TTA – Thermal Transient Anemometer. Anemos : Greek for wind Anemometer : to measure the wind Thermal Transient : A heated sensor will lose energy to the passing wind. The higher the speed, the faster the loss and the shorter the “time constant ( )” of the temperature decrease.
Anemos: Greek for wind
Anemometer: to measure the wind
Thermal Transient: A heated sensor will lose energy to the passing wind. The higher the speed, the faster the loss and the shorter the “time constant ()” of the temperature decrease.
Ergo: utilize as the anemometer’s output.
Developed for underhood cooling circuit diagnostic evaluations:
Developed under the sponsorship of
DiamlerChrysler Challenge Fund (originally with Mr. Clem Mesa, continued with Mr. Michael Zabat)
Patent Pending – MSU
Commercialized by DFTI – Digital Flow Technologies, Inc.
Underhood cooling circuit
HVAC ducts – flow rate distributions and thermal energy loss upstream of the register
Obvious objectives: transfer the thermal energy from the liquid media to the passing wind.
Obvious statement of success:
Obvious Problem: it is not feasible to construct a measurement scheme to obtain the infinite number of data points to evaluate the exit integral – assuming Tinlet=Tamb such that
TTA Strategy: obtain approximations to the spatial integral for area segments whose sum is the complete area of interest.
Diagnostic strategy: make the segments small enough that problem areas (e.g., downwind from crash members) are apparent.
(The control electronics schematic is provided in the TTA portion of www.dift-us.com.
See the MST article.)
A representative frame, mounted for calibration in the TSFL 22 (6161cm2) wind tunnel.
A 20-cell frame:
Typical Tungsten wire diameter = 5-8mil (0.127 to 0.203 mm)
Sensor wires are robust a la wind loads, dust, etc. impact.
1) Obtain Tamb from R(Tamb)=R(T0)[1+(TambT0)]
2) Introduce heating current (I) such that:
3) Cease heating current
For h ≈ constant, T(t) for heat transfer dominated by the forced convection term is exponential since
Rn = Rn(T0)[1+(TnT0)]
Fit R(t) data to:
Utilize calibration data to determine spatially averaged velocity for the cell as:
(Note, this form of the TTA transfer function is motivated by that for a constant temperature anemometer. It is supported by the observed agreement with experimental data.)
Can be influenced by the alloys in the Tungsten, by the annealing processes, by witchcraft.
Hence, a hot-box has been constructed to determine for each cell of a completed frame.
Symbols show R(T) for different cells.
( = [slope]-1)
Conflicting information from basic heat transfer sources.
Fabrication and use of a test facility to directly evaluate the effect of Tamb(test)≠Tamb(cal).
Ford Haus Heater cell)Ford Haus: A sub-atmospheric flow facility that allows the operator and test chamber to be on the upwind side of the external prime mover.
View from entry door into the 2.6m x 1.83m “Haus”.
Insulation is visible through the clear plastic side wall of the plenum chamber.
Solid State Temp. Sensors.
Pitot probe with adjacent Therms. Couple for velocity measure-ments.
5 lengths of 0.005” (0.127 mm) tungsten wire
← Location of Sensor Wire →
Tamb’ = 22°C V = 1.5 – 6.5 m/s
Tamb’’ = 72°C V = 1.5 – 6.0 m/s
Tamb’’’ = 103°C V = 1.5 – 6.0 m/s
It is inferred that the jump discontinuity for the 22°C=Tamb values represents the transition to vortex shedding. Future measurements for 72°C and 103°C=Tamb cases will test the hypothesis with higher velocity values.
The “A” terms, which represent free convection and heat loss by conduction, have been divided by their respective (Thot-Tamb) values. The averae of the three ratios was 0.0062. The three “low Re” data sets were brought to a common ordinate-intercept as A=0.0062 ΔT(°C). The three calibrations could then be made to agree by scaling the B’ terms with respect to ΔT.
1.) Step change in heat transfer, not previously seen with the TTA, is present with larger diameter sensor wires.
2.) Installed (in a frame) evaluation of is required for accurate Tambient measurements.
3.) Elevated (cf velocity calibration) temperature effects for a test condition must be addressed. (This presentation is advanced cf the associated SAE paper (#05VTMS-103). Further work is in progress.)