Thermodynamics ENERGY, WORK, AND HEAT Another type of heat is called latent heat.  Latent heat is the amount of heat added to or removed from  a  substance  to  produce  a  change  in  phase.    When  latent  heat  is  added,  no  temperature change occurs.   There are two types of latent heat.   The first is the latent heat of fusion.   This is the amount of heat added or removed to change phase between solid and liquid.   The second type  of  latent  heat  is  the  latent  heat  of  vaporization.    This  is  the  amount  of  heat  added  or removed to change phase between liquid and vapor.  The latent heat of vaporization is sometimes called the latent heat of condensation. Different substances are affected to different magnitudes by the addition of heat.  When a given amount of heat is added to different substances, their temperatures increase by different amounts. The ratio  of  the  heat (Q)  added to  or  removed from  a  substance to  the change  in  temperature (DT) produced is called the heat capacity (C_p) of the substance.  The heat capacity of a substance per unit mass is called the specific heat (c_p) of the substance.   The subscript p indicates that the heat capacity and specific heat apply when the heat is added or removed at constant pressure. (1-17) C_p Q DT c_p Q mDT c_p q DT where: C_p = heat capacity at constant pressure (Btu/°F) c_p = specific heat at constant pressure (Btu/lbm-°F) Q = heat transferred (Btu) q = heat transferred per unit mass (Btu/lbm) m = mass (lbm) DT = temperature change (°F) One lbm of water is raised 1°F and one Btu of heat is added.  This implies that the specific heat (c_p) of water is one Btu/lbm-°F.   The c_p of water is equal to one Btu/lbm-°F only at 39.1°F. By rearranging Equation 1-17 we obtain Q = mc_pDT, which is used to calculate latent heat.   By substituting mass flow rate in lbm/hr, , for m, we obtain .   This equation is used m Q mc_pDT to calculate heat transfer in Btu/hr and will be useful in later chapters. Rev. 0 Page 21 HT-01