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"CONTRIBUTIONS TO THERMODYNAMICS: THE SPECIFIC HEAT OF AN IDEAL GAS," BY J. McQUIRG WORDEN WARlNG Arthur D. Little. Inc., Cambridge, Massachusetts
I HAVE been asked to comment on Dr. McQuirg's and since dU and dT are both negative, C , is finite work.' Although I find it interesting, I do not agree and positive. If the steady state is isothermal, dq is positive and equals dw, and dU and d T each equal with his conclusions. Consider fist his discussion of the minimum specific zero; once again (as we know) C , is both finite and heat of an ideal gas. When a fluid flows through a pipe, positive. the effects of viscosity and turbulence tend to slow it In discussing the maximum specific heat, Dr. Mcdown. Exactly because of these, energy is required to Quirg uses the relation dU = C&T for an ideal gas, maintain the flow: the pressure driving the fluid de- but this does not include any kinetic energy term. If creases regularly along the pipe as the directed kinetic we are going to accelerate the gas and consider its energy is converted into vortices and ultimately to ran- kinetic energy as part of the internal energy, we should dom thermal motion. write dU = C,dT 1/2d(mv2)with appropriate conDr. McQuirg is in error in stating that "the net work version of units. Then dq = 0, dT = 0, and dU = done is p2& - p,K." Although this is true for the - dw = 1/2d(mv2). The fact that dU is greater than classical porous plug experiment, it is not true here zero depends not on C , and d T but on dv, the velocity because a particular mass of gas is not forced into, or increase.
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