Screw rotor device

Abstract

A screw rotor device includes a first rotor having a plurality of helical lobes about its periphery, a second rotor having a plurality of helical flutes about its periphery and a housing with a high pressure port and a low pressure port. The first and second rotors are rotatably mounted within the housing such that the lobes intermesh with the flutes for conveying, in use, a fluid between the high pressure port and the low pressure port. At least one of the rotors has a helical profile that changes along its length such that a gap is described between intermeshing lobes and flutes adjacent the high pressure port which is larger than a gap described between intermeshing lobes and flutes adjacent the low pressure port. The screw rotor device may be used for conveying a fluid.

1 . A screw rotor device comprising a first rotor having a plurality of helical lobes about its periphery, a second rotor having a plurality of helical flutes about its periphery and a housing with a high pressure port and a low pressure port, the first and second rotors being rotatably mounted within the housing such that the lobes intermesh with the flutes for conveying, in use, a fluid between the high pressure port and the low pressure port, wherein at least one of the rotors has a helical profile that changes along its length such that a gap is described between intermeshing lobes and flutes adjacent the high pressure port which is larger than a gap described between intermeshing lobes and flutes adjacent the low pressure port. 
     
     
         2 . Device according to  claim 1 , wherein the size of each flute adjacent the high pressure port is greater than its size adjacent the low pressure port. 
     
     
         3 . Device according to  claim 2 , wherein the circumferential width of each flute adjacent the high pressure port is greater than its circumferential width adjacent the low pressure port. 
     
     
         4 . Device according to  claim 2 , wherein the size of each lobe of the first rotor adjacent the low pressure port is greater than its size adjacent the high pressure port. 
     
     
         5 . Device according to  claim 4 , wherein the circumferential width of each lobe adjacent the low pressure port is greater than its circumferential width adjacent the high pressure port. 
     
     
         6 . Device according to  claim 1 , wherein the gap is described between driving surfaces of the intermeshing lobes and flutes. 
     
     
         7 . Device according to  claim 1 , wherein the rotors are driven in a first respective direction and the gap is described between a trailing surface of each intermeshing lobe and a facing surface of a cooperating flute. 
     
     
         8 . Device according to  claim 7 , wherein a further gap is described between a leading surface of each intermeshing lobe and a facing surface of a cooperating flute. 
     
     
         9 . Device according to  claim 1 , wherein the rotors are driven in a first respective direction and the gap is described between a leading surface of each intermeshing lobe and a facing surface of a cooperating flute. 
     
     
         10 . Device according to  claim 1 , wherein the at least one rotor has a helical profile that changes either gradually along at least part of its length or as a step transition part way along its length. 
     
     
         11 . Device according to  claim 1 , wherein the at least one rotor has a helical profile that is constant along part of its length. 
     
     
         12 . Device according to  claim 1 , wherein the at least one rotor comprises the first rotor. 
     
     
         13 . Device according to  claim 1 , wherein the at least one rotor comprises the second rotor. 
     
     
         14 . Device according to  claim 1 , wherein the device is free of lubricating oil. 
     
     
         15 . Device according to  claim 1 , wherein the device is free of timing gears. 
     
     
         16 . Device according to  claim 1 , comprising one or more further rotors each having helical lobes about its periphery and/or one or more further rotors each having a plurality of helical flutes, the further rotor or rotors being rotatably mounted within the housing such that the lobes or flutes intermesh with corresponding flutes or Lobes on another of the rotors for conveying, in use, a fluid between the high pressure port and the low pressure port. 
     
     
         17 . Device according to  claim 1 , further comprising an expander, wherein the high pressure port comprises an inlet of the expander and the low pressure port comprises an outlet of the expander. 
     
     
         18 . Device according to  claim 1 , further comprising a compressor, wherein the low pressure port comprises an inlet of the compressor and the high pressure port comprises an outlet of the compressor. 
     
     
         19 . A steam generator comprising
 a screw rotor device comprising a first rotor having a plurality of helical lobes about its periphery, a second rotor having a plurality of helical flutes about its periphery and a housing with a high pressure port,   the first and second rotors being rotatably mounted within the housing such that the lobes intermesh with the flutes for conveying, in use, a fluid between the high pressure port and the low pressure port,   wherein at least one of the rotors has a helical profile that changes along its length such that a gap is described between intermeshing lobes and flutes adjacent the high pressure port which is larger than a gap described between intermeshing lobes and flutes adjacent the low pressure port.   
     
     
         20 . A method of manufacturing a screw rotor for a screw rotor device, the method comprising forming at least one helical lobe or flute having a constant depth and a circumferential width that varies along its length. 
     
     
         21 . A method according to  claim 20  comprising forming the helical lobe or flute with leading and trailing surfaces, wherein only one of the leading and trailing surfaces varies along the length of the rotor.