Validation of measurements with conjugate heat transfer models

Abstract

Purpose – The purpose of this work is to propose a numerical method based on computational fluid dynamics (CFD) for reconstructing the heat transfer inside electrical machines. The used conjugate heat transfer (CHT) method takes heat convection and heat conduction into account to determine the temperature rise and the thermal losses in stator duct models of large hydro generators. Three different test cases are studied with different slot section components. The numerical models are validated with measurement data for a range of different mass flow rates. Design/methodology/approach – The work presented is based on the combination of two complementary approaches, namely numerical simulation and measurements. The measured data for the air mass flow and the heat losses are used as boundary conditions for the identification of the temperature distribution in the solid and fluid domains (using a commercial software for CFD). The CHT method is an additional application of CFD and is used to solve the energy equations in the solid domains. Therefore, it is possible to define a thermal source in the solid domains. Findings – The data obtained by the numerical computation are compared with measurement data for different mass flow rates of the cooling fluid. The quality of the computed values depending on the different mass flow rates shows a good agreement with the measured data. The temperature distribution in the solid domains depending on different material properties is also pointed out in this investigation. Research limitations/implications – The topic describes a method for solving the heat transfer in the fluid as well as the solid domains. The losses can be defined as sources in the solid domains, e.g. copper and iron, obtained by electromagnetic calculations. This boundary condition defines the situation more accurately than, for example, a constant value of the heat flux or the temperature at the walls like in common used CFD simulations. Another advantage of CFD over other approaches is the consideration of the actual wall heat transfer coefficient. Originality/value – The presented investigations show relevant issues influencing the thermal behaviour of electrical machines.