A heat source for infrared measurements (1977)
Question in 1977: Design and build a heat source for infrared measurements in the field and at sea.
Design and construction
For infrared measurements in the field, it is often desirable to have a reference radiator available that is easily transportable and has a temperature of, for example, 500 C above ambient temperature. For this purpose, the choice was made on a heat source with a large heat capacity consisting of a water-filled double-walled cylindrical vessel with a capacity of approximately 9 litres and dimensions of 400 x 400 mm (diameter x height). The thickness of the double wall is 15 mm. The water in this wall is heated by burners located under the bottom of the vessel.
The cross-section of the complete heat source is shown in the figure above. For heating. propane gas in bottles is used. The six burners are controlled by the thermostat so that the water remains constant in temperature within reasonable limits. The control principle corresponds to that of most central heating boilers, i.e. constant flame height and control over time. The even heating of the barrel is achieved by the natural circulation of the water. The warm water rises along the inner wall of the vessel and returns along the outer wall. Even with a strong cooling effect of wind on one side of the vessel, a temperature of ±10 C is maintained. In the heat radiation area, the emission coefficient is greater than 0.9.
The gas bottle with the control system and the shield plate for the burners are housed in the cylindrical space under the heat source in such a way that they can be easily removed. A cross-shaped mounting base is mounted under the cylinder so that there is room for the supply of combustion air; the combustion gases can escape through several holes in the wall of the combustion space.
To prevent the burning flame from blowing out in strong winds, a screen 300 mm high with closable ventilation holes at the top and bottom has been mounted around the combustion space with the drainage holes. These ventilation holes create a flow of outside air, which cools the screen and shields the warm combustion space.
For measurements at sea, the heat source, which has a net weight of 45 kg, can be mounted on a wood-reinforced polystyrene floating body with dimensions 1200 x 1200 x 400 mm. Temperature registration equipment can be placed in the lockable inner cylinder of the vessel.
The maximum operating time of the heat source is approximately 30 hours with a gas supply of 5 kg of propane. The heating time to a temperature of approximately 500 C is approximately half an hour.
Test on the Roeleveense Plas
After construction, the heat source was tested on the Roeleveense Plas. The system worked flawlessly.
With a 5 kg propane gas bottle, an air temperature of 250 C during the day and 150 C at night and the thermostat at position 4, the temperature of the heat source fluctuated accordingly to the air temperature. The temperature difference between the air and the vessel was 150 C.
With more consistent weather and less influence of the sun, the heat source temperature remained constant during day and night with a temperature difference between the air and the barrel of 200 C. The total duration of the test with one bottle of gas was 190 hours.
With a gas cylinder of 3.9 kg of propane, an average air temperature of 150 C, and the thermostat at position 8 (high), the temperature of the calibration vessel was 580 C. The temperature difference between the air and the barrel was 430 C. Total burning time with one gas cylinder was 42 hours.
Use on land
The heat source was used for infrared detection from the air on the Vliehors.
Use at sea
In the summer of 1978, the heat source was anchored at sea near Plymouth. During the remote infrared measurements, the heat source appeared not to be working. The next morning it became clear why. The entire device appeared to have been completely dismantled by one or more metal thieves. After that, no new version of this heat source was built.