Document 70Jy56pbYDQNmb9d4Bn6wbYwR

couple with relation to HVT (3) a reading of t multiple high-velocity thermocouple (MHVT). The MHVT--a delicate laboratory instrument not practicable for every day testa under operating conditions-- registers within a few degrees of the true gas temperature. HVT, a more rugged tool capable of use under actual operating test work conditions, may easily be corrected by the use of curve. True gas temperature or MHVT value, then, may, be used in design work. Both HVT and MHVT have the metal junctions shielded from the direct effects ol radiant heat. Gas Is aspirated over them ot increasing velocity until the reading levels off. Differences In temperature, such aa indicated on the curve throughout the range shown, are normally encountered in furnace exit gases. For this reason temperatures of this order should not bo specified without also defining the method by which they aro taken. Ash Characteristics, fn the design of the pulverised-coal-lired furnace, ash Influences a designer's work probably more than any factor he contends with. He cannot know too much about iL A notable contribution to clearer thinking on furnace design or specifi cations eon be made if Initial deforma tion, softening and liquid temperatures of ash on an oxidising as well as a re ducing beat* are given. SPECIAL SECTION POSTPONED Unsettled conditions in the print ing industry rnnke It necessary to postpone the 16-page Special Sec tion on low-voltage electrical pro tective devices scheduled far June POWER, if circumstances permit, it will. appear in July. Back in the days when stoker firing predominated, a laboratory procedure was established with the objective of determining the clinkering properties of coal when burned on grates. It involved the determination of these ash temperatures in a reducing atmosphere and this procedure is still the standard laboratory practice today. Under the circumstances prevailing then, this method made sense because it attempted to set up in the laboratory the condi tions under which the clinkering took place. Today, however, with pulverized coal firing, tight furnaces, and excess air admitted at the burner except for the zone of highly active combustion,* the ash particles are in an oxidizing atmosphere. At the 1940 annual meeting ot the ASME, Dailey and Ely presented data on the considerable difference in these ash properties when determination was in an oxidizing compared to atmosphere; differences were greater as iron content ol Fig. 4 end 5 show, Irom variety of coal ash samples lestea o period ol eight years at the fc ?? laboratory, that the )o*eu ioiOaj-a*; formation on an oxidizing bub t& has been found Is about 2250 p .Since the fuel is burned aod passes to the furnace e*h in an otidit ing atmosphere It would seem more realistic for us to talk artd in terms of ash temperature* o0'^ oxidizing basis and so have the *tl& we use moro in keeping with the pj&i nomenn we are describing. Experience and teats tell us that the average trua gas temperature eater, ing close-spaced tubes exceeds the oil- dizing initial deformation temperature of the ash, troublesome slag tctucmP lotion# may be expected. ^ Summery. Control ol the tempetsiuit. of gas leaving the furnace U a highly important aim of the specification writer. All the above is a plea lor realistic thinking on this and other related design requests in this phase of the power field. Realistic thinhiag, involve# using 0) termi *Hai ippijy (2) measurement methods that can fcc adapted to expected operating cendi: lion# (3) o full story on the chine? teriitics of the fuel, especially wtay they predict fuel behavior lit aenlcfc*' 1 INFLUENCE OF l0N on ASH 8 INITIAL-OEFORMAT ION TtMPlRSTURC iV l\\ * ( \ o Vi b o o o V* 1 a v V _ 0* Ci/ffp 0 ft SvJ , forme wM> x -- Tolfll Won In eol aid (ot F*| % 4lnltlol deformotlon of ash on both oxidizing and reducing boxes, helps set furnoce limit# for'pulverizer end stoker TolaI Iron CM) ath (ei F*| % C Pulverised cool bums (n on oxidizing atmoiphero so W esh-ioftening temperatures on this boils In ipcci'i0> .2'* 104 002} POWO Mar |W 2--Electron Flow In Conductors COT" is " ; " S 2_ ,i|Mr atom hos 47 alectronsT 46 In t inner oiWn. one In outer 28 In 3 lnnr orblivone in 0UTBr 7; ^ or J arffofn Si tltef'Wft P^.jA ,'***<**-x /\ $AAAAA |jj- How free electron*---represented by tntofl circles---fn outer orbit of ))? topper atoms may bo Influenced by the nucleus of two or more atom* L<T Vt<tronf f S/S// v,-. /\ V Hot so tone aco textbook# told us that the precise nature of electricity u not known, that it was an Invisible and mysterious agent manifesting It self in many way*. Today we know that ibis Invisible and mysterious agent it a flow of particles called electrons, which form part of all atoms. In the finv lessen (Power, April, p 105] we learned that the atoms of all elements are made up of a positively charged nucleus, or center, about which In orbita negatively charged electrons ro tate. We also learned that tbeir ar rangement In these orbits gives each element certain chemical qualities. With this conception of the atom's structure, let us consider electric-cur rent flow In a circuit, as well as other effects. Flow of an electric current 1* now accepted as being a alow drift of so-called free electrons through a conductor. How these free electrons are made available has' not yet been definitely established. One of the most rational conceptions maintains that electrons In the outer orbits of a con ductor's atoms may at times be sub jected to equal Influences of two or more stoma. ' Frot Electron*. The structure of good-conductor atoms gives a due to the free-elcctron theory. For example, consider the copper atom. Fig. 1, which has 23 electrons in three inner orbits and one in an outer orbit. The innerorbit electrons are closer to the nucleus than the outer ones. The three inner orbiu also have their full number of electrons, which is a stable condition; they do not have o tendency to lose or gain electrons, os explained In the ' 64 Arrow# iSow how the free electron*--Indicated by small circlet-- drift ot random from one atom to onother In the outer orbit of atoms April Issue. For these reasons the Inner-orbit electrons are bound mote tightiy to the nucleus than the single electron in the outer orbit. This single elec tron; outside of the three highly satis fied family circles, appears to be more Mry 1448 1303) I0S ii-r