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Lab 5 12 Pager Final Document Hot Dog Anemometer

Lab 5 12 Pager Final Document Hot Dog Anemometer - Hot Dog...

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Hot Dog Lab A report on an experiment performed for ME 115 Thermal Engineering Laboratory San Jose State University Department of Mechanical and Aerospace Engineering By
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Background and Objectives The purpose of this experiment is to correlate wind speed to transient heat conduction and convection using a pipe of known thermal properties. A wind tunnel may be used to provide an environment in which the wind speed can be controlled. Typically an orifice plate is used to gauge the mass flow rate and is related in Equation 1. Equation 1 ( 29 ( 29 2 4 2 orifice diameter 4 1 air P m C ρ π β = - & (Handout, 3) Where β is the ratio of orifice diameter to pipe diameter and C depends on geometry. Density may be calculated using the ideal gas law (Equation 2) with known temperature and density. Assuming an incompressible flow and a known cross-sectional area, average velocity can be determined using continuity which can be simplified to Equation 3 below. Equation 2 P RT ρ = (Cengel, 7) Equation 3 v = m/ t s air A ρ - & (Handout, 3) Experimental velocity may be determined from elapsed time and a set of midpoint temperatures measured in the hot dog. From the temperatures measured in a cylinder, the Heisler charts may be used to determine the Biot number (Bi) using non-dimensional time τ (Equation 4) and temperature θ (Equation 5). The Bi may be used to determine the heat transfer coefficient h using Equation 6 below. Equation 4 o o i T T T T θ - = - (Cengel, 232) Equation 5 2 / o t r τ α = (Cengel, 232) Equation 6 Bi=h /k o r q (Cengel, 220) Equation 7 Nu=h D/k (Cengel, 358) Equation 8 Re=v D/ ν (Cengel, 399) 2
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The Nusselt (Nu) number may be found using the heat transfer coefficient using found in Equation 6 and plugging into Equation 7. The Reynold’s (Re) number can be correlated to velocity using Equation 6, above. An Empirical correlation (Equation 9) may then be solved using Nu and Prandtl (Pr) numbers for the Reynolds’s number. From this, control air speed v can be found. Equation 9 4/5 5/8 1/2 1/3 2/3 1/4 0.62Re Pr Re Nu = 0.3 1 [1 (0.4 / Pr) ] 282000 + + + (Cengel, 413) Experimental Procedure & Apparatus Wind tunnel in room 114A of the San Jose State Engineering department was used. Values for temperatures of the plastic cylinder (T Cylinder ), case pressure (P case ), change of pressure due to the orifice plate (∆P Orifice Plate ) and the uncertainty estimate of manometer (+/- in H 2 O) was obtained using this chassis. The experiment was conducted using the following items: (1) Wind tunnel - with variable speed control (1) Plastic Cylinder (1) Barometer in room 113 (1) Omega T-type thermocouple with +/- 1°C (# SA1 – T), (1) Timer (1) Electronic kettle
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