Visualization Experiment Under Isothermal Conditions: Fig. 1 shows a diagram of the apparatus for the visualization experiment under isothermal conditions. The apparatus consists of the following components: a circulating pump, a flow rate measuring section, a flow-straightened section, a test section, a bag filter, and a mixing tank.
All piping materials and components have been made of polyvinyl chloride or acrylic materials etc. which co-exist in a stable state with the NaI solution. The magnetic pump circulates the working fluid inside the loop, and its maximum flow rate under obstacles packed conditions is approximately 200l/min.
The flow rate of the working fluid is adjusted by valves: two valves located between the magnetic pump and the flow rate measuring section and a valve of a bypass line which directly returns to the mixing tank from the magnetic pump.
A turbine flowmeter or an ultrasonic Doppler velocimeter is utilized to measure the flow rate. The mixing tank has the following functions: injection of tracer particles, de-aeration of bubbles existing in the fluid, and heat exchange to control the fluid temperature.
The section upstream of the test section has a flow-straightener with a honeycomb structure consisting of stainless steel pipes, which straightens and counteracts a swirling flow formed in the bend upstream. The bug filter is a polypropylene-made cartridge with strong corrosion resistance which separates the tracer particles from the NaI solution.