Thermo-hydraulics, colour and art

Abstract

This paper describes a thermo-hydraulics experiment performed on the mock-up of the liquid-metal cooled steel target container of a spallation neutron source. The beam of the Paul Scherrer Institute 600 MeV proton accelerator is used to obtain a high-neutron fl ux. This bombards a target under realistic experimental condi- tions, hence, becoming a probe for scientifi c experiments. The goal was to analyse and visualise the cooling of the target proton entrance window. In the mock-up, heat removal is realised by forced convection of a mercury coolant. A description of the test set-up is given and qualitative as well as quantitative results from the cooling process are presented visually. In addition, an improvement in interpretation of data is shown by using colours. In the fi nal section, an artistic output entitled 'The Collection' is presented; this consists of artifi cially-coloured infrared thermograms resembling, and compared with, butterfl ies. As part of the development programme of the Swiss Intense Neutron Source (SINQ) at the Paul Scherrer Institute (PSI) and the European Spallation Source (ESS), neutron spallation sources exper- imental concepts with liquid-metal (LM) targets have been proposed (1). One concept using a high-power neutron spallation source with a circulated LM target is shown in Fig. 1. The 600 MeV proton beam of the PSI accelerator penetrates into the target of the SINQ facility through a beam entry window. This window is strongly heated by the proton beam, the heat deposition in the steel wall resulting in a heat fl ux q* of up to 140 W/cm 2 at the inner surface of the window. The LM, in this case, mercury, is simultaneously used as target material and coolant. It is contained in an approximately 4-m long structure made of concentric pipes and vessels. The neu- tron-producing part of the target consists of two concentric steel pipes fi lled with mercury and placed in the centre of the SINQ moderator tank. The lower part of the outer pipe is closed off with a hemispherical shell, i.e. LM container (LMC), causing the LM fldown the annulus to perform a U-turn and to return upwards through the inner riser pipe (RP) to the electro-magnetic pump and the target heat exchanger. The experiments on the cooling of the proton beam entry window are part of the development pro- gramme for neutron spallation sources with LM targets at PSI. A two-dimensional and dynamic (2DD) method of using infrared thermography (IRT) techniques is applied for visualising the cooling effi - ciency of the heated window wall. This 2DD IRT methodology developed at PSI was around 2000 (2), and constantly improved upon subsequently (3, 4). It allows the elaboration of heat transfer coeffi cient (HTC) charts. The 2DD IRT methodology is based on the emissivity-corrected measurement of the thermal radiation fi eld emitted from the outer surface and arithmetical constructions of the temperature fi elds on outer and inner surfaces of the LMC window. Finally, the fi eld of the differential temperature, i.e. the difference between the inner-surface temperature and the bulk LM coolant temperature, is worked out. In this way, the differential temperature thermograms obtained, together with known val- ues of the applied heat fl ux, allow both qualitative and quantitative HTC characteristics of the cooling to be determined. The patterns of the fl ow in the boundary layer on the inner surface of the window wall are made visible. Finally, animated IR differential thermogram sequences can be generated, allowing