Energy and Environment II Recommended Answers in Red

QUIZ #2

1. The flat-plate tracking collector follows the sun, such that the sun beam is always perpendicular to the flat surface of the collector.

A. What is the value of the angle q for the tracking collector?

The tracking collector is rotated about two axes so that the sun beam is always normal (perpendicular) to the panel or aperture of the collector. Thus, q = 0 degrees. (q is the angle between the normal of the collector and the sun beam.)

B. How is the tilt angle b determined for the tracking collector?

In this case, the tilt angle, b, changes as the sun moves across the sky, and is always set equal to q_z, the angle between the normal to the horizontal ground and the sun beam.

2. Consider the concentrating collector.

A. Define the concentration ratio, X.

X = concentration ratio = area of aperture of collector/area of receiver

B. Show how the maximum temperature of the receiver depends on the concentration ratio.

Our equation for the energy (per second) balance of the collector is:

Q_fluid = G_bcA_ara – esT_r⁴A_r

For maximum receiver temperature, no energy is deposited in the fluid (flowing through the receiver). Thus:

T_r = (G_bcA_ara/ esA_r)^1/4

or:

T_r ~ (A_a/A_r)^1/4 = X^1/4

C. What is the maximum possible value of the concentration ratio for a line-focus concentrating collector?

X_max = 215