Popular Science Monthly/Volume 16/January 1880/Correspondence
A RECENT issue of your "Monthly" contained a criticism, by Mr. J. W. Cloud, of some points in my paper on "Wasted Forces" published in yours of July, in which it is alleged I am in error. I had intended replying at once to this criticism, but have been prevented until now by circumstances. My critic makes the point that, in my attempt to account for the low duty of the steam-engine, I have ignored one of the chief elements of the problem, namely, "the low efficiency of the medium."
To this criticism I beg to reply that for the purpose of showing the margin for possible improvement in engines, whether deriving their motive power from steam or any other medium, the only elements entering into the problem are those I have named in my article, to wit: 1. The amount of work that should be given out, and which is the equivalent of the number of heat-units imparted to the medium by the combustion of the fuel; and, 2. The amount of work actually realized. The difference is the loss, and this loss is due not to "the low efficiency of the medium," but to the low efficiency of the machine.
To make myself quite plain, I will add my understanding of what a perfect engine should be. The perfect engine, hypothetically stated, is an apparatus that will utilize all the heat-units evolved by the complete combustion of fuel in the generator in the generation of steam; that will use all the steam that the generator supplies, converting it into water in so doing; that will put that water back again into the generator whence it came; and that will give out during a given time an amount of work that shall be the equivalent of the number of heat-units that have disappeared during that time.
I confess my inability to perceive what the question of latent or sensible heat has to do with the problem; and, in view of the fact that my critic has taken the pains to warn the readers of the "Monthly" that my statements might give false impressions, I wish to reaffirm the strict correctness of the theoretical view I have advanced; and to assert, my critic to the contrary notwithstanding, that the difficulties in the way of increasing the duty of the steam-engine to a very close approximation to that which theory calls for are purely of a mechanical nature, and therefore not beyond the power of mechanical science to overcome.
This is the gist of the matter, and I take direct issue with my critic in denying that the element of the high latent as compared with the low sensible heat of the medium, whether it be steam or any other, that is used, is the impassable barrier to future improvement that he would make it appear.
On another point that my critic makes, namely, that I throw too much of the responsibility of the low duty of the steam-engine on the generator, I have no hesitation, after further inquiry into the subject, to yield to him, and to admit that fifty per cent, would have been nearer the truth than twenty-five per cent., which I gave in my paper. I gave that figure simply as an opinion derived from a practice that is exceedingly variable and complex, and therefore liable to wide differences of result.
|William H. Wahl.|