Thermal modelling of parabolic trough collectors - Solar Energy Sciences and Engineering Applications - page 190

Figure 6.3.5 Photograph of the collector installed at Archimedes Solar Energy Laboratory.

Table 6.3.2 Characteristics of the NEP solar collector installed at
Archimedes Solar Energy Laboratory.

Parameter Value

Collector Length 1993mm

Collector width 1208mm

Parabola focal distance 647mm

Mirror reflectivity 93.5%

Receiver material Stainless steel 304 L

Receiver external diameter 28mm

Receiver internal diameter 25mm

Glass tube transmittance 0.89

Selective coating absorptance 0.93

Selective coating emittance 0.18

900 W/m 2 , wind speed of 0.45 m/s, flow rate of 8.8 kg/s, ambient temperature of 25 ◦ C
and ambient air at atmospheric pressure in receiver annulus. It should be noted that
the manufacturer gives for these conditions an efficiency equal to 58%, which is very
close to the obtained result.
It should be noted that if vacuum exists in the receiver annulus the efficiency is
increased to 66.76% and the heat gain is equal to 735.8 W/m.
A major objective of the work carried out at Archimedes Solar Energy Labora-
tory is to develop improved selective coatings for parabolic trough collector receivers.