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A Flow Rate Dependent 1D Model for Thermally Stratified Hot-


Rendall, Joseph; Bulnes, Fernando ; Gluesenkamp, Kyle; Abu-Heiba, Ahmad; Worek, William; Nawaz, Kashif


: Stratified tank models are used to simulate thermal storage in applications such as residential or commercial hot-water storage tanks, chilled-water storage tanks, and solar thermal systems.The energy efficiency of these applications relates to the system components and the level of stratification maintained during various flow events in the tank. One-dimensional (1D) models are used inbuilding energy simulations because of the short computation time but often do not include flow-ratedependent mixing. The accuracy of 1D models for plug flow, plug flow with axial conduction, andtwo convection eddy-diffusivity models were compared with experimental data sets for discharginga 50-gal residential tank and recharging the tank with hot water from an external hot-water source.A minimum and maximum relationship for the eddy diffusivity factor were found at Re <2100 and>10,000 for recirculation of hot water to the top of the tank and vertical tubes inletting cold waterat the bottom. The root mean square error decreased from >4 C to near 2 C when consideringflow-based mixing models during heating, while the exponential decay of the eddy diffusion resultsin a root mean square error reduction of 1 C for cone-shaped diffusers that begin to relaminarizeflow at the inlet.



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