Open top Chamber (OTC)
Open Top Chmabers (OTCs) were extensively used as plant exposure units both in air pollution and in CO2 response studies in the field. OTC is used to expose aerial pollutants and CO2 on crop plants. Currently, it is being used in North America, Europe and South Asian countries.
Open Top Chambers structure having 3 m diameter and 3 m height with an automatic closing door and the top of chamber kept open to provide the near natural conditions. The structure of OTC are fabricated with aluminum rectangle shaped frame installed on the ground and is covered with polyvinyl chloride (PVC) sheet of 120 micron gauge to have more than 90% transmittance of light.
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Chambers are equipped with a frustum at the top to deflect air and prevent dilution of the desired CO2 concentrations within the chamber. There is a cylindrical double walled plenum around the base for uniform CO2 circulation. Inner side of the plenum is provided numerous gas outlets of different sizes, small being nearest to the gas inlet pipe. Blowers are used to distribute CO2 enriched air uniformly throughout the plant canopy. CO2 is supplied to the chamber from a manifold of 5 gas cylinders, each containing 45 Kg of CO2 gas. Gas cylinders are fitted in a row with thick copper outlet pipe and controlled with gas regulators and pressure gauze pipelines. CO2 gas is injected in the OTC along with ambient air using a blower to ensure through mixing. |
Air blower is used for maintaining desired concentration of CO2 into chamber tunnel. Blower also helps in maintaining inside air temperature closer to that of outside ambient atmosphere. The CO2 gas is supplied through copper tubing and the solenoid valves are fitted within the OTC. |
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The opening and closing of these valves are regulated on the basis of actual concentration of CO2 within the OTC and the set CO2 level for that particular OTC which is regulated by PC through program Logic Control and Supervisory Control And Data Acquisition (SCADA). To have manual regulation of CO2 supply, another set of Controlsrotameters are also fitted for extra safety.
The PC with 5 KV UPS with 30 min backup is etablished for uninterrupted data recording and storing. The data are continuously recorded for the temperature, relative humidity and actual CO2 concentration in ppm. The data of temperature (oC), relative humidity (%) and actual CO2 concentration inppm are displayed on the monitor continuoulsy and graphic display is also possible.
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