DIYbanter - View Single Post - (cargo?) WARM HEAVY work-pants? (google not much help)

BobK207

wrote:
Doug Miller wrote:

In general, radiation is about an order of magnitude less effective at
transferring heat than conduction or convection.

Here's how I figure it:

20 TDB=-2.2'average daily min temp in January in Duluth (F)
30 TDBC=(TDB-32)/1.8'dry bulb temp (C)
40 V=11.6'windspeed (mph)
50 W=.0012'average humidity ratio
60 PA=29.921/(1+.62198/W)'vapor pressure ("Hg)
70 E=3.3772*PA'vapor pressure (kPa)
80 TDP=9621/(17.863-LOG(PA))-460'dew point temp (F)
90 IF TDPTDB THEN TDP=TDB
100 TDPC=(TDP-32)/1.8'dew point temp (C)
110 GAMMA=.00066*101.325'constant for wet bulb temp calc
120 TDC=(TWBEC+TDPC)/2
130 DELTA=4098*E/(TDC+237.3)^2
140 TWBC=(GAMMA*TDBC+DELTA*TDC)/(GAMMA+DELTA)'wet bulb estimate (C)
150 IF ABS(TWBC-TWBEC).01 THEN TWBEC=TWBC:GOTO 120'iterate to 0.01 C
160 TWB=1.8*TWBC+32'wet bulb temp (F)
170 IF TWBTDB THEN TWB=TDB
180 A=.002056*TDP+.7378'coefficient in Niles equations
190 TS=92'skin temp (F)
200 QR=1.63E-09*((TS+460)^4-A*(TDB+460)^4)'radiation loss (Btu/h-ft^2)
210 QC=(.74+.3*V)*(TS-TDB)'convection loss (Btu/h-ft^2)
220 B=3.01*(.74+.3*V)*((TS+TWB)/65-1)
230 QE=B*(TS-TWB)-QC'evaporation loss (Btu/h-ft^2)
240 PRINT TDB,TWB,TDP
250 PRINT QR,QC,QE

dry bulb wet bulb dew point

-2.2 -2.2 -2.2 F

radiation convection evaporation

98.83666 397.524 59.00485 Btu/h-ft^2

NREL's V = 11.6 mph in line 40 was probably measured at an airport.
Changing to V = 0 lowers convection to 70 and evaporation to 10,
so radiation loss dominates.

NREL's 24-hour average humidity ratio makes the wet bulb and dew points
higher than the dry bulb, which probably means there's frost on
an average January night, which might warm you up.

Thanks for the "education" :-)

Nick

Heat transfer by radiation for bare skin?
What about the effect of clothing on radiation efficiency?

Won't your "TS" be much closer to air temp than body temp?

Or we're you just looking for SWAG on bare skin Q as a starting point?

In any case, for properly clothed human in a cold environment, QR
looks to be pretty low compared to other mechanisms

cheers
Bob

cheers