Lower critical solution temperature

The lower critical solution temperature (LCST) or lower consolute temperature is the critical temperature below which the components of a mixture are miscible in all proportions. The word lower indicates that the LCST is a lower bound to a temperature interval of partial miscibility, or miscibility for certain compositions only. The phase behavior of polymer solutions is an important property involved in the development and design of most polymer-related processes. Partially miscible polymer solutions often exhibit two solubility boundaries, the upper critical solution temperature (UCST) and the LCST, both of which depend on the molar mass and the pressure. At temperatures below LCST, the system is completely miscible in all proportions, whereas above LCST partial liquid miscibility occurs. In the phase diagram of the mixture components, the LCST is the shared minimum of the concave up spinodal and binodal (or coexistence) curves. It is in gene

Thermo-hydro-mechanical behavior of energy tunnels

Matthias Timothee Stanislas Wojnarowicz

Subsurface geothermal in combination with Ground Heat Exchanger (GHE) and heat pumps systems had proved over the past decade to be an effective way in space heating and cooling. GHE’s embedded in geostructures such as tunnels has become more and more attractive in the current state where we try to mitigate greenhouse gas effects. The scope of this paper is to provide a fully coupled numerical model to assess the different physical aspects of an energy tunnel such as the kinetic and thermal boundaries layers development, thermally induce stress, and the heat generation. To do so, a finite element model is used to assess the heat exchange between, the GHE, the concrete lining, the air within the tunnel, the surrounding ground, and groundwater flow. The numerical model is then confronted with data from real-scale experimentation that was performed in Torino in 2018. The predictions from the numerical model show a quite good match with the data from the experimental prototype. Later on, similar models are generated to assess the effect of the heat exchange on air velocity and temperature within the tunnel as well as the induced thermal stress. The numerical results highlight the formation of both the kinematic and thermal boundary layer and shows that those boundaries are affected by the GHE’s activation. For the kinematic aspect, the lower temperatures observed in the vicinity of the heat exchangers tend to lower the velocity magnitude especially close to the wall surface. This change in velocity may be linked to a buoyancy effect cause by the lower temperature of the air in this regions. Indeed natural convection occurs along the tunnel, cooler fluid is pushed down while the warmer fluid rise; locally a lower temperature tends to decrease the viscosity of the fluid and increase its volumic mass. It was observed that the activation of GHE’s enhances this phenomenon in their vicinity due to the temperature gradient that they produce. Moreover, GHE’s activation tends to increase the overall turbulence of the flow and thus the eddies’ formation. The locations of those disturbance are difficult to predict due to the fact that small disturbance may generate large vorticity within the flow. However, it is shown that after passing the GHE zone, the velocity profile tends to stabilize to the undisturbed case. The kinematic entry length seems to happen further down the stream in the case where GHE’s are activated. This is due to the temperature disturbance generated by GHE’s activation. This phenomenon is increased with respect to the number of GHE loops activated. Furthermore, some probing was performed in the vicinity of the heat exchanger to assess the thermal induce stress due to the heating operation. The recorded stress shows peaks at early stages due to the higher temperature gradient that is generated between the GHE’s and concrete at beginning. Finally, after some time, the temperature reaches a steady state hence the stabilized thermal response recorded.

2020

GHz spectroscopy on a rare-earth quantum magnet

Lev Bergsma

In this report, spectroscopy was used to track the energy of different states in a LiHoF4 sample around its critical temperature. The experimental setup consist of a Cooper cavity with the sample, an antenna and a resonator inside. This cavity is attached to a probe and put inside a cooled well and a transverse magnetic field. Two different frequency ranges were examined around, f0 = (1.18732 0.00001) Ghz and f0 = (3.32940 0.00001) Ghz. The energy difference between states was successfully tracked for different temperatures thanks to the Q factor plots. However, the lack of sufficient data points and the unexpected behaviour around Tc (there are no gaps and no discontinuities), implies that this is only the beginning of this experiment and more time and measurements is needed to claim reasonable results.

2022

Thermo-hydro-mechanical behavior of energy tunnels

Matthias Timothee Stanislas Wojnarowicz

2020

Lower critical solution temperature

Thermo-hydro-mechanical behavior of energy tunnels

GHz spectroscopy on a rare-earth quantum magnet

Synthesis and characterisation of amphiphilic ABA triblock copolymers with poly(dimethylsiloxane) as a central hydrophobic part using polymerization techniques

GHz spectroscopy on a rare-earth quantum magnet

Synthesis and characterisation of amphiphilic ABA triblock copolymers with poly(dimethylsiloxane) as a central hydrophobic part using polymerization techniques

Thermo-hydro-mechanical behavior of energy tunnels