• Energy Research

Waste heat recovery and upgrading is an effective measure for facing the energy problems in the industrial sector. This could even be more impactful when combined/boosted with compatible renewable energy systems. The objective of the present work is the comparison of three different collector types coupled to an absorption heat transformer for industrial process heat production. The absorption heat transformer operates with LiBr/water as a working pair and aims to upgrade the heat with a thermochemical process to cover a wide range of different temperature needs in the industrial sector from 80 °C up to 160 °C. The novelty of the present work is based on the systematic investigation and comparison of three different solar thermal collectors innovatively feeding an absorption heat transformer. Simple flat plate collectors, advanced flat plate collectors, and evacuated tube collectors are the investigated solar technologies. The investigation is conducted with a developed model in the Engineering Equation Solver tool. For industrial process heat temperatures from 95 °C up to 120 °C, the simple flat plate collector is the best choice, for greater temperatures up to 140 °C, the advanced flat plate collector is the best solution, and for higher temperatures, the evacuated tube collector outperforms others. For a solar energy input of 80 kW in these cases, the process heat supply at 115 °C by the system using simple flat plate collectors is 11.01 kW, at 130 °C using advanced flat plate collectors is 13.11 kW, and at 150 °C with evacuated tube collectors is 14.12 kW. The respective exergy efficiency values of these systems are 3.43 %, 4.86 %, and 5.60 %, respectively.

Since the last decades, solar energy has been used worldwide to overcome foreign dependency on crude oil and to control the pollution due to a limited source of non-renewable energy. Evacuated tube solar collectors are the most suitable solar technology for producing useful heat in both low and medium temperature levels. Evacuated tube solar collector is capable of working in hot, mild, cloudy or cold climates where flat plate collector is not an option. The objective of this review paper is the detailed investigation of evacuated tube solar collectors having heat pipe and direct flow are reviewed. All the design parameters which influence the collector performance are investigated and discussed in this work. More specifically, the tracking system, the collector design, the mass flow rate, the optical design and the kind of the working fluid are the main studied parameters. Moreover, this work focuses on the latest developments and advances, providing a review of experimental and numerical studies reported. Lastly, this work presents the future ideas that can be carried out to improve the performance of evacuated tube solar collectors.

Abstract The objective of this work is to examine a transcritical CO2 refrigeration system coupled to a single-effect absorption chiller. The role of the absorption machine is to create a subcooling after the gas-cooler in order to increase the COP. The absorption system is fed by waste heat after the CO2 compressor and so there is not any need for any external energy source. The analysis is conducted with a validated numerical model which is developed in Engineering Equation Solver. The system is studied and optimized for different heat rejection temperatures from 35 °C up to 50 °C and for different refrigeration temperatures from -35 °C up to 5 °C. It is found that there is COP enhancement in all the operating scenarios and especially in the cases with higher heat-rejection temperature and lower refrigeration temperature. The mean COP enhancement is about 23.4% which is an important enhancement for designing more efficient systems.

Abstract The objective of this study is to analyze and optimize a solar assisted gas turbine system. Parabolic trough collectors are used in order to supply a part of the demanded heat input, reducing the natural gas consumption and leading to an environmental friendly system. Emphasis is given in the pressure losses in the collector field loop which reduce the pressure level in the turbine inlet, leading to lower electricity production. In the first part of this study, the gas turbine and the collector field are investigated separately and in the second part, the solar assisted gas turbine is investigated parametrically and it is optimized. In the optimization part, a multi-objective optimization is performed by setting as goals the minimization of the collector area, of the fuel consumption and of the inversed electricity production. The final results proved that 1050 collector modules lead to 0.3389 kg/s natural gas consumption and to electricity production equal to 14.81 MWel. This optimum solution leads to 64% fuel savings with a 2.8% penalty on the produced electricity. The system is analyzed in steady state conditions with the Engineering Equator Solver (EES).

Abstract Linear Fresnel reflector is one promising solar concentrating technology for medium and high temperatures (200–400 °C) because of its simple design and its low cost. However, the greatest drawback of this collector is the increased optical losses and thus the emphasis is usually given to this issue. In this direction, the objective of this work is the development of analytical expressions for the incident angle modifiers of a linear Fresnel reflector for the longitudinal and the transversal directions. The goal is to create a simple and accurate formula for all the possible solar angles ranges. The developed equations are based on reasonable assumptions and on the geometric analysis of a simple collector with flat primary mirrors. The developed equations are tested with literature data from other studies and from commercial collectors. It is found that the developed equations lead to accurate results with mean deviations up to 5%. The developed analytical expressions can be used for the quick calculation of the optical performance of a linear Fresnel reflector, as well as they can be used for the geometry optimization of the collector.

Abstract The objective of this paper is the investigation of the annual performance of a solar power plant with linear Fresnel reflectors in the El-Oued region at Algeria. The solar collectors produce water steam that feeds a turbine to produce electricity. The System Advisor Model (sam) tool is used for simulation. The mean net daily electricity production rate from 8:30 am to 5:30 pm is 48 MWe, and the respective annual production is 210,336 MWh/year. The mean daily optical efficiency of the solar field was close to 52%, while the mean thermal efficiency was about 39%. The net daily cycle efficiency is found to be 24%. The net capital cost of the examined system is $393 million, and the developer net present value is $47 million; the investor net present value is $15 million, the entire period of capital recovery is 11 years, and the levelized cost of electricity is 0.0382 $/kWh. The solar power plant leads to the yearly avoidance of 420,672 tons carbon dioxide emissions (operational cost savings of $6.1 million). Based on the obtained results, linear Fresnel reflectors can be used to achieve satisfying, energetic, financial, and environmental performance that can lead to sustainability.

Abstract The use of nanofluids in parabolic trough collectors is a promising technique for enhancing their performance. This study investigates the dispersion of CuO nanoparticles in Syltherm 800 (thermal oil) and in nitrate molten salt (60% NaNO3 – 40% KNO3). The objective of this work is to examine the thermal efficiency enhancement margin of the utilization of nanofluids for two usual working fluids (thermal oil and molten salt) as base fluids. Moreover, this work includes hydraulic analysis about the pressure losses and exergetic analysis in order to evaluate the total performance of the collector. The module of LS-2 parabolic trough collector is examined with a computational fluid dynamics program developed in SolidWorks Flow Simulation. The model accuracy is checked with thermal efficiency and flow criteria using literature results. The simulations are conducted for temperatures up to 650 K for oil cases and up to 850 K for molten salt cases. According to the final results, the use of oil-based nanofluids leads to thermal efficiency enhancement up to 0.76%, while the use of molten salt-based nanofluid up to 0.26% thermal efficiency enhancement. The Nusselt number enhancement is found up to 40% for Syltherm 800-CuO and up to 13% for molten salt-CuO.