Part 16 (1/2)

It would appear that the nozzle illustrated is undoubtedly the best that has been developed for use in the determination of the moisture content of steah pressure stea Nozzle--The calorimeter should be located as near as possible to the point fro nipple should be placed in a section of the main pipe near the boiler and where there is no chance ofin the pipe The Aineers reco nipple, of which a description has been given, should be located in a verticalnearly across the pipe Where non-return valves are used, or where there are horizontal connections leading from the boiler to a vertical outlet, water may collect at the lower end of the uptake pipe and be bloard in a spray which will not be carried away by the stea to a lack of velocity A sareater aoose-neck connections a small amount of water may collect on the bottom of the pipe near the upper end where the inclination is such that the tendency to flow backward is ordinarily counterbalanced by the flow of steam forward over its surface; but when the velocity momentarily decreases the water flows back to the lower end of the goose-neck and increases theit an undesirable location for sa In any case, it should be borne in mind that with low velocities the tendency is for drops of entrained water to settle to the bottom of the pipe, and to be temporarily broken up into spray whenever an abrupt bend or other disturbance isthe Manner in which Erroneous CalorisNozzle

Case 1--Horizontal pipe Water flows at bottom If perforations in nozzle are too near bottoainst nozzle, flows into calori

Case 2--If nozzle located too near junction of two horizontal runs, as at a, condensation froainst the nozzle by the velocity of the stea Nozzle should be located far enough above junction to be removed from water kept in motion by the steam velocity, as at b Case 3--Condensation in bend will be held by velocity of the stea intervals and the likeis obtained A true reading will be obtained at b provided condensation is not blown over on nozzle Case 4--Where non-return valve is placed before a bend, condensation will collect on steaainst nozzle and false readings result]

Fig 19 indicates certain locations of sa nozzles fro obvious fro any calorih the instru a throttling caloriiven and the principle upon which it works

[Illustration: Babcock & Wilcox Superheater]

SUPERHEATED STEAM

Superheated steam, as already stated, is steam the temperature of which exceeds that of saturated steam at the same pressure It is produced by the addition of heat to saturated steam which has been reenerated The properties of superheated steaas rather than of a vapor Saturated steam cannot be superheated when it is in contact ater which is also heated, neither can superheated stea reduced to the te as its te pressure it is superheated, and before condensation can take place that superheat h radiation or soives such properties of superheated stea pressures as are necessary for use in ordinary engineering practice

Specific Heat of Superheated Steam--The specific heat of superheated steam at atmospheric pressure and near saturation point was deterives it the value of 048 Regnault's value was based on four series of experiments, all at ate, the rade For fifty years after Regnault's deterher pressures and tee of his experiations have shown that the specific heat is not a constant and varies with both pressure and the temperature A nuators and, up to the present, the most reliable appear to be those of knoblauch and Jacob Messrs Marks and Davis have used the values as deterhtof the curves at low pressures close to saturation because of thernault's determination at atrees of superheat to follow Holborn's and Henning's curve, which is accepted as authentic

For the sake of convenience, the mean specific heat of superheated steaiven in tabulated form in Table 25 These values have been calculated fro from the total heat of one pound of stearee of superheat the total heat of one pound of saturated stea the difference by the nurees of superheat and, therefore, represent the average specific heat starting from that at saturation to the value at the particular pressure and temperature[21] Expressed as a formula this calculation is represented by

H_{sup} - H_{sat} Sp Ht = ----------------- (8) S_{sup} - S_{sat}

Where H_{sup} = total heat of one pound of superheated steam at any pressure and temperature, H_{sat} = total heat of one pound of saturated steam at same pressure, S_{sup} = temperature of superheated steam taken, S_{sat} = te to the pressure taken

TABLE 25

MEAN SPECIFIC HEAT OF SUPERHEATED STEAM CALCULATED FROM MARKS AND DAVIS TABLES _______________________________________________________________ |Gauge | | |Pressure | Degree of Superheat | | |_____________________________________________________| | | 50 | 60 | 70 | 80 | 90 | 100 | 110 | 120 | 130 | |_________|_____|_____|_____|_____|_____|_____|_____|_____|_____| | 50 | 518| 517| 514| 513| 511| 510| 508| 507| 505| | 60 | 528| 525| 523| 521| 519| 517| 515| 513| 512| | 70 | 536| 534| 531| 529| 527| 524| 522| 520| 518| | 80 | 544| 542| 539| 535| 532| 530| 528| 526| 524| | 90 | 553| 550| 546| 543| 539| 536| 534| 532| 529| | 100 | 562| 557| 553| 549| 544| 542| 539| 536| 533| | 110 | 570| 565| 560| 556| 552| 548| 545| 542| 539| | 120 | 578| 573| 567| 561| 557| 554| 550| 546| 543| | 130 | 586| 580| 574| 569| 564| 560| 555| 552| 548| | 140 | 594| 588| 581| 575| 570| 565| 561| 557| 553| | 150 | 604| 595| 587| 581| 576| 570| 566| 561| 557| | 160 | 612| 603| 596| 589| 582| 576| 571| 566| 562| | 170 | 620| 612| 603| 595| 588| 582| 576| 571| 566| | 180 | 628| 618| 610| 601| 593| 587| 581| 575| 570| | 190 | 638| 627| 617| 608| 599| 592| 585| 579| 574| | 200 | 648| 635| 624| 614| 605| 597| 590| 584| 578| | 210 | 656| 643| 631| 620| 611| 602| 595| 588| 583| | 220 | 664| 650| 637| 626| 616| 607| 600| 592| 586| | 230 | 672| 658| 644| 633| 622| 613| 605| 597| 591| | 240 | 684| 668| 653| 640| 629| 619| 610| 602| 595| | 250 | 692| 675| 659| 645| 633| 623| 614| 606| 599| |_________|_____|_____|_____|_____|_____|_____|_____|_____|_____| |Gauge | | |Pressure | Degree of Superheat | | |-----------------------------------------------------| | | 140 | 150 | 160 | 170 | 180 | 190 | 200 | 225 | 250 | |---------+-----+-----+-----+-----+-----+-----+-----+-----+-----| | 50 | 504| 503| 502| 501| 500| 500| 499| 497| 496| | 60 | 511| 509| 508| 507| 506| 504| 504| 502| 500| | 70 | 516| 515| 513| 512| 511| 510| 509| 506| 504| | 80 | 522| 520| 518| 516| 515| 514| 513| 511| 508| | 90 | 527| 525| 523| 521| 519| 518| 517| 514| 510| | 100 | 531| 529| 527| 525| 523| 522| 521| 517| 513| | 110 | 536| 534| 532| 529| 528| 526| 525| 520| 517| | 120 | 540| 537| 535| 533| 531| 529| 528| 523| 519| | 130 | 545| 542| 539| 537| 535| 533| 531| 527| 523| | 140 | 550| 547| 544| 541| 539| 536| 534| 530| 526| | 150 | 554| 550| 547| 544| 542| 539| 537| 533| 529| | 160 | 558| 554| 551| 548| 545| 543| 541| 536| 531| | 170 | 562| 558| 555| 552| 549| 546| 544| 538| 533| | 180 | 566| 561| 558| 555| 552| 549| 546| 540| 536| | 190 | 569| 565| 562| 558| 555| 552| 549| 543| 538| | 200 | 574| 569| 566| 562| 558| 555| 552| 546| 541| | 210 | 578| 573| 569| 565| 561| 558| 555| 549| 543| | 220 | 581| 577| 572| 568| 564| 561| 558| 551| 545| | 230 | 585| 580| 575| 572| 567| 564| 561| 554| 548| | 240 | 589| 584| 579| 575| 571| 567| 564| 556| 550| | 250 | 593| 587| 582| 577| 574| 570| 567| 559| 553| |_________|_____|_____|_____|_____|_____|_____|_____|_____|_____|

Factor of Evaporation with Superheated Stea a boiler trial, where superheated stea the factor of evaporation is that already given, (2),[22] namely,

H - h Factor of evaporation = ----- L

Here H = total heat in one pound of superheated stea the same values as in (2)

Where no such tables are available but the specific heat of superheat is known, the formula becomes:

H - h + Sp Ht(T - t) Factor of evaporation = ---------------------- L

Where H = total heat in one pound of saturated stea in trial, h = sensible heat above 32 degrees in one pound of water at the te the boiler, T = temperature of superheated steam as determined in the trial, t = te to the boiler pressure, Sp Ht = mean specific heat of superheated steam at the pressure and temperature as found in the trial, L = latent heat of one pound of saturated steaes of the Use of Superheated Stea possible by the use of superheated stea in the pri which is at least partially offset by an increase in the fuel consu steam This misconception is due to the fact that the fuel consumption of the boiler is only considered in connection with a definite weight of steaht is to be superheated, an added aned superheater where the combined efficiency of the boiler and superheater will be at least as high as of a boiler alone, the approxiht of stearees_ _Per Cent_ 25 159 50 307 75 438 100 569 150 819 200 1058