Experimental Facility

Figure 1.1 shows the schematic of the experimental test rig. Driven compressed air goes through a filter, an orifice meter, and passes through a rotary seal and a hollow-rotating shaft to feed the test section. The test section is mounted in a horizontal plane. Air travels outward first pass and inward second pass to exhaust into the atmosphere. Slip rings transfer thermocouple outputs to data logger and power input from variac transformer to strip heaters, which is uniformly fixed under the copper plates. An electric motor with an adjustable frequency controller rotates the test section. A digital photo tachometer measures the rotational speed of the rotating shaft.

Teflon Plates

Teflon Plates

Figure 1.2 Cross sectional view of the two-pass rectangular test section.

Fig. 1.2 shows cross sectional view of the test section. The test section has two passes. Each pass is 12.7 mm by 25.4 mm in cross section. The first pass starts with an unheated teflon entrance channel to establish a hydro-dynamically fully developed flow at the entrance to the heated channel. It has twelve (12) hydraulic diameters length to achieve the task. The heated channel length-to-hydraulic diameter (L/D) ratio is 18, while each pass length-to-hydraulic diameter (L/D) ratio is 9, connected by a sharp 180° turn. The flow in the first pass is radially outward and the flow in the second pass in radially inward. The heated section is divided into twelve longitudinal sections, six sections in first pass and six in second pass, to obtain local heat transfer coefficients. Each section has four copper plates on four walls of the channel. Each copper plate is surrounded circumferencially by a thin teflon strip that has (1.59 mm) thickness to insulated from their neighbors. This teflon strip works as an insulation to reduce heat conduction from one plate to another. Each copper plate has a single thermocouple that gives the regional surface temperature. The inlet and exit bulk temperatures are measured by Thermocouples. Each surface receives constant heat flux from an individual transformer to maintain the surface temperature around 65° C.

0 0

Post a comment