Thermal Efficiency Evaluation of a Solar Thermal Steam Generating System Using Thermosiphon Technique with Parabolic Trough Collector

Abiem Louis Tersoo,Akoshile Clement Olufemi

doi:10.11648/j.jenr.20200901.14

Abstract

Parabolic trough solar collectors are the most widely used concentrators for solar thermal applications in the world. This is because very high temperatures of 150°C to 350°C can be attained with its use without any noticeable degradation in the performance of the collector. In this work, a parabolic trough collector (PTC) was designed using simple parabolic equations and constructed with locally sourced materials. The developed PTC was used to converge direct solar radiation to a heat receiver (a copper pipe enclosed in an evacuated glass tube) placed at the focal line of the trough to heat up the water in the pipe to steam. Natural circulation (thermosiphon) was employed to drive the water from the heat source to the heat sink (tank) with the difference in density as the driving force of the system. Temperature sensors were installed at different points of the solar thermal system to experimentally investigate temperature distribution within the system, hence thermal performance. A pressure sensor was also installed in the tank to measure the pressure within the system. The results obtained shows that the solar thermal system generated low-mid temperature steam of up to 105°C at a pressure of approximately 120 kPa on a day when the global solar radiation intensity attained a value of 1109.5 W/m2. A thermosiphon mass flow rate of up to 0.042 kg/s was also recorded through a constant orifice of 12 mm diameter. The instantaneous efficiency of the receiver reached 46.48%.

Highlights

Energy is a key factor for national development; as man’s activities, whether domestic or industrial depend largely on its availability and accessibility
The average temperatures and pressure distributions of the thermosiphon heat pipe parabolic trough collector (PTC) system for the two days examined are presented as a function of the time of the day in Figure 2
At the starting (a – b) stage, the receiver absorbs solar radiation reflected from the concentrator to converge on it, and a rise in its average temperature and with time that of the ascending pipe (Tout) as heat was transferred to the water in the pipe was observed

Summary

Introduction

Energy is a key factor for national development; as man’s activities, whether domestic or industrial depend largely on its availability and accessibility. There are several applications of solar thermal systems in the world that makes use of parabolic trough collectors (PTCs) The largest of such systems are the Southern California power plants, Solar Electric Generating Systems (SEGS) plants with a total installed capacity of 354 MW, the 280 MW Solana Generating Station with molten salt heat storage in Arizona, the 250 MW Genesis Solar Energy Project located in the Mojave Desert in California, the Spanish 200 MW Solaben Solar Power Station, and the 150 MW Andasol 1 solar power station, located near Guadix in Andalusia, Spain. Their suggested that an optimization on thermal insulation and collector exit design would increase the system’s efficiency and reliability [24] These works show that the generation of steam through free convective (or natural circulation) solar heat pipe have several advantages (simple to construct, widely adjustable, easier to control and high heat transfer ability even at low temperature differences etc.) when compared with forced circulation system.

Experimental Design

Thermal Characteristic of Thermosiphon Heat Pipe PTC System

Thermal Efficiency of Thermosiphonic Heat Pipe PTC System

Conclusion