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USION-7173; No. of Pages 5

Fusion Engineering and Design xxx (2014) xxx– xxx

Contents lists available at ScienceDirect

Fusion Engineering and Design

journa l h om epa ge: www.elsev ier .com/ locat e/ fusengdes

onceptual design of a helium heater for highemperature applications

ue Zhou Jin ∗, Yuming Chen, Bradut-Eugen Ghidersaarlsruhe Institute of Technology (KIT), P.O. Box 3640, D-76021 Karlsruhe, Germany

i g h l i g h t s

A special design of heater with two vessels is introduced for the operation at 10 MPa and 800 ◦C.The additional coupling between the cold leg and the hot leg of the loop due to the heater design has an impact on the loop energy budget.Reducing the heat transfer between the two flow channels inside the heater by means of a helium gap in the inlet nozzle is proven to be effective.

r t i c l e i n f o

rticle history:eceived 30 August 2013eceived in revised form0 December 2013ccepted 20 December 2013

a b s t r a c t

The Karlsruhe Advanced Technologies Helium Loop (KATHELO) has been designed for testing divertormodules as well as qualifying materials for high heat flux, high temperature (up to 800 ◦C) and highpressure (10 MPa) applications. The test section inlet temperature level is controlled using a processelectrical heater. To cope with the extreme operating conditions, a special design of this unit has beenproposed. In this paper the conceptual design of the unit will be presented and the impact of the coupling
vailable online xxx
eywords:ATHELOrocess heaterFD simulation

between the cold and hot helium gas on the overall efficiency of the loop will be investigated. The detailedthermal-hydraulic analysis of the feed through of the hot helium into the low temperature pressure vesselusing ANSYS CFX will be presented. The impact of the design choices on the overall energy budget of theloop will be analyzed using RELAP5-3D.

© 2014 Elsevier B.V. All rights reserved.
ELAP5-3D
. Introduction

The Karlsruhe Advanced Technologies Helium Loop (KATHELO)as been designed for testing the DEMO (DEMOnstration Powerlant) divertor modules as well as qualifying materials for high heatux, high temperature (up to 800 ◦C) and high pressure (10 MPa)pplications. The layout of the helium loop is illustrated in Fig. 1.he pressure level in the circuit is controlled by the pressure con-rol system (PCS), while the gas is accelerated using a circulatorPC-001) to obtain and maintain the required flow rate through theest section. The operating temperature of the circulator (50 ◦C) is

aintained using a water–helium heat exchanger (cooler as XH-02). The high temperature at the test module inlet is achieved byeans of an electrical process heater (RS-001). For saving energy

nd, in particular, for reduction of the requirements and dimen-

Please cite this article in press as: X.Z. Jin, et al., Conceptual design of a heliuhttp://dx.doi.org/10.1016/j.fusengdes.2013.12.055

ions for the cooler and heater, a helium–helium heat exchangereconomizer as XH-HT-001 and XH-LT-001) is used to transfer heatrom the hot leg (from the test module) to the colder leg (from

∗ Corresponding author. Tel.: +49 72160822998; fax: +49 72160823718.E-mail address: [email protected] (X.Z. Jin).

920-3796/$ – see front matter © 2014 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.fusengdes.2013.12.055

the circulator). The economizer is a compact printed circuit heatexchanger (PCHE) with very high efficiency of −90%. To reduce theneed of high temperature resistant material a two core solution hasbeen adopted: the low temperature core XH-LT-001 operates below550 ◦C and uses stainless steel (316 L), while the high temperaturecore XH-HT-001 operates between 500 ◦C and 800 ◦C using Inconelalloy 617. For the mass flow and temperature controls Bypass I–IIIare used. A more detailed description of this facility is given in [1].

The heater operates at high temperature and high pressure;therefore, it requires a special design. In the following sections theheater design and its thermal-hydraulic analysis using ANSYS CFX[2] will be presented. Based on the heater design, the dynamicbehavior of the whole helium loop will be demonstrated usinga model done with RELAP5-3D [3]. Boundary conditions consid-ered here are foreseen as the ones for divertor or material testingexperiments: 10 MPa, 800 ◦C and flow rates up to 200 g/s.

2. Design of the electrical heater

m heater for high temperature applications, Fusion Eng. Des. (2014),

The electrical heater is designed with a power capacity of200 kW and it is able to achieve temperature levels up to 800 ◦C atthe test module inlet. Operating simultaneously at high pressure

dx.doi.org/10.1016/j.fusengdes.2013.12.055


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2 X.Z. Jin et al. / Fusion Engineering and Design xxx (2014) xxx– xxx

LO pip

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Fig. 1. KATHE

10 MPa) makes a conventional solution economically impracti-able due to the use of high temperature resistant materials forhe pressure vessel. The solution adopted in KATHELO is a heaterith two vessels: an external one that forms the pressure barrier,hile the heater itself is installed in the second vessel, which is

ocated inside the first one. The external pressure vessel is main-ained at low temperature by the helium coming from the circulator∼70 ◦C), therefore it can be manufactured using stainless steel.he wall temperature of the inner vessel will be close to 470 ◦C,ince it is not a pressure vessel (it acts more like an in-liner), thehickness of the mantel can be reduced significantly. To accommo-ate this design, with a hot vessel immersed inside a (significantly)older one, one has to use concentric inlet and, correspondinglyutlet, nozzles for the two vessels. This solution avoids having hotenetration points in the large pressure vessels and allows design-

ng special transition pieces outside the vessel. While this solutionolves the problem of the design and manufacturing of the heaterressure boundary, it introduces an additional coupling betweenhe cold leg and the hot leg of the loop. Given the design of theeater, there are three main areas where this heat transfer occurs:he inlet, the main heater body and the outlet. The effect of the


eat transfer along the heater body has been accounted for byetting the power level of the unit, since it has been estimatedhat any other solution to reduce it would complicate the designnd increase cost. For the nozzles, however, one can increase the

Fig. 2. CFX-model for the heater inlet

ing layout [1]

thermal resistance between the two flow paths. The inlet has thelarge impact due to its length. In the following sections, the influ-ences of the heat transfer between the two flow channels at thelevel of the inlet and its influence on the loop dynamics will bediscussed.

3. CFD simulation for the heater inlet nozzle

Fig. 2 shows the CFX model of heater inlet part. The boundaryconditions used for the simulation are: helium flows from the ver-tical cold leg to the top and bottom inlets at 70 ◦C and 10.2 MPa;axially, helium flows from the hot leg at 800 ◦C and 10.1 MPa; massflow rates of 200 g/s for both flows. The outer wall to the environ-ment is considered as adiabatic. The simulation is done for the halfpart due to pipe symmetry. The model is ended at ∼1.4 m after theflange, distance at which the hot helium flows into the inner vesseland the cold helium into the shell of the outer pressure vessel.

Fig. 3 shows the temperature distribution in the helium flow(Fig. 3(a)) and in the walls (Fig. 3(b)). Due to the thermal conductionof the pipe wall for the hot flow, the inner hot helium is cooled down


to 705.9 ◦C and the outer cold helium is heated up to 160.4 ◦C. Thisheat removal will increase heater power to achieve the required800 ◦C at the outlet of the hot flow. To reduce the heat transportfrom the hot to the cold helium flow a wrapper which covers the

part and boundary conditions.




X.Z. Jin et al. / Fusion Engineering and Design xxx (2014) xxx– xxx 3

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Fig. 3. Temperature at symmetrical plane without helium gap.

ot pipe with stagnated helium filling in-between (helium gap) isdded to increase the thermal resistance. At the inlet of the hotide isolation is considered as well so that the inner hot pipe doesot have a thermal contact with the wall structure of the outer coldipe. In the CFD simulation this isolation is treated as 1 mm-helium-quivalent thermal resistance of 0.006329 mK/W, and it is assumedo be located in the middle of the inner wall thickness. Results inig. 4 show that the helium gap prevents the heat transport fromhe hot to the cold side effectively. Temperature behavior on theentral vertical line of the cross section A–A is compared betweenwo cases in Fig. 5. The intersection from inner flow convection to


all conduction is not placed on the inner radius of the inner wallecause of meshing size. Using the helium gap the temperature inhe hot flow is kept at 776.5 ◦C and the temperature in the cold flows at 93.8 ◦C at the outlet.

ig. 4. Temperature behavior with respect to 1 mm-helium-equivalent thermalesistance.

Fig. 5. Temperature behavior at the cross section A–A in half due to symmetry.

4. System analysis using RELAP5-3D

For simulating the thermal-dynamic behavior of the loop theRELAP-3D system code has been used. Fig. 6 shows the modeledhelium loop, in which piping size and piping nodalization are given.The study focuses on the thermal behavior of the loop in whichthe heater, the economizer, the loop piping system and valves aremodeled. However the circulator is replaced by imposing pressureand temperature boundary conditions at the corresponding inletand outlet pipes. The heater is modeled as concurrent pipe flow.The heat structure between the helium outer flow in the shell andthe helium inner flow of the core is defined as a convective bound-ary type. The heat transfer coefficient is obtained from RELAP5Heat Transfer Package 1 using the Gnielinski correlation. The heaterpower is applied to the heat structure that models the heatingelements. The two economizers have been modeled as counter-current flow pipes using the heat transfer coefficient as calculatedby the manufacturer. The efficiency of the RELAP modeled unitsshowed a good agreement with the values provided by the manu-facturer. Various control mechanisms are implemented to controldifferent loop parameters: in Bypass I the valve VC-002 controlsthe mass flow rate through the test module; for the test moduletemperature the power in the heater is adjusted and, in the casethat the power is zero but the temperature is higher than required,the valve VC-003 in Bypass III will intervene; the valve VC-001 inBypass II controls the temperature level at the inlet of the econo-mizer keeping it below 150 ◦C (Tref). For the present simulation itis assumed that the test module is thermally inert (no heat source)and it has only a defined pressure loss. For this reason the test mod-ule is replaced by a control valve in the simulation. The pressure atthe test module (valve) inlet is set to 10 MPa and the temperatureset-point is chosen to be 800 ◦C. The mass flow rate through thetest section is set to 200 g/s.

With respect to the two CFD simulations presented in Section1, two corresponding scenarios are carried out to analyze the loopdynamic. In the first scenario the heater is modeled without heliumgap, while in the second scenario the helium gap is modeled as aheat structure of the heater. In the scenario without the He gap,more heat is transported from the hot to the cold helium flow thanin the scenario with the gap; as a result the outlet temperature ofthe heater cold leg is higher by 37 ◦C (274.9 ◦C vs. 237.9 ◦C as indi-cated at T-002 in Fig. 6). Simultaneously more heater power is needin the first scenario than that in the second to obtain the required800 ◦C at the inlet of the test section (T-006). Fig. 7 shows the evo-lution of the heater power in the two cases as well as the effective


power and the power transferred into the cooling stream. Withouthelium gap the power limit of 200 kW is hit during the transientand at the steady state a power increase of 21.2 kW is needed. If




4 X.Z. Jin et al. / Fusion Engineering and Design xxx (2014) xxx– xxx

pe size and nodalization and simulation results at the steady state.

ticfpieptpd

Fig. 6. RELAP5-3D modeling for the helium loop including pi

he power is unlimited, the power peak would be 215.8 kW dur-ng the transient. This increased power increases at last the waterooling quantity (XH-002). In both cases the valve in Bypass II isully open because of the control temperature Tref and the tem-erature results at T-015 exceed Tref. Power increase in the heater

nduces temperature increase at T-015 that an unwanted cascadeffect is generated. Fig. 8 shows the transient behavior of the tem-erature at the test section inlet. It goes to steady state quicker in


he scenarios with helium gap than that without helium gap due toower efficiency. Concerning the thermal time constant, which is aefined time when 63% of the temperature increment is reached, it

Fig. 7. Power behavior of the heater in two scenarios.

Fig. 8. Temperature behavior at the test section inlet in two scenarios.

is about 26 s longer for the scenario without helium gap than thatwith helium gap. This difference is not significant.

5. Conclusions

Thermal-hydraulic and thermal-dynamic analyses have beenperformed for the special heater of the KATHELO facility usingANSYS CFX and RELAP5-3D respectively. The heater design withtwo vessels for the high temperature and high pressure require-


ments introduces an additional coupling between the cold leg andthe hot leg of the helium loop. The influences of this coupling andits influence on the loop dynamics have been analyzed.


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ARTICLEUSION-7173; No. of Pages 5

X.Z. Jin et al. / Fusion Engineer

The CFX simulation shows that a wrapper covering the heaterot pipe with helium gap is needed to prevent the heat transfer

rom the inner hot flow to the cold flow in the shell. The RELAPystem analysis shows that with the helium gap less heater power


s required than in the case of no helium gap. This makes again aower inlet temperature of the economizer at the cold leg, whicheads to a lower outlet temperature of the economizer at the hoteg. Consequently the cooler capacity can be reduced.

[[

PRESSd Design xxx (2014) xxx– xxx 5

References

1] B.E. Ghidersa, X. Jin, M. Rieth, M. Ionesc-Bujor, KATHELO: a new high heat flux


(2013) 854–857.2] ANSYS CFX Release 14.0, Ansys Inc., 2011.3] The RELAP5-3D Code Development Team, RELAP5-3D Code Manual, Revision

2.4, INL, 2005.


http://refhub.elsevier.com/S0920-3796(13)00769-2/sbref0005

















































conceptual design of a helium heater for high temperature applications

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