Coil Heat Exchanger
Coil heat exchangers, may represent a valid alternative to shell and tube heat exchangers, where, in addition to the heat exchange requirements, other factors can intervene, such as dimensions of installation and ease of cleaning and maintenance.
The typical configuration of these heat exchangers includes an external cylindrical container, called shell, inside which are contained one or more coils, realized by different spiral wound tubes, that may be concentric or aligned along the same axis, connected each other in series or parallel.
From the thermal standpoint, compared to shell and tube heat exchangers, the particular configuration of these heat exchangers not allow to achieve the same performance. The reason for this is rather simple: in practice the heat exchanger also serve as thermal storage. Indeed, the shell may contain volumes much bigger than the amount of fluid contained in the coil, as a result there is always a part of shell side fluid which remains stationary in the heat exchanger, preventing the convective motions. However, an appropriate design and the adoption of particular heat exchange configuration, like inserting more coils and forcing the fluid to perform obligated pass through the shell, allow to obtain efficiencies not very far from those of the shell and tube heat exchangers.
The real advantage of this technology are:
Reduced axial dimensions, a wound tube takes up less space than a straight pipe of equal length;
Ease of implementation, which help to reduce the costs;
Less fouling: the coil counteracts the deposition of impurity presents in the fluid, allowing them faster evacuation, being the convection currents, in the shell, reduced , the sediments tend to accumulate at the bottom and not on the pipes; this will reduce the maintenance and the heat exchanger remains efficient for longer;
Ease to clean: for the same reasons listed above the heat exchanger cleaning is facilitated;
Ability to have, shell side, several outputs at different temperatures: if placed in an upright position, and for large enough heat exchangers may occur the phenomenal of stratification, a bit as occur in the boiler, where, depending on the height at which you placed your sampling, the fluid can exit more or less hot.