In order to be consisting in the use of terms, we will use the phrase ‘concentrating collector’ to denote the whole system. The term ‘concentrator’ will be used only for the optical subsystem which directs the solar radiation on to the absorber, while the term ‘Receiver’ will normally be used to donate the subsystem consisting of the absorber, it cover and accessories.
We will define four terms: Aperture, Area Concentration Ration, Intercept Factor and Acceptance.
(1) APERTURE (W): Aperture is the plane opening of the concentrator through which the solar radiation passes. For a cylindrical or linear concentrator it is characterised by the width, while for a surface of revolution, it is characterised by the diameter of the opening.
(2) AREA CONCENTRATION RATIO (C): It is the ratio of the effective area of the aperture to the surface area of the absorber. Values of the concentration ratio vary from unity (which is the limiting case for a flat plate collector) to a few thousand for a paraboloid dish. This quantity is also referred to as the Geometric Concentration Ratio or simply concentration Ratio.
(3) INTERCEPT FACTOR(γ): The intercept factor (γ) is the fraction of the radiation, which is referred or refracted from the concentrator and is incident on the absorber. The value of the intercept factor is generally close to unity.
(4) ACCEPTANCE ANGLE (2qa): It is the angle over which beam radiation may deviate from the normal to the aperture plane and yet reach the absorber. Collectors with large acceptance angles require only occasional adjustments, while collectors with small acceptance angles have to be adjusted continuously.
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