What is heat pipe:
Heat pipe is an effective heat transfer device which provides benefits of both thermal conductivity and phase transaction in a single heat exchanger.
How heat pipes are constructed:
Heat pipe consist of evacuated pipe or tube, Working fluid and partition plate for heat transfer. as shown below
What is working fluid and how heat transfer takes place.
Working fluid is heat transfer media used to transfer heat from one section of heat pipe to the other, typically from bottom to top. Working fluid is stored in evacuated pipe or tube in bi phase. Liquid phase of working fluid is at the bottom while vapour phase is the top, when heat is applied at bottom of the heat pipe working fluid gets evaporated and moves upward. The heated vapour at the top gets in contact with cooler medium and allows working fluid to condense by transferring heating to cooling media, this cyclic process happens very fast allowing heat pipe to be super efficient. We can simply say Heat pipe is simply thermo siphon device rotating saturated liquid and vapour phase for effective heat transfer.
No of heat pipes are arranged with partition plate to achieve desired heat transfer as shown below:-
Why Heat pipes are efficient
In heat pipe, amount of heat transfer is transported through latent heat of vaporization of working fluid, which is normally very high than convective heat transfer system. Thermal conductivity and phase transaction takes place in a single heat exchanger. Hence heat pipes are super efficient heat exchanges in heat transfer.
How working fluid are selected:-
Working fluid are selected based on the temperature range across heat exchanger requirement, Working fluid must change phase from the heat available at hot side and condensed at cold side. Vacuum is applied to make working fluid suitable to operate on desired temperature range.
Correct selection of working fluid can make heat transfer 1000 times effective than normal copper tube heat exchanger.
Heat pipe tubes are generally made of Stainless steel, mild steel, copper and aluminium, While common working fluid are water, ammonia, refrigerants like R134a. For lower temperature application nitrogen, oxygen, neon, hydrogen etc can be used.
Finns are provided on heat pipe surface to further enhance heat transferring capacity.
Application of Heat pipe:
Heat pipes are mostly suitable for gas to gas and gas to liquid heat transfer.
Benefit of Heat pipe:
Lower surface area requirement, effective heat transfer, can be operated with various temperature range. Lower maintenance required.
Limitation of heat pipe:
Temperature range working fluid selection and operation is very important, Beyond temperature range of design it ceases to operate.