Accepted Manuscripts

Review Article  
David A. Shifler
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038037
It has been conjectured that if sulfur in fuel is removed, engine materials will cease to experience attack from hot corrosion, since this sulfur has been viewed as the primary cause of hot corrosion and sulfidation. Historically, hot corrosion has been defined as an accelerated degradation process that generally involves deposition of corrosive species (e.g., sulfates) from the surrounding environment (e.g., combustion gas) onto the surface of hot components, resulting in destruction of the protective oxide scale. Most papers in the literature, since the 1970s, consider sodium sulfate salt as the single specie contributing to hot corrosion. Recent Navy standards for Navy F-76 and similar fuels have dropped the sulfur content down to 15 parts per million (ppm). Most observers believe that the removal of sulfur will end hot corrosion events in the Fleet. However, the deposit chemistry influencing hot corrosion is known to be much more complex consisting of multiple sulfates and silicates. Sulfur species may still enter the combustion chamber via ship's air intake, which may include seawater entrained in the air. In addition to sodium sulfate, seawater contains magnesium, calcium and potassium salts, and atmospheric contaminants that may contribute to hot corrosion. This paper will cover some of the revised understanding of hot corrosion and consider other possible contaminants that could further complicate a full understanding of hot corrosion.
TOPICS: Corrosion, Sulfur, Seawater, Sodium, Navy, Fuels, Engines, Combustion gases, Combustion chambers, Potassium, Chemistry, Magnesium (Metal)
Klaus Brun, Rainer Kurz and Sarah Simons
J. Eng. Gas Turbines Power   doi: 10.1115/1.4034314
Pressure pulsations into a centrifugal compressor can move its operating point into surge. This is concerning in pipeline stations where centrifugal compressors operate in series/parallel with reciprocating compressors. Sparks (1983), Kurz et al., (2006), and Brun et al., (2014) provided predictions on the impact of periodic pressure pulsation on the behavior of a centrifugal compressor. This interaction is known as the “Compressor Dynamic Response” (CDR) theory. Although the CDR describes the impact of the nearby piping system on the compressor surge and pulsation amplification, it has limited usefulness as a quantitative analysis tool, due to the lack of prediction tools and test data for comparison. Testing of compressor mixed operation was performed in an air loop to quantify the impact of periodic pressure pulsation from a reciprocating compressor on the surge margin of a centrifugal compressor. This data was utilized to validate predictions from Sparks' CDR theory and Brun's numerical approach. A 50 hp single-stage, double-acting reciprocating compressor provided inlet pulsations into a two-stage 700 hp centrifugal compressor. Tests were performed over a range of pulsation excitation amplitudes, frequencies, and pipe geometry variations to determine the impact of piping impedance and resonance responses. Results provided clear evidence that pulsations can reduce the surge margin of centrifugal compressors and that geometry of the piping system immediately upstream and downstream of a centrifugal compressor will have an impact on the surge margin reduction. Surge margin reductions of <30% were observed for high centrifugal compressor inlet suction pulsation.
TOPICS: Compressors, Surges, Pressure, Pipes, Geometry, Piping systems, Testing, Dynamic response, Suction, Pipelines, Excitation, Resonance
shilpi agarwal, Puneet Rana and B. S. Bhadauria
J. Eng. Gas Turbines Power   doi: 10.1115/1.4028491
In this paper, we study the effect of local thermal non-equilibrium on the linear thermal instability in a horizontal layer of a Newtonian nanofluid. The nanofluid layer incorporates the effect of Brownian motion along with thermophoresis. A two-temperature model has been used for the effect of local thermal non-equilibrium among the particle and fluid phases. The linear stability is based on normal mode technique and for nonlinear analysis, a minimal representation of the truncated Fourier series analysis involving only two terms has been used. We observe that for linear instability, the value of Rayleigh number can be increased by a substantial amount on considering a bottom heavy suspension of nano particles. The effect of various parameters on Rayleigh number has been presented graphically. A weak nonlinear theory based on the truncated representation of Fourier series method has been used to find the concentration and the thermal Nusselt numbers. The behavior of the concentration and thermal Nusselt numbers is also investigated by solving the finite amplitude equations using a numerical method.
TOPICS: Equilibrium (Physics), Nanofluids, Rayleigh-Benard convection, Fourier series, Rayleigh number, Nanoparticles, Numerical analysis, Stability, Temperature, Fluids, Particulate matter, Brownian motion
Corey E. Clifford and Mark Kimber
J. Eng. Gas Turbines Power   doi: 10.1115/1.4028492
Natural convection heat transfer from a horizontal cylinder is of importance in a large number of applications. Although the topic has a rich history for free cylinders, maximizing the free convective cooling through the introduction of sidewalls and creation of a chimney effect is considerably less studied. In this study, a numerical model of a heated horizontal cylinder confined between two, vertical adiabatic walls is employed to evaluate the natural convective heat transfer. Two different treatments of the cylinder surface are investigated: constant temperature (isothermal) and constant surface heat flux (isoflux). To quantify the effect of wall distance on the effective heat transfer from the cylinder surface, 18 different confinement ratios are selected in varying increments from 1.125 to 18.0. All of these geometrical configurations are evaluated at seven distinct Rayleigh numbers ranging from 102 to 105. Maximum values of the surface-averaged Nusselt number are observed at an optimum confinement ratio for each analyzed Rayleigh number. Relative to the pseudo-unconfined cylinder at the largest confinement ratio, a 74.2% improvement in the heat transfer from an isothermal cylinder surface is observed at the optimum wall spacing for the highest analyzed Rayleigh number. An analogous improvement of 60.9% is determined for the same conditions with a constant heat flux surface. Several correlations are proposed to evaluate the optimal confinement ratio and the effective rate of heat transfer at that optimal confinement level for both thermal boundary conditions. One of the main application targets for this work is spent nuclear fuel, which after removal from the reactor core is placed in wet storage and then later transferred to cylindrical dry storage canisters. In light of enhanced safety, many are proposing to decrease the amount of time the fuel spends in wet storage conditions. The current study helps to establish a fundamental understanding of the buoyancy-induced flows around these dry cask storage canisters to address the anticipated needs from an accelerated fuel transfer program.
TOPICS: Heat, Natural convection, Cylinders, Storage, Heat transfer, Rayleigh number, Heat flux, Fuels, Safety, Computer simulation, Cooling, Temperature, Flow (Dynamics), Buoyancy, Spent nuclear fuels, Convection, Boundary-value problems

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