Typescript (photocopy). / Digitized by Kansas Correctional Industries

For a district heating company it is of importance to have an efficient and well performing system. A central part in the work to lower temperature levels in district heating networks is to acknowledge and improve cooling capability in substations. The aim of this thesis is to analyse substations in Polish district heating systems in order to identify reasons of poor cooling and to present suggestions of implementable measures. Furthermore, the economical saving potential from an improved cooling is evaluated. The analysis was carried out for two of the five Polish companies included in this report; Sydkraft EC Slupsk and MEC Koszalin. It was followed by two scenarios created for evaluation of improvement possibilities based on calculated financial savings from reduction of distribution heat losses and distribution pumping. The results show that there are significant improvement possibilities. From the carried out scenarios a saving potential between 15 000 to 20 000 PLN/substation is possible to achieve for selected worst substations, if their individual annual average cooling is set to 30°C. The analysis further shows that causes of poor cooling in substations are highly individual but points out that customer owned substations are represented in the majority of worst substations.

A comparative study was conducted to determine whether it would be advantageous to grow carbon nanotubes on the bottom surface of anisotropically-etched silicon microchannels to facilitate greater heat removal in electronic cooling applications. The effect of the samples was evaluated based on the fluid temperature rise through the channels, the silicon surface temperature increase above ambient, and the pressure drop. The height and deposition pattern of the nanotubes were the parameters investigated in this study. The working fluid, water, was passed through the microchannels at two different volumetric flow rates (16 mL/min and 28 mL/min). Additionally, two different heat fluxes were applied to the backside of the microchannel (10 W/cm2 and 30 W/cm2). Extensive validation of the baseline channels was carried out using a numerical model, a resistor network model, and repeatability tests. Finally, the maximum enhancement when using carbon nanotubes under single-phase, laminar, internal, forced convection was investigated using basic principles in regard to the additional surface area created by the carbon nanotubes, as well as their high thermal conductivity. For the devices tested, the samples with carbon nanotubes not only had a higher pressure drop, but also had a higher surface temperature. Therefore, the baseline samples had the best performance. Furthermore, based on a basic principles investigation, the increase to thermal performance gained by increasing the surface area with CNTs is overshadowed by the decrease in mass flow rate for a fixed pressure drop. The analysis suggests that the limiting factor for heat transfer in single-phase, laminar pressure driven flows is not convection heat transfer resistance, but the bulk resistance of the fluid.

An investigation was performed to demonstrate system design for the delivery of water required for evaporative cooling of a proton exchange membrane fuel cell (PEMFC). The water delivery system uses spray nozzles capable of injecting water directly and uniformly to the nickel metal foam flow-field (element for distributing the reactant gases over the surface of the electrodes) on the anode side from which water can migrate to the cathode side of the cell via electroosmotic drag. For an effective overall cooling, water distribution over the surface of the nickel foam has to be uniform to avoid creation of hotspots within the cell. A prototype PEMFC structure was constructed modeled after a 35 kW electrical output PEMFC stack. Water was sprayed on the nickel metal foam flow-field using two types of nozzle spray, giving conical fog type flow and flat fan type flow. A detailed investigation of the distribution pattern of water over the surface of the nickel metal flow field was conducted. The motive behind the investigation was to determine if design parameters such as type of water flow from nozzles, vertical location of the water nozzles above the flowfield, area of the nozzles, or operating variables such as reactant gas flow had any effect on water distribution over the surface of the Ni-metal foam flow field. It was found that the design parameters (types of flow, area and location of the nozzle) had a direct impact on the distribution of water in the nickel metal foam. However, the operating variable, reactant gas flow, showed no effect on the water distribution pattern in the Ni-foam.

Thesis (Ph. D.)--University of Oregon, 2003. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 235-246). Also available for download via the World Wide Web; free to University of Oregon users.

Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2003. / Thesis advisor(s): Ashok Gopinath. Includes bibliographical references (p. 31-32). Also available online.

Thesis (Ph. D. in Mechanical Engineering)--Naval Postgraduate School, June 2003. / Dissertation supervisor: Ashok Gopinath. Includes bibliographical references (p. 162-164). Also available online.

Most people would like to be less stressed. With our increasingly fast paced and busy lives it appears that stress related issues are increasing, with the addition of issues such as terrorist attacks, stress at times can be hard to avoid. Many studies have found that cooling the brain is beneficial for those who have sustained traumatic brain injuries and the process of cooling can often stop or prevent further damage (Qui et al, 2006). The body may also use a natural cooling mechanism, yawning, as a way of keeping the brain at optimum temperature, so it can perform at its best (Gallup & Gallup, 2008).There seems to be very little research on the effects of head cooling on psychological variables. It was hypothesised that cooling would reduce stress levels and when put in conjunction with a self-affirmation manipulation would decrease stress levels even further. Participants had their ear temperature measured, filled out a stress questionnaire and then were asked to sit in between two fans for 12 minutes. Their ear temperature was measured again, they then went on to complete another questionnaire, some containing a self-affirmation manipulation and then went on to a stressor task. Lastly, they received a final stress questionnaire. Results were nonsignificant, yet general trends headed in the hypothesised direction. The implications of the findings are discussed as are limitations and suggestions for future research.

No description available.

Current water-cooling technology used in the metallurgical industry poses a major safety concern. In addition, these systems are expensive to operate and result in significant energy losses. / The purpose of the research presented in this thesis was to develop a viable cooling system based on novel heat pipe technology which addresses these problems. This technology employs boiling as the means to store and transfer heat energy. The large heat extraction capacity of the device is owed to two design features: firstly, a separate return line that generates a column of liquid working fluid which drains into the evaporator by gravity, and secondly, a helical flow modifier in the evaporator that stabilizes annular two-phase flow. / A full-scale copper tapblock and launder were designed with water-based heat pipe cooling systems. These systems were successfully tested under industrial heat loading conditions, using a gas burner to simulate the heat loads. / The tapblock cooling system was able to dissipate 142 kW per heat pipe, at heat fluxes as high as 2.4 MW/m2. These values are the largest to date using the novel water-based heat pipe technology. The launder system was the first to incorporate horizontal heat pipes, as well as have multiple evaporators feeding a single condenser. / The cooling systems used in both experiments were fundamentally safer than watercooling systems, being operated at low pressures and with only several kilograms of water exposed to the heat source. The cooling water requirements of these systems represent a reduction of 80-95% compared to conventional water-cooling, with increased potential for energy recovery. / During the testing, dry-out and film boiling were identified as the main limitations. It was found that film boiling occurs when the flow in the evaporator is not great enough to generate a helical motion. The dry-out limitation was achieved when the velocity of the flow within the evaporator was too great, causing a large pressure gradient that opposes the gravity head of the return line. / Both of these limitations are related to the configuration of the evaporator, i.e. the return line and the flow modifier. A methodology was developed to model the evaporator numerically using computational fluid dynamics. This methodology can be used to understand how the design parameters of the evaporator affect the flow patterns during operation.