wrote:
Work in progress...
20 TA=84'ambient temp (F)
30 WA=.0185'ambient humidity ratio
40 PA=29.921/(.62198/WA+1)'ambient vapor pressure ("Hg)
50 TDP=9621/(17.863-LOG(PA))-460'dew point temp (F)
60 TWBL=460+(TA+TDP)/2'initial Twb estimate (R)...
airflow dry bulb wet bulb dew point drying time
free 84 F 77.61066 F 74.23621 F 3.130212 hours
100 cfm 161.7445 114.8843 118.6882 .4268011
120 157.2436 110.5703 114.3571 .4285108
140 157.7107 109.005 111.8636 .4106299...
The first is the clothesline. Why is the wet bulb less than the dew point?
20 TA=84'ambient temp (F)
30 WA=.0185'ambient humidity ratio
40 PA=29.921/(.62198/WA+1)'ambient vapor pressure ("Hg)
50 TDP=9621/(17.863-LOG(PA))-460'dew point temp (F)
60 TWBL=460+(TA+TDP)/2'initial Twb estimate (R)
70 TWB=9621/(22.468-LOG(TA+460+100*PA-TWB))'wet bulb temp (R)
80 IF ABS(TWB-TWBL)/TWB .01 THEN TWBL=TWB:GOTO 70
90 TWB=TWB-460'wet bulb temp (F)
100 CAREA=200'clothing area (ft^2, 1 side)
110 GC=1.5*2*CAREA'clothing-air conductance (Btu/h-F)
120 DRYRATE=(TA-TWB)*GC'drying rate (Btu/h)
130 WW=12'water weight (pounds)
140 DRYTIME=1000*WW/DRYRATE'drying time (h)
150 PRINT 0,TA,TWB,TDP,DRYTIME
170 FULLSUN=250'solar power (Btu/ft^2-h)
180 SUNPOWER=.9*16*16*FULLSUN'sun into greenhouse (Btu/h)
190 GG=256'greenhouse thermal conductance (Btu/h)
200 RHO=.075'nominal air density (lb/ft^3)
210 LAT=1000'latent heat (Btu/lb)
220 F1=60*LAT*RHO'factor
230 F2=60*LAT*RHO/GC'factor
240 TAR=TA+460'ambient temp (R)
250 FOR C=100 TO 200 STEP 20'greenhouse airflow (cfm)
260 GA=C+GG
270 GP=GC+GA
280 ALPHA=SUNPOWER+GG*TAR+WA*C*(F1+F2*(C+GG))+TAR*C
290 BETA=GG+C
300 GAMMA=C*(F1+F2*(C+GG))
310 TWBL=100+460'Twb initial est (R)
320 WI=(ALPHA-BETA*TWBL)/GAMMA'greenhouse humidity ratio
330 PI=29.921/(.62198/WI+1)
340 TGR=(SUNPOWER+GA*TAR+GC*TWBL)/GP
350 TWB=9621/(22.468-LOG(TGR+100*PI-TWBL))
360 IF ABS(TWB-TWBL)/TWB .01 THEN TWBL=TWB:GOTO 320
370 TWB=TWB-460'wet bulb temp (F)
380 TG=TWB+F2*C*(WI-WA)'greenhouse air temp (F)
390 DRYRATE=(TG-TWB)*GC'drying rate (Btu/h)
400 DRYTIME=1000*WW/DRYRATE'drying time (h)
410 TDP=9621/(17.863-LOG(PI))-460'greenhouse dew point (F)
420 PRINT C,TG,TWB,TDP,DRYTIME
430 NEXT
airflow dry bulb wet bulb dew point drying time
free 84 F 77.61066 F 74.23621 F 3.130212 hours
100 cfm 165.9619 F 121.7136 F 117.3342 F .4519949 hours
120 162.1941 117.9772 113.1386 .4523157
140 158.9697 114.9237 109.6841 .4540707
160 156.1529 112.3674 106.7763 .4567723
180 153.6542 110.1876 104.2872 .4601233
200 151.4108 108.3012 102.1281 .4639328
Ah, much better, about 7X faster than a clothesline in humid air, but
it looks like there will be condensation inside the R1 glazing, if it's
84 F outside and 166 inside with a 117 F dew point. How does that change
the picture? It would probably also help to bring fresh air in through
a poly duct surrounded by greenhouse air, with condensation on the
outside of the duct. How can we model that?
Paul might make a dryer design template. Just click here... :-)
Nick
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