Document wqVB4NX0eO6nja38r1J5pqmOB

238 W. N. W1THERIDGB Complete removal of a certain constituent would be rated as "100 'p$f efficient" cleaning, no matter how extravagant might be the consumption bf'e Recognizing the need for a better expression for this measure of performap[ engineers have used the terms per cent collection, per cent removal, jeS recovery, per cent retention, arrestance, among others. In .this discussion^ tiveness" is the preferred term, and the rating of performance on a 100-poi will be stated directly as "per cent" or "percentage." m The proportion of material escaping or passing through the sepanjfj sometimes identified as per cent passage or per cent penetration. B. SEPARATION DEGREE In view of the increasing necessity of high-quality air-cleaning equip! operating in the range of 95 to 100 per cent separation, it is the opinioplM' writer that a logarithmic scale of rating is in order. A mass transmission'll scale has been devised for use in the correlation of data on performance ofvi tion processes.6 Separation degree is defined here as the base-10 logarithm of the'?, incoming concentration to outgoing concentration: incoming concentration Separation degree = log outgoing concentration . -Sep.arAtio.njlegr.efi_roay..alaoJi.e.jifitermined.fxom_Rfii_5jgnJ;_iffgfitiyj 100 Separation degree = log 100 -E Qne-degree separation is defined as 90 per cent reduction in the con tion of air-borne matter from inlet to outlet of the air-cleaning deviblj outgoing concentration Vio that of the incoming concentration. The rel tween separation degree and per cent effectiveness may be indicated Ty||j tabulation. The symbol has been adopted for separation degree. ' ^ Effectiveness, rr.{i-dKtcent. So 96 95 99 99.9 99.99 99.999 Separation, --degrees--'- 0.3 1 1.3 .2 3 4 5 Concentration, in/out- 2/1 10/1 20/1 100/1 1000/1 10,000/1 100,000/1 * W. N. Witheridge, Fundamental Concepts in Gas Cleaning (PhX>. thesis, Michigan). University MicroBlms, Ann Arbor, Michigan, 1951. AIR CLEANING a logarithmic-scale of rating equipment performance are ***** ancj graphical. Correlation studies may be reported and J|||nient straight lines on logarithmic graphs, using-separation |fe scales. It is particularly helpful for reports of the performffi^"Tn"f'fwa^|'separating mechanisms,, such as highly effective multiple- systems, represented by the cascade impactor. For that air is filtered through a multiple-layer filter having ASM^VyaSp^Liin each layer, or stage, and that the air contains submicron ! times 0.3 = 3.0 degrees total; 3 degrees = 99.9 per cent REFERENT DIFFICULTY OF SEPARATION I^ates the effectiveness of various air-cleaning mechanisms ?c'omffinmahts arranged roughly according to particle size. For this pur- liSculty of separation has been selected, and the value chosen is cent separation. This is the ability of a cleaner to deposit Particle size, in microns, 90 per cent removed (one degree separation1) 50-100 20-50 20-50 5-10 5-20 10-20 5^-20 2-10 1-5 0.1-2 O-.l-l 5-10 ' 0.5-2 0.2-1 0.01-0.1 0.01-10 0.01-10 Molecular