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Stalcup, Erik JamesNumerical Modeling of Upward Flame Spread and Burning of Wavy Thin Solids
Master of Sciences, Case Western Reserve University, EMC - Aerospace Engineering
Flame spread over solid fuels with simple geometries has been extensively studied in the past, but few have investigated the effects of complex fuel geometry. This study uses numerical modeling to analyze the flame spread and burning of wavy (corrugated) thin solids and the effect of varying the wave amplitude. Sensitivity to gas phase chemical kinetics is also analyzed. Fire Dynamics Simulator is utilized for modeling. The simulations are two-dimensional Direct Numerical Simulations including finite-rate combustion, first-order pyrolysis, and gray gas radiation. Changing the fuel structure configuration has a significant effect on all stages of flame spread. Corrugated samples exhibit flame shrinkage and break-up into flamelets, behavior not seen for flat samples. Increasing the corrugation amplitude increases the flame growth rate, decreases the burnout rate, and can suppress flamelet propagation after shrinkage. Faster kinetics result in slightly faster growth and more surviving flamelets. These results qualitatively agreement with experiments.

Committee:

James T'ien (Committee Chair); Joseph Prahl (Committee Member); Yasuhiro Kamotani (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

modeling;simulation;numerical modeling;combustion;computational combustion;direct numerical simulation;flame spread;burning;wavy;corrugated;fire dynamics simulator;FDS;fuel structure;fuel geometry;complex geometry;cardboard;

ZHANG, JIEHAINUMERICAL SIMULATIONS OF STEADY LOW-REYNOLDS-NUMBER FLOWS AND ENHANCED HEAT TRANSFER IN WAVY PLATE-FIN PASSAGES
PhD, University of Cincinnati, 2005, Engineering : Mechanical Engineering
Extended or finned surfaces are widely used in compact heat exchangers to reduce the thermal resistance of air- or gas-side flows. Besides increasing the effective heat transfer surface area, geometrically modified finned surfaces also improve the heat transfer coefficient by altering the flow field. Wavy plate-fin surfaces have such properties and promote relatively high thermal-hydraulic performance. They are also attractive for their simplicity of manufacture and ease of use in compact heat exchangers. The current study numerically investigates the fluid flow and enhanced convection heat transfer in two-dimensional and three-dimensional wavy plate-fin passages with sinusoidal wall corrugations in the low Reynolds number regime. Constant property, periodically fully developed, and laminar or low Reynolds number forced convection are considered. The governing equations of continuity, momentum, and energy are solved computationally using finite-volume techniques. The solution procedure is based on the SIMPLE algorithm and a non-orthogonal, non-uniform grid. The influences of fin geometry (fin spacing, fin height, fin amplitude and fin length) on the enhanced heat transfer and fluid flow behaviors are investigated. The simulation results for the velocity and temperature distributions, isothermal Fanning friction f, and Colburn factor j are presented and discussed. The complex flow patterns in the wavy-fin channel are characterized by re-circulating and/or helical swirl flows with periodic flow separation and reattachment. Two flow regimes can be classified based on these results, namely, (1) low-Re streamline-flow regime where viscous forces dominate, and (2) high-Re swirl-flow regime characterized by flow recirculation and/or helical vortices. Heat transfer enhancement is observed in the swirl flow regime along with an increased pressure drop penalty, as a consequence of the periodic thermal boundary-layer thinning, strong flow mixing, and periodic generation and dissipation of vortices or re-circulating cells. In the streamline-flow regime, the flow and heat transfer behavior are similar to that in straight flow channel, though an enhanced performance is obtained. Also, results of flow visualization experiment for a two-dimensional wavy flow channel are shown to agree well with the numerical results. Finally, the computational methodology is extended to illustrate the flow behaviors in out-of-phase wavy flow passages.

Committee:

Dr. Raj Manglik (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

Wavy plate-fin; enhanced heat transfer; numerical modeling and simulation

Ravipati, DeepakFREE CONVECTION ALONG A VERTICAL WAVY SURFACE IN A NANOFLUID
Master of Science in Mechanical Engineering, Cleveland State University, 2012, Fenn College of Engineering
The study of this paper is to introduce a boundary layer analysis for the fluid flow and heat transfer characteristics of an incompressible nanofluid along a vertical wavy surface in a nanofluid. The Resulting transformed governing equations are solved numerically by an implicit finite-difference scheme (Keller-Box method). The results are presented for the major parameters including the wave amplitude , buoyancy ratio parameter , Brownian motion parameter , Thermophoresis parameter and Lewis number . A systematic study on the effects of the various parameters of the local frication factor, surface heat transfer rate (Nusselt number) and mass transfer rate (Sherwood number) characteristics is carried out. The Obtained results are presented graphically.

Committee:

Rama Gorla, PhD (Committee Chair); Majid Rashidi, PhD (Committee Member); Asuquo Ebiana, PhD (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Keywords: Nanofluid; Free Convection and Wavy Surface.

KUNDU, JAYDEEPNUMERICAL INVESTIGATION OF LAMINAR FORCED CONVECTION IN TWO-DIMENSIONAL AND THREE-DIMENSIONAL SINUSOIDAL CORRUGATED DUCTS
MS, University of Cincinnati, 2001, Engineering : Mechanical Engineering
Single-phase, periodically developed, constant property, laminar forced convection in two-dimensional and three-dimensional sinusoidal corrugated ducts, which are maintained at uniform wall temperature or uniform heat flux, are considered. The governing differential equations for continuity, momentum, and energy transfer are solved computationally using finite-volume/finite-difference techniques, where the pressure term is handled by the SIMPLE algorithm. The computational grid is non-orthogonal and non-uniform, and it is generated algebraically. All the dependent variables are stored in a non-staggered manner. For the two-dimensional problem, numerical solutions are obtained for different corrugation aspect ratios (γ = 2 x amplitude/wavelength), plate spacing ratio (ε = plate separation/amplitude), flow rates (Re). For the three-dimensional problem, different cross-stream aspect ratios (α = plate separation/width) are also considered. In pure Poisuelle flow, the flow pattern does not change with Reynolds number in the laminar regime. The flow remains always attached to the channel walls and viscous forces balance the pressure forces. Whereas in corrugated ducts, the flow pattern changes drastically with Reynolds number and the flow gets separated at a critical Re. This is because the pressure distribution ceases to be linear and local variations of pressure cause flow to separate. The size of the separation region is seen to be a function of Re, aspect ratio and spacing ratio and it increases with increasing Re and aspect ratio. With increasing spacing ratio, however, it first increases and then starts to decrease after a critical spacing ratio is reached. This behavior is also seen in the friction factor and Nusselt Number results, which increase to peak values corresponding to the critical spacing ratio value, and then begin to decrease. The corrugations essentially lead to periodic separation of boundary layers, thereby resulting in high local heat fluxes (boundary layer thickness almost equal to 0) at regions of reattachment and high local wall shear stresses at regions opposite to the regions of separation. As such, depending upon the aspect ratio, spacing ratio and Re, the average heat transfer coefficient increases many fold compared to that in a parallel flat-plate channel. The concomitant friction factor penalty, however, also increases. While the transverse vortex structure formed due to separation of flow is perpendicular to the direction of the primary flow in a two-dimensional wavy channel, there is another component of vorticity along the direction of primary flow in addition to the transverse component that comes into play in three-dimensional flows. This longitudinal component of vorticity arises because of the introduction of viscosity by the side walls that stretch and bend the transverse vortex lines. The strength of these vortices increases with increasing Re and decreases with increasing wall separation. This cross-stream longitudinal recirculation further increases the overall heat transfer coefficient. Both friction factor and Nusselt number results are presented for different corrugation aspect ratios and spacing ratios in the two-dimensional case, as well as for different cross-stream aspect ratios in the three-dimensional case, for a wide range of flow conditions (50 < Re < 1000) that highlight the enhanced thermal-hydraulic behavior of corrugated channels.

Committee:

Dr. Raj M. Manglik (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

LAMINAR FLOWS; CORRUGATED DUCTS; THREE DIMENSIONAL FLOWS; SINUSOIDAL WAVY DUCTS