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  • Posted By: yukiyuki
  • Date Posted: 02/23/2011
  • Category: Science
  • Words: 1299
  • Pages: 6
  • Views: 805
  • Rank: 763

Heat Exchangers

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Heat Exchangers

Most fluids used in the chemical, pharmaceutical, food, and biomedical industries can be classified as non-Newtonian, ie, the viscosity varies with shear rate at a given temperature. In contrast, Newtonian fluids such as water, air, and glycerin have constant viscosities at a given temperature. Examples of non-Newtonian fluids include molten polymer, aqueous polymer solutions, slurries, coal–water mixture, tomato ketchup, soup, mayonnaise, purees, suspension of small particles, blood, etc. Because non-Newtonian fluids are nonlinear in nature, these are seldom amenable to analysis by classical mathematical techniques.


The optimum design of process equipment which handles non-Newtonian fluids could be significantly improved once predictive capability were increased. However, the basic understanding of the fluid mechanical and heat-transfer behavior of non-Newtonian, ie, viscous and viscoelastic, fluids is limited (22). A better understanding of pressure drop and heat-transfer behavior of non-Newtonian flows applicable to typical heat-exchanger geometries should lead to the design and development of more energy-efficient processes and to better quality control of the final products. In general, the viscosity of a non-Newtonian fluid can be significantly larger than that of water. Therefore, the selection of a pump size to provide enough flow rate and subsequently to ensure adequate heat removal or supply is necessary.


A significant heat-transfer enhancement can be obtained when a noncircular tube is used together with a non-Newtonian fluid. This heat-transfer enhancement is attributed to both the secondary flow at the corner of the noncircular tube (23, 24) and to the temperature-dependent non-Newtonian viscosity (25). Using an aqueous solution of polyacrylamide the laminar heat transfer can be increased by about 300% in a rectangular duct over the value of water (23).


A knowledge of the viscous and thermal properties of non-Newtonian fluids is essential before the results of the analyses can be used for practical design purposes. Because of ...

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