What can termites teach us about thermoregulation and ventilation?

By Dr Bagus Muljadi; Assistant Professor in Chemical and Environmental Engineering in GERC

From May 8th to 11th I had the chance to attend and present our work at the 9th International Conference on Porous Media & Annual Meeting (INTERPORE), in Rotterdam, the Netherlands. Unlike the previous INTERPORE meetings I have attended, this time I did not talk about storage or extraction from natural rocks. In fact, what I think is fascinating about the work I presented is the fact that it begun from simple curiosity: how do termites regulate temperature, humidity, and gas exchange in their mounds?

Termites are very social animals that live in colonies. Like us, termites build an environment that suits them rather than adapting to their environment. For instance, they sometimes live in arid regions that would dry out their bodies but their mounds help counteract the problem by maintaining an environment that is cool and humid. Some termites grow fungus – which requires a rain forest-like environment ¬– to help them break down woody material into more digestible food. Although their sophisticated and innovative green-energy designs perfectly capture the current trend for environmentally friendly construction, there is very little information in the literatures on the fluid dynamics of these structures.

One of the challenges in understanding gas flow or heat transfer in termites’ mounds is the complexity of their pore structure. Crudely one can easily identify at least two scales of pore sizes: the first being the ones where termites dwell. These pores are connected and may be several mm or cm wide. The second type is much smaller: they are consisted of the gaps between the grains of soil termites build their mounds with. They may be several microns wide and may be not as well connected. To better understand how flow and transport occur in this complex topology, we borrow the state-of-the-art methodology from earth scientists and hydrologists, namely digital core analysis. Thanks to the advance of X-ray microtomography (XMT) and computational architecture, it is now possible to run fluid simulations directly in the pore spaces of rocks consisted of up-to a billion voxels [1].

Flow in the pore spaces of trinervitermes mounds. The image is 5 mm across, with 2 microns resolution

Together with our colleagues in the Mathematics and Earth Science departments, Imperial College London, and Centre de Recherches sur la Cognition Animale, France, we excavated several mounds (of trinervitermes geminatus) from the regions of Senegal and Guinea in Africa. We took small fractions from these samples and put them under the XMT scanner. From the images we generated 3-D topologies of the pore and the grain structures and conducted flow, diffusion, and heat transfer simulations directly in these topologies. We also conducted X-ray diffraction analysis (XRD) to identify different minerals in these samples. This is hugely collaborative project involving biologists, computational fluid dynamicists, and geochemists.

Using this approach we are able to better understand how termites maintain the habitability of their mounds: the seemingly random pore structures are built with a sophisticated thermal-buffering property.  The next challenge is to harvest meaningful signatures or statistics from these observed structures, and hopefully use them to inspire us to build houses or buildings which do not rely on a heavy amount of electricity for air conditioning.

This kind of work is what makes us excited in doing research: a multidisciplinary effort that provides new approaches for solving wider energy and environmental problems. By working in GERC I can draw on the support of colleagues in the Schools of Mathematical Sciences and Chemistry, which are vital for the success of this type of research.

[1] B. P. Muljadi, M. J. Blunt, A. Q. Raeini, B. Bijeljic,  ADVANCES IN WATER RESOURCES, 2015, "The Impact of Porous Media Heterogeneity on Non-Darcy Flow Behaviour from Pore-Scale Simulation"

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