RESULTS OF FIRST AND SECOND LAW ANALYSIS FOR STEADY-FLOW
COMPONENT
PROCESS s = Const.
FIRST LAW RESULT
1 2 3 4
Compressor
m (h2 h1 ) W in
0 W net Condenser P = Const Expansion Valve s > 0
Evaporator P = Const
m (h2 h3 ) Q H
h4 h3
m (h1 h4 ) Q L
COPR COPHP
Q h h L 1 4 W h2 h1 net , in Q h h H 2 3 Wnet ,in h2 h1
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P-H CHART
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MERITS & DEMERITS OF VAPOUR SYSTEM OVER AIR REFRIGERATION SYSTEM
• MERITS:
1. C.O.P. is quite high as the working of the cycle is very near to
that of reversed Carnot cycle.
2. When used on ground level the running cost of vapour
compression refrigeration system is only 1/5 of air refrigeration system. 3. For the same refrigeration effect the size of the evaporator is
smaller.
4. The required temperature of the evaporator can be achieved simply by adjusting the throttle valve of the same unit.
• DEMERITS
• 1. Initial cost is high. • 2. the major disadvantages are
•
• •
a) Inflammability
b) Leakage of vapours c) Toxity.
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VAPOUR COMPRESSION REFRIGERATION SYSTEM ON T-S.DIAGRAM
EFFECT OF SUCTION & DELIVERY PRESSURE
EFFECT OF SUPERHEATING & SUBCOOLING OF LIQUID
LIQUID- VAPOUR HEAT EXCHANGER
EFFECT OF CONDENSING & EVAPORATING TEMPERATURE ON C.OP & REFRIGERATING EFFECT
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EFFECT OF CONDENSER WATER TEMPERATURE ON POWER
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PULL –DOWN CHARACTRISTCS
• PURPOSE OF THE TEST – COMPARE THE VALUES FOR DIFFERENT REFRIGERATORS FOR DIFFERENT REFRIGERENTS • TESTING OF REFRIGERATORS ACCORDING TO ISI SPECIFICATIONS • ENVIORNMENT TEMPERATURE – MAINTAINED AT 430C. • NO-LOAD TEST • ADJUST THERMOSTAT –CABNET TEMP. 70C. • PURPOSE: • FIND PULL –DOWN PERIOD • NO LOAD POWER CONSUMPTION • % RUNNING TIME • PULL –DOWN PERIOD : TIME REQUIRED TO REACH THE SPECIFIED TEMP. INSIDE THE CABNET AFTER SWITCHING ON THE UNIT.
Ice making time test
• For this test: • Stable operating conditions after Pull-down test • Quantity of 0.5 kg of water at 30 10C in std tray – kept in the freezer • Time for each “ON” and “OFF” is noted. • After specified time of 3 hrs., ice tray is examined for the formation of ice. • Running time of the unit during 3 hrs of operation is obtained from DAS • DAS –to monitor ÖN-OFF cycle. • This running time of the unit is the ice making time. • For Freon -12 refrigerator: • • pull-down period – 90 min for 160L capacity ice making time – 125 min.
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