scholarly journals Sensitivity Study of Ice Accretion Simulation to Roughness Thermal Correction Model

Aerospace ◽  
2021 ◽  
Vol 8 (3) ◽  
pp. 84
Author(s):  
Kevin Ignatowicz ◽  
François Morency ◽  
Héloïse Beaugendre
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Sensitivity Study ◽  
Correction Coefficient ◽  
Ice Accretion ◽  
Roughness Parameters ◽  
Thermal Correction ◽  
The Impact

The effects of atmospheric icing can be anticipated by Computational Fluid Dynamics (CFD). Past studies show that the convective heat transfer influences the ice accretion and is itself a function of surface roughness. Uncertainty quantification (UQ) could help quantify the impact of surface roughness parameters on the reliability of ice accretion prediction. This paper aims to quantify ice accretion uncertainties and identify the key surface roughness correction parameters contributing the most to the uncertainties in a Reynolds-Averaged Navier-Stokes (RANS) formulation. Ice accretion simulations over a rough flat plate using two thermal correction models are used to construct a RANS database. Non-Intrusive Polynomial Chaos Expansion (NIPCE) metamodels are developed to predict the convective heat transfer and icing characteristics of the RANS database. The metamodels allow for the computation of the 95% confidence intervals of the output probability distribution (PDF) and of the sensitivity indexes of the roughness parameters according to their level of influence on the outputs. For one of the thermal correction models, the most influential parameter is the roughness height, whereas for the second model it is the surface correction coefficient. In addition, the uncertainty on the freestream temperature has a minor impact on the ice accretion sensitivity compared to the uncertainty on the roughness parameters.

Experimental Model of Temperature-Driven Nanofluid

2006 ◽  
Vol 129 (6) ◽  
pp. 697-704 ◽  
Author(s):  
A. G. Agwu Nnanna
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Small Volume ◽  
Volume Fraction ◽  
Convective Heat Transfer Coefficient ◽  
Isothermal Condition ◽  
Carrier Fluid ◽  
Small Volume Fraction ◽  
The Impact

This paper presents a systematic experimental method of studying the heat transfer behavior of buoyancy-driven nanofluids. The presence of nanoparticles in buoyancy-driven flows affects the thermophysical properties of the fluid and consequently alters the rate of heat transfer. The focus of this paper is to estimate the range of volume fractions that results in maximum thermal enhancement and the impact of volume fraction on Nusselt number. The test cell for the nanofluid is a two-dimensional rectangular enclosure with differentially heated vertical walls and adiabatic horizontal walls filled with 27 nm Al2O3–H2O nanofluid. Simulations were performed to measure the transient and steady-state thermal response of nanofluid to imposed isothermal condition. The volume fraction is varied between 0% and 8%. It is observed that the trend of the temporal and spatial evolution of temperature profile for the nanofluid mimics that of the carrier fluid. Hence, the behaviors of both fluids are similar. Results shows that for small volume fraction, 0.2⩽ϕ⩽2% the presence of the nanoparticles does not impede the free convective heat transfer, rather it augments the rate of heat transfer. However, for large volume fraction ϕ>2%, the convective heat transfer coefficient declines due to reduction in the Rayleigh number caused by increase in kinematic viscosity. Also, an empirical correlation for Nuϕ as a function of ϕ and Ra has been developed, and it is observed that the nanoparticle enhances heat transfer rate even at a small volume fraction.

scholarly journals Radiation heat transfer between human and cryocabin walls

2021 ◽  
Vol 2119 (1) ◽  
pp. 012146
Author(s):  
I A Burkov ◽  
S I Khutsieva ◽  
V A Voronov
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Human Body ◽  
Transfer Problem ◽  
Radiation Heat Transfer ◽  
Vertical Wall ◽  
Heat Transfer Problem ◽  
Radiation Heat ◽  
The Impact

Abstract The paper considers the particular case of intensive radiation heat transfer in the system consisting of a human body and cryocabin walls of cryosauna. Calculations for three models have been made, namely, human-vertical wall, which is arranged parallel to a human, human-vertical wall, which is positioned at a certain angle, and a human-cryosauna. Analytical calculations are compared with Ansys-bassed numerical calculations. The impact of radiation heat transfer in this radiation-convective heat transfer problem is estimated. Conclusions are drawn about taking into account the radiation heat transfer and a rational method for calculating this heat transfer problem.

scholarly journals A Simplified Technique for Thermal Analysis of a Fenestration system with a Venetian Blind

2021 ◽  
Author(s):  
Hidayat Ullah Shahid
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Thermal Performance ◽  
Approximate Model ◽  
Vertical Surface ◽  
Shading Devices ◽  
The One ◽  
The Impact ◽  
Venetian Blind

A simplified 1-D numerical model of a window and horizontal Venetian blind assembly has been developed. This model provides a realistic estimate of the advantage of using blinds to control the window heat gain or loss. The free convective heat transfer rate from an isothermal vertical surface adjacent to a set of horizontal louvres has been studied numerically. This configuration is an approximate model of an indoor window glazing with a Venetian-type blind. Knowledge of the effect of blinds on the free convection at the indoor window surface is important for understanding and predicting the impact of shading devices on the overall thermal performance of a window. The convective heat transfer results are used in the one-dimensional model of the complete fenestration system to study the effect on key performance parameters. The results show that louvred blinds can have a significant beneficial effect on window thermal performance.

scholarly journals Review of Convective Heat Transfer Modelling in CFD Simulations of Fire-Driven Flows

2021 ◽  
Vol 11 (11) ◽  
pp. 5240
Author(s):  
Georgios Maragkos ◽  
Tarek Beji
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Flame Spread ◽  
Wall Region ◽  
Advantages And Disadvantages ◽  
Wide Range ◽  
Liquid Evaporation ◽  
Transfer Modelling ◽  
The Impact

Progress in fire safety science strongly relies on the use of Computational Fluid Dynamics (CFD) to simulate a wide range of scenarios, involving complex geometries, multiple length/time scales and multi-physics (e.g., turbulence, combustion, heat transfer, soot generation, solid pyrolysis, flame spread and liquid evaporation), that could not be studied easily with analytical solutions and zone models. It has been recently well recognised in the fire community that there is need for better modelling of the physics in the near-wall region of boundary layer combustion. Within this context, heat transfer modelling is an important aspect since the fuel gasification rate for solid pyrolysis and liquid evaporation is determined by a heat feedback mechanism that depends on both convection and radiation. The paper focuses on convection and reviews the most commonly used approaches for modelling convective heat transfer with CFD using Large Eddy Simulations (LES) in the context of fire-driven flows. The considered test cases include pool fires and turbulent wall fires. The main assumptions, advantages and disadvantages of each modelling approach are outlined. Finally, a selection of numerical results from the application of the different approaches in pool fire and flame spread cases, is presented in order to demonstrate the impact that convective heat transfer modelling can have in such scenarios.

scholarly journals Auxiliary Draught Base Performance Improvement of Air Distribution System of Cold Store

2019 ◽  
Vol 8 (4) ◽  
pp. 4737-4748
Keyword(s):  
Heat Transfer ◽  
Flow Velocity ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Cold Storage ◽  
Distribution System ◽  
Storage System ◽  
Air Transport ◽  
Air Distribution ◽  
The Impact

Air distribution enable convective heat transfer in cold storage operation. Thermal behaviors of the cold storage system are based on air transport arrangements. Transport characteristics can handle with auxiliary arrangements such as induce draught system. Experimental investigation for the impact of auxiliary draught system (ADS) on air transportation is carried out. Air transport velocity was measured in the cold chamber with a hot wire anemometer. Experimental results show significant enhancement by three times mid-section air flow velocity and overall one- and half-time greater flow velocity observed, while return air velocity measured almost tow time of general condition during the experiment. COP of plant improve by 21% with 25% less time required to achieve desired temperature. 26% saving in power consumption observed during experiments. Auxiliary draught ensures homogeneous environment inside the plant through proper mixing of air and support convective heat transfer. Designing and analysis of airflow patterns with temperature distribution in large entity like cold storage is a difficult task thus Computational Fluid Dynamics (CFD) can address the issue with high degree of precision. It has been observed that SST K-ℇ model has average 26% error with experimental values

Thermal Behavior of Nominally Flat Silicon-Based Heat Spreaders

2005 ◽  
Vol 128 (4) ◽  
pp. 370-379
Author(s):  
Ta-Wei Lin ◽  
Ming-Chang Wu ◽  
Cheng-Hsien Peng ◽  
Po-Li Chen ◽  
Ying-Huei Hung
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Thermal Resistance ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Spreader ◽  
Heat Spreaders ◽  
Silicon Based ◽  
Maximum Thermal Resistance ◽  
Effect Of Surface

Thermal characteristics for a horizontal heated chip mounted with three types of nominally flat silicon-based heat spreaders have been systematically investigated. They include the natural convective and radiative heat transfer from the top surface of the heat spreaders to the external ambient, external thermal resistance, and maximum overall thermal resistance. In the aspect of natural convection, an axisymmetric bowl-shaped profile of local Nusselt number is achieved, and the highest convective heat transfer performance occurs at the location near the rim of the heat spreader. The effect of surface roughness on both local and average natural convective heat transfer behaviors from nominally flat silicon-based spreader surfaces to the external ambient is not significant. Two new generalized correlations of local and average Nusselt numbers for various heat spreader surfaces are presented. The contributions of convection and radiation on the total heat dissipated from the top surface of the heat spreader to the ambient are about 72% and 28%, respectively. The effect of surface roughness on external thermal resistance for nominally flat silicon-based surfaces is not significant. The influence of the conductive thermal resistance within the silicon-based heat spreader on the maximum thermal resistance is not significant. The maximum thermal resistance is mainly dominated by external thermal resistance for flat nominally silicon-based heat spreaders.

Influence of Various Nanofluid Types on Wavy Microchannels Heat Sink Cooling Performance

2013 ◽  
Vol 420 ◽  
pp. 118-122 ◽  
Author(s):  
Prem Gunnasegaran ◽  
Noel Narindra ◽  
Norshah Hafeez Shuaib
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Sink ◽  
Convective Heat Transfer Coefficient ◽  
Volume Fractions ◽  
The Impact

This paper discusses the impact of using various types of nanofluids and nanoparticle volume fractions on heat transfer and fluid flow characteristics in a wavy microchannel heat sink (WMCHS) with rectangular cross-section. Numerical investigations using three different types of nanofluids including Al2O3-H2O, CuO-H2O, and diamond-H2O with a fixed nanoparticle volume fraction of 3% and using a diamond-H2O with nanoparticle volume fractions ranging from 0.5% to 5% are examined. This investigation covers Reynolds numbers in the range of 100 to 1000. The three-dimensional steady, laminar flow and heat transfer governing equations are solved using the finite-volume method (FVM). The computational model is used to study the variations of convective heat transfer coefficient, pressure drop and wall shear stress. It is inferred that the convective heat transfer coefficient of a WMCHS cooled with the nanofluid flow showed marked improvement over the pure water with a smaller pressure drop penalty.

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