Coil type heat exchangers are mainly used as condensers, coolers, or re-boilers, apart from the general heat transfer function between two fluids at different temperatures. It is usually made of two components an outer jacket and an inner coil battery, which are welded together to make a one piece unit.
Coil type condensers are used for condensation of vapours and cooling of liquids. These are made by fusing a number of parallel coils in a glass shell. Coils are made in different concentric diameters using tubes of different nominal bores.
Usually, the coolant flows through the coils while the vapour flows through the jacket. Condensers with heat transfer area (HTA) up to 8m2 are readily available. Usually, it is accompanied by a reflux divider to ensure complete collection of the distillate.
Depending on the nature of the fluid through the jacket, the average heat transfer co-efficient can be considered as per the table below.
|Jacket side Media||Coil Side media||Heat Transfer Co-eff.(in Kcal/m2,Hr,°C)|
|Cooling Water||Cooling Water||Cooling Water|
Product coolers are used for cooling fluids and liquids, typically the distillates in the distillation column. They have construction similar to the coil type condenser. However, in product coolers, the product travels through the coils and coolant through the shell jacket. This increases the resident time of the product and hence results in more effective cooling.
Boilers are used for vaporization of the product fluid. Like condensers, boiler also contains a number of parallel coils fused together in a glass shell. However, the cross sectional area in the shell side is bigger in boiler as compared to a condenser. With the steam flowing through the coils, this results in effectively higher heat transfer. The heat transfer can be considered as 300kcal/ m2,Hr,°C on an average at a steam pressure of 3 bar in the coils.
Immersion Heat Exchangers:
Immersion heat exchangers are used to control exothermic reactions in glass vessels. They can be used with spherical vessels with large bottom outlet or with cylindrical vessels with nominal size bottom outlet. Cooling water or steam is used in coils.