Bacteria mediated heat sinks

Abstract

Many applications, such as laser diode technology, utilize components (eg. resistors) which have performance characteristics heavily dependent on temperature, and therefore, maintaining constant temperature is essential in order to eliminate drift in device efficiency. Constant temperature controllers, however, can often be complicated and only stay within a certain range of a set temperature. If temperature needs to be maintained, this thesis suggests a model instead to use ice as an isothermal heat sink. The model proposes to make use of thermodynamics and stabilize an isothermal solid-liquid interface created during ice formation, which will lead to having an isothermal free surface in the liquid phase. The model was validated using a Peltier device to freeze water by applying a constant DC current, and because the inefficiency of the module decreases with decreasing temperature, the heat dissipating power of the thermoelectric eventually equalizes with the ambient losses, stabilizing a solid-liquid interface. This stabilized interface was able to be maintained in experiments using deionized (DI) water, DI water with polystyrene (PS) micro-beads, and DI water with Pseudomonas syringae, a gram-negative bacteria. Pseudomonas syringae is known as an ice-nucleating agent that can reduce the amount of supercooling needed to nucleate ice. Experiments using the bacteria were observed to stabilize a solid-liquid interface faster than the control experiments, and this phenomenon was modeled as a two-fold reason: (1) by increasing nucleation temperature using the bacteria, a reduced input Peltier power is needed to nucleate ice, thereby making the Peltier device reach the steady-state heat losses faster; and (2) a possible decreased enthalpy of fusion caused by the bacteria leads to less latent heat released during the freezing process, putting less heat load on the Peltier device and allowing it to reach steady-state faster. This prediction regarding decreased enthalpy of fusion was validated using a heat flux sensor, as the preliminary results for a mixture of DI water with bacteria yielded an enthalpy of fusion of (199.1±20.2) kJ/kg, whereas the values for DI water and DI water with PS beads were (345.1±15.6) kJ/kg and (328.3±31.2) kJ/kg respectively.