For example, a heat exchanger with a bonnet at the front head (B channel) will often have a bonnet at the rear head (M channel) and be designated as BEM. The velocity must be high enough to prevent any suspended solids settling, but not so high as to cause corrosion. The most commonly used channel type is the bonnet. To enhance heat transfer by directing the flow through the shell in a desired pattern. Triangular pitch provides higher heat transfer and compactness. In the helical baffle heat exchanger that Schroeder mentioned, quadrant-shaped plate baffles are placed at an angle to the tube axis in a sequential arrangement to create a helical flow pattern. The minimum number of tie rods and spacers depends on the shell’s diameter and the size of the tie rod and spacers. This causes the fluid to follow an up-and-down path and prevents stratification with warmer fluid at the top of the shell and cooler fluid at the bottom of the shell. Viscosity=1 to 10mN s/m2, ΔP= 50-70 kN/m2, Above 10 bar: 0.1 x system gauge pressure, When a high-pressure drop is utilized, care must be taken to ensure that the resulting high fluid velocity does not cause erosion or flow-induced tube vibration, T1, T2 = Inlet and Outlet temperatures of hot fluid, t1, t2 = Inlet and Outlet temperatures of cold fluid, = shell fluid dynamic viscosity at the average temperature, C = specific heat of the shell side fluid, = tube fluid dynamic viscosity at the average temperature, Ro = outside dirt coefficient (fouling factor), Ri = inside dirt coefficient (fouling factor), N+1= number of crosses = Tube length / Baffle spacing, Ǿs= viscosity correction factor for shell-side fluid, Ǿt= viscosity correction factor for tube side fluid. We use cookies to ensure that we give you the best experience on our website. The orientation of the baffle cut is important for heat exchanger installed horizontally. Obtain Physical properties for both the fluids. The Tubular Exchanger Manufacturers Associationsets out guidelines. This style allows a full tube count and therefore maximizes utilization of shell space. The minimum value is restricted to 1.25 because the tube-sheet ligament (a ligament is the portion of material between two neighbouring tube holes) may become too weak for proper rolling of the tubes into the tube sheet. Typical design velocities are given below: For vapours, the velocity used will depend on the operating pressure and fluid density; the lower values in the range given below will apply to molecular weight materials. Stream exhibiting the highest fouling should be located on the tube side. A segment, called the baffle cut, is cut away to permit the fluid to flow parallel to the tube axis as it flows from one baffle space to another. Baffles in heat exchangers are often used as a core element in any shell and tube heat exchanger design. Tubes must be supported at intervals not more than 1.5 m (5 ft), this mainly depends on the diameter of the tube and material of construction. Pass partitions are required in channels of heat exchangers with multiple tube passes. Tubes are arranged with square pitch. Implementation of baffles is decided on the basis of size, cost and their ability to lend support to the tube bundles and direct flow: As mentioned, baffles deal with the concern of support and fluid direction in heat exchangers. What is the minimum baffle spacing recommended? A maximum number of tubes in the shell increase turbulence, which increases the heat transfer rate. For shell-side condensation, the baffle cut for segmental baffles is vertical to allow the condensate to flow towards the outlet without significant liquid holdup by the baffle. The first letter describes the front header type, the second letter the shell type, and the third letter the rear header type. Similarly, the rear head is classified (L, M, N, P, S, T, U, W).