Device efficiency equation

High efficiency and long lifetime aie essential factors for commercialization of O-and P> LEDs. There have been many attempts made to improve device performance sofar(10). Device efficiency, 7, is defined in the following equation(ll). 

In a liquid electrolyte DSSC, rapid re-reduction of dye cations by the redox electrolyte (equation 10.10) competes effectively with equation 10.8, and therefore charge recombination to the redox electrolyte, equation 10.9, is the primary recombination loss pathway limiting device efficiency. - In polymer electrolyte-based DSSC, however, the low ionic conductivity of the polymer electrolyte introduces the possibility that dye cation rereduction by the electrolyte may no longer compete effectively with the recombination pathway described in equation 10.8. As a consequence, charge recombination with dye cations may become critical in limiting device efficiency. 

It is also interesting to use Figure 6 to make a comparison of different aeration devices on the basis of energy-efficiency. From equation 6 and assuming a constant driving force... 

From equation 23, it can be seen that the higher the power input per unit volume, the lower the oxygen transfer efficiency. Therefore, devices should be compared at equal transfer rates. AH devices become less energy efficient as rates of transfer increase (3). 

Theoretical representation of the behaviour of a hydrocyclone requires adequate analysis of three distinct physical phenomenon taking place in these devices, viz. the understanding of fluid flow, its interactions with the dispersed solid phase and the quantification of shear induced attrition of crystals. Simplified analytical solutions to conservation of mass and momentum equations derived from the Navier-Stokes equation can be used to quantify fluid flow in the hydrocyclone. For dilute slurries, once bulk flow has been quantified in terms of spatial components of velocity, crystal motion can then be traced by balancing forces on the crystals themselves to map out their trajectories. The trajectories for different sizes can then be used to develop a separation efficiency curve, which quantifies performance of the vessel (Bloor and Ingham, 1987). In principle, population balances can be included for crystal attrition in the above description for developing a thorough mathematical model. 

When applying Equation 8.6, there is a tacit assumption that there is no turbulence in the settler. In practice, any turbulence will mean that a settling device sized on the basis of Equation 8.6 will have a lower efficiency than predicted. 

The detection performance of an LIF photometric device is governed by the emission filter(s), excitation filter(s), detector type, the excitation source and the detection scheme. The selection of optical elements and device configuration as it relates to the detection performance is further described by expanding the collection efficiency term in Equation 11.3 ... 

Cross-flow device sizing. Cross-flow devices obey the same genera) sizing equations as plate coalescers. Although some manufacturers claim these units arc more efficient than CPIs, the reason for this is neither apparent from theory nor from lab or field tests. 

Collection Efficiency. Single-Tube Denuders. For the appropriate design of a diffusion-based collection device for an intended application, the ability to estimate the collection efficiency a priori is of considerable help. Although the theoretical soundness of the Gormley-Kennedy equation (equation 1) is not questioned, it is based on the assumption that the uptake probability of the analyte gas at the wall is unity that is, the wall is truly a perfect sink , and every collision results in uptake. This assumption is unrealistic. In recent years, this issue has been reexamined. McMurry and Stolzenburg (42) showed for a liquid-coated denuder how the uptake probability (discussed by the authors in terms of the mass accommodation coefficient ) can be evaluated from collection efficiency measurements. Murphy and Fahey (43) utilized the mathematical solution originally developed for hemodialyzers by Cooney et al. (44) this treatment assumes a constant uptake probability that may be less than unity. To use the Murphy-Fahey approach, however, this probability must be precisely known. 

In order for a process to be controllable by machine, it must represented by a mathematical model. Ideally, each element of a dynamic process, for example, a reflux drum or an individual tray of a fractionator, is represented by differential equations based on material and energy balances, transfer rates, stage efficiencies, phase equilibrium relations, etc., as well as the parameters of sensing devices, control valves, and control instruments. The process as a whole then is equivalent to a system of ordinary and partial differential equations involving certain independent and dependent variables. When the values of the independent variables are specified or measured, corresponding values of the others are found by computation, and the information is transmitted to the control instruments. For example, if the temperature, composition, and flow rate of the feed to a fractionator are perturbed, the computer will determine the other flows and the heat balance required to maintain constant overhead purity. Economic factors also can be incorporated in process models then the computer can be made to optimize the operation continually. 

N-type semiconductors can be used as photoanodes in electrochemical cells Q., 2, 3), but photoanodic decomposition of the photoelectrode often competes with the desired anodic process (1 4 5). When photoanodic decomposition of the electrode does compete, the utility of the photoelectrochemical device is limited by the photoelectrode decomposition. In a number of instances redox additives, A, have proven to be photooxidized at n-type semiconductors with essentially 100% current efficiency (1, 2, 3, 6>, ], 8, 9). Research in this laboratory has shown that immobilization of A onto the photoanode surface may be an approach to stabilization of the photoanode when the desired chemistry is photooxidation of a solution species B, where oxidation of B is not able to directly compete with the anodic decomposition of the "naked" (non-derivatized) photoanode (10, 11, 12). Photoanodes derivatized with a redox reagent A can effect oxidation of solution species B according to the sequence represented by equations (1) - (3) (10-15). 

From this equation, the adiabatic heating rate AT/At can be obtained as 130 K s-1. This is only an estimated value neglecting heat losses to the walls and to the gas but it indicates that fast heat during the start of the engine should be possible. This heating mechanism is certainly also useful in immobile applications and it demonstrates clearly that efficient heat management by internal resistance heating is possible in micro structured devices. 

Equation (20) gives a global cell balance in a bioreactor of volume V operating with a perfusion rate D and using a cell retention device that gives a cell retention efficiency E. 

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