Effektivare kylsystem för kyl & och frysskåp Erik Björk, PhD student, KTH
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Transcript of Effektivare kylsystem för kyl & och frysskåp Erik Björk, PhD student, KTH
Erik Björk, M.Sc.Dept. of Energy TechnologyDiv. of Applied Thermodynamics and RefrigerationRoyal Institute of TechnologySweden
Effektivare kylsystem för kyl & och frysskåp
Erik Björk, PhD student, KTH
Björn Palm, Supervisor, KTH
Per Wennerström, controller, Electrolux/RDE
Erik Björk, M.Sc.Dept. of Energy TechnologyDiv. of Applied Thermodynamics and RefrigerationRoyal Institute of TechnologySweden
Background
Black box• Rule of thumb design
• Copy old designs
Open box• Design based on science (heat transfer, pressure drop and charge)
Energy consumption• Legislations
• Customers demand
Reduced Energy consumptioncompressor
evaporator
cap. tube
condenser
Erik Björk, M.Sc.Dept. of Energy TechnologyDiv. of Applied Thermodynamics and RefrigerationRoyal Institute of TechnologySweden
The plate evaporator (ER8893C)
• Aluminium, 660 x 490 mm
• Thickness 1.4 mm
• 1.35 kg
• White coated
• Tube length 6.22 m
• Hydraulic diameter 3.2 mm
• Total internal volume 115.7 ml
• Accumulator volume 45.6 ml
Erik Björk, M.Sc.Dept. of Energy TechnologyDiv. of Applied Thermodynamics and RefrigerationRoyal Institute of TechnologySweden
The plate evaporator (ER8893C)490,0
660,
0
R 17,5
295,0
35
Erik Björk, M.Sc.Dept. of Energy TechnologyDiv. of Applied Thermodynamics and RefrigerationRoyal Institute of TechnologySweden
On-off cycling characteristics
Erik Björk, M.Sc.Dept. of Energy TechnologyDiv. of Applied Thermodynamics and RefrigerationRoyal Institute of TechnologySweden
0
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10
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0 200 400 600 800 1000 1200 1400 1600
time (s)
ch
arg
e (
g)
evaporatorfilter driercondensercompressor oilcompressor vapour
Charge distribution – experimental results
Erik Björk, M.Sc.Dept. of Energy TechnologyDiv. of Applied Thermodynamics and RefrigerationRoyal Institute of TechnologySweden
Comparison theory - experimental results
Evaporator
Condenser
Erik Björk, M.Sc.Dept. of Energy TechnologyDiv. of Applied Thermodynamics and RefrigerationRoyal Institute of TechnologySweden
Downward slope reduces activation time
Erik Björk, M.Sc.Dept. of Energy TechnologyDiv. of Applied Thermodynamics and RefrigerationRoyal Institute of TechnologySweden
Accumulator delays activation
Erik Björk, M.Sc.Dept. of Energy TechnologyDiv. of Applied Thermodynamics and RefrigerationRoyal Institute of TechnologySweden
-15 °C, mass flow 0.3;0.45;0.6;0.75 g/s
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3500
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0 5000 10000 15000 20000 25000 30000 35000
heat flux (W/m²)
htc
(W
/m²K
)
Refrigerant side heat transfer – experimental results
Mass flow
Erik Björk, M.Sc.Dept. of Energy TechnologyDiv. of Applied Thermodynamics and RefrigerationRoyal Institute of TechnologySweden
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predicted pressure drop (Pa)
exp
erim
enta
l p
ress
ure
dro
p
(Pa)
1 2 3 4 5 10% -10%
Refrigerant side pressure drop – experimental results
Erik Björk, M.Sc.Dept. of Energy TechnologyDiv. of Applied Thermodynamics and RefrigerationRoyal Institute of TechnologySweden
Optimum pitch
0
0,2
0,4
0,6
0,8
1
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0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,1 0,11
pitch (m)
tem
per
atu
re lo
ss (
°C)
f in eff iciency loss
pressure drop loss
total
Erik Björk, M.Sc.Dept. of Energy TechnologyDiv. of Applied Thermodynamics and RefrigerationRoyal Institute of TechnologySweden
Fin efficiency for the whole evaporator ≈ 97,2%
Erik Björk, M.Sc.Dept. of Energy TechnologyDiv. of Applied Thermodynamics and RefrigerationRoyal Institute of TechnologySweden
Increased pitch
Distributed accumulator
Downward sloping channels
Small diameter at inlet – large at outlet
Channels close to plate edges
Conclusions improved evaporator design