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Modeling and simulation of heat exchanger with strong dependence of oil viscosity on temperature

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Heating of oil and oil products is widely used to reduce energy losses during transportation. The flow in the annular space of the heat exchanger is complex and depends on many factors. The use of thin tubes in helicoid-type heat exchangers makes it necessary to take into account the transition of the flow regime from laminar to turbulent. The semi-empirical turbulence models traditionally used in numerical calculations do not take into account the laminar-turbulent transition. An approach is developed to determine the effective length of the heat exchanger and the temperature of the cold coolant at its outlet in the case of a strong dependence of oil viscosity on temperature, taking into account the possibility of a laminar-turbulent transition. Oil is considered as a heated coolant, and water is considered as a heating component. The novelty of the developed approach lies in the application of the turbulence model, which takes into account the laminar-turbulent transition, to the calculation of helicoid-type heat exchangers. For numerical simulation, the Reynolds-averaged Navier–Stokes equations are used which are closed using γ–Reθt turbulence model that takes into account the laminar-turbulent transition. The results of numerical calculations are compared with the data obtained on the basis of the log-mean temperature difference method at constant and variable viscosity. In the case of variable oil viscosity, a transition from the laminar flow regime to the turbulent one is manifested which has a significant effect on the effective length of the heat exchanger. The results of numerical calculations can be useful in designing helicoid-type heat exchangers.

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