Modeling of a Bio-Thermo-Electric Micro-Cooler

Abstract

This work is a part of an on-going research effort to fabricate a device consisting of an array of micro thermoelectric coolers (μTECs) for highly localized control of temperature in biological systems. A preliminary lumped 1-D parameter model was developed and numerical simulations were carried out to identify the critical and optimal design parameters for a μTEC operating under steady state conditions. The lumped parameter analysis revealed the presence of a new limitation on the maximum possible current through the system, which we denoted as the secondary breakdown current (as opposed to the primary breakdown current associated with Joules heating). To further understand the effect of contact resistances (thermal and electrical), radiative effects, and lateral effects (interactions between μTECs) in our device, we developed a 3-D finite element model (FEM) using ANSYS®. The FEM analysis identified the optimal distance between μTECs to generate discrete and distinct temperatures within the cells located in the extracellular matrix and thus, generating the optimal design specifications for our device.

Numerical simulation of local temperature distortions during ice nucleation of cells in suspension

“…The current model also does not account for the presence of chemicals that are commonly added to biological systems during a freezing process. These chemical denoted as cryoprotective agents (CPAs) have been shown to alleviate the freezing injury and also tend to reduce the latent heat released by the extracellular solution during the freezing process [32]. Thus, the addition of CPAs will most definitely lower the Δ T and dt results obtained in the current study.…”

“…For example, an examination of the data shown in Table 2, suggests that the micro-thermocouples need to be placed within a spatial distance of ~10 μm from the nucleating cell with an ability to measure local temperature jump of ~0.2 °C and a temporal resolution of ~0.01 secs. Additionally, the simulations presented here are also of value in the development of micro-thermo electric coolers (μTECs), based on the Thompson effect [31,32]. For example, the local thermal fluctuations within the tissue system due to nucleation of ice within the embedded cells can be completely eliminated by cooling the nucleating region with the use of a specifically designed μTEC.…”

“…In addition, the model presented in this study assumes that the latent heat released by the extracellular solution during the freezing process follows the phase diagram (as stated earlier). One recent study [32] suggests that the latent heat released by the extracellular solution has a cooling rate dependence (i.e. it is both temperature and time dependent).…”