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Experimental and theoretical investigations of falling film evaporation

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Abstract

In this study, a mathematical model was developed for falling film evaporation in vacuum using heat transfer relations. An experimental device was designed. experimental set-up which was used was equipped with a triangular weir distribution device and it had the ability to record data up to 3 m. Experiments were performed in a single-effect process with sucrose–water solution varying from 3 to 20% concentration rate of sucrose and we used a vertical tube evaporator with the dimensions of laboratory scale. The model that was developed considers convection, shear stress, viscosity and conjugate heat transfer while most of the previous works ignored these factors. The main factors influencing the heat transfer mechanism performance of the unit were investigated and analyzed. We concluded that the experimental studies are verified by the developed model. Furthermore, it was also concluded that, the heat transfer is affected by the mass flow rate, sucrose concentration rate in solution, film thickness and pressure.

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Abbreviations

A :

Area (m2)

c :

Concentration (kg/kg)

d :

Thickness, diameter (m)

f :

Interfacial friction factor

g :

Gravity (m/s2)

h :

Heat transfer coefficient (W/m2 K)

h :

High (m)

i :

Enthalpy (kJ/kg)

k :

Heat transfer coefficient (W/m K)

Ka :

Kapitza number

l :

Characteristic length (m)

\( \dot{m} \) :

Mass flow rate (kg/s)

Nu :

Nusselt number

Pe :

Peclet number

Pr :

Prandtl number

q :

Heat flux (W/m2)

Q :

Heat (W)

Re :

Reynolds number

t :

Time (s)

T :

Temperature (°C)

U :

Overall heat transfer coefficient (W/m2 K)

V :

Velocity, liquid film velocity (m/s)

\( \dot{V} \) :

Volumetric rate (m3/s)

W :

Length (m)

μ:

Dynamic viscosity (Pa s)

ν:

Kinematic viscosity (m2/s)

τ:

Shear stress (N/m2)

ρ:

Density (kg/m3)

\( \delta \) :

Film thickness (m)

\( \alpha \) :

Heat transfer coefficient (W/m2 K)

\( \lambda \) :

Heat transfer coefficient (W/m K)

1:

Inlet

2:

Outlet

b :

Boiling

c :

Condensation

e :

Evaporation

f :

Saturated liquid

fg :

Difference in property between saturated liquid and saturated vapor

i :

Interface

l :

Loss, liquid

s :

Steam, sugar

v :

Vacuum

w :

Wall, water

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Acknowledgments

This project was financed by Kromel Mak. San. A. Ş. Turkey and Sakarya University BAPK.

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Authors and Affiliations

  1. Mechanical Engineering Department, Faculty of Engineering, Sakarya University, 54187, Sakarya, Turkey

    Hüseyin Pehlivan & Mustafa Özdemir

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  1. Hüseyin Pehlivan
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  2. Mustafa Özdemir
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Correspondence to Hüseyin Pehlivan.

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Pehlivan, H., Özdemir, M. Experimental and theoretical investigations of falling film evaporation. Heat Mass Transfer 48, 1071–1079 (2012). https://doi.org/10.1007/s00231-011-0962-x

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