A numerical study on heat transfer enhancement via mechanical aids

Abstract

The work deals with an experimental and numerical analysis on disturbed thermal boundary layer obtained in a heat exchanger by two rotating blades (scrapers). A three-dimensional numerical model of unsteady forced convection in an analyzed device is proposed and taken into consideration. The model allows for the transient nature of the processes occurring in a very efficient in terms of heat transfer the Scraped Surface Heat Exchanger (SSHE) and the impacts on the body forces such as gravity, centrifugal and Coriolis forces on processes. In order to validate the model, a specially constructed experimental test stand was designed and manufactured. The series of experiments for the Reynolds number equal to 1100 and the Nusselt number in the range of 10–25 were performed and compared with numerical results achieving satisfactory agreement, with the error smaller than 5% for temperature and 9% for the heat flux values. The set of governing equations of conservation of mass, momentum, and energy was solved within the framework of the Finite Volume Method (FVM). The movement of the scrapers was incorporated into the model with the use of the Sliding Mesh Method (SMM). The distributions of temperature and velocity were elaborated and scrutinized. It was found that in the analyzed flow regime, the gap width between the stator wall and the scraping blade tip highly affects the Nusselt number. Moreover, the numerical results were compared with other mathematical models available in the literature and the discrepancy between the conventionally used model based on penetration theory was found.