Investigation of Solar Parabolic Trough Collector for Industrial Process Heating

Abstract

In India, the pursuit of shifting to renewable energy due to environmental reasons and economic has become essential for the country’s better future development. The industrial sector is consuming the highest share of energy from the total energy generation and majorly contributes to the cause of pollution from it. Low and medium temperature industries have almost two-thirds of the thermal energy requirement below 250°C. In this research, a solar parabolic trough collector (PTC) was selected to meet thermal energy demand for industrial process heating (IPH) applications. The major hindrance of solar collector technology is cost, which does not compete with the conventional technologies available in the market. While talking about PTC from a performance and cost point of view, two major components are selected in this study, i.e., absorber tube and tracking system. In PTC, an absorber tube is considered to be the heart of the system, and its performance degrades due to heat losses, which is directly dependent on its operating temperature. Generally, a glass envelope is used to reduce the heat losses from it. However, the limitation of its use is high persisting cost, maintaining a vacuum and, broken glass incurred every time. The selection of proper solar tracking depends on the type of solar applications, operating temperature, and cost. The cost of solar tracking is an additional cost to the total system, which can be considered one of the significant factors. Therefore, the objectives of this research was to design, develop an indigenous PTC absorber tube and low-cost single-axis tracking system to investigate the performance of PTC experimentally for IPH. The total experimental research work was carried out into three parts. In part-I, an experimental investigation was conducted to improve the bare absorber tube’s performance without using a glass cover tube. The addition of selective coating and insulation over the surface of the bare absorber tube was studied. Selective coating such as matt black paint, black nickel chrome, and black chrome was examined. Furthermore, glass wool insulation covering 25% and 50% of the absorber tube upper surface was also studied. Results from the experiments work show a significant effect of coating and insulation on the bare absorber tube performance. In part-II, a new cut tube absorber technique was designed, developed and tested experimentally in the conditioned room by optimizing the area with 45% cut on the upper portion of the tube. Also, the presence of coating and insulation over the cut tube absorber was examined. Heat transfer mediums such as water and sigma therm-K were used to study the heat losses for the working fluid having a temperature range below and above 100°C. Experimental results reveal that the coating and reduction in total surface area of the tube cause decrement in thermal heat losses by 16.13% in water and 10.13% in sigma therm-K. The addition of insulation would reduce heat losses by 7.33% in water and 33.43% in sigma therm-K compared to an uncut tube with coating. In part-III, a small size PTC system was designed and fabricated to determine stagnation temperature using a cut tube absorber and tracking system. A low-cost single-axis tracking system has been developed to boost the performance of PTC. The tracking system attached to PTC was designed to track the sun position at every 0.5◦ movement precisely with the help of a linear actuator and microcontroller (Arduino). The novel tube performance is studied with and without insulation on the upper part of the tube. Experiments were conducted using working fluid as sigma therm-K. Results declared from the experiments reveal a maximum stagnation temperature of fluid about 142.26°C with no insulation and 169.96°C with insulation on the upper part of the tube. The experimental results from this research work showed the huge potential of using a cut tube absorber and chronological tracking system in PTC for low and medium temperature IPH applications. Keywords: Coating, Cut tube absorber, Industrial process heating, Insulation, Parabolic trough collector, Solar, Tracking.