Design Calculation Examples

Equation (8.5) can be used to provide values for the parameters. Thus  

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The reader will find additional design calculation examples in the two literature citations provided in this section, in addition, refer to the Suggested Readings section of this chapter for further information. 

These multidimensional analyses do not necessarily predict overall generator performance or operating characteristics significantly more accurately than do the qua si-one-dimensional analyses, which are more economical to mn. Thus the latter are used for general channel design calculations, and the more sophisticated codes mainly to deal with more detailed aspects of channel operation. For example, current concentrations at electrode edges can be predicted by use of the more sophisticated codes. This allows appropriate electrode design for the condition. 

Simplified formulas are applied in engineering design. For example, in the case of an air curtain with heated indoor air the necessary temperature of the supplied air may be calculated according to the following formula ... 

It is the prediction of performance in its broadest sense, including all the characteristics and properties of materials that are essential and relate to the processing of the plastic. To the designer, an example of a strict definition of a design property could be one that permits calculating product dimensions from a stress analysis. Such properties obviously are the most desirable upon which to base material selections. 

Rib design An example of how ribbing will provide the necessary equivalent moment of inertia and section modulus will be given. A flat plastic bar of IV2 in. x 3/8 in. thick and 10 in. long, supported at both ends and loaded at the center, was calculated to provide a specified deflection and stress level under a given load. The favorable material thickness of this plastic is 0.150 in. Using... 

The examples that follow assume constant physical properties and use Equation (5.28). Their purpose is to explore nonisothermal reaction phenomena rather than to present detailed design calculations. 

The reactor design calculations of Example 6.2 go here. They produce the total annualized cost, Total, that is the objective function for this optimization... 

For gases, the heats of mixing are usually negligible and the heat capacities and enthalpies can be taken as additive without introducing any significant error into design calculations as was done in Example 3.3. 

The sensitivity to the particular property how much will a small error in the property affect the design calculation. For example, it was shown in Chapter 4 that the estimation of the optimum pipe diameter is insensitive to viscosity. The sensitivity of a design method to errors in physical properties, and other data, can be checked by repeating the calculation using slightly altered values. 

Though Kern s method does not take account of the bypass and leakage streams, it is simple to apply and is accurate enough for preliminary design calculations, and for designs where uncertainty in other design parameters is such that the use of more elaborate methods is not justified. Kern s method is given in Section 12.9.3 and is illustrated in Examples 12.1 and 12.3. 

The solution to this example illustrates the iterative nature of heat exchanger design calculations. An algorithm for the design of shell-and-tube exchangers is shown in Figure A (see p. 684). The procedure set out in this figure will be followed in the solution. 

Using Bell s method, calculate the shell-side heat transfer coefficient and pressure drop for the exchanger designed in Example 12.1. 

Instead of using a 1-1 design in Example 7, a 1-2 design is to be used subject to Xp = 0.9. Assume that the overall heat transfer coefficient is unchanged. (In practice, it would be expected to increase). Calculate... 

The summation involves the effluent molal flow rates. This equation and equation 10.4.2 must be solved simultaneously in order to determine the tubular reactor size and to determine the manner in which the heat transfer requirements are to be met. For either isothermal or adiabatic operation one of the three terms in equation 10.4.7 will drop out, and the analysis will be much simpler than in the general case. In the illustrations which follow two examples are treated in detail to indicate the types of situations that one may encounter in practice and to indicate in more detail the nature of the design calculations. 

One must understand the physical mechanisms by which mass transfer takes place in catalyst pores to comprehend the development of mathematical models that can be used in engineering design calculations to estimate what fraction of the catalyst surface is effective in promoting reaction. There are several factors that complicate efforts to analyze mass transfer within such systems. They include the facts that (1) the pore geometry is extremely complex, and not subject to realistic modeling in terms of a small number of parameters, and that (2) different molecular phenomena are responsible for the mass transfer. Consequently, it is often useful to characterize the mass transfer process in terms of an effective diffusivity, i.e., a transport coefficient that pertains to a porous material in which the calculations are based on total area (void plus solid) normal to the direction of transport. For example, in a spherical catalyst pellet, the appropriate area to use in characterizing diffusion in the radial direction is 47ir2. 

Continuous binary distillation is illustrated by the simulation example CON-STILL. Here the dynamic simulation example is seen as a valuable adjunct to steady state design calculations, since with MADONNA the most important column design parameters (total column plate number, feed plate location and reflux ratio) come under the direct control of the simulator as facilitated by the use of sliders. Provided that sufficient simulation time is allowed for the column conditions to reach steady state, the resultant steady state profiles of composition versus plate number are easily obtained. In this way, the effects of changes in reflux ratio or choice of the optimum plate location on the resultant steady state profiles become almost immediately apparent. 

In this section we will present some modelling developments for various forms of composites. The purpose is not to propose a calculation method - excellent computer software programs exist for that - but to show the broad strength range according to the composite structure, to underline the separate effects of fibres and matrix, and to examine the effects of some service conditions. These examples cannot be used for design calculations. 

Again, these examples cannot be used for design calculations. 

Thermodynamic design, for example, can be relieved of repetitive hand calculation, iterative solution techniques, and two-way interpolations. Beyond this is a pervasive cultural preference of this generation towards interacting with computers. 

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