Browsing by Subject "Evaporative cooling"
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Item Mist cooling technology for thermoelectric power plants(2014-12) Gokkus, Enes; Bahadur, Vaibhav; Matthews, Ronald D.A novel mist-based cooling concept is analyzed with the objective of reducing water consumption in thermoelectric power plants. Additionally, this concept offers the potential to increase electricity generation capacity by lowering the steam condensation temperature. The mist-based cooling concept consists of two independent technologies. The first technology consists of replacing the cooling tower with a two stage heat exchanger consisting of air-cooled and water mist-cooled heat exchangers. The mist-cooled heat exchanger chills the cooling water to near wet bulb temperature ambients which enables lowering of condenser pressures and temperatures. The mist is a saturated air stream at wet bulb temperatures obtained by adding water droplets to ambient air. The air-water ratios and droplet sizes can be optimized to reach wet bulb temperatures with minimum water consumption. The enhanced control of evaporation through mist cooling will allow the mist to reach closer to wet bulb temperatures than cooling towers. The second technology consists of replacing the shell-and-tube condenser with a direct contact condenser, wherein the steam from the Rankine cycle condenses on water mist streams. The large area offered by mist droplets increases heat transfer rates significantly, resulting in compact and low maintenance condensers. Technical and techno-economic analyses are carried out to map the potential of mist cooling technology. The technical analyses show that mist cooling technology can reduce water consumption by up to 65 %, compared to present-day cooling towers of the same power output. Furthermore, by reducing the condenser pressure, the electricity generation capacity can be increased by 4 % while still consuming less water than existing cooling towers. First-order techno-economic analyses have also been conducted to quantify the economic benefits of mist cooling for thermoelectric power plants in Texas. These analyses reveal that mist cooling technology can greatly help 17 out of 18 coal-fired power plants in Texas. It is expected that this technology will significantly benefit other U.S. power plants located in water-stressed areas.Item The design and evaluation of a water delivery system for evaporative cooling of a proton exchange membrane fuel cell(2009-06-02) Al-Asad, Dawood Khaled AbdullahAn 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.