OPINIONS . FROM OTHERS.
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The Editor invites correspondence on ail subjects connected with the use of commercial motors. Letters should be on one side of the paper only and typewritten by preference. The right of abbreviation, is reserved, and no responsibility for
. views e.tpressed is accepted.
Steam Vehicle Developments.
The Editor, THE COMMERCIAL MOTOR.
[1,704] Sir,—I should be obliged if you would allow me to reply to kr. T. Ciarkeon's kindly criticism appearing in your issue of January 6th of my article on the above subject in your issue of Decem her 16th last.
In the first place, I should like to say that I have followed with great interest Mr. Clarkson's efforts to evolve a steam motor wagon which will successfully operate on coke fuel. It was not my intention to offer any misleading or inaccurate statements, but to put forward a criticism of what appears to me to be a fundamental defect in the most critical furiction of a steam' boiler.
I think Mr. Clarkson will agree that the most vital function of any steam boiler is circulation of the water.
Professor Osborne Reynolds, the Literary and Philospephical Society of. Manchester in 3874, entitled " On the Extent and Ate
tion of the Heating Sur,Hot Water\ face for Steam Boilers, '
M.A., in a paper to stated: "The heat carried oil by ,any fluid from a surface, apart from the effect of radiation, is proportional to the internal diffusion of the fluid at .and near the surface, i.e.,, is proportional to the rate at which the particles or molecules pass backwards _ and forwards from the surface to any given depth within the fluid. . . . • " Now the rate of this diffusion has been shown . . . to depend on two • things.:— " (1) The natural internal diffusion of the fluid when at rest.
. "(2) The eddies caused by visible motion which mixes the fluid up and continually brings fresh particles into contact with the surface.
"The first; of these A section of the Field tube causes is independent of showing inner tube c.nd the velocity of the fluid, water chaeation.
. . . . so that it may be
said to depend only on the nature of the fluid. "The second cause, the effect a eddies, arises entirely from the motion of the fluid, . . . . and is proportional to the velocity with which it flows past the surface."
The first cause is the same for all boilers using water, but the second clearly demonstrates the importance of rapid and continuous circulation. With thimble tubes, as stated by Mr. Clarkson, the initial action is the flowing of the water in and out of the tube in a double stream which continues until boiling point:is reached. Then, as steam commences to form, the action is checked until it is stopped en_ tirely, to allow the steam formed in the tube to escape. After the steam has escaped. water flows in again, and the-action proceeds, as before, in pulsations.
Apparently there is a continuous struggle between • e56 the water entering the tube and the steam issuing from it.
In these circumstances, it follows' that the second condition laid down by PrOfeaScr Reynolde is notfulfilled. The circulation is slow and intermittent, and, therefore, the number of particles which pass the heating surface is considerably reduced.
Again, as Mr. Clarkson is no doubt aware, thimble tubes were used very extensively in the "Field ". boiler ; but in this case the tubes were vertical and. contained an inner tube, as shown in the illustration..
Quoting from Professor Perry's book on "The Steam Engine ": "if these tubes were ordinary tubes, the water in them would get very hot and would occasionally burst out with violence, and this would form one of the very worst possible contrivances for heat-. ing 'water. In truth, however, there is an inner tube, so that the hot water rises in the outer space' and the cold water comes down the central tube, the circulation being very rapid."
It would be interesting to know whether Mr. Clark. son has tried central tubes in his thimble tubes.
It is impossible to. give anything like a complete. thesis of steam generation, without encroaching too much on your valuable space, but the following have long been accepted as ideal points in steam boiler design:—
Complete and rapid circulation of all the water in the boiler.
Water to flow in the opposite direction to the heatleg gases.
The streams of water to be as small as possible, and not to interfere with one another.
Ample water surface to give dry steam, Hot gases to be cooled down as low as possible before leaving the boiler.
Rapid circulation will also have the same cleansing action as the pulsating circulation described by Mr. Clarkson, and in a greater degree, according to the velocity of circulation.
With regard to forcing, my point was that it interferes with circulation, and was not intended to imply any mechanical defect, such as tube leakage.
I should like to add that I have never seen any figures published giving the result of 'a test with the " Clarkson " boiler ; these would, no doubt, be very interesting.--Yours faithfully, T. A. JONES.
Manufacturers and the Moulders.
/1,7051 Sir,—Although a lot of people have had their say about the moulders' strike and its effect on indnstry, few, if any, have mentioned, or prophesied, the after effeets on the British foundry trade, and through it on the moulders themselves.
As a manufacturer, until the moulders' strike almost paralysed the industry, I patriotically resolved to purchase castings obtained from British firms rather than to obtain thsse from tbs rontinent, in spite of the fact that castings suitable for the motor trade can be obtained from the Continent at, roughly, two-thirds of the cost of Brit'sh castings. This resolve, however, the moulders' strike has forced me to reconsider, and, even after the strike is finished, I. and probably a number of other manufacturers, will continue to contract for foreign castings and not rely on the whim of one section of tradesmen, who, for the sake of a few shillings a week, will probably sacri.6ce in the future a considerable ainennt in excess. of Chia by giving an opening to fercign competition, which they will find very diffieelt, to oust, as the quality of castings produced on the Continent is quito as e•orvl, and in some cases better than the quality
sastings produced in this conntrv.—Yours