04_thermal

5 w will keep the air moving nominal box aluminum foil

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Unformatted text preview: principle, we can: – – – – – – • We’ll use power resistors rated at 5 W to generate We’ the heat – – – – – measure the thermal conductivity of the insulation see the impact of emissivity changes see the impact of enhanced convection look for thermal gradients in the absence of circulation look at the impact of geometry on thermal state see how serious heat leaks can be 25 nominal P = V 2/R At 5 V, nominal value is 1 W can go up to 11 V with these resistors to get 5 W a 12 version puts us a bit over 2 W at 5 V • Fans to circulate – small fans operating at 5 V (and about 0.5 W) will keep the air moving • Nominal box: • Aluminum foil for radiation control – 10 cm side, 1-inch thick, about 1.5 W (with fan) – adhesive spray to attach to skin • Standard building insulation Winter 2008 21 Winter 2008 22 UCSD: Physics 121; 2008 UCSD: Physics 121; 2008 Lab Experimental Suite experiment • There are a variety of ways to measure temperature int. airflow int. ext. airflow int. foil int. ext. foil geom. geom. A (control) (control) 25 1 fan none no no 10 cm cube B (ext. convec) (ext. convec) 25 1 fan fan no no 10 cm cube C (ext. radiation) (ext. 25 1 fan none no yes 10 cm cube D (ext. conv/rad) (ext. conv/rad) 25 1 fan fan no yes 10 cm cube • Both the thermistor and RTD are resistive devices E (gradients) (gradients) 25 none none no no 10 cm cube – thermistor not calibrated, nonlinear, cheap, sensitive – platinum RTDs accurate, calibrated, expensive F (int. radiation) (int. 25 1 fan none yes no 10 cm cube G (radiation) (radiation) 25 1 fan none yes yes 10 cm cube H (more power) (more 12 1 fan none no no 10 cm cube I (larger area) (larger 12 2 fans none no no 17.5 cm cube J (area and thick.) 12 2 fans none no no...
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