In the present work, a plate freezer
consisting of two plates connected inparallel
and having a cooling load of 0.335 KW is to be designed. Installing formedtubing
between two metal plates, which are brazed together at the edges, forms
theplate surface evaporators.The
refrigerant used is R-134a a refrigerant which is now used as areplacement for R-12.
Conventional
food preservation is done by keeping the food inside chambershaving evaporator coils around it. This chamber is
insulated from the surroundings by acasing.
The vapour compression system is the most widely used system.
The heat
transfer takes place from the food to the freezer (chamber) surfacethrough the air gap. As
air is a bad conductor of heat, the freezing rate is low and time consuming. The
freezing rate was increased by the development of the freezer. Onlycompactable
foods can utilize this method.
The Plate freezer under
consideration is a multi plate freezer. In the plate freezer there are two
plates through which the refrigerant expands. The food is placed betweenthe plates and are
brought closer so that the food gets pressed to a pre-determined pressure. As the plates are in direct contact with
the food, there is better heat transfer andhence the freezing rate is
increased.
The
plate used is copper plate, which is having a high heat transfer coefficient.The two plates are brought closer manually.
Compared to the conventional method
of freezing this method takes only aQuarter of the time required to bring 1 kg of meat
from 30 ºC to -20 ºC, the freezing rateis increased about four times. This is the most
important reason why plate freezers arereplacing conventional
freezing equipments in the recent past.
CARNOT CYCLE
The Carnot cycle is the model of
perfection for a refrigeration cycle. However, itis not practicable to realize
this perfect thermodynamic cycle with hardware. Firstly, twocompression machines, one realizing isentropic compression,
the other realizingisothermal
compression would be required. Secondly, the small amount of expansionwork
available does not support the idea of incorporating a work producing expander
intothe system. The Carnot cycle is shown for a refrigerator. Heat is delivered
isothermally atTH and received.
Sign up here with your email
ConversionConversion EmoticonEmoticon