Showing papers on "Thermal efficiency published in 2017"

Wood–Graphene Oxide Composite for Highly Efficient Solar Steam Generation and Desalination

Abstract: Solar steam generation is a highly promising technology for harvesting solar energy, desalination and water purification. We introduce a novel bilayered structure composed of wood and graphene oxide (GO) for highly efficient solar steam generation. The GO layer deposited on the microporous wood provides broad optical absorption and high photothermal conversion resulting in rapid increase in the temperature at the liquid surface. On the other hand, wood serves as a thermal insulator to confine the photothermal heat to the evaporative surface and to facilitate the efficient transport of water from the bulk to the photothermally active space. Owing to the tailored bilayer structure and the optimal thermo-optical properties of the individual components, the wood–GO composite structure exhibited a solar thermal efficiency of ∼83% under simulated solar excitation at a power density of 12 kW/m2. The novel composite structure demonstrated here is highly scalable and cost-efficient, making it an attractive materia...

Solar-driven simultaneous steam production and electricity generation from salinity

Abstract: Solar-driven interfacial water evaporation, which concentrates solar heating at the water surface, has attracted increasing interest in pursuing highly efficient solar desalination. The rapid evaporation of water at the light absorber surface would induce a high concentration comparable with that of brine underlying the interface, which however has been paid much less attention and has never been proposed to produce electricity. Here in this work, we proved that, the theoretical real-time salinity power generated between the surface water and bulk seawater could be 12.5 W m−2 during steam production under one sun illumination. By employing a hybrid system based on a piece of carbon nanotube modified filter paper and a commercial Nafion membrane, we achieved a maximum solar thermal efficiency of up to 75% and derived extra electricity power of ∼1 W m−2 under one sun illumination. These results provide a novel avenue for blue energy utilization, demonstrating the potential for solar desalination and electricity generation under natural sunlight simultaneously.

Highly efficient electrocaloric cooling with electrostatic actuation

Abstract: Solid-state refrigeration offers potential advantages over traditional cooling systems, but few devices offer high specific cooling power with a high coefficient of performance (COP) and the ability to be applied directly to surfaces. We developed a cooling device with a high intrinsic thermodynamic efficiency using a flexible electrocaloric (EC) polymer film and an electrostatic actuation mechanism. Reversible electrostatic forces reduce parasitic power consumption and allow efficient heat transfer through good thermal contacts with the heat source or heat sink. The EC device produced a specific cooling power of 2.8 watts per gram and a COP of 13. The new cooling device is more efficient and compact than existing surface-conformable solid-state cooling technologies, opening a path to using the technology for a variety of practical applications.

Review on the management of RCCI engines

Abstract: RCCI (reactivity controlled compression ignition) engines are found to be capable of achieving higher thermal efficiency and ultra-low NOx and PM emissions. The reactivity controlled combustion is accomplished by creating reactivity stratification in the cylinder with the use of two fuels characterized by distinctly different cetane numbers. The low reactivity (i.e., low cetane number) fuel is firstly premixed with air and then charged into the cylinder through the intake manifold; later, the high reactivity (i.e., high cetane number) fuel is injected into the charged mixture through a direct injector. Subsequently, the reactivity stratification is formed. By strategically adjusting the ratio of two fuels and injection timings, the produced reactivity gradient is able to control the combustion phasing and mitigate the pressure rise rate, as well as the heat release rate. Alternatively, structural factors such as CR (compression ratio) and piston bowl geometries can also affect the combustion characteristics of RCCI. Besides the engine management, the fuels that could be utilized in RCCI engines are also crucial to determine the evaporation, mixing, and combustion processes. To gain a comprehensive knowledge on the state-of-the-art of RCCI combustion, detailed review on the management of RCCI engines has been presented in this paper. This review covers the up-to-date research progress of RCCI including the use of alternative fuels and cetane number improvers, and the effects of fuel ratio, different injection strategies, EGR rate, CR and bowl geometry on engine performance and emissions formation. Moreover, the controllability issues are addressed in this article.

Effects of physicochemical properties of biodiesel fuel blends with alcohol on diesel engine performance and exhaust emissions: A review

Abstract: In recent years, alternative fuel studies have been conducted thoroughly by researchers through their experimental work Depletion of fossil fuel raised the attention of researchers to investigate renewable energy sources such as biodiesel and alcohol There is a lack of literature review study on the viability of alcohol acting as additive in biodiesel-diesel fuel blends Thus, this review paper studies on the effects of various alcohol additives in biodiesel-diesel fuel blends on combustion behaviour, performance and emission characteristics of diesel engines The physicochemical properties of alcohol and biodiesel are rigorously discussed, in which they are the main factors in determining the quality of the blended fuel The aim of this paper is to identify the potential of alcohol fuel as an additive in the blended biodiesel and diesel fuel in correspond to the type of alcohol, blending ratio and engine operation conditions Wide range of results from previous research studies with different types of compression-ignition engine, different engine operation conditions and varieties of alcohol-biodiesel-diesel fuel blending ratios were collected in this literature review study Combustion behaviour such as coefficient of variations (COV), in-cylinder pressure, ignition delay, heat release rate and combustion duration are presented Low cetane number and high latent heat of vaporization of alcohol cause a longer ignition delay, produce higher rate of heat release and lower in-cylinder pressure when compared with that of diesel fuel Low density and viscosity of alcohol improve the spray characteristics and enhance air-fuel mixing process In terms of engine performance analysis, the presence of oxygen in alcohol fuel promotes a more complete combustion; hence, resulting in an increase of thermal efficiency In turn, emissions of carbon monoxide (CO), hydrocarbon (HC) and particulate matter (PM) are decreasing

An experimental analysis on the influence of fuel borne additives on the single cylinder diesel engine powered by Cymbopogon flexuosus biofuel

Abstract: Researchers all around the world are making strenuous efforts to find alternative fuel to ameliorate the problem of depletion of fossil fuel. we have identified a novel plant based biofuel, namely Cymbopogon flexuous biofuel. It has excellent fuel properties and is widely available in India and it seems to have the potential to make India self-sufficient in energy production. Cerium oxide nanoparticles were synthesized using sol–gel combustion methods. Their structural, morphological and elemental properties were studied with the help of XRD, SEM, TEM and EDS respectively. On volume basis, 20% raw Cymbopogon flexuous biofuel was blended with diesel fuel, and various proportions of Cerium oxide nanoparticles, namely C20-D80 + 10 ppm, C20-D80 + 20 ppm andC20-D80 + 30 ppm were prepared. The properties like density, kinematic viscosity, calorific value of the test fuel were measured as per ASTM standards and compared with those of diesel fuel. An experimental study of its performance, emission, and combustion behavior was conducted at varied load conditions at a constant speed of 1500 rpm. NO x and smoke emission was simultaneously reduced by 3% and 6.6% respectively as compared with biofuel blend. Due to higher thermal stability and oxygen buffer of Cerium oxide nanoparticle the brake thermal efficiency was higher by 4.76% and cylinder pressure and heat release rate was also higher.

Pumped thermal grid storage with heat exchange

Abstract: A thermal heat-pump grid storage technology is described based on closed-cycle Brayton engine transfers of heat from a cryogenic storage fluid to molten solar salt. Round-trip efficiency, computed as a function of turbomachinery polytropic efficiency and total heat exchanger steel mass, is found to be competitive with that of pumped hydroelectric storage. The cost per engine watt and cost per stored joule based are estimated based on the present-day prices of power gas turbines and market prices of steel and nitrate salt. Comparison is made with electrochemical and mechanical grid storage technologies.

Combined Heat and Power

Abstract: All combustion power plants operate inefficiently, with much of the fuel energy going to waste as heat. This heat can be exploited in a variety of ways, raising the overall efficiency of the power plant. Heat is used for district heating in some US and European cities but this has not proved widely popular. Some industries can also make use of steam for their processes. Wood and paper processing factories will often have their own power plant that supplies both heat and electricity. Combined heat and power plants are most effective when both electricity and heat are supplied to the same customers. Many types of power generation plant can be used for combined heat and power but coal-fired boilers, gas turbines and piston engine-based systems are the most common. Fuel cells can also be exploited. Sizing a combined heat and power plant correctly is the key to economic viability.