Sine ducts

The structures of interest for this paper are regular polygons (of which the square and the equilateral triangle are two members) triangles (of which the equilateral triangle is an end member) and sine ducts (of which the wrapped ceramic and metal structures are members). 

The sine ducts were chosen for this analysis because they appear to be a very good representation of the wrapped or corrugated structure (1). The derivations of the geometric surface area and open frontal area of this structure are based on the equation for a sine curve ... 

The open area of the sine duct is likewise defined by an integral, which is constructed by integrating Equation 13 over the full cycle. The solution of the integral for the open area is 2 a b, where 2 a and 2 b are the height and width of the open area of the sine duct, respectively. This solution is, for the case of 100% OF A, the reciprocal of the ceU density. For structures of finite wall thickness, the quantity 2 a b is the open frontal area divided by the ceU density. 

The values of Friction Factor and average Nusselt Number (9) are shown in Figure 5 for selected sine ducts as functions of the relative shape, where n here is the ratio of the inside open height to the inside open width of the duct. 

Combining the information in Figure 5 with the calculated open frontal area and geometric surface area values and through the use of Equations 2 and 4, the Heat Mass Transfer and Pressure Drop Factors can be calculated for the sine ducts. These results are shown in Figure 6. 

Figure 5 The Friction Factors and Average Nusselt Numbers for Several Sine Ducts.

Figure 6 The Heat Mass Transfer and Pressure Drop Factors for Several Sine Ducts.

A sine duct with associated coordinates is shown in Fig. 5.49. The characteristics of fully developed laminar flow and heat transfer in such a duct are given in Table 5.53. These results are based on the analysis by Shah [172]. 

TABLE 5.53 Fully Developed Fluid Flow and Heat Transfer Characteristics of Sine Ducts [172]... 

It has been shown recently [25] that concentrations of NOj, tend to reduce with increase in the amplitude of discrete-frequency oscillations. The mechanisms remain uncertain, but may be associated with the imposition of a near-sine wave on a skewed Gaussian distribution with consequent reduction in the residence time at the adiabatic flame temperature. Profiles of NO, concentrations in the exit plane of the burner are shown in Fig. 19.6 as a function of the amplitude of oscillations with active control used to regulate the amplitude of pressure oscillations. At an overall equivalence ratio of 0.7, the reduction in the antinodal RMS pressure fluctuation by 12 dB, from around 4 kPa to 1 kPa by the oscillation of fuel in the pilot stream, led to an increase of around 5% in the spatial mean value of NO, compared with a difference of the order of 20% with control by the oscillation of the pressure field in the experiments of [25]. The smaller net increase in NO, emissions in the present flow may be attributed to an increase in NOj due to the reduction in pressure fluctuations that is partly offset by a decrease in NOj, due to the oscillation of fuel on either side of stoichiometry at the centre of the duct. 

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