Search

A novel coaxial mixer was proposed,which had an outer wall-scrapingframe and a combined inner impeller consisting of a four-pitched-bladeturbine paddle (PBT-4) and a Rushton turbine paddle (RT-6). Its heattransfer performance in Newtonian fluid under different operatingmodes (single rotation of inner impeller, corotation and counter-rotation)was experimentally investigated in a stainless steel agitated vesselwith semicircle spiral jacket and ellipsoidal head by measuring theaverage heat transfer coefficient of the inner wall. Meanwhile, thewall temperature, the heat flow rate and the local heat transfer coefficientin the coaxial agitated vessel were determined with the help of numericalsimulation. The results show that the heat transfer coefficient nearthe inner wall surface of the agitated vessel will increase with theincreasing speed of the inner or outer impeller whether under single-shaftagitation or under coaxial agitation mode, whereas the effect of speedof the inner impeller on heat transfer is more obvious and efficient.Under the same conditions, the heat transfer of coaxial agitationis more efficient than that of single-shaft agitation, especiallythe local heat transfer coefficient on the upper and lower part ofthe agitated vessel, which is increased greatly. In addition, thelocal heat transfer coefficient varies with the axial position ofthe agitated vessel, and the heat transfer coefficient in zones betweenthe upper and lower impeller is relatively high. The effect of thecorotation mode and counter-rotation mode on heat transfer is of littledifference, but the corotation mode is recommended owing to its advantageof low power consumption and good mixing performance. [ABSTRACT FROM AUTHOR]

The magnetocaloric effect (MCE) is currently intensively investigated in various rare earths ( RE )-containing magnetic solids, not only for developing appropriate magnetocaloric materials (MCMs) for cryogenic magnetic cooling but also for deepening our understanding into the inherent physical properties of these materials. Here, we provide a systematic experimental investigation into a series of new RE 2 CuTiO 6 ( RE = Dy, Ho, Er) double-perovskite (DP) oxides regarding the structural and magnetic properties, especially for their cryogenic MCE and magnetic-phase transition (MPT). All of these RE 2 CuTiO 6 oxides crystallize in a B -site-ordered hexagonal DP-type structure with the symmetry of the crystallographic space group P 6̅ m 2. These DP oxides exhibit magnetic ordering, with MPT temperatures of approximately 2.7, 2.2, and 2.7 K for Dy 2 CuTiO 6 , Ho 2 CuTiO 6 , and Er 2 CuTiO 6 , respectively. The magnetocaloric performances of the RE 2 CuTiO 6 DP oxides were characterized by the peak values of magnetic entropy change, the temperature-averaged magnetic entropy change (5K-lift), and relative cooling powers. These magnetocaloric parameters were deduced to be 18.7/17.9 J/kgK and 298.2 J/kg for Dy 2 CuTiO 6 , 12.5/12.2 J/kgK and 273.9 J/kg for Ho 2 CuTiO 6 , and 13.8/12.9 J/kgK and 188.4 J/kg for Er 2 CuTiO 6 under a magnetic field change of 0-5 T. These values are comparable to those of most reported RE -containing magnetocaloric materials, indicating that these RE 2 CuTiO 6 DP oxides are promising candidates for cryogenic magnetic cooling applications.

The magnetocaloric (MC) and magnetic phase transition (MPT) properties in various types of rare earth ( RE )-based magnetic materials have been intensively investigated recently, which are aimed at developing suitable MC materials for low-temperature cooling applications and better elucidating their inherent physical properties. We herein provide a combined experimental and theoretical investigation into two new light RE -based magnetic materials, namely, PrZnSi and NdZnSi compounds, regarding their structural, magnetic, MPT, and low-temperature MC properties. Both of these compounds crystallize in an AlB 2 -type hexagonal structure with a symmetry of the crystallographic space group P6 / mmm and reveal a typical second-order-type MPT with ordering temperatures ( T C ) at approximately 13.5 and 18.5 K for PrZnSi and NdZnSi compounds, respectively. Moreover, they all exhibit large reversible low-temperature MC effects and remarkable performances, which are identified by the parameters of maximum magnetic entropy changes, relative cooling power, and temperature-averaged entropy change (temperature lift 5 K). The deduced values of these MC parameters under a magnetic field change of 0-7 T reach 16.3 J/kgK, 294.46 J/kg, and 15.79 J/kgK for PrZnSi and 15.4 J/kgK, 284.84 J/kg, and 14.95 J/kgK for NdZnSi, respectively, which are evidently better than those of most updated light RE -based magnetic materials with remarkable low-temperature MC performances, indicating that PrZnSi and NdZnSi compounds hold potentials for practical cooling applications.