INVESTIGATION OF HEAT TRANSFER CHARACTERISTICS

Categories: Chemistry Mechanical Engineering Physics

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Abstract

The experimental and, numerical results of trapezoidal channel provided with Semi-circular vortex generator on the flat plate for internal cooling are discussed.

From the literature survey conclude that the semi-circular vortex generator in inline arrangement has a high rate of heat transfer compared with other type of vortex generator. It is found that for the channel with inline arranged vortex generator, maximum heat transfer enhancement is attained. Staggered arrangement of the same vortex generator reduces pressure drop but also effects enhancement in heat transfer negatively.

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The thermal performance of the vortex generator size is an important parameter and its optimum value should be found out.

Enter key words- Semi-circular Vortex generator, Heat Transfer rate, Performance evaluation factor.

INTRODUCTION

The various techniques are used to enhance the rate of heat transfer over surface of plate. It may be passive or active technique. The significant pressure drag produced by the rib or pin fin protrusion into the flow. Heat transfer inside flow channels can be enhanced by using passive techniques such as rib tabulators, vortex, protrusions, fins, and dimples.

These heat transfer enhancement techniques have practical application for internal cooling of turbine blades, internal combustion chamber liners and electronics cooling devices, biomedical devices and heat exchangers. The heat transfer can be increased by the following different Techniques. They are broadly classified into three different categories:

Passive Techniques
Active Techniques
Compound Techniques.
Passive techniques

These techniques generally use surface or geometrical modifications to the flow channel by incorporating inserts or additional devices. They promote higher heat transfer coefficients by disturbing or altering the existing flow behaviour (except for extended surfaces) which also leads to increase in the pressure drop.

In case of extended surfaces, effective heat transfer area on the side of the extended surface is increased. Passive techniques hold the advantage over the active techniques as they do not require any direct input of external power. These techniques do not require any direct input of external power; rather they use it from the system itself which ultimately leads to an increase in fluid pressure drop. They generally use surface or geometrical modifications to the flow channel by incorporating inserts or additional devices. They promote higher heat transfer coefficients by disturbing or altering the existing flow behaviour except for extended surfaces.

Active techniques

These techniques are more complex from the use and design point of view as the method requires some external power input to cause the desired flow modification and improvement in the rate of heat transfer. It finds limited application because of the need of external power in many practical applications. In comparison to the passive techniques, these techniques have not shown much potential as it is difficult to provide external power input in many cases.

Compound Techniques.

A compound augmentation technique is the one where more than one of the above mentioned techniques is used in combination with the purpose of further improving the thermo-hydraulic performance of a heat exchanger.

When any two or more of these techniques are employed simultaneously to obtain enhancement inheat transfer that is greater than that produced by either of them when used individually, is termed as compound enhancement. This technique involves complex design and hence has limited applications.

Literature Survey:

CharbelHabchi, Serge Russeil, et al. Global and local analysis of the heat transfer in turbulent vortical flows is studied using three-dimensional numerical simulations. Vorticity is generated by inclined vortex generators in a turbulent circular pipe flow with twelve different configurations that fall into three categories is studied by CharbelHabchi.

Li Li, XiaozeIn 2015 Li Li, Xiaozepresent the paper onFin-and-tube heat exchangers with longitudinal vortex, plain fins are widely used in direct air-cooled condenser system in the power plant, because of its relatively simple property compared to some other fins with variable cross-sectional area channel.

Azitaabdollahi, Msc, Prof. Mehrzad Shams A three dimensional numerical investigation of the fluid flow and heat transfer behaviour of longitudinal vortex generator (LVG) has been carried out in a rectangular micro heat sink in the Reynolds number range between 200 and 1100 in the temperature range without involving phase change. These findings have important bearing on achieving enhanced cooling performance for small electronic devices not involving any complicated geometric arrangement.

P.W. Deshmukh, S.V. Prabhu, R.P. VedulaThe results of an experimental study for heat transfer enhancement in a circular tube fitted with a curved delta wing vortex generator insert are presented. The average Nusselt number ratio with and without the insert (Nua/Nus), at equal Reynolds number (Re) was found to be in the range of 5.0 to 15.0. The performance ratio R3, (Nua/Nuc), based on equal pumping power and constant heat transfer area, was found to be in the range of 1.0 to 6.0.

Mohammad Oneissi, CharbelHabchi, Serge Russeil, Daniel BougeardHeat transfer is a naturally occurring phenomenon that can be greatly enhanced with the aid of vortex generators (VG). Three-dimensional numerical simulations of longitudinal vortex generators were performed to analyze heat transfer enhancement in parallel plate-fin heat exchanger. This study highlights the different mechanisms involved in the convective heat transfer intensification by generating more vortices using more aerodynamic VG shape while decreasing the pressure drop penalty.

AnupamSinha, HimadriChattopadhyay, AshwinKannanIyengar, GautamBiswas had studied that simulates the air flow through fin-tube type heat exchangers with rectangular winglet pairs (RWP) of half the channel height as vortex generators (VG). They studied the in-line row of tubes, whereas with the staggered row of tubes, there was slight deviation of this trend. Due to the alternate CFD-CFU orientations of the VG, the performance improves with increase in angle of attack up to a certain point and afterwards it was going down.

KeWei Song, WanLing Hu, Song Liu, LiangBi Wang In 2016, KeWei Song publish paper on secondary flow intensity and heat transfer intensity in flat-tube-and-fin air heat exchanger with vortex generators. There was no corresponding relationship neither between Nu and Re nor between f and Re.

R.K. Ali this study investigated experimentally the effect of rectangular winglet vortex generators on thermal performance of square flat heat source near a wake region. Rectangular winglets were fixed on the base board with common inflow orientation to direct the flow toward the core of stagnation zone. For physical situation of two rows, of the downstream heat source with installing rectangular winglets vortex generators can be enhanced by 14.5% within at X=10/50,Y=10/50 and . An insignificant increase in the friction factor of 9.7% over was noticed.

A. Esmaeilzadeh, N. Amanifard, H.M. Deylamicomparison of simple and curved trapezoidal longitudinal vortex generators for optimum flow characteristics and heat transfer augmentation in a heat exchanger is studied. Numerical results showed that CTWP has a lower pressure drop and a better overall performance compared to TWP. To achieve a maximum heat transfer augmentation and a minimum pressure drop, optimal height and clearance between two vortex generators had been determined by using and combining computational fluid dynamics analysis, artificial neural networks and single-objective genetic algorithm.

Ralph Kristoffer B. Gallegosa, Rajnish N. Sharmaathe use of flexible plates or "flags" as vortex generators inside a channel was successfully demonstrated as an alternative heat transfer enhancement technique. This paper is a brief review of flag vortex generators for thermal enhancement. Although flag dynamics was widely reported. Extensive and intensive experimental results were lacking to validate numerical and theoretical predictions.

S.A. Isaev, A.V. Schelchkov, A.I. Leontiev, Yu F. GortyshovVortex heat transfer enhancement in the narrow plane-parallel channelwith the oval-trench dimple of fixed depth and spot area paper present. The article was devoted to the analysis of vortex heat transfer enhancement due to the use of oval-trench dimples. In this case, moderate hydraulic losses in the channel with an oval-trench dimple, when its length is increased to 6.78, were comparable to those in the channel with a basic spherical dimple.

Hung-Yi Li, Wan-Rong Liao, Tian-Yang Li, Yan-Zuo Chang in this paper the thermal-fluid characteristics of a pin-fin heat sink with delta winglet vortex generators in a cross flow are investigated experimentally and numerically. The thermal resistance of the heat sink with the vortex generators arranged in the common-flow-up configuration was lower than that of the heat sink with the vortex generators arranged in the common-flow-down configuration.

Lei Luo, Fengbo Wen, Lei Wang, BengtSund?n, Songtao Wang In this study, effects of dimples and their arrangement on the flow structure, heat transfer and friction factor in a solar receiver heated channel with delta-winglet vortex generators (DWVGs) were numerically studied. The thermal performance analysis indicates that the use of dimples increases the thermal performance by 28.50%. It was also found that the adoption of inline dimples contributes to the optimal thermal performance and mixing of the cold and hot fluid.

J. Ortega-Casanova, F. Molina-Gonzalez The consequences of installing one or two vortex generators on a flat plate under axisymmetric conditions were presented in the work in order to analyse if heat transfer from the plate can be enhanced. The averaged heat transfer on the tabbed plate can be improved up to around 4.5% with just a 2% of more pumping power due to pressure losses on the tabs. Furthermore, it is even more remarkable the fact that the averaged heat transfer can even be enhanced with around 25% of less pumping power requirements than when the plate is completely flat.

From above literature it can be conclude that very less work was reported on divergent channel with semi circular vortex generator.

Problem Statement

Experimental and Analytical Investigation of Heat Transfer Enhancement through Inline and Staggered vortex generator for divergent Channel.

Objectives of the Study

Thermal Performance enhancement analysis in semi-circularvortex generator.

Conduct the experimental study on semi-circular vortex generator for different parameters of performance (E.g. Nusselt Number, Arrangement of Geometry, Pressure drop & PEF etc)