Group Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Title: 13.7.1 - A new Microstructure Design for Evaporation and Superheating
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 Material Information
Title: 13.7.1 - A new Microstructure Design for Evaporation and Superheating Boiling
Series Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Physical Description: Conference Papers
Creator: Maikowske, S.
Anurjew, E.
Hansjosten, E.
Schygulla, U.
Brandner, J.J.
Publisher: International Conference on Multiphase Flow (ICMF)
Publication Date: June 4, 2010
 Subjects
Subject: evaporation
microstructure
phase transition
superheating
 Notes
Abstract: Evaporation of liquids is of major interest for many fields in process engineering. One of these is chemical process engineering, where evaporation of liquids and generation of superheated steam is mandatory for numerous processes. Generally, this is performed by use of classical pool boiling and evaporation process equipment providing often limited performance. Due to the advantages of microstructure devices especially in chemical process engineering (see e.g. Brandner et al. (2007)) the interest in microstructure evaporators and steam generators has been increasing through the last decade. Micro channel heat exchangers have been designed, manufactured and tested at the Institute for Micro Process Engineering of the Karlsruhe Institute of Technology for more than 15 years. Starting with the famous Karlsruhe Cube described, amongst others, by Brandner (2008), not only conventional heat transfer between liquids or gases have been theoretically and experimentally examined but also phase transition from liquids to gases (evaporation, Brandner et al. (2006a)), partly also condensation from gases to liquids. To obtain more information onto the evaporation process itself, an electrically powered device for optical inspection of the microstructures and the processes inside has been designed and manufactured (see e.g. Brandner et al (2006), Henning et al. (2004), Henning et al. (2005)). Exchangeable metallic micro channel array foils as well as an optical inspection of the evaporation process via a high-speed video camera have been integrated into this test system. Fundamental research on the influences of the geometry and dimensions of the integrated micro channels, the inlet flow distribution system geometry as well as the surface quality of the micro channels have been performed. While evaporation of liquids in crossflow and counterflow or co-current flow micro channel devices is possible, it is, in many cases, not possible to obtain superheated steam due to certain boundary conditions. Some theoretical background to this is given by Bosnjakovic (1998). Thus, a new design was proposed to obtain complete evaporation and superheating of the generated steam. This microstructure evaporator consists of a concentric arrangement of semi-circular walls or semi-elliptic walls providing at least two nozzles to release the generated steam, taking care for the volume increase while the evaporation takes place. Results of evaporation inside circular blanks will be presented. A maximum power density of 1400 kW ⋅ m-2 has been transferred using similar systems, while liquid could be completely evaporated and the generated steam superheated. It could also be shown that the arrangement in circular blanks acts as a micro mixer and, therefore, enhances the evaporation. Aside of the experimental results obtained with different microstructure devices, examples for possible applications in laboratory and industry will also be presented briefly.
General Note: The International Conference on Multiphase Flow (ICMF) first was held in Tsukuba, Japan in 1991 and the second ICMF took place in Kyoto, Japan in 1995. During this conference, it was decided to establish an International Governing Board which oversees the major aspects of the conference and makes decisions about future conference locations. Due to the great importance of the field, it was furthermore decided to hold the conference every three years successively in Asia including Australia, Europe including Africa, Russia and the Near East and America. Hence, ICMF 1998 was held in Lyon, France, ICMF 2001 in New Orleans, USA, ICMF 2004 in Yokohama, Japan, and ICMF 2007 in Leipzig, Germany. ICMF-2010 is devoted to all aspects of Multiphase Flow. Researchers from all over the world gathered in order to introduce their recent advances in the field and thereby promote the exchange of new ideas, results and techniques. The conference is a key event in Multiphase Flow and supports the advancement of science in this very important field. The major research topics relevant for the conference are as follows: Bio-Fluid Dynamics; Boiling; Bubbly Flows; Cavitation; Colloidal and Suspension Dynamics; Collision, Agglomeration and Breakup; Computational Techniques for Multiphase Flows; Droplet Flows; Environmental and Geophysical Flows; Experimental Methods for Multiphase Flows; Fluidized and Circulating Fluidized Beds; Fluid Structure Interactions; Granular Media; Industrial Applications; Instabilities; Interfacial Flows; Micro and Nano-Scale Multiphase Flows; Microgravity in Two-Phase Flow; Multiphase Flows with Heat and Mass Transfer; Non-Newtonian Multiphase Flows; Particle-Laden Flows; Particle, Bubble and Drop Dynamics; Reactive Multiphase Flows
 Record Information
Bibliographic ID: UF00102023
Volume ID: VID00335
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: 1371-Maikowske-ICMF2010.pdf

Full Text


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


A new Mlicrostructure Design for Evaporation and Superheating


Stefan Maikowske, Eugen Anurjew, Edgar Hansjosten,
Ulrich Schygulla and Juergen J. Brandner

Karlsruhe Institute of Technology, Institute for Micro Process Engineering, Thermal Micro Process Engineering,
Campus North, Hermann-von-Helmholtz-Platz 1, Eggenstein-Leopoldshafen, D-76344, Germany
juergen.brandner akit.edu


Keywords: evaporation, microstructure, phase transition, superheating




Abstract

Evaporation of liquids is of major interest for many fields in process engineering. One of these is chemical process engineering,
where evaporation of liquids and generation of superheated steam is mandatory for numerous processes. Generally, this is
performed by use of classical pool boiling and evaporation process equipment providing often limited performance. Due to the
advantages of microstructure devices especially in chemical process engineering (see e.g. Brandner et al. (2007)) the interest in
microstructure evaporators and steam generators has been increasing through the last decade.
Micro channel heat exchangers have been designed, manufactured and tested at the Institute for Micro Process Engineering of
the Karlsruhe Institute of Technology for more than 15 years. Starting with the famous Karlsruhe Cube described, amongst
others, by Brandner (2008), not only conventional heat transfer between liquids or gases have been theoretically and
experimentally examined but also phase transition from liquids to gases (evaporation, Brandner et al. (21is in,l!!, partly also
condensation from gases to liquids.
To obtain more information onto the evaporation process itself, an electrically powered device for optical inspection of the
microstructures and the processes inside has been designed and manufactured (see e.g. Brandner et al (2006),
Henning et al. (21 r'4), Henning et al. (2005)). Exchangeable metallic micro channel array foils as well as an optical inspection
of the evaporation process via a high-speed video camera have been integrated into this test system. Fundamental research on
the influences of the geometry and dimensions of the integrated micro channels, the inlet flow distribution system geometry as
well as the surface quality of the micro channels have been performed. While evaporation of liquids in crossflow and
counterflow or co-current flow micro channel devices is possible, it is, in many cases, not possible to obtain superheated steam
due to certain boundary conditions. Some theoretical background to this is given by Bosnjakovic (1998). Thus, a new design
was proposed to obtain complete evaporation and superheating of the generated steam. This microstructure evaporator consists
of a concentric arrangement of semi-circular walls or semi-elliptic walls providing at least two nozzles to release the generated
steam, taking care for the volume increase while the evaporation takes place.
Results of evaporation inside circular blanks will be presented. A maximum power density of 1400 kW m-2 has been
transferred using similar systems, while liquid could be completely evaporated and the generated steam superheated. It could
also be shown that the arrangement in circular blanks acts as a micro mixer and, therefore, enhances the evaporation. Aside of
the experimental results obtained with different microstructure devices, examples for possible applications in laboratory and
industry will also be presented briefly.


Introduction

Microstructured devices have become increasingly
important in thermal and chemical process engineering
within the last years. These devices are often made out of
micro structured metal foils, which are connected by
diffusion bonding (see Brandner (2008),
Brandner et al.(2006)). The hydraulic diameters of the
micro channels, generated by precision machining or wet
chemical etching, are in the range of a few hundred
nucrometres.
Metallic microstructured devices provide high pressure
resistance and small residual volumes. Due to the size of the
microstructures they act as flame arresters or explosion


barriers; thus they are well suited to handle dangerous or
explosive fluids (see e.g. Schubert et al. (2001), Goedde et
al. (2009)). The small dimensions of micro channels enable
very high surface-to-volume ratios up to 30 000 m2 m-3
which are about one or two orders of magnitude higher than
those of conventional process engineering equipment
devices. Moreover, the distances for heat and mass transfer
are in the range of the diffusion length of the fluids, as
explained by Brandner (2008) or Brandner et al. (2006).
Therefore, microstructured devices are well suited for
operations dealing with high heat fluxes and rapid mass
transfer like evaporation.
Phase transition and multiphase flow in macro channels
have been intensively investigated and are well known and






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

Several experiments with those devices showed that
evaporation of water is possible, using hot thermo oil in the
heating passage of the device. However, total evaporation
was hard to obtain, wet steam was generated containing
very high percentage of droplets, and no superheating could
be performed. This was, at least partly, due to short
residence time of the fluid and limited temperature of the
heating side. Thus, electrically powered micro heat
exchangers have been developed, manufactured and tested
to provide higher temperatures with good controllability of
the power supplied. These devices have been described in
details by Henning et al. (21***4) and Henning et al. (2007).
With these devices, not only straight rectangular micro
channels but also semi-elliptic micro channels in convoluted
or sinusoidal arrangements have been tested for evaporation.
Figure 2 shows an electrically powered rod evaporator. This
device provides good evaporation performance
independently of the direction of the steam outlet.


understood. In micro channels, phase transition, related
phenomena and multiphase flow have been partially
investigated (see e.g. Thome (2006)). Many results
presented so far have been obtained with single micro
channels, sometimes multi-micro channel arrays have been
investigated for their behaviour in evaporation. However,
results about the phenomena occurring in multi micro
channel arrays are often not consistent, depending on the
experimental setup, the fluid looked at and the measurement
methods. Moreover, in most cases researchers do not take
care for the volume increase while the fluid is transferred
from the liquid to the gas phase. Thus, microstructure
devices taking this effect into account should provide better
performance in terms of phase transition than the simple
micro channel devices.

Nomenclature


mass flow (kg h ')
pressure (N m-2)
Time (s)


Greek letters
a heat transfer coefficient (W m-2 K ')
r viscosity (Pa s)

Subsripts
max maximum
turb turbulent


Metallic Multi-Micro Channel Devices


First attempts to evaporate water have been done using
micro channel heat exchangers in crossflow design.
Manufacturing of these devices was described before in
details (see, e.g., Brandner (2008), Brandner et al. (2006) '
Schubert et al. (2001)). Figure 1 shows different examples
for micro channel foils integrated into crossflow or
counter-/co-current flow heat exchangers made of stainless
steel


Figure 2: Electrically
evaporator.


powered micro channel rod


It could be shown by Vittoriosi (2009) and
Knauss et al. (2009) that, depending on the applied mass
flow, either a single microstructure device or a
two-stage-arrangement, which means two devices in a row'
can be used for complete evaporation and superheating of
water and other liquids. Substantial data on the droplet
content contained in the vapour flow could be obtained by a
simple photometer setup. A photo current was measured,
obtained by scattered laser light in full reflection from the
vapour outlet of different arrangements of electrically
powered devices. The amplitude of photo current could
directly be correlated to the droplet content of the vapour as
well as to the vapour temperature, as it is described by
Brandner (2008) and Vittoriosi et al. (2010).


Multi-Micro Channel Device for Visualization of
Evaporation Process

Although evaporation of liquids can be performed
successfully using devices like those described in the
section above, it was still not quite clear which parameters
strongly influence the evaporation process inside a
multi-micro channel system. Numerous research activities
have been done to clarify the evaporation processes taking
place in single micro channels (see e.g. Bauer (2007),
Cortina-Diaz (2008), Chen et al. (2002), Coleman et al.
(1999) or Cubaud et al. (21***4);, but not so many research
activities have been dedicated to multi-micro channel array


I 0~18 BOpm JEOtI 0(1


I -- 600m dEOt


Figure 1: Micro channel structures manufactured in
stainless steel integrated into crossflow or
counter-/co-current flow heat exchangers.






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

100 pLm (depth).
Vapour plugging at channel inlets occurs when existing
vapour bubbles, which have been generated by boiling
inside the inlet void, agglomerate at channel entrances.
These bubbles are temporarily fixed and expand by
capturing small bubbles. The fixed bubbles can partially be
discharged by micro channels when a specific bubble size is
reached. Consequently, channel entrances are temporarily
plugged by bubbles. Figure 4 shows a picture sequence of
plugged channel entrances. Gas fractions inside of these
channel inlets (indicated on the right-hand side of Figure 4)
indicate bubble drainages by micro channels.

Fluid flowv direction





Draining bubbles




t =1.08 s



Chnesplugged
by bubbles



t = 2.16 s



Draining bubbles




Figure 4: Vapour plugging at channel inlets, temperature
is 1000C, the multi-micro channel array is located on the
right side.

Another type of vapour plugging is the plugging inside
micro channels. Rapidly growing bubbles are accompanied
by accelerated bubble-endings and decelerated
bubble-beginnings. If the motion of a bubble beginning
stops due to the bubble-growing, the corresponding micro
channel is temporarily plugged by vapour. Another effect of
this channel-plugging is the reversal of flow direction of
bubble beginnings caused by explosively growing bubbles.
Figure 5 shows a section of a multi-micro channel array at
different time steps. Fluid flow direction is from left to right.
The movement of bubble beginnings in both channels
decreases continually until it stops. At this point
(t = 221 10" s) both channels are temporarily plugged by
stagnant bubble beginnings. Eventually, the bubble
beginnings start moving in the opposite direction to the fluid
flow and thereby transport liquid fluid backwards.


evaporators.
An electrically powered stainless steel frame was
manufactured to allow the exchange of micro channel
structures as well as the optical inspection of the processes
inside the micro channels using high speed videograplw.
More details of the design are given by Brandner (2008) or
Henning et al. (2007). An improved device providing the
same characteristics but better performance is shown in
Figure 3 and was described by Maikowske et al. (2010),
Maikowske et al. (2010a).


Figure 3: Electrically powered microstructure device'
providing exchangeable micro channel foils and a glass lid
for high speed videograplw.

The apparatus design provides the possibility to vary
different parameters like temperature, applied electrical
power, volume flow rate or pressure drop. Additionally,
microstructured metal foils including multi-micro channel
arrays are exchangeable. Thus, phase transition and
multiphase flow in several kinds of different micro channel
geometries and arrangements could be investigated.
The method of visualization by high speed videography has
been applied to perform initial investigations on phase
transition as well as on the dynamics of gas-liquid flows in
narrow channels, as described by Bauer (2007),
Henning et al. (2007), Maikowske et al (2008) or
Maikowske et al. (2010a). The experimental setup used here
contains a microscope in combination with a digital
high-speed camera. The microscope is arranged above the
horizontal multi-micro channel layer. The digital high-speed
camera records pictures at frequencies of up to 200,000
frames per second with very low motion blur. Special
computational algorithms can be used to analyse these
recorded high-speed picture sequences to extract
information about different phases.

Phase Transition Phenomena

Phase transition in micro channels is accompanied by
several phenomena like vapour plugging or vapour slugging.
which occur only to a minor extent or are not available in
macro channels. Two different types of vapour plugging
were observed vapour plugging at channel inlets and
vapour plugging inside of micro channels. All these
observations of evaporation were performed with liquid
water and related steam in micro channels with rectangular
cross-sections in the range of about 200 pLm (width) and









Fluid flow direction





I fl= 4.1 nun a


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

to all micro channels and, therefore, an equal distribution of
the residence time in the evaporation area. Figure 7 shows a
microstructure foil with conventional distribution system on
the left side and a tree-like distribution system on the right
side. Flow direction can easily be changed with this foil.
The reabt-1 hea hyt was tsted, and nas expected,d the
drastically changed to a phase transition front more or less
perpendicular to the streamline and the micro channel
direction.


t= 70 s


t = 7110 10- s

t =147 10- s

t =184 10; s
t = 221 105 s

t = 294 10.3 s

t = 331 10-' s


Figure 7: Multi-micro channel foil providing a standard
flow distribution void (left) and a tree-like distribution
system (right). Evaporation takes place in a three-staged
multi-micro channel array (center).

The tree-like structure is designed for branching of the flow
into sub-flows providing the same hydrodynamic properties
at any position in the distribution system. Aside of this, the
micro channel arrays are separated into three stages with
connecting voids in between to allow evaporation and
superheating.
It could be shown by CFD simulations by Wiesegger (2009)
or Wiesegger et al. (2009a) that the open, triangular void
results in a parabolic phase transition line, while the
tree-like branching system will lead to an almost rectangular
phase transition line inside the multi-micro channel array.
Figure 8 shows CFD simulation pictures as well as
experimental results for both cases, the triangular and the
tree-like inlet structure.

Evaporator Design with Circular Blanks

Due to the strong increase in volume while the phase
transition takes place evaporation in long straight micro
channels is limited. This is based on thermodynamic
considerations. It is, in many cases, possible to evaporate a
liquid volume flow completely, but superheating is difficult.
A flow velocity limit, depending on the temperature and the
pressure inside the evaporation system, can be obtained, as
derived from the descriptions by Bosnjakovic (1998). This
flow velocity limit provides information on the maximum
volume flow which can be evaporated and superheated
using straight micro channels.
It is, thus, useful to think about micro evaporator designs
which are not limited by a flow velocity. One possibility is
the use of concentric circular blanks. This new design
consists of circular or elliptically shaped ring walls which
are arranged concentrically around a feed hole. Each of the
ring walls show two overflow openings, which act as
expansion nozzles. The position of those overflow openings
is changed by 900 from each ring to the next. Figure 9
shows two principle examples of such microstructures, each
generated on a round plate with 1.7 cm diameter. The first
devices have been manufactured from a polymer by


Figure 5: Vapour plugging inside of micro channels'
reversal of flow direction by rapidly growing bubbles'
temperature at 1500C.

Vapour slugging is also caused by rapidly growing bubbles.
Liquid fractions, trapped between two bubbles, are slugged
out of the micro channel by accelerated bubble-endings. The
contact time between these liquid fractions and the heated
micro channel wall is too low for a complete evaporation.
The above mentioned phase transition phenomena lead to
non-uniform fluid flow distribution in multi-micro channel
arrays and result mn non-uniform vapour quality at
evaporator outlets. Controlling or reducing these phenomena
results in a nearly constant phase transition inside of
multi-nucro channel arrays and in a related constant vapour
quality at the evaporator outlet. Figure 6 shows an example
of such a nearly constant phase transition inside of a
multi-nucro channel array.


Figure 6: Nearly constant phase transition inside of a
multi-micro channel array at a temperature of about 1300C.

The parabolic shape is probably caused by non-uniform
fluid flow distribution at the channel entrances.
The parabolic shape might be avoided by use of a tree-like
distribution system at the entrance of the multi-micro
channel array to provide equal distribution of flow velocity

































































Water mass flow. 0. 07 10
[kg hK ]
Heating surface 130 140 155 170
temeraure[oq]
Applied electrical
power 254 407 560 820
[W]
Evaporation power 190 306 430 600
[W]

Figure 10 shows the outlet steam temperature obtained with
the same water mass flow of 0.7 kg hk' and the same


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


micro-stereolithography (see Brandner (2008), Brandner et
al. (2006) and Brandner et al. (2007a)), later devices have
been manufactured by precision micromachining from
copper to obtain higher steam temperatures.


Figure 8: CFD-simulation and experimental results for a
triangular inlet and a tree-like inlet for the multi-micro
channel evaporator. Left column: Triangular inlet void, right
column: tree-like shaped inlet structure.

The experiments have been performed using a metallic
adapter system to house the circular blank arrangements.
Water inlet and steam outlet as well as electric heaters and
sensors have been integrated into the adapter system, which
is shown in Figure 10.
Water mass flow was varied between 0.3 kg and
1.0 kg h', and evaporation was performed with ambient
outlet pressure. The electrical heating power applied was
varied according to this mass flow range to obtain full
evaporation and superheating. A heating surface temperature
limit of 1700C was randomly set, resulting in an applied
electrical power of about 820 W and an evaporation power
of 600 W for the maximum mass flow.
A brief summary of experimental parameters is given in
Table 1. The differences between applied electrical power
and evaporation power are heat losses as well as the power
consumed for superheating. It was, at least in the existing
experimental setup, not possible to determine the heat losses
exactly. However, the power applied for superheating can be
neglected in comparison to what is needed for evaporation.
thus the most of the difference is most likely heat losses.
Numerous designs have been tested experimentally. The
main focus was set to three points: how many semi-circular
walls (semi-elliptic walls) are really necessary for
evaporation and superheating, what is the influence of the
position of these walls, and is there a connection between
the steam temperature and the number and arrangements of
walls?


Figure 9: Examples for circular blank arrangements used
for water evaporation.

It was experimentally shown that it is possible to generate
superheated steam with a single sidewall around a circular
or elliptic blank, if it is arranged at the outermost
circumference of the microstructure inlay. A single circular
blank with sidewalls arranged directly around the water inlet
will lead to complete evaporation, but almost no
superheating is possible with this arrangement. Results of
further experiments are given in Figure 11 and Figure 12.
Here, the outlet steam temperature is plotted against time for
complete evaporation. This plot style was chosen to show
the transient behaviour of superheating. In all experiments
the flow velocity of the steam was increased drastically due
to an increase in volume by the evaporation inside the
circular blanks. Maximum flow velocity and maximum
superheating temperature are coincident, which is shown in
both figures Figure 11 and Figure 12 by reaching the
saturation.


Table 1: Experimental parameters used
and superheating with different geometries.


for evaporation






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


electrical power. It is clear shown that evaporation and
superheating can be obtained with the sidewalls arranged at
the outer limit of the circular blank, but not with those
arranged at the inner limit.


5o soO -5 -o -s m s 404


time [s]


Figure 12: Steam outlet temperature obtained with different
numbers of sidewalls.

evaporation pressure to the larger numbers of circular
blanks, but the pressure difference between the two
structures used for the middle and the upper plot are within
measurement uncertainty. Thus, more experiments have to
be performed to clarify the influence of pressure inside the
circular blanks. However, the steam temperature shown in
Figure 12 was measured at ambient pressure.
The plots shown in Figure 11 have been obtained with a
lower water mass flow of 0.7 kg h'. Thus, a mass flow
limit for the use of a single sidewall arrangement for
superheating seems to be somewhere in between 0.7 kg K '
and 1.0 kg h'. According to this finding, an optimum
design in terms of evaporation, superheating temperature
and pressure drop can probably be defined for every mass
flow range. However, more work has to be done in future to
find this optimum. A theoretical model description which
allows a pre-calculation of the design is currently under
evaluation.

Summary

Several metallic microstructure devices with multi-micro
channel array arrangements for evaporation of liquids,
especially water, have been designed, manufactured and
tested. Fluid driven devices in crossflow and counter-current
or co-current design are quite limited in temperature, while
electrically powered devices are much more flexible to use.
A special device was generated to allow optical inspection
of the evaporation process through a glass lid by high speed
videography. Several evaporation effects like micro channel
plugging have been visualized, and different designs of the
inlet for flow distribution into the micro channel array have
been tested. It was found that long straight micro channels
are not optimal for evaporation. Thus, a new design based
on circular blanks including numerous circular or elliptic
sidewalls at different positions have been tested. It was
shown that full evaporation and superheating could be
obtained with a single side wall at the outer limit. This
arrangement is only suitable for a certain mass flow range,
as it was shown. Further investigations will be done to
optimize the performance and to allow a pre-calculation of
the design to the desired mass flow as well as to the
superheating temperature.


Figure 10: Test adapter system to
blanks.


outer limit si



a rr




so inner lirnit sidowall
111


house copper circular


o so 1on iso a om 39 4eo
time [s]


Figure 11: Results obtained with two different sidewall
arrangements, obtained with the same electrical power and
water mass flow. It is clearly to see that only the
arrangement of sidewalls at the outer limits of the circular
blank leads to steam superheating.

More experiments showed that the number of sidewalls or
structures inside the outer limits of the circular blanks
influences the exit temperature of the steam. At the same
water mass flow of 1.0 kg h' and the same electrical power
applied three different arrangements have been tested for
their capability to generate superheated steam. It was shown
that a slight superheating was possible with a single sidewall
arrangement at the outer limits. Higher temperatures have
been obtained when several inner sidewalls or structures
have been used. The same results have been obtained with
circular sidewalls, as it is shown in Figure 12. Similar
results have been obtained with elliptic sidewalls.
The plots in Figure 12 show that the steam temperature is
decreasing with decreasing number of sidewalls, and that
steam superheating is slightly possible with a single
sidewall arrangement at the outer blank limit. No higher
temperature is possible, no matter what electrical power is
applied. This can partly be explained by an increase of






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

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Separation and Continuous Contacting in Novel
Microstructures, Proc. 1. GASMEMS Workshop. Eindhoven,
6.&7.09.2009, published as CD-ROM (2009a)


Acknowledgements
Part of the research leading to these results has received
funding from the European Community's Seventh
Framework Program (FP7/2007-2013) under grant
agreement no215504.

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