What is a Scraped Surface Heat Exchanger？
Scraper heat exchanger is a heat exchange equipment especially suitable for processing viscous, high viscous, granular liquid or liquid products requiring certain crystallization applications. It is usually used for heating and cooling, crystallization, pasteurization, steaming, disinfection, gel, concentration, freezing, evaporation and other continuous production processes in food processing, petrochemical, pharmaceutical and other industries. In the treatment process of the scraper heat exchanger, the feed liquid is in contact with the heat transfer surface. At the same time, the boundary layer of the feed liquid is continuously replaced by new feed liquid by continuously scraping the heat transfer surface through the scraper. While obtaining a very high heat transfer coefficient, it can avoid adverse phenomena such as coking film on the heat transfer surface. Due to the scraping and stirring of the scraper, the materials can be fully mixed, so the scraper heat exchanger has the advantages of high heat transfer efficiency and uniform heat exchange effect. In addition, in the continuous production process, the materials usually stay in the scraper heat exchanger for only a few seconds, so the higher temperature gradient can be used for instantaneous heat transfer, and other undesirable side effects will rarely occur. Therefore, scraper heat exchanger is favored by candy, ice cream and other manufacturers.
Scraped Surface Heat Exchangers Diagram
Scraped surface heat exchanger were designed to improve upon issues that their predecessors were having problems with. Scraped surface heat exchangers incorporates an internal mechanism which periodically removes the product from the heat transfer wall. Most technologies in direct heat transfer use tubes or flat surface. The goal is to exchange the maximum of heat per unit area by generating as much turbulence as possible. This is achieved by consistently corrupting the tubes, or plates, or extending their surface with fins.
However, in these geometry conformation technologies the calculation of optimum mass flows and other turbulence related factors become diminished at the appearance of fouling. With the appearance of fouling designers are obliged to fit significantly longer heat transfer areas. The different types of fouling, include particulate accumulation, precipitation, sedimentation, generation of ice layer etc.
Scraped Surface Heat Exchangers
Another factor posing difficulties to heat transfer is viscosity. Highly viscous fluids tend to generate deep laminar flow, a condition with very poor heat transfer rates and high-pressure losses involving a considerable pumping power, often exceeding the exchange design limits. This problem becomes measured frequently when processing non-Newtonian fluids.
Scraped surface heat exchangers has been designed to face the above-mentioned problems. It incorporates an internal mechanism which periodically removes the product from the heat transfer wall. The product side is scraped by blades attached to rotating shaft. The blades are made of a rigid plastic material to prevent damage to the scraped surface. This material is FDA approved in the case of food applications.
Video of different Surface scraped heat exchanger .
Scraped surface heat exchanger can be used to heat and cool products of various viscosities, especially suitable for extremely viscous and viscous products, Learn more in this video.
Surface scraped heat exchanger Videos
What Products Does Scraped surface heat exchanger Do?
In the ice cream production plant, appropriate ice cream mixing raw materials and air are pumped into the scraper heat exchanger together, and the materials are mixed, cooled, crystallized and semi solidified through the heat transfer of the refrigeration medium (usually ammonia, Freon or carbon dioxide) in the jacket of the scraper heat exchanger and the strong stirring of the scraper, so as to obtain the ice cream products with fine, smooth, good shape and high expansion rate. In the margarine manufacturer, the scraper heat exchanger is applied to the quenching process of grease. Under the extremely high cooling efficiency, the grease completes the process of inflation, supercooling, and crystal nucleus formation, and then through the crystal shape adjustment in the kneading process, the margarine products with fine luster, certain ductility, stability, and whip ability can be produced. Some food manufacturers take advantage of the characteristics of scraper heat exchanger, such as a certain shear rate, high heat transfer efficiency and little damage to particles, and apply it to the production of butter sandwich products with a certain stability, starch pasting, emulsifier mixing, caramelization and concentration in candy production, and sterilization processes in strawberry jam, pudding production. Some chemical manufacturers use the scraper heat exchanger for the crystallization performance in highly viscous liquids, and apply it to dewaxing (petroleum, oil and fat), separation (xylene and chlorobenzene), and preparation of various fatty acids. Some large biogas plants plan to use scraper heat exchanger to recover waste heat to increase biogas production capacity. Some cosmetic manufacturers improved the production process of emulsion-based lipstick by using the mixing and crystallization functions of the scraper heat exchanger. Some gelatin manufacturers use scraper heat exchanger to complete the gelatin concentration and gelation process. Some food manufacturers use scraper heat exchangers to complete the continuous ultra-high temperature sterilization process for highly viscous materials (yogurt, sugar, dairy products, mashed potatoes, etc.) . In addition, scraper heat exchangers are also used to study the shear rate, pressure, temperature, residence time Heat transfer rate and other key production parameters are optimized.
Industrial Applications of SSHE Process
Scraped Surface Heat Exchangers can be employed in the continuous, closed processing of virtually any pump able ﬂuid or slurry involving:
Applications of Scraped surface heat exchanger
Heat Sensitive Products– Products which are degraded by prolonged exposure to heat are effectively processed in Scraped Surface Heat Exchangers. The scraper blades prevent product from remaining on the heat transfer surface by continuously removing and renewing the film. Because only a small amount of product is exposed to heat for just a short time, burn-on is minimized or eliminated.
Viscous Products–Scraped Surface Heat Exchangers process viscous products far more efﬁciently than conventional plate or tubular heat exchangers. Product ﬁlm is continually scraped from the heat transfer wall to induce high heat transfer rates; constant agitation causes turbulent ﬂow and more consistent heating or cooling; pressure drop is effectively controlled by the product annulus area; agitation eliminates stagnant areas and product build-up; and cleaning is easier.
Particulate-Laden Products– Products with particulates which tend to plug conventional heat exchangers are handled easily in Scraped Surface Heat Exchangers, and the particulates maintain maximum product identify.
Crystallized Product– Products which crystallize are ideal candidates for Scraped Surface Heat Exchanger processing. As product crystallizes on the heat transfer wall, the scraper blades remove it and keep the surface clean.
Chemical Processing– The chemical, pharmaceutical, and petrochemical industries can employ general categories.
• Particulate-Laden Products – Products with particulates which tend to plug conventional heat exchangers are handled easily in scraped surface heat exchangers, and the particulates maintains maximum product identify.
Typical application objects of scraper heat exchanger
Heat sensitive materials
Custard sauce, Costa, egg products, gravy, fruit preparation, cream cheese, milk，Clear, soy sauce, protein liquid, minced fish, etc.
High viscosity materials
Surimi, tomato paste, chocolate paste, whipped/aerated products, peanut butter, mashed potatoes, Starch paste, sandwich sauce, gelatin, mechanical boneless meat paste, baby food, nougat, Skin cream, shampoo, etc.
Crystallization and Phase Transformation
Margarine, shortening, lard, butter, soft candy, solvent, fatty acid, Vass, Forest, beer and wine, etc.
Shredded meat, chicken nuggets, fish meal, pet food, preserves, fruit yogurt, fruit ingredients, cakes Stuffing, sand ice, pudding, vegetable slices, Lagoona, etc.
Caramel, cheese sauce, lecithin, cheese, candy, yeast extract, mascara, teeth Paste, wax, etc.
1 Ndoye F T, Hernandez-Parra O, Benkhelifa H, et al. Influence of operating conditions on residence time distributions in a scraped surface heat exchanger during aerated sorbet production. Journal of Food Engineering, 2018, 222:126-138.
2 Hernandez-Parra O, Ndoye F T, Benkhelifa H, et al. Effect of process parameters on ice crystals and air bubbles size distributions of sorbets in a scraped surface heat exchanger. International Journal of Refrigeration. 2018,92: 225-234
3 Saraceno L, Boccardi G, Celata G P, et al. Development of two heat transfer correlations for a scraped surface heat exchanger in an ice-cream machine. Applied Thermal Engineering, 2011, 31(17-18):4106-4112.
4 Eisner M D, Wildmoser H, Windhab E J. Air cell microstructuring in a high viscous ice cream matrix. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2005, 263(1-3):390-399.
5 Sullo A, Arellano M, Norton I T. Formulation engineering of water in cocoa – Butter emulsion. Journal of Food Engineering, 2014, 142:100-110.
6 Rønholt S, Kirkensgaard J J K, Høyer K F, et al. The effect of capacity, rotational speed and storage on crystallization and rheological properties of puff pastry butter. Journal of the American Oil Chemists Society, 2014, 91(1):29-38.
7 émilie Lefébure, Sébastien Ronkart, Brostaux Y, et al. Investigation of the influence of processing parameters on physicochemical properties of puff pastry margarines using surface response methodology. LWT-Food Science & Technology, 2013, 51(1):225-232.
8 Miskandar M S, Man Y B C, Yusoff M S A, et al. Effect of scraped-surface tube cooler temperatures on the physical properties of palm oil margarine. Journal of the American Oil Chemists' Society, 2002, 79(9):931-936.
9 S. Rønholt, Kirkensgaard J J K, K. F. Høyer, et al. The Effect of Capacity, Rotational Speed and Storage on Crystallization and Rheological Properties of Puff Pastry Butter. Journal of the American Oil Chemists' Society, 2014, 91(1):29-38.
10 Luca D’Addio, Carotenuto C, Natale F D, et al. A new arrangement of blades in scraped surface heat exchangers for food pastes. Journal of Food Engineering, 2012, 108(1):143-149.
11 Wang Y Y, Russell A B, Stanley R A. Mechanical damage to food particles during processing in a scraped surface heat exchanger. Food and Bioproducts Processing, 2002, 80(1):3-11.
12 Rao C S, Hartel R W. Scraped surface heat exchangers. Critical Reviews in Food Science & Nutrition, 2006, 46(3):207-219.
13 Chen J, Ma C, Ji X, et al. Mechanism of waste-heat recovery from slurry by scraped-surface heat exchanger. Applied Energy, 2017, 7: 146-155.
14 Beri A, Pichot R, Norton I T. Physical and material properties of an emulsion-based lipstick produced via a continuous process. International Journal of Cosmetic Science, 2014, 36(2):148-158.
15 Regand A, Goff H D. Effect of Biopolymers on Structure and Ice Recrystallization in Dynamically Frozen Ice Cream Model Systems. Journal of Dairy Science, 2002, 85(11):2722-2732.
16 Depypere F, Verbeken D, Torres J D, et al. Rheological properties of dairy desserts prepared in an indirect UHT pilot plant. Journal of Food Engineering, 2009, 91(1):140-145.
17 Härröd M. Scraped surface heat exchangers: A literature survey of flow patterns, mixing effects, residence time distribution, heat transfer and power requirements. Journal of Food Process Engineering, 1986, 9(1):1-62.
18 Abichandani H, Sarma S C, Heldman D R. Hydrodynamics and heat transfer in thin film scraped surface heat exchangers—A review. Journal of Food Process Engineering, 1986, 9(2):143-172.
19 Dehkordi KS, Fazilati M A, Hajatzadeh A. Surface Scraped Heat Exchanger for cooling Newtonian fluids and enhancing its heat transfer characteristics, a review and a numerical approach. Applied Thermal Engineering, 2015, 87:56-65.