This type of heat exchanger consist of cylindrical Shell (a large pressure vessel) with a bundle of tubes and battle, tie rod inside it. One fluid runs through the tubes and another fluid flows over the tubes ( though the shell) from the town mains or a cooling tower or an ethylene glycol solution from a chiller unit to transfer heat between the two fluids. This system is suitable for both cooling and heating application. In certain circumstances this flow arrangement can be revised. The tubes are positioned into the cylinder using a tube bundle or “tube stack” which can either have fixed tubes plates (permanently fixed to the shell) or floating tube stack which allows the tube bundle to expand and contract with varying heat conditions as well as allowing the tube bundle to be easily removed for servicing and maintenance. These are typically used for high pressure applications. These are robust, compact, cost efficient, low power and long life.