Heat Pipe Heat Exchanger Explained
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Basic Information About Heat Pipes
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Heat Pipe Heat Exchanger Explained
- 2. 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?
- 3. Working Principle • The 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
- 4. • Container • Working fluid • Wick or Capillary structure
- 5. 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 ratio Thermal conductivity Ease of fabrication, including welding, machineability and ductility Porosity Wettability
- 6. Container materials Of the many materials available for the container, three are by far the most common in use—name copper, aluminum, and stainless steel. Copper is eminently satisfactory for heat pipes operating between 0–200◦C 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.
- 7. The prime requirements are: 1.compatibility with wick and wall material 2.Good thermal stability 3.wettability of wick and wall materials 4.vapor pressure not too high or low over the operating temperature range 5.high latent heat 6.high thermal conductivity 7.low liquid and vapor viscosities 8.high surface tension 9.acceptable freezing or pour point
- 8. Examples of Working Fluid Medium Melting Point (°C) Boiling Point at Atm. Pressure (°C) Useful Range (°C) Helium -271 -261 -271 to -269 Nitrogen -210 -196 -203 to -160 Ammonia -78 -33 -60 to 100 Acetone -95 57 0 to 120 Methanol -98 64 10 to 130 Flutec PP2 -50 76 10 to 160 Ethanol -112 78 0 to 130 Water 0 100 30 to 200 Toluene -95 110 50 to 200 Mercury -39 361 250 to 650 Sodium 98 892 600 to 1200 Lithium 179 1340 1000 to 1800 Silver 960 2212 1800 to 2300
- 9. 1. It is a porous structure made of materials like steel,alumunium, nickel or copper in various ranges of pore sizes. 2. The prime purpose of the wick is to generate capillary pressure to transport the working fluid from the condenser to the evaporator. 3. 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.
- 10. 4. 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. 5. The maximum capillary head generated by a wick increases with decrease in pore size. 6. The wick permeability increases with increasing pore size. 7. 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. 8. Other necessary properties of the wick are compatibility with the working fluid and wettability.
- 12. Wick Design Two main types of wicks: homogeneous and composite. 1.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 . 2.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.
- 14. Three properties effect wick design 1. High pumping pressure- a small capillary pore radius (channels through which the liquid travels in the wick) results in a large pumping (capillary) pressure. 2. 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. 3. Thermal conductivity - a large value will result in a small temperature difference for high heat fluxes.
- 15. Fig: The actual test results of heat pipe with different wick structure at horizontal and vertical (gravity assist) orientations.
- 16. Types of Heat Pipes Thermosyphon Leading edge- Rotating and revolving- Cryogenic pumped loop heat pipe Flat Plate- Micro heat pipes- Variable conductance- Capillary pumped loop heat pipe-
- 17. Advantages Of Heat Pipes May 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 and Are environmentally safe.
- 19. Heat transport limitationHeat transport limitation description Cause Potential solution Viscous Viscous forces prevent vapor flow in the heat pipe Heat pipe operating below recommended operating temperature Increase heat pipe operating temperature or find alternative working fluid Sonic Vapor flow reaches sonic velocity when exiting heat pipe evaporator resulting in a constant heat transport power and large temperature gradients Power/temperature combination, too much power at low Operating temperature This is typically only a problem at start up. The heat pipe will carry a set power and the large temperature will self correct as heat pipe warms up Entrainment(Floodi ng) High Velocity vapor flow prevents condensate from returning to evaporator Heat pipe operating above designed power input or at too low an operating temperature Increase vapor space diameter or operating temperature Capillary Sum of gravitational, liquid and vapor flow pressure drops exceed the capillary pumping head of the heat pipe wick structure Heat pipe input power exceeds the design heat transport capacity of the heat pipe Modify heat pipe wick structure design or reduce power input Boiling Film boiling in heat pipe evaporator typically initiates at 5- 10 W/cm2 for screen wicks and 20- 30 w/cm2 for powder metal wicks High radial heat flux causes film boiling resulting in heat pipe dry out and large thermal resistances Use a wick with a higher heat flux capacity or spread out the heat load
- 20. Heat Pipe Applications Electronics 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.
- 21. Applications LAPTOP HEAT PIPE SOLUTION
- 22. Heat pipes used in processor
- 23. Space craft
- 25. HEAT PIPE IN CPU
- 26. Camera Cooler Combined Heat pipe / water cooling Jacket for hi-def CCD camera.
- 27. 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.com www.wikipedia.org
- 28. THANK YOU
Editor's Notes
- 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.