Noise and vibration are problems that are inherent in screw compressors and other Positive Displacement (PD)Machines. This problem is driven partly by the lobe passing frequencies inside these machines that are generated due to the meshing between the gate and main rotors teeth. Because these compressors are operated over a wide speed range and at various loads they usually run at off-design conditions leading to either over or under-compression. In both scenarios, the pressure within the compressor always changes rapidly to match the discharge or process pressure when the discharge opens thus leading to pulsation and noise. To ensure that the compressor is operated without over and or under compression, which also negatively affects the compressor efficiency Hi-Bar Blowers, Inc developed a Shunt Pulsation Trap (SPT) that will contain and reduce the pulsation inside the compressor cavities thus eliminating the use of a silencer at the inlet and the discharge. During the SPT development the CVS Silo King (SKL 1100) compressor was selected for benchmarking this technology. CFD was used extensively to simulate the SKL 1100 without and with the SPT integrated, which allowed the SPT design to be optimized. This paper will present the results obtained to demonstrate that this technology has the potential to eliminate over and under compression while at the same time leading to energy savings and reducing the compressor footprint and the noise and vibration that are commonplace in screw compressors.

Some positive displacement (PD) compressors are equipped with automatic discharge valves such as reed valves that open automatically whenever the cavity pressure is slightly larger than the outlet pressure to deal effectively with varying pressure ratio applications. Screw compressors today do not have such valves, resulting in off-design conditions known as the under-compression or over-compression when the cavity pressure at discharge is deviating from the outlet pressure. Compressor efficiency suffers and pulsation/noise becomes worse under these conditions. Some type of controls are desired such as a discharge pulsation dampener or a variable volume ratio (often called variable Vi) slide valve design to lessen or cure the discharge pressure mismatch problems. Injecting gas vapor into a screw compressor cavity during internal compression phase has been known to be beneficial in enhancing compressor performance and has been widely used in HVAC&R industry known as the Economizer. However, the underlining principle of the Economizer has thus far not been explored for optimizing compression schemes of a screw compressor in general. This paper introduces a self-sensing and self-correcting compression process that can be “derived or deduced” from the Perfect Gas Law by optimizing for multiple design criteria such as compressor efficiency, pulsation/noise abatement, and cost and footprint reduction for a screw operating over a wide range of pressures. The scheme, called SECAPT (Shunt Enhanced Compression And Pulsation Trap), is then investigated and optimized numerically by a new CFD code for one industrial case: a bulk truck loading application where compressor pressure varies from no pressure rise to maximum load. The numerical simulations illustrate that SECAPT is tentatively capable of achieving multiple targets as theorized.