Performance and scaling

In this article, we first review the methods of growing amorphous silicon for solar cells. The next part covers the material properties that are relevant to the development of efficient, stable a-Si H solar cells. In Part IV, we discuss the fabrication, performance, and scale-up of a-Si H solar cells, and in Part V, we consider the economics of these cells for various applications. We conclude with some projections for the future of a-Si H photovoltaics. 

Karr, A. E., and T. C. Lo, Performance and Scale-up of a Reciprocating Plate Extraction Column, Proceedings of International Solvent Extraction Conference, Vol. 1, 299-320 (1971). 

Smith, K. H., T. Bowser, and G. W. Stevens, Performance and Scale-up of Karr Reciprocating Plate Extraction Columns, Ind. Eng. Chem. Research, 47, 8368 (2008). 

Smith, G, D. and Ganesan, P., Performance and Scale Formation of Selected High Temperature Alloys in Simulated Waste Incineration Environments Containing Gaseous Bromides and Chlorides," presented at Corrosion 87, 9-13 March 1987, San Francisco, CA, National Association of Corrrosion Engineers, Houston, TX,... 

Simulations are a reasonable way of extrapolating performance and scaling up processes. By incorporating fundamental mechanisms into process simulations, system performance can be predicted in new and different operating regions. 

Performance and scaling of the simulator program were measured via parallel efficiency. Parallel efficiency refers to the ratio of the ideal run time to the actual run time. For example, if the perfeet speed-up would have given a run time of 10 seconds and the actual run time was 12 seconds, then the parallel efficiency is 10/12, or 83.3%. Care must be taken while measuring parallel efficiencies so that there are no other jobs running on the cluster that would share the CPU time with the benchmark runs. 

How can tracer methods help us in solving these two problems We know that reactor performance, as measured by conversion of the limiting reactant or by product selectivity, is a function of kinetics, flow pattern and mixing pattern in the reactor. The flow and mixing phenomena in various reactor geometries are complex, and we are currently unable to characterize them completely (at an economical cost). The only reactors that we know how to design, predict their performance and scale up with confidence, are those that behave as the two ideal reactor types, i.e. the plug flow (PFR) and the continuous flow stirred tank reactor (CSTR). 

Fig. 3. Performance (top) and scaling behavior (bottom) of D-PMTA on the Cray T3E when simulating 70,000 particles.

Scale-up and performance of a 1.47-m Scheibel column have been reported (98,154,155), as have detailed description and design criteria for the Scheibel column (156) and scale-up procedures (157). The same stage efficiency can be maintained on scale-up, and total throughput can be increased by three and one-half times at the expense of higher HETS. As of this writing, Scheibel columns up to 2.75 m in diameter are in service. 

W. J. Dawson and M. K. Han, "Development and Scale-Up of Hydrothermal Processes for Synthesis of High Performance Materials," Proceedings of the Milton E. Wadsworth IH International Symposium on Mydrometallurgy, Aug. 1—5,1993. 

Whereas considerable progress has been made towards achieving acceptable channel performance (power and enthalpy extraction) and durabiUty, as of this writing performance and durabiUty have not been demonstrated simultaneously. A larger scale demonstration plant has been proposed in the United States by the MHD Development Corp. (112). 

Y. Kobayashi and H. Nakamura, "MRF Reactor, Commercially Proven Performance and Enhancement for Large Scale Methanol Plant," HIChE... 

Dimensional Analysis. Dimensional analysis can be helpful in analyzing reactor performance and developing scale-up criteria. Seven dimensionless groups used in generalized rate equations for continuous flow reaction systems are Hsted in Table 4. Other dimensionless groups apply in specific situations (58—61). Compromising assumptions are often necessary, and their vaHdation must be estabHshed experimentally or by analogy to previously studied systems. 

Hierarchical Structure of PVC. PVC has stmcture that is built upon stmcture which is, in turn, built upon even more stmcture. These many layers of stmcture are all important to performance and are interrelated. A summary of these stmctures is Hsted in Table 2 Figure 5 examines a model of these hierarchies on three scales. 

Often the catalysts described in the Hterature are not quite the same as those used in industrial processes, and often the reported performance is for pure single-component feeds. Sometimes the best quantitative approximations that can be made from the available Hterature are those based on reported kinetics of reactions with pure feeds and catalysts that are similar to but not the same as those used in practice. As a first approximation, one may use the pubHshed results and scale the activity on the basis of a few laboratory results obtained with reaHstic feeds and commercially available catalysts. 

The recycle requirements of products in different apphcations can vaiy substantially depending upon the scale of operation, the ease of diying, and the finished-product specification. The location of reintroduction of undried material back into the diying medium has a significant impact upon the dryer performance and final-product characteristics. 

While research has developed a significant and detailed filtration theory, it is still so difficult to define a given liquid-solid system that it is both faster and more accurate to determine filter requirements by performing small-scale tests. Filtration theoiy does, however, show how the test data can best be correlated, and extrapolated when necessary, for use in scale-up calculations. 

---