Temperature profiles within a double-pipe heat exchanger with countercurrent turbulent flow of newtonian fluids: Derivation, validation, and application to food processing

Pasteurization or sterilization of food and bioproducts is mostly performed using heat exchangers in countercurrent flow. The lack of appropriate analytic solutions for temperature profiles in the heating and cooling sections of such processes is most likely the main reason for the traditional cautious approach of disregarding the contribution of these stages in the total thermal history calculation. This approach leads to excessive thermal abuse of the product. The current manuscript describes the derivation and validation of an analytic solution for the temperature profiles within a double-pipe heat exchanger with countercurrent turbulent flow of Newtonian fluids, at any possible flow rate and not necessarily assuming an isothermal heating medium or coolant. The presented solution is based on application of the "heat exchanger effectiveness" concept in a partial heat exchanger, and can be easily solved and plotted using a spreadsheet. An interactive Excel™ workbook was developed for fast prediction of temperature profiles and used in a simulated case study to demonstrate the influence of operating conditions on the temperature profile and thermal history of a pasteurized liquid product.