Investigation of heat transfer during boiling on a flat surface by a nonstationary method

AbstractAn unsteady, laminar, mixed convective stagnation point nanofluid flow through a permeable stretching flat surface using internal heat source or sink and partial slip is investigated. The effects of thermophoresis and Brownian motion parameters are revised on the traditional model of nanofluid for which nanofluid particle volume fraction is passively controlled on the boundary. Spectral relaxation method is applied here to solve the non-dimensional conservation equations. The results show the illustration of the impact of skin friction coefficient, different physical parameters, and the heat transfer rate. The nanofluid motion is enhanced with increase in the value of the internal heat sink or source. On the other hand, the rate of heat transfer on the stretching sheet and the skin friction coefficient are reduced by an increase in internal heat generation. This study further shows that the velocity slip increases with decrease in the rate of heat transfer. The outcome results are benchmarked with previously published results.

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A Numerical Study of Turbulent Boundary Layer Flow Over a Flat Surface With a Single Dimple

10.1115/imece2000-1282 ◽

2000 ◽

Author(s):

Mark E. Kithcart ◽

David E. Klett

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Turbulent Boundary Layer ◽

Boundary Layer Flow ◽

Flat Surface ◽

Numerical Study ◽

Heat Transfer Augmentation ◽

Study Results ◽

Turbulent Boundary Layer Flow ◽

Layer Flow

Abstract Turbulent boundary layer flow over a flat surface with a single dimple has been investigated numerically using the FLUENT CFD software package, and compared to an experiment by Ezerskii and Shekhov [1989], which studied the same configuration. The impetus for this work developed as a result of previous studies. Kithcart and Klett [1996], and Afanas’yev and Chudnovskiy [1992], showed that dimpled surfaces enhance heat transfer comparably to surfaces with protrusion roughness elements, but with a much lower drag penalty. However, the actual physical mechanisms involved in this phenomena were only partially known prior this study. Results obtained numerically are in good agreement with the experiment, most notably the confirmation of the existence of a region of enhanced heat transfer created by interaction of the flow with the dimple. In particular, the simulation indicates that heat transfer augmentation is a consequence of the development of a stagnation flow region within the dimple geometry, and the existence of coherent vortical structures which create a periodic flow-field within and immediately downstream of the dimple. This periodicity appears to govern the magnitude of the heat transfer augmentation.

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AERODYNAMICS OF JETS INTERACTING WITH A FLAT SURFACE

Izvestiya Ferrous Metallurgy ◽

10.17073/0368-0797-2019-4-263-269 ◽

2019 ◽

Vol 62 (4) ◽

pp. 263-269

Author(s):

I. A. Pribytkov ◽

S. I. Kondrashenko

Keyword(s):

Heat Transfer ◽

Critical Point ◽

Flat Surface ◽

Stokes Equations ◽

Thermal State ◽

Exchange Process ◽

Three Dimensional ◽

Internal Diameter ◽

Three Dimensional Model ◽

Aerodynamic Properties

In this paper, the development features of a single free jet of hightemperature nitrogen interacting with a ﬂat surface were studied. Calculation of the heat exchange process during heating by the attacking jets is very difficult to implement analytically due to complexity of the gas-dynamic processes occurring both in a single jet and in a system of jets interacting with the metal. The computational difficulties are aggravated by the fact that when interacting with the surface the jet as such disappears. The ﬂat (fan) ﬂow interacts with the surface: form, aerodynamic properties and thermal state of the ﬂow strongly diﬀer from those of the original jet. The studies were conducted on the basis of numerical simulation in the FloEFD software and computing complex for multiphysical simulation based on solution of the equations of gas dynamics and heat transfer. The solved system of equations consisted of Navier-Stokes equations, equations of energy and continuity and was supplemented by k – ε turbulence model. A three-dimensional model was developed for simulation, the necessary properties, initial and boundary conditions were specified. In the study of aerodynamics of a single high-temperature jet interacting with the surface, the main defining values were: nitrogen ﬂow rate from the nozzle U0 , nitrogen temperature T, internal diameter of the nozzle d0 , distance from the nozzle section to the surface h, distance from the critical point (point of intersection of the jet axis with the surface) along the ﬂow radius r. Data on the gas velocity decrease as the jet develops due to the loss of initial energy to engage the motionless surrounding gas in motion, is presented. The studies have shown that increase in the initial velocity of gas outﬂow brings the area of higher velocities closer to the surface both in the jet itself and in the fan jet. This factor contributes to heat transfer intensification. In addition, high speeds increase the total thickness of the fan ﬂow and reduce the thickness of hydrodynamic boundary layer, which increases with distance from the critical point.

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Free-convection effects in the boundary layer along a vertically stretching flat surface

Canadian Journal of Physics ◽

10.1139/p92-204 ◽

1992 ◽

Vol 70 (12) ◽

pp. 1253-1260 ◽

Cited By ~ 16

Author(s):

John E. Daskalakis

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Free Convection ◽

Skin Friction ◽

Flat Surface ◽

Relaxation Method ◽

Boussinesq Approximation ◽

Axial Coordinate ◽

Prandtl Numbers ◽

Energy Equations

We assess the effects of free convection on the boundary layer formed along a flat surface stretching vertically in a quiescent fluid. The flow is laminar and incompressible, the buoyancy forces conform to the Boussinesq approximation and the surface temperature is variable. The two-point boundary value problem of the coupled momentum and energy equations is solved using a simple and accurate relaxation method that provides the general nonsimilar solution to the flow. The effect of free-convection currents on velocity and temperature profiles, skin friction, and heat transfer is studied by varying the flow Grashof and Prandtl numbers. Zero shear stress and heat-transfer rate are predicted at some axial coordinate on a surface with decreasing wall temperature. Also the skin friction is markedly modified by the buoyancy while the heat transfer at the surface is correspondingly only moderately influenced.

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