Effect of Reynolds Number on Deposition in Fuels Flowing Over Heated Surfaces

2013 ◽  
Author(s):  
Clifford Moses
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Chemical Reactions ◽  
Initial Conditions ◽  
The Other ◽  
Heat Transfer Analysis ◽  
Surface Deposition ◽  
Conflicting Evidence ◽  
Increasing Demand ◽  
The One

An increasing demand is being put on the fuel as a heat sink in modern aircraft. In the end, the fuel flows through the atomizer which on the one hand is the hottest part of its thermal history, but on the other hand the most critical for resisting deposition. Most studies have concentrated on the chemistry of deposition, and in recent years there have been modeling efforts. Deposition is really the end product of a coupling between heat transfer to the fuel, chemical reactions to form insoluble gums, followed by the transport of these gums to the surface to form deposits. There is conflicting evidence and theory in the literature concerning the effect of turbulence on deposition, i.e., whether deposition increases or decreases with increasing Reynolds number. This paper demonstrates through a heat transfer analysis that the effect of Reynolds number depends upon the boundary/initial conditions. If the flow is heated from the surface, deposition decreases with increasing Reynolds number; however, for isothermal flows, i.e., preheated, deposition will increase with Reynolds number.

Effect of Reynolds Number on Deposition in Fuels Flowing Over Heated Surfaces

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
Clifford Moses
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Chemical Reactions ◽  
Thermal History ◽  
Initial Conditions ◽  
Heat Transfer Analysis ◽  
Surface Deposition ◽  
Conflicting Evidence ◽  
History Of ◽  
Increasing Demand

An increasing demand is being put on the fuel as a heat sink in modern aircraft. In the end, the fuel flows through the atomizer, which is both the hottest part in the thermal history of the fuel and the most critical for resisting deposition. Most studies have concentrated on the chemistry of deposition and in recent years there have been modeling efforts. Deposition is really the end product of a coupling between heat transfer to the fuel, chemical reactions to form insoluble gums, followed by the transport of these gums to the surface to form deposits. There is conflicting evidence and theory in the literature concerning the effect of turbulence on deposition, i.e., whether deposition increases or decreases with increasing Reynolds number. This paper demonstrates, through a heat transfer analysis, that the effect of the Reynolds number depends upon the boundary/initial conditions. If the flow is heated from the surface, deposition decreases with increasing Reynolds number; however, for isothermal flows, i.e., preheated, deposition can increase with the Reynolds number.

Measured Heat Transfer Coefficients at and Adjacent to the Tip of a Wall-Attached Cylinder in Crossflow—Application to Fins

1981 ◽  
Vol 103 (4) ◽  
pp. 778-784 ◽  
Author(s):  
E. M. Sparrow ◽  
F. Samie
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Visualization ◽  
Cylindrical Surface ◽  
The Other ◽  
Heat Transfer Analysis ◽  
End Effect ◽  
Transfer Coefficients ◽  
End Effects ◽  
Heat Transfer Coefficients

Wind tunnel studies encompassing both heat transfer measurements and flow visualization were performed for a cylinder in crossflow, with one end of the cylinder attached perpendicular to a wall and with the other end free. The focus of the work was to obtain heat transfer coefficients for the tip of the cylinder, for the tip-adjacent portion of the cylindrical surface, and for a portion of the cylindrical surface where there are no end effects. The flow visualization studies were performed to assist in the explanation and rationalization of the heat transfer results. They revealed the presence of spanwise flows adjacent to both ends of the cylinder, with accompanying modifications of the size of the separated region that washes the rear of the cylinder. The flow passing over the tip separates on the fore portion of the tip, but reattaches on the aft portion. The tip heat transfer coefficients are higher than those for the end-effect-free portion of the cylindrical surface, with deviations which grow with increasing Reynolds number (about a factor of two at Re = 25,000). For the tip-adjacent portion of the cylindrical surface, the coefficients are about fifty percent higher than those uninfluenced by end effects. The ramifications of these findings on the heat transfer analysis of fins are discussed.

Entropy generation and heat transfer analysis for ferrofluid flow between two rotating disks with variable conductivity

2021 ◽  
pp. 095440622199118
Author(s):  
Anupam Bhandari
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Differential Equations ◽  
Entropy Generation ◽  
Heat Transfer Analysis ◽  
Entropy Generation Rate ◽  
Geometrical Parameters ◽  
Rotating Disks ◽  
Coupled Differential Equations ◽  
Lower Disk

Present model analyze the flow and heat transfer of water-based carbon nanotubes (CNTs) [Formula: see text] ferrofluid flow between two radially stretchable rotating disks in the presence of a uniform magnetic field. A study for entropy generation analysis is carried out to measure the irreversibility of the system. Using similarity transformation, the governing equations in the model are transformed into a set of nonlinear coupled differential equations in non-dimensional form. The nonlinear coupled differential equations are solved numerically through the finite element method. Variable viscosity, variable thermal conductivity, thermal radiation, and volume concentration have a crucial role in heat transfer enhancement. The results for the entropy generation rate, velocity distributions, and temperature distribution are graphically presented in the presence of physical and geometrical parameters of the flow. Increasing the values of ferromagnetic interaction number, Reynolds number, and temperature-dependent viscosity enhances the skin friction coefficients on the surface and wall of the lower disk. The local heat transfer rate near the lower disk is reduced in the presence of Harman number, Reynolds number, and Prandtl number. The ferrohydrodynamic flow between two rotating disks might be useful to optimize the use of hybrid nanofluid for liquid seals in rotating machinery.

scholarly journals Purcell’s Three-Link Swimmer: Assessment of Geometry and Gaits for Optimal Displacement and Efficiency

Mathematics ◽  
2021 ◽  
Vol 9 (10) ◽  
pp. 1088
Author(s):  
Cristina Nuevo-Gallardo ◽  
José Emilio Traver ◽  
Inés Tejado ◽  
Blas M. Vinagre
Keyword(s):  
Reynolds Number ◽  
Multiobjective Optimization ◽  
The Other ◽  
Optimal Method ◽  
Optimal Velocity ◽  
Motion Primitives ◽  
Motion Primitive ◽  
Control Objective ◽  
Optimal Efficiency ◽  
The One

This paper studies the displacement and efficiency of a Purcell’s three-link microswimmer in low Reynolds number regime, capable of moving by the implementation of a motion primitive or gait. An optimization is accomplished attending to the geometry of the swimmer and the motion primitives, considering the shape of the gait and its amplitude. The objective is to find the geometry of the swimmer, amplitude and shape of the gaits which make optimal the displacement and efficiency, in both an individual way and combined (the last case will be referred to as multiobjective optimization). Three traditional gaits are compared with two primitives proposed by the authors and other three gaits recently defined in the literature. Results demonstrate that the highest displacement is obtained by the Tam and Hosoi optimal velocity gait, which also achieves the best efficiency in terms of energy consumption. The rectilinear and Tam and Hosoi optimal efficiency gaits are the second optimum primitives. Regarding the multiobjective optimization and considering the two criteria with the same weight, the optimum gaits turn out to be the rectilinear and Tam and Hosoi optimal efficiency gaits. Thus, the conclusions of this study can help designers to select, on the one hand, the best swimmer geometry for a desired motion primitive and, on the other, the optimal method of motion for trajectory tracking for such a kind of Purcell’s swimmers depending on the desired control objective.

LES Simulations of Rotating Two-Pass Ribbed Duct With Coriolis and Centrifugal Buoyancy Forces at Re=100,000

2016 ◽  
Author(s):  
Cody Dowd ◽  
Danesh Tafti
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Large Eddy Simulations ◽  
The Other ◽  
Coriolis Forces ◽  
Flow And Heat Transfer ◽  
Large Eddy ◽  
Buoyancy Forces ◽  
First Pass ◽  
Duct Geometry

The focus of this research is to predict the flow and heat transfer in a rotating two-pass duct geometry with staggered ribs using Large-Eddy Simulations (LES). The geometry consists of a U-Bend with 17 ribs in each pass. The ribs are staggered with an e/Dh = 0.1 and P/e = 10. LES is performed at a Reynolds number of 100,000, a rotation number of 0.2 and buoyancy parameters (Bo) of 0.5 and 1.0. The effects of Coriolis forces and centrifugal buoyancy are isolated and studied individually. In all cases it is found that increasing Bo from 0.5 to 1.0 at Ro = 0.2 has little impact on heat transfer. It is found that in the first pass, the heat transfer is quite receptive to Coriolis forces which augment and attenuate heat transfer at the trailing and leading walls, respectively. Centrifugal buoyancy, on the other hand has a bigger effect in augmenting heat transfer at the trailing wall than in attenuating heat transfer at the leading wall. On contrary, it aids heat transfer in the second half of the first pass at the leading wall by energizing the flow near the wall. The heat transfer in the second pass is dominated by the highly turbulent flow exiting the bend. Coriolis forces have no impact on the augmentation of heat transfer on the leading wall till the second half of the passage whereas it attenuates heat transfer at the trailing wall as soon as the flow exits the bend. Contrary to phenomenological arguments, inclusion of centrifugal buoyancy augments heat transfer over Coriolis forces alone on both the leading and trailing walls of the second pass.

scholarly journals A heat transfer analysis from a porous plate with transpiration cooling

2019 ◽  
Vol 23 (5 Part B) ◽  
pp. 3025-3034 ◽  
Author(s):  
Mustafa Kilic
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Porous Plate ◽  
Particle Diameter ◽  
Heat Transfer Analysis ◽  
Transpiration Cooling ◽  
Cooling Efficiency ◽  
Cooling Effectiveness ◽  
Cooling Effects ◽  
Air Channel

Present study is focused on improving heat transfer from a porous plate by cooling of air with transpiration cooling. Effects of Reynolds number of the air channel flow and particle diameter on cooling effectiveness of porous plate and efficiency of system were investigated experimentally. It was observed that increasing Reynolds number of 15.2% causes a decrease of 6.9% on cooling efficiency of the system and a decrease of 8.6% on cooling effectiveness of porous plate. Decreasing particle diameter causes a significant decrease on surface temperature and an increase on cooling effectiveness of porous plate. Difference of cooling effectiveness of porous plate from dp = 40-200 ?m is 12%. Verification of this study was also shown by comparing experimental results of this study with literature.

Thermodynamic Analysis of the Internal Melt-Ice-on-Tube during Melting under Natural Convection

2014 ◽  
Vol 937 ◽  
pp. 375-380
Author(s):  
Yi Liu ◽  
Xin Chen
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Storage System ◽  
Heat Transfer Process ◽  
The Other ◽  
Ice Storage ◽  
Ice Melting ◽  
Single Tube ◽  
Initial Stage ◽  
The One

The numerical simulation of the ice melting processes in internal melt-ice-on-tube which is applied widely in the ice storage system is carried out. The dynamic mathematical models about melting are established and solved by using enthalpy method. Natural convection of the melted water in the course of melting is studied, and natural convection influences on single tube in melting heat transfer process is analyzed under the related parameters. Several conclusions are obtained:1. Because of natural convection of the melted water, the curve of melting interface is no longer a circle, but a curve changing with angle. The melting radius reaches minimum at the bottom and maximum at the top.2. The one with natural convention is compared to the other not considered. At initial stage, the influence of natural convection is smaller in the course of melting. However, the influence of natural convention increases along with melting.

Heat transfer analysis of a ventilated room with a porous partition: LB-MRT simulations

2020 ◽  
Vol 91 (2) ◽  
pp. 20904
Author(s):  
Zouhira Hireche ◽  
Lyes Nasseri ◽  
Djamel Eddine Ameziani
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Natural Convection ◽  
Reynolds Numbers ◽  
Darcy Number ◽  
The Other ◽  
Flow In Porous Media ◽  
Heat Transfer Analysis ◽  
Maximum Deviation ◽  
Important Conclusion

This article presents the hydrodynamic and thermal characteristics of transfers by forced, mixed and natural convection in a room ventilated by air displacement. The main objective is to study the effect of a porous partition on the heat transfer and therefore the thermal comfort in the room. The fluid flow future in the cavity and the heat transfer rate on the active wall have been analyzed for different permeabilities: 10−6 ≤ Da ≤ 10. The other control parameters are obviously, the Rayleigh number and the Reynolds number varied in the rows: 10 ≤ Ra ≤ 106 and 50 ≤ Re ≤ 500 respectively. The transfer equations write were solved by the Lattice Boltzmann Multiple Relaxation Time method. For flow in porous media an additional term is added in the standard LB equations, to consider the effect of the porous media, based on the generalized model, the Brinkman-Forchheimer-extended Darcy model. The most important conclusion is that the Darcian regime start for small Darcy number Da < 10−4. Spatial competition between natural convection cell and forced convection movement is observed as Ra and Re rise. The effect of Darcy number values and the height of the porous layer is barely visible with a maximum deviation less than 7% over the ranges considered. Note that the natural convection regime is never reached for low Reynolds numbers. For this Re values the cooperating natural convection only improves transfers by around 10% while, for the other Reynolds numbers the improvement in transfers due to natural and forced convections cooperation is more significant.

scholarly journals Heat Transfer Analysis of Two Pass Cooling Channel of Gas Turbine Blade With Analytical Wall Function Turbulence Approach

2013 ◽  
Author(s):  
Hitoshi Arakawa ◽  
Shaohua Shen ◽  
Ryo S. Amano
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Analysis ◽  
Computational Studies ◽  
Cooling Channel ◽  
Wall Function ◽  
Square Duct ◽  
Flow And Heat Transfer ◽  
Predicting Performance ◽  
Function Models

This paper reports experimental and computational studies of flow and heat transfer through a square duct with a sharp 180 degree turn. The main purpose of this research is to study flow and heat transfer predictions of the Analytical Wall-Function (AWF). To compare the predicting performance of the AWF, the standard Log-Law Wall-Function (LWF) and Low-Reynolds-number (LRN) k-ε model were applied. Their results were also compared with the experimental results for validation. In addition, three extended forms of the AWF were tested. Computational results showed better agreement with the experimental data, especially after the turn of the channel. It was also found that the wall-function (WF) models predicted more reasonable results as Reynolds number increased. The both wall-function models predicted similar results except for separation/reattachment regions where the LWF predicted lower Nusselt number than the other models.

scholarly journals Lack of high-mass pre-stellar cores in the starless MDCs of NGC 6334

2019 ◽  
Vol 622 ◽  
pp. A99 ◽  
Author(s):  
F. Louvet ◽  
S. Neupane ◽  
G. Garay ◽  
D. Russeil ◽  
A. Zavagno ◽  
...  
Keyword(s):  
Initial Conditions ◽  
Compact Objects ◽  
The Other ◽  
High Mass ◽  
Mass Star ◽  
Dense Cores ◽  
Other Hand ◽  
Static Models ◽  
Ngc 6334 ◽  
The One

Context. The formation of high-mass stars remains unknown in many aspects. There are two competing families of models to explain the formation of high-mass stars. On the one hand, quasi-static models predict the existence of high-mass pre-stellar cores sustained by a high degree of turbulence. On the other hand, competitive accretion models predict that high-mass proto-stellar cores evolve from low or intermediate mass proto-stellar cores in dynamic environments. Aims. The aim of the present work is to bring observational constraints at the scale of high-mass cores (~0.03 pc). Methods. We targeted with ALMA and MOPRA a sample of nine starless massive dense cores (MDCs) discovered in a recent Herschel/HOBYS study. Their mass and size (~110 M⊙ and r = 0.1 pc, respectively) are similar to the initial conditions used in the quasi-static family of models explaining for the formation of high-mass stars. We present ALMA 1.4 mm continuum observations that resolve the Jeans length (λJeans ~ 0.03 pc) and that are sensitive to the Jeans mass (MJeans ~ 0.65 M⊙) in the nine starless MDCs, together with ALMA-12CO(2–1) emission line observations. We also present HCO+(1–0), H13CO+(1–0) and N2H+(1–0) molecular lines from the MOPRA telescope for eight of the nine MDCs. Results. The nine starless MDCs have the mass reservoir to form high-mass stars according to the criteria by Baldeschi et al. (2017). Three of the starless MDCs are subvirialized with αvir ~ 0.35, and four MDCs show sign of collapse from their molecular emission lines. ALMA observations show very little fragmentation within the MDCs. Only two of the starless MDCs host compact continuum sources, whose fluxes correspond to <3 M⊙ fragments. Therefore, the mass reservoir of the MDCs has not yet been accreted onto compact objects, and most of the emission is filtered out by the interferometer. Conclusions. These observations do not support the quasi-static models for high-mass star formation since no high-mass pre-stellar core is found in NGC 6334. The competitive accretion models, on the other hand, predict a level of fragmentation much higher than what we observe.

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