Hybrid Darrieus - Savonius Wind Turbine

HEAT PIPE Presented by:Subrat Kumar DashRoll no:11/ME-113Regd no:1221225088

Contents

A heat pipe heat exchanger is a simple device which is made use of to transfer heat from one location to another, using an evaporation-condensation cycle.Heat pipes are referred to as the "superconductors" of heat due to their fast transfer capability with low heat loss.

What is a Heat Pipe?

Working PrincipleThe heat input region of the heat pipe is called evaporator, the cooling region is called condenser.In between the evaporator and condenser regions, there may be an adiabatic region

Components of Heat Pipe Container Working fluid Wick or Capillary structure

1.Container The function of the container is to isolate the working fluid from the outside environment. Selection of the container material depends on many factors. These are as follows:

Compatibility (both with working fluid and external environment)Strength to weight ratioThermal conductivityEase of fabrication, including welding, machineability and ductilityPorosityWettability

Container materialsOf the many materials available for the container, three are by far the most common in usename copper, aluminum, and stainless steel. Copper is eminently satisfactory for heat pipes operating between 0200c in applications such as electronics cooling. While commercially pure copper tube is suitable, the oxygen-free high conductivity type is preferable. Like aluminum and stainless steel, the material is readily available and can be obtained in a wide variety of diameters and wall thicknesses in its tubular form.

2.Working Fluid The prime requirements are:Compatibility with wick and wall materialGood thermal stabilityWettability of wick and wall materialsVapor pressure not too high or low over the operating temperature rangeHigh latent heatHigh thermal conductivityLow liquid and vapor viscositiesHigh surface tensionAcceptable freezing or pour point

Examples of Working FluidMediumMelting Point

(C)Boiling Point at

Atm. Pressure

(C)Useful Range

(C)

Helium-271-261-271 to -269Nitrogen-210-196-203 to -160Ammonia-78-33-60 to 100Acetone-95570 to 120Methanol-986410 to 130Flutec PP2-507610 to 160Ethanol-112780 to 130Water010030 to 200Toluene-9511050 to 200Mercury-39361250 to 650Sodium98892600 to 1200Lithium17913401000 to 1800Silver96022121800 to 2300

3.Wick StructureIt is a porous structure made of materials like steel,alumunium, nickel or copper in various ranges of pore sizes.The prime purpose of the wick is to generate capillary pressure to transport the working fluid from the condenser to the evaporator. It must also be able to distribute the liquid around the evaporator section to any area where heat is likely to be received by the heat pipe.

Wicks are fabricated using metal foams, and more particularly felts, the latter being more frequently used. By varying the pressure on the felt during assembly, various pore sizes can be produce.The maximum capillary head generated by a wick increases with decrease in pore size.The wick permeability increases with increasing pore size. Another feature of the wick, which must be optimized, is its thickness. The heat transport capability of the heat pipe is raised by increasing the wick thickness. Other necessary properties of the wick are compatibility with the working fluid and wettability.

Wick working phenomenon

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Wick DesignTwo main types of wicks: homogeneous and composite.Homogeneous- made from one type of material or machining technique. Tend to have either high capillary pressure and low permeability or the other way around. Simple to design, manufacture, and install .Composite- made of a combination of several types or porosities of materials and/or configurations. Capillary pumping and axial fluid transport are handled independently . Tend to have a higher capillary limit than homogeneous wicks but cost more.

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Three properties effect wick designHigh pumping pressure - a small capillary pore radius (channels through which the liquid travels in the wick) results in a large pumping (capillary) pressure.Permeability - large pore radius results in low liquid pressure drops and low flow resistance. Design choice should be made that balances large capillary pressure with low liquid pressure drop. Composite wicks tend to find a compromise between the two.Thermal conductivity - a large value will result in a small temperature difference for high heat fluxes.

Fig: The actual test results of heat pipe with different wick structure athorizontal and vertical (gravity assist) orientations.

Types of Heat PipesThermosyphonLeading edgeRotating and revolvingCryogenic pumped loop heat pipe Flat Plate-Micro heat pipesVariable conductanceCapillary pumped loop heat pipe

Advantages Of Heat PipesMay reduce or eliminate the need fir reheat,Allow cost effective manner to accommodate new ventilation standards,Requires no mechanical or electrical input,Are virtually maintenance free,Provide lower operating costs,Last a very long time,Readily adaptable to new installations and retrofiting existing A/C units andAre environmentally safe.

Lift and Drag Drag-based wind turbine In drag-based wind turbines, the force of the wind pushes against a surface, like an open sail. In fact, the earliest wind turbines, dating back to ancient Persia, used this approach. The Savonius rotor is a simple drag-based windmill that you can make at home (Figure 1). It works because the drag of the open, or concave, face of the cylinder is greater than the drag on the closed or convex section. Lift-based Wind Turbines More energy can be extracted from wind using lift rather than drag, but this requires specially shaped airfoil surfaces, like those used on airplane wings (Figure 2). The airfoil shape is designed to create a differential pressure between the upper and lower surfaces, leading to a net force in the direction perpendicular to the wind direction. Rotors of this type must be carefully oriented (the orientation is referred to as the rotor pitch), to maintain their ability to harness the power of the wind as wind speed changes. Airflow over any surface creates two types of aerodynamic forces drag forces, in the direction of the airflow, and lift forces, perpendicular to the airflow. Either or both of these can be used to generate the forces needed to rotate the blades of a wind turbine. 18

Ideal Thermodynamic Cycle

Heat Pipe ApplicationsElectronics cooling- small high performance components cause high heat fluxes and high heat dissipation demands. Used to cool transistors and high density semiconductors.

Aerospace- cool satellite solar array, as well as shuttle leading edge during reentry.

Heat exchangers- power industries use heat pipe heat exchangers as air heaters on boilers.

Other applications- production tools, medicine and human body temperature control, engines and automotive industry.

Conclusion

REFERENCES

Andrews, J; Akbarzadeh, A; Sauciue, I.: Heat Pipe Technology, Pergammon, 1997.Dunn, P.D.; Reay, D.A.: Heat Pipes, Pergammon, 1994.www.heatpipe.com.www.cheresources.com.www.indek.comwww.wikipedia.org

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