The electrical resistance of the tantalum–hydrogen system at low temperatures

The data on electroresistance of samples TaH_x (x=0.0016,0.0071,0.04) in the interval 5–100 K, that is in two-phase area, are given. The residual resistance is caused mainly by electrons scattering on the hydride precipitates. With increase of temperature the excess resistance, caused by hydrogen, depends on temperature non-monotonously, passing through a maximum in region 50 K. A minimum near 90 K is observed, connected with growth of resistance due to formation of a homogeneous solid solution of hydrogen.     

Investigation on Ti–Zr–Cr–Fe–V based alloys for metal hydride hydrogen compressor at moderate working temperatures

Ti_0.85Zr_0.17Cr_1.2-xFe_0.8V_x (x = 0–0.2), Ti_0.85Zr_0.17Cr_1.2-yFe_0.7+yV_0.1 (y = 0–0.25) and Ti_0.87-zZr_0.15+zCr_0.95Fe_0.95V_0.1 (z = 0–0.04) alloys for metal hydride hydrogen compressor at moderate working temperatures were prepared by induction levitation melting. Their microstructures and hydrogen storage properties were systematically investigated. The results show that all Ti–Zr–Cr–Fe–V based alloys have a single C14 Laves phase structure. As the V content in the Ti_0.85Zr_0.17Cr_1.2-xFe_0.8V_x (x = 0–0.2) alloys increases, better activation kinetics and larger hydrogen storage capacity are achieved, while the plateau pressure decreases and the plateau slope factor increases. Similarly, the hydrogen storage capacity, the plateau pressure and the plateau slope factor of the Ti_0.87-zZr_0.15+zCr_0.95Fe_0.95V_0.1 (z = 0–0.04) alloys vary identically with Zr content increasing. Conversely, these three properties vary oppositely with increasing Fe content in the Ti_0.85Zr_0.17Cr_1.2-yFe_0.7+yV_0.1 (y = 0–0.25) alloys. Among the studied alloys, Ti_0.85Zr_0.17Cr_0.95Fe_0.95V_0.1 possesses the best overall properties for the designed moderate hydrogen compression application.     

Theoretical analysis of a CO2–NH3 cascade refrigeration system for cooling applications at low temperatures

As a result of environmental problems related to global warming and depletion of the ozone layer caused by the use of synthetic refrigerants (CFC’s, HCFC’s and HFC’s) experienced over the last decades, the return to the use of natural substances for refrigeration purposes, appears to be the best long-term alternative. In this paper, a cascade refrigeration system with CO₂ and NH₃ as working fluids in the low and high temperature stages, respectively, has been analysed. Results of COP and exergetic efficiency versus operating and design parameters have been obtained. In addition, an optimization study based on the optimum CO₂ condensing temperature has been done. Results show that following both method’s exergy analysis and energy optimization, an optimum value of condensing CO₂ temperature is obtained. The compressor isentropic efficiency influence on the optimum system COP has been demonstrated. A methodology to obtain relevant diagrams and correlations to serve as a guideline for design and optimization of this type of systems has been developed and it is presented in the paper.     

Advanced fuel cell based on semiconductor perovskite La–BaZrYO3-δ as an electrolyte material operating at low temperature 550 °C

As an electrolyte, enough ionic conductivity, either proton (H⁺) or oxide (O²⁻) conduction, has demanded the better performance of low-temperature (especially below 550 °C) solid oxide fuel cell (LT-SOFCs). Notably, that either conductivity, higher performance, reliability, or higher cost is hampering the LT-SOFC marketing. In our current subject, we report the La-doped BZY proton conductor as an electrolyte has exhibited high ionic conductivity of 0.15 S/cm with a higher performance of 0.78 W/cm² at 550 °C. Also, the performance of LBZY is superior to the un-doped BZY electrolyte. Such high performance mainly ascribed due to the doping of La into BZY. Besides, the mechanism for high ion conductivity is explained. This work manifests that using the LBZY semiconductor perovskite as an electrolyte is more suitable for fuel cell technology.     

Nuclear fuel rod cladding oxidation and hydrogen production model based on diffusion theory in a multiphase environment of ZrO2, α-Zr(O), and β-Zr at high temperatures (1273 K–1800 K)

This paper proposes a mathematical model for the oxidation process of zirconium under the theory of oxygen diffusion in Zircaloy. The model considers ZrO₂, α-Zr(O), and β-Zr phases at high temperatures (1273 K–1800 K) in an equivalent fuel rod. The model also considers the heat transfer phenomenon, the decay heat after shutdown, the heat released by the oxidation reaction, the loss of coolant water in the core and the heat transported by the steam produced. A computer program was coded in the C++ environment. The accident scenario of a BWR short term station blackout was simulated with this model. The results are compared with the ones obtained using MELCOR and RELAP/SCDAP codes. The comparison yielded an approximate result for total hydrogen production at the end of the simulation, with a difference of ?2.7% compared with RELAP/SCDAP, and a difference of ?1.11% with MELCOR. With the present model it is possible to calculate the growth of ZrO₂, α-Zr(O), and β-Zr phases through the cladding.