Krishnamurti 



T. are the temperatures of the four aluminum blocks. The sub- 

 scripts are ordered from bottom to top. The conductivities kp and 

 k' are measured in terms of that of the liquid when it is known that 

 the liquid layer is in a state of steady conduction. Then the following 

 relations hold: 



V Tp - T, T, 



^ d P 



-I2 = k' -^^ 

 P d. 



where k- is the molecular conductivity of the fluid. Thus, once the 

 conductivity and depth of the poor conductors is determined, a 

 measurement of the temperatures in the four metal blocks allows 

 the determination of the Rayleigh number and the heat flux. 



Fine aluminum flakes suspended in the liquid were used to 

 visualize the flow. The aluminum flakes become aligned in a shear 

 flow, and because they are flakes, reflect light more strongly in 

 certain directions, depending upon the direction of the shear and of 

 the illumination. In a uniform shear, the brightness is uniform; 

 where there is a differential shear, there will be corresponding 

 bright and dark regions. In the case of water, aluminim flakes 

 would not stay in suspension sufficiently long, so another tracer 

 called 'rheoscopic fluid AQW 010' was added to the water. This 

 tracer displays differential shears, just as do the aluminum flakes, 

 but remains in suspension about 10 times as long. 



Since the fluid layer is bounded above and below by opaque 

 boundaries, the plan form of convection is obtained by viewing the 

 flow from the side as shown in Fig. 2. The tracers were illuminated 

 at mid-depth by narrow overlapping beams of collimated light from 

 two 2 W zirconium arc lamps. The two beams directed at each other 

 allow visualization of shear regions at both positive and negative 

 angles to the line of sight. This line of sight is perpendicular to the 

 beam. As the light beam is moved horizontally, illuminating differ- 

 ent regions of the fluid, a camera is moved horizontally on a threaded 



Camera 

 position A 



Camera 

 position B 



Illumination 

 at xg 



Fig. 2. Geometry for photographing plan form of convection 



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