Chris Menictas

Thermal Stability of Concentrated V(V) Electrolytes in the Vanadium Redox Cell

The vanadium redox battery currently employs solutions of up to 2 M V(II)/V(III) and 2 M V(IV)/V(V) as the negative and positive half-cell electrolytes. This concentration is limited by the solubility of the different vanadium ions in the temperature range of 10 to 40 C. Generally, the solubility of V(II), V(III), and V(IV) increases with an increase in temperature; however, the V(OV) electrolyte suffers from the effect of thermal precipitation at temperatures of 40 C and above. While thermal precipitation is a serious problem in solutions of V(V) concentrations between 1.5 and 2.0 M, a surprising result was observed at concentrations above 3.0 M. As the results presented here show, at higher vanadium concentrations the V(V) solution demonstrated increased stability and there was no evidence of thermal precipitation over a 30 day period at temperatures above 40 C.

Evaluation of an NH4VO3-derived electrolyte for the vanadium-redox flow battery

Abstract The electrolyte used in the vanadium-redox flow battery provides an energy storage system the produces no waste products. Initially, the electrolyte was derived from VOSO4 and significant cost reductions were obtained by using an electrolyte derived from V2O5. The use of NH4VO3 as the starting material for electrolyte production offers further possible cost reductions. A coulombic efficiency of 98%, a voltage efficiency of 94%, and an overall energy efficiency of 91.8% are obtained at a constant charging and discharging current density of 14.5 mA cm−2 for a test vanadium-redox flow cell that employs an electrolyte derived from NH4VO3. The electrolyte has been further treated to examine the possibility of ammonium removal. Cell-resistance measurements and cyclic voltammetry studies are reported for the treated and untreated NH4VO3 electrolyte.

Frequency response analysis of anode current signals as a diagnostic aid for detecting approaching anode effects in aluminum smelting cells

Modern cell control aims to prevent anode effects by controlling the alumina feeding rate based on the change in cell resistance or voltage and the preset limits of these values. Success of this approach depends on the uniform distribution of dissolved alumina across the cell and the anode current distribution. As this is not always the case in practice, the control procedure sometimes fails and the cell undergoes anode effect. Monitoring of the anode current signals has been suggested as an alternative way for early anode effect detection. This paper presents frequency response analysis of anode current signals obtained from an operating cell and shows the ability for early detection of an anode effect. It has been found that the frequency response peak associated with bubble dynamics of the corresponding anode disappears as it undergoes partial anode effect prior to the cell approaching full anode effect. The results show that the analysis can provide further information to identify a localized anode effect which can facilitate cell control for more effective anode effect prevention.

Thermal modelling of controlled scalp hypothermia using a thermoelectric cooling cap

This study presents a novel, thermoelectric cryotherapy cap that aims to provide effective and controlled scalp cooling to prevent hair loss for chemotherapy patients. The caps design consists of multiple thermoelectric coolers (TECs) evenly spaced and bonded to a soft thermal interface material, tightly fitted to a patients head. A numerical model is developed to assess the performance of alternative cap designs in relation to their ability to achieve hair follicle hypothermia. Under ideal conditions, 26.5 W of heat removal from the scalp is required to achieve the clinically-significant follicle temperature target of 22 °C. Temperature maps of the subcutaneous tissue are generated to visualise the development of hypothermic follicles, and thereby assess the effectiveness of the cap design. Transient studies show that cooling to the therapeutic temperature can be achieved within 40 min. To avoid the possibility of cold-induced tissue damage, individual thermoelectric cooling modules should not be operated at a cooling flux beyond approximately 3175 W/m2. This may be achieved with 38 modules evenly spaced in a checkerboard arrangement, each providing 0.7 W of cooling to the scalp.

Impacts of Anode Set on the Energy Re-distribution of PB Aluminum Smelting Cells

Since the introduction of prebaked anodes technology in Hall-Heroult process, anode setting has become one of the routine work practices. As all anodes in different parts of the cell are changed in turn at short regular intervals, the operation is always subject to a different degree of disturbances. This paper presents a dynamic thermal model that can be used to simulate the impact of anode setting on the local thermal balance and hence the overall operating condition by incorporating individual anode current signals as model inputs. This is done by discretizing the bath into multiple subsystems based on the position of each anode. The model can predict the local thermal conditions during the increase of current pick up of a newly replaced anode when based on online measurements of current distribution. A model incorporated with anode current distribution as model inputs can be employed as a foundation for future development of an online fault diagnostic system to help isolating other disturbances, hence improve early detection of impending abnormal conditions.