re: cooling of pv modules (was calculating windload...) SOLAR.KnowledgePublications.com

re: cooling of pv modules (was calculating windload...)
31 dec 2002
>>>> the second approach recognizes that each hole decreases the flow in
>>>> the pipe, which decreases the velocity and the pressure. this allows
>>>> a smaller pipe with a constant diameter and constant diameter holes and
>>>> decreasing hole spacing along the pipe in the direction of flow...
 
here's a more accurate calc, with jim miller's help... with a mere 4%
difference in flow rate and a warmer array in the center, the holes
might as well be evenly-spaced, eg every 3".

10 pi=4*atn(1)
20 h=.5'head (feet)
30 l=.5'pipe length (feet)
40 q=8'flow rate (gpm)
50 dip=1.5'pipe id (inches)
60 dp=dip/12'pipe id (feet)
70 a=pi*(dp/2)^2'flow area (ft^2)
80 c=150'plastic pipe roughness factor for the hazen-williams equation
90 dh=3/32'hole diam (inches)
100 ah=pi*(dh/(2*12))^2'hole area (ft^2)
110 n=n+1'hole number
120 qv=q/8/60'volumetric flow rate (ft^3/sec)
130 v=qv/a'ft/sec
140 headloss=3.022*l*(v/c)^1.852*dp^-1.167'hazen-williams head loss (feet h20)
150 h=h-headloss'head loss in pipe (feet)
160 flowh=3840*ah*sqr(h)'flow through hole (gpm)
170 q=q-flowh'pipe flow after hole (gpm)
180 print n,h,d,dc,flowh
190 l=flowh/.5'distance to next hole (feet)
200 d=d+12*l'next hole location (inches)
210 dc=d*2.54'next hole location (cm)
220 if d<16*12 goto 110
                                hole position
hole #   head (ft)         inches       centimeters    flow (gpm)

 1      .4971865           0             0             .1297959
 2      .4957693           3.115101      7.912356      .1296108
 3      .4943971           6.225759      15.81343      .1294313
 4      .4930688           9.332109      23.70356      .1292573
 5      .4917838           12.43428      31.58308      .1290887
 6      .4905411           15.53241      39.45233      .1289255
 7      .48934             18.62663      47.31163      .1287676
 8      .4881797           21.71705      55.1613       .1286148
 9      .4870594           24.8038       63.00166      .1284672
10      .4859783           27.88702      70.83301      .1283245
11      .4849356           30.9668       78.65568      .1281868
12      .4839306           34.04329      86.46994      .1280539
13      .4829625           37.11658      94.27611      .1279257
14      .4820305           40.1868       102.0745      .1278023
15      .4811341           43.25405      109.8653      .1276833
16      .4802723           46.31845      117.6489      .1275689
17      .4794445           49.3801       125.4255      .127459
18      .4786499           52.43912      133.1953      .1273533
19      .477888            55.4956       140.9588      .1272519
20      .4771578           58.54964      148.7161      .1271547
21      .4764589           61.60136      156.4674      .1270615
22      .4757903           64.65083      164.2131      .1269723
23      .4751516           67.69816      171.9533      .1268871
24      .474542            70.74345      179.6884      .1268056
25      .4739608           73.78678      187.4184      .1267279
26      .4734072           76.82826      195.1438      .1266539
27      .4728808           79.86795      202.8646      .1265835
28      .4723807           82.90595      210.5811      .1265165
29      .4719064           85.94235      218.2936      .126453
30      .4714571           88.97722      226.0022      .1263928
31      .4710322           92.01065      233.7071      .1263358
32      .470631            95.04271      241.4085      .126282
33      .470253            98.07348      249.1066      .1262313
34      .4698973           101.103       256.8017      .1261835
35      .4695634           104.1314      264.4938      .1261387
36      .4692506           107.1588      272.1832      .1260967
37      .4689582           110.1851      279.8701      .1260574
38      .4686857           113.2105      287.5546      .1260208
39      .4684322           116.235       295.2368      .1259867
40      .4681973           119.2586      302.9169      .1259551
41      .4679801           122.2816      310.5952      .1259258
42      .4677801           125.3038      318.2716      .1258989
43      .4675966           128.3254      325.9464      .1258743
44      .467429            131.3463      333.6197      .1258517
45      .4672765           134.3668      341.2916      .1258311
46      .4671385           137.3867      348.9623      .1258126
47      .4670143           140.4062      356.6318      .1257958
48      .4669032           143.4253      364.3003      .1257809
49      .4668046           146.4441      371.9679      .1257676
50      .4667178           149.4625      379.6347      .1257559
51      .466642            152.4806      387.3008      .1257457
52      .4665767           155.4985      394.9663      .1257369
53      .4665209           158.5162      402.6312      .1257294
54      .4664741           161.5337      410.2956      .1257231
55      .4664356           164.5511      417.9597      .1257179
56      .4664045           167.5683      425.6235      .1257137
57      .4663801           170.5854      433.287       .1257104
58      .4663618           173.6025      440.9503      .1257079
59      .4663486           176.6195      448.6134      .1257061
60      .4663397           179.6364      456.2765      .125705
61      .4663345           182.6533      463.9394      .1257043
62      .4663319           185.6702      471.6024      .1257039
63      .4663311           188.6871      479.2653      .1257038
64      .4663311           191.704       486.9282      .1257038

nick