When solid materials are loaded above a critical level, they may change their shape permanently: they undergo plastic deformation. Consider, for example, a cylinder which we compress by pushing from top to bottom. If the load is small, the cylinder first deforms elastically (it reverts to its original shape after the load is removed). Above a certain load, some permanent deformation remains. Now if we use a macroscopic cylinder, say, several centimetres in size, then the stress (the force per unit area) needed to obtain a given relative deformation will not depend on the size of the cylinder. It will increase gradually with increasing deformation, and this 'hardening behavior' will be identical for cylinders made of the same material and deformed under the same conditions. If the stress is everywhere the same in the cylinder, also the deformation will be homogeneous - the cylinder will get shorter and thicker but will retain its cylindrical shape.
But when the deforming body becomes very small - of the order of a few micrometers in diameter - then we observe quite different behavior: (1) The stress required to deform samples of material increases as the samples become smaller. (2) Even if the stress is increased slowly and steadily, the deformation does not increase gradually but in large jumps. These jumps occur randomly, and lead to large deformations in small parts of the sample. As a consequence, in our cylinder example the samples assume irregular accordeon-like shapes. If we bend very thin wires, they may not deform into smoothly curved but into random shapes resembling mis-shapen paperclips. (3) Even if the material properties are the same (for instance, if all our cylinders have been machined out of the same block) the stresses required to deform samples may scatter hugely. In two apparently identical micrometer sized samples, the stresses required to initiate or sustain plastic deformation may easily differ by a factor of two. Obviously this poses serious problems if we want to avoid or control irreversible deformation in very small components.
The research focuses on develop a microwave swing technique to selectively heat solid at molecular level for adsorbent regeneration, and then compare the results with temperature swing. The project is supported by EPSRC.
New ideas for carbon capture are urgently needed to combat climate change. Retro-fitting post-combustion carbon capture to existing power plants has the greatest potential to reduce CO2 emissions considering these sources make the largest contribution to CO2 emissions in the UK. Unfortunately, carbon capture methods based on existing industrial process technology for separation of CO2 from natural gas streams (i.e. amine scrubbing) would be extremely expensive if applied on the scale envisaged. Moreover, many of the chemical absorbents used, typically amines, are corrosive and toxic and their use could generate significant amounts of hazardous waste. So, more efficient and 'greener' post-combustion CCS technologies are urgently needed if CCS is to be adopted on a global scale.
Power plants constitute one of the largest CO2 emitting sectors. With increased emphasis on abatement of emissions to meet the 2030 deadline set by the UK Committee on Climate Change, the power-plant sector is relying on CCS retrofits using post-combustion capture to clean up flue gases. However, despite the highly transient nature of power plant operation characterised by frequent shut-downs and start-ups (up to twice a day), the retrofits are currently designed for a constant base-load operation and hence cannot maintain even liquid distribution during unsteady loading.
Carbon Capture and Separation Processes
Multiphase flows, interfaces and phase change from nano- to macro-scales