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Experimental Study of Thermal Loading on a Plate from a Triple Round Jet Array

Kristo, Paul (2016) Experimental Study of Thermal Loading on a Plate from a Triple Round Jet Array. Master's Thesis, University of Pittsburgh. (Unpublished)

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Temperature fluctuations are known to occur in the mixing region of non-isothermal flows, and can cause undesired thermal stresses. One relevant application where this is a major concern is the very high temperature gas reactor (VHTR), a next generation nuclear reactor, which uses helium as the primary coolant. In the lower plenum of the VHTR, coolant enters from multiple channels at different temperatures and mixes together before being routed to a gas turbine or hydrogen production facility. Incomplete mixing of the coolant can be the root of thermal stresses both within the lower plenum as well as downstream components (e.g., gas turbine blades). For acceptable predictions of this phenomenon, fundamentally based experiments along with properly verified and validated models are needed. The objectives of this study are to gain insight into the thermal loading conditions expected in the VHTR lower plenum and provide valuable experimental validation data for current and future modeling efforts. To this end, an experimental study is conducted for three non-isothermal parallel round jets whose axis to axis separation distance is 1.41 jet diameters. A central cold jet is surrounded on either side by an adjacent hot jet in a planar configuration with air as the working fluid. All of the jets are turbulent with a jet Reynolds number between 5.5 × 103 and 1.8 × 104, and the mixing is quantified via temperature measurements on a flat polycarbonate plate mounted parallel to the axial direction of the jets. The full field temperatures of the plate surface are captured via infrared thermography. Two different plate to jet spacings are considered: 0.5 and 1.0 jet diameters. Other variables include the cold to hot jet velocity ratio, set at three levels of 0.50, 1.00, and 1.51, and the temperature difference between the cold and hot jets, set at two different values of 33.3˚C and 44.4˚C. Horizontal line traces of the plate surface temperature are analyzed in the range of 2-20 jet diameters downstream. The line traces suggest that with decreasing velocity ratios, the induced turbulence provided by higher jet velocities promotes mixing further upstream. Results also suggest the most severe temperature gradients on the plate surface occur in the area that is characteristic of the convective mixing region (8 to 16 jet diameters downstream). Observations of the maximum surface temperature on the plate describe the influence of the plate to jet spacings in the entrance region (2 to 8 jet diameters downstream) in that with increased spacing, the maximum temperatures are closer to the axial center of the cold jet. Past the entrance region and with increasing values of jet velocity ratio, the maximum temperature location spreads much more rapidly. The thermal mixing initiated further upstream by increasing values of jet velocity ratios and the rapid spreading of maximum plate surface temperatures for decreasing jet velocity ratios are both notable concerns in the analysis of reactor coolant channel outlet conditions and their thermal hydraulic interactions with solid boundaries. This research represents preliminary predictions of the thermal loading in the VHTR lower plenum and provides validation data for fundamental and applied thermal mixing simulations.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Kristo, Paulpjk26@pitt.eduPJK260000-0001-6881-7816
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Thesis AdvisorKimber, Markmlk53@pitt.eduMLK53
Committee ChairSchmidt, Daviddes53@pitt.eduDES53
Committee ChairBrigham, Johnbrigham@pitt.eduBRIGHAM
Date: 25 January 2016
Date Type: Publication
Defense Date: 19 November 2015
Approval Date: 25 January 2016
Submission Date: 27 November 2015
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 60
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Mechanical Engineering
Degree: MS - Master of Science
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: lower plenum; parallel triple jet; round jet; thermal loading; very high temperature reactor
Date Deposited: 25 Jan 2016 16:13
Last Modified: 15 Nov 2016 14:31


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