Scraped Surface Heat Exchangers
Scraped Surface Heat Exchangers are commonly used for high fouling and viscous fluid applications. They are consisting of a jacketed cylinder with a rotating dasher holding rows of scraper blades. The product is pumped through the cylinder while the heating or cooling medium is circulated between the cylinder and the jacket. The medium can be steam, water or a refrigerant such as ammonia or freon. Liquid foods that contain large solid particles are heated in scraped-surface heat exchangers. These heat exchangers use blades to continuously scrape the inside surface of the heating chamber. The scraping action protects highly viscous foods from being burned on the heating surface.
Design Principles
The design is based on a traditional Shell Heat Exchangers and Tube Heat Exchangers with scraping elements inside each interior tube. The scrapers are moved back and forth by hydraulic action. The scraping action has two very important advantages: The reciprocating movement of the scrapers cleans the heat exchange surface. This keeps heat transfer high and reduces downtime as cleaning in place can be avoided. Besides, the scraping movement introduces turbulence in the fluid increasing heat transfer.
The gentle movement of the scrapers allows working with delicate products (such as food products with whole fruit or vegetable pieces) without destroying the integrity of the product.
Advantages
The scraping system consists of a stainless steel rod to which the scraping elements are fitted. Various types of scrapers have been developed for the different applications the Scraped Surface Heat Exchangers can handle. Materials such as Teflon and Peek (polyaryletheretherketone) are used. 120º scrapers allow for working with big particulates. The 360º scrapers are ideal for viscous fluid without particulates. As the product changes we adapt the geometry of the scraper. Scraping means fouling free heat transfer surfaces. No loss of heat transfer due to fouling.
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