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Modelling and simulation of a pillow plate thermosiphon reboiler

  • Robert Goedecke
  • Stephan Scholl
Original
  • 34 Downloads

Abstract

Thermosiphon reboilers are the most widely used evaporators in the process industry. Experimental studies suggested a superior performance of pillow plate thermosiphon reboilers over conventionally used tubular designs. This contribution presents a comprehensive model to simulate fluid dynamic as well as thermal performance of pillow plate thermosiphon reboilers. Experimental heat transfer coefficients are extracted from measurements at a thermosiphon reboiler test rig. With this information, correlations for the single phase heat transfer coefficient and the heat transfer coefficient with nucleate boiling as well as convective boiling are presented. A correlation for the heat transfer coefficient for film condensation inside the pillow plate and the two-phase pressure drop between the pillow plates is presented. These correlations are implemented in a modular structured simulation program. Good agreements were shown for the heat transfer with water experiments. The fluid dynamic could be described satisfactory with larger uncertainties at small circulation rates.

Nomenclature

A

Area (m2)

cp

Spec. heat capacity (J kg−1 K−1)

dh

Hydraulic diameter (m)

f

Darcy friction factor (−)

H

Height (m)

h

Heat transfer coefficient (W m−2 K−1)

hB

Flow boiling heat transfer coefficient (W m−2 K−1)

hCB

Convective boiling heat transfer coefficient (W m−2 K−1)

hNB

Heat transfer coefficient at nucleate boiling (W m−2 K−1)

hs*

Submergence ratio (%)

L

Length (m)

\( {\dot{m}}_C \)

Mass flow working fluid

ns

Number of plates

Nu

Nusselt number (−)

pOP

Operation pressure (Pa)

Pr

Prandtl number (−)

Heat flow (W)

Heat flux (W m−2)

s

Mean wall thickness (m)

rcr

Critical radius (m)

Ra

Arithmetic mean roughness (m)

Re

Reynolds number (−)

T

Temperature (K)

T*

Temperature (°C)

Tpinch

Pinch temperature (K)

Tsat

Saturation temperature (K)

u

Flow velocity (m s−1)

U

Overall heat transfer coefficient (W m−2 K−1)

W

Pillow plate width (m)

x

Vapor mass fraction (kgvapor/kgtotal)

xW

Water mole fraction (molwater/moltotal)

X

Lockhardt-Martinelli parameter

Greek symbols

Γ

Coefficient for equation 18

Δp

Pressure drop (Pa)

ΔT

Temperature difference (K)

λ

Thermal conductivity (W m−1 K−1)

μ

Dynamic viscosity (kg m−1 s−1)

ρ

Density (kg m−3)

ρ’

Liquid density at saturation temperature (kg m−3)

ρ’

Gas density at saturation temperature (kg m−3)

Subscripts

a

Acceleration

c

Condensate

cor

Correlated

EZ

Evaporation zone

exp

Experimental

F

Flow

f

Friction

g

Hydrostatic

HS

Heating section

HZ

Heating zone

I

Inner

in

Inlet

int

Integral

l

Liquid

LO

Liquid only

o

Outer

out

Outlet

OV

Overall

sim

Simulation

v

Vapor

w

Wall

W

Width

Notes

Acknowledgements

Financial support by the “Bundesministerium für Bildung und Forschung” within the collaborative research project “Innovative equipment and plant concepts for increased efficiency of production processes – InnovA2” (033RC1013A) is gratefully acknowledged.

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Institute for Chemical and Thermal Process Engineering (ICTV)Technische Universität BraunschweigBraunschweigGermany

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