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12INCORPORATING CHAOS THROUGH A BUNIMOVICH INSPIRED STADIUM DESIGN FOR UV-C
DISINFECTION CHAMBER
SWATI MISHRA1, DEVENDRA SINGH2, HARSHAWARDHAN WANARE23
'Department of Biological Sciences & Bioengineering, Indian Institute of Technology, Kanpur, India-208016 2Centre for Engineering in Lasers & Photonics and 3Department of Physics, Indian Institute of Technology, Kanpur, India- 208016
hwanare@iitk.ac.in
ABSTRACT
UV-C radiation has been used extensively in disinfection chambers to neutralize a variety of microorganisms. The UV-C radiation is used to steralize air, water, food and a variety of tools in medical as well as food industry. The microorganisms like Clostridium spores and Klebsiella pneumoniae commonly found on frequently touched surfaces in healthcare settings that were not killed by the standard disinfecting procedure are removed by 254 nm UV-C wavelength [1]. Paramount in the above applications is that the UV-C radiation must efficiently reach every nook and cranny of the chamber evenly, which is extremely challenging to ensure in most disinfection chamber designs [2,3]. In actual practice, this is not guaranteed and the radiation dosage available may be differ widely at different spatial locations within the chamber, even leading to dark regions wherein radiation levels could be negligible. The light intensity distribution depends on the light source's placement, the chamber's design that supports reflections from the walls and the nature and location of the object placement. The presence of "dark spots" severely compromises complete sterilization. In order to address this issue, we propose a stadium design chamber with specific shape parameters that results in chaotic dynamics of the radiation leading to uniform UV-C radiation distribution. We demonstrate the use of chaotic Buminovich stadium design to ensure space-fillig characteristics of the underlysing chaotic UV-C field distribution. This leads to a complete elimination of the "dark spots" within the chamber. We show other advantages of such a UV-C which ensures a more evenly distributed UV-C light intensity distribution in the proposed stadium chamber in comparison to the commonly used cuboidal box. This chaotic field distribution mechanism has been adapted in the photovoltaic cells to maximize the trapped sun rays' trajectories for enhanced absorption within the active medium [4]. This effect has also been used in a microcavity laser wherein cavity modes' interaction with the lasing medium caused due to deformation of the two-dimensional cavity shape that led to chaotic dynamics simultaneously resulted in a single-mode lasing [5]. It should be noted that the parameters chosen for the Bunimovich stadium lie well within the completely chaotic regime as presented by Lopac et al., i.e. there is a complete absence of islands of stability that involve regular periodic orbits [6]. The presence of such islands of stability would imply that light cannot escape these regions and in other words, the light from the surrounding region gets delimited from these regions leading to the formation of "dark spots". Hence, one needs to choose the parameters of the Bunimovich stadium that correspond to the completely chaotic regine. The other important aspect is that of dimensionality, the Bunimovich stadium is a two-dimensional system, yet we simply extend the third dimension and arrange the UV -C source lamp parallel to this third dimension that provides the depth to the enclosure for undertaking radiation disinfection and individual planes themselves would support the chaotic dynamics. The 2-D Bunimovich stadium is characterized by two shape parameters in the x-y plane of the central rectangle where 25 is its horizontal width and 2y is its vertical height, the radius of the curved region is 1 - 5. We provided an extra depth to the chamber along the z-direction, the experiments involved a sealed stadium shaped chamber made of metallic aluminium sheets with a rectangular front door opening as shown in Figure 1. The UV-C light sources are the Philips TUV PL-S lamp placed along the four edges of the chamber parallel to the depth. A Lutron UVC- 254 UV light meter probe placed inside the chamber measures the intensity, whereas the controller unit is placed outside which displays the readings in mW/cm2.
Figure 1. Design of the UV chamber. TL: Top Left; TR: Top Right; BL: Bottom Left; BR: Bottom Right is the location of the UV-C light source placed parallel to the z- axis.
The UV-C probe is kept at the center of the rectangular stage (about 6 inches from the chamber floor) inside the UV chamber facing upwards in the x-direction and tilted at various angles using a goniometer. The range of the angles was [-70,+70] degrees about both the z- and y- direction. The measurements are made in two different scenarios, namely when the chamber is empty with only the UV-C probe placed on the stage, and the second when a stack of papers cover about two-third of the stage with the probe in both sections. The second measurement protocol is to test out the effect of shadow regions that invariably results from keeping multiple object within the chamber. Its computational simulations was performed in COMSOL 5.6 Ray Optics Module.
Figure 2 demonstrates that the stadium design significantly aids in uniform distribution of the radiation due to the chaotic scattering of the light trajectories. Note that the geometery leads to an exponential separation (related to the Lyapunov
exponent that characterizes Chaos) of the light rays after multiple reflections that were nearly identical to being with. The space filling nature of the light field also arises due to the same underlying chaotic dynamics. This central advantage is lost in the conventional cuboidal or circular geometry chambers. Our experimental results are validated by quantifying the the standard deviation of the UV-C intensity in stadium (std.stadium) and cuboidal chambers (std.cubodal) which reveals a more uniform light intensity distribution in the proposed stadium chamber in comparison to more the commonly used cuboidal counterpart, shown in the yellow panel in Fig. 2.
Incorporation of a simple design variation offers tremendous benefits by invoking chaotic dynamics and we believe this strategy is quite powerful and can easily be adapted in multifarious applications requiring unform radiation distribution.
Angle (degrees) Ang le (deg rees)
Figure 2. Experimental results showing comparison of the light intensity distribution to the angle at which the probe is tilted (left) contains only probe in z- direction in cuboidal and stadium chambers when the top lamps are switched on [std. stadium — 0.174; std. cuboidal 0.265] and when the bottom lamps are on [std.stadium — 0.006; std. cuboidal — 0.022] (right) contains both the stack of papers and the UV-C probe when all the four lamps are switched on in y-axis [std.stadium — 0.283; std.cuboidal — 0.460] and z-axis [std.stadium — 0.198; std.cuboidal — 0.307]
REFERENCES
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