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Julius Kondratyev
Julius Kondratyev

Kays and London's Compact Heat Exchangers: A Classic Reference for Engineers



Compact Heat Exchangers: What They Are and Why They Matter




Heat exchangers are devices that transfer heat between two or more fluids or solid surfaces at different temperatures. They are widely used in various industries, such as power generation, chemical processing, refrigeration, air conditioning, and aerospace. Heat exchangers can improve the efficiency, performance, and safety of many processes and systems by reducing energy consumption, waste heat, and environmental impact.




Compact Heat Exchangers, Kays And London, Mcgraw Hilll


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However, not all heat exchangers are created equal. Some heat exchangers are more compact than others, meaning that they have a high ratio of heat transfer surface area to volume. Compact heat exchangers can offer significant advantages over conventional heat exchangers, such as higher heat transfer rates, lower pressure drops, smaller sizes, lighter weights, and lower costs. However, they also pose some challenges, such as higher complexity, lower reliability, and higher fouling potential.


In this article, we will explore the basics of heat exchangers, the advantages of compact heat exchangers, the design and analysis of compact heat exchangers, and the book by Kays and London on compact heat exchangers. By the end of this article, you will have a better understanding of what compact heat exchangers are and why they matter.


The Basics of Heat Exchangers




What is a heat exchanger?




A heat exchanger is a device that transfers heat between two or more fluids or solid surfaces at different temperatures. The fluids or surfaces can be in direct contact or separated by a solid wall. The direction of heat transfer can be parallel, counterflow, crossflow, or mixed flow. The purpose of a heat exchanger is to either increase or decrease the temperature of one or both fluids or surfaces.


Types of heat exchangers




There are many types of heat exchangers, depending on the configuration, construction, and operation. Some common types are:


  • Shell-and-tube: This type consists of a series of tubes enclosed in a cylindrical shell. One fluid flows inside the tubes and another fluid flows outside the tubes. The tubes can be arranged in different patterns to enhance heat transfer.



  • Plate: This type consists of a stack of thin metal plates separated by narrow gaps. One fluid flows in alternate gaps and another fluid flows in the remaining gaps. The plates can have different shapes and corrugations to enhance heat transfer.



  • Fin: This type consists of a base surface with extended fins attached to it. One fluid flows over the base surface and another fluid flows over the fins. The fins increase the surface area for heat transfer.



  • Regenerative: This type consists of a rotating wheel or drum filled with a porous material that absorbs and releases heat. One fluid flows through the wheel or drum and another fluid flows around it. The wheel or drum alternately heats up and cools down as it rotates.



  • Heat pipe: This type consists of a sealed tube containing a working fluid that evaporates and condenses at different locations. One end of the tube is in contact with a hot fluid or surface and the other end is in contact with a cold fluid or surface. The working fluid transfers heat from the hot end to the cold end.



Applications of heat exchangers




Heat exchangers are widely used in various industries, such as:


  • Power generation: Heat exchangers are used to convert thermal energy into mechanical or electrical energy, such as in steam turbines, gas turbines, nuclear reactors, and solar panels.



  • Chemical processing: Heat exchangers are used to control the temperature and phase of chemical reactions, such as in distillation columns, reactors, and heat recovery systems.



  • Refrigeration: Heat exchangers are used to transfer heat from a low-temperature medium to a high-temperature medium, such as in refrigerators, freezers, air conditioners, and heat pumps.



  • Aerospace: Heat exchangers are used to cool or heat the air and fuel in aircraft engines, rockets, satellites, and space vehicles.



The Advantages of Compact Heat Exchangers




What is a compact heat exchanger?




A compact heat exchanger is a heat exchanger that has a high ratio of heat transfer surface area to volume. There is no universal definition of what constitutes a compact heat exchanger, but a common criterion is that the ratio should be greater than 700 m/m. Compact heat exchangers can achieve this ratio by using small-diameter tubes, thin plates, or extended fins. Compact heat exchangers can also be classified into two types: primary surface and secondary surface. Primary surface compact heat exchangers have only one type of surface for heat transfer, such as tubes or plates. Secondary surface compact heat exchangers have two types of surfaces for heat transfer, such as fins or louvers.


Benefits of compact heat exchangers




Compact heat exchangers can offer significant advantages over conventional heat exchangers, such as:


  • Higher heat transfer rates: Compact heat exchangers have higher surface area per unit volume, which means that they can transfer more heat per unit volume. This also means that they can achieve higher temperature differences between the fluids or surfaces.



  • Lower pressure drops: Compact heat exchangers have smaller hydraulic diameters, which means that they have lower resistance to fluid flow. This also means that they require less pumping power and reduce the risk of leakage.



  • Smaller sizes: Compact heat exchangers have smaller volumes, which means that they occupy less space. This also means that they can fit into tighter spaces and reduce the weight and cost of the system.



  • Lower costs: Compact heat exchangers have lower material and fabrication costs, which means that they are more economical. This also means that they can reduce the operating and maintenance costs of the system.



Challenges of compact heat exchangers




However, compact heat exchangers also pose some challenges, such as:


  • Higher complexity: Compact heat exchangers have more complicated geometries and configurations, which means that they are more difficult to design and manufacture. This also means that they require more advanced tools and techniques for analysis and optimization.



  • Lower reliability: Compact heat exchangers have thinner walls and smaller gaps, which means that they are more prone to failure and damage. This also means that they require more careful inspection and testing for quality assurance.



  • Higher fouling potential: Compact heat exchangers have smaller passages and higher velocities, which means that they are more susceptible to fouling and corrosion. This also means that they require more frequent cleaning and protection for performance preservation.



The Design and Analysis of Compact Heat Exchangers




Design criteria for compact heat exchangers




The design of compact heat exchangers involves selecting the appropriate geometry, configuration, material, and operating conditions for a given application. The design criteria for compact heat exchangers depend on the objectives and constraints of the system, such as:


  • Heat duty: This is the amount of heat that needs to be transferred between the fluids or surfaces.



  • Temperature difference: This is the difference between the inlet and outlet temperatures of the fluids or surfaces.



  • Pressure drop: This is the loss of pressure due to fluid friction and flow resistance in the heat exchanger.



  • Size and weight: This is the physical dimensions and mass of the heat exchanger.



  • Cost and performance: This is the trade-off between the initial and operating expenses and the effectiveness and efficiency of the heat exchanger.



The design criteria for compact heat exchan