An internal cusp reflector for an evacuated tubular heat pipe solar thermal collector

A Review of the Compound Parabolic Concentrator (CPC) with a Tubular Absorber

“…There are mainly two types of curves for the tubular absorber CPC (Figure 1), in which the involute segment is similar and the curved segment is different. Winston [4] and Ortabasi et al [8] proposed the first type of curve and derived its curve formula (Figure 1a). Another type uses a flat CPC curve by replacing the flat receiver with a tubular absorber and an involute segment.…”

“…The profile curve of a tubular absorber CPC contains an involute segment and a curve segment. The coordinates of the CPC curve are given by Equations (2) and 3 [8].…”

“…Mcintire proposed a W-shaped curve instead of the sharp corner of the reflector to avoid gap loss, but this reduced the concentration ratio by 15% [10,11]. Ortabasi [8] proposed another method to form a gap in the CPC by changing the starting point of the involute. A CPC reflects all light within the maximum half acceptance angle θ max to the receiver, where θ max is defined as the maximum angle between the incident light, which can reach the receiver, and the axis of symmetry of the CPC.…”

“…Mcintire proposed a W-shaped curve instead of the sharp corner of the reflector to avoid gap loss, but this reduced the concentration ratio by 15% [10,11]. Ortabasi [8] proposed another method to form a gap in the CPC by changing the starting point of the involute. Wang et al [27] proposed a tubular absorber CPC with a V-shaped profile at the bottom of the reflector based on the edge-ray principle (Figures 3 and 4).…”

“…The basic design of the CPC employed a flat absorber, but a circular tube groove was later proposed [3]. Different additions to the original CPC design have been proposed such as a secondary compound parabolic reflection [5], an optimal gap between the concentrator and receiver [6], non-imaging condensers [7], internal cusp reflectors with a heat pipe [8], truncated CPCs [9], and W-shaped and multi V-shaped surfaces [10,11].…”