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Developing nanogenerators (NGs) is achieved by exploiting the piezoelectric, triboelectric, and pyroelectric effects of both organic and inorganic materials. Many exhibit beneficial electrical properties (dielectric, conductive, or insulating) or have surfaces that are polarizable upon friction or physical contact. Recently, biomass-derived materials and recycled materials, whose electrical activity can be induced, are explored for application in the design of more sustainable, cost-effective, biodegradable, disposable NGs, and have demonstrated a wide range of output (microenergy) power densities. Among them, cellulose, the most abundant biopolymer, is found to offer excellent opportunities for designing and manufacturing NGs with multifunctional capacities. Cellulose can be derived into varied forms with multifunctionalities and physical morphologies. This account provides an overview of how cellulose is utilized in creating NGs based on piezoelectric, triboelectric, and pyroelectric effects. Because the mechanical properties of cellulose are tunable, current research trends on NGs originate with the triboelectric effect. The discussion here focuses on design, fabrication methods, achievable electrical power output, and combinations with other materials and devices. Challenges in efficient fabrication and consistent power densities, and opportunities for integrating different technologies and developing more sustainable (in terms of economic, environmental, and ecological) nature–human–machine interfacial devices are also discussed. © 2021 Wiley-VCH GmbH

Despite appearing as a promising technology for distributed generation, micro Gas Turbines (mGTs) have not yet managed to penetrate the small-scale Combined Heat and Power (CHP) market. The energy efficiency of mGTs amounts to 80% whenever both heat and electricity are required. However, when the heat demand is low, the hot exhaust gases have to be directly blown off and the electrical efficiency of the unit (∼30%) is not high enough to sustain profitable operation. Water injection, achieved when transforming the mGT into a micro Humid Air Turbine (mHAT), allows making use of the exhaust gas heat in such cases, thus increasing electrical efficiency of the technology and improving its feasibility. Although the enhanced performance of the mHAT cycle has been thoroughly investigated from a numerical point of view, results regarding the experimental behaviour of this technology remain scarce. In this paper, we present the experimental characterisation of the mHAT located at Vrije Universiteit Brussel (VUB) which is based on the T100 mGT equipped with a spray saturation tower. These are the first experimental results of such an engine working at nominal load with water injection. In addition, the control system of the unit has been modified so that it can operate either at constant electrical power output (the default setting) or at constant rotational speed. The latter option allowed better assessing the effect of water injection. Experimental results demonstrate the patent benefits of water injection on mGT performance: at fixed rotational speed, the power output of the mHAT increases by more than 30% while fuel consumption rises only by 11%. Overall, the electrical efficiency in wet operation increases by up to 4.2% absolute points. © 2017 Elsevier Ltd

Introduction of water in a micro Gas Turbine (mGT) has proven to be a very effective method to recover waste heat into the cycle, since it increases the mGT electrical efficiency significantly. Different routes exist for water introduction in the mGT cycle. Classical routes, like injection of steam/preheated water or the micro Humid Air Turbine (mHAT) concept, where water is introduced in the cycle by means of a saturation tower, have shown to have high potential. However none of the previously mentioned cycles exploits the full thermodynamic potential for waste heat recovery through water introduction. More advanced humidified Gas Turbine (GT) cycles have been proposed and studied for large scale GTs. So far, none of these concepts have been applied on mGT scale, despite their high potential. In this paper, we study the impact of these different, more advanced, humidified GT cycle concepts on the mGT performance. The different selected cycles – next to the classical steam injection or injection of (preheated) liquid water in the recuperated cycle and the mHAT – were: micro Humid Air Turbine Plus (mHAT+), Advanced Humid Air Turbine (AHAT) and the REgenerative EVAPoration (REVAP®) cycle concept. The impact of these concepts on the mGT cycle performance has been studied on the Turbec T100 mGT. Simulations indicated that humidifying the air of the mGT has a significant beneficial effect on cycle performance due to the increased waste heat recovery, resulting in a higher electrical power output (at constant rotational speed) or reduced fuel consumption (at constant power output), both leading to an increased electrical efficiency. Depending on the different cycle layout used, more or less waste heat could be recovered from the exhaust gas. The REVAP® concept with feedwater preheat was identified as the optimal cycle layout within the selected options. By applying this concept to the Turbec T100, most waste heat could be recovered, achieving the highest electrical effici

Despite the potential of micro Gas Turbines (mGTs) for Combined Heat and Power (CHP), this technology still poses limitations that curb its widespread adoption, especially for applications with a variable heat demand. In fact, whenever the user heat demand is low, mGTs are generally shut down. Otherwise, the high temperature exhaust gases have to be blown off and the resulting electrical efficiency is not high enough to sustain a profitable operation. If, instead of released, the heat in the exhaust gases is re-inserted in the cycle by injecting hot water and transforming the mGT into a micro Humid Air Turbine (mHAT) the electrical efficiency can be increased during periods of reduced heat demand, thus improving the economics of the technology. Although the enhanced performance of the mHAT cycle has been thoroughly investigated from a numerical point of view, results regarding the experimental behaviour of this technology remain scarce. In this paper, we present the experimental characterisation of the mHAT located at the Vrije Universiteit Brussel (VUB): based on the T100 mGT and equipped with a spray saturation tower. These are the first experimental results of such an engine working at nominal load with water injection. In addi tion, the control system of the unit has been modified so that it can operate either at constant electrical power output (the default setting) or at constant rotational speed. The latter option allowed to better assess the effect of water injection. Eperimental results demonstrate the patent benefits of water injection on mGT performance: At fixed rotational speed, the power output of the mHAT increases by more than 30%while the fuel consumption rises only by 11%. Overall, the electrical efficiency in wet operation increases by up to 4:2% absolute points. Future work will involve further optimising the current facility to reduce pressure losses in the air and water circuits. In addition, we will carry out transient simulations and experime

Externally fired gas turbines open the possibility of using fuels of lower quality than conventional gas turbines and internal combustion engines. This is because in externally fired gas turbines, the flue gases heat the compressed air in a high temperature heat exchanger. This heat exchanger can more easily deal with contaminants present in the flue gases. In this regard, the configuration of externally fired gas turbines represents an interesting option for biomass gasification gas. The contaminants and low heating value (LHV) of this fuel have made it difficult to find a conversion technology for heat and power generation. For this reason, it is important to study the influence of biomass derived gas as fuel on the performance of this system and consider the effects of the contaminants in the high temperature heat exchanger. This is studied in this work through simulations using Aspen Plus and Matlab. The test data of an externally fired micro gas turbine prototype was used to validate the simulation. The fuel considered was biomass gasification gas with varying concentrations of benzene 100, 10 and 1 g/Nm3 (hereafter named m100, m10, and m1 respectively). Additionally, mixtures of biomass derived gas and methane were studied for 10 and 50% of the thermal power of the combustor. The fuel inlet temperature to the combustor varied from 150 °C to 750 °C in order to represent the fuel gas after removal of particles by a cyclone and a filter. The results showed that the electrical power output increases when high fuel inlet temperatures to the combustor are used. Additionally, although it would be expected that fuels with higher LHV (lower heating value) show higher temperatures and higher output power, this does not always occur because of the composition of the fuels and their respective flue gas temperatures. The addition of methane does not have a large effect on the electrical power output. For a fixed temperature limit in the heat exchanger, the composition of t, QC 20150629. Updated from manuscript to article in journal.

Commonly, the thermal behavior of solar cell modules is calculated with analytical approaches using non wavelength-dependent optical data. Here, we employ ray tracing of entire solar modules at wavelengths of 300-2500 nm to calculate heat sources. Subsequently, finite element method (FEM) simulations are used to solve the semiconductor equations coupled with the thermal conduction, thermal convection, and thermal radiation equations. The implemented model is validated with measurements from an outdoor test over the period of an entire year. Our ray tracing analysis of different solar modules under the AM.15G spectrum shows that, for a standard module about 18.9% of the sun's intensity becomes parasitically absorbed. A loss analysis shows that the biggest parasitic heat source is the cell's full-area rear side metallization. We hence propose the use of a SiNx layer as rear side mirror to reduce the parasitic absorption to 11.7%. This change can lead to a 3.2 °C lower module operating temperature, which results in an about 5 W higher electrical power output when considering a typical 260 W module.

Commonly, the thermal behavior of solar cell modules is calculated with analytical approaches using non wavelength-dependent optical data. Here, we employ ray tracing of entire solar modules at wavelengths of 300-2500 nm to calculate heat sources. Subsequently, finite element method (FEM) simulations are used to solve the semiconductor equations coupled with the thermal conduction, thermal convection, and thermal radiation equations. The implemented model is validated with measurements from an outdoor test over the period of an entire year. Our ray tracing analysis of different solar modules under the AM.15G spectrum shows that, for a standard module about 18.9% of the sun's intensity becomes parasitically absorbed. A loss analysis shows that the biggest parasitic heat source is the cell's full-area rear side metallization. We hence propose the use of a SiNx layer as rear side mirror to reduce the parasitic absorption to 11.7%. This change can lead to a 3.2 °C lower module operating temperature, which results in an about 5 W higher electrical power output when considering a typical 260 W module.