**Subscripts**

*h*: Heat transfer coefficient (kW m-2 K‐1

26 Heat Exchangers– Advanced Features and Applications

)

*M: Molecular weight (*kg kmol‐1

Re: Reynolds number, Re *GD*

*i*: Enthalpy (kJ kg‐1

*L*: Tube Length (m)

*n*: Number of data *p*: Pressure (kPa)

*Q*: Electric power (kW) *q*: Heat flux (kW m-2)

*RMS:* Root mean square

*m* : Mass flow rate (kg s‐1

*X*: Lockhart‐Martinelli parameter

*T*: Temperature (K)

*x*: Vapour quality

**Greek letters**

*α*: Void fraction

*ρ*: Density (kg m‐3

ϕ2

*σ*: Surface tension (N m‐1

*z*: Length (m)

)

<sup>1</sup> MD d d 100 / d

)

)

)

æ ö = -´ ç ÷

*pp p*

*MD*: Mean deviation, (( pred exp ) exp ) 1

è øå

*n*

)

m=

)

Δ*i*: The enthalpy rise across the tube (kJ kg‐1

)

(d*p*/d*z F*): Pressure gradient due to friction (N m-2m‐1

*µ*: Dynamic viscosity (N s m-2)

)

: Two‐phase frictional multiplier

**Gradients and differences**

(d*p*/d*z*): Pressure gradient (N m-2 m‐1

*n*

crit: Critical point

exp: Experimental value

