Screw Chillers

Screw Chillers Points : screw chillers, main components of screw chillers, screw compressor, oil coller, condenser, evaporator, capacity control, Screw chillers are either water cooled or air cooled. Energy-efficient water cooled screw chillers are widely used to replace the water-cooled reciprocating chillers employed in thermal storage system. More energy-efficient & more compact air cooled screw chillers are used to replace air cooled centrifugal chillers & air cooled reciprocating chillers in new & retrofit installations.

A water cooled screw chiller has live main components In addition to a screw compressor, a shell & tube liquid cooled as evaporator, a shell-& -tube water cooled condenser, & orifice plates or ‘flat valves as throttling device, oil cooler is used to cool & supply oil to the compressor. Screw Compressor Twin-screw compressors are more widely used than single-screw compressors because their isentropic efficiency is slightly higher than that of single screw compressors. A typical twin screw compressor consists of an our-lobe male rotor &, a six lobe female rotor when the lobes are separated at the suction port, vapor refrigerant is drawn in & the intake process continues until the inter-lobe space is out of contact with the suction port. The volume trapped in the inter-lobe space within the meshing point is compressed during successive rotations of the when the inter-lobe space makes contact with the discharge port, the compressed gas discharge port, the compressed gas discharge through the outlet. Oil Coller The hot gas & oil mixture discharge from the screw compressor enters an oil gas separator, in which oil is separated from the gaseous refrigerant. The oil is cooled in the oil cooled flows through a filter & flows to the compressor oil in the compressor lubricate the driving mechanism & cools the refrigerant during compression. In an oil cooler, oil is usually cooled by cooling water from the cooling tower. Condenser The condenser a shell & tube heat exchanger-receives compressed refrigerant vapor from the compressor the vapor condenses inside the shell & is collected as a liquid before being fed to the evaporator the condenser water that carries away the beat of condensation is carried in tubes inside the shell. Evaporator It is a shell & tube liquid cooler. Refrigerant in the evaporator is in the shell & the water is pumped through the tubes heat is transferred from the water to the liquid refrigerant causing it to boil & vaporize. Orific Plates Or Float Valves Orific plates (arrange in series) or float valves are used as throttling devices in screw chillers. Capacity Control Cooling capacity is controlled by moving a suing valve b/w the discharge end of the male rotor & the discharge port. The sliding valve is driven by the oil pressure. When the sliding valve moves toward the discharge port, it opens a bypass passes on the rotor housing. A portion of the tapped gaseous refrigerant returns to the suction port through this bypass passage, so the mass flow rate of refrigerant & thus the cooling capacity are reduced. This, kind of capacity control is step-less continuous modulation.