In its most complex form there is little difference between a multi tube double pipe and a shell and tube exchanger. However, double pipe exchangers tend to be modular in construction and so several units can be bolted together to achieve the required duty.
The book by E. Saunders [Saunders ] provides a good overview of tubular exchangers. Furnaces —the process fluid passes through the furnace in straight or helically wound tubes and the heating is either by burners or electric heaters.
Tubes in plate—these are mainly found in heat recovery and air conditioning applications. The tubes are normally mounted in some form of duct and the plates act as supports and provide extra surface area in the form of fins. Electrically heated—in this case the fluid normally flows over the outside of electrically heated tubes, see Joule Heating. Air Cooled Heat Exchangers consist of bundle of tubes, a fan system and supporting structure.
The tubes can have various type of fins in order to provide additional surface area on the air side. Air is either sucked up through the tubes by a fan mounted above the bundle induced draught or blown through the tubes by a fan mounted under the bundle forced draught.
They tend to be used in locations where there are problems in obtaining an adequate supply of cooling water. A heat pipe consists of a pipe, a wick material and a working fluid. The working fluid absorbs heat, evaporates and passes to the other end of the heat pipe were it condenses and releases heat.
The fluid then returns by capillary action to the hot end of the heat pipe to re-evaporate. Agitated vessels are mainly used to heat viscous fluids. They consist of a vessel with tubes on the inside and an agitator such as a propeller or a helical ribbon impeller.
The tubes carry the hot fluid and the agitator is introduced to ensure uniform heating of the cold fluid. Carbon block exchangers are normally used when corrosive fluids need to be heated or cooled. They consist of solid blocks of carbon which have holes drilled in them for the fluids to pass through. The blocks are then bolted together with headers to form the heat exchanger. Plate heat exchangers separate the fluids exchanging heat by the means of plates.
These normally have enhanced surfaces such as fins or embossing and are either bolted together, brazed or welded. Plate heat exchangers are mainly found in the cryogenic and food processing industries. However, because of their high surface area to volume ratio, low inventory of fluids and their ability to handle more than two steams, they are also starting to be used in the chemical industry. Plate and Frame Heat Exchangers consist of two rectangular end members which hold together a number of embossed rectangular plates with holes on the corner for the fluids to pass through.
Each of the plates is separated by a gasket which seals the plates and arranges the flow of fluids between the plates, see Figure 9. This type of exchanger is widely used in the food industry because it can easily be taken apart to clean.
If leakage to the environment is a concern it is possible to weld two plate together to ensure that the fluid flowing between the welded plates can not leak. However, as there are still some gaskets present it is still possible for leakage to occur. Brazed plate heat exchangers avoid the possibility of leakage by brazing all the plates together and then welding on the inlet and outlet ports.
Plate Fin Exchangers consist of fins or spacers sandwiched between parallel plates. The fins can be arranged so as to allow any combination of crossflow or parallel flow between adjacent plates.
It is also possible to pass up to 12 fluid streams through a single exchanger by careful arrangement of headers. They are normally made of aluminum or stainless steel and brazed together.
Their main use is in gas liquefaction due to their ability to operate with close temperature approaches. Lamella heat exchangers are similar in some respects to a shell and tube. From Next: Generalized Conduction and Previous: Thermodynamics and Propulsion. The basic component of a heat exchanger can be viewed as a tube with one fluid running through it and another fluid flowing by on the outside.
Heat exchange is complex and confusing. I spent a long time reading up on the math and understanding how to explain counterflow vs parallel flow and I realized that the only real explanation would end up like this:. Now, first thing to understand: the amount of heat transferred per second increases and decreases as the heat differential the difference in temperature between the hot and the cold substance increases or decreases.
So let's take an absurdly simplified example. They both exit at 50 F or very, very near that. The cooling relationship is logarithmic. In a parallel flow setup, both the hot fluid and cold fluids are travelling in the same direction as each other. On the diagram above they both flow from right to left. This will still cool the hot fluid down by a considerable amount but is not as efficient as the counter flow system.
The amount of efficiency gained by using a counter flow system depends on several factors including the flow rates and temperatures these affect the efficiency on their own but it will be most noticeable in a larger cooler.
At Thermex we always design coolers with a counter flow configuration so it is important to install the heat exchangers correctly. More information about how to install a heat exchanger can be found in our installation, operation and maintenance manual.
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