Photo of a 'salt bath' experiment, showing a jet of dyed saline hitting a surface, modelling a fan heater directed downwards towards the floor.  Planar Light-Induced Fluorescence (PLIF) using a light sheet and fluorescein dye has been used to visualise the flow.

Photo of a 'salt bath' experiment, showing a jet of dyed saline hitting a surface, modelling a fan heater directed downwards towards the floor.  Planar Light-Induced Fluorescence (PLIF) using a light sheet and fluorescein dye has been used to visualise the flow.

Experiments

Saline sinks in fresh water in the same way that heat rises in air (albeit upside-down). Small-scale 'salt bath' laboratory experiments allow us to isolate, visualise and investigate all sorts of fluid dynamical phenomena - from localised jets of hot air to whole-building ventilation flows to sandstorms more than a kilometre in height - anything where differences in temperature (and therefore density) are involved.

 1:50 scale model of a naturally ventilated three-storey building with an exhaust stack.  Saline, dyed red, is supplied to the storeys to model heat generated by people and equipment. The buoyant air rises upwards and leaves the building through the stack, causing fresh air to be drawn into the storeys through floor-level ventilation openings. Note that this photo is upside-down!

1:50 scale model of a naturally ventilated three-storey building with an exhaust stack.  Saline, dyed red, is supplied to the storeys to model heat generated by people and equipment. The buoyant air rises upwards and leaves the building through the stack, causing fresh air to be drawn into the storeys through floor-level ventilation openings. Note that this photo is upside-down!

During 2015, Andy worked with the University of Cambridge and Dyson on an experimental project to better understand how to efficiently heat and cool our indoor spaces. By projecting jets of dyed saline into fresh water, he was able to model the jets of hot or cool air produced by fan heaters or cooling devices, and to explore how best to provide personalised comfort, whilst minimising energy use.

Zooming out to the level of a whole building, the salt bath technique can also be used to model natural ventilation flows. In this case, inputs of saline represent the heat generated by people and equipment within the building, as well as solar gains. The newly constructed James Dyson building, at the Cambridge University Engineering Department, will be naturally ventilated and Andy has designed a series of experiments to model the system.