Mumbai University > Mechanical Engineering > Sem 8 > Refrigeration and air conditioning

Marks: 5M

Year: May 2016

• After Condenser condenses the refrigerant, it is passed through an expansion valve to reduce its pressure to evaporator pressure. But while doing so, some of the liquid converts to vapor again. Now we know that evaporator is waste process. So to avoid vapor to enter evaporator, a flash chamber is used.

• A flash chamber is a device which separates liquid from vapors. Only liquid is then passed to evaporator and the vapors will be passed to the compressor directly. This flash chamber between the condenser and evaporator is known as flash intercooling.

• To ensure perfect pressure reduction and maximum liquid to be passed through evaporator, multiple no of flash chamber can be used in VCRS cycle. See fig. 1

                                 Fig.1: three sage compression with flash intercoolers.
  

  Why flash intercooling is not preferred for R-12 (Freon)?

  • In R-12 the constant entropy lines in the superheated zone are almost parallel. So work consumed is not affected by intercooling and the temperature rise also is not large enough for proper heat rejection to take place in water intercooler.

  • Also the value of hfg (specific heat of evaporation) is less. So mass of liquid refrigerant that would evaporate due to flash intercooling will be more. Therefore the compressor of the next stage has to compress not only the refrigerant coming from previous stage via intercooler, but also this extra refrigerant generated from the intercooler. As a result the compression work rather increases for R-12 if intercooling is used.