Improving Heat Exchange Performance of Massive Concrete Using Annular Finned Cooling Pipes

Cracks will be generated due to high internal temperature of the massive concrete. Postcooling method is widely employed as a standard cooling technique to decrease the temperature of the poured mass concrete. In this paper, an annular finned cooling pipe which can increase the heat transfer area between the flowing water and its surrounding concrete is proposed to enhance the cooling effect of the postcooling method. Analysis of the interior temperature variation and distribution of the concrete block cooled by the annular finned cooling pipe system and the traditional cooling pipe system was conducted through the finite element models. It is found that, for the concrete block using the proposed annular finned cooling pipe system, the peak value of the interior temperature can be further lowered. Compared with the traditional cooling pipe, the highest temperature of concrete with an annular finned cooling pipe appears earlier than that with the traditional cooling pipe.

Prediction of J-Integrals at Defects in W-9CR Steel Sandwich-Type Cooling Pipes

Sandwich-type cooling pipes of the first wall of future fusion nuclear reactors (i.e. DEMO) will likely consist of tungsten brazed to a Reduced Activation Ferritic Martensitic (RAFM) steel. Under a high heat flux (HHF) (1–5 MW/m2) the mismatch in thermal expansion between tungsten and steel results in significant thermal stresses in the brazing region. These stresses can cause crack initiation and growth and thus compromise the structural integrity of such pipes. Finite element analyses have been performed on the brazed joints of a reference cooling assembly under HHF. Thermal stresses and resulting plastic strains were estimated for both the braze interlayer and parent materials. As images of brazed joints revealed, brazing processes are very likely to induce defects near the edges of the joints. A crack is therefore introduced in the brazed region where simulated stresses and strains are found to be the highest. J-integrals were calculated for cracks growing from an edge to the center of the considered piping assembly. The results are discussed in relation to the current sandwich-type piping design of the DEMO reactor.

Mechanical and Microstructural Characterisation of Cooling Pipes for the Compact Muon Solenoid Experiment at CERN

The Compact Muon Solenoid (CMS) is a particle physics experiment situated on the Large Hadron Collider (LHC) at CERN, Switzerland. The CMS upgrade (planned for 2025) involves installing a new advanced sensor system within the CMS tracker, the centre of the detector closest to the particle collisions. The increased heat load associated with these sensors has required the design of an enhanced cooling system that exploits the latent heat of 40 bar CO2. In order to minimise interaction with the incident radiation and improve the detector performance, the cooling pipes within this system need to be thin-walled (~100 μm) and strong enough to withstand these pressures. The purpose of this paper is to analyse the microstructure and mechanical properties of thin-walled cooling pipes currently in use in existing detectors to assess their potential for the tracker upgrade. In total, 22 different pipes were examined, which were composed of CuNi, SS316L, and Ti and were coated with Ni, Cu, and Au. The samples were characterised using computer tomography for 3D structural assessment, focused ion beam ring-core milling for microscale residual stress analysis, optical profilometry for surface roughness, optical microscopy for grain size analysis, and energy dispersive X-ray spectroscopy for elemental analysis. Overall, this examination demonstrated that the Ni- and Cu-coated SS316L tubing was optimal due to a combination of low residual stress (20 MPa axial and 5 MPa hoop absolute), low coating roughness (0.4 μm Ra), minimal elemental diffusion, and a small void fraction (1.4%). This result offers a crucial starting point for the ongoing thin-walled pipe selection, development, and pipe-joining research required for the CMS tracker upgrade, as well as the widespread use of CO2 cooling systems in general.

Effect of elevated temperature on solid waste shear strength and landfill slope stability

Slope instability occurs in landfills owing to increased internal temperatures. However, strength characteristic tests for solid waste (SW) and landfill slope stability (SS) calculations that consider temperature variations are scarce in the literature. In this study, we conducted triaxial tests on SW under a range of temperature conditions and proposed the circular slide method (CSM) for calculating SS in consideration of temperature effects. SW cohesion decreased linearly with increasing temperature, whereas the internal friction angle remained essentially unchanged. Our results showed that higher temperatures reduced the SW shear strength, changing the most dangerous sliding arc away from the slope toe. The landfill slope safety factor decreased by more than 20% with an increase of the maximum temperature from 20°C to 50°C. Reduction of the leachate level (LL) led to a decrease in the landfill high-temperature zone and the safety factor increased according to LL and temperature distribution. If cooling pipes are used to control the SW temperature, we recommend arranging the cooling pipes on the landfill liner. The proposed CSM can be used to analyse landfill SS.