OVERVIEW:
Although double-pipe heat exchangers(Helical-coil heat exchangers) are the simplest to design, the better choice in the following cases would be the helical-coil heat exchanger (HCHE):
- The main advantage of the HCHE, like that for the SHE, is its highly efficient use of space, especially when it’s limited and not enough straight pipe can be laid.
- Under conditions of low flowrates , such that the typical shell-and-tube exchangers have low heat-transfer coefficients and becoming uneconomical.
- When there is low pressure in one of the fluids, usually from accumulated pressure drops in other process equipment.
- When one of the fluids has components in multiple phases (solids, liquids, and gases), which tends to create mechanical problems during operations, such as plugging of small-diameter tubes.Cleaning of helical coils for these multiple-phase fluids can prove to be more difficult than its shell and tube counterpart; however the helical coil unit would require cleaning less often.
About Helical-coil heat exchangers:
These have been used in the nuclear industry as a method for exchanging heat in a sodium system for large liquid metal fast breeder reactor since the early 1970s, using an HCHE device invented by E.Boardman . There are several simple methods for designing HCHE for all types of manufacturing industries, such as using the Ramachandran (et al.) method from India and the Scott method from the united states.
Current View:
However, these are based upon assumptions of estimating inside heat transfer coefficient, predicting flow around the outside of the coil, and upon constant heat flux. Yet, recent experimental data revealed that the empirical correlations are quite in agreement for designing circular and square pattern HCHEs. During studies published in 2015, several researchers found that the boundary conditions of the outer wall of exchangers were essentially constant heat flux conditions in power plant boilers, condensers and evaporators; while convective heat transfer conditions were more appropriate in food, automobile and process industries.