A New Design of the Tooth Profile for Single Screw Compressors
The wear of star wheel teeth is an importance issue in the single screw compressor. In order to enhance the wearresistance of star wheel teeth, some new profiles of the meshing pair were proposed to replace the currently used straight line envelope profile, such as single column envelope, multi-straight line (or multi-column) envelope. In this paper, a curved surface of the tooth flank is suggested. The groove flank is the envelope surface corresponding to the curved surface of the tooth flank. Section profile of the new tooth flank is a curved line, which could be elliptical, hyperbolic or involute. During the tooth meshing with the groove, the contact line between the tooth flank and the groove flank could move back and forth in the whole area of the tooth flank. This design is expected to improve the lubricating between the tooth flank and the groove flank, and to prolong the service life of the single screw compressor. Geometric and kinematic investigation of the star wheel and the screw rotor is established. And a new designed tooth flank of the meshing pair is introduced in this paper. Numerical control high-velocity cutting technology is suggested to fabricate the new star-wheel and the screw rotor.
Column envelope meshing pair and its design method for single screw compressors
A single screw compressor (SSC) is an important component found in many refrigeration systems. However, the durability is not so good because of the friction between its meshing pair. Therefore the column envelope meshing pair was proposed to prolong the operating life of SSCs, although it has not been applied to commercial refrigeration systems. To accelerate the industrial application, a mathematical model for analyzing the column envelope meshing pair is established based on the geometry and kinematics. Equations giving the flanks of column envelope grooves are obtained, and teeth flank meshing with the groove is designed. Results show that this model could be applicable in the design of the column envelope type SSC.
Improved culture method for the isolation of Histoplasma capsulatum and Blastomyces dermatitidis form contaminated specimens.
Studies were performed to evaluate a method for selective isolation of Histoplasma capsulatum and Blastomyces dermatitidis from contaminated specimens. Ammonium hydroxide placed on an agar medium surface was found to inhibit the growth of many bacteria, yeasts, and saphrophytic fungi normally found in specimens such as animal tissues and sputum. In one study involving the culture of B. dermatitidis from canine tissues, 24% more isolations were obtained on a medium using NH4OH compared with a similar medium. Increases in the isolation of H. capusulatum from sputum specimens were also obtained, ranging from 20 to 32% compared with four other media without NH4OH.