A User's Manual for DELSOL3 - prod.sandia.gov - Sandia National ...

eceiver) or with aperture area (cavity receiver) from some reference system in
which the losses are well characterized.
a) IRADFL = 0, Direct Calculation of Losses (References 6 and 7)
For this option, the individual losses for radiation and forced and natural con-
vection are calculated separately and summed as
PLOST,R = Qrrtd + Qconv
(1II.G - 4)
In order to calculate the losses, the code assumes that the loss is not a function of
time or method of operation of the receiver. This allows the approximation that
the range of temperature operation gives an average wall temperature, Twall, of
753 K (48OOC). Further assumptions are that receiver emissivity e = 0.90, average
wind speed urn = 7.2 meters/second, and ambient air temperature T, = 20.0"C
(Reference 29).
The thermal radiation heat loss is expressed as a function of receiver area (ex-
ternal receivers) or aperture area (cavity receivers) in the following manner:
Qrad = EaATw,11 4
Qrad = (0.90)(5.669 x 10-8W/m2K4)(A)(753K)4
Qrad = 16,403A
(1II.G - 5)
where u is the Stefan-Boltzmann constant and A is the receiver or aperture area.
The convection heat loss is calculated differently depending on whether the
receiver is a cavity or a cylindrical external receiver. For an external receiver,
The mixed convection coefficient for an external receiver is calculated accord-
ing to Reference 29 as
(II1.G - 7)
where hn,t=g.Og (W/m2"C) based on the assumed temperatures and hforced is
separated into three cases depending on the receiver diameter (Reference 6).
80
In all cases, the Reynolds number is Re = (1.751 x 105)D.
.