2–28 Consider a medium in which the heat conduction equation is given in its simplest form as 1 ???? ???? ???? ???? ???? ???? ???? ???? ???? ???? + ???? ? gen = 0 (a) Is heat transfer steady or transient? (b) Is heat transfer one-, two-, or three-dimensional? (c) Is there heat generation in the medium? (d) Is the thermal conductivity of the medium constant or variable?