Everything about Shell and Tube type Heat Exchanger

Shell and Tube type Heat exchangers, are one of the most common types used onboard vessels and in general in industries like petrochemical industry and other industries with cooling requirements like HVAC where predominantly use of shell and tube type is considered economically viable. 

Major advantages of shell and tube type includes easier manufacturing, low maintenance, easier fault finding and henceforth low downtime. 

Materials knowledge:

Tubes are generally made up of Aluminum Brass (76% Cu, 22% Zn, and 2% Al). The Aluminum in this alloy is there to make a protective layer of AlO2. In case of corrosion, this ability makes Al more stronger rather than the case of Iron alloys. Also just to add, there is Zn anode also provided to save the whole system from corrosion. 

Some coolers can also be found with 70/30 Cupro-Nickel. 

What flows through tubes and what goes through the shell....?

Perhaps this question makes everyone scratch their heads. The common perseption would always lead to ask the question that what diffrence does it makes, its all about heat exchange which will always happen no matter the configuration. But there is significant changes which occurs in this.

So staying in the cooling configuration, the major objective is to  provide as much cooling to the concerned medium as possible. So, the cooling medium lets say Sea water remains in the shell outside the tubes and the other fluid lets say Lube oil stays inside the tubes. This has other implications too though, as flowing Sea water through the tubes might cause corrosion damage overtime and maintenace will be more often required. But, you get the idea right..!

Maintenenace:

1. Often problems like the leakages get introduced in system which is very necessary to be identified early. On ships, systems like LO system, is under constant supervision, where monthly tests, and parameters are observed regulary. As per my idea, temperatures and pressures around the cooler must be checked atleast 2x a day. Which gives you hint how system is performing over time. 

For the operational POV working pressure is so adjusted such that prssure inside the tubes is always higher than the outside inside shell so the fluid inside is saved from any contamination. Generally the leaks are situated by the pressure testing or by the removing the pipework and end covers to expose the end plates, then looking again for signs of leakage. If possible, pressurise the other side of the cooler slightly, and look for leakage. Often you will find that one tube may be leaking, so this can be sealed up by making tapered brass plugs that can be hammered into the leaking tube to seal it off on both ends.

Repeat this process until the cooler can hold a pressure without leakage. With every tube that you plug, you reduce the cooling capacity of the unit, so don’t plug more than 25%, otherwise the cooler will not be effective any more. Sometimes you can also opt for replacing tubes with new tubes, so its virtually a new cooler after that. 

Additional systems:

Tell-tale holes:

The tell tale hole as named, denotes the are for suspected leakages, helping to locate them early on and saving heavier plausible damage in future. Following is a general arrangement you can find in a shell & tube type Cooler. 

Baffles: 

Baffels are there to promote randomness and keep the cooling medium for a little more time in contact with the concerned fluid (Oil, Fresh water, etc. ). This in a way increases the efficiency of the heat transfer.  

Floating tubesheet:

This is just there to accomodate for any changes in the length of the tubes, due to the temperature.