2013/03/16

A Cool Object Reduces Energy loss from a Hot Object

A quick post as the method needs changing.

A heated plate in a well insulated box with 2 IR transmissive windows.
A small window for thermal camera measurements
A larger window to allow passage of IR from/to an external Plate

All wires passing through the insulated box have wires looped and buried in thermal insulation to reduce conduction.
The external plate is 9cm from the IR window. There is no enclosure round the external plate so convection will have no effect on  the internal plate.
Each IR window is double glazed with cling film with an air gap of 2cm.

The internal plate is warmed by a resistor network (12 resistors) evenly spaced on the reverse of the plate (away from window) dissipating a total power of 1.88 watts.

The system was setup as indicated with a ambient temperature external plate and allowed to stabilise (unfortunately not log enough).
The external plate was then replaced with a warm identical plate. This was then allowd to cool.
The cold plate warm plate cycle was repeated. (this time temperatures had stabilised)


External Plate view

Thermal Camera View



Overall view showing holder for external plate


Note that 1st measurement did not allow sufficient time for temperature to stabilise



This shows a significant increase in temperature when the warm plate is in position (0.3C)


NOTE This is not increasing the temperature of the heated plate it is just adding energy to the plate. This therefore is has to warm since the total power input to the plate is greater.

During the last sequence the ambient was measured at a constant 19C

Note IR camera temperatures have been corrected by changing standard emissivit of 0.92 to 0.54 to allow for 2 layers of cling film.

The external plate also has had a double layer of cling film placed between it and the camera.
hot plate on right IR window on Left

IR window on left Cold plate on right (only just visible against background)

Box Dimensions 127x120x80 mm
Internal space 80x80x40 mm

heated plate dimension (Forgot to measure before sealing in compartment)
35x35x6 mm approx

Plate centre is monitored by an attached thermocouple (not used in this test)

This is another experiment showing that a cool object can add energy to a hotter object!

This needs to be repeated with a self heating external object to show that internal temperature will stabilise at a higher value.



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