Evaluating all necessary optical properties of the glass glazing, the amount of solar radiation actually absorbed by the collector can be easily deduced. The total incident radiation aimed at each wing of the collector is
Ici = "IbRbi + 2 [°.5Id + °.% + Ib)] (17)
the total absorbed solar radiation of each wing is
^ = (ta)b VIbRbi + 2(ta)b [0.5Id + 0.1 (Id + Ib)] (18)
= ( Ta)b VIbRbi + (Ta)b [Id + °.2 (Id + Ib)] (19)
The mean absorbed solar radiation, S, of the whole collector plate is evaluated by the relation
S = 1/3 [>1 + S2 + S3 ] (20)
Applying the above expressions with other expressions for optical properties for calculating the absorbed radiation, the values calculated are tabulated as shown in Table 5.
|
7-8 |
8-9 |
9-10 |
10-11 |
11-12 |
12-1 |
1-2 |
2-3 |
3-4 |
4-5 |
|
|
Ib (MJ/m2) |
0.0246 |
0.2423 |
0.0371 |
1.0621 |
1.1144 |
1.1992 |
1.2452 |
1.1076 |
0.7478 |
0.3078 |
|
Id (MJ/m2) |
0.1086 |
0.2239 |
0.2287 |
0.2255 |
0.2242 |
0.2216 |
0.2200 |
0.2244 |
0.2290 |
0.2250 |
|
S (MJ/m2) |
0.136 |
0.384 |
0.418 |
0.389 |
0.240 |
0.507 |
0.505 |
0.464 |
0.380 |
0.275 |
|
Vx |
1 |
1 |
1 |
1 |
1 |
0.4260 |
0.1870 |
0.1010 |
0.0590 |
0.0320 |
|
Rb1 |
1.7480 |
0.8260 |
0.3940 |
0.1030 |
0.1400 |
0.3800 |
0.6540 |
1.0200 |
1.6200 |
2.993 |
|
(™)b1 |
0.774 |
0.720 |
0.572 |
0.214 |
0.302 |
0.640 |
0.768 |
0.808 |
0.820 |
0.823 |
|
(T«)d1 |
0.757 |
0.757 |
0.700 |
0.757 |
0.757 |
0.757 |
0.757 |
0.757 |
0.757 |
0.757 |
|
S2 (MJ/m2) |
0.124 |
0.377 |
0.593 |
0.793 |
0.797 |
0.840 |
0.889 |
0.873 |
0.743 |
0.516 |
|
V2 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
1 |
|
Rb2 |
1.247 |
0.795 |
0.627 |
0.551 |
0.520 |
0.520 |
0.551 |
0.627 |
0.795 |
1.247 |
|
(T«)b2 |
0.691 |
0.709 |
0.722 |
0.730 |
0.733 |
0.733 |
0.730 |
0.722 |
0.709 |
0.691 |
|
(™)d2 |
0.757 |
0.757 |
0.757 |
0.757 |
0.757 |
0.757 |
0.757 |
0.757 |
0.757 |
0.757 |
|
S3 (MJ/m2) |
0.104 |
0.259 |
0.357 |
0.465 |
0.488 |
0.434 |
0.416 |
0.621 |
0.766 |
0.667 |
|
V3 |
0.032 |
0.059 |
0.101 |
0.187 |
0.426 |
1 |
1 |
1 |
1 |
1 |
|
Rb3 |
2.993 |
1.620 |
1.020 |
0.654 |
0.380 |
0.140 |
0.103 |
0.394 |
0.826 |
1.748 |
|
(Ta)b3 |
0.823 |
0.820 |
0.808 |
0.768 |
0.640 |
0.302 |
0.214 |
0.572 |
0.720 |
0.774 |
|
(Ta)d3 |
0.757 |
0.757 |
0.757 |
0.757 |
0.757 |
0.757 |
0.757 |
0.757 |
0.757 |
0.757 |
|
S (MJ/m2) |
0.121 |
0.430 |
0.466 |
0.549 |
0.568 |
0.594 |
0.603 |
0.653 |
0.630 |
0.486 |
|
Table 5. Measured insolation data for each of the absorbers |
5.1. The collector efficiency factor and the collector loss coefficient
Despite the unusual configuration of the tri-wing absorber plate, a section of it reduces to a vertical flat-plate collector over both sides of the plate without back insulation. This implies that a wing of the absorber can be treated as a flat-plate air heater with flow over both sides of the plate. To conform to the performance equation of a flat-plate collector, the configuration of the chimney collector is transformed to suit the equation. Criteria for the transformation are as follows:
1. The total area of the tri-wing absorber plate is equal to the total area of the flat absorber plate.
2. The height of the chimney collector is the same as the height of the resulting flat absorber plate.
3. The area of the circular inlet column of the chimney collector and the rectangular area inlet column of the resulting flat-plate collector are equal throughout the height of the collector.
4. The resulting flat-plate absorber is positioned within the rectangular column such that the flow is halved.
5. Size difference of the glass glazing of the two cases is neglected. The resulting flat-plate collector has an absorber plate 5.3m in height and 2.4m in breadth enclosed by a rectangular channel of glass glazing measuring 2.46m by 0.8587m in length and breadth. Thus, the flow width on either side of the plate is about 43cm.
