05-10-2016, 09:50 AM
1457774415-MECHHeatPipesPPT.pptx (Size: 257.46 KB / Downloads: 4)
Introduction
A heat pipe is a device that efficiently transports thermal energy from its one point to the other.
It utilizes the latent heat of the vaporized working fluid instead of the sensible heat.
As a result, the effective thermal conductivity may be several orders of magnitudes higher than that of the good solid conductors.
Working
The first consideration in the identification of the working fluid is the operating vapor temperature range.
Within the approximate temperature band, several possible working fluids may exist and a variety of characteristics must be examined in order to determine the most acceptable of these fluids for the application considered.
The prime requirements are
Compatibility with wick and wall materials
Good thermal stability
Wettability of wick and wall materials
High latent heat
High thermal conductivity
Low liquid and vapor viscosities
High surface tension
Different Types of Heat Pipes
Vapor chamber or flat heat pipes
Variable Conductance Heat Pipes (VCHPs)
Diode Heat Pipes
Thermosyphons
Loop heat pipe
Heat applications
Heat pipe heat exchanger enhancement can improve system latent capacity. For example, a 1°F dry bulb drop in air entering a cooling coil can increase the latent capacity by about 3%.
Both cooling and reheating energy is saved by the heat pipe's transfer of heat directly from the entering air to the low-temperature air leaving the cooling coil.
It can also be used to precool or preheat incoming outdoor air with exhaust air from the conditioned spaces.
Best application
Where lower relative humidity is an advantage for comfort or process reasons, the use of a heat pipe can help.
A heat pipe used between the warm air entering the cooling coil and the cool air leaving the coil transfers sensible heat to the cold exiting air, thereby reducing or even eliminating the reheat needs.
Also the heat pipe precools the air before it reaches the cooling coil, increasing the latent capacity and possibly lowering the system cooling energy use.
Applications
Where the intake or exhaust air ducts must be rerouted extensively, the benefits are likely not to offset the higher fan energy and first cost.
Use of heat pipe sprays without careful water treatment. Corrosion, scale and fouling of the heat pipe where a wetted condition can occur needs to be addressed carefully.
Advantages
Passive heat exchange with no moving parts,
Relatively space efficient,
The cooling or heating equipment size can be reduced in some cases,
The moisture removal capacity of existing cooling equipment can be improved,
No cross-contamination between air streams.
Disadvantages
The use of the heat pipe
Adds to the first cost and to the fan power to overcome its resistance,
Requires that the two air streams be adjacent to each other,
Requires that the air streams must be relatively clean and may require filtration.
CONCLUSION
Heat pipe is a thermal super conductor under certain heat transfer condition they can transfer the heat energy 100 times more than available best conductive materials, because of negligible temp. Gradient exist in heat pipe.
The heat pipe has compactness, light weight, reversible in operation and high thermal flux handling capability makes heat pipe to use new modern era and in many wide variet application to overcome critical heat dissipation problem.