Anyone designing a shell and tube heat exchanger should consider a number of bounds and constraints to ensure that the design being made will exhaust all cases.
Jiutepec, Morelos -- (SBWIRE) -- 06/04/2014 -- The shell and tube heat exchanger, being the most common kind of heat exchanger used in oil refineries and other large chemical processes, have certain parameters when it comes to design. The number one factor affecting its design is deciphering the type of fluid that should enter the shell side and the tube side where the fluid shoud go. With this being said, anyone designing a shell and tube heat exchanger should consider a number of bounds and constraints to ensure that the design being made will exhaust all cases.
The folllowing should be considered when designing a shell and tube heat exchanger:
1. The tube side should have a corrosive fluid. The purpose of this is to cut costs from expensive materials as only the tubes, tubesheets, heads, and channels would need costly corrosion-defiant alloys. Acidic solution on the shell side needs the entire exchanger to make use of the materials.
2. The tube side should have high pressure to reduce exchanger costs. Take note that a large diameter shell has a lower pressure rating unlike the smaller tube diameter which, for the similar metal thickness, would yield a higher pressure.
3. The shell side should be where the fluid would go. The cut should be a mixture of consufing cuts, spacing, and different forms such as segmental, double segmental, rod-baffle cut, and the like to put up with different sorts of pressure-drop requirement. For pressure drop sensitivity, services under vacuum should always be on the side of the shell.
4. It is imperative for the condensing fluid to go to the shell side. A low velocity shell side would result to the separation of the vapor and the liquid inside the exchanger. Thus, the falling of the liquids results to a leaner vapor lessening the required temperature for a more condensed liquid from the vapor that was left over.
5. The shell side should have more allocation for vapor for pressure reduction at certain volumes for a higher heat-transfer coefficient.
6. The tube side should have more fluid with a propensity to foul normally as it is way effortless to clean straight tubes as compared to the shell. The same concept goes for comparatively bulk tube pitch or square tube pattern. Using a permanent tubesheet requires placing a clean fluid on the shell side since the exchanger configuration greatly impacts the options. The fixed tubesheet is usually difficult to clean unless a chemical cleaning material is used. U-tubes, on the other hand, are way difficult to clean as compared to the straight tubes.
7. A shell and tube exchanger with an increased risk of solidification or freezing must be avoided. Whenever an exchanger is being used, the fluid with a risk of solidification must be included in the tubes to that the tube bundle can be pulled out and replaced once the fluid solidifies. But once the solid is on the shell side already, it would be difficult or could even be impossible to get rid of the tube bundle and would eventually need replacement.
8. The exchange in viscious services are intricate. A thick fluid on the tube siden would yield increased pressure drop but minimum heat transfer favoring shell-side distribution. Heat transfer is being reduced with igh pressure drop on the shell side that is considerably being promopted by going around baffles. It is important for the user to be mindful of the need for shell side modification to minimize damages on the shell side to prevent vibration damage caused by high pressure.
There are but advantages however in the distribution of fluid susceptible to freezing in the shell side. Exchanger is being put back to service via heating on the exterior of the shell with the use of electric tracing that facilitates melting of ample fluid needed.
Local plugs are being produced in all types of allocation patterns. Fluid will be set solid with the dropping of the velocity caused by enough temperature needed on the other side of the exchanger occuring on the shell side after the baffles on the edge of the shell. The same goes with tubes which can have various flow rates. A low flow rate attaining a lower temperature cause more freezing or setting up. Freezing fluids yield large areas for the exchangers.
About MPGIA SA de CV
MPGIA SA de CV is professional services company providing qualified personnel, technical consulting and advising on the implementation of quality systems for the development and installation of projects in the metal mechanic field, both in the industrial and in the commercial sectors. MPGIA SA de CV, is located in Cuernavaca city, in the state of Morelos, Mexico. MPGIA SA de CV’s objective is to guarantee their clients the highest quality in product fabrication and technical services assistance, supported by the experience and expertise their personnel, in order to satisfy the needs of the metal mechanic industry.