Drawing from the lessons of plant transpiration, this dissertation explores a biomimiced system for fluid transport and thermal regulation. This system utilizes evaporation and benefits from the associated passive pumping with an application of a rooftop solar radiation barrier in mind. By directing the incoming energy towards the phase change of water, lower surface temperatures can be maintained thus reducing heat transfer into the structure by conduction. In order to design and construct such a bio-inspired system, several parameters, i.e., the evaporation surface, the delivery path and the working fluid, must be understood as to how they affect and limit operations. Performance factors such as evaporation rate and suction pressure were monitored for the various design constraints of feeding tube length and diameter, membrane area, and working fluid. Additionally, as a heat flux was imposed on the membrane from above and below, the substrate temperature became important. Over the range of parameters tested, hydrodynamic resistances of the delivery path were shown to affect pumping height but not the evaporation rate. Instead, the evaporation rate was controlled by the substrate temperature. Furthermore, the normalized evaporation rate was found to be inversely related to the evaporation surface area. Under contaminated working fluid conditions, particles deposited in the membrane caused decreases in evaporation rates. When applied to a simulated roof situation, the evaporation system was successful at maintaining considerably lower surface temperatures than other conventional and unconventional roof albedos, which, in turn, would reduce heat flux into the interior by conduction. Lastly, in estimating the water consumption, on a typical August day in Austin, TX, the system could use up to 2 gallons/m² while providing enhanced cooling. When the system's resources were compared to being purposed in other ways, they were arguably better utilized in providing evaporative cooling. / text

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The purpose of this report is to present the results of the study and analysis of loss-of-coolant and loss-of-flow simulations performed on the Modular Helium Reactor developed by General Atomics using the thermal-hydraulics code RELAP5-3D/ATHENA. The MHR is a high temperature gas cooled reactor. It is a prismatic core concept for New Generation Nuclear Plant (NGNP). Very few reactors of that kind have been designed in the past. Furthermore, the MHR is supposed to be a highly passively safe concept. So there are high needs for numerical simulations in order to confirm the design. The project is dedicated to the assessment of the passive decay heat capabilities of the reactor under abnormal transient conditions. To comply with the requirements of the NGNP, fuel and structural temperatures must be kept under design safety limits under any circumstances. During the project, the MHR has been investigated: first under steady-state conditions and then under transient settings. The project confirms that satisfying passive decay heat removal by means of natural heat transfer mechanisms (convection, conduction and radiation) occurs.

The purpose of this report is to present the results of the study and analysis of loss-of-coolant and loss-of-flow simulations performed on the Modular Helium Reactor developed by General Atomics using the thermal-hydraulics code RELAP5-3D/ATHENA. The MHR is a high temperature gas cooled reactor. It is a prismatic core concept for New Generation Nuclear Plant (NGNP). Very few reactors of that kind have been designed in the past. Furthermore, the MHR is supposed to be a highly passively safe concept. So there are high needs for numerical simulations in order to confirm the design. The project is dedicated to the assessment of the passive decay heat capabilities of the reactor under abnormal transient conditions. To comply with the requirements of the NGNP, fuel and structural temperatures must be kept under design safety limits under any circumstances. During the project, the MHR has been investigated: first under steady-state conditions and then under transient settings. The project confirms that satisfying passive decay heat removal by means of natural heat transfer mechanisms (convection, conduction and radiation) occurs.

ABSTRACT HEAT REMOVAL FROM A LARGE SCALE WARM WATER STORAGE Kayserilioglu, Yavuz Selim M.S., Department of Mechanical Engineering Supervisor: Prof. Dr. R&uuml / knettin Oskay August 2004, 88 Pages A preliminary experimental study was performed in order to investigate the charging and heat removal characteristics of a sensible heat storage. Two sets of experiments were performed at two aspect ratios. Heat removal processes of these two sets were different while the charging processes were similar. In the first set of experiments, after the charging of the storage unit with relatively warm water was complete, heat removal process was started with simple heat exchangers from different elevations within the storage while the charging of the storage unit was continued. In the second set of experiments, after the charging of the storage unit was complete, heat removal from the storage unit was started without further charging of the storage unit. Charging water was fed into the storage from the top of one side and relatively colder water was drained from the bottom of the opposite side. Internal heat exchangers were used for the heat removal. Vertical temperature profile developments during the charging and heat removal periods were investigated. Thermal stratification was observed in all experiments. Heat exchangers extracted heat from different elevations in different experiments and the trend was that more heat can be extracted in upper elevations. Comparable heat can be extracted from the same elevation of lower and higher aspect ratio. Keywords: Sensible Heat Storage, Heat Removal, Thermal Stratification, Warm Water Storage

An experimental study of a low-frequency transcritical thermoacoustic device has been conducted at Purdue University's Maurice J. Zucrow Laboratories. The purpose of this study was to characterize the thermoacoustic response of transcritical R-218 and asses it's feasibility for energy extraction and waste heat removal. This rig operated as a standing-wave configuration and achieved pressure amplitudes as high as 690 KPa (100 psi) at a temperature difference of 150 K and a bulk pressure of 1.3 P/P_cr(3.43 MPa). To the author's knowledge, this is the highest ever thermoacoustic pressure amplitude achieved in a non-reacting flow. The thermoacoustic response was characterized by varying temperature difference and bulk pressure parametrically. The effect of resonator length was characterized in a set of tests where resonator length and bulk pressure was varied parametrically at a single temperature difference. Finally, the feasibility for energy extraction was assessed in a set of tests which characterized the ability of the working fluid to pump itself through a recirculation line with check valves. This set of tests showed that the working fluid was able to create self-sustained circulation by inducing a pressure differential across the check valves with the thermoacoustic response. This circulation was induced while still maintaining a significant pressure amplitude, demonstrating promising results as a feasible method for energy extraction and waste heat removal.

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This thesis is devoted to the investigation of passivesafety and inherent features of subcritical nucleartransmutation systems - accelerator-driven systems. The generalobjective of this research has been to improve the safetyperformance and avoid elevated coolant temperatures inworst-case scenarios like unprotected loss-of-ow accidents,loss-of-heat-sink accidents, and a combination of both theseaccident initiators. The specific topics covered are emergencydecay heat removal by reactor vessel auxiliary cooling systems,beam shut-off by a melt-rupture disc, safety aspects fromlocating heat-exchangers in the riser of a pool-type reactorsystem, and reduction of pressure resistance in the primarycircuit by employing bypass routes. The initial part of the research was focused on reactorvessel auxiliary cooling systems. It was shown that an 80 MWthPb/Bi-cooled accelerator-driven system of 8 m height and 6 mdiameter vessel can be well cooled in the case of loss-of-owaccidents in which the accelerator proton beam is not switchedoff. After a loss-of-heat-sink accident the proton beam has tobe interrupted within 40 minutes in order to avoid fast creepof the vessel. If a melt-rupture disc is included in the wallof the beam pipe, which breaks at 150 K above the normal coreoutlet temperature, the grace period until the beam has to beshut off is increased to 6 hours. For the same vessel geometry,but an operating power of 250 MWth the structural materials canstill avoid fast creep in case the proton beam is shut offimmediately. If beam shut-off is delayed, additional coolingmethods are needed to increase the heat removal. Investigationswere made on the filling of the gap between the guard and thereactor vessel with liquid metal coolant and using water spraycooling on the guard vessel surface. The second part of the thesis presents examinationsregarding an accelerator-driven system also cooled with Pb/Bibut with heat-exchangers located in the risers of the reactorvessel. For a pool type design, this approach has advantages inthe case of heat-exchanger tube failures, particularly if wateris used as the secondary uid. This is because a leakage ofwater from the secondary circuit into the Pb/Bi-cooled primarycircuit leads to upward sweeping of steam bubbles, which wouldcollect in the gas plenum. In the case of heatexchangers in thedowncomer steam bubbles may be dragged into the ADS core andadd reactivity. Bypass routes are employed to increase the owspeed in loss-of-ow events for this design. It is shown thatthe 200 MWth accelerator-driven system with heat-exchangers inthe riser copes reasonably well with both a loss-of-ow accidentwith the beam on and an unprotected loss-of-heat-sink accident.For a total-loss-of-power (station blackout) and an immediatebeam-stop the core outlet temperature peaks at 680 K. After acombined loss-of-ow and loss-of-heat-sink accident the beamshould be shut off within 4 minutes to avoid exceeding the ASMElevel D of 977 K, and within 8 minutes to avoid fast creep.Assuming the same core inlet temperature, both the reactordesign with heat-exchanger in the risers and the downcomershave similar temperature evolutions after a total-loss-ofpoweraccident. A large accelerator-driven system of 800 MWth with a 17 mtall vessel may eventually become a standard size. For thishigher power ADS, the location of the heat-exchangers hasgreater impact on the natural convection capability. This isdue to that larger heatexchangers have more inuence on thedistance between the thermal centers during a lossof- owaccident. The design with heat-exchangers in the downcomers,the long-term vessel temperature peaks at 996 K during aloss-of-ow accident with the beam on. This does not pose athreat of creep rupture for the vessel. However, the locationof the heat-exchangers in the downcomers will probably requiresecondary coolant other than water, like for example oil (fortemperatures not higher than 673 K) or Pb/Bi coolant.

<p>This thesis is devoted to the investigation of passivesafety and inherent features of subcritical nucleartransmutation systems - accelerator-driven systems. The generalobjective of this research has been to improve the safetyperformance and avoid elevated coolant temperatures inworst-case scenarios like unprotected loss-of-ow accidents,loss-of-heat-sink accidents, and a combination of both theseaccident initiators. The specific topics covered are emergencydecay heat removal by reactor vessel auxiliary cooling systems,beam shut-off by a melt-rupture disc, safety aspects fromlocating heat-exchangers in the riser of a pool-type reactorsystem, and reduction of pressure resistance in the primarycircuit by employing bypass routes.</p><p>The initial part of the research was focused on reactorvessel auxiliary cooling systems. It was shown that an 80 MWthPb/Bi-cooled accelerator-driven system of 8 m height and 6 mdiameter vessel can be well cooled in the case of loss-of-owaccidents in which the accelerator proton beam is not switchedoff. After a loss-of-heat-sink accident the proton beam has tobe interrupted within 40 minutes in order to avoid fast creepof the vessel. If a melt-rupture disc is included in the wallof the beam pipe, which breaks at 150 K above the normal coreoutlet temperature, the grace period until the beam has to beshut off is increased to 6 hours. For the same vessel geometry,but an operating power of 250 MWth the structural materials canstill avoid fast creep in case the proton beam is shut offimmediately. If beam shut-off is delayed, additional coolingmethods are needed to increase the heat removal. Investigationswere made on the filling of the gap between the guard and thereactor vessel with liquid metal coolant and using water spraycooling on the guard vessel surface.</p><p>The second part of the thesis presents examinationsregarding an accelerator-driven system also cooled with Pb/Bibut with heat-exchangers located in the risers of the reactorvessel. For a pool type design, this approach has advantages inthe case of heat-exchanger tube failures, particularly if wateris used as the secondary uid. This is because a leakage ofwater from the secondary circuit into the Pb/Bi-cooled primarycircuit leads to upward sweeping of steam bubbles, which wouldcollect in the gas plenum. In the case of heatexchangers in thedowncomer steam bubbles may be dragged into the ADS core andadd reactivity. Bypass routes are employed to increase the owspeed in loss-of-ow events for this design. It is shown thatthe 200 MWth accelerator-driven system with heat-exchangers inthe riser copes reasonably well with both a loss-of-ow accidentwith the beam on and an unprotected loss-of-heat-sink accident.For a total-loss-of-power (station blackout) and an immediatebeam-stop the core outlet temperature peaks at 680 K. After acombined loss-of-ow and loss-of-heat-sink accident the beamshould be shut off within 4 minutes to avoid exceeding the ASMElevel D of 977 K, and within 8 minutes to avoid fast creep.Assuming the same core inlet temperature, both the reactordesign with heat-exchanger in the risers and the downcomershave similar temperature evolutions after a total-loss-ofpoweraccident.</p><p>A large accelerator-driven system of 800 MWth with a 17 mtall vessel may eventually become a standard size. For thishigher power ADS, the location of the heat-exchangers hasgreater impact on the natural convection capability. This isdue to that larger heatexchangers have more inuence on thedistance between the thermal centers during a lossof- owaccident. The design with heat-exchangers in the downcomers,the long-term vessel temperature peaks at 996 K during aloss-of-ow accident with the beam on. This does not pose athreat of creep rupture for the vessel. However, the locationof the heat-exchangers in the downcomers will probably requiresecondary coolant other than water, like for example oil (fortemperatures not higher than 673 K) or Pb/Bi coolant.</p>

No description available.