Boiling heat transfer enhancement for ammonia using micro fabrication surface on plate evaporator

(1)

1.

(OTEC)

OTEC 30℃

25℃

OTEC

OTEC 30℃

(1) (2) (3) (4)

Djordjevic ⁽⁵⁾ ^{(1) (2)}

/

( )

*1 *2 *3 *4 *1

Boiling heat transfer enhancement for ammonia using micro fabrication surface on plate evaporator

(Effect of micro groove direction)

Hirofumi ARIMA

^*5

, Nobuhiko MATSUO, Keita SHIGYOU, Akio OKAMOTO and Yasuyuki IKEGAMI

*⁵ Institute of Ocean Energy, Saga University

1-48 Kubara-aza, Hirao, Yamashiro-machi, Imari-shi, Saga 849-4256, Japan

The experimental study has been performed for the heat transfer enhancement in ammonia on this new plate evaporator which treated the surface on the micro groove. The micro groove is depth of 30 micro meters and width of 200 micro meters. The local boiling heat transfers were measured on the evaporator surface using 10-thermocouples inside evaporator. For comparison of the heat transfer characteristic of the evaporator, the local boiling heat transfer coefficient on a flat surface and two micro grooved surface which have vertical and horizontal directions to ammonia flow, were measured in a range of mass flux (2 - 7.5 kg/m² s), heat flux (10 - 20kW/m²), and saturation pressure (0.7 - 0.9 MPa).

The result shows that, the local boiling heat transfer coefficient increased with an increase mass flux, averaged heat flux and vapor quality in all surface conditions. The heat transfer coefficient of horizontal and vertical micro grooved surface was larger than that of flat surface. Especially, the horizontal micro grooved surface had best heat transfer coefficient. In case of low vapor quality which was in nucleate boiling region, the heat transfer coefficient of horizontal and vertical surfaces showed large increment from that of flat surface.

However, in case of high vapor quality which was added the slightly effect of convective boiling, the heat transfer of vertical surface showed small increment from that of flat surface though that of horizontal surface showed large increment.

Key Words : Heat transfer enhancemnet, Ammonia, Plate heat exchanger, Micro grooved surface

* 2010 7 31

*1

*2

*3

*4

E-mail: [email protected]

(2)

(3) (4)

/ ( 90%)

Djordjevic

(5)

OTEC

(6)

(7) (8) (7)

(8)

30µm

10 ~ 40%

(8)

2.

G [kg/m²s]

h [W/m²K]

i [J/kg]

ifg [J/kg]

isat.liq [J/kg]

k [W/mK]

li [m]

Psat [Pa]

qav [W/m²]

rc [m]

Ti [℃]

Tsat [℃]

Twall [℃]

w [m]

x [-]

δ [m]

3.

3 1 Fig. 1

(8) (

)

3

2kW

PROMASS 83A ± 0.1%

FD-M, FD-P ± 1.6%

FP101

0 ~ 2MPa ± 0.25%

K ST6 1

±1.5℃

PC

0.1^oC Fig. 2

SUS304 ( 370mm 220mm)

SUS304 ( 2mm)

5 2 10 K

40mm, 59mm

100V-1050W

100mm 250mm 20mm

150W

(3)

P

1

2

3

4

5 6

7 8

9

10

11 12

13

Cold water circuit Working fluid circuit

P

T

P

T P 14

T

P T

15

16

T T

1. Test plate (Evaporator) 2. Pre-heater 3. Condenser 4. Working fluid tank 5. Sub cooler 6. Electric heater

7. Cold water tank 8. Refrigerator 9. Hot water tank 10. Working fluid pump 11. Hot water pump 12. Cold water pump 13. Mass flow meter 14. Volumetric flow meter 15. Degassed valve 16. Release valve

Hot water circuit

T

T T

Fig. 1 Schematic of experimental apparatus

40

l₂

S1, S3: l₂= 5.02 S2: l2= 5.01 Frame

Heat transfer plate Spacer

B

Heater block

5

A A

TC wells

Fig. 2 Assembly of test plate

7

Fig. 3 (w) 100mm (δ) 2 mm

Fig. 2 B Fig. 4

T1, T2,

l1, T2 l2

2

Fig. 3 Cross sectional view of test plate (A-A’ cross section of Fig. 2)

(4)

T

2

T

1

T

wall

Ti Thin plate

Ti base plate Solder

4 . 55 0 . 4

l₃ = S1, S3: 0.07, S2: 0.06.

l1 = 40 l2 = 5.02

l3

Fig. 4 Configuration of thermocouples inside test plate (Detail of circle “B” area of Fig. 2) 3 2

Fig. 5 3

3 ( Ti)

220mm,

370mm 50mm 100mm 250mm

0.4mm

Ti Ti (a) ~ (c)

Ti

Ti (a) ~ (c)

(a) ( S1) : 0.6 µm

(b) ( S2) :

(c) ( S3) :

Fig. 6 (b), (c) Ti

Fig. 6 (b) 200µm,

100µm, 30µm

0.6 µm 5 µm

3 3

3.3.1

q Fig. 4 T1

T2 l1 k

1 2 1

l T kT

q −

= (1)

Twall (1)

k T ql

T_wall = ₂− ² (2)

h

Twall Tsat

) (T_wall T_sat h q

= − (3)

Tsat

Psat

3.3.2

x ( )

fg liq , sat

i i x i−

= (4)

i isat.liq ifg

i ⁽⁸⁾

P-PROPATH⁽⁹⁾

3 4 Table 1

5 2

(5)

(a)

(b)

(c)

(i) General view (ii) Side view

Fig. 5 Photographs of three test heat transfer plates

(a) S1: Flat surface, (b) S2: Vertical grooved surface, (c) S3: Horizontal grooved surface

Fig. 6 Detail of S2 and S3 plate surface

Table 1 Experimental Conditions

Working fluid Pure ammonia

Plate surface

S1: Flat surface S2: Vertical grooved surface S3: Horizontal grooved surface

Plate substance Titanium

Mass fluxG[kg/ m²s] 2, 5, 7.5 Average heat flux

qav [kW/ m²] 10, 15, 20 Saturation pressure

Psat [MPa] 0.7, 0.8, 0.9 Ti thin grooved plate

Ti base Ti thin flat surface

Ti base

Ti base Ti thin grooved plate 250

100

(6)

4.

4 1 Fig. 7 (a) (b) G = 5 7.5 kg/m²s

S1 ~ S3 (x = 0.2)

(x = 0.7)

(10)

(Psat = 0.7MPa) Fig. 7 (a) G = 5 kg/m²s

S1 ⁽¹⁰⁾

S1

S2 S3 qav =10kW/m²

S3 0.5K

S2 S3

S1

qav = 10kW/m² S1 ~ S3 0.2K qav > 15kW/m²

S1, S2, S3

S1

Fig. 7 (b) G = 7.5 kg/m²s

S1 ~ S3 Fig. 7 (a)

G 5 7.5

0 1 2 3 4

0 10000 20000

∆T_sat [K]

Average heat flux qav [W/m2 ]

G=5.0 kg/m²s P_sat=0.7MPa

S1 S2 S3 high low

low : quality x= 0.2 high : quality x= 0.7

0 1 2 3 4

Pool boiling (0.7MPa) Pool boiling on Porous (0.7MPa) [ by Arima et al. ⁽¹⁰⁾]

(a) G = 5 kg/m²s

0 1 2 3 4

0 10000 20000

∆T_sat [K]

Average heat flux qav [W/m2 ]

G=7.5 kg/m²s P_sat=0.7MPa

S1 S2 S3 high low

low : quality x= 0.2 high : quality x= 0.7

0 1 2 3 4

Pool boiling (0.7MPa) Pool boiling on Porous (0.7MPa) [ by Arima et al. ⁽¹⁰⁾]

(b) G = 7.5 kg/m²s

Fig. 7 Boiling curve at different plate surfaces

4 2 Fig. 8

(a) (b) (qav = 10 kW/m²)

(Psat = 0.7 MPa)

Fig. 8 (a) (b)

Fig. 8 (a) S2

G = 2

5 kg/m²s 30%

G = 5 7.5 kg/m²s Fig. 8 (b) S3

(3) G = 7.5 ~ 15 kg/m²s

G = 2 kg/m²s

(7)

3 ~ 11 mm/s

0 0.2 0.4 0.6 0.8 1

0 5000 10000

Vapor quality x [-]

Local heat transfer coefficient hloc [W/(m2 K)]

q_av=10kW/m² P_sat=0.7MPa

G[kg/m²s]

2.0 5.0 7.5

(a) S2

0 0.2 0.4 0.6 0.8 1

0 5000 10000

Vapor quality x [-]

q_av=10kW/m² P_sat=0.7MPa

G[kg/m²s]

2.0 5.0 7.5

(b) S3

Fig. 8 Comparison between boiling heat transfer coefficient at different mass fluxes on S2 and S3

4 3 Fig. 9 (a)

(b) (qav = 20 kW/m²) (Psat = 0.7 MPa) S1, S2, S3

Fig. 9 (a) G = 5 kg/m²s, Fig. 9 (b) 7.5kg/m²s

Fig. 9 (a) (b)

(x < 0.3) S1 S2 12%, S3 16 ~ 22%

(x > 0.3)

S1 S2 0 ~ 2%

, S3 10%

S3 S2

rc (11)

rc = 2 µm (Psat = 0.7MPa, ∆Tsat = 1℃) S1 0.6µm

S2 S3 200µm 30µm

rc

S2 S3

Fig. 6 S2

S3 S3

0 0.2 0.4 0.6 0.8 1

0 5000 10000

Vapor quality x [-]

G=5 kg/m²s qav=20kW/m² P_sat=0.7MPa

S1 S2

(S2/S1) 11% S3

(S3/S1) 16%

(S2/S1) 2%

(S3/S1) 10%

(a) G = 5 kg/m²s

0 0.2 0.4 0.6 0.8 1

0 5000 10000

Vapor quality x [-]

G=7.5 kg/m²s qav=20kW/m² Psat=0.7MPa

S1 S2

(S2/S1) 12% S3

(S3/S1) 22%

(S2/S1) 0%

(S3/S1) 10%

(b) G = 7.5 kg/m²s

Fig. 9 Comparison between boiling heat transfer coefficient for plate S1, S2 and S3

(8)

S2

S1 S2

S3 S2

5.

(1) (2) (3) (4)

G = 2 kg/m²s

OTEC

(1) Kushibe M. et al., Trans. JSRAE, Vol. 22, No. 4 (2005) , pp. 403-415 (in Japanese).

(2) Kushibe M. et al., Trans. JSRAE, Vol. 23, No. 4 (2006), pp. 389-397 (in Japanese).

(3) Arima H. et al., Int. J. Refrigeration, Vol. 33, No. 2 (2010), pp. 359-370.

(4) Okamoto A. et al., Trans. JSRAE, Vol. 26, No. 2 (2009), pp. 131 - 139 (in Japanese).

(5) Djordjevic E. et al., Int. J. Heat Mass Trans., Vol. 51 (2008), pp. 6235-6242.

(6) The Japan Society of Mechanical Engineers ed., Boiling heat transfer and cooling, (1989), pp. 347- 367, Japan industrial publishing (in Japanese).

(7) Ikegami Y. et al., Proceedings of 37th National heat transfer symposium of Japan, Vol. 37, No. 3, (2000), pp.

825-826 (in Japanese).

(8) Arima H. et al., OTEC, Vol. 14, (2009), pp. 11-19 (in Japanese).

(9) P-Propath

http://www2.mech.nagasaki-u.ac.jp/PROPATH/p-propath.

html (2006.4).

(10) Arima H., et al., Thermal Science and Engineering, Vol. 9, No. 4, (2001), pp. 65-66

(11) Griffith P. et al., Chem. Eng. Progress Symp. Series, Vol.

56, No. 30, (1960) , pp. 39 - 48.