Hybrid Car – More Fun with Less Gas

Re: Recuperate some of the heat from a group of showers - Page 5

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Posted by nicksanspam on September 4, 2007, 11:43 am
 

OTOH, with full mixing vs stratification, if dp pounds of 60 F water
flows into the 2-pound bottle and dp pounds of T (F) water flows out and
Tnew = (60dp+T(2-dp)/2 = T+dp(30-T/2), Tnew-T = dt, and dt/dp + T/2 = 30
(an equation of form dx/dt+cx = d with solution x = -d/c+(x0-d/c)e^(-ct)),
T = 60+(140-60)e^(-P/2) = 90 when P = -2ln((90-60)/(140-60)) = 1.96 pounds.

Nick


Posted by nicksanspam on August 31, 2007, 12:42 pm
 

We could use a float switch and a metering pump like the $85 Mec-O-Matic
D75 to move 64.3 gpd at C = 22 Btu/h-F (0.044 gpm) with NTU = 30x27/22
= 36 and E = 0.97. Preheated water might thermosyphon into the lower part
of a water heater from the fresh water heat exchanger outlet 3' above
the floor into a T 3' above the floor, connecting the upper and lower
parts of the tank, with a common cold water connection at floor level,
with the lower tank heating element disconnected.

This looks promising, with Poiseuille's equation for thermosyphoning:

20 PI=4*ATN(1)
30 TC=(50-32)/1.8'cold temp (C)
40 TW=(75-32)/1.8'warm temp (C)
50 RSLOPE=(998.2-988)/(20-50)'density slope
60 RHOC8.2+(TC-20)*RSLOPE'cold density (kg/m^3)
70 RHOW8.2+(TW-20)*RSLOPE'warm density (kg/m^3)
80 H=3*.3048'height diff (meters)
90 DP=(RHOC-RHOW)*H*9.8'pressure difference (N/m^2)
100 VSLOPE=(.001002-.000547)/(20-50)'viscosity slope
110 VC=.001002+(TC-20)*VSLOPE'cold viscosity (Ns/m^2)
120 VW=.001002+(TW-20)*VSLOPE'warm viscosity (Ns/m^2)
130 RC$/2/12*.3048'cold pipe radius (meters)
140 RW=1.049/2/12*.3048'warm pipe radius (meters)
150 LC=3*.3048'cold pipe length (meters)
160 LW0*.3048'warm pipe length (meters)
180 NE=6'number of elbows
190 LC=LC+50*RC'equivalent cold pipe length (meters)
200 RESC=8*VC*LC/(PI*RC^4)'cold flow resistance
210 RESW=8*VW*LW/(PI*RW^4)'warm flow resistance
220 V=DP/(RESC+RESW)'flow (m^3/s)
230 GPM=V*15850!'flow (gpm)
240 PRINT GPM

 .2886552 gpm

Nick


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