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

controlled by the IAUTOP parameter in namelist REC and are illustrated in Fig-
ure 11-15. All “smart” aiming options are time dependent; i.e., the number of aim
points can change over the year if the image changes.
II.F-I. Single Aim Point (IAUTOP=l)-This is the simplest of all aiming op-
tions. All heliostats are pointed at the center (when viewed from the heliostat
surface) of the receiver (Figure 11-15(A)). This option produces the maximum flux
on the receiver.
II. F-2. One-Dimensional “Smart ”Aiming (IA UTOP=l)-The heliostat images
are spread out along the “height” of the receiver or aperture until the spillage
starts to increase. As seen in Figure II-l5(B), the smaller images of the inner (or
best focused) heliostats can be spread out over more aim points than the larger
images of the outer (or less well focused) heliostats. This option reduces both
the peak flux and the flux gradients on the receiver. This is the “smart” aiming
option to use with external receivers (IREC=O) and with cavity or flat plate re-
ceivers of elliptical shape (IREC=l or 3). Since the size of the images from the
heliostats can change with time, the one-dimensional smart aiming also changes
with time, so that both the number and position of the aimpoints may change.
II. F-9. Two-Dimensional “Smart” Aiming (Rectangular Cavity Apertures
or Flat Plates Only, IA UTOP=2)-This option is similar to IAUTOP=l except
that the images are spread out in two dimensions as shown in Figure II-l5(C).
This results in even smaller peak fluxes than IAUTOP=l. However, this option
should only be used with rectangular cavity apertures (IREC=2) or rectangular
flat plates (IREC=4). If used with elliptical receivers the spillage will increase.
Furthermore, if used with external cylinders much of the flux will be incident on
the receiver at grazing angles where the absorption is poor, and the flux normal
to the receiver (as calculated by DELSOL) will not be representative of the actual
peak flux that could be incident on a single tube of the receiver.
II.F-4. Single Aim Point at the Lower Part of the Receiver (IAUTOP=$)-The
heliostats are aimed as close to the bottom of the receiver as is possible without
increasing spillage significantly as shown in Figure 11-15(d). The aimpoints will
vary somewhat with time as the heliostat image sizes vary, so that spillage re-
mains relatively constant. There are several reasons for considering this strategy.
First, if the fluid enters from the bottom of the receiver the peak fluxes will occur
near the colder (and presumably stronger) end of the piping. The penalty is in-
creased radiation and convection losses in real life, since the average receiver tem-
perature is increased. However, if the fluid enters from the top of the receiver the
radiation and convection losses are minimized, but the peak flux occurs near the
hot end of the tube. Typically, peak fluxes will be close to those levels resulting
from the single aimpoint strategy (IAUTOP=l).
II.F-5. One-Dimensional Aiming at the Lower Part of the Receiver
(IA UTOP=4)-Similar to IAUTOP=3 except that the images are spread out
along the bottom of the receiver, as shown in Figure II-l5(E). This option should
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