MECHANICAL WORK AT A BOUNDARY AND ITS ASSOCIATED EXERGY TRANSFER

This paper is a didactic discussion of mechanical work at a boundary f rom the standpoint of exergy analysis. It is shown that the use of the material velocity vector and the mechanical stress tensor of continuu m mechanics allows the magnitude and direction of the energy flux vect or at a point to be determined unambiguously. Hence, the amount and di rection of the energy transfer at a boundary can be established. This methodology is then extended to the calculation of the associated exer gy flux vector and the exergy transfer at the boundary. It is noted th at the exergy transfer is not always equal to the energy transfer as m echanical work. In general, the exergy transfer also involves a term c onsisting of the product of the environmental pressure and a volume di splacement or transfer.