Heat Release Source Research Articles

Features of the transverse discharge glow depending on the gas flow rate in a vortex chamber

Experimentally observed features in the formation of glowing zones in gas discharge at various mass flow rates are qualitatively explained based on the numerical simulation of a turbulent swirling flow with a local source of heat release.

Influence of the intensity of chemical heat-release source on the heat exchange at a flow of pseudo-plastic liquid in the initial interval of coaxial duct

The critical regimes of heat exchange at a laminar steady flow of a pseudo-plastic liquid in the initial interval of a coaxial duct are investigated with regard for both dissipative and chemical sources in the Arrhenius representation [5] under the conditions of an insignificant variation of the concentrations of reacting substances.

Rankine vortex evolution in a gas with heat release source

The influence of a heat release source with temperature-dependent power on the stability of a Rankine vortex has been studied. A condition for the formation of a radially convergent swirling flow with increasing vorticity is found for a medium with a positive feedback between nonequilibrium heat release perturbations and the pressure at the vortex core.

Mathematical simulation of thermal friction processes under conditions of nonideal contact

Analytical solutions are obtained for problems on unsteady-state thermal conductivity under conditions of nonideal frictional contact of two solid isotropic half-bounded bodies for cases such as a system of two half-spaces, a system of two unbounded cylindrical bodies, and a system of two half-spaces in the presence of volume source of heat release.

A111 FDSによるトンネル火災時の熱気流挙動の数値シミュレーション(燃焼科学と技術の新展開I)

To reduce victims, a ventilation system has important role at tunnel fire. In this study, thermal flow behavior is numerically predicted in several ventilation wind velocity at one-way tunnel fire. Fire Dynamics Simulator (FDS) is employed for this study. Heat release source is put as a box on the center in tunnel. Heat release rate and box size are given at several conditions as a car, bus and so on. The numerical results show hot gas flows downward when a ventilation wind is fast. Hot gas, however, goes upward along a ceiling, when a ventilation velocity is slowed down. The critical ventilation wind velocity with each condition is estimated.

Gas motion through porous objects with nonuniform local distribution of heat-release sources

The gas motion through porous objects in the gravity force field with a non-uniform distribution of heat sources, which may arise as a result of natural or man-caused catastrophes (as the damaged power unit of the Chernobyl NPP), is investigated. The influence of different parameters of the heat-releasing zone on the process of cooling of such objects is analyzed with the aid of computational experiment. It is shown that the porous element heating is affected not only by the height of the heat-releasing zone and the heat-release intensity therein but also by the distance of the heat-releasing zone from the element inlet as well as by the width of the heat-releasing zone. The phenomenon of a reduction of the porous element heating with increasing distance of the heat-releasing zone from the porous element inlet is revealed. An ambiguous dependence of the porous object heating on the width of the heat-release zone is identified: at a growth of the heat-releasing zone width, the heating of the element may both increase and decrease depending on the distance of the heat-release zone from the element inlet.

The simulation of heat transfer and flow of generalized Newtonian liquid in the initial region of coaxial channel with arrhenius source of heat release

The simulation of heat transfer and flow of generalized Newtonian liquid in the initial region of coaxial channel with arrhenius source of heat release

Mathematical modelling of heat and mass transfer under conditions of mixed convection in rectangular region with heat source and heat-conducting walls

Numerical modelling of a conjugate convective-conduction heat transfer in a rectangular region with a heat-release source was carried out in the presence of forced flow and mass exchange. The distributions of thermal and hydrodynamic characteristics, which describe the specific peculiarities of flow regimes under study, were obtained. The mutual influence of forced and free-convective flow was analysed. The scales of the effect of determining dimensionless complexes (Gr, Br, Re) on flow regimes were established. The evolution of analysed process was shown.

Conjugate problem of thermogravitational convection in a rectangular region with a local heat source

Mathematical simulation of conjugate convective-conductive heat transfer in a closed rectangular region in the presence of a heat-release source is carried out. The distributions of the thermal and hydrodynamic parameters that characterize the basic laws of the process investigated have been obtained. The possibilities of a more detailed description of both the temperature fields of the system as a whole and of maximum temperatures using a plane conjugate model of convective-conductive heat transfer are shown.

Combustion dynamics linked to flame behaviour in a partially premixed swirled industrial burner

Previous work [Biagioli, F., Stabilization mechanism of turbulent premixed flames in strongly swirled flows, Combustion, Theory and Modelling 10 (3) (2006) 389–412; Guethe, F., Lachner, R., Schuermans, B., Biagioli, F., Geng, W., Inauen, A., Schenker, S., Bombach, R., Hubschmid, W., Flame imaging on the ALSTOM EV-burner: thermo acoustic pulsations and CFD-validation, in: AIAA Paper 2006-437 presented at the 44th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, January 9–12, 2006] has shown that turbulent dry low NO x (partially premixed) flames in high swirl conical burners may be subject to a large change of their anchoring location at the symmetry axis when a critical value of the bulk equivalence ratio is reached, i.e. they are bi-stable. This flame behavior is linked here to combustion pressure dynamics measured in an atmospheric test rig for a prototype version of the Alstom EnVironmental (EV) conical burner. The link is made via the solution of the problem of the ‘travelling flameholder’, which shows that the unsteady displacement of the flame anchoring location implies an unsteady variation of the flame surface area and therefore unsteady heat release. The relevance of this source of unsteady heat release—which is different from more usual ones due to variations in turbulent burning rate and in the sensible enthalpy jump across the flame—to the generation of combustion dynamics in strongly swirled flows is confirmed here by the strong positive correlation between the tendency of the flame to be displaced and the measured amplitude of pressure pulsations.

Heat-release mechanism in ammonium dinitramide flame

To verify the adequacy of various models of heat release in ammonium dinitramide flame to real processes, chemical processes in products of thermal decomposition at a pressure of 10 torr and in ammonium dinitramide [ADN; NH4N(NO2)2] flame at a pressure of 0.4 to 60 atm are numerically simulated. The calculations are performed on the basis of a detailed kinetic mechanism and boundary conditions correlated with experimental data, thermodynamic properties, and chemical composition of ADN. The kinetic mechanism includes submechanisms that describe high-temperature chemical processes in NH3/N2O/NO/NO2/HNO2/HNO3 and NH3/HN(NO2)2 mixtures, and the global stages of aerosol decomposition. Based on calculated and experimental data, the role of dinitraminic acid HN(NO2)2, aerosols, and ADN vapor in heat release in the ADN flame zone adjacent to the burning surface is estimated. The calculations predict that the main source of heat release in the cold flame zone at p ≥ 3 atm is dinitraminic acid incoming through the channel of dissociative evaporation ADNliq → NH3 + HN(NO2)2 from the burning surface. In the high-temperature flame zone, heat release is caused by the reaction that occurs in the NH3/N2O/NO/NO2/HNO2/HNO3 mixture. At moderate pressures, the high-temperature and low-temperature zones are separated by an induction zone. The stage governing production of the OH radical, which plays an important role in combustion, in the induction zone is the reaction HNO3 + M → OH + NO2 + M. Because of a high activation energy of the stage, small temperature perturbations in the induction zone at low pressures lead to a finite change in the stand-off distance between the high-temperature flame zone and the burning surface. Therefore, small temperature perturbations in the induction zone, which are caused by admixtures in the sample or by heat transfer between the reacting gas and the ambient medium, may be responsible for disagreement between various experimental data and between experimental and calculated data on the stand-off distance between the high-temperature flame zone and the burning surface. In numerical calculations, the position of the high-temperature zone is effectively controlled by varying rate constants of elementary stages within admissible limits.

Modelling of thermogravitation convection in closed volume with local sources of heat release

A mathematical model is presented for unsteady conjugate convective-conductive heat transfer in a closed volume with local sources of heat release under the conditions of a convective-radiation heat exchange on one of external faces of the solution region. The thermogravitation convection regime was analysed for moderate Grashof numbers. The typical temperature and velocity fields were obtained, and the fields of desired quantities were compared for the planar and three-dimensional models in one of the typical sections of the solution region.

Two-dimensional problem of natural convection in a rectangular domain with local heating and heat-conducting boundaries of finite thickness

Time-dependent natural convective heat transfer in a closed rectangular domain with heat-conducting boundaries of finite thickness is investigated numerically in the case of local heating on the inner side of the vertical wall. Convection-radiation heat transfer takes place on one of the outer boundaries of the solution domain. The inhomogeneous temperature distribution in the gas cavity is clearly manifested when the Grashof number Gr > 106. Circulation flows can be distinguished in various zones of the solution domain on the basis of the numerical investigations carried out. These flows are due to the effect of the heat-release source, the propagation of perturbations induced by elements of the rigid wall, and the dynamics of conductive heat transfer in the solid material. The scales of the effect of the Grashof number on the hydrodynamic and thermal characteristics are indicated.

Conjugate heat transfer in a closed domain with a locally lumped heat-release source

Free convective heat transfer in a solution domain quite accurately modeling the cross section of the object of heat consumption has been investigated numerically. Typical velocity and temperature fields have been presented.

Premixed flamelet modelling: Factors influencing the turbulent heat release rate source term and the turbulent burning velocity

A flamelet approach is adopted in a study of the factors affecting the volumetric heat release source term in turbulent combustion. This term is expressed as the product of an instability enhanced burning rate factor, P bi , and the mean volumetric heat release rate in an unstretched laminar flamelet of the mixture. Included in the expression for P bi are a pdf of the flame stretch rate and a flame stretch factor. Fractal considerations link the turbulent burning velocity normalised by the effective rms turbulent velocity to P bi . Evaluation of this last parameter focuses on problems of (i) the pdfs of the flame stretch rate, (ii) the effects of flame stretch rate on the burning rate, (iii) the effects of any flamelet instability on the burning rate, (iv) flamelet extinctions under positive and negative flame stretch rates, and (v) the effects of the unsteadiness of flame stretch rates. The Markstein number influences both the rate of burning and the possibility of flamelet instabilities developing which, through their ensuing wrinkling, increase the burning rate. The flame stretch factor is extended to embrace potential Darrieus–Landau thermo-diffusive flamelet instabilities. A major limitation is the insufficient understanding of the effects of negative stretch rates that might cause flame extinction. The influences of positive and negative Markstein numbers are considered separately. For the former, a computed theoretical relationship for turbulent burning velocity, normalised by the effective rms velocity, is developed which, although close to that measured experimentally, tends to be somewhat lower at the higher values of the Karlovitz stretch factor. This might be attributed to reduced flame extinction and reduced effective Markstein numbers when the increasingly nonsteady conditions reduce the ability of the flame to respond to changes in flame stretch rates. As the pressure increases, Markstein numbers decrease. For negative Markstein numbers the predicted values of P bi and turbulent burning velocity are significantly increased above the values for positive Markstein numbers. This is confirmed experimentally and these values are close to those predicted theoretically. The increased values are due to the greater stretch rate required for flame extinction, the increased burning rate at positive values of flame stretch rate, and, in some instances, the development of flame instabilities. At lower values of turbulence than those covered by these computations, burning velocities can be enhanced by flame instabilities, as they are with laminar flames, particularly at negative Markstein numbers.

Underground railway environment in the UK: Part 3: Methods of delivering cooling

Ventilating an underground railway environment in which there is to be heavy traffic of electrically propelled rapid transit trains differ from those normally encountered in air-conditioning work. The heat generated by the train motors and electric lighting, together with body heat from passengers, is so great that excessive temperatures would prevail in summer unless a volume of air in excess of that required for breathing is supplied. The installation of in car air-conditioning units adds another major heat release source in the tunnel. This heat must be ejected to make using in car air-conditioning units worthwhile. This part of the paper investigates potential methods of delivering cooling to underground railways environment. The suitability of each cooling method is assessed with the help of a purposely developed mathematical model, which has been discussed at length in part two of the paper, to investigate the heat load in a generic underground railways environment. For each cooling method, the model predicts the tunnel and train carriage temperatures and relative humidities together with the PPD.

Study of heat leaks to copper nuclear demagnetization stage

Heat leaks to a copper nuclear stage at ultra-low temperatures have been investigated. We have constructed a massive copper nuclear stage and performed its cooling with negligible amount of heat release sources such as plastics and epoxies. With this stage we have managed to cool a Pt-NMR thermometer down to 45 μK at the bottom of the stage. The whole heat leaks were found to be 1 nW at a final field of 10 mT on the 10th day after cooldown to 4.2 K and remain fairly constant during 2 months. The small and time-independent heat leaks enable us to obtain the lowest temperature rapidly and maintain temperatures below 100 μK for several weeks.

CONVECTION TREATMENT AND PRESSURE SPLITTING FOR SEQUENTIAL SOLUTION PROCEDURES, PART I: THEORY AND ONE-DIMENSIONAL TEST CASES

Abstract Treatment ofconvective and pressure fluxes in the Euler and Navier-Stokes equations using splitting formulas for convective velocity and pressure, with a view to incorporate them in sequential pressure-based methods, is investigated. Two schemes—a controlled variation scheme (CVS) and an advection upstream splitting method (AUSM)—are explored for their accuracy in resolving sharp gradients. In Part I, basic concepts and the derivation of the CVS, along with its comparison to the AUSM scheme, are presented. To demonstrate the performance of the CVS and AUSM, flows involving moving or reflecting shock waves, as well as a one-dimensional combusting flow with a strong heat release source term, are investigated

Supersonic flow over a cone with heat release in the neighborhood of the apex

Supersonic flow over a cone mounted in the wake of a spherical source of heat release is investigated. The free-stream nonuniformity generated by the source leads to effective drag reduction.

Analysis of oscilliating combustion by the energy method

1. An energy equation was derived for the small nonisentropic oscillations of an ideal gas in a uniform flow with heat release sources. Using it, the correctness of applying the known equation of the acoustic energy balance to the analysis of the mechanism of oscillating combustion with a longitudinal gas oscillation was substantiated. 2. The analysis of the oscillating combustion regime was based on a numerical integration of the system of differential equations using a limited amount of experimental data. The obtained estimates of the gas parameters makes it possible to find the location and intensity of the individual sources of the generation and dissipation of the oscillation energy in the chamber, which are described by the pertinent terms in the acoustic energy balance equation. 3. The possibility is demonstrated of the maintenance of gas oscillation in the oscillating combustion regime due to the periodic formation of large-scale vortices in the medium behind the flame stabilizer.