Vol. 04, Issue 07, July 2019 Available Online: www.ajeee.co.in/index.php/AJEEE THERMAL ANALYSIS OF THE MICRO CHANNEL IN HEAT EXCHANGER
Praween Kumar Prajapati1 and Ram Kumar Vishwakarma2
1Research Scholar, Department of Mechanical Engineering
2Assistant Prof., Department of Mechanical Engineering Swami Vivekananda University Sagar (MP)
Abstract:- A 3D micro channel in transient condition by the hydro progressively completely created was explored. The primary mean to build the disturbance of the liquid by the a helical curved tape supplement and the contrast and the channel without turned tape. Since the more the disturbance in liquid more the convective warmth move. A business CFD bundle is a utilized for examination. An isothermal wall condition by the Re equivalent to 100 which is a equivalent to delta speed of the 0.67m/s is a taken as limit condition. the primary point is a to think about the warmth move rate, hub wall shear pressure, skin erosion coefficient, Nusselt number, wall fluxes and the warmth move coefficient for the channel by the wound tape as for the without contorted tape. It is a discovered that the expansion in choppiness happens in micro channel because of the bent tape embed. Likewise it is a discovered that warmth move attributes like hub wall shear pressure, skin grinding coefficient, surface nusselt number and the surface warmth move coefficient are more prominent in by the curved tape regarding without wound tape.
1. INTRODUCTION
The investigation of the reduced gadgets has been conspicuousness in the previous multi decade. We as-a whole realize that the fundamental driver for harming the gadget's segment is the high warmth motion produced in the devices. to spare the part from the harm the warmth evacuation instrument must be investigated. Small scale gadgets are micron in size and the have numerous application in miniaturized scale electro mechanical framework, incorporated circuit, biochemical application since it is a most appropriate strategy for expelling warmth motion.
Classification of the Micro channel It is a very debatable topic between the researchers to define a definition of the micro channel. Mehendale et al. (2000) used a classification technique which is a based on manufacturing to obtain various varieties of the channel dimensions, where D is the smallest channel dimension.
1 μm < D < 100: Micro Channel 100
μm < D < 1 mm: Mini Channels
1 mm < D < 6 mm: Compact Passages
6 mm < D: Conventional Passages Kandlikar and the Grande (2003) adopted a different classification based on the
200 μm < D < 3mm: Mini channels
3mm < D: Conventional Passages Heat transfer enhancement technique It is a technique used to increase thermo hydraulic properties of the heat exchanger devices. It can be classified into three ways i.e.
1.1 Active Technique
From assembling perspective these strategies are intricate and the some outer power is a required for wanted stream to improve the warmth move rate. In view of the outside power expected to make is a has restricted application.
Distinctive dynamic procedures are as:-
• Mechanical aids: Scrapped heat exchanger and the turning cylinder heat exchanger are produced by the help of mechanical guide strategies.
Working guideline of the this methods is a blending the fluid by the help of methods for turning the surfaces.
• Surface vibration: Mostly it have been utilized in single stage stream.
To get a higher convective warmth move coefficient a recurrence of the low or high plenty fullness is a
Vol. 04, Issue 07, July 2019 Available Online: www.ajeee.co.in/index.php/AJEEE AC or DC sources to build the
warmth move by the help of blending of the fluid. It utilizes dielectric fluid of the warmth move process.
1.2 Passive technique
These techniques use the power from itself rather than external source which results in increase in pressure drop of the fluid. Some modification in geometry or surface cause higher heat transfer rate by the help of disturbing the behavior of the fluid.
Different active techniques are as:-
Treated surface: This techniques includes alteration of the surfaces like pits, cavity or scratches at the heat transfer area. This method are mainly used in boiling and the condensation purposes.
Rough Surface: by the help of employing this method a disturbance is a created in the region of the viscous sub layer. This method is a mainly used in single phase turbulent flows.
Extended surfaces: the most commonly used extended surfaces are plain fins which is a mainly used in heat exchanger. In the present era
finned surfaces become very popular due to their ability to interrupt the flow field which in turns the increase the heat transfer rate.
Displaced enhancement devices:
this method are mainly used in forced convection. They enhance the heat transfer indirectly at the surface of the heat exchanger by the help of shifting the fluid from the surface which is a heated or cooled by the bulk fluid.
Swirl Flow devices: they create the swirl flow in the axial direction of the channel. The common example of the swirl flow devices are helical twisted tape and the twisted ducts. It can be used in both type of the flow i.e. single phase flow and the double phase flow.
Coiled Tubes: In single phase flow generation of the vortices are caused by the help of curvature of the coiled which results in higher heat transfer coefficient. This phenomenon is a mainly occurs in regions of the boiling.
2. MATHEMATICAL MODELLING Computational domain
Case 1
Figure 3.1 Square micro channel without twisted tape Case 2
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Figure 3.2 Square micro channel by the twisted tape
3. PROBLEM FORMULATION 3.1 Problem Description
A 3D laminar and the unsteady state flow through a square micro channel has been analyzed. Dimension of the micro channel are in micro meter. The cross section of the micro channel is a 0.15×0.15 mm and the length of the channel is a 100 mm and the thickness of the channel is a 0.15 mm along all four side of the wall over the entire length. The side wall of the micro channel is a considered to be isothermal condition i.e.
constant temperature. At the inlet fluid is a entering at ambient temperature i.e. 300 K and the leaving at the outlet where the
gauge pressure is a zero. Pressure driven flow is a considered. The isothermal wall considered as-a temperature of the 335 K.
the geometry is a created in ANSYS WORKBENCH and the simulation is a done by the help of the FLUENT. Flow variable like velocity, temperature and the pressure have been analyzed at different cross section of the pipe. For convective heat transfer Nusselt number plays a very significant role are plotted. Main aim to investigate the compare Nusselt number, skin friction coefficient, axial wall shear stress, convective heat transfer for the two cases.
3.2 Simulation Approach
The above stated 3D geometry of the 2 cases is a created by the help of using ANSYS WORKBENCH 15.0. Total number of the meshed cell is a equal to 160000. the detailed meshed geometry is a shown in fig. Apply all the boundary condition and the initialize the problem by the help of choosing a suitable solver iterate the problem. the convergence of the residual is a shown in fig
Case 1
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Figure 2 Completed meshed geometry of the micro channel by the twisted tape
3.3 Convergence limit Case 1
Figure 3 Convergence residual of the micro channel without twisted tape Case 2
Figure 4 Convergence residual of the micro channel by the twisted tape
Vol. 04, Issue 07, July 2019 Available Online: www.ajeee.co.in/index.php/AJEEE 4. RESULTS AND THE DISCUSSION
4.1 Axial wall shear stress
Figure 5 Wall shear stress vs axial distance 4.2 Skin Friction Coefficient
Figure 6 Skin friction coefficient vs axial distance Surface heat transfer coefficient
Vol. 04, Issue 07, July 2019 Available Online: www.ajeee.co.in/index.php/AJEEE Fig 5 shows the trend of the axial wall
shear stress along the axial length. From the diagram it can be seen that the value of the axial wall shear stress is a more for twisted tape than the without the twisted tape. This is a due to the reason of the increase in velocity of the at the wall by the help of twisted tape. Fig 6 shows the trend of the skin friction coefficient along the axial length. From the diagram it can be seen that the value of the skin friction coefficient is a more for twisted tape than without twisted tape.
This is a due to the reason of the increase in wall shear stress at the wall by the help of twisted tape. Fig.7 shows the trend of the surface heat transfer coefficient along the axial length. From the diagram it can be seen that the value of the surface heat transfer coefficient is a more for twisted tape than without twisted tape. This is a due to the reason that the more convective heat transfer in twisted tape due to turbulence in fluid.
4. CONCLUSION
1. It is a found that the axial wall shear stress increases when the twisted tape insert is a employed by the conventional micro channel.
2. It can be concluded that the skin friction coefficient increases when the twisted tape insert is a employed by the conventional micro channel.
3. From the above results it is a found that surface nusselt number increases when the twisted tape insert is a employed by the conventional micro channel.
4. Also Surface heat transfer coefficient increases when the twisted tape insert is a employed by the conventional micro channel.
5. Due to twisted tape insert the increase in turbulence occurs which results in higher convective heat transfer.
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