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

5

10

15

20

25

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

0

500

1000

1500

2000

2500

3000

3500

4000

4500

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

0

2000

4000

6000

8000

10000

0 2000 4000 6000 8000 10000

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

1,2

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