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Transcript
Basic Refrigeration Star Refrigeration Wednesday 12 September 2007 Agenda AM Refrigeration basics Simple systems The refrigerant The evaporator The condenser Agenda - continued PM The compressor The expansion device Star designs - LPR - RCD - Indigochiller - CO2 sytems Simple Refrigeration System Heat Out High Pressure Liquid Condenser Expansion Device Work In Low Pressure Liquid & Vapour Evaporator Heat In High Pressure Vapour Compressor Low Pressure Vapour Basic Physics WATER (or Refrigerant) Fundamental “STATES” Solid (ICE) Liquid (Apply heat) Solid (ICE) (WATER) Vapour (Apply heat) Liquid (Remove heat) (WATER) (STEAM) Vapour (Remove heat) (STEAM) Basic Refrigeration Vapour Compression Cycle In the Evaporator (Evaporation) Liquid Vapour (Apply heat) In the Condenser (Condensation) Liquid Vapour (Remove heat) Heat Transfer Hot Always Goes To Cold Heat from the product will migrate to the colder refrigerant THE REFRIGERANT WILL BOIL EVAPORATION THE REFRIGERANT WILL LIQUEFY CONDENSATION Heat Transfer : Examples of Evaporation At 100oC Water will boil. The energy the water uses to boil in the kettle is heat from the electric element. The energy a refrigerant uses to boil in the evaporator is heat from the product. Heat Transfer: Examples of Condensation Steam will condense on kitchen tiles – heat transfer from hot steam to colder tile. • A refrigerant will condense when it is exposed to a medium at a lower temperature, such as water or air. • Second Law of Thermodynamics • 2nd Law of Thermodynamics States: “Heat cannot of itself pass from one body to a hotter body” • Need to do work to compress this refrigerant gas • RRefrigeration cycle needs A Compressor A Condenser An Expansion Device An Evaporator A Refrigerant A pressure – enthalpy (P-H) diagram is a useful device to understand what is happening in the cycle The Refrigerant In a refrigeration system, the working fluid is the Refrigerant. Different refrigerants have different boiling temperatures – well below that of water! For example Ammonia will boil at –33oC (at atmospheric pressure). Saturation Temperature Saturation Temperature (C) Pressure 24 19 14 9 4 -1 -40 -30 -20 -10 0 10 20 R717 Ammonia 30 40 50 Examples of Refrigerants R22: Ammonia: CO2: Currently being phased out because of its Ozone Depleting Potential (ODP). Star’s preferred refrigerant. Good refrigerating properties. Zero ODP and Zero Global Warming Potential (GWP) “Back to the Future”. Excellent refrigerating properties, where appropriate. Zero ODP. GWP = 1. Also: New HFC synthetic Refrigerants – R134a, R404A, R407C Zero ODP but High GWP R410A, etc. Typical Star Refrigeration System Evaporator(s) Expansion Device Compressor(s) Condenser Heat Transfer The units for heat energy transferred in the refrigeration system for each kg of refrigerant flowing in the circuit is referred to as the refrigerating effect and has units in kiloJoule/kg (kJ/kg). One kJ/s is equal to one kiloWatt (kW) Summary • Star design and build very efficient customised refrigeration plant going into several industrial sectors Star Refrigeration design systems that give maximum refrigeration energy for minimum electrical energy input required to run the plant. Star plant is : ENERGY EFFICIENT