Efficiency of Recycling Double-Pass V-Corrugated Solar Air Collectors
Abstract
:1. Introduction
2. Theoretical Analysis
3. Experimental Setup
4. Collector Efficiency Improvement
5. Results and Discussion
6. Conclusions
Acknowledgment
Author Contributions
Conflicts of Interest
Nomenclature
Surface area of the collector = LW (m2) | |
Bi | Coefficients defined in Equations (A1)–(A6) |
Ci | Coefficients defined in Equations (A16) and (A17) |
Specific heat of air at constant pressure (J/(kg K)) | |
Equivalent diameter of downward-type single-pass device (m) | |
Equivalent diameter of lower subchannel of double-pass device (m) | |
Equivalent diameter of upper subchannel of double-pass device (m) | |
Deviation of the experimental measurements from theoretical predictions, defined in Equation (11) | |
Fi | Coefficients defined in Equations (A18)–(A20) |
Fanning friction factor | |
Coefficients defined in Equations (A7)–(A13) | |
Hg | Height of channels (m) |
ha | Convection coefficient between the absorber plate and subchannel a (W/(m2 K)) |
hb | Convection coefficient between the absorber plate and subchannel b (W/(m2 K)) |
Radiation heat transfer coefficient between cover 1 and absorber plate (W/m2 K) | |
Radiation heat transfer coefficient between absorber plate and bottom plate (W/m2 K) | |
hw | Convective heat transfer coefficient for air flowing over the outside surface of glass cover (W/(m2 K)) |
Incident solar radiation (W/m2) | |
Percentage of collector efficiency improvement, defined in Equation (12) | |
Power consumption increment, defined in Equations (20)–(22) | |
Percentage of collector efficiency improvement, defined in Equation (13) | |
Percentage of collector efficiency improvement, defined in Equation (14) | |
ks | Thermal conductivity of insulator (W/(m K)) |
Channel length (m) | |
ls | Thickness of insulator (m) |
Lower subchannel friction loss of double-pass device (J/kg) | |
Upper subchannel friction loss of double-pass device (J/kg) | |
Friction loss of downward-type single-pass device (J/kg) | |
Total air mass flow rate (kg/h) | |
N | Number of glass cover |
Number of experimental measurements | |
Nu | Nusselt number |
PD | Power consumption of the flat plate double-pass device (W) |
PS | Power consumption of downward-type single-pass device (W) |
PV | Power consumption of the V corrugated double-pass device (W) |
PW | Power consumption of the wire mesh packed double-pass device (W) |
Useful energy gained by air (W) | |
R | Recycle ratio, reverse air mass flow rate divided by input air mass flow rate |
The experimental uncertainty of an individual measurement | |
The mean value of | |
Re | Reynolds number |
Inlet air temperature (K) | |
The mixing temperature of the subchannel a at x = 0 (K) | |
The temperature of the subchannel a at x = L (K) | |
The temperature of the subchannel b at x = 0 (K) | |
The temperature of the subchannel b at x = L (K) | |
Axial fluid temperature distribution in subchannel a (K) | |
Axial fluid temperature distribution in subchannel b (K) | |
Temperature of glass cover 1 (K) | |
Temperature of absorbing plate (K) | |
Mean temperature of absorbing plate (K) | |
Ambient temperature (K) | |
Loss coefficient from the bottom of solar air heater to the ambient environment (W/(m2 K)) | |
Loss coefficient from the surfaces of edges and the bottom of the solar collector to the ambient environment (W/m2 K) | |
Loss coefficient from the inner cover to the ambient environment (W/m2 K) | |
Loss coefficient from the top of solar air heater to the ambient environment (W/m2 K) | |
W | Width of both upper and lower subchannels (m) |
Mean air velocity in the downward-type single-pass device (m/s) | |
Mean air velocity in subchannel a of double-pass device (m/s) | |
Mean air velocity in subchannel b of double-pass device (m/s) | |
Yi | Coefficients defined in Equations (A14) and (A15) |
Axial coordinate (m) | |
Greek Letters | |
Absorptivity of the absorbing plate | |
Collector efficiency of the flat-plate double-pass device | |
Collector efficiency of the downward type single-pass device | |
Collector efficiency of the double-pass V-corrugated solar air ter | |
Collector efficiency of the double-pass wire mesh packed solar air heater | |
Experimental data of collector efficiency | |
The mean value of the experimental data | |
Theoretical prediction of collector efficiency | |
Air viscosity (kg/ms) | |
Transmittance of glass cover | |
Emissivity of glass cover | |
Emissivity of absorbing plate | |
Air density (kg/m3) | |
Dimensionless channel length |
Appendix A
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Mass Flow Rate | Recycle Ratio | I0 = 830 (W/m2) | I0 = 1100 (W/m2) | ||
---|---|---|---|---|---|
m (kg/h) | R | ||||
38.52 | 0.25 | 0.487 | 57.60 | 0.510 | 69.51 |
0.5 | 0.511 | 65.52 | 0.535 | 77.85 | |
0.75 | 0.538 | 73.99 | 0.563 | 86.88 | |
1 | 0.565 | 82.89 | 0.592 | 96.58 | |
1.25 | 0.593 | 91.86 | 0.623 | 106.87 | |
1.5 | 0.608 | 96.79 | 0.655 | 117.45 | |
1.75 | 0.618 | 99.97 | 0.685 | 127.48 | |
2 | 0.632 | 104.58 | 0.704 | 134.01 | |
57.96 | 0.25 | 0.503 | 35.98 | 0.530 | 45.62 |
0.5 | 0.526 | 42.07 | 0.553 | 52.01 | |
0.75 | 0.565 | 52.76 | 0.578 | 58.86 | |
1 | 0.597 | 61.34 | 0.622 | 70.99 | |
1.25 | 0.630 | 70.32 | 0.658 | 80.84 | |
1.5 | 0.663 | 79.15 | 0.697 | 91.55 | |
1.75 | 0.676 | 82.65 | 0.744 | 104.32 | |
2 | 0.688 | 85.97 | 0.766 | 110.40 | |
77.04 | 0.25 | 0.508 | 21.94 | 0.508 | 29.34 |
0.5 | 0.536 | 28.46 | 0.536 | 36.06 | |
0.75 | 0.580 | 39.11 | 0.580 | 43.41 | |
1 | 0.614 | 47.29 | 0.614 | 55.44 | |
1.25 | 0.651 | 56.04 | 0.651 | 64.83 | |
1.5 | 0.688 | 65.03 | 0.688 | 75.58 | |
1.75 | 0.703 | 68.68 | 0.703 | 85.69 | |
2 | 0.715 | 71.41 | 0.715 | 92.99 |
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Ho, C.-D.; Hsiao, C.-F.; Chang, H.; Tien, Y.-E.; Hong, Z.-S. Efficiency of Recycling Double-Pass V-Corrugated Solar Air Collectors. Energies 2017, 10, 875. https://doi.org/10.3390/en10070875
Ho C-D, Hsiao C-F, Chang H, Tien Y-E, Hong Z-S. Efficiency of Recycling Double-Pass V-Corrugated Solar Air Collectors. Energies. 2017; 10(7):875. https://doi.org/10.3390/en10070875
Chicago/Turabian StyleHo, Chii-Dong, Ching-Fang Hsiao, Hsuan Chang, Yi-En Tien, and Zih-Syuan Hong. 2017. "Efficiency of Recycling Double-Pass V-Corrugated Solar Air Collectors" Energies 10, no. 7: 875. https://doi.org/10.3390/en10070875