Fluid will flow with the energy, the form of these energies are kinetic energy, potential energy and thermal energy. Figure 1 will show balance energy of fluid that occurs.
If the potential energy and kinetic energy are ignored, then the fluid flow is only affected by thermal energy which is possessed by fluid. If fluid flow has different temperatures with the surrounding environment, it the heat transfer will happen so temperature of fluid will change. This heat transfer can occur by convection, conduction, or radiation.
In general, the amount of energy transfer is formulated as follows:
Q = m cp (T2 - T1)
The rate of energy which is transferred by convection is formulated as:
Q = h A (T2 - T1)
h = coefficient of heat which is transfer by convection (W/m2K)
The rate of energy which is transferred by conduction is formulated as:
Q = k A (T2 - T1) / x
k = thermal conductivity (W/mK)
The rate of energy which is transferred by radiation is formulated as:
Q = ε A σ (Ts4 - Tsur4)
ε = emissivity (0 <ε <1)
σ = Stefan-Boltzmann constant (5.67 E-8 W/m2K4)
Ts = Surface temperature (K)
Tsur = surrounding temperature (K)