Experimental investigation of the bending of absorber tube of solar parabolic trough concentrator and comparison with analytical results

The distribution of the solar flux on the circumference of the absorber tube of the parabolic trough concentrator is non-uniform. It leads to circumferential non-uniformity in the tube temperature which causes bending and stresses in the absorber tube. Thus, the absorber tube gets deflected from the focal line of the trough which can damage the glass cover. In the current work, an experimental set-up has been described which is created to achieve a non-uniform distribution of the temperature on the circumference of the tube (using electrical heating) and to measure the corresponding deflection of the tube due to bending (in the vertical plane passing through the central axis of the tube). The deflection of the tube has also been calculated using analytical equations (derived in the previous work) and compared with the measurements. The results show that the analytical calculations differ from the measurements within the range of -0.26 mm to +0.50 mm (i.e. -15.4% to 16.9%). For the chosen tube dimensions and the maximum circumferential temperature difference of 30 °C, the maximum deflection due to bending is 3.2 mm. It decreases to 2.6 mm for the maximum circumferential temperature difference of 22 °C. The bending (due to circumferential temperature gradient) between 1st and 2nd support is downwards. Between 2nd and 3rd support, it is upwards. It is again downwards for the portion of the tube lying between 3rd and 4th support. The same trend of bending has been found out by analytical calculations.