Why do we have winter heating? S.J.T.U. Phase Transformation and Applications We suppose,to correspond to the actual state of affairs,that the pressure of the air in a room always equals that of the external air.In the usual notation,the energy is,per unit mass, u=C,T Then the energy content is,per unit volume, u C.pT SJTU Thermodynamics of Materials Spring2006©X.J.Jin IntroductionPhase Transformation and Applications S. J. T. U. SJTU Thermodynamics of Materials Spring 2006 © X. J. Jin Introduction Why do we have winter heating? We suppose, to correspond to the actual state of affairs, that the pressure of the air in a room always equals that of the external air. In the usual notation, the energy is, per unit mass, TCu = v Then the energy content is , per unit volume, = vρTCu