Timothy J. Rennie

Computerized monitoring and control for a research controlled-atmosphere storage facility

An automated computerized monitoring system for a controlled-atmosphere research facility was developed and implemented. A proportional gain (Kc) that characterizes the dynamics of the system was modeled. Based on a proportional and integral controller, the custom-made control software corrects errors caused by physiological changes within stored commodities. Control parameters are continuously adjusted to maintain desired gas conditions in the chambers. Imbedded in user-friendly software, the computerized monitoring system was tested on storage chambers with different volumes. Maximum average errors obtained in any mini-chamber were 0.0035 and 0.0016% for the CO2 and O2 concentrations, respectively, which demonstrates the ability of the controller to maintain the desired set points. The system was reasonably stable with maximal S.D. of 0.051 and 0.077% for the CO2 and O2 concentrations, respectively. The software allows different gas set points, keeps record of all operations, acquires data and can operate unattended. Crown Copyright # 2003 Published by Elsevier Science B.V. All rights reserved.

Advection-Diffusion Model for Diffusion Channel Storage

An advection-diffusion model is proposed for determining the gas concentrations in a diffusion channel storage system over time. The model was solved numerically and compared to experimental data. The numerical results followed the same trend as the experimental, though there was significant difference between the magnitudes of the results. It is believed that this difference may be due to the respiration rate model used, and the value of the respiration rate. The diffusive and advective components of the oxygen flux into the chamber have been presented. The diffusive and advective components were of the same order of magnitude, though with increasing time, the diffusive component becomes dominant. Simulations of chambers with carbon dioxide scrubbing were also performed. The advective component of the flux was much higher in these chambers.