Adam C. Gladen

A Head and Neck Support Device for Inducing Local Hypothermia

The present work describes the design of a device/system intended to induce local mild hypothermia by simultaneously cooling a patients head and neck. The therapeutic goal is to lower the head and neck temperatures to 33-35 °C, while leaving the core body temperature unchanged. The device works by circulating a cold fluid around the exterior of the head and neck. The head surface area is separated into five different cooling zones. Each zone has a cooling coil and can be independently controlled. The cooling coils are tightly wrapped concentric circles of tubing. This design allows for a dense packing of tubes in a limited space, while preventing crimping of the tubing and minimizing the fluid pressure head loss. The design in the neck region also has multiple tubes wrapping around the circumference of the patients neck in a helix. Preliminary testing indicates that this approach is capable of achieving the design goal of cooling the brain tissue (at a depth of 2.5 cm from the scalp) to 35 °C within 30- 40 min, without any pharmacologic or circulatory manipulation. In a comparison with examples of current technology, the device has shown the potential for improved cooling capability.

The Effect of a Thermotropic Material on the Optical Efficiency and Stagnation Temperature of a Polymer Flat Plate Solar Collector

Solar hot water and space heating systems constructed of commodity polymers have the potential to significantly reduce the initial cost of solar thermal systems. However, a polymer absorber must be prevented from exceeding its maximum service temperature during stagnation. Here we consider the addition of a thermotropic material to the surface of the absorber. The thermotropic layer provides passive overheat protection by switching from high transmittance during normal operation to high reflectance if the temperature of the absorber becomes too high. In this paper, a one dimensional model of a glazed, flat-plate collector with a polymer absorber and thermotropic material is used to determine the effects of the optical properties of a thermotropic material on optical efficiency and stagnation temperature of the collector. A key result is identification of the reflectance in the translucent state required to provide overheat protection for potential polymer absorber materials. For example, the reflectance of a thermotropic material in the translucent state should be greater than or equal to 51% for a polypropylene absorber which has a maximum service temperature of 115 °C.Copyright

A Parametric Numerical Study of Optical Behavior of Thermotropic Materials for Solar Thermal Collectors

A Monte Carlo model is applied to determinate the steady state, solar-weighted optical properties of potential thermotropic composite materials for overheat protection of polymer solar absorbers. The key results are dimensionless plots of normal-hemispherical transmittance, reflectance and absorptance as a function of particle size parameter, scattering albedo, and overall optical thickness. The optical behavior of thermotropic materials at different temperatures is represented by a change in the relative refractive index which affects the scattering albedo and optical thickness. At low temperatures where overheat protection is not required, referred to as the clear state, the overall optical thickness should be less than 0.3 to ensure high transmittance for the preferred particle size parameter of 2. At higher temperatures where overheat protection is required, referred to as the translucent state, the overall optical thickness should be greater than 10 and the scattering albedo should be greater than 0.995 to achieve 50% reflectance. A case study of low molecular weighted polyethylene in poly(methyl methacrylate) is presented to illustrate use of the results to guide the design of thermotropic materials.