Heat Transfer Characteristics of Steady Electroosmotic Flows in Two-Dimensional Straight Microchannels

2003 ◽  
Author(s):  
Keisuke Horiuchi ◽  
Prashanta Dutta
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Joule Heating ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Two Dimensional ◽  
Heat Transfer Characteristics ◽  
Temperature Distributions ◽  
Electroosmotic Flows

Analytical solutions for the temperature distributions, heat transfer coefficients and Nusselt numbers of steady electroosmotic flows are obtained for two-dimensional straight micro-channels. This analysis is based on infinitesimal electric double layer (EDL) in which flow velocity becomes “plug-like” uniform except very close to the wall. Both constant surface temperature and constant surface heat flux conditions are considered in this study. Separation of variables techniques are applied to obtain analytical solutions of temperature distributions from the energy equation in which Joule heating is a significant contributor due to the applied electric field. The thermal analysis considers interaction among inertial, diffusive and joule heating terms in order to obtain the thermally developing behavior of electroosmotic flows. Heat transfer characteristics are presented for low Reynolds number microflows where the viscous and electric field terms are very dominant. For the parameter range studied here (Re ≤ 0.7), the Nusselt number is independent of the thermal Peclet number, except in the thermally developing region. In both isothermal and constant surface heat flux boundary conditions, the Nusselt number becomes constant in the fully developed region for a uniform volumetric heat generation. Analytical results for no Joule heating cases are also compared with the classical heat transfer results, and in the thermally fully developed region an excellent agreement is obtained between them.

Heat Transfer Characteristics of Downward Facing Hot Horizontal Surfaces Using Mist Jet Impingement

2017 ◽  
Author(s):  
Ashutosh Kumar Yadav ◽  
Parantak Sharma ◽  
Avadhesh Kumar Sharma ◽  
Mayank Modak ◽  
Vishal Nirgude ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Heat Flux ◽  
Cooling System ◽  
Water Pressure ◽  
Jet Impingement ◽  
Surface Heat ◽  
Heat Transfer Characteristics ◽  
Impingement Cooling ◽  
Transfer Characteristics

Impinging jet cooling technique has been widely used extensively in various industrial processes, namely, cooling and drying of films and papers, processing of metals and glasses, cooling of gas turbine blades and most recently cooling of various components of electronic devices. Due to high heat removal rate the jet impingement cooling of the hot surfaces is being used in nuclear industries. During the loss of coolant accidents (LOCA) in nuclear power plant, an emergency core cooling system (ECCS) cool the cluster of clad tubes using consisting of fuel rods. Controlled cooling, as an important procedure of thermal-mechanical control processing technology, is helpful to improve the microstructure and mechanical properties of steel. In industries for heat transfer efficiency and homogeneous cooling performance which usually requires a jet impingement with improved heat transfer capacity and controllability. It provides better cooling in comparison to air. Rapid quenching by water jet, sometimes, may lead to formation of cracks and poor ductility to the quenched surface. Spray and mist jet impingement offers an alternative method to uncontrolled rapid cooling, particularly in steel and electronics industries. Mist jet impingement cooling of downward facing hot surface has not been extensively studied in the literature. The present experimental study analyzes the heat transfer characteristics a 0.15mm thick hot horizontal stainless steel (SS-304) foil using Internal mixing full cone (spray angle 20 deg) mist nozzle from the bottom side. Experiments have been performed for the varied range of water pressure (0.7–4.0 bar) and air pressure (0.4–5.8 bar). The effect of water and air inlet pressures, on the surface heat flux has been examined in this study. The maximum surface heat flux is achieved at stagnation point and is not affected by the change in nozzle to plate distance, Air and Water flow rates.

Effect of Edge Conditions on Natural Convective Heat Transfer From a Narrow Vertical Flat Plate With a Uniform Surface Heat Flux

2007 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Jane T. Paul
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Surface Heat Flux ◽  
Three Dimensional ◽  
Surface Heat ◽  
Heated Plate ◽  
Two Dimensional ◽  
Adiabatic Surface

Two-dimensional natural convective heat transfer from vertical plates has been extensively studied. However, when the width of the plate is relatively small compared to its height, the heat transfer rate can be greater than that predicted by these two-dimensional flow results. Because situations that can be approximately modelled as narrow vertical plates occur in a number of practical situations, there exists a need to be able to predict heat transfer rates from such narrow plates. Attention has here been given to a plate with a uniform surface heat flux. The magnitude of the edge effects will, in general, depend on the boundary conditions existing near the edge of the plate. To examine this effect, two situations have been considered. In one, the heated plate is imbedded in a large plane adiabatic surface, the surfaces of the heated plane and the adiabatic surface being in the same plane while in the second there are plane adiabatic surfaces above and below the heated plate but the edge of the plate is directly exposed to the surrounding fluid. The flow has been assumed to be steady and laminar and it has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces, this having been treated by using the Boussinesq approach. It has also been assumed that the flow is symmetrical about the vertical centre-plane of the plate. The solution has been obtained by numerically solving the full three-dimensional form of the governing equations, these equations being written in terms of dimensionless variables. Results have only been obtained for a Prandtl number of 0.7. A wide range of the other governing parameters have been considered for both edge situations and the conditions under which three dimensional flow effects can be neglected have been deduced.

scholarly journals Nanofluid Flow on a Shrinking Cylinder with Al2O3 Nanoparticles

Mathematics ◽  
2021 ◽  
Vol 9 (14) ◽  
pp. 1612
Author(s):  
Iskandar Waini ◽  
Anuar Ishak ◽  
Ioan Pop
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Friction Factor ◽  
Surface Heat Flux ◽  
Transfer Rate ◽  
Surface Heat ◽  
Al2o3 Nanoparticles ◽  
Nanofluid Flow ◽  
Curvature Parameter ◽  
Over Time

This study investigates the nanofluid flow towards a shrinking cylinder consisting of Al2O3 nanoparticles. Here, the flow is subjected to prescribed surface heat flux. The similarity variables are employed to gain the similarity equations. These equations are solved via the bvp4c solver. From the findings, a unique solution is found for the shrinking strength λ≥−1. Meanwhile, the dual solutions are observed when λc<λ<−1. Furthermore, the friction factor Rex1/2Cf and the heat transfer rate Rex−1/2Nux increase with the rise of Al2O3 nanoparticles φ and the curvature parameter γ. Quantitatively, the rates of heat transfer Rex−1/2Nux increase up to 3.87% when φ increases from 0 to 0.04, and 6.69% when γ increases from 0.05 to 0.2. Besides, the profiles of the temperature θ(η) and the velocity f’(η) on the first solution incline for larger γ, but their second solutions decline. Moreover, it is noticed that the streamlines are separated into two regions. Finally, it is found that the first solution is stable over time.

A New Experimental Technique for Measuring Surface Heat Transfer Coefficients Using Uncalibrated Liquid Crystals

1999 ◽  
Author(s):  
Wayne N. O. Turnbull ◽  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Experimental Technique ◽  
Surface Heat Flux ◽  
Local Heat ◽  
Surface Heat ◽  
Phase Delay ◽  
Transfer Coefficients ◽  
Periodic Surface ◽  
Heat Transfer Coefficients

Abstract A new experimental technique has been developed that permits the determination of local surface heat transfer coefficients on surfaces without requirement for calibration of the temperature-sensing device. The technique uses the phase delay that develops between the surface temperature response and an imposed periodic surface heat flux. This phase delay is dependent upon the thermophysical properties of the model, the heat flux driving frequency and the local heat transfer coefficient. It is not a function of magnitude of the local heat flux. Since only phase differences are being measured there is no requirement to calibrate the temperature sensor, in this instance a thermochromic liquid crystal. Application of a periodic surface heat flux to a flat plate resulted in a surface colour response that was a function of time. This response was captured using a standard colour CCD camera and the phase delay angles were determined using Fourier analysis. Only the 8 bit G component of the captured RGB signal was required, there being no need to determine a Hue value. From these experimentally obtained phase delay angles it was possible to determine heat transfer coefficients that compared well with those predicted using a standard correlation.

Boiling Heat Transfer Characteristics of Rotary Hollow Cylinders with In-Line and Staggered Multiple Arrays of Water Jets

2021 ◽  
Author(s):  
Mohammad Jahedi ◽  
Bahram Moshfegh
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Stagnation Point ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Maximum Heat ◽  
Water Jets ◽  
Maximum Heat Flux ◽  
Inner Surface ◽  
Hollow Cylinders

Abstract Transient heat transfer studies of quenching rotary hollow cylinders with in-line and staggered multiple arrays of jets have been carried out experimentally. The study involves three hollow cylinders (Do/d = 12 to 24) with rotation speed 10 to 50 rpm, quenched by subcooled water jets (ΔTsub=50-80 K) with jet flow rate 2.7 to 10.9 L/min. The increase in area-averaged and maximum heat flux over quenching surface (Af) has been observed in the studied multiple arrays with constant Qtotal compared to previous studies. Investigation of radial temperature distribution at stagnation point of jet reveals that the footprint of configuration of 4-row array is highlighted in radial distances near the outer surface and vanishes further down toward the inner surface. The influence of the main quenching parameters on local average surface heat flux at stagnation point is addressed in all the boiling regimes where the result indicates jet flow rate provides strongest effect in all the boiling regimes. Effectiveness of magnitude of maximum heat flux in the boiling curve for the studied parameters is reported. The result of spatial and temporal heat flux by radial conduction in the solid presents projection depth of cyclic variation of surface heat flux in the radial axis as it disappears near inner surface of hollow cylinder. In addition, correlations are proposed for area-averaged Nusselt number as well as average and maximum local heat flux at stagnation point of jet for the in-line and staggered multiple arrays.

Finite Element Formulation for Two-Dimensional Inverse Heat Conduction Analysis

1992 ◽  
Vol 114 (3) ◽  
pp. 553-557 ◽  
Author(s):  
T. R. Hsu ◽  
N. S. Sun ◽  
G. G. Chen ◽  
Z. L. Gong
Keyword(s):  
Heat Flux ◽  
Finite Element ◽  
Heat Conduction ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Element Formulation ◽  
Two Dimensional ◽  
Inverse Heat Conduction ◽  
Discrete Point ◽  
Element Algorithm

This paper presents a finite element algorithm for two-dimensional nonlinear inverse heat conduction analysis. The proposed method is capable of handling both unknown surface heat flux and unknown surface temperature of solids using temperature histories measured at a few discrete point. The proposed algorithms were used in the study of the thermofracture behavior of leaking pipelines with experimental verifications.

scholarly journals Dryline Bulge Evolution in a Two-Dimensional Mixed-Layer Model

2004 ◽  
Vol 61 (21) ◽  
pp. 2528-2543 ◽  
Author(s):  
Glenn M. Auslander ◽  
Peter R. Bannon
Keyword(s):  
Heat Flux ◽  
Mixed Layer ◽  
Surface Heat Flux ◽  
Mixed Layer Depth ◽  
Surface Heat ◽  
Two Dimensional ◽  
Layer Model ◽  
Layer Depth ◽  
Inversion Strength ◽  
Mixed Layer Model

Abstract This study examines the diurnal response of a mixed-layer model of the dryline system to localized anomalies of surface heat flux, topography, mixed-layer depth, and inversion strength. The two-dimensional, mixed-layer model is used to simulate the dynamics of a cool, moist layer east of the dryline capped by an inversion under synoptically quiescent conditions. The modeled domain simulates the sloping topography of the U.S. Great Plains. The importance of this study can be related to dryline bulges that are areas with enhanced convergence that may trigger convection in suitable environmental conditions. All anomalies are represented by a Gaussian function in the horizontal whose amplitude, size, and orientation can be altered. A positive, surface-heat-flux anomaly produces increased mixing that creates a bulge toward the east, while a negative anomaly produces a westward bulge. Anomalies in topography show a similar trend in bulge direction with a peak giving an eastward bulge, and a valley giving a westward bulge. Anomalies in the initial mixed-layer depth yield an eastward bulge in the presence of a minimum and a westward bulge for a maximum. An anomaly in the initial inversion strength results in a westward bulge when the inversion is stronger, and an eastward bulge when the inversion is weak. The bulges observed in this study at 1800 LT ranged from 400 to 600 km along the dryline and from 25 to 80 km across the dryline. When the heating ceases at night, the entrainment and eastward movement of the line stops, and the line surges westward. This westward surge at night has little dependence on the type of anomaly applied. Whether a westward or eastward bulge was present at 1800 LT, the surge travels an equal distance toward the west. However, the inclusion of weak nocturnal friction reduces the westward surge by 100 to 200 km due to mechanical mixing of the very shallow leading edge of the surge. All model runs exhibit peaks in the mixed-layer depth along the dryline at 1800 LT caused by enhanced boundary layer convergence and entrainment of elevated mixed-layer air into the mixed layer. These peaks appear along the section of the dryline that is least parallel to the southerly flow. They vary in amplitude from 4 to 9 km depending on the amplitude of the anomaly. However, the surface-heat-flux anomalies generally result in peaks at the higher end of this interval. It is hypothesized that the formation of these peaks may be the trigger for deep convection along the dryline in the late afternoon.

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