Flow round

If the two junctions of a circuit of two wires of different metals are maintained at different temperatures, Ti > T2, an electric current flows round the circuit, its direction and magnitude depending on the nature of the metals and on the temperatures (Seebeck, 1821). 

If two zinc electrodes are set up in opposition to one another as in Figure 6.12 (A), the difference of potential between them, measured by a potentiometer or voltmeter, is zero. If an infinitesimally small external emf is applied to the electrodes so that A is positive and B is negative, a very small current flows round the circuit, and Zn atoms pass from A into solution as Zn2+ ions, and Zn2+ ions leave the solution and are deposited as Zn atoms on B. If the small emf is reversed so that B is positive and A is negative, the current flows in the opposite direction, and zinc is dissolved from B and deposited on A. An electrode such as the zinc electrode, which reacts thus to an infinitesimal applied emf, is known as a reversible electrode. The hydrogen electrode described earlier is a reversible electrode. If two molar hydrogen electrodes are set up in opposition to one another, Figure 6.12 (B), the... 

If the composition (or flow-rate) of one stream is fixed by internal or external constraints, this may fix the composition and flows of other process streams. In Chapter 1, the relationship between the process variables, the design variables and design equations was discussed. If sufficient design variables are fixed by external constraints, or by the designer, then the other stream flows round a unit will be uniquely determined. For example, if the composition of one product stream from a distillation column is fixed by a product specification, or if an azeotrope is formed, then the other stream composition can be calculated directly from the feed compositions see Section 2.10. The feed composition would be fixed by the outlet composition of the preceding unit. 

The final main category of non-Newtonian behaviour is viscoelasticity. As the name implies, viscoelastic fluids exhibit a combination of ordinary liquid-like (viscous) and solid-like (elastic) behaviour. The most important viscoelastic fluids are molten polymers but other materials containing macromolecules or long flexible particles, such as fibre suspensions, are viscoelastic. An everyday example of purely viscous and viscoelastic behaviour can be seen with different types of soup. When a thin , watery soup is stirred in a bowl and the stirring then stopped, the soup continues to flow round the bowl and gradually comes to rest. This is an example of purely viscous behaviour. In contrast, with certain thick soups, on cessation of stirring the soup rapidly slows down and then recoils slightly. 

Section 1.5). In flowing round the sphere, the fluid has to accelerate and therefore, by Bernoulli s equation, the pressure falls towards the midpoint of the sphere s surface. 

Equations 9.6 and 9.8 were derived by Stokes and are known as Stokes s equations for steady creeping flow round a sphere. 

When a pipe is extruded, the melt has to flow round the spider at which the... 

Discharge of the Daniell cell causes zinc metal to ionize at one electrode and copper ions to deposit at the other. The net result of charge flow round the circuit is therefore equivalent to the reaction... 

If one of the metals (commonly referred to as superconductors) is castin the form of a ring and an external magnetic field is applied perpendicularly to its plane and then removed, a current will flow round the ring induced by-Faraday induction. This current will produce a magnetic field, proportional to the current, and the size of the current may be observed by measuring dm field. Were the ring (e g., one made of lead) at a temperature above 7.2 K, this current and field would decay to zero in a fraction of a second. 

Any control system may be more simply represented in the form of a block diagram. This shows how information flows round the control loop, the function of each constituent section or block, and its relation to adjacent sections or blocks. Each block represents the relation between the signal entering the block and the signal leaving it. Figure 7.2 is the block diagram of the process illustrated in Fig. 7.1. 

In this method a mandrel is placed in the mould of an injection moulding machine, the mould heated, and thermoplastic forced in to flow round the mandrel and form a tube with a closed end mandrel and plastic then are removed and passed while still hot to the blowing mould, where air introduced through the mandrel blows the material to the shape required. 

In the cross-flow air classifier (Figure 5.7) the main air is introduced at (a,) and secondary air at ( 2)- Both streams are bent round a solid wall (b) and the resulting flow follows the bend without leaving the wall or forming vortices. The so-called Coanda effect helps to maintain the flow round the bend for approximately 90° and this is enhanced by the application of suction. 

During battery discharge, as shown in Figure 1 with the Daniell cell as an example, the electrode (a zinc rod immersed in a zinc sulfate solution) at which the oxidation reaction takes place is called the anode, and is the negative electrode. The other electrode (a copper rod immersed in a copper sulfate solution) at which the reduction reaction takes place is called the cathode and is the positive electrode. The electron flow in the external circuit is from anode to cathode (the current, /, conventionally flows in the opposite direction to that of the electrons), and in the electrolyte phase the ionic flow closes the circuit. The net result of the charge flow round the circuit is the cell reaetion, which is made up of the two half-reactions of charge transfer that describe the chemical changes at the two electrodes. 

Carrica, P.M., Drew, D.A., Bonetto, F. and Lahey, R.T. (1999), A polydisperse model for bubbly two phase flow round a surface ship, Int. J. Multiphase Flow, 25, 257. 

Further work for comparing different models with wind tunnel experiments and their improvement is required. The main weak point of all the above mentioned simple models is that the models wind flow does not follow building structure. Therefore, the canalling effects (a very important for street canyons) are not reproduced in the models. Instead for the building effects they use an extra dispersion and porosity (e.g., dispersion coefficient corrections and puff splitting) approach, which is very limited. As seen from Figure 9.19, the plume penetrates the buildings, but does not flow round them. Besides, urban sub-layer wind profiles and fluxes are not considered in most of these models. 

Standard k-s The most widely used model, it is robust, economical, and time tested. The Reynolds stresses are not calculated directly, but are modeled in a simplified way by adding a so-called turbulent viscosity to the molecular viscosity. Its main advantages are a rapid, stable calculation, and reasonable results for many flows, especially those with a high Reynolds number. It is not recommended for highly swirling flows, round jets, or flows with strong flow separation... 

The flow round the stirrer blades interacts with the stationary baffles and produces a complex, circulating turbulent flow. When gas is sparged in a tank it collects in low pressure zones behind the stirrer blades forming gas cavities, which considerably influence the flow and the turbulence in the vessel. 

The circumstance that the stirrer speed no.g needed for h = 0.9 is related to the sinking behavior of the particle, is clearly evident from Fig. 5.5, which represents the stirrer speed for h = 0.9 = a = 0.5 as a function of particle diameter dp. For small dp, n oc dp applies, for large dp on the other hand n oc dp is found. This is consistent with the particle sinking behavior. According to Stokes s law, iVjs oc dp applies to very small particles (laminar flow round particles), Wss oc d° for large particles (turbulent flow round particles). The exponents in the two dependences differ by a factor of 4. The transition range lies approximately between Rep = 10 and 100. 

Gidaspow D (1974) Introduction to Modeling of Two-Phase Flow. Round Table Discussion (RT-1-2). Proc 5th Int Heat Transfer Conf Vol VII, p. 163. 

EFFECTIVE (OR AERODYNAMIC) PARTICLE DENSITY is when the measured volume includes both the closed and the open pores. This volume is within an aerodynamic envelope as seen by the gas flowing past the particle the value of density measured is therefore a weighted average of the solid and immobilised gas (or liquid) densities present within the envelope volume. The effective density is clearly of primary importance in applications involving flow round particles like in fluidization, sedimentation or flow through packed beds. 

An electric current flowing round a coil of radius r exerts a force F on a small magnet whose axis is at some point on a line drawn through the centre and perpendicular to the plane of... 

Dimensional CFD Modeling of Flow Round a Threaded Friction Stir Welding Tool Profile, J. Mater. Process. Technol, Vol 169,2005, p 320-327... 

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