Heat dissipation investigation by thermovision

Transcription

1 Heat dissipation investigation by thermovision Virgilijus MINIALGA, Rolandas PAULAUSKAS Kaunas University of Technology, Physics department, Studentu st. 50, Kaunas LT-51368, Lithuania 1

2 Goals of the work To find the best method for heating a substance under investigation To ascertain the main way of heat dissipation from heated area To investigate material thermal properties using heating and measurement of heat dissipation by thermovision 2

3 Fig. 1. The ways of heat spread from heated area 3

4 Theoretical investigation We found that equation describing reduction of temperature by thermal conductivity is, T T a ( T 0 Ta ) e 3 t 4c d 2 (1) where T is temperature, Ta is environment temperature, λ is thermal conductivity constant, T 0 is initial temperature, c is specific heat, is mass density, and d is diameter of heated zone 4

5 Theoretical investigation Thermal conductivity constant λ can be calculated by formula 4c 3 e d (2) where e is time constant of exponential reduction of temperature 5

6 Experimental measurements Fig.2. Thermovisor FLIR A20 could take thermoimages and make thermomovies of thermal radiation in 7,5-13μm wavelength region. Range of temperatures is -20 C C with 2% error. The device has three changeable lenses for different distances of measurement. Thermovisor is connected to computer over FireWare and data are saved as photos or movies using ThermaCam Research Lab PRO 2.8 software. 6

7 Experimental measurements Three ways for heating surface area under investigation were discussed: Heating of surface by powerful laser s beam; Temperature increase after hammer impact; Touching and contact heating. 7

8 Experimental measurements Fig. 3. Thermoimage of wood heated by laser. The investigated materials were heated using 100mW laser 8

9 Experimental measurements Fig. 4. Thermophoto of wood after hammer impact. Heated areas on the ground are bright places in the center part of thermoimage. The object 1 was moved to the right side after strong hammer impact. The white area of object 1 surface means the most heated place. 9

10 Experimental measurements In case of heating by touching heat was transferred from the hot material to the cold one because of heat diffusion. Difficulty of this way is the necessity of massive heated body. It should have good thermal contact with object under investigation. This process takes long time comparing with earlier mentioned processes. Also the narrow places are not accessible for such heating. Finally we decided to use laser beam for samples heating as non-contact universal method 10

11 Results T, K t, s Fig.5. Theoretical and experimental graphs of temperature reduction on the wood surface. 11

12 Results Fig.6. Theoretical and experimental graphs of temperature reduction on the ceramics surface. 12

13 Results Fig. 7. Theoretically calculated graphs of temperature reduction on the carbon and silicon surface. 13

14 Conclusions The best way of three investigated methods for objects heating was laser heating. The possibilities to avoid infection and reach narrow places in medical applications are the main advantages of this method. Theoretical evaluation and thermovision investigation of laser heated material surfaces temperature reduction show that the main way of heat dissipation is conductivity. Thermal conductivity of real material can be calculated using experimental graphs of temperature reduction of heated area in time. This method allows non-contact investigation of material thermal properties that is necessary for thin tissues and hard accessible places. Sometimes laser beam can damage the material s surface under investigation like body tissues, so it is important to take attention to laser s output power. Acknowledgment Authors acknowledge the Mechatronics Centre for research, studies and information at Kaunas University of Technology for the ability to use thermovisor FLIR A20 and notebook software. 14