Scraped Surface Heat Exchanger for Dairy Industry- A Review 

Abstract

Scraped surface heat exchanger (SSHE) is more suitable for heat transfer for viscous and heat sensitive products in dairy industry. It is easier to control time, temperature and pressure in a SSHE than in a kettle. The use of SSHE for the manufacture traditional Indian Dairy Product helps in reducing man power and improving quality as well as shelf life of the product. SSHE of various design are being used for manufacture of TIDP as well as for western product such as icecream, cheese etc. The choice and design of heat exchanger depends on Flow rate of both streams, Heat sensitivity and corrosivity of the fluids, Terminal temperatures, Properties of both streams, Operating pressure and temperature, Pressure drop, Fouling tendencies, Type and phase of fluids, Material of construction, Heat recovery, Flow arrangement etc. The scraping action of the blades rotating within the heat transfer tube continuously removes the product film from the heat exchanger surface and prevents burning-on, scaling or crystal build up on the wall. This type of heat exchangers can be used for batch or continuous heating or cooling of products. The major advantages of SSHE include short residence time in heated zone so heat sensitive product can be conveniently processed, high heat transfer coefficient, narrow residence time distribution, wide viscosity range, minimum surface fouling. SSHE basically consists of a cylindrical rotating shaft within a concentric hollow stationary cylinder so as to form an annular region along which the process fluid is pumped. In a typical SSHE there are usually two or four blades located periodically around the rotor throughout the product tube, though sometimes they are axially staggered in order to improve mixing. Liquid-full operation and thin-film operations are very commonly used in SSHE. Thermal and electrical energy are required in operations of SSHE. The electrical energy required for driving the rotor is very small as compared to the thermal energy required to evaporate the water. Structural design of SSHE includes the calculation of size, shape and strength of each component of the SSHE to handle the product efficiently, material of construction require to meet the requirements from the view point of food hygiene and sensory attributes of the product, the finish of the surface and the mechanical power to run the unit successfully and efficiently. More advanced designs of SSHE are available in the market for various applications. There is a good scope for SSHE to prepare indigenous milk products viz., basundi, peda, khoa, halava or in general any khoa based sweets on commercial basis.