Optimal expander outlet porting

Abstract

An optimized mechanical expander or fluid expansion device with a delayed opening timing is disclosed. In the optimized design, rotors in the expander alternatingly rotate sequentially through an intake position in which the transport volume is open to the housing inlet, a closed position in which the transport volume is closed to the housing outlet, and a discharge position in which the transport volume is open to the housing outlet. During rotation, a first opening forms between the housing and each rotor. After further rotation, a second opening is formed that is located between the first opening and a back end of the rotor. In one aspect, the mechanical expander has an opening profile including an initial opening phase in which the opening between the rotor and outlet forms at a lesser rate than during a subsequent secondary opening phase.

What is claimed is: 
     
         1 . A mechanical expander comprising:
 a. a housing having an interior structure defining an interior volume, an inlet, and an outlet;   b. a pair of parallel helical rotors disposed within the housing in a counter rotating non-contacting arrangement, each of the rotors:
 i. having a plurality of lobes, wherein each lobe defines a cusp extending between a front end and a back end; and 
 ii. being rotatable within the housing to form a transport volume between a leading lobe cusp, a trailing lobe cusp, and the housing interior structure, 
   c. each rotor being sequentially rotatable through:
 i. an intake position in which the transport volume is open to the housing inlet; 
 ii. a closed position in which the transport volume is closed to the housing outlet; and 
 iii. a discharge position in which the transport volume is open to the housing outlet; 
   d. wherein, as each rotor is being rotated from the closed position to the discharge position:
 i. a first opening forms between the housing interior structure and the leading lobe cusp proximate the front end; 
 ii. a second opening forms between the housing interior structure and the leading lobe cusp between the first opening and the leading lobe cusp back end, the second opening forming after the first opening has been at least partially formed. 
   
     
     
         2 . The mechanical expander of  claim 1 , wherein, as each rotor is being rotated from the closed position to the discharge position, a third opening forms between the housing sidewall and the leading lobe cusp between the second opening and the leading lobe cusp back end, the third opening forming after the second opening has been at least partially formed. 
     
     
         3 . The mechanical expander of  claim 1 , wherein the first opening is at least partially open when the rotor has been rotated by about three degrees of rotation from the closed position. 
     
     
         4 . The mechanical expander of  claim 3 , wherein the second opening remains closed when the rotor has been rotated by less than about thirteen degrees of rotation from the closed position. 
     
     
         5 . The mechanical expander of  claim 1 , wherein the mechanical expander has an opening profile including an initial opening phase followed by a secondary opening phase, wherein only the first opening is enlarged during the initial opening phase and both the first and second openings are enlarged during the secondary opening phase. 
     
     
         6 . The mechanical expander of  claim 5 , wherein a first rate of enlargement of a total opening area during the initial opening phase is less than a second rate of enlargement of the total opening area during the secondary opening phase. 
     
     
         7 . A mechanical expander comprising:
 a. a housing having an interior structure defining an interior volume, an inlet, and an outlet;   b. a pair of parallel helical rotors disposed within the housing in a counter rotating non-contacting arrangement, each of the rotors:
 i. having a plurality of lobes, wherein each lobe defines a cusp extending between a front end and a back end; and 
 ii. being rotatable within the housing to form a transport volume between a leading lobe cusp, a trailing lobe cusp, and the housing interior structure, 
   c. each rotor being sequentially rotatable through:
 i. an intake position in which the transport volume is open to the housing inlet; 
 ii. a closed position in which the transport volume is closed to the housing outlet; and 
 iii. a discharge position in which the transport volume is open to the housing outlet; 
   d. wherein the mechanical expander has an opening profile between the leading lobe cusp and the housing outlet including an initial opening phase followed by a secondary opening phase, wherein only the first opening is enlarged during the initial opening phase and both the first and second openings are enlarged during the secondary opening phase   
     
     
         8 . The mechanical expander of  claim 7 , wherein a first rate of enlargement of a total opening area of the opening profile during the initial opening phase is less than a second rate of enlargement of the total opening area of the opening profile during the secondary opening phase. 
     
     
         9 . The mechanical expander of  claim 7 , wherein the initial opening phase occurs when the rotor is rotated such that the leading lobe cusp edge is initially moved past the closed position and the secondary opening phase occurs when the rotor is rotated such that the leading lobe cusp edge is rotated between about 12 and 14 degrees. 
     
     
         10 . The mechanical expander of  claim 7 , wherein the initial opening phase includes a first portion and a subsequent second portion, wherein a first rate of enlargement of a total opening area of the opening profile during the initial opening phase first portion is greater than a second rate of enlargement of the total opening area of the opening profile during the initial opening phase second portion. 
     
     
         11 . The mechanical expander of  claim 10 , wherein the second rate of enlargement is less than a third rate of enlargement of the total opening area of the opening profile during the secondary opening phase.