Explanation of shell side

The shell is the enclosure and passage of shell-side fluid. It has a circular cross-section and made by rolling a metal plate of suitable dimension into a cylinder and welding along the length. Above fingers show the different types of shell.

Shell configuration

TEMA defines various shell patterns based on the flow of the shell-side fluid through the shell see Figure 1

Single-pass shell

In a single-pass shell, the shell side fluid enters the shell at one end and leaves from the other end. This is the most common shell type— more heat exchangers are built to this configuration than all other configurations combined.

Two-pass shell

A two-pass shell has a longitudinal baffle that divides the shell into two passes.  The shellside fluid enters at one end, traverses the entire length of the exchanger through one-half the shell cross-sectional area, turns around and flows through the second pass, then finally leaves at the end of the second pass. The longitudinal baffle stops well short of the tube sheet, so that the fluid can flow into the second pass.  This shell is used for temperature-cross situations — that is, where the cold stream leaves at a temperature higher than the outlet temperature of the hot stream. If a two-pass shell has only two tube passes, this becomes a true countercurrent arrangement where a large temperature cross can be achieved.

Divided Flow Shell:

A shell is a divided-flow shell wherein the shellside fluid enters the shell at the center and divides into two halves, one flowing to the left and the other to the right and leaving separately.  They are then combined into a single stream. This is identified as a Divided Flow 1–2 shell. Alternatively, the stream may be split into two halves that enter the shell at the two ends, flow toward the center, and leave as a single stream, which is identified as a Divided Flow 2–1 shell.Split Flow Shell:

A shell is a split-flow shell (see Figure ). This construction is usually employed for horizontal thermo syphon reboilers. There is only a central support plate and no baffles. A split-flow shell cannot be used for heat exchangers with tube lengths greater than 3 m, since this would exceed the limit on maximum unsupported tube length specified by TEMA— typically 1.5 m, though it varies with tube O.D., thickness, and material.

Double Split Flow shell:

When a larger tube length is needed, a Double Split Flow shell (see Figure ) is used. An Double Split Flow shell is basically two Split Flow shells placed side-by-side, so that there are two full support plates. This is described as a double-split configuration, as the flow is split twice and recombined twice. This construction, too, is invariably employed for horizontal thermo syphon reboilers.  The advantage of Split Flow and Double Split Flow shells is that the pressure drop is drastically less and there are no cross baffles.

Cross Flow shell

A Cross Flow shell (see Figure) is a pure cross-flow shell where the shellside fluid enters at the top (or bottom) of the shell, flows across the tubes, and exits from the opposite side of the shell.  The flow may be introduced through multiple nozzles located strategically along the length of the shell in order to achieve a better distribution.  The pressure drop will be extremely low — in fact, there is hardly any pressure drop in the shell, and what pressure drop there is, is virtually all in the nozzles. Thus, this configuration is employed for cooling or condensing vapors at low pressure, particularly vacuum. Full support plates can be located if needed for structural integrity; they do not interfere with the shellside flow because they are parallel to the flow direction.

Kettle-Type Reboiler: TEMA K

A Kettle-Type Reboiler shell (see Figure ) is a special cross-flow shell employed for kettle reboilers . It has an integral vapor-disengagement space embodied in an enlarged shell. Here, too, full support plates can be employed as required