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. When the shell side heat transfer is sensible heating or cooling with no phase change, the baffle cut should be horizontal. The orientation of the baffle cut is essential for the heat exchanger installed horizontally. The baffle pitch and the baffle cut determine the cross-flow velocity, and so the rate of heat transfer and the pressure drop. The spacing between baffles is called the baffle pitch. Holes are drilled in the tube sheet generally in either of two patterns, triangular or square.ġ) Support the tubes during assembly and operationĢ) Prevent vibration from flow-induced eddies and maintain the tube spacingģ) Direct the flow of fluid in the desired pattern through the shell side.Ī 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. A rolled joint is the common term for a tube to tube sheet joint resulting from a mechanical expansion of the tube against the tube sheet. The tubes are inserted through the holes in the tube sheets and held firmly in place either by welding or mechanical or hydraulic expansion. Tubes are appropriately attached to the tube sheet, so the fluid on the shell side is prevented from mixing with the fluid on the tube side. Generally, the tube sheet material is the same as the tube material. Tube sheets are made from a round flat piece of metal with holes drilled for the tube ends in precise location and pattern relative to one another. Finned tubes are also used when fluid with low heat transfer coefficient flows in the shell side. A maximum number of tubes in the shell increase turbulence, which increases the heat transfer rate. Tubes of larger diameter are sometimes used either to facilitate mechanical cleaning or to achieve lower pressure drop. Longer tube reduces shell diameter at the expense of higher shell pressure drop. Tube lengths of 6, 8, 12, 16, 20, and 24 feet are commonly used. The tube thickness is expressed in terms of BWG and true outside diameter (OD). Tube thickness should be maintained to withstand:ġ) Pressure on the inside and outside of the tubeģ) Thermal stress due to the differential expansion of the shell and the tube bundleĤ) Corrosive nature of both the shell-side and the tube-side fluid. Standard tube diameters of 5/8 inch, 3/4 inch, and 1 inch are preferably used to design compact heat exchangers. Tubes are made from low carbon steel, stainless steel, titanium, Inconel, Copper, etc. Seamless tubing is produced in an extrusion process welded tubing is produced by rolling a strip into a cylinder and welding the seam. Tubes are generally made seamless or welded. The pass partition plates direct the tube side fluid through multiple passes. Pass partitions are required in channels of heat exchangers with multiple tube passes. 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 rear channel is often selected to match the front channel. The removable cover permits access to the channel and tubes for inspection or cleaning without removing the tube side piping. The removable cover channel can be either flanged or welded to the tube sheet. It is used for services that do not require frequent removal of the channel for inspection or cleaning.
The most commonly used channel type is the bonnet. The channel type is selected based on the application. Most channels can be removed for access to the tubes.
#TEMA HEAT EXCHANGER FULL#
This style allows a full tube count and therefore maximizes utilization of shell space.įig 2: Impingement Plate in Tube Layout 2.2 Channels (Heads) The impingement plate can be installed in a domed area (either by reducing coupling or a fabricated dome) above the shell.
#TEMA HEAT EXCHANGER INSTALL#
An impingement plate can be installed inside the shell, eliminating the need to install a full tube bundle, which would provide a less available surface.
In applications where the fluid velocity for the nozzle diameter is high, an impingement plate is specified to distribute the fluid evenly to the tubes and prevent fluid-induced erosion, cavitation, and vibration. Roundness and consistent shell inner diameter are necessary to minimize the space between the baffle outside edge and the shell, as excessive space allows fluid bypass and reduces performance. Using commonly available shell pipe to 24-inch diameter reduces cost and ease of manufacturing, partly because they are generally more perfectly round than rolled and welded shells. For reasons of economy, low carbon steel is standard, but other materials suitable for extreme temperatures or corrosion resistance are often specified. The shell is constructed either from pipe up to 24 inches or rolled and welded plate metal.