Presented by

Poovanna Thimmaiah

Co-authors

Amir Sharafian, Wendell Huttema, Majid Bahrami

IVth International Symposium on

Innovative Materials for Processes in Energy Systems

Sicily, Italy

October 26th, 2016

2

Low pressure evaporator in adsorption cooling system

Gaseous refrigerant

Two phase liquid + Vapor

T=5oC P=0.8 kPa

T=30oC P=4.2 kPa

Liquid water

Water vapor

Operating pressure is very low (close to vacuum) Water as an refrigerant

Low Pressure (LP) evaporator

3

Water height issue in the evaporator

The hydrostatic pressure should be minimized inside the low operating pressure evaporators

A conventional evaporator fails to perform efficiently

o 5 cm of water height causes:

The cooling power reduces drastically

𝑃 = 𝑃𝑣𝑎𝑝

𝑃 = 𝑃𝑣𝑎𝑝 + 𝜌𝑔𝐻𝑟𝑒𝑓

𝐻𝑟𝑒𝑓

1 kPa

1.3 kPa

13°C

7°C

5 cm

4

Available solution

• Falling film evaporation

Side view Front view

Limitations:

Equal distribution of refrigerant

Internal pump (active pumping)

Complex

Higher weight

5

Proposed solution

Capillary-assisted evaporation Capillary water

Pooled water

Fins Inspiration: Plants use capillary action to draw water from the ground

Passive pumping

Advantages:

Uniform evaporation rate along

the circumference of the tube

No parasitic energy consumption

Lower weight

No complexity

6

Previous studies on capillary-assisted evaporation

Dr. Wang Shanghai Jiao Tong University of China

Dr. Lanzerath RWTH Aachen University, Germany

Dr. Schnabel Fraunhofer Institute for Solar Energy Systems ISE , Germany

7

Tested tubes and fin structures

Industrial partners

Wolverine Tube Inc., USA

Wieland Thermal Solutions., Germany

Plain tube

Turbo Chil-26 FPI (Wolverine Tube Inc.)

Turbo Chil-40 FPI (Wolverine Tube Inc.)

Turbo ELP (Wolverine Tube Inc.)

Turbo CLF-40 FPI (Wolverine Tube Inc.)

GEWA-KS-40 FPI (Wieland Thermal Solutions)

Confidential-NDA (Wieland Thermal Solutions)

8

Low pressure evaporator experimental setup

TCS

To

Ti

T1

T1T

F

T

Camera & LED

P

Makeup water Control

valve Vacuum pump

Cold trap dry ice and IPA, -78°C

Temperature Control System

Href

Challenge: Vacuum seal Outgassing

9

Plain Tube Vs. Finned tube

280

300

320

340

360

380

400

420

0 5000 10000 15000

Evapora

tor

heat tr

anfe

r coeffic

ient, U

evap,

(W/m

2K

)

Time (s)

Plain tube

The plain tube fails to maintain the evaporator heat transfer coefficient

700

720

740

760

780

800

2500 3500 4500 5500 6500 7500

Eva

po

rato

r h

eat tr

an

fer

co

effic

ien

t, U

evap,

(W/m

2K

)

Time (s)

Turbo Chil-40 FPI

Maintains constant evaporator heat transfer coefficient

10

Performance of finned tubes

0

0.003

0.006

0.009

0.012

0.015

0.018

0.021

0.024

Ext. convectionresistance

Conductiveresistance

Int. convectionresistance

Overall thermalresistance

Th

erm

al re

sis

tan

ce

, [

K/W

]Turbo Chil-40 FPI

Turbo Chil-26 FPI

GEWA KS-40 FPI

Plain tube

Plain tube-

2.7E-05 K/W

Chilled water mass flow rate : 2.5 LPM Chilled water inlet temperature: 15oC

11

Smaller diameter finned tube

15 mm 7.9 mm

40 FPI, 0.6 mm fin spacing 26 FPI, 1 mm fin spacing

Partial

capillary

Pooled water

(colored)

Type – 2nd Generation (2G)

To

Ti

T1

T1

12

Behaviour of overall heat transfer coefficient

0

500

1000

1500

2000

2500

3000

3500

4000

700 1400 2100 2800 3500 4200 4900

Overa

ll heat tr

ansfe

r coeffcie

nt

[W/(

m2.K

)]

Time [s]

Region I

Region II

Region III

Region I

Region II

Region III

• In region I (tube is fully submerged)- overall U is about 1600 W/(m2K).

• In region II- the hydrostatic pressure is reduced and the overall U increases by 45% from 1600 to 2320 W/(m2K)

• In region III, U decreases to 1720 W/(m2K) as the water level drops further as capillary force fails to cover the entire surface.

Chilled water inlet temp : 20oC Chilled water mass flow rate: 2.5 LPM

13

Porous copper coated evaporator

The porous copper coating from thermal spray deposition technology

SEM images of the porous coatings

Deposition is compatible with the material of evaporator

Substrate (copper fin)

coatings

14

Behaviour of the porous coated surface

Dry surface- Hydrophobic Wetted surface- Enhances wicking

15

Comparison between uncoated and coated evaporator

0.0E+00

1.0E-03

2.0E-03

3.0E-03

4.0E-03

5.0E-03

6.0E-03

Uncoated Coated

Overall resistance (K/W)

Uncoated

Coated

20%

Coated

30%

2 times Uncoated

16

Conclusions

The tube internal dia was reduced to increase the hi (αi)

Porous copper coatings to improve the capillary evaporation.

The overall U of the coated evaporator increased by 30%

The cooling power of the coated evaporator improved by 2 times.

17

Acknowledgements

Automotive Partnership Canada (APC)

Natural Sciences and Engineering Research Council of Canada (NSERC)

Dr. Karine Brand, Dr. Achim Gotterbarm, Director Global R&D

Dr. Evraam Gorgy, Director of R&D Mr. Bill Korpi Wolverine Tube, Inc.

18

Thanks for your attention Questions/Comments

Black bear poses next to SFU sign in best advertising photo ever

19

Why Design of Evaporator of an ACS is Different? Contd.

19

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 2000 4000 6000 8000 10000

Eva

po

rato

r p

ressu

re (

kP

a)

Time (s)

7

9

11

13

15

17

0 2000 4000 6000 8000 10000

Tem

pera

ture

( C

)

Time (s)

Ti

To

T1,2

Tliq1,2

o All thermocouples have same reading at the beginning (Equilibrium State)

o Evaporator pressure reduces when the control value is opened and remains constant until evaporator runs out of water

o For all calculations, data were extracted from demarcated region (Steady state)

To

Ti

T1

T1

20

Quantifying the evaporator performance

20

,

1 1 1o finned tube

o o i i

RUA h A h A

External Resistance

External Resistance

Internal Resistance

Internal Resistance

Material Resistance Material Resistance

,o finned tube fin wallR R R

21

Future work

21

22

CALPE- Capillary Assisted Low Pressure Evaporator

22

Height of the water

Dia of the tube