heat transfer is negligible. The nonlinear mechanical properties of silicone rubber are studied. It is regarded as isotropic and incompressible material, which is characterized by strain energy per unit volume. The material constant coefficients C10 and C20 are determined through the uniaxial tensile test, and the software gripper is simulated on the ABAQUS platform. The bending deformation models of grippers with three different force-bearing cavity structures are analyzed and compared, and the software clamping structure with the bending deformation most in line with the application conditions is selected. The limit input air pressure of the gripper and the situation of enveloping the clamping target object are analyzed. Through the bending deformation experiment, the maximum deformation angle is 72.4°. The relative error between the simulation analysis data and the prediction results of the mathematical model is no more than 3.5%, which verifies the effectiveness of the simulation and the correctness of the mathematical theoretical model of bending deformation. The soft manipulator proposed in this paper has good adaptability to grasping objects of different shapes and sizes. The minimum diameter of the target object that can be clamped is 0.1 mm. It can clamp the object weighing up to 1 kg. It has compact size, light weight, high ductility, and flexibility.

Heat transfer in a dense gas between two parallel plates

Time-dependent heat transfer in a dense gas between two parallel plates, which is initiated by an abrupt change in temperature of one plate, is numerically investigated on the basis of the Enskog equation under the diffuse reflection boundary condition. Numerical computation is carried out by a finite-difference scheme combined with the Fourier spectral method for the efficient computation of the collision term of the Enskog equation. As a result, macroscopic quantities of the gas, such as heat flux and temperature, are obtained for various Knudsen numbers and ratios of the molecular diameter to the distance between plates. Compared to the case of an ideal gas, the heat flux in the stationary state is enhanced due to an effect of the finite size of molecules for not only small but also intermediate Knudsen numbers. The results imply that the finite-size effect also affects the propagation of disturbances in the initial stage, particularly for small Knudsen numbers.

Atmospheric pollution from rockets

We address the impact of rocket exhaust gases on atmospheric pollution through high-resolution computational fluid dynamics simulations. We have modeled the exhaust gases and developing plume at several altitudes along a typical trajectory of a standard present-day rocket, as a prototypical example of a two-stage rocket to transport people and payloads into Earth's orbit and beyond. The modeled rocket uses RP-1 as the propellant and liquid oxygen as the oxidizer to generate ∼6806 kN of thrust via a total of nine nozzles, matching—as closely as possible based on available data—the specifications to the Thaicom 8 launch mission of the Falcon 9 rocket manufactured by SpaceX. We have used high-order discretization methods, 11th-order accurate, in conjunction with implicit large eddy simulations to model exhaust gas mixing, dispersion, and heat transfer into the atmosphere at altitudes up to 67 km. We show that pollution from rockets should not be underestimated as frequent future rocket launches could have a significant cumulative effect on climate. The production of thermal nitrogen oxides can remain considerable up to altitudes with an ambient atmospheric pressure below but of the same order of magnitude as the nozzles exit pressure. At the same time, the emitted mass of carbon dioxide in the mesosphere is equivalent to that contained in 26 km3 of atmospheric air at the same altitude.

Rarefaction Effect, Heat Transfer, and Drag Coefficient for Gas Flow Around Square Cylinder in Transition Flow Regime

Abstract In this work, rarefaction effect, heat transfer, and drag coefficient for gas flow around a square cylinder in transition flow regime are numerically studied using unified gas kinetic scheme (UGKS). To reduce computational cost, a mirror symmetry boundary treatment for UGKS is proposed and applied in this study. It is found that: (1) velocity slip is not obvious on upwind and downwind surfaces of square cylinder due to the tangential gas flow being weak in these surfaces; (2) with the increase of local Knudsen number, velocity slip on upper surface always increases, but temperature jump can decrease, which indicates that Knudsen number is not the decisive parameter to characterize temperature jump; (3) the heat transfer between gas and square cylinder enhances with the increase of inflow Knudsen number and cylinder temperature due to the increase of temperature jump and deteriorates with the increase of inflow Mach number on account of gas stagnation; and (4) the drag coefficient increases with the increase of inflow Knudsen number, the decrease of inflow Mach number, and the increase of cylinder temperature. To further predict the variation of average Nusselt number and drag coefficient, correlations for average Nusselt number and drag coefficient with inflow Mach number ranging from 0.05 to 0.3, inflow Knudsen number ranging from 0.1 to 10, and cylinder temperature ranging from 320 K to 380 K are proposed. This research can improve the understanding for mechanisms of gas flow and heat transfer in micro-electromechanical system (MEMS) devices.

Characterization of opportunity for upgrading of the system based on arc plasma torch for thermal spaying of ceramic materials, by means of use of fuel vortex intensifier. Part II. Thermal engineering estimation and experimental testing

The main trends in the field of improving thermal spraying processes for ceramic coatings formation is, along with enhancement of coating properties, also the reducing the energy consumption for the process. In this regard, one of the important directions for improving these technologies with plasma is the development of their new versions, using the principle of adding inexpensive fuel-oxidizing mixtures based on hydrocarbons (natural gas, liquefied gas) with air. This type of plasma-fuel type of spraying will be promising for application at the present time, first of all, in order to obtain refractory functional coatings. For this purpose, the opportunity for upgrading an industrial unit/system for plasma spraying of powder materials with arc plasma torch of 25–40 kW power was investigated with the use of experimental variant of a fuel gas-vortex intensifier. Herewith the thermal engineering assessment for possible parameters of the generated high-temperature flow from the torch with this intensifier was carried out to compare these with established thermodynamic characteristics on the applicability range of this system for optimization of the oxide and carbide coating spraying process (using the examples of Al2O3, Cr3C2 and other powders); and gas dynamic and heat transfer calculations of the intensifier operating regimes in this model unit was also performed. New regimes, which were analyzed in our research as the simulants of Al2O3 spraying, have the advantage over the N2-plasma regimes from the point of view of such kinetic parameter of powder processing as ability of heating factor of hot gas medium. Taking into account the calculated data, the experimental system was developed based on the standard spraying unit UPU-3D with a fuel intensifier of the selected design and the preliminary testing of its operation was carried out at the power of 30±2 kW under the following combination of gases in the torch: nitrogen and mixture of liquefied petroleum gas with air. This system has shown the stable operation in certain range of parameters and, according to the zonal calorimetrical measurement and photo-registration of jets, it provides 30–35 % more energy emission from torch generated jet (with attached fuel vortex chamber) in atmospheric conditions, in a comparison with the torch regime with pure N2-plasma with the same power on the arc of plasma heater. Use of the system creates an opportunity to spray carbide powders as well as oxide ones at improved intensity of coating producing in a comparison with standard regimes of commercial spraying units with N2 or Ar plasmas.

Modeling of multifield coupling interactions in an aerobic landfill based on the finite volume method

Aeration, which creates an aerobic environment by air injection, has been proven to be an effective method to accelerate waste stabilization and reduce pollution load in landfills. To reveal the multi-field coupling interactions in an aerobic landfill, this study developed a three-dimensional multifield coupled model involving anaerobic–aerobic biodegradation, gas–liquid flow, methane oxidation, water evaporation, multicomponent gas diffusion (CO2, CH4, O2, N2 and H2O) and heat transfer. The model with spaced aeration wells and recovery wells is solved by OpenFOAM based on the finite volume method. The results show that a certain amount of oxygen is distributed around the aeration well, while the methane volume fraction decreases to approximately zero in most regions except around the recovery well. In the aerobic reaction area, the temperature increased up to 60 ℃, accelerated water evaporation and inhibited the reaction. The maximum vapor volume fraction occurs at the aerobic front due to the injection of dry air at the aeration well and liquefaction outside the aerobic zone. To achieve high-efficiency aerobic remediation, aeration well screens should be buried at a depth of 43% of waste thickness (from the longitudinal midpoint of the well) with a length accounting for 40–53% of waste thickness.