- #1

Juanda

- 299

- 102

I was checking the book THERMODYNAMICS AN ENGINEERING APPROACH (the 2023 version) because I saw it recommended on the internet.

I was surprised to find an error in one of their examples because it is already on the 10th edition. I'm pretty sure about the error but I wanted to confirm it with someone else and maybe contact the writers if necessary and if possible.

I am attaching a picture with the wrong example. It is on page 154, unit 4, example 4-4.

The error is born from the definition of the initial state of the system. For context, the pressure of the gas must always be the same as the pressure at the face of the piston (boundary conditions and quasi-equilibrium states). However, in the initial state, it declares the force of the spring is 0 while the pressure in the cylinder is 200 kPa. As a result, later on, they obtain a different number for the energy accumulated in the spring and the work done by the gas which is impossible since all that work will be accumulated as potential energy in the spring.

It is especially surprising to me such an error appears in the book because they are showing the difference in work from the gas and energy in the spring which is not possible so I consider it boils down to a lack of fundamentals. I understand errors are something to be expected with books this long but I would imagine such a mistake would be solved by the 10th edition so I am doubting myself a little.

For the problem to be correct, the force of the spring at the initial state cannot be 0. In fact, its value can be obtained from the provided data and it should be 50kPa (F = P*A). Once doing so, the work done by the gas is the same as the potential elastic energy accumulated by the spring.

Do you also think the book is mistaken?

Do you know how to contact the writers about it?BR