Jonathan L. Gaspredes

Feasibility Study of a Residential Hybrid Ground Source Heat Pump System

A residential hybrid ground source heat pump (HGSHP) model is presented, which integrates a compact cooling tower with a GSHP. The base case GSHP model is for a single story, 195 m2 house with a 14 kW heat pump and four 68.8 m deep vertical boreholes and uses Austin, TX weather data. The GSHP model was run for a range of supplemental heat rejection (SHR) capacities of an unidentified device located between the heat pump outlet and ground loop inlet, and estimates of improved heat pump performance and ground temperature effects are presented. Then, a compact closed wet cooling tower (CWCT) model is presented and coupled to the GSHP model. The towers 7 kW capacity represents the smallest commercially available cooling tower. Each of the four HGSHP boreholes was reduced to 26.5 m. The operational and economic performance of the HGSHP is compared to a GSHP alone. Metrics include estimates of initial and lifetime operational costs, ground temperature effects, and heat pump efficiency. Simulations for ten years of operation show that adding the compact CWCT is cost effective, extends the lifetime of the borehole system, and maintains high heat pump efficiencies.

Histological evaluation and optimization of surgical vessel sealing systems

Surgical vessel sealing systems are widely used to achieve hemostasis and dissection in open surgery and minimally invasive, laparoscopic surgery. This enabling technology was developed about 17 years ago and continues to evolve with new devices and systems achieving improved outcomes. Histopathological assessment of thermally sealed tissues is a valuable tool for refining and comparing performance among surgical vessel sealing systems. Early work in this field typically assessed seal time, burst rate, and failure rate (in-situ). Later work compared histological staining methods with birefringence to assess the extent of thermal damage to tissues adjacent to the device. Understanding the microscopic architecture of a sealed vessel is crucial to optimizing the performance of power delivery algorithms and device design parameters. Manufacturers rely on these techniques to develop new products. A system for histopathological evaluation of vessels and sealing performance was established, to enable the direct assessment of a treatment’s tissue effects. The parameters included the commonly used seal time, pressure burst rate and failure rate, as well as extensions of the assessment to include its likelihood to form steam vacuoles, adjacent thermal effect near the device, and extent of thermally affected tissue extruded back into the vessel lumen. This comprehensive assessment method provides an improved means of assessing the quality of a sealed vessel and understanding the exact mechanisms which create an optimally sealed vessel.

Corrosion and wear in plasma electrosurgical devices

Data were previously reported on studies of the effects of electrical discharges on the corrosion and wear of simple, single-wire test devices immersed in isotonic saline 1 . This work showed that there are a wide variety of mechanisms that can explain various aspects of electrode mass loss, even with very simple electrode geometries and operating conditions. It was found that the electrode material composition played an important role. Subsequently, our studies were expanded to include more realistic device geometries and operating conditions. This paper shows the results of studies on wear characteristics of electrodes made from a variety of highly corrosion resistant metals and alloys, including Waspaloy, Hastelloy, Inconel, Havar, Monel, and other pure metals such as Hafnium. All of these metals underwent wear testing under clinically relevant conditions. Depending on the operating conditions, multiple discrete physical and chemical effects were observed at different locations on the surface of an individual millimeter-scale device electrode. Scanning electron microscope (SEM) micrographs, Energy-dispersive X-ray spectroscopy (EDS) and area loss data will be presented for a variety of test conditions and electrode materials.

The differing behavior of electrosurgical devices made of various electrode materials operating under plasma conditions

Coblation® is an electrosurgical technology which employs electrically-excited electrodes in the presence of saline solution to produce a localized and ionized plasma that can cut, ablate, and otherwise treat tissues for many different surgical needs. To improve our understanding of how Coblation plasmas develop from devices made from different electrode materials we describe several experiments designed to elucidate material effects. Initial experiments studied simple, noncommercial cylindrical electrode test devices operating in buffered isotonic saline without applied suction. The applied RF voltage, approximately 300 V RMS, was sufficient to form glow discharges around the active electrodes. The devices exhibited significantly different operating characteristics, which we ascribe to the differing oxidation tendencies and other physical properties of the electrode materials. Parameters measured include RMS voltage and current, instantaneous voltage and current, temporally-resolved light emission and optical emission spectra, and electrode mass-loss measurements. We correlate these measured properties with some of the bulk characteristics of the electrode materials such as work functions, standard reduction potentials and sputter yields.