Specifications –Visualization windows
1/ Context
Located in the ICARE laboratory of CNRS in Orléans (France), our team conduct combustion studies. We are currently making a new combustion vessel where we will be able to study phenomena of flame acceleration. In order to observe the flame propagation inside the vessel, we will need sapphire windows with different dimensions.
2/ Combustion Vessel
Figure 1: Représentations du tube d’accélération de flamme
Our vessel will include 9 commutable successive tubes. Two of them will receive 4 rectangular windows in order to operate flame visualization. The other tubes will receive 3 circular windows in order to detect the flame position by using photomultipliers. The vessel will be able to be heated at steady temperature up to 200°C. During experiences, the maximal pressure generated by the combustion could reach 120 Bar.
3/ Mechanical and thermal restrictions
3-1 Rectangular windows
The Figure 2 shows different front views of the rectangular windows housing. The dimensions of the housing and aperture from the housing to the inner vessel are also indicated. The windows are wedged between two seals in order to avoid contact between glass and vessel metal.
Figure 2: Front views of a window housing, without window (a) and with window (b)
Here are presented the rectangular windows dimensions:
- Height: 306 mm
- Width: 74 mm
- An estimation locally performed permit us to determine a sapphire thickness of 30 mm for pressure resistance
However, the supplier will have to take into account the housing dimensions and the pressure and temperature constraints mentioned above in order to make sure that:
- The calculation of windows thickness will permit the windows pressure resistance
- There will be no contact between the glass and the vessel metal due to sapphire thermal expansion
In his offer, the supplier will have to give the details about his calculations.
Thereby, we wish to have 8 identical rectangular windows having the following geometrical characteristics:
Material / Height (mm) / Width (mm) / Thickness (mm) / FilletSapphire / 306 +/- 0.5 / 74 +/- 0.5 / 30 +/- 0.5 / 5 mm
As these windows will be used tovisualize phenomena occurring inside the cylindrical vessel by optical diagnostics, they will have good quality of polishing and parallelism.
scratch-dig specification / Optical quality polishing60/40 / λ/2
The visualization will be performed in the visible and UV domain. The sapphire will have to present a good quality in order to have a minimum of default(doping and inclusions) and have a good transmissivity (more than 50% for the proposed thickness) in the 300-1000 nm spectral domain.
3-2 Circular windows
The Figure 3 represents the dimensions of the circular windows and their housing.
Figure 3: Top and front views of a circular window and its housing
Here are presented the rectangular windows dimensions:
- Diameter: 10 mm
- An estimation locally performed permit us to determine a sapphire thickness of 5 mm for pressure resistance
However, the supplier will have to take into account the housing dimensions and the pressure and temperature constraints mentioned above in order to make sure thatthewindows thicknesswill permit to resist at those conditions.
In his offer, the supplier will have to give the details about his calculations.
Thereby, we wish to have 33 identical circular windows having the following geometrical characteristics:
Material / Diameter (mm) / Thickness (mm)Sapphire / 10 +/- 0.1 / 5 +/- 0.1
As these windows will be used todetect the flame propagating inside the cylindrical vessel by using optical diagnostics, they will have good quality of polishing and parallelism.
scratch-dig specification / Optical quality polishing20/10 / λ/4
The visualization will be performed in the UV domain. The sapphire will have to present a good quality in order to have a minimum of default(doping and inclusions) and have a good transmissivity (more than 70% for the proposed thickness) in spectral domain upper than 300 nm.