Shell and Tube Heat Exchangers

View of the inside of a shell and tube heat exchanger shows
the tubes through which one of the transfer fluids passes.

Automobiles are part of the backbone of modern society, for both personal and commercial use. While being familiar everyday objects, they also contain systems which need to be constantly maintained and in-sequence to ensure the safety of both the machine and the driver. One of the most essential elements of car ownership is the understanding of how heat and temperature can impact a car’s operation. Likewise, regulating temperature in industrial operations, which is akin to controlling heat, is a key process control variable relating to both process operation and operator safety. Since temperature is a fundamental aspect of both industrial and consumer life, heat management must be accurate, consistent, and predictable. Many devices have been developed for the transfer of heat from one substance to another, with myriad applications throughout modern society.

A common design of heat exchangers used in the oil refining and chemical processing industries is the shell and tube heat exchanger. A pressure vessel, the shell, contains a bundle of tubes. One fluid flows within the tubes while another floods the shell and contacts the outer tube surface. Heat energy conducts through the tube wall from the warmer to the cooler substance, completing the transfer of heat between the two distinct substances. These fluids can either be liquids or gases. If a large heat transfer area is utilized, consisting of greater tube surface area, many tubes or circuits of tubes can be used concurrently in order to maximize the transfer of heat. There are many considerations to take into account in regards to the design of shell and tube heat exchangers, such as tube diameter, circuiting of the tubes, tube wall thickness, shell and tube operating pressure requirements, and more. In parallel fashion to a process control system, every decision made in reference to designing and practically applying the correct heat exchanger depends on the factors present in both the materials being regulated and the industrial purpose for which the exchanger is going to be used.

Schematic of shell and tube heat exchanger

The industrial and commercial applications of shell and tube heat exchangers are vast, ranging from small to very large capacities. They can serve as condensers, evaporators, heaters, or coolers. You will find them throughout almost every industry, and as a part of many large HVAC systems. Shell and tube heat exchangers, specifically, find applicability in many sub-industries related to food and beverage: brewery processes, juice, sauce, soup, syrup, oils, sugar, and others. Pure steam for WFI production is an application where special materials, like stainless steel, are employed for shell and tube units that transfer heat while maintaining isolation and purity of a highly controlled process fluid.

Shell and tube heat exchangers are rugged, efficient, and require little attention other than periodic inspection. Proper unit specification, selection, and installation contribute to longevity and solid performance.

Analynk Wireless manufactures wireless connectivity solutions for industrial applications and process control. Making cable free connections among process control equipment and instruments, across the room, across the property, across the globe.

Cooling Towers: Operating Principles and Systems

Cooling towers are found in a wide range of sizes
and configurations

The huge, perfectly shaped cylindrical towers stand tall amidst a landscape, with vapor billowing from their spherical, open tops into the blue sky. Such an image usually provokes a thought related to nuclear power or a mysterious energy inaccessible to the millions of people who drive by power plants every day. In reality, cooling towers – the hyperboloid structures most often associated with the aforementioned nuclear power plants – are essential, process oriented tools that serve as the final step in removing heat from a process or facility. The cooling towers at power plants serve as both an adjuster of a control variable essential to the process and also as a fascinating component of the process behind power creation. The importance and applicability of cooling towers is extensive, making them fundamentally useful for industrial operations in power generation, oil refining, petrochemical plants, commercial/industrial HVAC, and process cooling.

In principle, a cooling tower involves the movement of water through a series of different parts or sections to eventually result in the reduction of its heat content and temperature. Water heated by the process operation is pumped through pipes to reach the tower, and then gets sprayed through nozzles or other distribution means onto the ‘fill’ of the tower, reducing the flow of water to appropriate levels; this maximizes the amount of surface area for contact between water and air. Electric motor driven fans pull air into the tower, and when the air meets the water, a percentage of the water evaporates, carrying heat from the water to the air and resulting in the water being cooled. The cooled water then gets transferred back to the process-related equipment, and absorbs heat again, allowing for the cycle to repeat. The process and associated dispersion of heat allows for the cooling tower to be classified as a heat rejection device, resulting in waste heat being rejected to the atmosphere. Towers depend on either evaporation to remove the process heat (open loop) or solely on air (closed loop), without evaporation, to reduce the water temperature.

Thanks to their range of applications, cooling towers vary in size from the monolithic structures utilized by power plants to small rooftop units. Removing the heat from the water used in cooling systems allows for the recycling of the heat transfer fluid back to the process or equipment that is generating heat. This cycle of heat transfer enables heat generating processes to remain stable and secure. The cooling provided by an evaporative tower allows for the amount of supply water to be vastly lower than the amount which would be otherwise needed. No matter whether the cooling tower is small or large, the components of the tower must function as an integrated system to ensure both excellent performance and longevity of use. Additionally, understanding elements which drive performance - variable flow capability, potential HVAC ‘free cooling’, the splash type fill versus film type fill, drift eliminators, nozzles, fans, and driveshaft characteristics - is essential to the success of the cooling tower and its use in both industrial and commercial settings.

So, the next time an imposing tower cracks the horizon underneath a pillar of drifting vapor, imagine all the components inside working together in a beautifully aligned system towards a common industrial goal. Such is the ingenuity of technology.

Analynk Wireless manufactures wireless communications equipment that can be used to establish radio connections between remote located cooling tower monitoring equipment and central control stations. Fan motor current, air or fluid flow and temperature characteristics, and outdoor air conditions are just some of the cooling tower performance parameters that can be monitored.