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LEGEND High press Low press

LEGEND High press Low press. Liquid vapour mixture. Direct expansion evaporator. Vapour. Expansion valve. Seawater out. Liquid. Oil separator. Receiver with gauge glass. Refrigeration compressor. Condenser. Seawater in. Oil return to sump. Compressor Type. Reciprocating

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LEGEND High press Low press

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  1. LEGEND High press Low press Liquid vapour mixture Direct expansion evaporator Vapour Expansion valve Seawater out Liquid Oil separator Receiver with gauge glass Refrigeration compressor Condenser Seawater in Oil return to sump

  2. Compressor Type • Reciprocating • Centrifugal • Screw

  3. Compressors Reciprocating: • Suction must be dry • Low capacity • High leakage factor; air entry

  4. Compressors Centrifugal: • Not flexible to demand • Large installation ; high speed operation • Simple design ; wear to bearing only • Care as liquid may enter compressor

  5. Screw Compressor Inlet Lobes Drive shaft Max Min Discharge Port Unloader piston Bypass gas Slide valve Outlet Cylinder

  6. Compressors: Screw: • Large capacity • Oil injection for lubrication and oil film • Capacity control by sliding vanes

  7. Mechanical Seal oil securing bolt cover plate seal retainer spring jointing stationary seal rotating seal drive end o-ring grub screw to secure seal retainer to shaft drive shaft

  8. Gas to condenser Gas from compressor Float Oil to compressor crankcase Oil

  9. Condensers Shell and tube: • Aluminium – brass tubes with fins • Iron plugs • Velocity < 2.5m/s to reduce erosion

  10. Compressor Problems • High Load leading to: • high temperature ; oil soluble in Freon • more oil carried away • liquid returning causing valve damage; also evaporation cause seizure • Moisture causing Freon and copper to react • Sticking of unloading gear • Broken valves causing overheating

  11. High Temperature (cause) • Condenser • Compressor jacket cooling • High suction pressure • Leaky valves – recompression • Above rated speed • Choked discharge passages

  12. Crankcase Oil • Low pour point -35 oC • Miscible with refrigerant • Anti foaming + pour point depressant • No air or moisture • S.G ~ 0.9 • Viscosity index > 25 • Low floc point – (wax precipitation)

  13. Primary Refrigerant • Halogenated hydrocarbons • Numerical code used for naming • Non toxic; • except ammonia – separate compartment • Design pressure related to maximum operational temperature expected. • Miscibility with oil – for easy retrieval

  14. R12 Miscible with oil under all condition 30 % less refrigerating effect R22 Miscible with oil up to -9oC Water more soluble by ratio 3 : 1 more desiccant Comparison

  15. Precautions with Freon • Goggles • No heating to cylinder or system if under pressure • Blow out gas before brazing • Max cap of cylinder < 85% • When charging : • inspect lines first. • use gauge • no charging of liquid to suction side • Frost bite – special medication to eyes ; no rubbing • Phosgene gas –ventilation important

  16. Secondary Refrigerant • Save on: • primary refrigerant • high pressure piping • Intermediate temperature range possible with injection • Improve suction as need for high velocities to improve return of oil reduced

  17. Brine • Mixture of Calcium Chloride & Water • To prevent corrosion maintained at Ph 8 to 8.5 by adding say hydrochloric acid

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