Subscripts

1 Inlet

m\_ <sup>h</sup> Mass flow rate of the hot fluid, kg/s N Actual transverse distance, mm

88 Heat Exchangers– Advanced Features and Applications

NTU Number of transfer unit

Pf Perimeter of the fin, m Pr Prandtl number

Re Reynolds number

T Temperature, °C

Tp Tube pitch, mm Tw Wall temperature, °C

St Stanton number

Greek letters

ε Effectiveness η Flow efficiency

η<sup>f</sup> Fin efficiency

ρ Density, kg/m3

υ Kinematic viscosity, m2

Q\_ Average heat transfer rate, W

Q\_ <sup>c</sup> Heat transfer rate of the cold fluid, W Q\_ <sup>h</sup> Heat transfer rate of the hot fluid, W Q\_ max Maximum heat transfer rate, W

Tc,<sup>i</sup> Inlet temperature of the cold fluid, °C Tc, <sup>o</sup> Outlet temperature of the cold fluid, °C

Th,<sup>i</sup> Inlet temperature of the hot fluid, °C Th, <sup>o</sup> Outlet temperature of the hot fluid, °C

u Free velocity of the external fluid, m/s umax Maximum velocity of the external fluid, m/s U Overall heat transfer coefficient, W/(m<sup>2</sup>

UA Overall thermal conductance, W/°C

δ Thickness of the fin material, mm δ<sup>t</sup> Thickness of the flat tube material, mm

η<sup>c</sup> Surface effectiveness of the cold side

/s

ReLp Reynolds number based on the louver pitch

ΔTm Logarithmic mean temperature difference, °C

Th Parameter with the tube pitch and the major tube diameter: Tp−Dm, mm

°C)

P Pressure, Pa

