There has been a recent surge in interest for Tesla turbines used in renewable energy applications such as power extraction from low-quality steam generated from geothermal or concentrated solar sources as well as unfiltered particle-laden biomass combustion products. High interest in these bladeless turbines motives renewed theoretical and experimental study. Despite this renewed interest, no systematic Tesla turbine design process based in foundational theory has been published in the peer reviewed engineering literature. A design process is thus presented which is flexible, allowing an engineering designer to select and address goals beyond simply maximizing turbine output power. This process is demonstrated by designing a Tesla turbine where Reynolds number can be easily varied while holding all other parameters fixed. Tesla turbines are extremely sensitive to inter-disk spacing. It is therefore desirable to design the experiment to avoid turbine disassembly/reassembly between tests; this assures identical disk spacing and other parameters for all tests. It is also desirable to maintain similar working fluid mass flow rate through the turbine in all tests to minimize influence of losses at the nozzle impacting shaft power output differently across experiments. Variation in Reynolds number over more than two orders of magnitude is achieved by creating a set of two-component working fluid mixtures of water and corn syrup. Increasing mixture mass fraction of corn syrup achieves increased working fluid viscosity but only small increase in density with a corresponding decrease in working fluid Reynolds number. The overall design goal is to create a turbine that allows modulating Reynolds number impact on Tesla turbine performance to be evaluated experimentally. The secondary goal is to size the turbine to maximize sensitivity to changes in Reynolds number to make experimental measurement easier. The presented example design process results in a Tesla turbine with 8-cm-outer-diameter and 4-cm-inner-diameter disks. The turbine will be able to access a range of Reynolds numbers from 0.49 < Re m < 99.50. This range represents a Reynolds number ratio of Re m,max /Re m,min = 202.8, more than two orders of magnitude and spanning the lower part of the laminar range. The turbine’s expected power output will be Ẇ = 0.47 Watts with a delivered torque of 0.024 mN-m at a rotation rate of ω max = 1197 rev/min. Combining the analytical equations underpinning the design process with similarity arguments, it is shown that shrinking the Tesla turbine’s physical scale drives the Reynolds number toward 0. The resulting velocity difference between the working fluid and the turbine disks gets driven toward infinity, which makes momentum transfer and the resulting turbine efficiency extremely high. In other words, unlike conventional turbines whose efficiency drops as they are scaled down, the performance of Tesla turbines will increase as they are made smaller. Finally, it is shown through similarity scaling arguments that the 8-cm-diameter turbine resulting from the design process of this paper and running liquid Ethylene Glycol working fluid can be used to evaluate and approximate the performance of a 3-mm-diameter Tesla turbine powered by products of combustion in air.

The combustion characteristics of single fuel droplets of soybean oil (SBO) and butanol binary blends simply mixed by volume were experimentally examined. The droplets were supported at an intersection of microfibers in a 100°C combustion chamber at atmospheric pressure in normal gravity. Ignition was achieved via a hot wire igniter. Ignition characteristics and burning behaviors including burning to completion, burning with microexplosion and incomplete combustion were analyzed for initial concentrations ranging from 25–75% butanol. Droplet size and temperature measurements were analyzed throughout the droplet lifetimes. Relative concentrations prior and during combustion were estimated. Temperature measurements at ignition and above the burning droplet were analyzed. The addition of butanol significantly lowered the droplet ignition temperature. All mixtures studied ignited similarly to pure butanol droplets. The results showed consistency with closed-cup flashpoint temperatures of butanol-soybean oil blends. A three-staged burn including a microexplosion was observed for all mixed droplets, which burned completely. The disruptive burning proved to be a result of a diffusion limited gasification mechanism that has been previously linked to bi-component droplets with high volatility differentials. Microexplosions occur as a result of homogeneous nucleation due to superheating of the more volatile component trapped within the droplet at flame shrinkage. Results show that more butanol is burned in the first stage for Bu75 droplets resulting in microexplosions occurring late in the combustion process. For droplets of near equal initial concentrations, the microexplosions occur earlier resulting in less fuel burned in the first stage of combustion and therefore higher concentrations of butanol trapped within the droplet at flame shrinkage. Consequently these mixtures experience more microexplosions and at a greater intensity. The reduced tendency for Bu75 droplets to experience microexplosions suggest that the maximum droplet surface temperature may be depressed compared to droplets of near equal concentrations reducing the possibility for superheating of the droplet interior. Blends of near equal concentrations by volume proved to exhibit the most favorable combustion characteristics. Bu40 exhibited the most violent microexplosions of all mixtures studied.

Kinetic analysis is essential for chemical reactor modeling. This study proposes a methodology to use available kinetic analysis methodologies, including conventional (modelistic) graphical representation, isoconversional (model free), models based on first principles and reduced time scale analysis (Sharp and Hancock procedure) to predict the kinetics of an investigated reaction. Even though these methods have some limitations, a methodology comprised of combining their results can help in determining the kinetic parameters for reaction. The isoconversional approach can be used to determine the activation energy without the need of using a reaction model. The modelistic graphical representation can aid is determining the group (i.e. diffusion, first order, phase boundary or nucleation) to which the reaction generally belongs. The reduced time scale analysis can guide in isolating the reaction kinetics in the early stages of the reaction when the conversion ranges between 0.15 and 0.5. This proposed methodology uses the various methods and applies them to experimental data for high temperature reactions in fluidized bed reactors. Particular attention is given to steam driven iron oxidation kinetics for hydrogen production. When only the modelistic approach is used, the activation energy computed using the selected models varies from 59–183 kJ/mol, depending on the model used. However, by combining the predictive capabilities of various approaches discussed in this study, the activation energy range narrows to 80–147 kJ/mol. It is also shown that the iron oxidation with steam under the studied conditions can be described by a combination of two models. The early stage of the reaction is represented by either a contracting volume or first order model. Later stages of reaction can be described by either a contracting volume, first order or 3-D diffusion model. In addition, when analyzing reaction kinetics using a fundamental approach, it is observed that the fluidized bed oxidation reaction of iron with pure steam can be best represented by a combination of two mechanisms, namely shrinking sphere surface area and diffusion controlled mechanisms and the estimated activation energy is 103 kJ/mol.

Syngas production via a two-step H 2 O/CO 2 -splitting thermochemical cycle based on FeO/Fe 3 O 4 redox reactions is considered using highly concentrated solar process heat. The closed cycle consists of: 1) the solar-driven endothermic dissociation of Fe 3 O 4 to FeO; 2) the non-solar exothermic simultaneous reduction of CO 2 and H 2 O with FeO to CO and H 2 and the initial metal oxide; the latter is recycled to the first step. The second step was experimentally investigated by thermogravimetry for reactions with FeO in the range 973–1273 K and CO 2 /H 2 O concentrations of 15–75%. The reaction mechanism was characterized by an initial fast interface-controlled regime followed by a slower diffusion-controlled regime. A rate law of Langmuir-Hinshelwood type was formulated to describe the competitiveness of the reaction based on atomic oxygen exchange on active sites, and the corresponding Arrhenius kinetic parameters were determined by applying a shrinking core model.

Adverse environmental effects resulting from fossil fuel usage as well as foreseeable conventional energy depletion lead to the exploration of alternative fuel materials especially the renewable ones. In this work, characterization of synthetic fuel material formed by pelletization of Jatropha residue (physic nut) using glycerol waste as a binder was carried out in order to investigate the feasibility of utilizing these waste materials as another renewable energy source. Both wastes are by products from biodiesel manufacturing process. Synthetic fuel materials of Jatropha residue mixed with 0–50% glycerol waste were formed to length of about 11 mm and diameter of about 13 mm under pressure of 7 MPa in a hydraulic press. Maximum compressive stress (2.52×10 5 N/m 2 ) of the fuel pellet occurred at 10% glycerol waste. Thermal conversion characteristic of solid fuel was studied by using single particle reactivity testing scheme at temperature of 500–900°C under partial oxidation atmosphere. In general, higher glycerol content in solid fuel as well as oxygen concentration in reacting gas resulted in greater decomposition rate from 0.006–0.110 g/sec. Burning started with a relative short drying phase, followed with a longer pyrolysis time and thereafter the dominated char combustion time which took around 35–57% of total conversion time. The average total conversion time varied from 26 to 288 sec, depended mainly on reaction temperature. Higher glycerol content resulted in char with lower density and higher shrinkage with greater porosity. Greatest changes in pellet diameter, height, and density of 75.6%, 89.2%, and 91.5%, respectively, were exhibited at 5% oxygen atmosphere and 900°C. The results suggested that Jatropha residue mixed with glycerol is suitable for utilization as quality solid fuel.

One of the most important steps in the wet limestone-gypsum flue gas desulphurization (WFGD) process is CaCO 3 dissolution, which provides the dissolved alkalinity necessary for SO 2 absorption. Accurately evaluating the CaCO 3 dissolution rate is important in the design and efficient operation of WFGD plants. In the present work, the dissolution of limestone from different sources in South Africa has been studied in a pH-stat apparatus under conditions similar to those encountered in wet FGD processes. The influence of various parameters such as the reaction temperature (30 ≤ T ≤ 70°C), CaCO 3 particle size (25 ≤ dp ≤ 63μm), solution acidity (4 ≤ pH ≤ 6), and chemical composition were studied in order to determine the kinetics of CaCO 3 dissolution. The results obtained indicate that the dissolution rate increased with a decrease in particle size and an increase in temperature. The dissolution curves were evaluated in order to test the shrinking core model for fluid–solid systems. The analysis indicated that the dissolution of CaCO 3 was controlled by chemical reaction, i.e. 1 − (1 − X ) 1/3 = kt .