Heat exchangers are devices that transfer energy, within the type of heat, from one working fluid to the subsequent, whether that be solids, liquids, or gases. These devices are essential for refrigeration, power generation, HVAC, and more, and are available in many shapes and sizes that may both introduce heat or remove it. Understanding what makes one device unique from another is usually difficult, so this text will help readers gain an introductory knowledge on one among the foremost popular heat exchangers, the shell and tube device. This text aims to reveal what shell and tube heat exchangers are, how they work, what types exist, and the way they're utilized in industry.
All heat exchangers are built on the identical principle, namely that a hot fluid flowing over/around a colder fluid will transfer its heat (and therefore its energy) within the direction of cold flow (to review your laws of thermodynamics, try our article on understanding heat exchangers). consider after you first grab your handwheel on a chilly day: initially, the temperature difference between your hand and therefore the wheel is large, and you'll feel how frigid it is; however, if you retain gripping the wheel, a number of the warmth in your hand are going to be absorbed by the cold wheel, and therefore the wheel “warms up”. This instance is intuitive thanks to understanding the fundamental principles of any heat exchanger: get two fluids with different temperatures approximate, and permit them to “exchange” heat through some conductive barrier.
Shell and tube heat exchangers are, simply put, a tool that puts two working fluids in thermal contact using tubes housed within an outer cylindrical shell. These two integral pathways are usually built out of thermally conductive metals that allow easy heat transfer (steel, aluminum alloys, etc.). The tubes carry a fluid from their inlet to their outlet (the “tube-side” flow), while the shell passes a separate fluid over these tubes (the “shell-side” flow). The quantity of tubes, referred to as the tube bundle, will dictate what quantity extent is exposed to the shell-side flow, and thus determines what quantity heat is transferred. These devices are among the foremost effective means of exchanging heat, as they're easily built, maintained, are compact, and supply excellent heat transfer. they're cosmopolitan in industry, being useful for condensers, turbine coolers, evaporators, feed water preheating, and far more.
As previously explained, the elemental point of shell and tube heat exchangers is to pass a hot fluid through a chilly fluid without mixing them, so only their heat is transferred. The above diagram shows two inlets and two outlets, where each fluid starts at their respective inlet and exits the device at their outlets. The tube-side flow passes through the tube bundle (secured by metal plates called tubesheets or tubeplates) and exits the tube outlet. Similarly, the shell-side flow starts at the shell inlet, passes over these tubes, and exits at the shell outlet. The headers on either side of the tube bundle create reservoirs for the tube-side flow and may be split into sections in line with heat energy exchanger types.
Each tube contains an insert called a turbulator which causes flow through the tubes and prevents sediment depositing, or “fouling”, still as increases the exchanger’s heat transfer capacity. Designers also cause turbulence within the shell with barriers called baffles, which maximize the quantity of thermal mixing that happens between the shell-side fluid and therefore the coolant pipes. The shell-side fluid must work its way around these baffles, which causes the flow to repeatedly leave out the tube bundle, thus transferring energy and exiting the warmth exchanger at a lower temperature. Certain shell and tube exchangers use differing baffle shapes to maximise heat transfer, and a few use none the least bit.
Shell and tube heat exchangers are single-phase, or two-phase. A single-phase exchanger keeps the fluid’s phase constant throughout the method (e.g. liquid water enters, liquid water leaves) while a two-phase exchanger will cause a natural process during heat transfer process (e.g. steam enters and liquid water leaves). they'll even be single pass or multi pass, which simply describes what percentage times the tube-side/shell-side flows withstand the device. Figure 1 shows a multi-pass configuration, where the shell-side flow passes over the coolant pipes multiple times before exiting through its outlet. If the baffles weren't in Figure 1, then the warmth exchanger would be considered a one pass device, as both the tube-side flow and shell-side flow only pass one another one time.
The standard kinds of shell and tube heat exchangers are regulated by the Tubular Exchangers Manufacturers Association or TEMA. They split all device designs into three main parts: the face header, the shell, and therefore the prat header, and designate them with letters. There are many styles of each component, but this text will only target the foremost common TEMA standard heat exchangers, as they're the three preferred models. These three types are the U-tube, fixed tube sheet, and floating head heat exchangers.
The tube bundle is formed of continuous tubes that bend into a “U” shape, and are secured to the shell using one tubeplate (shown above). The coolant flows from the highest half the header, through the u-tubes, to the underside half the header, creating an inherent multi-pass design. The bend allows for thermal expansion to occur without implementing any quiet expansion joints, because the bend side is free-floating within the shell and has room to expand/contract. they're excellent when using high-temperature differences where expansion is predicted, and therefore the only major downside of those exchangers is that their bends are difficult to wash.
The fixed tube sheet exchanger uses two stationary tube sheets (labeled above) that are welded onto the shell. they're the foremost cost-effective version of the shell and tube design, as they're the simplest to manufacture. However, since the tubes are rigidly attached to the shell via the tube sheets, expansion must be prevented. If there's a high-temperature difference between the tube-side and shell-side flows, operators risk expansion and damage, therefore the temperature difference must be kept small. Another disadvantage of fixed tube sheet models is that the surface of their tubes can't be accessed for cleaning. The shell-side fluid being employed must not foul the skin of the tubes, or the warmth exchanger’s efficiency will decrease.
The floating head exchanger combines the simplest aspects of both the previous designs. One end of the tubes is held stationary to the housing with a hard and fast tubesheet, but the opposite side is unengaged to expand employing a component called a floating tubesheet. This part allows the tubes to expand with increased temperatures, with no need to bend the pipes. Operators can access the tubes for simple cleaning, while also having the ability to form a high-temperature difference without worrying of breaking the device. The floating head exchanger is, therefore, the simplest device in terms of efficiency and maintenance, but naturally comes at a better cost.
