There is enough room for corrosion That flow-induced vibration has resistance Axial strength Availability of spare parts
§ Tube diameter: Using a small tube diameter makes the heat exchanger both economical and compact. However, it is more likely for the heat exchanger to foul up faster and the small size makes mechanical cleaning of the fouling difficult. To prevail over the fouling and cleaning problems, larger tube diameters can be used. Thus to determine the tube diameter, the available space, cost and the fouling nature of the fluids must be considered.
§ Tube thickness: The thickness of the wall of the tubes is usually determined to ensure:
§ There is enough room for corrosion
§ That flow-induced vibration has resistance
§ Axial strength
§ Availability of spare parts
§ Hoop strength (to withstand internal tube pressure)
§ Buckling strength (to withstand overpressure in the shell)
§ Tube length: heat exchangers are usually cheaper when they have a smaller shell diameter and a long tube length. Thus, typically there is an aim to make the heat exchanger as long as physically possible whilst not exceeding production capabilities. However, there are many limitations for this, including the space available at the site where it is going to be used and the need to ensure that there are tubes available in lengths that are twice the required length (so that the tubes can be withdrawn and replaced). Also, it has to be remembered that long, thin tubes are difficult to take out and replace.
§ Tube pitch: when designing the tubes, it is practical to ensure that the tube pitch (i.e., the centre-centre distance of adjoining tubes) is not less than 1.25 times the tubes' outside diameter. A larger tube pitch leads to a larger overall shell diameter which leads to a more expensive heat exchanger.
§ Tube corrugation: this type of tubes, mainly used for the inner tubes, increases the turbulence of the fluids and the effect is very important in the heat transfer giving a better performance.
§ Tube Layout: refers to how tubes are positioned within the shell. There are four main types of tube layout, which are, triangular (30°), rotated triangular (60°), square (90°) and rotated square (45°). The triangular patterns are employed to give greater heat transfer as they force the fluid to flow in a more turbulent fashion around the piping. Square patterns are employed where high fouling is experienced and cleaning is more regular.
Part | Component | Function |
1 | Electronic Controller | to control the valve position |
2 | Electronic Temperature Sensor | to sense the heat exchanger water temperature |
3 | Safety Valve | to protect the heat exchanger from overpressure |
4 | Isolating Valve | to isolate the installation from the supply steam |
5 | Strainer | to protect the installation from detritus |
6 | E/P Valve Positioner | to ensure the valve operates accurately at all loads |
7 | Pneumatic Actuator | to drive the valve |
8 | Control Valve | to control the flow of steam at the required pressure |
9 | Isolating Valve | to isolate the installation from the supply steam |
10 - 15 inc. | Steam Supply Steam Trap Set |
|
16 - 21 inc. | Heat Exchanger Coil Steam Trap Set |
|
22 | Air Filter/Regulator | to clean and regulate the air to the valve positioner |
23 | Strainer | to protect the circulating pump from detritus |
hydraulic oil cooler