Turbulence exchangers

Airflow between different building zones caused by pressure and temperature differences, or turbulent exchange, addressed in Section 7.8.5. 

Temperature and contaminant gradients along the room height and separation stability between the upper and lower zones are influenced by turbulent exchange between these zones. The heat flux density due to turbulent exchange can be determined as ... 

Energy generated by physical activity in the room (i.e., movement of people, transport, conveyor, operation of machines) increases turbulent exchange between the upper and the lower zones and may even disrupt temperature and contaminant stratification along the room height. 

Turbulent exchange between air in different zones due to energy-introduced by supply air jets, convective currents, or moving objects. In this case the resulting mass transferred between the zones equals 0 (Fig. 7.108d). 

Another factor influencing contaminant and heat transfer from dirty to clean zones against the stable airflow is a turbulent exchange between these zones. This process should be considered in the design of displacement or natural ventilation systems and evaluation of the emission rate of contaminants from the encapsulated process equipment (Fig. 7.111a). 

The effect of turbulent exchange l>etween the contaminated air in the process equipment enclosure and the room air (Fig. 7.11 lb) is described by Elter-nian. According to Elterman, the air velocity in the process equipment enclosure opening assuring contaminant concentration Q at the distance / from the opening can be calculated from... 

FIGURE 7.111 Contaminant and heat transfer due to turbulent exchange between building zones (o> contaminant movement ablest the airflow near the vicinity of local exhaust (b) heat and contaminant transfer between the lower and upper zones of the building with displacement ventilation. 

The first expression here is very similar to the Damkohler result for A and B equal to 1. Since the turbulent exchange coefficient (eddy diffusivity) correlates well with IqU for tube flow and, indeed, /0 is essentially constant for the tube flow characteristically used for turbulent premixed flame studies, it follows that... 

For small-scale, high-intensity turbulence, Damkohler reasoned that the transport properties of the flame are altered from laminar kinetic theory viscosity y0 to the turbulent exchange coefficient e so that... 

The Damkohler turbulent exchange coefficient e is the same as vT, so that both expressions are similar, particularly in that for high-intensity turbulence e v. The Damkohler result for small-scale, high-intensity turbulence that... 

Winterfeld, G. 1965. On process of turbulent exchange behind flame holder. 10th Symposium (International) on Combustion Proceedings. Pittsburgh, PA The Combustion Institute. 1265-75. 

The basic nature of the turbulent exchange process is not yet well enough known to allow accurate prediction of behavior without recourse to experiment. Correlation of the growing body of experimental knowledge in this field, however, offers the possibility of evaluating time-averaged point values of thermal and material transport for many conditions of industrial interest. It is the purpose of this discussion to present some of the more elementary considerations of the nature of turbulent flow with particular emphasis upon thermal and material transport. 

Turbulent exchange velocity between epilimnion and hypolimnion Vth= ttAh 0.05 m d"1... 

Turbulent Exchange Model Reynolds Splitting Model Vertical Turbulent Diffusion... 

Although dispersion can be described by the same law as diffusion, its nature is different. Dispersion is the result of the velocity shear, that is, of the velocity difference between adjacent streamlines in an advective flow. Due to turbulent exchange perpendicular to the direction of flow, water parcels continuously change the streamline along which they move. Since these streamlines move at different speeds, each water parcel has its own individual history of speed and thus its individual mean velocity. 

The macroscopic leveling of a in turbulent exchange is characterized by a time of order r = L2/k = L2/ul so that, taking (8) into account,... 

One of the most accurate methods for determining gas exchange in this region of the boundary layer is called the eddy covariance or eddy correlation method. To apply the method, scientists measure the individual upward and downward components of the turbulent exchange and calculate a net difference (48,49). Stated mathematically, the relationship becomes ... 

In addition to the results presented above, we should also note the studies of the climatic BSGC [56] based on the basic Russian prognostic model [57]. The distinctive features of [56] were related to the dependence of the coefficients of horizontal turbulence on lateral velocity shears and to the specifying of the monthly climatic temperature and salinity field at the surface [29] instead of the heat and moisture fluxes. Despite the relatively coarse horizontal calculation grid (about 22 km), this allowed the authors to reproduce [56] a relatively distinct MRC jet and the known NSAEs off the Turkish and Caucasian coasts and off the Danube River mouth. The results of the tuning in [56] of the Munk-Anderson s formula for the coefficient of the vertical turbulent exchange from the point of view of reproduction of the actual CIL were used in [53,54]. 

The T,S structure of the Black Sea waters presented in Fig. 3 is caused by the weak turbulent diffusion below the UML, which is characterized by a diffusivity of about 10 5 m2 s 1 [6,7,11-13], which is one to two orders of magnitude lower than the values usual in the open ocean. The reason for the weak vertical turbulent exchange in the Black Sea is the great differences in the densities of the primary water masses (the freshwater mass and that of the Sea of Marmara). 

The principal features of this structure are related to the very weak vertical turbulent exchange of the T,S properties between, on the one hand, the freshened surface and the cold intermediate water masses and, on the other hand, the significantly more saline deep water mass. 

The T,S structure of the Black Sea waters consists of a few characteristic layers with different thickness top-down the upper mixed layer, the seasonal pycnocline (thermocline) the cold intermediate layer (C1L), the main pycnocline (halocline), the isothermal intermediate layer, the thickest deep layer with a slow temperature and salinity increase with depth, and the nearbottom mixed layer. The principal features of this structure are related to the very weak vertical turbulent exchange of the T,S properties between, on the one hand, the freshened surface and the cold intermediate water masses and, on the other hand, the significantly more saline deep water mass. 

Just like the turbulent viscosity, the turbulent fractions of the thermal dif-fusivity, thermal conductivity and the diffusion coefficient have to disappear at the solid wall. In contrast, at some distance away from the wall the turbulent exchange is far more intensive than the molecular motion. This leads to good mixing of the fluid particles. The result of this is that the velocity, temperature and concentration profiles are more uniform in the core than those in laminar flows, as shown in Fig. 3.15 for the velocity profiles in flow over a body. 

Consider the external atmospheric flow now, z > h. The external profiles U z) and E(z) are formed by the impulse flux rh and by the moisture flux jEh from the rough surface z = h that are taken constant over it, t(z) = rh and jE(z) = jEh. The algebraic turbulence model (3.131) links the turbulence exchange coefficients with the air velocity gradient... 

Wright, J.L., and Lemon E.R. (1966) Photosynthesis under field conditions, VIII. Analysis of wind speed fluctuation data to evaluate turbulent exchange within a corn crop, Agron. J. 58, 255-261. 

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