Effect of some process variables

B Marcoccia, DAI Goring, and DW Reeve. Photo-enhanced Oxygen Delignification of Softwood Kraft Pulp Effect of Some Process Variables. J Pulp Paper Sci 17 134—138, 1991. 

Kymalainen, M., Holmstrom, M., Forssen, M., Hupa, M. (2001). The fate of nitrogen in the chemical recovery process in a kraft pulp mill. Part III The effect of some process variables. Journal of Pulp and Paper Science, 27(9), 317-324. 

The properties of thermally modified wood are highly dependent upon the thermal treatment employed, and it is very important to take these into account when comparing the various treatment methods employed. This chapter examines the effect of the process variables upon the properties of thermally modified wood, and then considers the chemistry of thermal modification. Studies of physical changes are discussed, followed by an overview of the biological properties of thermally modified wood. A short description of some recent literature on the use of thermal treatment combined with compression and on hot oil treatments is also included. 

Thus even approximate analytical solutions are often more instructive than the more accurate numerical solutions. However considerable caution must be used in this approach, since some of the approximations, employed to make the equations tractable, can lead to erroneous answers. A number of approximate solution for the hot spot system (Eq 1) are reviewed by Merzhanov and their shortcomings are pointed out (Ref 14). More recently, Friedman (Ref 15) has developed approximate analytical solutions for a planar (semi-infinite slab) hot spot. These were discussed in Sec 4 of Heat Effects on p H39-R of this Vol. To compare Friedman s approximate solutions with the exact numerical solution of Merzhanov we computed r, the hot spot halfwidth, of a planar hot spot by both methods using the same thermal kinetic parameters in both calculations. Over a wide range of input variables, the numerical solution gives values of r which are 33 to 43% greater than the r s of the approximate solution. Thus it appears that the approximate solution, from which the effect of the process variables are much easier to discern than from the numerical solution, gives answers that differ from the exact numerical solution by a nearly constant factor... 

Here the critical process variables are identified from the selected list of process variables. The model library or process data (if available) are used for this analysis. To perform the sensitivity analysis, the process operational model is simulated through ICAS-MoT. The effect of each process variable on the target product properties is analyzed systematically through open loop simulation. The operational objectives have to be assessed first. If an operational objective is not achieved, then the process variables have to be analyzed. The variables which violate the operational limit and have a major effect on the product quality are considered as the critical process variables. For some of the variables which can not be modeled the sensitivity analysis has to be performed qualitatively through inference from the knowledge base and/or by the use of process data. All the critical process variables need to be monitored and controlled. For some of the critical variables that can not be measured in real time, other correlated properties have to be measured so that all critical variables can be measured and controlled by using the correlations to the measurable variables. 

Some studies, such as Fujima et al., concentrate on one aspect of this multi-faceted problem [105]. For example, they set out to show the relationship between sulfur capture, particle concentration, and firing conditions. Boyd and Friedman, on the other hand, summarize the effect of many process variables on combustion performance [107]. The final DOE report concerning the NUCLA experimental program concludes that radial gas mixing is poor Gas samples withdrawn across the radius of the reactor at two heights 7 m apart had similar concentration profiles [106]. They also found that secondary air had little effect on gas phase hydrodynamics... 

The effects of the many variables that bear on the magnitudes of individual heat transfer coefficients are represented most logically and compactly in terms of dimensionless groups. The ones most pertinent to heat transfer are listed in Table 8.8. Some groups have ready physical interpretations that may assist in selecting the ones appropriate to particular heat transfer processes. Such interpretations are discussed for example by GrOber et al. (1961, pp. 193-198). A few are given here. 

Some practical cases are determination of residual stress in steel springs, the effect of mechanical loading on stress relaxation of machined and shot-peened nickel-base alloys,65 determination of residual stress level in turbine engine disks as they accumulate engine cycles,65 66 effect of manufacturing processes on residual stress, measurement of stress gradients in mechanical, electronic and structural components, effect of heat treatment on residual stress in steel coil springs, effect of variable heat treatment temperature on residual stress in iron alloys, measurement of stress in multiphase materials and composites and stress measurements at locations of stress concentrations. 

These ideas of impeller flow, head and power input as related to operating variables have some merit for a qualitative description of the effects of the operating variables on the process. However, it requires extensive experience, and usually actual experiments, to decide whether a system performance is favored by a particular combination of flow and head. (Rushton and Oldshue (R12) note that high values of Q/3Care preferred for blending and solid suspension, low ratios for liquid-liquid and gas-liquid operations.) This approach still requires the systematic study of impeller speed and diameter as process variables. 

Unlike W plasma etch back process, the typical W CMP process usually removes the adhesion layer such as Ti/TiN or TiN during the primary polish. As a result, during the over polish step there is some oxide loss. Since the oxide deposition, planarization CMP (oxide CMP), and tungsten CMP steps are subsequent to each other, the oxide thickness profile could become worse further into the process flow. Therefore, the across-wafer non-uniformity of the oxide loss during W CMP process is one of the very important process parameters needs to be optimized. To determine the effect of the process and hardware parameters on the polish rate and the across-wafer uniformity, designed experiments were run and trends were determined using analysis of variance techniques. Table speed, wafer carrier speed, down force, back pressure, blocked hole pattern, and carrier types were examined for their effects on polish rate and across-wafer uniformity. The variable ranges encompassed by the experiments used in this study are summarized in Table I. 

Hoblitzell, J.R. Rhodes, C.T. Instrumented tablet press studies on the effect of some formulation and processing variables. Drug Dev. Ind. Pharm. 1990, 16 (3), 469-507. 

Polymers may often be made successfully in a nonsystematic manner. However, higher quality polymers and higher yields are obtained by attention to the effects of some of the many process variables. Several of the more important ones are listed in Table IV. 

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