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Thermophysics and Aeromechanics

2019 year, number 3

Heat transfer in a phase change material under constant heat flux

M.I. Nizovtsev1, V.Yu. Borodulin1, V.N. Letushko1, V.I. Terekhov1, V.A. Poluboyarov2, L.K. Berdnikova2
1Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
2Institute of Solid Chemistry and Mechanochemistry SB RAS, Novosibirsk, Russia
Keywords: композитный материал, фазоизменяемый компонент, теплоаккумулирующие свойства, тепловая инерция, энтальпийная модель, фазовый переход, composite material, phase change material, heat-accumulating properties, thermal inertia, enthalpy model, phase transition

Abstract >>
A new composite phase change material based on porous diatomite, saturated with paraffin by immersion method, has been developed. The results of the study of heat propagation in this material heated from one side with a constant power source are presented. On the basis of the enthalpy model, numerical computations were carried out, a comparison with the experimental results was made, and the influence of the properties of the composite material on the thermal processes in it was analyzed. In the computations, the heat flux power, the phase transition temperature range, and the characteristics of the phase change material were varied. The analysis of the computation results has shown that the use of the phase change material allows not only increasing the heat-storage capacity of the composite material, but also controlling the heat fluxes. As a result, it becomes possible to reduce the peak values of the heat flux passing through the material and to limit the material temperature range during heating for a long time.

Numerical simulation of natural convection heat transfer of copper-water nanofluid in a vertical cylindrical annulus with heat sources

F. Mebarek-Oudina1, R. Bessaih2
1University of 20 August 1955, Skikda, Algeria
2University of Mentouri-Constantine, Constantine, Algeria
Keywords: естественная конвекция, наножидкость, источник тепла, кольцевой канал, natural convection, nanofluid, heat sources, cylindrical annulus

Abstract >>
In this work, natural convection of Cu-water nanofluid in a vertical cylindrical annulus enclosure with two discrete heat sources of different lengths is numerically investigated using the finite volume method with SIMPLER algorithm. The adiabatic unheated portions and the discrete heat sources are mounted at the inner wall. The top and bottom walls are thermally isolated, while the outer wall is maintained at a lower temperature. The effects of nanofluid solid volume fraction on hydrodynamic and thermal characteristics such as average and local Nusselt numbers, streamlines, and isotherm patterns for the Rayleigh number ranges from 103 to 106 and solid volume fraction ranges from 0 to 0.1 are presented. The heat transfer and temperature of heaters depend on the Rayleigh number, the solid volume fraction of nanoparticles, and the length of heaters.

Investigation of a stable boundary layer using an explicit algebraic model of tur-bulence

A.F. Kurbatskii1, L.I. Kurbatskaya2
1Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
2Institute of Computational Mathematics and Mathematical Geophysics SB RAS, Novosibirsk, Russia
Keywords: турбулентность, устойчивый планетарный пограничный слой, явная алгебраическая модель турбулентных потоков, постоянный форсинг поверхности, численное моделирование, turbulence, stable planetary boundary layer, explicit algebraic model of turbulent fluxe, constant surface forcing, numerical simulation

Abstract >>
Using the recently developed explicit anisotropic algebraic Reynolds-stress model, calculations were performed to study the stable boundary layer dynamics according to the well-known test case of the GABLS1 (Global Energy and Water Cycle Experi-ment Atmospheric Boundary Layer Study) project, where the Richardson number Ri > 1. The model includes the effect of gravity waves, which allows taking into account the momentum maintenance under strong stability conditions. The model shows good agreement with the results of LES simulation. The study aims at obtaining a much more realistic boundary layer, shallower in depth than in traditional first-order models. The case of a constant surface cooling rate is considered. Some interesting features of the model are related to its deduction based on physical principles. In particular, the use of a larger number of prognostic equations in the model makes it possible to obtain more realistic dynamic behavior.

Turbulent transport in a swirling jet with vortex core breakdown. PIV/PLIF-measurement and numerical simulation

A.S. Lobasov1,2, V.M. Dulin1,2, Ar.A. Dekterev1, A.V. Minakov1,3
1Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
3Siberian Federal University, Krasnoyarsk, Russia
Keywords: закрученная струя, распад вихревого ядра, турбулентный перенос, оптические методы диагностики потока, численное моделирование турбулентного потока, swirling turbulent jet, vortex breakdown, turbulent transport, optical methods for flow diagnostics, CFD simulation of turbulent flow

Abstract >>
Paper reports on optical diagnostics and numerical simulation of the flow structure and transport of a passive scalar in a turbulent swirling jet with vortex core breakdown. Based on the measurements of the instantaneous velocity and concentration fields by PIV and PLIF techniques, the Reynolds stresses and Reynolds fluxes are evaluated and compared to those obtained from URANS and LES simulations. Based on the experimental data and LES-simulation results, the local convective and turbulent transport of the passive scalar are analyzed.

Numerical investigation and optimization of airfoil flow control using passive air-jet

M.A. Aziz1, A.M. Elsayed2
1Institute of Aviation Engineering and Technology, Giza, Egypt
2Fayoum University, Fayoum, Egypt
Keywords: пассивное управление течением, вычислительная гидродинамика, оптимизация, симплексный алгоритм, passive, flow control, CFD, optimization, simplex algorithm

Abstract >>
In this paper, a numerical investigation of airfoil flow control using passive air jet is presented. The study of generate a passive jet from pressure side to suction side was conducted in order to improve the airfoil characteristics. Such characteristics include boundary layer separation and stall inception. The numerical simulations conducted using CFDRC software. Different structured and unstructured finite volume technique is used to solve the steady compressible Navier-Stokes equations. The code results were validated with the experimental testing results for different turbulence model. Parametric study is performed for the location, slot width and angle of a synthetic jet on the suction side of a subsonic flow over a NACA 23012C airfoil. The maximum lift is achieved with the jet flow being normal to suction side surface but this come with penalty of the high drag. The maximum lift to drag ratio was accompanying with synthetic jet being located at 43% chord and 30° jet angle. Finally, optimum geometry of jet is obtained using simplex algorithm with initial shape obtained from the parametric study.

Laminar-turbulent transition of supersonic boundarylayer in the presence of external disturbances

S.A. Gaponov
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: сверхзвуковой пограничный слой, ламинарно-турбулентный переход, рейнольдсовы напряжения, гидродинамическая устойчивость, внешние возмущения, supersonic boundary layer, laminar-turbulent transition, Reynolds stresses, hydrodynamic stability, external disturbances

Abstract >>
A method for estimating the location of the laminar-turbulent transition is described, which is based on the theory of linear stability under the condition of the acoustic field presence. In the stable region near the stability loss location, the amplitude of the velocity disturbances is determined, which are excited by an external sound wave. By virtue of the proximity of sound wave parameters and proper oscillations, the obtained value of the amplitude is accepted to be equal to the amplitude of the growing wave of the boundary layer. At some downstream point, the Reynolds stresses corresponding to this amplitude become equal to several percents of laminar stresses of the undisturbed boundary layer. Based on experimental data it is accepted in the work that at the transition onset, the Reynolds stresses amount to 12 % of laminar stresses. The use of the proposed criterion accounting for external disturbances gives a good agreement between the computed and experimental data. Right up to the transition, the growth of disturbances in boundary layer is des-cribed well by the linear equations of stability.

Liquid atomization in a high-speed coaxial gas jet

V.M. Boiko, A.Yu. Nesterov, S.V. Poplavski
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: высокоскоростные струи, газокапельные потоки, аэродинамическое разрушение капель, high-speed jet, gas-droplet flow, droplets aerobreak

Abstract >>
The paper studies the process of liquid atomization in high-speed gas jets with application to a subject of high-rate fuel nozzles. Experiments were carried out for gas-liquid jet with the central-axis feeding of liquid to the outlet of a confuser-type nozzle with pumping of air in subsonic and supersonic flow regimes. The energy balance approach was developed for describing a gas-liquid jet. This provided us the needed data for comprehensive description of the gas-liquid jet: gas velocity field without liquid, shadow visualization of geometry and wavy structure of a jet with liquid and with pure gas, velocity profiles for liquid phase, spray droplet size, spray concentration and spatial distribution. The gas-liquid flow was characterized by Weber number from the time of liquid jet breakup till the final spray.

Interaction of a burning gas jet with a permeable rotating barrier

A.N. Bazhaikin
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: картина течений, концентрация газов, вращающийся проницаемый диск, горение топливной струи, flow pattern, gas concentration, rotating permeable disk, fuel-jet burning

Abstract >>
The interaction of a carbon-dioxide jet and a burning propane-butane jet with a rotating disk prepared from a cellular porous nickel highly permeable to gases has been experimentally studied. Visual pictures of the flow pattern and the spatial distributions of gas concentrations and temperatures were obtained. Modeling of the fuel mixing with air using carbon dioxide has shown that there exists a certain correlation between the initial distribution of CO2 concentrations and the distributions of temperatures and propane-butane combustion product components. It is shown that the burning of a propane-butane mixture on the disk is accompanied by the heating of the disk surfaces to 800-900 °C. The steady burning modes are identified versus the rate of fuel consumption, the disk-to-nozzle separation, and the speed of disk rotation.

Studying the effective longitudinal turbulent transfer at transverse streamlining of in-line tube bundles

V.I. Rachkov, V.N. Fedoseev, M.I. Pisarevskiy, A.S. Korsun, I.G. Merinov, Yu.N. Balberkina
National Research Nuclear University, Moscow, Russia
Keywords: коридорная упаковка стержней, турбулентное течение, эффективная теплопроводность, интегральная модель турбулентности, модель анизотропного пористого тела, пучки труб, пучки стержней, in-line rod packing, turbulent flow, effective thermal conductivity, integral model of turbulence, model of an anisotropic porous solid, tube bundles, rod bundles

Abstract >>
The experimental values of the effective thermal conductivity of water at transverse streamlining of the in-line rod bundles with square packing have been obtained. The effective thermal conductivity of water was measured in the direction parallel to the axes of the rods. The measurement method implied mixing of two flat parallel water flows in the working area; the latter moved at the same velocities, but had different temperatures. By measuring the flow temperatures before and after the mixing area, the amount of heat transferred from the hot to the cold flow was determined and the effective thermal conductivity of the liquid was calculated. In the investigated range of Reynolds numbers (from 7× QUOTE 103 to 8× QUOTE 104), calculated by the velocity in a narrow section, the experimental effective thermal conductivity of water showed a linear increase with increasing velocity and good agreement with the results of calculations by the integral turbulence model. The obtained experimental data have confirmed the possibility of using an integral turbulence model to calculate the parameters of the anisotropic porous solid model, used in CFD codes simulating thermal-hydraulic processes in the active zones of nuclear reactors and heat exchangers.

Influence of sound-absorbing coatings on the development of disturbances in a flowing mixture of vibrationally excited gases

T.V. Poplavskaya, A.I. Reshetova, I.S. Tsyryulnikov
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: гиперзвуковые течения, неравновесность, высокопористые материалы, hypersonic flows, non-equilibrium, highly porous materials

Abstract >>
In the present paper, we study the development of disturbances on a solid (continuous) plate and on a plate covered with a sound-absorbing coating, both installed at an angle of attack in a hypersonic flow (М¥ = 8.44) of a vibrationally excited mixture of carbon dioxide with nitrogen. The rms fluctuations of pressure were measured on the surface of the plates in a short-duration IT-302M wind tunnel of ITAM SB RAS. The numerical simulation was performed on the basis of solving the two-dimensional unsteady Navier-Stokes equations and a two-temperature model of relaxation flows. In modeling a real porous coating, a skeletal model was used. The model is formed by square elements arranged in staggered order with a distance between elements equal to the diameter of the pores in the sound-absorbing material used in the experiment. Data on the dynamics of the disturbance development on the solid plate and on the plate with the sound-absorbing coating under different conditions of the incident flow are reported. The effect of various parameters of the sound-absorbing coating (depth, length, and location on the plate) was studied. It is shown that the sound-absorbing coating significantly (up to 50 %) suppresses the intensity of pressure fluctuations on the plate surface as compared with the solid surface. A good agreement between the calculated and experimental data on the pressure pulsations on the surface of the plates is demonstrated.

Effect of Hall current on MHD slip flow of Casson nanofluid over a stretching sheet with zero nanoparticle mass flux

M. Abd El-Aziz1, A.A. Afify2
1King Khalid University, Abha, Saudi Arabia
2Qassim University, Buraidah, Saudi Arabia
Keywords: наножидкость Кассона, граничное условие скольжения, ток Холла, тепловыделение/поглощение, Casson nanofluid, slip boundary condition, Hall current, heat generation/absorption

Abstract >>
The influences of Hall current and velocity slip on MHD Casson nanofluid flow and heat transfer over a stretching sheet have been analyzed numerically. The Casson fluid model is applied to characterize the non-Newtonian fluid behavior. Physical mechanisms responsible for Brownian motion and thermophoresis with non-uniform internal heat generation/absorption are accounted for in the model. A recently proposed boundary condition requiring zero nanoparticle mass flux is applied to achieve practically applicable results. The partial differential equations are transformed into the system of ordinary differential equations by applying similarity transformation, which is then solved numerically. A validation of the work is presented by comparing the current results with existing literature. The results have revealed that the axial skin friction, the transverse skin friction, the heat, and mass transfer rates are significantly boosted with an increase in Hall parameter.

Concerning the adequacy of the emissivity model to experimental data when determining the true temperature of an opaque material by the thermal radiation spectrum

S.P. Rusin
Joint Institute for High Temperatures RAS, Moscow, Russia
Keywords: истинная температура, спектр теплового излучения, неизвестная излучательная способность, true temperature, thermal radiation spectrum, unknown emissivity

Abstract >>
When determining the thermodynamic (true) temperature of an opaque material by the thermal radiation spectrum, the parametric model of spectral emissivity is chosen so that this model and sought material temperature can be considered adequate to the initial experimental data. The possible adequacy conditions are analyzed. The process of choosing a model on the basis of experimental data published for a tungsten sample heated in vacuum at a constant temperature is considered as an example.

Numerical investigation on the effect of vortex generator shapes on film cooling performance

D. Zheng, X. Wang, Q. Yuan
1Xi’an Jiaotong University, Xi’an, China
2University of Toronto, Toronto, Canada
Keywords: пленочное охлаждение, профилированный вихрегенератор, численное исследование, эффективность адиабатического охлаждения, film cooling, shaped vortex generator, numerical investigation, adiabatic cooling effectiveness

Abstract >>
This paper presents a numerical investigation on the concept for enhancing film cooling performance by placing shaped vortex generators (VG) upstream of the film hole. Nine cases with different shapes of vortex generators are investigated, including the rectangular shape, triangular shape, parallelogram shape, and trapezoid shape. The film cooling performance is evaluated at the density of 0.97 with the blowing ratios ranging from 0.5 to 1.5. Results obtained show that the film cooling performance is greatly improved by the upstream VG. The twisted flow rotates in the opposite direction of kidney vortices, attenuating its effect. Furthermore, the case with rectangular VG shows the most uniform coolant layer in the spanwise direction and the highest averaged adiabatic cooling effectiveness while the total pressure loss increases a bit as a penalty.

Crisis of heat transfer on a micro-finned heater with gas-driven FC-72 film flow in a mini-channel

V.V. Cheverda1,2, O.A. Kabov1,3
1Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
2ovosibirsk State University, Novosibirsk, Russia
3Tomsk Polytechnic University, Tomsk, Russia
Keywords: двухфазные потоки, пленочные течения, локальный нагрев, кризис теплообмена, микрооребрение, two-phase flows, film flows, local heating, heat transfer crisis, micro-finning

Abstract >>
The crisis of heat transfer in a FC-72 liquid film moving under the action of a gas flow along a smooth or micro-finned heater was experimentally investigated. It is shown that the use of micro-finning leads to an increase in the critical heat flux, since additional washing of the heated surface occurs due to the capillary effect.