6. NOMENCLATURE

The following is the nomenclature in the International System (SI) of different equations relating to heat exchangers. It must be said, is not strictly necessary to use this nomenclature, but if that match all units. If the temperature is in degrees Celsius (° C), the expression of temperature will be in lowercase (Ex: t₁₀):

Ai	Area inside the inner tube (m2)
A0	Area outside the inner tube (m2)
∆Hphase change	Enthalpy of the fluid to phase change (J/Kg)
∆T1	Difference of temperatures of hot fluid (1) (∆K)
∆T2	Difference of temperatures of cold fluid (2) (∆K)
∆Tlog	Difference of temperatures logarithmic (∆K)
∆Tm	Difference of temperatures logarithmic means (∆K)
C1	Total heat capacity of hot fluid (1) (J/K)
C2	Total heat capacity of cold fluid (2) (J/K)
Cp1	Heat capacity of hot fluid (1) (J/Kg·K)
Cp2	Heat capacity of cold fluid (2) (J/Kg·K)
ε	Epsilon
F	Factor de correction
hi	Convection coefficient inside of the hot fluid (1) (W/m2K)
ho	Convection coefficient outside of the cold fluid (2) (W/m2K)
k	Thermal conductivity of tube material (W/m·K)
k'	Thermal conductivity of the resistance (W/m·K)
L	Pipe length (m)
NTU	Number of Transfer Units
P	The value of the factor graph F
q	Heat is transmitted from one to another fluid (J/s)
R	The value of the factor graph F
Ri	Internal resistance due to fouling of the hot fluid (1) (m2·K/W)
R0	Resistance due to fouling of the outer cold fluid (2) (m2·K/W)
T1i	Initial temperature of the hot fluid (1) (K)
T10	Final temperature of the hot fluid (1) (K)
T2i	Initial temperature of the cold fluid (2) (K)
T20	Final temperature of the cold fluid (2) (K)
Ui	Convection coefficient referred to the internal area (J/s·m2K)
U0	Convection coefficient referred to the external area (J/s·m2K)
W1	Mass flow of hot fluid (1) (Kg/s)
W2	Mass flow of cold fluid (2) (Kg/s)
x	Thickness of the resistance (m)
Z	Value of the graph ε-NTU