In my experimental work, I am studying the photothermal conversion of nanofluids which exposed to incident light from a solar simulator. The insulation layers around the nanofluid glass container (sides and bottom) is white and reflects the transmitted light from the container bottom back to the nanofluid. This light reflection will increase the photothermal conversion efficiency of nanofluid more than its real value. The question now, if I insert a black layer in-between the bottom of glass container and the white insulation underneath to prevent that light reflection, in the same time the transmitted light will be absorbed by the black layer inserted and converted to heat, however this heat won't be lost because of the existence of the insulation underneath the black layer. I am not sure if this will be the right solution or not, so please let me what you think or any alternative suggestions. Thanks
In fact, the black layer can reduce the light reflection, but you need to ensure that temperature of the bottom surface will not increase due to radiation absorption, since thermal energy could be returned to the working fluid by convection, consequently, you cannot measure the efficiency of photo-thermal energy conversion without considering the temperature of bottom surface.
If temperature of the black layer increased unproportionally to the temperature working fluid, you can think about a transparent bottom surface, although this concept will suffer thermal losses without insulation. If you can use double glass layers with vacuum gap, it will be great. Or,
Another option to design the test section in a way that prevent the light beam from penetrating the full depth of fluid; you can increase height of the container or increase the loading of nanoparticles.
Best regards!
Vacuum insulating won't prevent light travel through it, electromagnetic waves travel faster in vacuum, what I want to insulate here, not heat (however, thermal radiation is possible here), it's the light.
The insertion of black surface will definitely absorb the radiations but it will not increase the photo Thermal conversion. Our aim is to absorb maximum radiant energy from the incoming radiations. In your case the radiations will be absorbed but that will not impact the overall heat gain by the nanofluids as the same is absorbed by an external surface rather than nanofluid.
Hope it serves the purpose
In fact, the black layer can reduce the light reflection, but you need to ensure that temperature of the bottom surface will not increase due to radiation absorption, since thermal energy could be returned to the working fluid by convection, consequently, you cannot measure the efficiency of photo-thermal energy conversion without considering the temperature of bottom surface.
If temperature of the black layer increased unproportionally to the temperature working fluid, you can think about a transparent bottom surface, although this concept will suffer thermal losses without insulation. If you can use double glass layers with vacuum gap, it will be great. Or,
Another option to design the test section in a way that prevent the light beam from penetrating the full depth of fluid; you can increase height of the container or increase the loading of nanoparticles.
Best regards!
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