For an engineer and designer heat transfer equipments are the most important equipments or the devices which he comes through during his career, for that a good theoretical knowledge on the concept of heat transfer is required and well ideology on the equipment selection, it working principle will help to design for a particular purpose and even to operate them in safe and economical mode. It is vast topic which has its importance in every field of engineering and science.
From the basic concept it will help you to understand and gain the subject at your finger tips, although there are lots of study material and lectures available, to obtain good job for an engineer it is first and foremost topic which make him stand in front line. Showing interest on heat transfer one will automatically learn all the topics related which are useful in the area of software design using latest software’s platform, research and development, logical calculation. These are made easy by the heat transfer because it is application oriented as you can feel, measure and sense the heat flow and mechanisms where your brain can understand when you can see some not just studying by imagination.
|Baffle cross section|
A plate and frame
Design of a shell and tube heat exchanger
In case of a shell and tube heat exchanger, the minimum shell thickness for carbon steel (inclusive of corrosion allowance) depends on shell diameter and is in the range of 5 – 11mm.The ratio of tube length to shell diameter in case of liquid shell and tube heat exchanger ranges from 4 to 8. Steam is preferred to be used as a heating medium in heat exchangers, because of its high latent heat. High specific heat of water makes it a widely used coolant in heat exchangers.
Ratio of tube length to shell diameter for a shell and tube heat exchanger is 4:1 to 8:1 for liquid – liquid exchanger and< 4:1 for gas – gas exchangers. In a shell and tube heat exchanger, the overall heat transfer co-efficient is proportional to the tube side (volumetric flow rate)0.8. This is valid, only when the ratio of the tube side film resistance to the total resistance is almost equal to 1. In a multipass shell and tube heat exchanger, the problem of differential expansion between the shell and tube passes is taken care of by using a U-bend or floating head tube sheet.
For multipass shell and tube heat exchanger, when the flow is a mixed one that is co-current and counter current, LMTD correction factor is used. The various types of baffles used in heat exchanger are
2. Disc and doughnut
Shell side pressure drop depends on
1. Mass velocity of shell side fluid
2. Baffle spacing
3. Shell diameter
4. Tube pitch and diameter
5. Density and viscosity of the shell side fluid.
The main disadvantages of concentric pipe heat exchangers are:
Comparatively less heating surface
Considerable space requirement
Prone to leakage
High maintenance cost
1.Easily accessible for external cleaning
2.Low pressure drop
The following characteristics of the fluid are to be considered while decreasing its route in heat exchanger: