APPENDIX 2: Useful Formulas (Thermodynamics)

1. Thermal power P_t produced by a circulating fluid with a flow rate q [kg/s], whose temperature increases from T₁ to T₂:

   Pt=csq(T2-T1)

   [W]

   where c_s is the specific heat of the fluid under consideration (Jkg^-1°C^-1); the problem is exactly the same when the opposite situation is considered (a fluid that cools down, thereby changing its temperature from T₂ to T₁).

2. Calculating the thermal energy E_t created in a period of time t:

   Et=Ptt

   [J]

3. The thermal energy E_t of a fluid or solid of mass m [kg] at a temperature T with respect to a reference temperature T_r [°C]:

   Et=csm(T-Tr)

   [J]

   For c_s, see point a).

4. Thermal power P_t transmitted by an environment at temperature T₁ to an environment at temperature T₂>T (the two environments are separated by a wall with a surface area of S [m²] and thermal conductivity k [Wm^-2°C^-1]):

   Pt=kS(T2-T1)

   [W]

   for calculation of the energy see point b).