Thermal stratification and mixing in confined spaces

Box plot of hourly temperature recorded in July 2022 by sensors at four different heights.*

The fluid dynamics found in buildings results from a complex interplay among sources of energy at different spatial scales, forced by large-scale convective motions and dissipated by diapycnal mixing. Predicting how this interplay produces or destroys thermal stratification in an enclosed space is an open question that needs to be addressed to enable energy consumption estimations and mitigation of risks related to contaminant transport.

We use a highly instrumented computer laboratory to investigate the problem of thermal stratification in a mechanically ventilated room. Heating sources at the floor level are typically non-uniform and time-dependent. Such thermal boundary conditions are particularly challenging as they lie between localised sources of buoyancy, which would lead to turbulent plumes and tend to maintain a stable stratification, and distributed sources that have a destabilising effect. Temperature and CO2 are measured at key positions within the room, yielding insights into the flow and mixing occurring in the room. In addition, the heat input due to computers is metered and the room occupancy is recorded. These measurements enable us to estimate the room energy budget.

This work is part of the project DStratify.

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