Heuristics pumping

These results show that, for practical purposes, we can treat bacteriorhodopsin as a converter that utilizes light of a certain thermodynamic potential to create a gradient of protons of a certain electrochemical potential, and that the rate at which this converter operates is sensitive to a sort of respiratory control phenomenon it is inhibited by the proton gradient which it generates (for review see Ref. 36). Such apparently orthodox behaviour of a light-driven proton pump has been held improbable [12], because it would contradict the idea that photochemical reactions are irreversible . At least (but see also Refs. 29, 30] in this sense the application of MNET to bacteriorhodopsin liposomes has had heuristic value. 

The following heuristic should be obvious Do not separate two components and then remix them at a reactor inlet. We must also have in mind the significant difference between the cost of recycling a gas or a liquid. Compressors are very expensive and the cost of compression is very high, whereas the cost of pumping is much lower, except in special applications (viscous liquids, slurries, aggressive solutions, etc). 

Note that an alternative flowsheet would place operations 1 and 2 after operation 3. However, this is very uneconomical, as the cost of compressing a vapor is far greater than the cost of pumping a liquid because the molar volume of a vapor is so much greater than that of a liquid (typically, a factor of 100 times greater). For a more complete discussion of this observation, which is just one of many design heuristics or rules of thumb, see Section 5.7. 

Heuristic 16 When employing multiple effects, the liquid and vapor flows may be in the same or different directions. Use forward feed, where both liquid and vapor flow in the same direction, for a small number of effects, particularly when the liquid feed is hot. Use backward feed, where liquid flows in a direction opposite to vapor flows, for cold feeds and/or a large number of effects. With forward feed, intermediate liquid pumps are not necessary, whereas they are for backward feed. 

Liquids If the pressure of a liquid is to be increased, a pump is used. The following heuristic is useful for determining the types of pumps best suited for a given task, where the head in feet is the pressure increase across the pump in psf (pounds force/ft ) divided by the liquid density in Ib/ft. ... 

When pumping a liquid from an operation at one pressure, /, to a subsequent operation at a higher pressure, P2, the pressure increase across the pump must be higher than P2 — P[ in order to overcome pipeline pressure drop, control valve pressure drop, and possible increases in elevation (potential energy). This additional pressure increase may be estimated by the following heuristic. 

The following heuristic provides an estimate of the theoretical pump Hp. Unlike the case of gas compression, the temperature change across the pump is small and can be neglected. 

Heuristic 39 Estimate the theoretical horsepower (THp) for pumping a liquid from ... 

Heuristic 43 To increase the pressure of a stream, pump a liquid rather than compress a gas, unless refrigeration is needed. 

Heuristic 46 For pressures down to 10 torr and gas flow rates up to 10,000ft /min at the inlet to the vacuum system, use a liquid-ring vacuum pump. For pressures down to 2 torr and gas flow rates up to 1,000,000 ft /min at the inlet to the vacuum system, use a steam-jet ejector system (one-stage for 100 to 760 torr, two-stage for 15 to 100 torr, and three-stage for 2 to 15 torr). Include a direct-contact condenser between stages. 

This chapter presents brief descriptions and some theoretical background of the most widely used pumps for liquids, and compressors and expanders for gases, all of which are modeled in simulators. Heuristics for the application of these devices during the synthesis of a chemical process are presented in Chapter 5. Further information on their selection and capital cost estimation is covered in Chapter 16. More comprehensive coverage of the many types of pumps, compressors, and expanders available is presented in Sandler and Luckiewicz (1987) and in Perry s Chemical Engineers Handbook (1997). After studying this chapter and the materials on pumps, compressors, and turbines on the multimedia CD-ROM that accompanies this book, the reader should be able to explain how the more common types of pumps, compressors, and expanders work and how a simulator computes their power input or output... 

Heuristic Evaluation was used as a first step to evaluate the usability of three IV pumps for the Calgary Health Region. According to Nielsen (2003), three to five evaluators provide the best cost-benefit tradeoff. We chose to have five evaluators inspect each pump independently. Evaluators judged the human factors compliance of each pump with a set of human factors design guidelines. These guidelines included ... 

Chisholm S., Kramer S., and Lockhart, J. Heuristic comparison of two PCA pumps. Cognitive Ergonomics Research Laboratory, University of Calgary, 2005. 

Heuristics for Cnmprcssnrs, Fans, Blowers, and Vacuum Pumps... 

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