Investigation of free and forced flows of relevance to fast reactor thermohydraulics using the ultrasonic Doppler method.

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Submitted to:

Fjrst International Symposium on Ultrasonic Doppler Methods for Fluff Mechanics and Fhiid Engineering, 9.-11.

5eptember 1996, Paul Scherrer Institute, Villigen, Switzerland.

Investigation of free and forced flows of relevance to fast reactor thermohydraulics using the ultrasonic Doppler method.

A. Tokuhiro

*PNC International Fell ow, Reactor Engineering Sectio n, Safety Engineering

Div isi o n, Oarai Engineering Center, Power Reactor and Nuclear Fuel Develop ment

Corporation (PNC), 4002 Narita, Oarai-machi, Ibaraki, Japan, 311-13.

KEY  WO RD_S: II IP, water, mix ed cocv e ctive flo›r, peetrating flo w, vertical mix in g la y er, bno yant jet, stirred vortex flo w, flow mapp in g, two-dimensiona I v elo c it y field, stead y- and transie at measurement, spectral anal ysis.

Extended Abstract 

y March 1996, a.ioLuhiro

This extended abstract describes two experimental investigation of general interest to the convective heat transfer community, but of particular interest to those engaged in the design of liquid metal-cooled, energy intensive facilities such as the liquid metal fast breeder reactor.

1. Thermal Striping

Tliemial striping refers to the phenomenom of fluid-structure interactions in nuclear reactors (specifically liquid-metal cooled reactors), the result of which reactor structures and components incur undesireable thermal stresses. The thermal-hydraulics aspects of this problem concern the random streams of poorly mixed hot and cold coolant. One critical area is the above-core structure of a LMFBR, which due to flow of hot/cold jets out of the core, may experience thermal striping. Since the themal fatigue behavior of above-core components and their locaaons are generally known, understanding the convective mixing (or non-mixing) of buoyant and forced-flow is important to the safe design of the reactor. In the present case a basic experiment using a water test facility and consisting of LDA, UVP and recently PIV velocity measurement techniques, as well as temperature measurement has been initiated. The flow geometry is a central cold jet surrounded by two hotter jets, each exiting out of of a rectangular nozzle.

R Figure 1 we a show a schemaic of the test section and a magnified view of the probe orientation with respect to the jet nozzles. The UVP transducer was set at a 10‘ incline with respect to the horizontal and measurements were taken kom both 4e left and right sides. Unless noted the vertical transverse increments were 5 mm. In the uses shown here, the central jet was set a 30‘C while the two a acent jets were at 35"C. All three jets had equal fiowrates out of the nozzle and an exit average velocity of

0.5 mls.

Figure 2, 3, 4 and 5 show some typical results and these are summarized as

follows. They are:

Figure 2. A sequence of four consecutive images as digitized fxom video pictures during an experimental run. A laser sheet was introduced from the right of ie image in order to enhance visualizaCon of the flow.

Figure 3. A grayscale image of the temperature fluctuation distribution as taken with a spanwise array of 35 thermocouples positioned on a traversing mechanism. Two spanwise profiles at z

45 and 200

from the exit

inset. The vertical and horizontal axes are respectively, the spanwise width covering the exit of ie three jets and the axial distance along which temperature measurements were made.

Figure 4. A grayscale image of the velocity fluctuation distribution that nearly corresponds to w . The vertical aad horizontal axes are respectively, the spanwise width covering the exit of the three jets aad the axial distance along which UVP measurements were made.

Figure 5. The constructed turbulent heat flux distribution, w’t = f (x, z), where and I’ are respectively, the fluctuating component of velocity, as measured using the UVP, and that of the temperature, as measured using a thermocouple array. The distribution shows that under these condtions, most of the thermal mixing takes place

within the lust z


from the exit of the jets aid that spanwise, the regions with the highest calculated fluxes are approximately those in between the cold and hot jets.