Role of ‘Bejan’s heatlines’ in heat flow visualization and optimal thermal mixing for differentially heated square enclosures

2008 ◽  
Vol 51 (13-14) ◽  
pp. 3486-3503 ◽  
Author(s):  
Tanmay Basak ◽  
S. Roy
Keyword(s):  
Heat Flow ◽  
Flow Visualization ◽  
Thermal Mixing

Modelling the Air-Cooled Gas Turbine: Part 1 — General Thermodynamics

2001 ◽  
Author(s):  
J. B. Young ◽  
R. C. Wilcock
Keyword(s):  
Gas Turbine ◽  
Performance Prediction ◽  
Real Gas ◽  
Thermal Mixing ◽  
Ideal Gases ◽  
Formal Framework ◽  
Considerable Simplification ◽  
Cycle Efficiency ◽  
General Thermodynamics

This paper is Part I of a study concerned with developing a formal framework for modelling air-cooled gas turbine cycles and deals with basic thermodynamic issues. Such cycles involve gas mixtures with varying composition which must be modelled realistically. A possible approach is to define just two components, air and gas, the latter being the products of stoichiometric combustion of the fuel with air. If these components can be represented as ideal gases, the entropy increase due to compositional mixing, although a true exergy loss, can be ignored for the purpose of performance prediction. This provides considerable simplification. Consideration of three idealised simple cycles shows that the introduction of cooling with an associated thermal mixing loss does not necessarily result in a loss of cycle efficiency. This is no longer true when real gas properties and turbomachinery losses are included. The analysis clarifies the role of the cooling losses and shows the importance of assessing performance in the context of the complete cycle. There is a strong case for representing the cooling losses in terms of irreversible entropy production as this provides a formalised framework, clarifies the modelling difficulties and aids physical interpretation. Results are presented which show the effects on performance of varying cooling flowrates and cooling losses. A comparison between simple and reheat cycles highlights the rôle of the thermal mixing loss. Detailed modelling of the heat transfer and cooling losses is discussed in Part II of this paper.

The Role of Vortices and Unsteady Effects During the Hovering Flight of Dragonflies

1979 ◽  
Vol 83 (1) ◽  
pp. 59-77 ◽  
Author(s):  
STUART B. SAVAGE ◽  
BARRY G. NEWMAN ◽  
DENIS T.-M. WONG
Keyword(s):  
Steady State ◽  
Flow Field ◽  
Flow Visualization ◽  
Inviscid Flow ◽  
Physical Explanation ◽  
Hovering Flight ◽  
Wing Motion ◽  
Unsteady Effects ◽  
Animal Flight

Weis-Fogh and Norberg concluded that steady-state aerodynamics is incapable of explaining how the dragonfly supports its weight during hovering. Norberg also concluded that the wing kinematics of Aeschna juncea L., as determined photographically, are incompatible with those proposed by Weis-Fogh for his Flip mechanism. The present paper has proposed an alternative lift-generating mechanism, various aspects of which are novel from the standpoint of animal flight. Flow visualization tests performed in water established the flow field during a complete cycle of the idealized wing motion. Using this information and unsteady inviscid flow theory the forces were analysed. A plausible balance of horizontal forces and more than sufficient lift were obtained. A physical explanation of the theory is provided for those who do not wish to study the mathematical details.

Numerical heat flow visualization analysis on enhanced thermal processing for various shapes of containers during thermal convection

2019 ◽  
Vol 30 (7) ◽  
pp. 3535-3583 ◽  
Author(s):  
Leo Lukose ◽  
Tanmay Basak
Keyword(s):  
Finite Element ◽  
Heat Flow ◽  
Flow Visualization ◽  
Thermal Processing ◽  
Bottom Wall ◽  
Heat Distribution ◽  
Content Type ◽  
Class 1

Purpose The purpose of this paper is to study thermal (natural) convection in nine different containers involving the same area (area= 1 sq. unit) and identical heat input at the bottom wall (isothermal/sinusoidal heating). Containers are categorized into three classes based on geometric configurations [Class 1 (square, tilted square and parallelogram), Class 2 (trapezoidal type 1, trapezoidal type 2 and triangle) and Class 3 (convex, concave and triangle with curved hypotenuse)]. Design/methodology/approach The governing equations are solved by using the Galerkin finite element method for various processing fluids (Pr = 0.025 and 155) and Rayleigh numbers (103 ≤ Ra ≤ 105) involving nine different containers. Finite element-based heat flow visualization via heatlines has been adopted to study heat distribution at various sections. Average Nusselt number at the bottom wall ( Nub¯) and spatially average temperature (θ^) have also been calculated based on finite element basis functions. Findings Based on enhanced heating criteria (higher Nub¯ and higher θ^), the containers are preferred as follows, Class 1: square and parallelogram, Class 2: trapezoidal type 1 and trapezoidal type 2 and Class 3: convex (higher θ^) and concave (higher Nub¯). Practical implications The comparison of heat flow distributions and isotherms in nine containers gives a clear perspective for choosing appropriate containers at various process parameters (Pr and Ra). The results for current work may be useful to obtain enhancement of the thermal processing rate in various process industries. Originality/value Heatlines provide a complete understanding of heat flow path and heat distribution within nine containers. Various cold zones and thermal mixing zones have been highlighted and these zones are found to be altered with various shapes of containers. The importance of containers with curved walls for enhanced thermal processing rate is clearly established.

Numerical Visualization of Heat Flow and Thermal Mixing in Various Differentially Heated Square Cavities Using Bejan’s Heatlines

2011 ◽  
Author(s):  
Ram Satish Kaluri ◽  
Tanmay Basak
Keyword(s):  
Heat Flow ◽  
Bottom Wall ◽  
Temperature Fields ◽  
Heat Distribution ◽  
Heat Sources ◽  
Large Area ◽  
Thermal Mixing ◽  
Uniform Heat ◽  
High Heat Transfer ◽  
Lower Corner

A comprehensive analysis of heat distribution and thermal mixing in steady laminar natural convective flow in discretely heated square cavities has been carried out via Bejan’s heatlines. Heatlines are analogous to streamlines and heat energy flow may be visualized by heatlines similar to streamlines which display fluid flow. The trajectories of heatlines indicate direction and magnitude of heat flow and zones of high heat transfer. The heatline approach is implemented to study heat flow in the following three different square cavities which are filled with water (Pr = 7): (1) uniformly heated bottom wall (2) distributed heating with heat sources present on central portions of the walls and (3) multiple heat sources on the walls of the cavity. Top wall is maintained adiabatic in all the cases. Galerkin finite element method with penalty parameter has been used to solve non-linear coupled partial differential equations for flow and temperature fields over a range of Rayleigh numbers (Ra = 103–105). The Galerkin method is further employed to solve the Poisson equation for streamfunctions and heatfunctions. Finite discontinuity exists at the junction of hot and cold walls leading to mathematical singularity. Solution of heatfunction for such type of situation demands implementation of non-homogeneous Dirichlet conditions. Heatlines illustrate that in uniformly heated bottom wall case, the heat from the bottom wall is not adequately distributed to the lower portion of side walls which leads to low temperature in those regions (case 1). In order to improve the heat distribution, the uniform heat sources is divided into three parts and are applied along the central regimes of the walls (case 2). It is observed that, heat distribution and thermal mixing in the cavity is significantly enhanced. However, the lower corner portions are still retained cold. In case 3, multiple heat sources are placed along the walls of the cavity along with heat sources at lower corner regions of the cavity. Heatlines indicate that, the temperature at the core is reduced compared to case 2, but uniform heat distribution results in uniformity of temperature across large area of cavity.

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