Heat Transfer Enhancement equations , is that the required surface area can be accommodated in a smaller volume leading to a smaller and lighter heat exchanger - this is the idea of compactness , such as provided by plate-type heat exchangers . Analogous to this idea is that in some cases , the ∆T is either fixed or may not exceed a predefined limit that leads to unusually large surface areas which are not practical for S & T exchangers . In this first article of the series , we will look at generic aspects of enhancement – advantages , different types of enhancement , costs , and what precautions are necessary .
Advantages of enhancement Here is a summary of the various advantages to be gained by heat transfer enhancements . They include capital and operating expense reduction , and lower energy and emission costs . Other benefits may be obtained if there is close collaboration with process engineers during the early stages of project planning and equipment selection . If the standard S & T is replaced by a smaller one : lower fabrication cost , lower weight and correspondingly lower installation and maintenance costs , and smaller plot space especially for new construction . If the enhancement is for fouling reduction : fewer process interruptions for cleaning and fewer incidents of throughput reduction , lower cleaning costs , lower energy and emissions costs when a loss of heat duty is compensated by higher fuel consumption . If the S & T is replaced by a non-tubular heat exchanger ( plate-type ): lower weight and correspondingly lower installation and maintenance costs , and smaller plot space especially for new construction . Debottlenecking : If the heat duty of a heat exchanger needs to increase due to a process expansion or other changes , enhancement can allow the change with the same size and footprint as the existing heat exchanger .
Enhancement types Four categories of enhancement are usually applicable in process S & T heat exchangers :
• Increase surface area , typically by forming or attaching fins on the outside or inside of tubes .
• Increase in the heat transfer coefficient by enhancing turbulence or by improved mixing .
• Decrease in the fouling margin ( and therefore excess surface area ) by mitigating fouling by using techniques such as inserts , coatings , or vibration .
Upcoming in this series
In upcoming articles , we will look at details of specific technologies available for heat transfer enhancement - how they work , advantages and disadvantages , applicability , precautions to be taken , costs , maintenance aspects , and field experience .
• Change to non-tubular heat exchangers ( plate-type ) such as Plate-and-Frame , Spiral , or Plate-Fin .
Each category has different advantages to be assessed to verify expected benefits and precautions to be taken to ensure applicability .
Costs In addition to the cost to purchase one of the technologies mentioned above , there are costs of implementation such as field work to change piping , and some techniques may require a change to a higher priced metallurgy . These other costs may or may not apply depending on whether we are replacing a standard S & T design in a new project , whether it is part of a revamp or debottleneck of existing facilities , or whether it is used just to replace tube bundles without any other changes . If a decision is to be made based on the benefit vs cost , it is necessary to add up all the cost components ( such as the total installed cost and lifecycle cost ), not just the price of initial purchase .
Precautions Plain tube S & T heat exchangers can be designed to withstand a wide range of pressures and temperatures required by most processes , by sizing diameters and thicknesses . Additionally , they can be the minimum capital cost choice due to the use of low cost metallurgies , such as standard carbon steel . Any enhancement technique must ensure that it has equivalent or better mechanical reliability . The aspect of reliability also extends to maintenance . If enhancement results in increased or more difficult maintenance ( e . g ., difficulty in cleaning ) or a technology requires periodic expenditure for refurbishment , those lifecycle costs should be included in the initial benefit / cost evaluation .
About the authors
Himanshu Joshi retired from Shell in 2021 after 34 combined years with ExxonMobil and Shell , during which he specialized in heat exchangers and fouling . He was part of a team that was granted a patent related to fouling deposit analysis at ExxonMobil , and led applied fouling R & D projects at both companies . He has made several presentations about the field aspects of fouling and fouling mitigation , and deployed many mitigation technologies in the field . He can be reached by email at alph . hmj @ gmail . com .
Lou Curcio has over 30 years of experience in design , troubleshooting and repair of all types of heat exchangers . Leader of technology development projects and advisor for ExxonMobil ’ s global manufacturing teams . Co-inventor of two U . S . patents and co-author of papers on enhanced heat transfer and fouling of heat exchange . www . heat-exchanger-world . com Heat Exchanger World December 2024
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