Convection flow

Convective heat transfer is classified as forced convection and natural (or free) convection. The former results from the forced flow of fluid caused by an external means such as a pump, fan, blower, agitator, mixer, etc. In the natural convection, flow is caused by density difference resulting from a temperature gradient within the fluid. An example of the principle of natural convection is illustrated by a heated vertical plate in quiescent air. 

Characterization and influence of electrohydro dynamic secondary flows on convective flows of polar gases is lacking for most simple as well as complex flow geometries. Such investigations should lead to an understanding of flow control, manipulation of separating, and accurate computation of local heat-transfer coefficients in confined, complex geometries. The typical Reynolds number of the bulk flow does not exceed 5000. 

Macromixing is estabflshed by the mean convective flow pattern. The flow is divided into different circulation loops or zones created by the mean flow field. The material is exchanged between zones, increasing homogeneity. Micromixing, on the other hand, occurs by turbulent diffusion. Each circulation zone is further divided into a series of back-mixed or plug flow cells between which complete intermingling of molecules takes place. 

In considering the effect of mass transfer on the boiling of a multicomponent mixture, both the boiling mechanism and the driving force for transport must be examined (17—20). Moreover, the process is strongly influenced by the effects of convective flow on the boundary layer. In Reference 20 both effects have been taken into consideration to obtain a general correlation based on mechanistic reasoning that fits all available data within 15%. 

The first term may be considered as the contribution of the internal circulation or convective flow to the stage length, the second term as the contribution of the axial diffusion to the stage length. The stage separation factor is given by... 

Has a specific location in relation to the seal to optimize the convective flow. 

Dry Running Pump Again, no lubrication or dissipation of hear. Remove the heat with a double seal and barrier tank with forced convective flow. 

Gases and Liquids Tending to Gas Gases cannot lubricate the seal fltees. No dissipation of heat. Use a dual seal with forced convective flow. 

These two equations arenicelysoluble,butbefore we solve themweshould discuss them further. Notice that the convective flow rates are divided by the volumes of each phase. 

The combination of the second-order kinetics plus the convective flow term is enough to requiretheuse ofnumerical methods. Toprovethis to ourselves,wecan redo theproblem afterremovingtheconvectiveflowterm.Thatisdoneinthecellthatfollows. 

The reaction can be considered to take place in the volume above the membrane. Only hydrogenistransportedthroughthemembrane,whereuponitleavesthelowervolumevia convective flow. Unconverted alkane A, the product alkene B, andhydrogen are also con-vectedoutofthevolumeabovethemembrane.Considerboththevolumesaboveandbelow themembranetobewellmixed. 

Free convection flows along heated and cooled vertical surfaces and above heat sources, covered in Section 7.5 ... 

Gases, vapors, and small dust particulates are distributed in the space by airflows produced by supply jets, convective flows, or air currents entering the building through the building apertures and cracks. Also, gases and vapors are distributed due to turbulent and molecular diffusion. Distribution of contaminants with airflows is significantly faster (hundreds of times) than distribution due to molecular diffusion. 

Resistance and arc welding operations, and plasma and laser cutting produce fumes by expulsion or evaporation of the base material, coating, and electrode wear. Larger particles deposit on the surrounding surfaces, while smaller particles move upward with convective flows. Specific contaminants associated with different welding and cutting operations are listed in AWS. ... 

As can be seen from Figs. 7.58 and 7.59, the amount of air in the convection flows increases with height, due to entrainment of the surrounding air. The amount of air transported in a natural convection flow depends on the temperature and the geometry of the surface or source and the temperature of the surrounding air. Because the driving force in convection flows... 

FIGUftE 7.58 Convection flows along vertical surfaces. 

Natural convection flows in nonconfined and nonstratified environments (Section 7.5.2)... 

The influence of a confined space on convection flows (Section 7.5.4)... 

Convection flow along vertical surfaces (Fig. 7.63) is also of major interest in industrial ventilation, where large production units with a vertical extension are often present. When the vertical extension of the surface is small, the convection flow is mainly laminar, but at larger extensions the flow is tiir-... 

Convection flows from horizontal surfaces are very difficult to determine in the same basic way as for point, line, or vertical sources. The reason is that the flows behave in a very unstable way and leave the fiat surface from different positions at different times, partly depending on the total air movement in... 

Conclusion According to the maximum and minimum method, die convection flow rate through a level 2 m above the fliKir is between 0,35 m /s and 0.48 m%. 

Mundt, E. 1 992. Convection flows in rooms with temperature gradients Theory and measurements. In Roomvent 92 Proceedings of the Third International Conference on Air Distrihii-tion in Rooms, vol. 3. Aalborg, Denmark. 

Airflow near the hood can be influenced by drafts created directly by the supply air jets (spot-cooling jets) or by turbulence of the ambient air caused by the jets, upward/downward convective flows, moving people, and drafts from doors and windows. 

The convection flows from the heat sources V and Z as well as contaminant flows from contaminant sources are flows loading the room. In the sources additional heat and pollutant flows may be generated, which are exhausted directly out by local ventilation and are not included in the balance calculation. 

E. Sandbetg, H. Koskela, and T. Hautalampi, Convective flows and vertical temperature gradi ent with the active displacement air distribution, in Roomvent 9H, Stockholm,. Sweden, 1998,... 

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