A random distribution reacting mixing layer model

Temperature and velocity fields in high-temperature lead coolant flows in a circular clearance for controlled oxygen impurity content in a flow were experimentally studied at the Nizhny Novgorod State Technical University by R.E. Alekseev (NNSTU). Temperature and velocity fields were simultaneously studied in “cold” and “hot” parts of the circuit in the following operating conditions: the lead temperature is t = 400–550 °C, the thermodynamic activity of oxygen is a = 10−5–100; the Peclet number is Pe = 500–7000, the coolant flow velocity is w = 0.1–1.5 m/s, and the average heat flux is q = 50–160 kW/m2. It has been found that the oxygen impurity content and characteristics of protective oxide coatings affect temperature and velocity fields in round and circular channels. This is due to the fact that oxygen in a coolant and oxide coatings on the surfaces limiting a liquid metal flow influence characteristics of the wall boundary region. The heat transfer process that occurs when HLMC transversely flows around heat exchange pipes is investigated now at the NNSTU. The experimental facility is a combination of two high-temperature liquid-metal stands, i.e., FT-2 with the lead coolant and FT-1 with the lead-bismuth coolant combined with an experimental section. The temperature of a heat-exchange surface is measured by thermocouples of diameter 1 mm mounted in walls of heat-exchange pipes. Velocity and temperature fields in a high-temperature HLMC flow are measured by special sensors placed in the flow cross section between rows of heat-exchange pipes. Heat transfer characteristics and temperature and velocity fields in a high-temperature lead coolant flow are studied in the following operating conditions: the lead temperature is t = 450–500 °C, the thermodynamic activity of oxygen is a = 10−5–100, and the coolant flow rate through the experimental setup is Q = 3–6 m3/h, which corresponds to coolant flow velocities of V = 0.4–0.8 m/s. Integrated experimental studies of characteristics of the heat transfer that occurs when the lead coolant transversely or obliquely flows around pipes have been carried out for the first time and the dependences Nu = f(Pe) for controlled content of thermodynamically active oxygen impurity and sediments of impurities have been obtained. It is assumed that the obtained experimental data on distribution of velocity and temperature fields in a HLMC flow will permit to study heat transfer processes and to use them for developing program codes for engineering calculations of heat exchange surfaces (steam generators) with a HLMC flow around them.

Physical and logistical considerations of using ultrasonic anemometers in aeolian sediment transport research

We analyze the velocity and temperature fields due to thermocapillary convection around a gas bubble that is stationary in a liquid. A linear temperature field is imposed in the undisturbed liquid. Our interest is in the effect of convective transport of momentum and energy on the velocity and temperature fields. We assume that buoyant convection is negligible. The relevant Reynolds and Marangoni numbers are assumed to be small compared with unity. When the Reynolds and Marangoni numbers are set equal to zero, the steady velocity field far from the bubble decays inversely with distance from it. We show that this behavior of the velocity field, coupled with the linear variation of the imposed temperature far away from the bubble, leads to an ill-posedness in the problem for the perturbation temperature field at steady state for small Marangoni numbers, when the Reynolds number is zero. We also consider the effect of convective transport of momentum for small Reynolds number, when the Marangoni number is zero. In this case, the velocity field far away from the bubble decays inversely as the distance from the bubble even in the presence of inertia. It follows that, for a fixed Prandtl number, when both the Marangoni and Reynolds number are nonzero, the behavior of the velocity field far from the bubble continues to yield an ill-posed problem for the steady perturbation temperature field. Therefore, inertia cannot relieve the ill-posedness of the perturbation problem for the steady temperature field. In order to understand the origin of this ill-posedness, we analyze a related problem involving the unsteady development of the temperature field in the liquid from the moment that a point force is applied to it, and held constant subsequently. We show that including the effect of convective transport of energy by a perturbation expansion leads to a temperature field in the liquid that is always time dependent. The temperature field never achieves a steady state.

Simultaneous measurement of microscale fluid viscosity, temperature, and velocity fields by tracking Janus particle on microparticle image velocimetry

Full-scale experimental and computational fluid dynamics (CFD) methods were used to investigate the velocity and temperature fields in a mechanically ventilated room. Detailed airflow fields were measured in three cases of ventilation air temperature: an isothermal case, a hot case and a cold case. The ventilation system created a round jet which developed near the ceiling. The experimental data were used to test two turbulence models: a first order k-ε turbulence model and a second order RSM turbulence model. The RSM model predicted the temperature and velocity fields better than the k-ε turbulence model. In particular, experimental global values of velocity and temperature were in good agreement with the RSM turbulence model. This model is recommended for simulation of ventilated enclosures with thermal effects.

In this study, the flow behavior of deionized water through the staggered circular micro pin fin arrays with three longitudinal spacings (S L = 2D, 3D and 4D) is investigated using flow visualization technology of micro particle image velocimetry (micro-PIV) in the range of Re = 100–800. The streamline distribution and velocity field in the three micro pin fin arrays are obtained. Experimental results indicate that the longitudinal spacing has considerable effect on both the extension of the wake region and velocity field around pin fins. The small longitudinal spacing hinders the extension of the wake region behind the pin fin and delays the vortex shedding. The micro pin fin array with S L = 2D provides maximum velocity span and transverse velocity, indicating intense local fluid mixing. The flow and heat transfer characteristics in the microchannel with a single circular micro pin fin are also studied. By comparison, the feature of the wake region in the micro pin fin array with a large longitudinal spacing is similar to that in the flow past a single micro pin fin. Moreover, vortex shedding occurs in the micro pin fin array at higher Reynolds number. The correlation between velocity field and temperature field around the pin fin is investigated. The belt zone with enhanced heat transfer around the pin fin is consistent with the distribution of fluid with high velocities. Vortex shedding can obviously enhance the heat transfer downstream of the micro pin fin.

The present paper is concerned with the application of a high-resolution scheme for a finite volume discretization method. The capability of the chosen scheme is evaluated for the numerical simulation of three-dimensional flowfields. Special emphasis lies in the calculation of the processes in the mixing zone of gas turbine combustors. Thus, numerical results are compared with detailed measurements of velocity and temperature in a model mixing zone. The velocity field as well as the temperature field strongly depend on the scheme used for the discretization of the momentum and energy equations. The proposed high-resolution scheme and the well-known QUICK scheme yield similar results, which are superior to those obtained with the simple UPWIND scheme. For the simulation of turbulent transport, the standard fc, € model is employed. The effect of numerical diffusion caused by the usual UPWIND discretization of the convective transport of A and e is assessed by the application of the high-resolution scheme of the discretization of the A and e equations. As a result, it is found that the velocity and temperature fields are insensitive to the scheme that is applied for the discretization of the A and e equations.

Research on the field strength characteristics and the flammable area of refrigerants leakage into a confined space

Heat transfer and flow characteristics of forced convection in PDMS microchannel heat sink

An analytical investigation is conducted to study the unsteady free convection heat and mass transfer flow through a non-homogeneous porous medium with variable permeability bounded by an infinite porous vertical plate in slip flow regime while taking into account the thermal radiation, chemical reaction, the Soret number, and temperature gradient dependent heat source. The flow is considered under the influence of magnetic field applied normal to the flow. Approximate solutions for velocity, temperature, and concentration fields are obtained using perturbation technique. The expressions for skin-friction, rate of heat transfer, and rate of mass transfer are also derived. The effects of various physical parameters, encountered in the problem, on the velocity field, temperature field, and concentration field are numerically shown through graphs, while the effects on skin-friction, rate of heat, and mass transfer are numerically discussed by tables.

There are two major issues of interest in relation to Newton's law of cooling. The first is its applicability to flow bounded by a nonisothermal wall where the wall surface temperature is nonuniform. The second is the restriction by the basic linear assumption. In terms of the first issue, a general Green's function-based framework exists but its implementation as a working method has been lacking, attributable to the inherent locality of Green's function. Instead of setting up and solving the local–local influence and response, a new spectral heat transfer coefficient (SHTC) method takes a different avenue. It sets up and solves global-to-local temperature-heat flux influences for a small number of low order spectral modes of wall temperature disturbances. The SHTC approach covers a range of physically relevant and numerically resolvable length scales, which have been missing in the conventional cooling law. The present work is aimed at applying the SHTC methodology to turbine blade aerothermal analysis. Two aerothermal regimes are considered, respectively. In the first part (Part 1 of the two-part article), the SHTC approach is described and case-studied for a linear aerothermal regime where the flow energy equation behaves linearly and the corresponding temperature (thermal) field is passively dictated by the velocity (momentum) field. In the companion paper (Part II), the methodology will be extended to a nonlinear regime, where the temperature field will be actively interacting with (rather than passively influenced by) the velocity field.

Droplet on oil impregnated surface: Temperature and velocity fields

In an open channel, a change from a supercritical to subcritical flow is a strong dissipative process called a hydraulic jump. Herein some new measurements of free-surface fluctuations of the impingement perimeter and integral turbulent time and length scales in the roller are presented with a focus on turbulence in hydraulic jumps with a marked roller. The observations highlighted the fluctuating nature of the impingement perimeter in terms of both longitudinal and transverse locations. The results showed further the close link between the production and detachment of large eddies in jump shear layer, and the longitudinal fluctuations of the jump toe. They highlighted the importance of the impingement perimeter as the origin of the developing shear layer and a source of vorticity. The air–water flow measurements emphasised the intense flow aeration. The turbulent velocity distributions presented a shape similar to a wall jet solution with a marked shear layer downstream of the impingement point. The integral turbulent length scale distributions exhibited a monotonic increase with increasing vertical elevation within 0.2 < Lz/d1 < 0.8 in the shear layer, where Lz is the integral turbulent length scale and d1 the inflow depth, while the integral turbulent time scales were about two orders of magnitude smaller than the period of impingement position longitudinal oscillations.

The problem of a three dimensional free convection flow with mass transfer of an incompressible viscous electrically conducting fluid past a uniformly moving porous vertical plate with transverse sinusoidal suction velocity is considered. A magnetic field of uniform strength is assumed to be applied normal to the plate. The expressions for skin-friction at the plate in the direction of flow, rate of heat transfer in terms of Nusselt number, rate of mass transfer in terms of Sherwood number, velocity field, temperature field and species concentration field are obtained in non-dimensional forms. The effects of Hartmann number, Schmidt number, Soret number, Reynolds number on the skin friction, Nusselt number, Sherwood number, velocity field, temperature field and concentration field are discussed graphically and the results are physically interpreted.

A procedure for initializing parameterizations for cumulus convection in numerical weather prediction models is described. The initialization adjust the temperature and humidity fields such that a simplified version of the Kuo cumulus parameterization will yield diagnosed convective precipitation and vertical heating profiles, if a specified velocity field can support them. In an unfavorable velocity field, the initialization will yield the closest approach to diagnosed convective precipitation possible. The initialization minimizes changes in the humidity and temperature fields while satisfying constraints imposed by the cumulus parameterization. Slight adjustments in the temperature field and relatively larger adjustments in the humidity field can modify the large scale from a state which does not support cumulus convection to a state whose convective heating, as parameterized by the simplified version of the Kuo scheme, agrees to the extent possible for an imposed velocity field. Use of more complicated versions of the Kuo cumulus parameterization with the initialized temperature and humidity profiles yields heating rates agreeing reasonably with diagnosed beating. If used in conjunction with an initialization for the velocity field, cumulus initialization may ameliorate problems associated with spinup of physical processes in numerical weather prediction.