Đang chuẩn bị liên kết để tải về tài liệu:
The MEMS Handbook MEMS Applications (2nd Ed) - M. Gad el Hak Episode 2 Part 1

Tham khảo tài liệu 'the mems handbook mems applications (2nd ed) - m. gad el hak episode 2 part 1', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 8-2 MEMS Applications p FIGURE 8.1 Representative performance Q N of selected macro- and mesoscale vacuum pumps from Table 8.1 as a function of pressure ratio p . This chapter will address how to approach identifying microscale and mesoscale vacuum pumping capabilities consistent with the volume and energy requirements of meso- and microscale instruments and processes. The mesoscale pumps now available are discussed. Existing microscale pumping devices are not reviewed because none are available with attractive performance characteristics a review of the attempts has recently been presented by Vargo 2000 Young et al. 2001 Young 2004 see also NASA JPL 1999 . In the macroscale world vacuum pumps are not very efficient machines ranging in thermal efficiencies from very small fractions of one percent to a few percent. They generally do not scale advantageously to small sizes as is discussed in the section on Pump Scaling. Because there is a continuing effort to miniaturize instruments and chemical processes there is not much desire to use oversized power intensive vacuum pumps to permit them to operate. This is true even for situations where the pump size and power are not critical issues. Because at present microscale pump generated vacuums are unavailable serious limits are currently imposed on the potential microscale applications of many high performance analytical instruments and chemical processes where portability or autonomous operations are necessary. To illustrate this point the performance characteristics of several types of macroscale and mesoscale vacuum pumps are presented in Figure 8.1 and Table 8.1. Pumping performance is measured by Q N which is derived from the power required Q W and the pump s upflow in molecules per unit time N s . Representative vacuum pumping tasks are indicated by the inlet pressure pp and the pressure ratio p through which Nis being pumped. The reversible constant temperature compression power required per molecule of upflow Q N