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Design Version 3

The final design solution was a vertical oriented wind tunnel equipped with a fan, heated plate, temperature sensors, and temperature and fan speed controller. The wind tunnel is an acrylic tube with an inner diameter of 8.255 cm. Air is pushed through the wind tunnel using a Sunan Fan PF80381BX which is PWM controlled using LabView. Within the wind tunnel is a layer of honeycomb and mesh screens with varying fineness to create uniform flow. At the base of the wind tunnel is a copper plate, which is heated using an Omega heating pad. The heating pad is attached to a LabView temperature controller to produce accurate temperature set points. Surrounding the copper plate is promalight insulation and teflon PTFE which ensures the heat from the Omega heating pad is transferred to the surface of the copper plate and there is no other significant heat loss. Finally, the temperature of both the airflow within the wind tunnel and at the copper plate will be measured using RTDs. RTDs are located within the copper plate and on the inner side of the wind tunnel duct, and are wired to LabView which displays the temperature enabling students to easily record temperature measurements at free stream and at the copper plate.

Copper Plate and Insulation 

The heated plate was made from a tellurium copper alloy due to its high thermal conductivity and machinability. An Omega heating pad was used to heat the copper plate. The heating pad has a watt density of 15500 W/m2, which provides more than sufficient power to heat a 0.635 cm-thick copper plate fast enough that students would be able to reach multiple temperature set points within the time frame designated for the experiment. The two insulation materials utilized were Promalight microporous material— wherever structural integrity was unnecessary— and Teflon PTFE— where material strength was necessary. In order for the copper plate to be held concentric to the wind tunnel to simulate stagnation point-flow, the copper plate-insulation setup was attached to a plate mount. Flathead screws clamped the Teflon PTFE and the aluminum base together such that the heating pad and copper plate were spring-loaded. An aluminum stand of 10.16cm was attached to hold the entire setup upright; its length was ample to ensure that the axisymmetric flow around the plate was undisturbed. Two pockets were machined into the sides of the copper plate for placement of the RTDs. Though the temperature distribution of the copper would essentially be uniform, having two RTDs for an average value allowed for identification of any error.

Design Version 2

Wind Tunnel Duct

 

The wind tunnel, was determined to be an acrylic cylinder with an inner diameter of 8.255 cm, slightly greater than the copper plate diameter of 7.62 cm to ensure that the entire copper plate experienced perpendicular uniform flow. The wind tunnel was a mere 15 cm in length to minimize the boundary layer development. A section of honeycomb was placed immediately after the fan to reduce the non-uniform characteristics of the rotating blades’ airflow. Meshes were then placed in order of decreasing opening size at the exit of the wind tunnel to ensure uniform flow. An RTD was also positioned within the wind tunnel to measure the free stream temperature.

The following are some specifications of the Sunan PF80381BX:

Mesh Screen Specifications

Design Version 1

Honeycomb and Wire Meshes

The purpose of the honeycomb and wire meshes is to straighten out the air flow in the wind tunnel, to ensure that the flow hitting the copper plate is uniform. However, the layers of meshes causes an unforeseen pressure drop due to decreased cross-sectional area, so the selected fan may not have enough power to pull the air through the wind tunnel at speeds of 3 meters per second. One possible solution is taking out the finest wire mesh to reduce the pressure drop created. Another solution is purchasing a centrifugal fan; these types of fans are unaffected by mass flow rate, so a change in cross-sectional area due to the wire meshes would no longer be an issue.

Insulation Material for Copper Plate - Promalight 1000R

Relevant Specifications

The insulation is marketed as easily machinable, but the compressed powder composition is leaving us with few options for attaching it to the copper plate and the mount to hold it in the center of the wind tunnel. Furthermore, it requires sealing with resin and/or glass cloth tape.

High Risk Component Analysis: Wind Tunnel Flow

Goal: Ensure flow through wind tunnel is uniform with the honeycomb, meshes, a pulling fan, and whether or not mounts will disrupt the uniform flow.

Method 1: Flow Visualization with Fog Machine

Assumptions:

Results:

Method 2: CFD Analysis

Assumptions:

Results:

Analysis shows that we have uniform flow at the entrance of the wind tunnel. The copper plate mounts do not affect the flow onto the copper plate.

The video below first shows the top view of the wind tunnel, and then the side view.

High Risk Component Analysis: Copper Plate (3" diameter, 1/4" thickness)

Goal: Ensure that the copper plate can reach a uniform temperature distribution across its flat face at steady state.

Method: Solidworks Thermal Simulation

Assumptions:

Results:

The silicone heating pad has sufficient power at 10W/in2 to heat the copper plate to the temperature set points required for the experiment relatively quickly. In addition, the plate has fairly uniform temperature distribution, with a difference of about 0.5oC across the surface of the plate.