Adding the Teaching of Claw Rotor Compressors to Fluid Machinery Courses

Abstract

This paper deals with a rotary positive-displacement machine with built-in compression, the study of which is usually neglected in courses on fl uid machinery for mechanical engineering students. First, the working principles of the claw rotor compressor are presented; then basic thermodynamic considerations, leading to the formulation of volumetric effi ciency, are reported. The volumetric effi ciency of the compressor is reviewed as a function dependent on fi lling and leakages, leading to the defi nition of the delivery effi ciency. Considering the fi lling effi ciency alone, formulated according to a thermodynamic analysis of the closed system, it is possible to determine the limit pressure ratio that causes no fl ow from the compressor. The ideal work is also formulated and a comparison with the sliding vane compressor is made. Some considerations that deprive the compressor of its ideality are advanced in order to avoid misleading conclusions.

Investigation of a novel circular arc claw rotor profile for claw vacuum pumps and its performance analysis

“…3, There are three circular arcs and three epitrochoidal arcs used to generate the reference profile [7]. The epitrochoidal arc ab is Curve 1; and the epitrochoidal arc cd and ef are the same curves as Curve 1.…”

“…These claw rotor profiles have the same basic shape parameters except circular arc radius r. R 1 ¼ 65 mm, R 2 ¼ 50 mm, R 3 ¼ 35 mm, and circular arc radius r equal 0 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm and 8 mm, respectively. When r ¼ 0 mm, the claw rotor profile becomes the reference profile [7]; and when r is more than 8 mm, the rotor profile cannot be formed. It can be seen that the more value of r, the little volume of recess.…”

“…Hsieh [5,6] proposed a profile of claw rotor by means of the theory of gearing and the equation of undercutting, which helped to improve gas sealing and reduce carryover; and Hsieh also presented a simple mathematical model for the geometric design of a claw type rotor, using different parameters to discuss its influences on the gas port and pump performance. Giuffrida [7] presented the working principles of the claw rotor compressor and reported the formulation of volumetric efficiency; and Giuffrida [8] also proposed a rotor profile suitable for the claw-type mechanism, which seems to be preferable compared with a reference profile [7]. Ioffe et al [9] developed a model based on algebraic and differential equations to describe pressure and temperature time dependence for a multistage claw rotor vacuum pump.…”

“…Aiming at solving the disadvantages caused by cusps of the reference profile [7] for claw rotors, this paper proposes a novel circular arc claw rotor profile, in which circular arcs are employed instead of cusps to improve the performances for claw vacuum pumps. Differences between the proposed profile and the reference profile are compared by employing numerical simulation of the working process and stress calculation of claw rotors.…”