Energy Transfer Equation

The energy transfered with a substance can be expressed as

Q = m c_p dt                                   (1)

where

Q = quantity of energy transferred (kJ, Btu)

m = mass of substance (kg, lb)

c_p = specific heat of the substance (kJ/kg^oC, kJ/kg^oK, Btu/lb^oF)

dt = temperature difference (rise or fall) in the substance (^oC, K, ^oF)

Example - Energy Transfer with Water

2 kg of water is heated from 20 ^oC to 60 ^oC. The specific heat of water is 4.2 kJ/kg^oC. The heat transfered can be calculated as

Q = (2 kg) (4.2 kJ/kg^oC) ((60 ^oC) - (20 ^oC))

= 336 kJ

         = (336 kWs) (1/3600 h/s)

         = 0.093 kWh   

• Energy Stored in Heated Water - kWh