Effects of the Reynolds Number (Re) on Heat and Mass Transfer Phenomena

CHAPTER 4 RESULTS AND DISCUSSION

4.4 Three-Dimensional Channel Model of a Plate Methanol Steam Micro-Reformer with

4.4.2 Effects of the Reynolds Number (Re) on Heat and Mass Transfer Phenomena

In the study of the effects of the Reynolds number (Re) on the transport phenomena and micro-reformer performance, understanding the detailed distributions of heat and mass transfer is important to the design of a micro-reformer with a combustor. The Reynolds number (Re) is one of the key thermo-fluid parameters in the micro-reformer and combustor channels which would affect the micro-reformer performance. Therefore, effects of the Reynolds number (ReC) on the combustion channel side on the temperature distributions along the centerline of the top reforming channel (Y=0.333) and CH3OH mole fraction distributions along the centerline of the reforming channel (Y=0.167) with counter-current flow are examined in Figure 4-40. A careful examination of Fig. 4-40(a) shows that the temperature increases with an increase in the Reynolds number (ReC) on the combustor side

reforming chemical reaction. It is also shown that the CH3OH mole fraction distributions decrease with increasing Reynolds number in the combustor channels. This can be made plausible by noting the fact that the chemical reaction increases as the temperature distributions increase.

Figure 4-41 presents the effects of the Reynolds number (ReR) on the micro-reformer side on the temperature distributions along the centerline of the top reforming channel (Y=0.333) and CH3OH mole fraction distributions along the centerline of the reforming channel (Y=0.167) with counter-current flow. The results in Fig. 6(a) reveal that the temperature distributions are enhanced by the decreased Reynolds number (ReR) on the micro-reformer channels. This is due to a higher Reynolds number (ReR) significantly increasing the heat leaving the flow channel, which decreases the temperature rise. In addition, it is seen in Fig. 4-41(b) that the CH3OH mole fraction distributions decrease with a lower Reynolds number due to a longer time of gas residence and a higher temperature, which results in a better methanol conversion.

Figure 4-42 demonstrates the effects of the Reynolds number (ReC) for the combustor on the methanol conversion and wall temperature of the reforming channel in the plate methanol steam micro-reformer. For comparison, the results without the wall conduction effect in the model are also presented. An overall inspection of Fig. 4-42 shows that the wall temperature increases with increase of the Reynolds number (ReC) on the combustion channel side. This is plausible because the inlet fuel velocity increases in the channel as the Reynolds number increases. As for the methanol conversion, the results show that the methanol conversion increases as the Reynolds number of the combustion channel increases, which in turn increases the wall temperature. In addition, the wall conduction effect is also shown in Fig.

4-42. The deviations in the methanol conversion between the results with and without consideration of wall conduction effects are larger. This means that the wall conduction effect

on the methanol conversion and wall temperature become significant and cannot be neglected in the modeling.

4.5 Three-Dimensional Model of a Plate Methanol Steam Micro-Reformer with Methanol Catalytic Combustor for Parallel Flow Field and Serpentine Flow Field

This section is to establish the three-dimensional computational models of a plate methanol steam micro-reformer with a methanol catalytic combustor to investigate the performance and transport phenomena for the parallel flow field and serpentine flow field.

The dimensions of a plate methanol steam micro-reformer with a methanol catalytic combustor in this section are 40mm(L)x15mm(W)x2.5mm(H), the inlet and outlet cross-sections of the flow channel are 1.0mmx0.5mm, and the rib width is 2 mm. The thicknesses of the catalyst layer are set to be 0.05mm. Because of the discrepancies in the flow channel design, the flow channel length and the turning points among various flow field designs, the fuel consumption and temperature distributions inside the micro-reformer are different. The effects of the flow field designs on the temperature, CH3OH mole fraction, H2

mole fraction and CO mole fraction distributions are presented in this section. The base conditions of the properties are in the following: the operating pressure and temperature of both micro-reformer and combustor are 1 atm and 393 , respectively. The inlet flow rates at ℃ the reforming side and at the combustion side are 7.5 cm³/min and 75 cm³/min as the base case, respectively. The parameters used in this section are listed in Table 4-10.

for various flow field designs. The results reveal that the wall temperature is enhanced by the decreased Reynolds number (ReR) on the micro-reformer. This is due to a higher Reynolds number (ReR) significantly increasing the heat leaving the flow channel, which decreases the temperature rise. The serpentine flow field with combustor and the serpentine flow field with micro-reformer have a higher wall temperature of the reforming channel than any other flow fields. In addition, it is seen in Fig. 4-43(b) that a higher methanol conversion increases with a lower Reynolds number due to a longer time of gas residence and a higher temperature. The methanol conversion for the serpentine flow field with combustor and the serpentine flow field with micro-reformer is the best due to a higher wall temperature.

The effects of the flow field designs on the Reynolds number (ReC) of the combustor and wall temperature of the reforming channel are presented in Fig. 4-44(a). It indicates that the temperature increases with an increase in the Reynolds number (ReC) on the combustor side due to a higher inlet flow rate. This is because higher combustion energy is released for a higher inlet flow rate. The wall temperature increases in the following order: (I) the parallel flow field with combustor and the parallel flow with micro-reformer; (II) the serpentine flow field with combustor and the parallel flow field with micro-reformer; (III) the parallel flow field with combustor and the serpentine flow with micro-reformer field with combustor; (IV) the serpentine flow field with combustor and the serpentine flow field with micro-reformer. It is due to the improvement of the heat transport with the flow field design. In addition, the effects of the flow field designs on the Reynolds number (ReC) of the combustor and methanol conversion in the plate methanol steam micro-reformer are shown in Fig. 4-44(b).

As for the methanol conversion, the results indicate that the methanol conversion increases as the Reynolds number of the combustion channel increases. Therefore, it is concluded that increasing the corner number and the channel length to the various flow fields can effectively raise the temperature distribution, and enhance the methanol conversion.

The temperature distributions on the top cross-section of reforming channel are presented in Fig. 4-45. Constant flow rate approach is utilized in this analysis. The temperature distribution increases along the channel for each flow field designs. Fig. 4-46 presents the CH3OH mole fraction distributions on the middle cross-section of the reforming channel for the various flow fields. It shows that the CH3OH mole fraction decreases along the channel for the four flow fields. The methanol conversion at the exit of channel are 52%, 62%, 68%, and 79% for (I) the parallel flow field with combustor and the parallel flow with micro-reformer, (II) the serpentine flow field with combustor and the parallel flow field with micro-reformer, (III) the parallel flow field with combustor and the serpentine flow with micro-reformer field with combustor, (IV) the serpentine flow field with combustor and the serpentine flow field with micro-reformer, respectively. Therefore, it is expected that the methanol conversion would be highest for the serpentine flow field with combustor and the serpentine flow field with micro-reformer.

The distributions of the H2 mole fraction on the middle cross-section of the reforming channel are shown in Fig. 4-47 for the various flow fields. A higher H2 mole fraction along the flow channel represents a higher methanol conversion. Thus, the variation of the H2

fraction is opposite to that of the CH3OH mole fraction. A higher H2 mole fraction is found for the serpentine flow field with combustor and the serpentine flow field with micro-reformer.

Figure 4-48 presents the variations of the CO mole fractions on the middle cross-section of the reforming channel for the various flow fields. It is found that the CO distributions have the same trends as the H2 distributions. This confirms the common concept that a micro-reformer with a H2 production indicates a higher CO concentration.

(ReR) on the micro-reformer side. The serpentine flow field with combustor and the serpentine flow field with micro-reformer is the best design by considering the H2 production rate.

Table 4-1 Parameters used in the two-dimensional channel model of a plate methanol steam micro-reformer

Channel length L (m) [16] 3.3 x10^-2

Channel height H (m) [16] 2.0x10^-4

Flow channel height δ1 (m) 1.7x10^-4

Catalyst layer thickness δ2 (m) 3.0x10^-5

Inlet average velocity u0 (m s^-1) [16] 0.266

Inlet average temperature T0 (°C) [16] 393

Operation pressure (atm) [16] 1

Activation energy for steam reforming (kJ mol^-1) [66] 76 Activation energy for reverse water gas shift (kJ mol^-1) [66] 108

Catalyst density (kg m^-3) [51] 1480

Catalyst thermal conductivity (W m^-1K^-1) [51] 0.3

Catalyst layer porosity [52] 0.38

Catalyst permeability (m²) [52] 2.379x10^-12

Mass diffusion coefficient (m²s^-1) [51] 6.8 x10^-5

Table 4-2 Methanol mole fractions for the various grids x(m)

Gridlines

0.005 0.010 0.015 0.020 0.025 0.030 71x16 0.377 0.309 0.261 0.224 0.194 0.171 91x26 0.378 0.309 0.261 0.224 0.194 0.171 111x41 0.378 0.309 0.261 0.224 0.194 0.173

Table 4-3 The cases with various aspect-ratio channels used in this work

Case 1 Case 2 Case 3 Case 4

γ 0.25 0.5 1.0 2.0

δ1+δ2 (mm) 0.179 0.214 0.286 0.429

WR (mm) 0.714 0.429 0.286 0.214

Table 4-4 Parameters used in the three-dimensional channel model of a plate methanol steam micro-reformer

Channel length L (m) 3.3 x10^-2

Channel width WR (m) 4.29x10^-4

Channel height δ1+δ2 (m) 2.14x10^-4

Flow channel height δ1 (m) 1.84x10^-4

Catalyst layer thickness δ2 (m) 3.0x10^-5

Average inlet temperature (°C) 120

Operating pressure (atm) 1

Activation energy for steam reforming (kJ/mol) [66] 76 Activation energy for reverse water gas shift (kJ/mol) [66] 108

Catalyst density (kg m^-3) [51] 890

Catalyst layer porosity [52] 0.38

Catalyst permeability (m²) [52] 2.379x10^-12

Table 4-5 Mole fractions of methanol for the various grid tests at different axial locations x(m)

IxJxK 0.005 0.010 0.015 0.020 0.025 0.030

41x16x18 0.381 0.314 0.266 0.230 0.200 0.176 51x21x23 0.382 0.316 0.269 0.232 0.203 0.179 71x31x33 0.382 0.316 0.269 0.233 0.204 0.179

Table 4-6 Parameters used in the three-dimensional model of the plate methanol steam micro-reformer with serpentine flow field design

Channel width WC (m) 1.0x10^-3

Channel height H (m) 1.0x10^-3

Flow channel height δ1 (m) 9.5x10^-4

Catalyst layer thickness δ2 (m) 5.0x10^-5

Average inlet temperature (°C) 120

Operating pressure (atm) 1

Catalyst density (kg m^-3) [51] 1480

Catalyst thermal conductivity (W m^-1 k^-1) [51] 0.3 Activation energy for steam reforming (kJ mol^-1) [66] 76 Activation energy for reverse water gas shift (kJ mol^-1) [66] 108

Catalyst layer porosity [52] 0.38

Catalyst permeability (m²) [52] 2.379x10^-12

Mass diffusion coefficient (m² s^-1)[51] 6.8 x10^-5

Table 4-7 Temperature distributions ( ) ℃ for the various grid tests at different axial locations X

IxJxK 0 0.152 0.303 0.455 0.606 0.758 0.909

67x16x3 120 176 202 218 224 227 228 133x26x5 120 174 201 217 224 227 228 265x36x9 120 169 200 216 223 226 228

Table 4-8 Parameters used in the three-dimensional channel model of a plate methanol steam micro-reformer with methanol catalytic combustor

Flow channel length L (m) 4x10^-3

Combustion catalyst layer thickness δC (m) 5.0x10^-5 Reforming catalyst layer thickness δR (m) 5.0x10^-5

Combustion flow channel HC (m) 4.5x10^-4

Reforming flow channel HR (m) 4.5x10^-4

Average inlet temperature (°C) 120

Operating pressure (atm) 1

Catalyst density (kg m^-3) [51] 1480

Catalyst thermal conductivity (W m^-1 k^-1) [51] 0.3

Catalyst layer porosity [52] 0.38

Catalyst permeability (m²) [52] 2.379x10^-12

Mass diffusion coefficient (m² s^-1) [51] 6.8 x10^-5 Activation energy for steam reforming (kJ mol^-1) [41] 109 Activation energy for the reverse water gas shift (kJ mol^-1) [41] 115 Activation energy for decomposition reaction (kJ mol^-1) [41] 142 Activation energy for combustion reaction (kJ mol^-1) [80] 13

Table 4-9 Temperature distributions (ºC) for the various grid tests at different axial locations X

IxJxK 0.125 0.250 0.375 0.500 0.625 0.750 0.875 1.000

101x62x11 239.0 239.8 240.6 241.4 241.9 242.1 241.7 210.0 121x81x21 235.9 236.7 237.6 238.3 238.9 239.1 238.7 207.6 141x100x31 233.4 234.2 235.1 235.8 236.3 236.6 236.1 205.7

Table 4-10 Parameters used in the three-dimensional model of a plate methanol steam micro-reformer with methanol catalytic combustor

Flow channel length L (m) 4x10^-3

Combustion catalyst layer thickness δC (m) 5.0x10^-5 Reforming catalyst layer thickness δR (m) 5.0x10^-5

Combustion flow channel HC (m) 4.5x10^-4

Reforming flow channel HR (m) 4.5x10^-4

Steel width W1 (m) 1x10^-3

Channel width W2 (m) 1x10^-3

Rib width W3 (m) 2x10^-3

Catalyst density (kg m^-3) [51] 1480

Catalyst thermal conductivity (W m^-1 k^-1) [51] 0.3

Catalyst layer porosity [52] 0.38

Catalyst permeability (m²) [52] 2.379x10^-12

0 20 40 60 80 100

200 210 220 230 240 250 260

Present Results u

0=0.266m/s

Experimental Study of Park et al. [16], u

0=0.266m/s Present Results u₀=0.531m/s

Experimental Study of Park et al. [16], u₀=0.531m/s Present Results u₀=1.062m/s

Experimental Study of Park et al. [16], u

0=1.062m/s

Tw(^oC)

η(%)

Fig. 4-1 Comparison of predicted methanol conversion with the experimental data of Park et al. [16]

200 210 220 230 240 250 260

L=22mm, H=0.2mm, δ₂=30μm,ε=0.38 L=33mm, H=0.2mm, δ

2=30μm,ε=0.38 L=44mm, H=0.2mm, δ₂=30μm,ε=0.38 L=33mm, H=0.1mm, δ

2=30μm,ε=0.38 L=33mm, H=1.0mm, δ₂=30μm,ε=0.38 L=33mm, H=0.2mm, δ

200 210 220 230 240 250 260

L=22mm, H=0.2mm, δ₂=30μm,ε=0.38 L=33mm, H=0.2mm, δ₂=30μm,ε=0.38 L=44mm, H=0.2mm, δ₂=30μm,ε=0.38 L=33mm, H=0.1mm, δ

Fig. 4-2 Effects of geometric parameters and wall temperature on (a) the methanol conversion and (b) the CO concentration (ppm) at the outlet

0 L=33mm, H=0.2mm, δ₂=30μm,ε=0.38 L=44mm, H=0.2mm, δ L=33mm, H=0.2mm, δ₂=10μm,ε=0.38 L=33mm, H=0.2mm, δ

L=22mm, H=0.2mm, δ₂=30μm,ε=0.38 L=33mm, H=0.2mm, δ₂=30μm,ε=0.38 L=44mm, H=0.2mm, δ₂=30μm,ε=0.38 L=33mm, H=0.1mm, δ L=33mm, H=0.2mm, δ₂=30μm,ε=0.28 L=33mm, H=0.2mm, δ₂=30μm,ε=0.48

C CO(ppm)

S/C(mole/mole) (b)

Fig. 4-3 Effects of geometric parameters and H2O/CH3OH molar ratio on the CO concentration at (a)T w=200 °C and (b) T w=260 °C

90 0

50 100 150 200 250 300

0 0.2 0.4 0.6 0.8 1

L=33mm, H=0.1mm, δ

2=30μm,ε=0.38 L=33mm, H=0.2mm, δ

2=30μm,ε=0.38 L=33mm, H=1.0mm, δ

2=30μm,ε=0.38

T(o C)

Tw=260℃

Tw=200℃

Fig. 4-4 Effects of the channel heights on temperature distributions along the centerline of the channel at T w=200 °C and T w=260 °C

180

Fig. 4-5 Effects of wall temperature on the cross-sectioned temperature at different axial locations for H=1.0mm (a)T w=200 °C and (b) T w=260 °C

(a) Flow Channel Catalyst Layer

Fig. 4-6 Effects of wall temperature on the cross-sectioned velocity at different axial locations for H=0.2mm (a)T w=200 °C and (b) T w=260 °C

Fig. 4-7 Variations of the mole fraction of the various species along the channel (a)T w=200

°C and (b) T w=260 °C.

94 L=33mm, H=0.2mm, δ₂=50μm,ε=0.38 L=33mm, H=0.2mm, δ

2=30μm,ε=0.28 L=33mm, H=0.2mm, δ₂=30μm,ε=0.48

M CH3OH

Fig. 4-8 Effects of geometric parameters on the local CH3OH mole fraction along the channel (a)T w=200 °C and (b) T w=260 °C

L=22mm, H=0.2mm, δ₂=30μm,ε=0.38 L=33mm, H=0.2mm, δ₂=30μm,ε=0.38 L=44mm, H=0.2mm, δ

L=33mm, H=0.2mm, δ₂=10μm,ε=0.38 L=33mm, H=0.2mm, δ₂=50μm,ε=0.38 L=33mm, H=0.2mm, δ

L=22mm, H=0.2mm, δ₂=30μm,ε=0.38 L=33mm, H=0.2mm, δ₂=30μm,ε=0.38 L=44mm, H=0.2mm, δ₂=30μm,ε=0.38 L=33mm, H=0.1mm, δ

Fig. 4-9 Effects of geometric parameters on the local H2 mole fraction along the channel at T

w=200 °C and (b) T w=260 °C

L=22mm, H=0.2mm, δ₂=30μm,ε=0.38 L=33mm, H=0.2mm, δ₂=30μm,ε=0.38 L=44mm, H=0.2mm, δ

L=22mm, H=0.2mm, δ₂=30μm,ε=0.38 L=33mm, H=0.2mm, δ L=33mm, H=0.2mm, δ₂=30μm,ε=0.28 L=33mm, H=0.2mm, δ

2=30μm,ε=0.48

M CO

X (b)

Fig. 4-10 Effects of geometric parameters on the local CO mole fraction along the channel at (a)T w=200 °C and (b) T w=260 °C

Fig. 4-11 Effects of thermo-fluid parameters on the local CH3OH mole fraction along the channel at (a)T w=200 °C and (b) T w=260 °C

Fig. 4-12 Effects of thermo-fluid parameters on the local H2 mole fraction along the channel at (a)T w=200 °C and (b) T w=260 °C

0 10⁰

Fig. 4-13 Effects of thermo-fluid parameters on the local CO mole fraction along the channel at (a)T w=200 °C and (b) T w=260 °C

100 0

50 100 150 200 250

0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

0 0.2 0.4 0.6 0.8 1

Without wall conduction With wall conduction

M CH3OH

T(o C)

Re=3.14, S/C=1.1, T

0=120 , T℃

w=200℃

Fig. 4-14 Comparisons of the predicted results with and without wall conduction effects for the temperature and CH3OH mole fraction distributions along the centerline of the channel (Y=0.5).

0 50 100 150 200

200 210 220 230 240 250 260

Present Results u

0=0.266m/s

Experimental Study of Park et al. [16], u

0=0.266m/s Present Results u₀=0.531m/s

Experimental Study of Park et al. [16], u

0=0.531m/s Present Results u₀=1.062m/s

Experimental Study of Park et al. [16], u

0=1.062m/s Present Results u

0=1.594m/s

Experimental Study of Park et al. [16], u

0=1.594m/s

Experimental Study of Park et al. [16], H₂ Experimental Study of Park et al. [16], CO

Present Results, CO

Experimental Study of Park et al. [16], CO

CO product gas composition fraction

H 2 and CO 2 product gas composition fraction

X (b)

Fig. 4-15 Comparison of predicted methanol conversion with previous experimental data of

102 0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0 0.2 0.4 0.6 0.8 1

Tw=200℃

Tw=260℃

CH3OH

H2O

CO2

CO CH3OH

M i

H2O

Fig. 4-16 Variations of the mole fractions of the various species along the channel center line (γ=0.5)

20 30 40 50 60 70 80 90 100

0 5000 10000 15000 20000

200 210 220 230 240 250 260

γ=2.00 γ=1.00 γ=0.50 γ=0.25

η(%)

Tw(^oC)

C CO(ppm)

Fig. 4-17 Effects of aspect ratios of channel and wall temperature on methanol conversion and CO concentration (ppm) at outlet of channel

104 0

20 40 60 80 100

0 0.2 0.4 0.6 0.8 1

γ=2.00 γ=1.00 γ=0.50 γ=0.25

η(%)

Tw=200℃

Tw=260℃

Fig. 4-18 Effects of aspect ratios of channel on local methanol conversion along center line of channel at T w=200 °C and T w=260 °C

mole fraction and (b) local CO mole fraction along center line of channel

106 velocity and (b) local pressure along center line of channel

120 temperature along center line of channel and (b) local reaction rates of methanol

108 40

50 60 70 80 90 100

100 200 300 400 500 600

4 6 8 10 12

γ=2.00 γ=1.00 γ=0.50 γ=0.25

η(%)

Q H2(cm3 /min)

Fig. 4-22 Effects of aspect ratios of channel and Reynolds number on methanol conversion and H2 production rate at T w=260 °C

120 140 160 180 200 220 240 260

0 0.2 0.4 0.6 0.8 1

L=33mm, δ

1+δ

2=1.500mm, W

R=0.750mm L=33mm, δ

1+δ

2=0.429mm, W

R=0.214mm

T(o C)

X Tw=260℃

Tw=200℃

Fig. 4-23 Effects of geometric size of channel on local temperature along center line of channel at T w=200 °C and T w=260 °C

110

Fig. 4-24 Effects of geometric size of channel and Reynolds number on local CH3OH mole fraction along center line of channel at (a)T w=200 °C and (b) T w=260 °C.

Fig. 4-25 Effects of various wall temperatures on (a) the temperature distributions and (b) the

112

Fig. 4-26 Effects of various wall temperatures on (a) the local velocity and (b) the local pressure along the centerline of the serpentine flow field (Y=0.5).

Fig. 4-27 Effects of Reynolds numbers at Tw=230°C on (a) the temperature distributions and

114 distributions and (b) the CH3OH mole fraction and CO mole fraction distributions along the center line of the serpentine flow field (Y=0.5)

Inlet Outlet

(a)

(b)

(c)

116

Fig. 4-30 Local distributions of (a) CH3OH mole fraction, (b) H2 mole fraction and (c) CO mole fraction along the interface between the flow channel and catalyst layer (Y=0.95) at Tw=230°

Inlet Outlet

(a)

(b)

(c)

0 20 40 60 80 100

0 20 40 60 80 100 120 140 160

20 30 40 50 60 70 80

Tw=200℃

Tw=230℃

Tw=260℃

Q H2(cm3 min-1 )

η(%)

S/C=1.3, T

0=120℃

Fig. 4-31 Effects of wall temperature and inlet fuel Reynolds number on the methanol conversion and H2 production rate

118 0

0.2 0.4 0.6 0.8 1

0 0.1 0.2 0.3 0.4 0.5

0 0.2 0.4 0.6 0.8 1

Top heated plate (Y=1) Bottom heated plate (Y=0)

M CH3OH

Re=41, S/C=1.3, T

0=120 , T℃

w=230℃

Fig. 4-32 Effects of heating different channel plates on the temperature and CH3OH mole fraction distributions along the center line of the serpentine flow field (Y=0.5)

180 200 220 240 260 280 300 320

0.3 0.35 0.4 0.45

Present Results

Experimental Study of Won et al. [24]

T w(o C)

u0,C(m s^-1) (a)

0 20 40 60 80 100

200 220 240 260 280 300

Present Results

Experimental Study of Won et al. [24]

η(%)

Tw(^oC) (b)

Fig. 4-33 Comparison of theoretical simulation of present results with previous experimental

120

Fig. 4-34 Comparisons of the simulation results with and without wall conduction effects for the temperature distributions and CH3OH mole fraction distributions along the centerline of the channel

120

Fig. 4-35 Effects of co- and counter-current flow configurations on (a) the temperature distributions along different axial location lines and (b) the local distributions of the

122

Fig. 4-36 Effects of the channel height of the combustor on (a) the temperature distributions along the top centerline of the reforming channel and (b) the CH3OH mole fraction distributions along the center line of the reforming channel

180

Fig. 4-37 Effects of the channel height of the reformer on (a) the temperature distributions along the top centerline of the reforming channel and (b) the CH3OH mole fraction

124

Fig. 4-38 Effects of the channel width on (a) the temperature distributions along the top centerline of the reforming channel (Y=0.333) and (b) the CH3OH mole fraction distributions along the center line of the reforming channel (Y=0.167)

200

Fig. 4-39 Effects of the steel widths on (a) the temperature distributions along the top centerline of the reforming channel (Y=0.333) and (b) the CH3OH mole fraction

126

Fig. 4-40 Effects of the Reynolds number (Re) for the combustor on (a) the temperature distributions along the top centerline of the reforming channel (Y=0.333) and (b) the CH3OH mole fraction distributions along the centerline of the reforming channel (Y=0.167)

180

Fig. 4-41 Effects of the Reynolds number (Re) for the reformer on (a) the temperature distributions along the top centerline of the reforming channel (Y=0.333) and (b)

128 0

50 100 150 200 250 300

0 20 40 60 80 100

5 10 15 20 25

Without wall conduction With wall conduction

ReC

T w(o C) η(%)

ReR=0.7, H

C=0.45mm, H

R=0.45mm, W

R=0.5mm, W

L=0.5mm Counter-current flow

Fig. 4-42 Effects of the Reynolds number (Re) of the combustor on wall temperature and methanol conversion

200

Combustor (Parallel Flow Field), Reformer (Parallel Flow Field) Combustor (Parallel Flow Field), Reformer (Serpentine Flow Field) Combustor (Serpentine Flow Field), Reformer (Parallel Flow Field) Combustor (Serpentine Flow Field), Reformer (Serpentine Flow Field)

Q0,R(cm³/min)

η(%)

(b)

Q0,R(cm³/min)

Fig. 4-43 Effects of the inlet flow rate (Q0,R) of the reformer and various flow field designs on (a) wall temperature and (b) methanol conversion

130

T w(o C)

η(%)

(b)

Q0,C(cm³/min)

Fig. 4-44 Effects of inlet flow rate (Q0,C) of the combustor and various flow field designs on (a) wall temperature and (b) methanol conversion

Inlet Outlet

Combustor (Parallel Flow Field) Reformer (Parallel Flow Field)

Inlet Outlet

Combustor (Parallel Flow Field) Reformer (Serpentine Flow Field)

Inlet Outlet

Combustor (Serpentine Flow Field) Reformer (Parallel Flow Field)

Inlet Outlet

Combustor (Serpentine Flow Field) Reformer (Serpentine Flow Field) (a)

(b)

(c)

(d)

132

Fig. 4-46 The CH3OH mole fraction distributions on the middle cross-section of the reforming channel for reformer and combustor with various flow field designs

Inlet Outlet

Combustor (Parallel Flow Field) Reformer (Serpentine Flow Field)

Inlet Outlet

Combustor (Parallel Flow Field) Reformer (Parallel Flow Field)

Inlet Outlet

Combustor (Serpentine Flow Field) Reformer (Parallel Flow Field)

Inlet Outlet

Combustor (Serpentine Flow Field) Reformer (Serpentine Flow Field) (a)

(b)

(c)

(d) (K)

Inlet Outlet

Combustor (Parallel Flow Field) Reformer (Parallel Flow Field)

Inlet Outlet

Combustor (Parallel Flow Field) Reformer (Serpentine Flow Field)

Inlet Outlet

Combustor (Serpentine Flow Field) Reformer (Parallel Flow Field)

Inlet Outlet

Combustor (Serpentine Flow Field) Reformer (Serpentine Flow Field) (a)

(b)

(c)

(d)

134

Fig. 4-48 The CO mole fraction distributions on the middle cross-section of the reforming channel for reformer and combustor with various flow field designs

Inlet Outlet

Combustor (Parallel Flow Field) Reformer (Parallel Flow Field)

Inlet Outlet

Combustor (Parallel Flow Field) Reformer (Serpentine Flow Field)

Inlet Outlet

Combustor (Serpentine Flow Field) Reformer (Parallel Flow Field)

Inlet Outlet

Combustor (Serpentine Flow Field) Reformer (Serpentine Flow Field) (a)

(b)

(c)

(d)

0 2 4 6 8 10

2 4 6 8 10 12

Q H2(cm3 /min)

Q0,R(cm³/min)

Fig. 4-49 Effects of the inlet flow rate (Q0,R) of the reformer and various flow field designs on the H2 production rate

136

CHAPTER 5 CONCLUSIONS AND RECOMMENDATION

5-1 Conclusions

This present study investigates heat and mass transport phenomena in the plate methanol steam micro-reformer (including methanol steam micro-reformer and methanol catalytic combustor). In this work, an attempt is made to examine the detailed fluid flow, heat and mass transfer coupled with chemical reactions in the plate methanol steam micro-reformer.

This work can accurately predict methanol conversion and local transport phenomena in the channel of a plate steam methanol micro-reformer, thus giving the following conclusions:

Firstly, this study numerically investigated the effects of the geometric and thermo-fluid

在文檔中平板式微型甲醇蒸汽重組器熱質傳特性與流道設計之研究 (頁 93-172)