Abstract:
A method of treating, tuning, assembling, and/or overhauling a twin rotor device ( 200, 1200 ) includes applying a coating material ( 102 ) on an internal set of working surfaces ( 218, 222, 224, 226, 228, 1218, 1222, 1224, 1226, 1228 ) of the twin rotor device when at least partially assembled. The coating may be factory or field applied to a new or used twin rotor device. The working surfaces may be uncoated or previously coated and may be built-up as the coating material forms a coating ( 206, 1206 ) on at least some of the working surfaces. Manufacturing variations of a pair of rotors ( 220, 1220 ) and a housing ( 210, 1210 ) may be compensated by the coating. One or more performance characteristics of the twin rotor device may be improved by the coating, and variation between a series of twin rotor device may be reduced or substantially eliminated. The coating may reduce internal leakage and increase volumetric efficiency of the twin rotor device. The twin rotor device may be a supercharger  200 , a screw compressor  1200 , or other twin rotor device.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application is being filed on Jul. 1, 2015, as a PCT International Patent application and claims priority to U.S. Patent Application Ser. No. 62/020,494 filed on Jul. 3, 2014, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to twin rotor devices (e.g., Roots-style superchargers, Roots-style expanders, screw compressors, screw expanders, etc.). Such twin rotor devices can be used to pump and/or compress fluids (e.g., gasses, air, mixtures, etc.) using shaft power and/or can be used to extract shaft power from fluids (e.g., by expanding compressed gas). 
       BACKGROUND 
       [0003]    The present invention relates to twin rotor blowers/compressors, twin rotor expanders, etc. Such twin rotor blowers/compressors have been used for supercharging internal combustion engines (e.g., Diesel cycle engines, Otto cycle engines, etc.). When used on internal combustion engines, such twin rotor blowers/compressors may be a component of a forced induction system that supplies air or an air/fuel mixture to the internal combustion engine. Such forced induction systems supply the internal combustion engine with the air or the air/fuel mixture at a higher pressure than atmospheric pressure. In contrast, naturally aspirated internal combustion engines are supplied with air or an air/fuel mixture at atmospheric pressure. By supplying pressurized air or a pressurized air/fuel mixture to the internal combustion engine, the engine is supercharged. The twin rotor blowers/compressors may be known as positive displacement superchargers. Such positive displacement superchargers displace a given volume of gas for every revolution of an input shaft at a given pressure and a given temperature. In contrast, certain other superchargers may be non-positive displacement superchargers. 
         [0004]    The twin rotor blowers/compressors may take a form of a Roots-type device, a form of a screw compressor, etc. The Roots-type device may have a pair of rotors that intermesh with each other. In particular, each of the rotors may define a similar plurality of lobes with valleys between adjacent lobes. The lobes and valleys of the pair of rotors may be mirror images of each other (e.g., if helically twisted). The lobes and valleys of the pair of rotors may be identical to each other (e.g., if straight along an axial direction of the rotor). The lobes and valleys may be defined by alternating tangential sections of hypocycloidal or hypocycloidal-like curves and epicycloidal or epicycloidal-like curves. When each of the pair of rotors is spun, fluid is trapped in the valleys and bounded by the adjacent lobes and walls of a housing and carried from an intake side to an exhaust side of the Roots-type device. The twin rotor blowers/compressors (e.g., the Roots-type device) may move the fluid from the intake side to the exhaust side without compression until the fluid is exposed to the exhaust side (e.g., an exhaust port). As the fluid is forced out of the exhaust port, it may be compressed. 
         [0005]    The screw compressor (e.g., a twin-screw type supercharger) may have a pair of rotors that intermesh with each other. In particular, the pair of rotors may include a male rotor and a female rotor that intermesh with each other. The male rotor and the female rotor may have different numbers of lobes or a same number of lobes. A working volume may be defined as an inter-lobe volume between the male and the female rotors. When each of the pair of rotors is spun, fluid is trapped in the working volume bounded by the adjacent lobes and walls of a housing and carried from an intake end to an exhaust end of the screw compressor. The working volume may be larger at the intake end. The working volume may decrease along an axial length of the rotors toward the exhaust end. Fluid is drawn in at the intake end of the rotors between the male and female lobes. A corresponding reduction in the working volume toward the exhaust end may result in compression of the fluid that is trapped in the working volume. For example, at the intake end, the male lobes of the male rotor (and corresponding valleys of the female rotors) may be larger than corresponding female lobes of the female rotor (and corresponding valleys of the male rotors), and at the exhaust end, the male lobes (and corresponding valleys of the female rotors) may be smaller than corresponding female lobes (and corresponding valleys of the male rotors). Thus, relative sizes of the male and female lobes may reverse proportions along axial lengths of both of the rotors (e.g., the male lobes become larger and the female lobes become smaller). The increase in volume of the female lobes may result in a reduction in volume of the fluid carrying cavity and thereby cause the compression of the fluid before the fluid carrying cavity is in fluid communication with the exhaust end. 
         [0006]    Other methods of reducing the working volume toward the exhaust end may be used. In certain embodiments, a screw-compressor like device may not necessarily reduce the working volume toward the exhaust end. 
         [0007]    An example Roots-style supercharger is disclosed at U.S. Pat. No. 7,866,966, assigned to the assignee of the present disclosure, and incorporated herein by reference in its entirety. Another example Roots-style supercharger is disclosed at U.S. Pat. No. 4,828,467, also assigned to the assignee of the present disclosure, and also incorporated herein by reference in its entirety. As such Roots-style superchargers (and other twin rotor superchargers) typically draw air in through an inlet at atmospheric pressure and deliver compressed air from an outlet to an intake manifold of the internal combustion engine at an elevated pressure, the elevated pressure from the outlet of the Roots-style supercharger (and other twin rotor superchargers) typically tends to leak back across clearances within the supercharger. Such clearances may be between lobes of a pair of rotors within the supercharger. Clearances may also exist between tips of the lobes of the rotors and a housing of the supercharger. Clearances may further exist between an end of the rotors of the supercharger and corresponding surfaces of the housing. Such clearances are often determined, at least in part, by manufacturing tolerances of the rotors and the housing of the supercharger. For example, a Roots-style supercharger made with a collection of components at a minimum material condition with respect to the manufacturing tolerances will have leakage rates higher than another Roots-style supercharger assembled from components at a maximum material condition with respect to the manufacturing tolerances. This may lead to certain Roots-style superchargers that are nominally identical having different performance characteristics that are caused by the different leakage rates. Furthermore, it is generally desired to reduce such clearances and thereby minimize leakage within the supercharger. However, increasing precision of the manufacturing tolerances may increase manufacturing costs. Furthermore, a number of different dimensions and corresponding dimensional tolerances together determine the clearances that exist at final assembly. It is desired to reduce the leakage rate within a supercharger (and other twin rotor devices) without depending upon high precision dimensional tolerances from the set of individual components in the assembled supercharger and/or twin rotor device. 
         [0008]    Typical screw compressors have similar leakage issues caused by clearances between lobes of the pair of rotors, clearances between tips of the lobes of the rotors and a housing, and clearances between an end of the rotors and corresponding surfaces of the housing. Likewise, increasing precision of the manufacturing tolerances may increase manufacturing costs, and a number of different dimensions and corresponding dimensional tolerances together may determine the clearances that exist at final assembly. It is also desired to reduce the leakage rate within a screw compressor without depending upon high precision dimensional tolerances from the set of individual components in the assembled screw compressor. 
         [0009]    When Roots-style superchargers or similar twin rotor devices are run in reverse (i.e., when fluid pressure and flow are converted into shaft power), a Roots-type device (and/or other twin rotor device) may serve as a Roots-style expander (and/or other twin rotor expander). Such expanders may have similar leakage issues caused by clearances between lobes of the pair of rotors, clearances between tips of the lobes of the rotors and a housing, and clearances between an end of the rotors and corresponding surfaces of the housing. It is also desired to reduce the leakage rate within a Roots-style expander without depending upon high precision dimensional tolerances from the set of individual components in the assembled Roots-style expander. 
         [0010]    Similarly, when screw compressors or similar devices are run in reverse (i.e., when fluid pressure and flow are converted into shaft power), a screw-type device may serve as a screw expander. Such screw expanders may have similar leakage issues caused by clearances between lobes of the pair of rotors, clearances between tips of the lobes of the rotors and a housing, and clearances between an end of the rotors and corresponding surfaces of the housing. It is also desired to reduce the leakage rate within a screw expander without depending upon high precision dimensional tolerances from the set of individual components in the assembled screw expander. 
       SUMMARY 
       [0011]    An aspect of the present disclosure relates to various improvements made to twin rotor devices (e.g., Roots-style superchargers). The improvements may result from reduced internal clearances between intermeshing lobes of the Roots-style supercharger, between tips of the lobes and corresponding surfaces of a housing of the Roots-style supercharger, and/or from reduced clearances between ends of the rotors and corresponding surfaces of the housing. In particular, the twin rotor device may be partially or fully assembled and a coating (e.g., an abradable coating) may be applied to the assembled or partially assembled twin rotor device. If partially assembled, the pair of rotors and the housing may be sub-assembled. The rotors may be rotating as the coating is applied and/or as the coating is curing. The rotors may be driven by an input shaft of the twin rotor device and/or may be driven by a pressure differential across an inlet and an outlet of the twin rotor device. The coating may cure and adhere to some or all of the internal surfaces of the twin rotor device. 
         [0012]    In embodiments where differential pressure drives the rotors and/or otherwise exists between the inlet and the outlet of the twin rotor device, leakage resulting from internal clearances may draw a coating precursor material as the coating precursor material passes through the twin rotor device. As the coating precursor material is deposited on surfaces defining the internal clearances, a coating is formed on the surfaces defining the internal clearances, and the coating reduces the various clearances, and the leakage is thereby reduced in areas where the coating has been deposited/formed. Other areas with remaining clearances (e.g., larger remaining clearances that result in greater leakage rates) thereby attract the coating precursor material, and the remaining clearances are also reduced as a coating is also formed on the surfaces defining the remaining clearances. 
         [0013]    By measuring and monitoring the pressure differential between the inlet and the outlet and/or rotor speed of the rotors, the leakage rate (e.g., an overall internal leakage rate) may be monitored and the coating process may be continued until the internal leakage rate is reduced to a desired level and/or a predetermined level. The internal leakage may be measured by various means that may include measuring the pressure differential with pressure sensors and/or the rotor speed with a tachometer. A series of twin rotor devices from a given assembly line and/or multiple assembly lines across the world can thereby be tuned to have identical or near identical performance characteristics that are independent of the manufacturing variability of the components. 
         [0014]    In methods using powder-coating techniques and/or other techniques that require an electrical connection, portions of the housing that cover a gear set of the rotors may be left off during the coating process thereby allowing a grounding brush to contact a shaft of one or both of the rotors to provide an electrical ground and facilitate electrostatic depositing of powder coating material on the rotors (e.g., while the rotors are spinning). The other internal surfaces (e.g., of the housing) may also be grounded to facilitate electrostatic depositing of powder coating material. In certain embodiments, the rotors and the housing may both be grounded. In other embodiments, the rotors and the housing may be oppositely charged. In certain embodiments, the electric charge applied to the rotors and/or the housing may be positive or negative. In other embodiments, the electric charge applied to the rotors and/or the housing may alternate between positive and negative. 
         [0015]    The coating may be cured by conventional means. For example, the coating may be cured by evaporation of volatile organic compounds, a chemical reaction of a two-part epoxy, heat, ultraviolet energy, powder-coating curing methods, etc. A catalyst may be applied to the rotors and/or the housing prior to the coating material being applied (e.g., before assembly or sub-assembly). The catalyst may facilitate curing of the coating on the rotors and/or the housing. The rotors and/or the housing may be coated or partially coated (e.g., before assembly or sub-assembly) before a final coating is applied on the assembled or sub-assembled twin rotor device. In certain embodiments, a dry low flash point solvent may be used to carry the coating. The coating and/or the solvent may be entrained in a fluid flow (e.g., an air flow) that is run through the twin rotor device. In certain embodiments, the coating is cured while the rotors are spinning. In certain embodiments, the solvent may evaporate before the coating material touches the surfaces of the rotor and/or the housing. In certain embodiments, multiple layers of the coating may be deposited (i.e., applied). 
         [0016]    Another aspect of the present disclosure relates to improvements in reducing leakage of a twin rotor device. In particular, a method of treating the twin rotor device includes providing an at least partially assembled twin rotor device that includes a pair of rotors and a housing with a first port and a second port. The rotors and the housing define a set of working surfaces. The working surfaces are adapted to interface with each other and thereby interact with gas that passes through the twin rotor device. The method includes inducing a coating material to flow from the first port to the second port of the housing and thereby depositing a coating on the working surfaces. In certain embodiments, the first port is an inlet of the twin rotor device, and the second port is an outlet of the twin rotor device. In other embodiments, the first port is an outlet of the twin rotor device, and the second port is an inlet of the twin rotor device. 
         [0017]    The method of applying the coating may include providing a coating material dispenser. The coating material dispenser may be fluidly connected to the first port of the housing. The coating material may be entrained in a carrier fluid by the coating material dispenser. In other embodiments, the second port of the housing is fluidly connected to the coating material dispenser. 
         [0018]    In certain embodiments, a torque is applied to at least one of the rotors and thereby spins the rotors and thereby induces the coating material to flow through the twin rotor device. In certain embodiments, a differential pressure may be applied across the first port and the second port of the housing and thereby induce the coating material to flow and further induce the rotors to spin. The differential pressure may be created by applying a suction at one of the ports of the twin rotor device, and/or applying a pressure to the other of the ports of the twin rotor device. 
         [0019]    A variety of additional aspects will be set forth in the description that follows. These aspects can relate to individual features and/or to combinations of features. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad concepts upon which the embodiments disclosed herein are based. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a cross-sectional elevation view, including schematic elements, of a Roots-type device and post-assembly coating system according to the principles of the present disclosure, a first portion of the cross-section passes through a center-line of a rotor of the Roots-type device and a second portion of the cross-section passes through a center of an outlet flow handling assembly of the post-assembly coating system; 
           [0021]      FIG. 2  is the cross-sectional elevation view of  FIG. 1 , but with additional schematic elements and with a portion of a housing of a shaft drive of the Roots-type device and a portion of the shaft drive of the Roots-type device removed thereby allowing direct electrical and/or mechanical connection to a shaft of the rotor, according to the principles of the present disclosure; 
           [0022]      FIG. 3  is a perspective view of the Roots-type device of  FIG. 1 ; 
           [0023]      FIG. 4  is the perspective view of  FIG. 3 , but partially exploded; 
           [0024]      FIG. 5  is another perspective view of the Roots-type device of  FIG. 1 ; 
           [0025]      FIG. 6  is the perspective view of  FIG. 5 , but exploded; 
           [0026]      FIG. 7  is a graph illustrating performance characteristics of a Roots-type device and improvements in the performance characteristics that may result upon applying a coating to internal features of the Roots-type device according to the principles of the present disclosure; 
           [0027]      FIG. 8  is a perspective view of a screw compressor finished with a post-assembly coating system, similar to the post-assembly coating system of  FIG. 1 , according to the principles of the present disclosure; 
           [0028]      FIG. 9  is the perspective view of  FIG. 8 , but with a cut-away taken through center-lines of rotors of the screw compressor: 
           [0029]      FIG. 10  is another perspective view of the screw compressor of  FIG. 8 ; 
           [0030]      FIG. 11  is the perspective view of  FIG. 10 , but with a first cut-away taken through an exhaust port of the screw compressor and a second cut-away taken through a rotor and a housing of the screw compressor; and 
           [0031]      FIG. 12  is an exploded perspective view of the screw compressor of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Reference will now be made in detail to example embodiments of the present disclosure. The accompanying drawings illustrate examples of the present disclosure. When possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. 
         [0033]    According to the principles of the present disclosure, clearances may be reduced and thereby internal leakage may be reduced within a twin rotor device (e.g., a Roots-type supercharger, a screw compressor, etc.) by applying a coating to internal surfaces of the twin rotor device after rotors and a housing assembly of the twin rotor device have been assembled together. In certain embodiments, the coating or coatings may be applied at a factory and be part of a finishing process of the twin rotor device. In certain embodiments, the twin rotor device may be refurbished by applying the coatings to a twin rotor device that has already been in service. Such refurbishment may refurbish the coatings of the internal surfaces. In other embodiments, such refurbishment may apply a coating to some or all of the internal surfaces for the first time. Such refurbishment may be combined with other new or refurbished parts (e.g., new seals, new bearings, etc.). Such refurbishment may be done in a factory setting or in a field setting. 
         [0034]    Turning now to  FIGS. 1-6 , a Roots-type supercharger is illustrated according to the principles of the present disclosure. In other embodiments, a Roots-type expander may be subject to the same or similar treatment and/or finishing techniques described herein. As illustrated at  FIGS. 1-6 , a Roots-type supercharger  200  includes an inlet  202  and an outlet  204 . In operation on an internal combustion engine, air is drawn through the inlet  202  and pumped from the inlet  202  to the outlet  204 . As a displacement of the supercharger  200  may exceed a displacement of the internal combustion engine, a pressure at the outlet  204  may be greater than a pressure at the inlet  202 . The supercharger  200  thereby compresses air or an air-fuel mixture that it delivers to the internal combustion engine. An amount of compression of the air may be referred to as a pressure ratio. In graphs illustrated at  FIG. 7 , certain tests were conducted at a pressure ratio of 1.4:1. 
         [0035]    The supercharger  200  further includes a set of rotors  220 . The set of rotors  220  includes a first rotor  220 A and a second rotor  220 B. As illustrated at  FIGS. 1, 2, and 4 , a drive shaft  294  may coaxially align with a rotor shaft  280  of the rotor  220 A. The rotor  220 B may be powered by a gear set  286 . The rotors  220 A,  220 B include a plurality of lobes  230  and valleys  232 . Each of the lobes  230  further includes a tip  228 . As illustrated, the lobes  230  and the valleys  232  extend along a helical path. In other embodiments, the lobes  230  and the valleys  232  may be straight. As depicted, the lobes  230  and the valleys  232  define a screw surface  226 . The lobes  230  and the valleys  232  of the rotors  220 A,  220 B substantially extend between a first end  222  and a second end  224  (see  FIGS. 4 and 6 ). 
         [0036]    The supercharger  200  further includes a housing assembly  210 . As depicted, the housing assembly  210  includes a main housing  210   a , an end cap portion  210   b , and an input power portion  210   c . The housing assembly  210  defines the inlet  202  and the outlet  204 . The housing assembly  210  includes an input end  212  and an output end  214  (see  FIG. 1 ). As depicted, the input end  212  and the output end  214  are substantially perpendicular to each other. In other embodiments, the input end  212  and the output end  214  may be substantially parallel to each other. In still other embodiments, the input end  212  and the output end  214  may be arranged at an angle with respect to each other. As depicted, the housing assembly  210  further includes a drive end  216 . As depicted, the rotor shafts  280  generally longitudinally extend between the input end  212  and the drive end  216  of the housing assembly  210 . 
         [0037]    The housing assembly  210  includes a set of sealing surfaces  218 . In the depicted embodiment, the main housing  210   a  of the housing assembly  210  defines sealing surfaces  218   a ,  218   b  of the sealing surfaces  218  that seal with the tips  228  of the rotors  220 A,  220 B when they are adjacent to each other (see  FIGS. 3 and 4 ). By sealing with each other, as used herein, it is understood that running clearances may exist between the sealing surfaces  218   a ,  218   b  and the tips  228 , and that leakage may occur between the sealing surfaces  218   a ,  218   b  and the tips  228 . As depicted, the tips  228  of the rotor  220 A seal with the circular sealing surface  218   a , and the tips  228  of the rotor  220 B sealed with the circular sealing surface  218   b . The circular sealing surfaces  218   a  and  218   b  may intersect each other at a pair of cusps. 
         [0038]    As depicted, the ends  222  of the lobes  230  of the rotors  220 A,  220 B may seal against a planar sealing surface  218   d  of the sealing surfaces  218  (see  FIGS. 4 and 6 ). Likewise, the ends  224  of the lobes  230  may seal against a planar sealing surface  218   c  of the sealing surfaces  218  (see  FIGS. 1 and 6 ). By sealing with each other, as used herein, it is understood that running clearances may exist between the sealing surfaces  218   c ,  218   d  and the ends  224 ,  222 , respectively, and that leakage may occur between the sealing surfaces  218   c ,  218   d  and the ends  224 ,  222 . 
         [0039]    Turning now to  FIGS. 8-12 , a screw compressor is illustrated according to the principles of the present disclosure. In other embodiments, a screw expander may be subject to the same or similar treatment and/or finishing techniques described herein. As illustrated at  FIGS. 8-12 , a screw compressor  1200  includes an inlet  1202  and an outlet  1204 . In operation on an internal combustion engine, air is drawn through the inlet  1202  and pumped from the inlet  1202  to the outlet  1204 . As a displacement of the screw compressor  1200  may exceed a displacement of the internal combustion engine and/or as compression may be imposed on a working fluid within the screw compressor  1200 , a pressure at the outlet  1204  may be greater than a pressure at the inlet  1202 . The screw compressor  1200  may thereby compress air or an air-fuel mixture that it delivers to the internal combustion engine. As mentioned above, an amount of compression of the air may be referred to as a pressure ratio. 
         [0040]    The screw compressor  1200  further includes a set of rotors  1220 . The set of rotors  1220  includes a first rotor  1220 A and a second rotor  1220 B. In the depicted embodiment, the first rotor  1220 A is a male rotor, and the second rotor  1220 B is a female rotor. As illustrated at  FIG. 9 , a drive shaft may coaxially align with a rotor shaft of the rotor  1220 A. The rotor  1220 B may be powered by a gear set or directly by the rotor  1220 A. The rotors  1220 A,  1220 B include a plurality of lobes  1230  and valleys  1232 . Each of the lobes  1230  further includes a tip  1228  (see  FIG. 12 ). As illustrated, the lobes  1230  and the valleys  1232  extend along a helical path. As depicted, the lobes  1230  and the valleys  1232  define a screw surface  1226 . The lobes  1230  and the valleys  1232  of the rotors  1220 A,  1220 B substantially extend between a first end  1222  and a second end  1224  (see  FIGS. 11 and 12 ). 
         [0041]    The screw compressor  1200  further includes a housing assembly  1210 . As depicted, the housing assembly  1210  includes a main housing  1210   a , a first end cap portion  1210   b , and a second end cap portion  1210   c . The housing assembly  1210  defines the inlet  1202  and the outlet  1204 . The housing assembly  1210  includes an input end  1212  and an output end  1214  (see  FIGS. 8 and 10 ). As depicted, the input end  1212  and the output end  1214  are substantially parallel to each other. In other embodiments, the input end  1212  and the output end  1214  may be substantially perpendicular to each other. In still other embodiments, the input end  1212  and the output end  1214  may be arranged at an angle with respect to each other. As depicted, the housing assembly  1210  further includes a drive end  1216  (see  FIG. 8 ). As depicted, the rotor shafts generally longitudinally extend parallel to the input end  1212  and the output end  1214  and exit perpendicular to the drive end  1216  of the housing assembly  1210 . 
         [0042]    The housing assembly  1210  includes a set of sealing surfaces  1218  (see  FIG. 11 ). In the depicted embodiment, the main housing  1210   a  of the housing assembly  1210  defines sealing surfaces  1218   a ,  1218   b  of the sealing surfaces  1218  that seal with the tips  1228  of the rotors  1220 A,  1220 B when they are adjacent to each other. By sealing with each other, as used herein, it is understood that running clearances may exist between the sealing surfaces  1218   a ,  1218   b  and the tips  1228 , and that leakage may occur between the sealing surfaces  1218   a ,  1218   b  and the tips  1228 . As depicted, the tips  1228  of the rotor  1220 A seal with the circular sealing surface  1218   a , and the tips  1228  of the rotor  1220 B sealed with the circular sealing surface  1218   b . The circular sealing surfaces  1218   a  and  1218   b  may intersect each other at a pair of cusps. 
         [0043]    As depicted, the ends  1222  of the lobes  1230  of the rotors  1220 A,  1220 B may seal against a planar sealing surface  1218   d  of the sealing surfaces  1218  (see  FIG. 11 ). Likewise, the ends  1224  of the lobes  1230  may seal against a planar sealing surface  1218   c  of the sealing surfaces  1218  (see  FIG. 9 ). By sealing with each other, as used herein, it is understood that running clearances may exist between the sealing surfaces  1218   c ,  1218   d  and the ends  1224 ,  1222 , respectively, and that leakage may occur between the sealing surfaces  1218   c ,  1218   d  and the ends  1224 ,  1222 . 
         [0044]    As illustrated at  FIGS. 4, 6, 9, 11, and 12 , the lobes  230 ,  1230  and the valleys  232 ,  1232  of the rotors  220 A,  220 B,  1220 A,  1220 B intermesh with and seal with each other, respectively. By sealing with each other, as used herein, it is understood that running clearances may exist between the lobes  230 ,  1230 , including the tips  228 ,  1228  and the valleys  232 ,  1232  of the opposite rotor  220 B,  220 A,  1220 A,  1220 B, and that leakage may occur between the lobes  230 ,  1230 , including the tips  228 ,  1228  and the corresponding valleys  232 ,  1232 . As the rotors  220 A,  220 B,  1220 A,  1220 B rotate, the screw surfaces  226 ,  1226  and the tips  228 ,  1228  move in and out of intermeshing with the screw surfaces  226 ,  1226 , and the tips  228 ,  1228  of the opposing rotor  220 B,  220 A.  1220 A,  1220 B and the tips  228 ,  1228  transition to sealing with the corresponding circular sealing surfaces  218   a ,  218   b ,  1218   a ,  1218   b.    
         [0045]    As depicted, an inlet volume  240  is defined by the circular sealing surface  218   a ,  218   b ,  1218   a ,  1218   b , the planar sealing surface  218   c ,  1218   c , and the screw surfaces  226 ,  1226 , respectively. As defined herein, the inlet volume  240  is open to the inlet  202 ,  1202 . Upon the rotors  220 A,  220 B,  1220 A,  1220 B rotating, portions of air within the supercharger  200  or the screw compressor  1200  become closed off from the inlet  202 ,  1202  and thereby are transferred from the inlet volume  240  to a transfer volume  242 . The transfer volume  242  is closed off from both the inlet  202 ,  1202  and the outlet  204 ,  1204 . As the rotors  220 A,  220 B,  1220 A,  1220 B further rotate, portions of air within the supercharger  200  or the screw compressor  1200  that were part of the transfer volume  242  are open to the outlet  204 ,  1204  and thereby become part of an outlet volume  244 . In this way, air is moved through the supercharger  200  or the screw compressor  1200  by transferring through the inlet  202 ,  1202  and becoming part of the inlet volume  240 , passing from the inlet volume  240  to the transfer volume  242 , and further passing from the transfer volume  242  to the outlet volume  244 . As the pressure at the outlet  204 ,  1204  is typically higher than the pressure at the inlet  202 ,  1202 , air (or other gas) within the outlet volume  244  is urged to leak to the transfer volume  242 , and air within the transfer volume  242  may be urged to leak to the inlet volume  240 . 
         [0046]    According to the principles of the present disclosure, clearances between the tips  228 ,  1228  of the rotor  220 A,  1220 A and the circular sealing surface  218   a ,  1218   a , clearances between the tips  228 ,  1228  of the rotor  220 B,  1220 B and the circular sealing surface  218   b ,  1218   b , clearances between the end  222 ,  1222  of the lobes  230 ,  1230  and the planar sealing surface  218   d ,  1218   d , clearances between the end  224 ,  1224  of the lobes  230 ,  1230  and the planar sealing surface  218   c .  1218   c , and clearances between the intermeshing lobes  230   1230  and valleys  232 ,  1232  of the rotors  220 A,  220 B,  1220 A,  12208  are reduced and thereby leakage within the supercharger  200  and/or the screw compressor  1200  is reduced. 
         [0047]    In the embodiment depicted at  FIG. 1 , an application assembly  100  is formed by assembling the supercharger  200  to application hardware  300 . The application hardware  300  may include a holding fixture  400  to which the supercharger  200  may be mounted. As depicted, the holding fixture  400  is holding the supercharger  200  with the axes of the rotors  220 A,  220 B extending in a horizontal plane. In other embodiments, the holding fixture  400  may hold the supercharger  200  such that the axes of the rotors  220 A,  220 B extend horizontally but a plane that includes both of the axes extends vertically. In still other embodiments, the holding fixture  400  may hold the supercharger  200  such that the axes of the rotors  220 A,  220 B are each aligned vertically. In yet other embodiments, the holding fixture  400  may hold the supercharger  200  in other orientations. As depicted, a mounting plate  450  may be included between the holding fixture  400  and the housing assembly  210  of the supercharger  200 . As depicted, the holding fixture includes a passage  402 , and the mounting plate  450  includes a passage  452  that substantially aligns with the outlet  204  of the supercharger  200 . In other embodiments, the holding fixture  400  may be arranged such that the passage  402  and/or the passage  252  align with the inlet  202 . As depicted, the holding fixture  400  further holds outlet side hardware  500  of the application hardware  300 . In other embodiments, the outlet side hardware  500  may mount directly to the outlet  204  of the supercharger  200 . 
         [0048]    In the embodiment depicted at  FIG. 2 , an application assembly  100 ′ is formed by assembling certain parts of the supercharger  200  to the application hardware  300 . In the depicted embodiments, the application assembly  100 ′ is similar to the application assembly  100 , except the input power portion  210   c  of the housing assembly  210 , the drive shaft  294 , a drive pulley  292 , and other parts of a drive assembly  290  are removed to provide access to the rotor shafts  280 . In particular, by removing the portion  210   c  of the housing assembly  210 , a first end  282  of each of the rotor shafts  280  is exposed. In other embodiments, provisions may be made to expose a second end  284  of each of the rotor shafts  280 . Removing the portion  210   c  of the housing assembly  210  may also expose the gear set  286  and interfere with a lubrication system that otherwise lubricates the gear set  286 . However, a temporary lubrication system  800  with a lubrication nozzle  802  may be directed at the gear set  286  to provide lubrication. 
         [0049]    An application assembly, similar to the application assemblies  100 ,  100 ′, may be formed by assembling the screw compressor  1200  to application hardware similar to or the same as the application hardware  300 . Furthermore, an application assembly, similar to the application assemblies  100 ,  100 ′, may be formed by assembling a twin rotor device to application hardware similar to or the same as the application hardware  300 . 
         [0050]    The outlet side hardware  500  may include a coating material collector  520 ; a flow device  530 ; a heat exchanger  540 ; a contoured flow passage  550 ; and/or flow control, instrument, and/or material injection/recovery equipment  560 . 
         [0051]    As schematically depicted, the equipment  560  is arranged in a housing with a first port  562  and a second port  564 . The contoured flow passage  550  includes a first port  552  and a second port  554 . A passage  556  connects the first port  552  to the second port  554 . As depicted, the first port  552  is mounted to the passage  402  of the holding fixture  400 . In other embodiments, the contoured flow passage  550  may connect directly to the outlet  204 ,  1204  of the supercharger  200 , the screw compressor  1200 , or other twin rotor device. The second port  554  of the contoured flow passage  550  may be fluidly connected to the first port  562  of the housing of the equipment  560 . 
         [0052]    The application hardware  300  may further include inlet side hardware  600 . As depicted, the inlet side hardware  600  may mount directly to the inlet  202 ,  1202  of the supercharger  200 , the screw compressor  1200 , or other twin rotor device. In other embodiments, the holding fixture  400  holds the inlet side hardware  600  of the application hardware  300 . The inlet side hardware  600  may include a material dispenser  610 ; a flow device  630 ; a heat exchanger  640 ; a contoured flow passage  650 ; and/or flow control, instrument, and/or material injection/recovery equipment  660 . 
         [0053]    As schematically depicted, the equipment  660  is arranged in a housing with a first port  662  and a second port  664 . The contoured flow passage  650  includes a first port  652  and a second port  654 . A passage  656  connects the first port  652  to the second port  654 . As depicted, the first port  652  is mounted directly to the inlet  202 ,  1202  of the supercharger  200 , the screw compressor  1200 , or other twin rotor device. In other embodiments, the contoured flow passage  650  may connect to the passage  402  of the holding fixture  400 . The second port  654  of the contoured flow passage  650  may be fluidly connected to the first port  662  of the housing of the equipment  660 . 
         [0054]    In alternative embodiments, a material dispenser  510  may be included with the outlet side hardware  500 , and/or a material collector  620  may be included with the inlet side hardware  600  (see  FIG. 2 ). 
         [0055]    In certain embodiments, a coating material  102  is entrained by a carrier material  104  (e.g., air, nitrogen, argon, etc.) by the material dispenser  510  or the material dispenser  610  (see  FIGS. 1 and 2 ). If the coating material  102  is supplied by the material dispenser  510 , the supercharger  200 , the screw compressor  1200 , or other twin rotor device is run in reverse and thereby the coating material  102 , entrained in the carrier material  104 , is moved first into the outlet  204 ,  1204  of the supercharger  200 , the screw compressor  1200 , or other twin rotor device and backward through the supercharger  200 , the screw compressor  1200 , or other twin rotor device toward the inlet  202 ,  1202 . If the coating material  102  is supplied by the material dispenser  610 , the supercharger  200 , the screw compressor  1200 , or other twin rotor device is run in a normal direction and thereby the coating material  102 , entrained in the carrier material  104 , is moved first into the inlet  202 ,  1202  of the supercharger  200 , the screw compressor  1200 , or other twin rotor device and forward through the supercharger  200 , the screw compressor  1200 , or other twin rotor device toward the outlet  204 ,  1204 . 
         [0056]    In certain backward running embodiments, excess coating material of the coating material  102  that passes through the supercharger  200 , the screw compressor  1200 , or other twin rotor device without adhering may be collected by the material collector  620  within the housing of the inlet side hardware  600 . Likewise, in certain forward running embodiments, excess coating material of the coating material  102  that passes through the supercharger  200 , the screw compressor  1200 , or other twin rotor device without adhering may be collected by the material collector  520  within the housing of the outlet side hardware  500 . 
         [0057]    In certain embodiments, recirculation plumbing  310  is connected between the second port  664  of the housing of the equipment  660  and the second port  564  of the housing of the equipment  560 . In particular, a first port  312  of the recirculation plumbing  310  may be connected to the second port  664  of the housing of the equipment  660 , and a second port  314  of the recirculation plumbing  310  may be connected to the second port  564  of the housing of the equipment  560 . In certain embodiments, the carrier material  104  is recirculated. In certain embodiments, the carrier material  104  along with unused coating material of the coating material  102  may be recirculated. In still other embodiments, the recirculation plumbing  310  is not used, and instead fresh coating material  102  and/or fresh carrier material  104  is used. 
         [0058]    As the coating material  102  passes through the supercharger  200 , the screw compressor  1200 , or other twin rotor device, a portion of the coating material  102  will adhere to the sealing surfaces  218 ,  1218  of the housing assembly  210 ,  1210  and the ends  222 ,  224 ,  1222 ,  1224 , screw surfaces  226 ,  1226 , and tips  228 ,  1228  of the rotors  220 A,  220 B,  1220 A,  1220 B. The clearances between these surfaces  218 ,  222 ,  224 ,  226 ,  228 ,  1218 ,  1222 ,  1224 ,  1226 ,  1228  may create leakage between the adjoining surfaces  218 ,  222 ,  224 ,  226 ,  228 ,  1218 ,  1222 ,  1224 ,  1226 ,  1228 . Such leakages will encourage the coating material  102  and/or the carrier material  104  to pass through the clearances and deposit the coating material  102  on the surfaces  218 ,  222 ,  224 ,  226 ,  228 ,  1218 ,  1222 ,  1224 ,  1226 ,  1228 . As the coating material  102  collects on the surfaces  218 ,  222 ,  224 ,  226 ,  228 ,  1218 ,  1222 ,  1224 ,  1226 ,  1228 , a coating  206 ,  1206  is formed on the surfaces  218 ,  222 ,  224 ,  226 ,  228 ,  1218 ,  1222 ,  1224 ,  1226 ,  1228 . As will be described hereinafter, the coating  206 ,  1206  may cure into a solidified coating surface  206 ,  1206 . The coating  206 ,  1206  may form a permanent or a semi-permanent coating on the surfaces  218 ,  222 ,  224 ,  226 ,  228 ,  1218 ,  1222 ,  1224 ,  1226 ,  1228 . 
         [0059]    In certain embodiments, the coating  206 ,  1206  is cured while the rotors  220 A,  220 B,  1220 A,  1220 B are spinning. In certain embodiments, the coating  206 ,  1206  may further wear-in and thereby further finish itself over a wear-in period. In certain embodiments, the coating material  102  and/or the carrier material  104  may be run through the supercharger  200 , the screw compressor  1200 , or other twin rotor device in a first direction from the inlet  202 ,  1202  to the outlet  204 ,  1204  and additional material may be applied by running the supercharger  200 , the screw compressor  1200 , or other twin rotor device in reverse with the coating material  102  and/or the carrier material  104  generally passing from the outlet  204 ,  1204  to the inlet  202 ,  1202 . In certain embodiments, the coating material  102  may be first applied by running the supercharger  200 , the screw compressor  1200 , or other twin rotor device in the reverse direction. 
         [0060]    Turning again to  FIGS. 1 and 2 , a control system  900  may be used in applying the coating material  102 , emitting the carrier material  104 , and/or curing the coating material  102  into the coating  206 ,  1206 . As depicted at  FIGS. 1 and 2 , the control system  900  may include and/or interface with one or more flow monitors  910  (i.e., flow sensors), pressure monitors  920  (i.e., pressure sensors), temperature monitors  930  (i.e., temperature sensors), state sensors  940 , tachometers  950 , rotary inputs  960  (e.g., motors, speed controllers, torque controllers, etc.), electrostatic generators  700 , etc. As mentioned above, the supercharger  200 , the screw compressor  1200 , or other twin rotor device may be run in the forward direction or in the reverse direction. The various components of the control system  900  and equipment  560 ,  660  may be arranged to match the direction chosen to run the supercharger  200 , the screw compressor  1200 , or other twin rotor device when applying the coating material  102 . The supercharger  200 , the screw compressor  1200 , or other twin rotor device may also be run in both the forward and the reverse rotational directions when applying the coating material  102  to form the coating  206 ,  1206 . 
         [0061]    As depicted, various sensors and application hardware are schematically illustrated in the outlet equipment group  560  and the inlet equipment group  660 . In certain embodiments, the various sensors and application equipment may only be located in the outlet equipment group  560  or the inlet equipment group  660 . Certain equipment and/or certain sensors may be located in both the outlet equipment group  560  and the inlet equipment group  660 . In particular, the flow monitor  910  may include an outlet flow monitor  9100   o  and an inlet flow monitor  910   i . Likewise, the pressure monitor  920  may include an outlet pressure monitor  920   o  and an inlet pressure monitor  920   i . The pressure monitors  920   o ,  920   i  may be used to measure a differential pressure across the outlet  204 ,  1204  and the inlet  202 ,  1202  of the supercharger  200 , the screw compressor  1200 , or other twin rotor device. The temperature monitor  930  may include an outlet temperature monitor  930   o  and an inlet temperature monitor  930   i . The state sensor  940  may include an outlet state sensor  940   o  and an inlet state sensor  940   i . The state sensors  940 ,  940   o ,  940   i  may be used to measure an amount of the coating material  102  and/or the carrier material  104  and a percentage (e.g., by weight) of the coating material  102  and/or the carrier material  104  that are in solid, liquid, and/or gaseous form. 
         [0062]    The control system  900  may send commands to the flow device  530  and/or the flow device  630  and thereby generate differential pressure across the inlet  202 ,  1202  and the outlet  204 ,  1204  of the supercharger  200 , the screw compressor  1200 , or other twin rotor device. The control system may further initiate coating material  102  and/or carrier material  104  being dispensed from the material dispenser  510  and/or the material dispenser  610 . 
         [0063]    By monitoring a rotational speed of the rotors  220 A,  220 B,  1220 A,  1220 B with the tachometer  950 , the development of the coating  206 ,  1206  may be estimated. In particular, as the coating material  102  is converted into the coating  206 ,  1206 , the various clearances within the supercharger  200 , the screw compressor  1200 , or other twin rotor device may be reduced and the leakage across the clearances may be reduced. Under a given differential pressure generated by the flow device  530  and/or the flow device  630 , the speed of the rotors  220 A,  220 B,  1220 A,  1220 B may increase with decreasing internal clearances. By monitoring the increase in the rotor speed, the condition of the coating  206 ,  1206  may be estimated. Upon a certain condition of the coating material  206 ,  1206  being reached, the injection of the coating material  102  and/or the carrier material  104  may be suspended. As mentioned above, the supercharger  200 , the screw compressor  1200 , or other twin rotor device may continue to run after the suspension of the coating material  102  and/or the carrier material  104 . In particular, the coating  206 ,  1206  may be allowed to cure while the supercharger  200 , the screw compressor  1200 , or other twin rotor device is running (i.e., the rotors  220 A,  220 B,  1220 A,  1220 B are spinning). 
         [0064]    In certain embodiments, the rotary input  960  may be connected to the rotors  220 A,  1220 A and/or  220 B,  1220 B directly or indirectly. As illustrated at  FIG. 1 , the rotary input  960  is connected to the drive pulley  292  by a drive belt  962 . The rotary input  960 , under the control of the control system  900 , may apply a resisting torque that slows down (i.e., retards) the rotation of the rotors  220 A,  220 B,  1220 A,  1220 B. The torque supplied by the rotary input  960  may vary as the coating material  102  is applied to form the coating  206 ,  1206 . The rotary input  960  may be set to maintain a given speed of the rotors  220 A,  220 B,  1220 A,  1220 B while allowing the drag torque (i.e., the resisting torque) to vary. In general, the drag torque will be increased as the coating  206 ,  1206  is formed and the differential pressure across the inlet  202 ,  1202  and the outlet  204 ,  1204  is maintained. Feedback from the rotary input  960  may thereby be used to indicate when the coating  206 ,  1206  has reached various states including a state where emission of the coating material  102  is suspended. 
         [0065]    In certain embodiments, the rotary input  960  may drive the supercharger  200 , the screw compressor  1200 , or other twin rotor device and induce flow through the supercharger  200 , the screw compressor  1200 , or other twin rotor device and create a pressure differential across the supercharger  200 , the screw compressor  1200 , or other twin rotor device (i.e., across the inlet  202 ,  1202  and the outlet  204 ,  1204 ). The flow created by the rotary input  960  when driving the supercharger  200 , the screw compressor  1200 , or other twin rotor device may entrain the coating material  102  and/or the carrier material  104  and thereby form the coating  206 ,  1206 . The coating  206  may reduce internal clearances and thereby result in an increase in the pressure differential across the supercharger  200 , the screw compressor  1200 , or other twin rotor device. By monitoring the pressure differential across the supercharger  200 , the screw compressor  1200 , or other twin rotor device, the state of the coating  206 ,  1206  may be estimated. When a state of the coating  206 ,  1206  reaches a predetermined level, further application of the coating material  102  and/or the carrier material  104  may be suspended. 
         [0066]    In addition to the aforementioned parameters of rotor rotational speed, rotor retarding torque, and pressure differential being used as feedback to monitor the state of the coating  206 ,  1206 , leakage across the supercharger  200 , the screw compressor  1200 , or other twin rotor device may also be measured and/or estimated. The leakage may likewise be used to suspend further application of the coating material  102  and/or the carrier material  104  when a state of the coating  206 ,  1206  reaches a predetermined level. 
         [0067]    As the coating material  102  and/or the carrier material  104  flow through the supercharger  200 , the screw compressor  1200 , or other twin rotor device, the coating material  102  and/or the carrier material  104  will generally follow a path of least resistance. The coating material  102  and/or the carrier material  104  will therefore seek out larger clearances between the surfaces  218 ,  222 ,  224 ,  226 ,  228 ,  1218 ,  1222 ,  1224 ,  1226 ,  1228  and pass through and fill the larger clearances first. In certain embodiments, as the coating material  102  and/or the carrier material  104  flow through the clearances, thermodynamic properties of the coating material  102  and/or the carrier material  104  may change and thereby assist in depositing the coating material  102  as the coating  206 ,  1206 . In certain embodiments, leakage across the clearances produces heat from work being provided by the air, the coating material  102 , and/or the carrier material  104  flowing across a pressure drop. The heat from the leakage may be used to assist in depositing the coating material  102  as the coating  206 ,  1206 . 
         [0068]    The supercharger  200 , the screw compressor  1200 , or other twin rotor device may be run without the coating material  102  and/or without the carrier material  104  for a given period to heat the supercharger  200 , the screw compressor  1200 , or other twin rotor device. Upon a desired temperature profile of the supercharger  200 , the screw compressor  1200 , or other twin rotor device being reached, the coating material  102  and/or the carrier material  104  may be applied. 
         [0069]    As mentioned above, the coating material  102  may include powder coating components or other components that may be activated or otherwise affected by application of electricity (e.g., electric charge). As illustrated at  FIG. 2 , the electrostatic generator  700  is connected to one or both of the rotor shafts  280  by a conductive lead  702  (e.g., a brush). A conductive lead may also be connected to one or more parts of the housing assembly  210 . The rotor shaft  280  and the rotors  220 A,  220 B,  1220 A,  1220 B may be made of a conductive material and thereby charge the surfaces  218 ,  220 ,  224 ,  226 ,  228 ,  1218 ,  1222 ,  1224 ,  1226 ,  1228  with electricity (e.g., static electricity). Such static electricity may draw the coating material  102  to the surfaces  218 ,  222 ,  224 ,  226 ,  228 ,  1218 ,  1222 ,  1224 ,  1226 ,  1228  and thereby assist in converting the coating material  102  to the coating  206 ,  1206 . In certain embodiments, the coating material  102  and/or the carrier material  104  may be electrically charged. 
         [0070]    The carrier material  104  may include a low flash point solvent. The coating material  102  may be carried by the carrier material  104 , and the carrier material  104  may evaporate prior to the coating material  102  reaching the surfaces  218 ,  222 ,  224 ,  226 ,  228 ,  1218 ,  1222 ,  1224 ,  1226 ,  1228 . The coating material  102  may thereby be applied to the surfaces  218 ,  222 ,  224 ,  226 ,  228 ,  1218 ,  1222 ,  1224 ,  1226 ,  1228  dry. 
         [0071]    Turning now to  FIG. 7 , a graph  1000  showing experimental results of applying a particular coating material  102  to a particular supercharger  200  is illustrated. In particular, the graph  1000  illustrates a relationship between a baseline performance  1030  of the supercharger  200  and an enhanced performance achieved with the coating material  102  freshly applied as the coating  206 , as illustrated at curve  1040 . A curve  1050  illustrates a performance of the coating  206  after the coating  206  has worn-in. The graph  1000  plots the rotational speed of the rotors  220 A,  220 B along an X-axis  1020  and plots a volumetric efficiency  1010  of the supercharger  200  along a Y-axis  1010 . As can be seen, initial application of the coating material  102  increased the volumetric efficiency of the supercharger  200  between the speeds of 4,000 and 8,000 revolutions per minute. The experimental coating  206  was applied via a spray-on dry graphite material  102 . The experiment illustrates that the coating  206  of the coating material  102  was effective in increasing the volumetric efficiency of the supercharger  200 . 
         [0072]    In various embodiments, twin rotor devices with coatings such as the coatings  206 ,  1206 , described above, may be used to pump compressible and/or non-compressible fluids. In various embodiments, twin rotor devices with coatings such as the coatings  206 ,  1206 , described above, may be used to extract shaft power from compressible and/or non-compressible fluids. 
         [0073]    From the forgoing detailed description, it will be evident that modifications and variations can be made without departing from the spirit and scope of the disclosure.