Fluid Temperature and Mixed Convection Effects in Hot-Wire Measurements of Natural Convection Flows

1979 ◽  
Vol 46 (1) ◽  
pp. 231-233 ◽  
Author(s):  
Y. Jaluria
Keyword(s):  
Natural Convection ◽  
Mixed Convection ◽  
Fluid Temperature ◽  
Hot Wire

Calibration of Constant-Temperature Hot-Wire Anemometers at Low Velocities in Water with Variable Fluid Temperature

1972 ◽  
Vol 94 (1) ◽  
pp. 17-22 ◽  
Author(s):  
K. Hollasch ◽  
B. Gebhart
Keyword(s):  
Experimental Study ◽  
Natural Convection ◽  
Constant Temperature ◽  
Fluid Temperature ◽  
Hot Wire ◽  
Temperature Variations ◽  
Wire Probe ◽  
Temperature Mode

Calibration of hot-wire probes operated in a constant-temperature mode in water at low velocities is discussed. Operation under circumstances where natural convection effects are important is considered. A method of calibrating a constant-temperature hot-wire probe for variations in fluid temperature is presented. The method consists of varying wire overheat during calibration at a constant fluid temperature. A relation is derived analytically relating anemometer output with a variable overheat resistance to anemometer output with fluid temperature variations. An experimental study to verify the analysis is presented.

scholarly journals Numerical Simulation of Natural Convection in a Transient Short-Hot-Wire Thermal Conductivity Cell

Netsu Bussei ◽  
2008 ◽  
Vol 22 (4) ◽  
pp. 217-222 ◽  
Author(s):  
Peter L. Woodfield ◽  
Jun Fukai ◽  
Motoo Fujii ◽  
Yasuyuki Takata ◽  
Kanei Shinzato
Keyword(s):  
Thermal Conductivity ◽  
Numerical Simulation ◽  
Natural Convection ◽  
Hot Wire ◽  
Transient Short Hot Wire ◽  
Thermal Conductivity Cell ◽  
Conductivity Cell

Experimental and Numerical Study for Improved Understanding of Mixed-Convection Type of Flows in Turbine Casing Cavities During Shut-Down Regimes

2021 ◽  
Author(s):  
Oguzhan Murat ◽  
Budimir Rosic ◽  
Koichi Tanimoto ◽  
Ryo Egami
Keyword(s):  
Natural Convection ◽  
Flow Field ◽  
Mixed Convection ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Scale Model ◽  
Unsteady Temperature ◽  
Numerical Predictions ◽  
Wide Range ◽  
Turbine Casing

Abstract Due to increase in the power generation from renewable sources, steam and gas turbines will be required to adapt for more flexible operations with frequent start-ups and shut-downs to provide load levelling capacity. During shut-down regimes, mixed convection takes place with natural convection dominance depending on the operating conditions in turbine cavities. Buoyant flows inside the turbine that are responsible for non-uniform cooling leading to thermal stresses and compromise clearances directly limits the operational flexibility. Computational fluid dynamics (CFD) tools are required to predict the flow field during these regimes since direct measurements are extremely difficult to conduct due to the harsh operating conditions. Natural convection with the presence of cross-flow -mixed convection has not been extensively studied to provide detailed measurements. Since the literature lacks of research on such flows with real engine representative operating conditions for CFD validation, the confidence in numerical predictions is rather inadequate. This paper presents a novel experimental facility that has been designed and commissioned to perform very accurate unsteady temperature and flow field measurements in a simplified turbine casing geometry. The facility is capable of reproducing a wide range of Richardson, Grashof and Reynolds numbers which are representative of engine realistic operating conditions. In addition, high fidelity, wall resolved LES with dynamic Smagorinsky subgrid scale model has been performed. The flow field as well as heat transfer characteristics have been accurately captured with LES. Lastly, inadequacy of RANS for mixed type of flows has been highlighted.

Double-diffusive natural convection in an inclined enclosure with heat generation and Soret effect

2018 ◽  
Vol 35 (8) ◽  
pp. 2753-2774 ◽  
Author(s):  
Safae Hasnaoui ◽  
Abdelkhalek Amahmid ◽  
Abdelghani Raji ◽  
Hassen Beji ◽  
Mohammed Hasnaoui ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Fluid Flow ◽  
Natural Convection ◽  
Finite Difference ◽  
Heat Generation ◽  
Soret Effect ◽  
Internal Heat ◽  
Vertical Position ◽  
Fluid Temperature ◽  
Content Type

PurposeThe purpose of this paper is to study numerically thermosolutal natural convection within an inclined rectangular cavity in the presence of Soret effect and heat generation. The enclosure is heated and salted from its long sides with constant but different temperatures and concentrations. The study focuses on the effects of three main parameters which are, the Soret parameter (Sr = 0 and –0.5), the internal to external Rayleigh numbers ratio 0 ≤ R ≤ 80 and the cavity inclination γ, varied from 0° (vertical position) to 60°. The combined effects of these parameters on fluid flow and heat and mass transfer characteristics are examined for the external Rayleigh numberRaE = 105, the Prandtl numberPr = 0.71, the buoyancy ratioN = 1, the Lewis numberLe = 2 and the aspect ratio of the cavityA = 2.Design/methodology/approachA hybrid lattice Boltzmann-finite difference method (LBM-FD) was used to tackle the problem under consideration. The LBM with the simple relaxation time was used for the fluid flow in the presence of the gravity force, while the temperature and concentration equations were solved separately using an explicit finite-difference technique at the Boltzmann scale.FindingsThe monocellular nature of the flow, obtained forR = 0 is not destroyed by varying the cavity inclination and the Soret parameter but rather by the increase of the parameter R. The Soret parameter and the cavity inclination become perceptible at high values ofR. The inclinationγ = 60° leads to high mean temperatures compared to the other inclinations. The effect ofRon mean concentration is amplified in the presence of Soret effect but limited in the absence of the latter. The negative Soret parameter combined with high internal heat generation and a relatively high inclination is important when the objective is to maintain the fluid at a high concentration of species. The presence of bicellular flow combined with the important elevation undergone by the fluid temperature, makes both the cold and hot walls playing a cooling role with the most important exchanges taking place at the upper part of these walls. The analysis of the mean mass transfer shows that the increase of the inclination may lead to an increase or a decrease of the mass transfer depending on the range ofR, in the case of Sr = 0. However, for Sr = −0.5, it is observed that the increase ofγis generally accompanied by a reduction of the mass transfer.Originality/valueTo the best of the authors’ knowledge, the hybrid LBM-FD was not used before to study such a problem. Combined effect ofRand inclination may be useful in charging the fluid with species when the objective is to maintain high concentrations in the medium.

A Natural Convection Fin with a Solution-Determined Nonmonotonically Varying Heat Transfer Coefficient

1981 ◽  
Vol 103 (2) ◽  
pp. 218-225 ◽  
Author(s):  
E. M. Sparrow ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Transfer Coefficient ◽  
First Principles ◽  
Numerical Solutions ◽  
Flow Direction ◽  
Operating Conditions ◽  
Fluid Temperature ◽  
Wide Range

A conjugate conduction-convection analysis has been made for a vertical plate fin which exchanges heat with its fluid environment by natural convection. The analysis is based on a first-principles approach whereby the heat conduction equation for the fin is solved simultaneously with the conservation equations for mass, momentum, and energy in the fluid boundary layer adjacent to the fin. The natural convection heat transfer coefficient is not specified in advance but is one of the results of the numerical solutions. For a wide range of operating conditions, the local heat transfer coefficients were found not to decrease monotonically in the flow direction, as is usual. Rather, the coefficient decreased at first, attained a minimum, and then increased with increasing downstream distance. This behavior was attributed to an enhanced buoyancy resulting from an increase in the wall-to-fluid temperature difference along the streamwise direction. To supplement the first-principles analysis, results were also obtained from a simple adaptation of the conventional fin model.

Velocity Field Measurements in Leading Edge Wing Compartments

2008 ◽  
Author(s):  
V. Egan ◽  
D. T. Newport ◽  
V. Larcarac ◽  
B. Estebe
Keyword(s):  
Natural Convection ◽  
Leading Edge ◽  
Field Measurements ◽  
Dominant Mode ◽  
Fluid Temperature ◽  
Velocity Measurements ◽  
Thermal Boundary Conditions ◽  
Single Compartment ◽  
Image Velocimetry ◽  
Convection Cooling

For many applications the optimisation of natural convection cooling is a major design consideration due to factors such as weight, accessibility, cost and power consumption. In aircraft wing compartments, natural convection is the dominant mode of heat transfer due to high wall temperatures resulting from solar loading and heat dissipating internal electronics. This paper investigates the flow structures in a leading edge compartment subject to various thermal boundary conditions. The experimental configuration consisted of two leading edge enclosures; the first is a single compartment while the second has an attached wing box. Particle image velocimetry (PIV) was employed to obtain velocity measurements of the flow in both leading edge enclosures. The second compartment investigated the effect of an adjacent fluid filled enclosure on the flow regime in the leading edge compartment. Higher local velocities were found in the second compartment due to an increase in buoyancy forces resulting from a lower of the average fluid temperature within the compartment. The introduction of a heat dissipating component gave rise to two separate convection structures and in general increased the fluctuations in the both temperature and velocities within the compartment.

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