# Energy Transfer Equation

## Fluid energy transfer

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^{o}C,kJ/kg^{o}K,Btu/lb^{ o}F)

dt = temperature difference (rise or fall) in the substance (^{o}C, K,^{o}F)

### Example - Energy Transfer with Water

*2 kg* of water is heated from *20 ^{o}C* to

*60*. The specific heat of water is

^{o}C*4.2 kJ/kg*. The heat transfered can be calculated as

^{o}C*Q = (2 kg) (4.2 kJ/kg ^{o}C) ((60^{o}C) - (20^{o}C))*

*= 336 kJ*

* **= (336 kWs) (1/3600 h/s)*

* = 0.093 kWh *

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