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Fin tube vs flashing solar collectors

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Posted by nicksanspam on May 30, 2006, 10:06 am
John Siegenthaler kindly supplied an equation for the heat output Q of 1' of
baseboard radiator fin tube with a low water-air temperature difference:

Q=G^.04*Nom*9.6865E-04*(Tw-Ta)^1.4172 Btu/h-ft,

where G is the flow rate in gpm, Nom is the nominal heat output in Btu/h-ft
with 200 F water and 65 F air, and Tw and Ta (F) are water and air temps.

I used this backwards in line 100 below to estimate the air-water conductance
of 64' (about $28) of Argo Technology Lo Trim fin tube containing 100 F water
near the top of an air heater on an average 32 F December day in Rochester NY,
to compare its output with 4 10'x21" homebrew collectors made with 40' x 2' of
0.018" Amerimax Home Products brown aluminum flashing silicone-caulked to 12
10' x 1/2" copper pipes (about $34.)

The air heater modeled had 144 ft^2 of single-layer Dynaglas US R1 corrugated
polycarbonate ("solar siding") with 90% light transmission inside 144 ft^2 of
U0.58 Thermaglas Plus twinwall polycarbonate with 80% light transmission.
The fin tube won in this case, with less labor and more confidence in
the output estimate.

20 SUN=.8*.9*560/6'solar gain (Btu/h-ft^2)
30 GG4/(1+1/.58)'glazing conductance (Btu/h-F)
40 TT2+144*SUN/GG'Thevenin equivalent temp (F)
50 NFT=8'number of 8' fin tubes
60 FTL=8*NFT'total fin tube length (ft)
70 GF=FTL*5'initial air-fin conductance (Btu/h-F)
80 FINGAIN=(TT-100)/(1/GG+1/GF)'useful heat output (Btu/h)
90 TA0+FINGAIN/GF'air heater temp (F)
100 GF=FTL*5^.04*690*9.6865E-04*(TA-100)^0.4172'adj fin conductance (Btu/h-F)
110 IF ABS(TA-TAL)>0.1 THEN TAL=TA: GOTO 80'iterate
130 BFU=4'number of 3-pipe Big Fin units
140 AU*17.55'Big Fin area (ft^2)
150 AC=1.75/6'half-fin area for conductance calc (ft^2)
160 GSF=2*.535'half-fin metal conductance (Btu/h-F)
170 GFP=2.35'half-fin to pipe conductance (Btu/h-F)
180 RC=1/GSF+1/GFP'sun-fin + fin-pipe resistance (F-h/Btu)
190 GSWF=A/(AC*RC)'sun-water fin conductance (Btu/h-F)
200 TTF0+SUN*A/GSWF'Thevenin equivalent temp (F)
210 GFA=1.5'fin-air conductance (Btu/h-F-ft^2)
220 TTG2+SUN*(144-A)/GG'glazing Thev equivalent temp (F)
230 FINLOSS=(TTF-TTG)/(1/GSWF+1/(3*A)+1/GG)'heat loss from fin to air (Btu/h)
240 FINGAIN=SUN*A-FINLOSS'useful heat output (Btu/h)
250 TA2+(144*SUN-FINGAIN)/GG'air heater temp (F)

units     air temp (F)  output (Btu/h)
8         126.2808      4693.044
4         126.7552      4667.969


Posted by Day Brown on May 31, 2006, 5:26 am
nicksanspam@ece.villanova.edu wrote:

seems like it wouldnt be that big a deal to get up to 171deg F. for a
solar ethanol still.

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