This is another type of heat exchanger, which is vital during energy recovery systems and normally finds its application in HVAC systems. It has the general appearance of a plate-finned water coil although in this case, the tubes are never interconnected. A typical heat pipe is separated into two sections using a closed/sealed dividing wall. When placed in an air handling system, hot exhaust air stream passes through the evaporator and gets cooled, while the cool incoming air stream is passed through the condenser. Although, heat pipes are levelheaded heat exchangers, if the condition of the air is in such a way that condensation happens on the fins, there may be some transfer of latent heat, leading to improved efficiency. The working fluids in heat pipes, normally Class I refrigerants, are always selected in accordance with the preferred temperature conditions (Kroger 198). Most HVAC systems have heat pipes made of copper and which have fins made of aluminium. Enhancement of heat pipe heat exchangers will generally improve the latent capacity of a system. For instance, a dry bulb drop of 10 F in the air that enters a cooling coil will amplify the latent capacity by approximately 3% (Kroger 200). In this case, the heat exchanger’s transfer of heat straight from the incoming vapor to the cold air leaving the cooling coil conserves both the cooling and reheating energy. Heat pipe heat exchangers normally have an effectiveness of between 45 to 65 percent.
This is one of the most common types of counter-flow heat exchangers, which is used in energy recovery systems. It is normally placed within the exhaust and supply streams of air of an industrial process to recover or reclaim waste heat. This type of heat exchanger is used regularly alongside the burner section of a heat engine to boost its overall efficiency (Shurcliff 74). In a gas turbine engine, for instance, air is compressed before being mixed with fuel. The mixture of compressed air and fuel is then burned to generate the energy needed to drive the turbine (Shurcliff 76). A recuperator then transfers some percentage of the waste heat from the exhaust to the already compressed air, preheating it just prior to the fuel burner stage.
It consists of a series of parallel aluminium or stainless steel plates on which alternating pairs are enclosed on both sides to create identical sets of ducts arranged orthogonally to enclose the extract and supply air streams. This arrangement allows heat from the exhaust air stream to be transferred into the supply stream via these separating plates.
A rotary heat exchanger, also known as a heat recovery wheel, Kyoto wheel, or thermal wheel, is another type of heat exchanger used in energy recovery systems. It consists of a rounded honeycomb matrix, which is of a heat-absorbing medium, rotated slowly within the supply and exhaust streams of air in an air handling system (Shurcliff 88). The wheel is made of a material having a very high thermal...