Heat Transfer Engineering, 21:5± 17, 2000
Copyright ° C 2000Taylor & Francis
0145± 7632/00$12.00 + .00

heat in history

The Power Industry’s View
of Past, Present, andFuture Two-Phase Flow
Testing
HOLGER SCHMIDT, WOLFGANG KASTNER, and WOLFGANG KÖHLER
Siemens AG, Power Generation Group (KWU), Erlangen, Germany

Since 1974, Siemens’ Power Generation Group (KWU) has been operating a high-pressure
two-phase  ow test loop—called the Benson test rig—which offers a range of operating conditions
that is unique in the world (1 to 330 bar, 20 to 600±C, and 0 to 2 MW electric heating power). The
25th anniversary of the  rst tests performed at this test rig presents a good occasion not only forreviewing the past, but also for contemplating the future of two-phase  ow experiments.
The past was characterized by integral and separate effect tests for power generation using
nuclear, fossil, and renewable energy sources as well as for process industries. This article will
present examples demonstrating the  exible and broad range of applications for the Benson test rig.
The results of the tests have been used to develop algorithms for implementation in computer
programs and also for validating such programs.
Usually these computer programs—so-called analysis tools—are used for analyzing systems orcomponents. From an analyst’s point of view, two-phase  ow experiments serve either to verify
global  ow conditions or to supply inputs such as boundar y conditions and material laws and/or
initial conditions for the analysis tools. An advanced way of making sure that all available
knowledge can be input into the analysis tools is to collect and store it in a program system fromwhich it can be called up, whenever required, according to the task in hand. Siemens’ KWU Group
has started developing such a system. Apart from integral tests conducted for new power plants,
future two-phase  ow experiments will probably focus on expanding this program system’s database.

Siemens’ Power Generation Group (KWU ) has been
operating the Benson test rig—a test rig that is unique inthe world due to its wide range of operating conditions —in one of its accredited laboratories since 1974. The test
rig’s 25th anniversary is an exceptional event for any test
facility and thus offers a good occasion for reviewing
the past and contemplating the future. As the name of
the test rig implies, its main purpose is to investigate
topics associated with the design, operation, or further

A slightly different version of this article was presented at the 37th
European Two-Phase Flow Group Meeting in London, 1999.
Address correspondenc e to Dr. Holger Schmidt, Siemens AG, Power
Generation Group (KWU), P.O. Box 3220, 91050 Erlangen, Germany.
E-mail: Holger.Schmidt@erl11.siemens.d e5development of Benson boilers, i.e., fossil- red oncethrough boilers. However, the test facility’s  exibility
also enables it to be used for other applications in the nuclear and renewable power industries as well as processindustries. Some of the investigation s have been performed in cooperation with universities and research
institutes . Based on our 25 years of industrial experience concerning two-phase  ow tests and applications ,the following should also throw light on the purpose of
future two-phase  ow testing.
BENSON TEST RIG
Figure 1 shows a section of the Benson test rig, andFigure 2 its  ow diagram. Its range of operating conditions is unique throughout the world:
Pressure
Temperature
Power
Mass  ow

1 – 330 bar
20 – 600 ±C
0 – 2 MW0 – 28 kg/s

The main sections of the test facility comprise a water
treatment system including injection and recirculation
systems, the object to be tested, a pressurizer, and acooling system. Demineralized and deaerated water is
injected into the test loop by a piston pump. A damping vessel is installed directly downstream of the piston
pump to prevent oscillations . The test rig can be operated in the recirculation mode for high  ow rates or in
the once-through mode for low  ow rates. To maintain aconstant water chemistry, a certain amount of the wateris exchanged in the recirculation mode.
The water is heated by being passed through one
main heater and up to two preheaters. Depending on
the size of the object being tested, heating can take theform of direct electric heating—i.e., the wall of the test
object acts as a resistor—or indirect heating via wires
mounted on or in the wall. Since the preheater as wellFigure 1

6

Benson test rig.

heattransfer engineering

Figure 2

Benson test rig,  ow diagram.

vol. 21 no. 4 2000

Figure 3

Data acquisition and visualization.

as the test object are electrically heated, it is possible toestablish any enthalpy at the inlet and outlet of the test
section via energy balances. Heat losses are included inthis balance despite the fact that they are very low dueto the insulation , which is over 50 mm thick. A spraytype condenser installed downstream of the test object
condenses and subcools the water.
System pressure is adjusted by a large thermal pressurizer and a throttling valve downstream of the test
object. Assurance of a constant pressure during steadystate tests is very important, especially near the criticalpoint, because pressure oscillation s affect heat transfer
conditions in the test object. With this combination ofvalve and pressurizer it is also possible to perform tests
with prede ned pressure gradients.
The Benson test rig as well as the test object are instrumented in such a way that all relevant parameters
are measured. The data acquisition and visualizatio nequipment has been constantly adapted to the state of
the art over the past 25 years. Figure 3 shows the structure of the present data acquisition and visualizatio nsystems. Visualization on two screens, as shown in Figure 3, ensures that the operator has a clear picture at all
times of current thermal-hydraulic conditions as wellas measured parameters such as the temperatures in thewall of the test object.
DESCRIPTION AND CHARACTERIZATION OF
TYPICAL RESEARCH WORK
Regardless of the speci c types of experiments thathave been performed at the Benson test rig, all of thetests can basically be broken down into the following
two categories:
heat transfer engineering

1. Integral tests. The aim of these tests is to verify thefunctional behavior of components such as heat exchangers, or to develop measuring equipment.
2. Separate effect tests. The aim of these tests is toinvestigate separate two-phase  ow effects. They canbe subdivided into two groups:
a. Stand-alone tests. These tests are interesting intheir own right, such as investigation s of erosion
corrosion.
b. Boundary tests. The aim of these tests is to investigate  ow behavior in or around structures.
The information gained from the tests is used incomponent analyses. In many cases, this information comprises boundary or initial conditions
and material laws for analysis tools such as  niteelement (FE ) programs, which need heat transfer
coef cients as inputs for temperature distributio ncalculations.
Integral Tests
Examples of integral tests are functional tests carriedout on a safety condenser (SACO ) and tests performed
to develop a compact wet steam measuring system.
In the case of the SACO, the aim of the experiments
was to determine the heat exchange characteristic of
the component which had been developed for the next
generation of pressurized water reactors (PWR). The
design of the SACO is based on the idea of using analmost passive-decay heat removal system for the eventof a loss of heat sink on the secondary side. Figure 4
shows how the SACO could be installed downstreamof a steam generator. In the event of a secondary-side
loss of the heat sink, the steam would be condensed byevaporating water on the tertiary side. As the temperature differences are expected to be high, heat  uxes of
up to 600 kW/m2 would occur at mass  uxes of less than
40 kg/m 2 s. The pressure would be near the containmentpressure and thus in the range 1.35 – 5 bar. The SACO
is designed as a tubular heat exchanger with condensation taking place inside the tubes. Heat transfer wasinvestigated in two phases. In the  rst phase, only thetertiary side was considered by electrically heating tube.
In the second phase, a section (3 £ 3 tube bundle ) of the
SACO—shown on the right-hand side of Figure 4—wasbuilt into the Benson test rig. The secondary-side steam
was provided from the Benson test rig itself. The heightof all connecting pipes was scaled 1:1 in order to consider elevation effects. During the test campaign, heatexchange characteristics as well as transient behavior
were investigated .
The main result of these tests was that the heat exchange behavior of the SACO was veri ed. For example, Figure 5 shows the exchangeable heat  ow forvol. 21 no. 4 2000

7

Figure 4

Investigation on the integration of a safety condenser (SACO) to the secondary side of a PWR.

steady-state conditions . One interesting effect of theheat exchange characteristic is that the exchangeable
heat  ow is independent of the pressure on the secondary side over a wide range. An explanation for thisis that the tertiary side dominates the heat exchange
process. As the tests showed, the boiling crisis occurs
at high steam qualities. In the postdryout region, heattransfer is low compared to the regions with nucleate and subcooled boiling, and thus the contributio n
to heat exchange is also small. The experiments alsoveri ed that the critical steam quality, which is thesteam quality at which the boiling crisis occurs,
depends mainly on the mass  ux and is largely independent of the heat  ux. In the case of a higher secondarypressure, the temperature difference between the secondary and tertiary sides is larger, and thus the heat  ux
in the nucleate boiling region is also higher than whensecondary-side pressure is low. This means that, for highsecondary-side pressures, a smaller heat exchange surface area is needed to reach the critical steam quality.
In each case, the same amount of heat is exchanged atsimilar mass  uxes, since only the area involved prior
to the boiling crisis is relevant for the heat exchange
process and the magnitude of heat exchange is simi8

heattransfer engineering

lar at approximately constant critical heat  uxes (seealso [1]).
Another typical kind of integral test is for calibrating
measuring equipment. For example, Siemens’ KWUGroup developed a mass  ow and steam quality measuring device—shown schematically in Figure 6—which
was then calibrated in the Benson test rig. This system
consists of a venturi tube, a one-beam gamma densitometer, a temperature sensor, a differential pressure sensor, and an absolute pressure sensor. The  ow throughthe venturi creates a pressure drop that is proportiona lto the square root of the mass  ow for a certain density
and is measured by the gamma densitometer. The  ow
through the venturi leads to such a high degree of homogenization that a one-beam gamma densitometer canbe used. Based on the measured temperature and pressure, the properties of the  uid are taken into account.
The calibration measurements were used to develop an
algorithm for calculating the steam quality, the mass ow, and the  uid enthalpy (see also [2]).
Use of such a device installed at the end of the boiler
section to control the feedwater of a fossil- red oncethrough steam generator was compared to the method
presently employed and was found to have certain
vol. 21 no. 4 2000

Figure 5

SACO power with gravity and forced feed.

advantages. Up until now, it has been common practice to measure temperature and pressure downstreamof the  rst superheater. However, measurement of theenthalpy at the outlet of the boiler results in faster response, meaning that the effects of changes in  ringor transient heating effects are detected earlier. This
has a positive effect on the service life of the highpressure components installed downstream of the boiler
section.
Stand-Alone Tests
The aim of stand-alone tests is not to develop a database which can be used to supply boundary conditions
for component analyses. Instead, the results of thesetests are interesting just in their own right. For example, tests have been performed at the Benson test rig toinvestigate erosion corrosion, a corrosion mechanismthat is greatly in uenced by  ow behavior. This type ofcorrosion occurs only if the wall is wetted—for example, in the case of single-phase  ow or two-phase  ow
with bubbly, strati ed, or annular  ow patterns—and if
the corrosion resistance of the wall is dependent upon
the formation of a protective oxide layer. The condiheat transfer engineering

Figure 6

Wet steam measuring system.

tions promoting this kind of corrosion are so complex
that it is not possible to describe them in a way that enables the two-phase  ow conditions to be investigate dseparately from the metallurgical and chemical effects(e.g., as mass transfer coef cients ). Hence, the reductions in wall thickness were measured directly. For thispurpose, various objects were tested in the Benson testrig (plates, tubes, bends, reducers, and increasers ). Wallthinning was measured for conditions based on various  ows, temperatures, water chemistries, and materials. Using this data—a couple of examples are shownin Figure 7, where the experimental determined wall
thickness reduction due to erosion corrosion is plotted as the wall thinning measured in mm/year versus
some typical parameters—a computer program (called
WATHEC) was developed which is employed in power
plant design to avoid signi cant erosion corrosion. For
existing power plants, it is also possible to identify locations at which the wall thickness should be measured,
meaning that the scope of in-service inspections can be
reduced (see also [3 – 5]).
vol. 21 no. 4 2000

9

Waterwall Tubes for Benson Boilers

Figure 7 Wall thinning due to erosion corrosion (effect of thermal
hydraulics and water chemistry).

Boundary Tests
Most of the tests performed at the Benson test rig
have been part of component analyses for the power andprocess industries. In the following, examples will bepresented of individual boundary tests carried out for
the fossil, nuclear, and solar power industries as well
as for a process industry in order to demonstrate the exibility of the Benson test rig and to explain typicalboundary test applications .

Figure 8

10

Benson boilers are once-through steam generators.
The steam is generated in tubes which are welded together to form gas-tight walls. These walls surroundthe combustion chamber where the fuel is  red. In designing the combustion chamber, both the  ue-gas sideand the water side have to be taken into consideration .
The steam quality at the outlet of a once-through boiler
is higher than 1; i.e., the steam is superheated, withthe consequence that all of the  ow patterns shown in
Figure 8 as well as the boiling crisis occur in the boiler
section. Subcooled boiling also typically occurs, this isindicated in Figure 8 by two different de nitions of thesteam quality ( Çx and Çx mass ). From the design point ofview this is the energy-balanced steam quality Çx—in thefollowing called just steam quality—which is de ned
as the ratio of the difference between the cross sectionaveraged enthalpy minus the saturation enthalpy and theheat of evaporation. The mass-balanced steam quality
Çx mass is de ned as the ratio of the actual steam to thesum of steam and water  ow. The mass-balanced steam
quality together with the energy-balanced steam quality
give a hint as to where a nonequilibriu m condition may
occur in a cross section. For the design of boilers, it isessential to know where the boiling crisis is located andto have information on heat transfer at this position. It
is generally an advantage if the boiling crisis occurs at
high steam qualities and thus at a high position in thewaterwall that is relatively far away from the burners.
Another advantage of high critical steam qualities is therelatively good heat transfer behavior due to the highsteam velocities. In view of the relevance of heat transfer conditions in waterwall tubes, a variety of different

Wall temperature and pressure loss in an uniformly heated, vertical, smooth evaporator tube.

heattransfer engineering

vol. 21 no. 4 2000

Figure 9
gations.

Test matrix for heat transfer and pressure drop investiFigure 10 Effect of mass  ux on the inner wall temperature of asmooth tube.

measurements have been performed in the Benson test
rig. The main parameters of these tests are summarized
in Figure 9. Different types of tubes were installed in
the Benson test rig downstream of the heater so that the
inlet steam quality could be varied. The electrical resistance of their walls was employed for heating the tubes.
In some of the tests, the wall thickness was reduced
over half of the tube circumference to simulate nonuniform heating. Pressure drops as well as wall temperatures were measured for different  ow conditions . Using the results of these measurements, algorithms weredeveloped which are being applied in steam generator
design.
As an example taken from the database, Figure 10
shows the in uence of the mass  ux on the inner wall
temperature. At low mass  uxes, the boiling crisis occurs at lower steam qualities and the waterwall temperatures are high. In the case of 900 kg/m2 s, they would
be much higher than the creep temperature of typicalwaterwall materials. For this reason, mass  uxes for
200 bar in the range between 1,400 and 2,000 kg/m2 s
are required. The tubes have to be installed at an inclination of approximately 30± because the size of the
combustion chamber is governed by the design of the ue-gas side. This inclination requires supporting structures in order to avoid excessive bending stresses in the
tubes. The waterwall tubes can only be installed in a
vertical position if ri ed tubes are used. The enhanced
heat transfer behavior of ri ed tubes is demonstrated by
Figure 11, which shows the inner wall temperatures of
two uniformly heated tubes, one smooth and one ri ed.
Although  ow conditions are similar, the boiling crisis
occurs in the ri ed tube at a much higher steam quality
heat transfer engineeringthan in the smooth tube. The reason for this effect is the
swirl induced by the ri e geometry. The corresponding
centrifugal forces imparted to the liquid phase inside thetube are responsible for rewetting of the wall and thus
for the high critical steam quality. More than 100,000
temperature measurements taken on smooth tubes and
150,000 on ri ed tubes presently form the basis forheat transfer correlations which, together with correlations for pressure drop, are key elements of design andanalysis tools for Benson boilers. These tools include,for example, dynamic programs for analyzing startup
and shutdown processes, and FE programs for calculating stresses and temperatures in waterwalls (see also
[6 – 10]).

Figure 11

Wall temperatures in smooth and ri ed tubes.

vol. 21 no. 4 2000

11

are lower than the corresponding heat  uxes during theTMI-2 accident. Although a detailed analysis of theTMI-2 accident would be very complex, comparison of
the heat  uxes gives a rough explanation of why the
RPV retained its structural integrity. In order to obtaina deeper understandin g of the accident and to transfer
the new knowledge about heat transfer behavior in the
gap to safety analyses for existing plants, it is possible
to use an algorithm based on the results of these tests
to describe the heat transfer boundary conditions (seealso [11]).
Figure 12

Test setup heat removal during the accident at TMI-2.

Heat Transfer between a Debris Crust and the Reactor
Pressure Vessel Wall
During the Three Mile Island-2 (TMI-2) accident, thecore of the reactor was partly melted. The molten debris penetrated into the lower plenum. Contrary to mostassumptions , subsequent inspections revealed that thewall of the reactor pressure vessel (RPV ) showed nosigns of melting. This discovery could not be explainedby the existing reactor safety codes. One main question
was how large the maximum removable heat would havebeen if a gap between the debris crust and the RPV wall
had been  lled with water still present in the vessel. Ina joint research program headed by the German Society for Reactor Safety (GRS ), Siemens’ KWU Groupinvestigated the heat transfer conditions in such a gap.
For this purpose a vessel was built and integrated into
the Benson test rig as shown in Figure 12. The lower
part of the vessel had a spherical shape, similar to thebottom head of the RPV. In order to simulate the debris
crust, a heating element was mounted in the vessel, thiselement being movable in order to vary the gap width.
Figure 13 shows the measured critical heat  uxes. They

Heat Transfer in Solar Farm Absorber Tubes
Among the various concepts for utilizing solar energy, solar thermal power generation in solar farms isthe most widely used. At present, only farms employing thermal oil in absorber tubes to generate steam in a
separate heat exchanger are in operation. As this thermal oil limits the maximum process temperatures andis also dif cult to handle, new process concepts are under development to generate the steam directly in theabsorber tubes. These processes are shown schematically in Figure 14. They are to be tested at Plata Forma
Solar in Almeria (Spain ). In a step preceding this development, the heat transfer conditions were investigated in the Benson test rig as part of a joint research
project headed by the German Aerospace Research Establishment. The  ow diagram of these tests is given
in Figure 15, along with a picture showing the tubes
in front of the building of the Benson test rig. Various
tube geometries as well as heat  uxes and  ow conditions were tested. Pressure drops and temperatures
were measured. As an example, Figure 16 shows theinner wall temperatures. The results of these tests havebeen used to develop algorithms used in design studies
for the solar power industry. One speci c feature requiring investigatio n is deformation of the tubes due tononuniform heating in order to avoid positionin g outside of the focus of the mirrors or destruction of thesurrounding glass insulation . Performing these kinds ofinvestigation s with an FE program requires heat transfer coef cients as boundary conditions which can beselected using the results of the tests performed in the
Benson test rig (see also [12]).
Pressure Drop Tests

Figure 13 Validation of the heat removal from the molten debris
during the TMI-2 accident.

12heattransfer engineering

In most of the tests conducted at the Benson test
rig, temperatures and pressure drops were measured.
The pressure drops are important for component design
and analysis as well as heat transfer behavior. Basedon knowledge about pressure drops it is possible, forexample, to analyze mass  ow distribution s in piping
vol. 21 no. 4 2000

Figure 14

Concepts for direct solar steam generation.

networks or to size pumps, etc. Frictional pressure drops
are typically represented as two-phase  ow multipliers, which are dependent on  ow conditions and geometry. For instance, it is interesting that the generalcharacteristics of the two-phase  ow multipliers forsmooth and ri ed tubes are different, as can be seen from
Figure 17.
Pressure drops were the focus of a series of investigations of steam piping networks for the heavy-oil

Figure 15

industry. These steam networks are used, especially in
Venezuela, to inject steam into boreholes to increase
output. As these networks are of a large size, a portionof the steam condenses inside the pipes. Many investiga tions were carried out to develop or validate algorithms
for the pressure drop, including tests at the Benson test
rig. Figure 18 shows the setup used for the test object
and the main parameters of the test matrix. Figure 19
shows some selected results for a pipe bend, an inclined

Test setup for direct steam generation investigations.

heat transfer engineering

vol. 21 no. 4 2000

13

Figure 16

Temperatures at the upper side of the absorber tube.
Figure 19

Two-phase  ow pressure drop in various pipes.

pipe, and a horizontal pipe. The results were integrated
into a simulation program which uses them mainly asboundary conditions (such as frictional pressure drops )or as material laws (such as for two-phase mixture densities ) (see also [13] ).
FUTURE PROSPECTS FOR TWO-PHASE FLOW
EXPERIMENTS

Figure 17 Effect of mass  ux on pressure drop of smooth andri ed nonheated tubes.

Figure 18 Test setup for pressure drop measurements in a pipe
conveying wet steam.

14

heattransfer engineering

From the point of view of the power industry, twophase  ow investigation s are interesting as long as thesteam cycle is an essential element of power generation. At present, most power plants comprise gas turbine plants combined with a steam cycle (combinedcycle plants ), coal- red plants, and nuclear plants. At
combined-cycle plants, the steam cycle is of minor importance. The main requirements to be met by the steam
cycle are ease of design and low-cost construction . At
coal- red and nuclear power plants, the steam cycles
are very important. Especially in the case of new nuclear power plant designs, such as the EPR and the SWR
1000, it can be expected that integral tests will be necessary in order to verify the functional behavior of their
new systems. These tests are dependent on the stage
reached in the design process and it is dif cult to foresee what kind of integral tests will have to be performed,
and when. The situation is similar with regard to standalone tests. The requirements for new stand-alone tests
will be governed by new developments in power plantwater treatment, such as injection concepts for reducing
60
Co activity at nuclear power plants (see also [14]).
vol. 21 no. 4 2000

Figure 21
Figure 20

Engineering process for systems with two-phase  ow.

Boundary tests are related to analysis tools and to thespecial conditions associated with certain applications .
Hence, it can be expected that tests for waterwall tubes
in, for example, once-through boilers will continue.
From a general point of view, one can see two trends.
First, competition in the power plant market is verystrong, meaning that those who want to survive on thismarket will have to optimize their engineering processes. The second major trend is that the commerciallyavailable analysis tools will become more and more
powerful and user-friendly. Looking at the engineering
processes for systems in which two-phase  ow occurs,
one  nds a structure of the kind shown schematicallyin Figure 20. The two main steps are general modeling, which includes description of the geometry and theloads, and two-phase  ow input, which includes the description of material laws as well as initial and boundary
conditions.
One example taken from an engineering process isanalysis of the deformation of a header. For the analysis
the header is a piping system with one big central tube
and a large number of inlets and outlets. Under fullload conditions, it conveys superheated steam. During
start-up, some of the inlets on the sides may be closed
and the steam may be in a saturated state. This may result in condensation in some sections of the header. To
investigate the deformation of such a system it is common practice to use  nite-element programs. In a  rst
step the temperature distributio n in the header is calculated, which requires heat transfer coef cients—withand without phase change—as boundary condition, inorder to determine the deformation in a second step withstandard tools. The general procedure as well as temperature and deformation distributio n for one time step
are shown schematically in the middle of Figure 20. Another example is the estimation of the change in inventory in a drum boiler during load changes. These kindsof investigation s are typically performed with simulation tools by solving the conservation equations for the
mass, the momentum, and the energy. Therefore it isnecessary to consider the structure of the boiler as wellheat transfer engineering

Automated two-phase  ow input.

as the control system as it is shown schematically at thebottom of Figure 20. By considering the water– steam
mixture in the boiler it is possible to neglect the twophase  ow frictional and the acceleration pressure drop.
The remaining two-phase- ow input is the density ofthe two-phase mixture, which can be regarded as a material law. In both of the examples shown in Figure 20,
two-phase- ow inputs are required. When one compares the modeling and input steps, it becomes clearthat the modeling tools have reached a high standard
which will become even higher in the future. The twophase- ow input step is unique to each task in hand andis often very time-consuming and expensive. In manycases only a small portion of the knowledge available on
two-phase  ow is taken into consideration , somethingwhich also has an in uence on quality.
Siemens’ KWU Group has started developing a program (called In-2-Flow ) for automating the input stepin such engineering processes, as outlined in Figure 21.
This program will be employed in the general engineering process after speci cation of the modeling inputs
and before performance of the analysis. It will automate
the two-phase  ow inputs. The  rst step is to assess theavailable methods. For tubes, for example, a large variety of different methods are available for calculating thevoid fraction, pressure drop, and heat transfer for various applications . Based on the most suitable method,
it will then be possible to prepare the inputs in order
to link them to the analysis tool. As can be seen from
Figure 22, a database is the core component of such

Figure 22vol. 21 no. 4 2000

Main structure of the input tool.

15

a program. Although only heat transfer and pressure
drop are mentioned in Figure 22, it is also planned forother two-phase  ow data such as  ow forces or leakage mass  ows through small cracks (see also [15, 16])
to be considered as well. Relevant two-phase  ow data
will be collected in a database. For the purposes of thisprogram, it will be necessary to store not only equations
but also all additional information in order that a decision can be made. A search assistant will help the user
 nd the most suitable method, although it might turnout that different methods should be used for different
applications within the same simulation. Depending on
the requirements of the simulation tool, it will be necessary to prepare the inputs as single values, tables, or
subroutines . Initially, the knowledge base of this program will be taken from the available literature. Storing
information in a database will also provide other advantages. One of these is that certain items of knowledge
can be permanently retained. Also, a program of thiskind can provide an overview of all of the knowledge
that is available on a speci c topic. This can be helpful
for identifying areas in which there is a lack of information. Missing information can then be supplied by
performing new boundary tests as part of a continuous
process for enhancing the quality of the input tool.
CONCLUSION
Although a large variety of different two-phase  ow
experiments have been performed in the past, tests ofthis kind will still be needed in the future. These tests
will be related to new developments in the  elds ofcoal- red and nuclear power generation and will takethe form of integral tests or boundary tests for, e.g.,waterwall applications . In addition, it can be expectedthat two-phase  ow tests will also be performed in the
future for enhancing the quality of a data input program
currently under development at Siemens, the aim of thisprogram being to automate the input of two-phase  ow
data in modern analysis tools.

[4] Kastner, W., Riedle, K., and Tratz, H., Experimental Investigations on Material Loss Due to Erosion-Corrosion,
VGB Kraftwerkstechnik, vol. 64, no. 5, pp. 411– 423,
1984.
[5] Kastner, W., Nopper, H., and Rößner, R., Vermeiden von Erosionskorrosionsschäden in Rohrleitungen, 3R Int., vol. 33,
no. 8, pp. 423– 428, 1994.
[6] Griem, H., Köhler, W., and Schmidt, H., Heat Transfer, Pressure Drop and Stresses in Evaporator Water Walls—From Experiment to Design, VGB PowerTech, vol. 79, no. 1, pp. 26 – 35,
1999.
[7] Köhler, W., Kefer, V., and Kastner, W., Heat Transfer in Verticaland Horizontal One-Side-Heated Evaporator Tubes, Exp. Heat
Transfer, pp. 397 – 409, 1990.
[8] Kefer, V., Köhler, W., and Kastner, W., Critical Heat Flux
(CHF) and Post-CHF Heat Transfer in Horizontal and Inclined
Evaporator Tubes, Int. J. Multiphase Flow, vol. 15, no. 3,
pp. 385 – 392, 1989.
[9] Köhler, W., and Kastner, W., Heat Transfer and Pressure Lossin Ri ed Tubes, 8th Int. Heat Transfer Conf., vol. 6, pp. 2861 –
2865, 1986.
[10] Franke, J., Köhler, W., and Wittchow, E., Evaporator Designs
R
for BENSON ° Boilers—State of the Art and Latest Development Trends, VGB Kraftwerkstechnik, vol. 73, no. 4, pp. 307 –
315, 1993.
[11] Schmidt, H., Köhler, W., Herbst, O., and Krätzer, W., Experiments on Heat Removal in a Gap between Debris Crust and
RPV Wall, 1st European-Japanes e Two-Phase Flow Group
Meeting, 1998.
[12] Köhler, W., Herbst, O., and Kastner, W., Thermal Designof Solar Absorber Tubes with Direct Steam Generation, 8thInt. Symp. on Solar Thermal Concentrating Technologies,
1996.
[13] Gonzales, M., Kastner, W., Künstle, K., Lezuo, A., Ostendorf,
F. J., Reiter, K., Rodriguez, J., and Thelen, H., Upgrading ofVenezuelan Crude Oil—Continuation of the Orinoco Feasibility Study within the Venezuelan/German Agreement (Annex III B), Final Report BMFT—Reference No. 03E-6400B,
1989.
[14] Nieder, D., Schneider-Kühnle, P., and Wolter, D., Introductionof Zinc Injection in NPP Biblis, Unit B, VGB PowerTech, no. 6,
pp. 61– 63, 1999.
[15] Kefer, V., and Kastner, W., Leckagen bei unterkritischen Rohrleitungsrissen—Ausströmraten und ihre Geräusche,
BWK, vol. 39, no. 6, pp. 310 – 315, 1987.
[16] Kefer, V., Kastner, W., Westphal, F., John, H., Reimann, J.,
and Friedel, L., Vorhersagegenauigkeit von Modellen für
Leckraten aus Rissen in druckführenden Komponenten,
DECHEMA—Monographien, Band 111, Fortschritte derSicherheitstechnik II, 1988.

REFERENCES[1] Köhler, W., Herbst, O., and Kastner, W., Thermal-HydraulicBehavior of a Safety Condenser, Int. Conf. on New Trends in
Nuclear System Thermohydraulic, vol. 1, pp. 609– 614, 1994.
[2] Kastner, W., Fischer, C., and Krätzer, W., Verbesserte Speisewasserregelung durch kompaktes Meßsystem zur Massenstrom- und Dampfgehaltsbestimmung, BWK, vol. 45, no. 12,
pp. 510 – 514, 1993.
[3] Heitmann, H. G., and Kastner, W., Erosion-Corrosion in
Water-Steam Cycles—Causes and Countermeasures, VGB
Kraftwerkstechnik, vol. 62, no. 3, pp. 180 – 187, 1982.

16

heattransfer engineering

Holger Schmidt is currently a manager in the
Department of Thermal Hydraulics and Fluid Dynamics of Siemens AG Power Generation Group(Siemens/KWU) in Erlangen, Germany. He is a
Mechanical Engineer and received his Ph.D. fromthe University of Darmstadt, Germany. For morethan 13 years he has been involved in experiments,
modeling and developing programs for thermal
hydraulics and stress analysis.

vol. 21 no. 4 2000

Wolfgang Kastner is currently a director at
Siemens AG Power Generation KWU, where heheads the Thermal Hydraulics and Fluid Dynamics Department in Erlangen, Germany. For morethan 25 years he has been active in nuclear safety(UFTF and PKL), in research on fossil-fueledboilers (Benson), and on solar-powered steam
generation. He is also responsible for product development in the  eld of  ow-accelerated corrosion (WATHEC and DASY).

heat transfer engineering

Wolfgang Köhler is a Scienti c Advisor in the
Thermal Hydraulics Laboratories of Siemens AG
Power Generation KWU. He is a Mechanical Engineer and received his Ph.D. from the Technical
University in Munich, Germany. For more than
25 years he has been involved in experimental
and theoretical work concerning the thermal hydraulics of nuclear reactors, fossil-fueled boilers,and solar-powered steam generators.

vol. 21 no. 4 2000

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