Environmental Engineering Reference
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Figure 6.1.3 Piecewise two-dimensional model of the receiver assembly with the receiver divided into
longitudinal and isothermal nodal sections (Karini et al., 1986).
are found, especially in stratified flow at higher void fractions. The numerical solution
showed that a sudden drop of irradiation induces a very high temperature gradient
inside the absorber tube in a short period of time.
Thomas and Thomas (1994) studied the design data required for the computation
of thermal loss in the receiver of a parabolic trough concentrator for specific absorber
tube diameters, various ambient temperatures, wind velocity and absorber tempera-
tures from 50 to 350 C in steps of 10 C. Curve-fitting equations based on a numerical
heat transfer model for the heat losses for the above parameters are given to enable the
designer to generate the required data for any absorber temperature, absorber diame-
ter, ambient temperature, wind velocity and emissivity of the solar selective coating of
the absorber.
Dudley et al. (1994) developed an analytical model of SEGS LS-2 parabolic solar
collector. The thermal loss model for the heat collection element was a one dimensional
steady state model based on thermal resistance analysis. This model was validated
with experimental data collected by Sandia National Laboratories (SNL) for different
receiver annulus conditions: vacuum intact, lost vacuum (air in annulus), and broken
annulus cover (bare tube). The results showed a reasonable agreement between the
theoretical and experimental heat losses.
Odeh et al. (1998) studied the thermal performance of a parabolic trough solar
collector used as direct steam generator for different solar radiation levels and geomet-
ric configurations. This heat transfer model showed better agreement with the in-focus
test results than the polynomial curve fit equation obtained by Dudley et al. (1994).
The thermal losses calculated for water were based on the receiver wall temperature
and the results showed that thermal losses calculated for steam as heat transfer fluid
were lower than those obtained for synthetic oil.
Forristall (2003) built and analysed both a 1-D and a 2-D heat transfer models
of a PTC receiver implemented in EES software. For this purpose a detailed heat
transfer solar receiver model was used. A one-dimensional energy balance for several
segments was used for short and long receivers respectively. This model was used
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