Temperature-aware time-varying convection over a duty cycle for a given system thermal-topology

Abstract

Smart dynamic thermal management (SDTM) is a key enabling technology for optimal design of the emerging transient heat exchangers/heat sinks associated with advanced power electronics and electric machines (APEEM). The cooling systems of APEEM undergo substantial transition as a result of time-varying thermal load over a duty cycle. Optimal design criteria for such dynamic cooling systems should be achieved through addressing internal forced convection under time-dependent heat fluxes. Accordingly, an experimental study is carried out to investigate the thermal characteristics of a laminar fully-developed tube flow under time-varying heat fluxes. Three different transient scenarios are implemented under: (i) step; (ii) sinusoidal; and (iii) square-wave time-varying thermal loads. Based on the transient energy balance, exact closed-form relationships are proposed to predict the coolant bulk temperature over time for the aforementioned scenarios. In addition, based on the obtained experimental data and the methodology presented in Fakoor-Pakdaman et al. (2014), semi-analytical relationships are developed to calculate: (i) tube wall temperature; and (ii) the Nusselt number over the implemented duty cycles. It is shown that there is a ‘cut-off’ angular frequency for the imposed power beyond which the heat transfer does not feel the fluctuations. The results of this study provide the platform for temperature-aware dynamic cooling solutions based on the instantaneous thermal load over a duty cycle.