Empirical Investigation of the Hygrothermal Diffusion Properties of Permeable Building Membranes Subjected to Variable Relative Humidity Condition

Hygrothermal modelling is increasingly used to inform building envelope design. A key input for these calculations is the material’s vapour diffusion properties. Respecting a growing international concern, this research has questioned the appropriateness of the current test method to establish construction material for vapour diffusion properties. This article reports on the empirical measurement of the vapour diffusion properties of two vapour-permeable building membranes commonly used in Australia residential systems when subjected to variable relative humidity conditions. The method involved completing dry cup and wet cup standard tests as specified in ISO 12572, (23 °C and 50% relative humidity RH). Further tests were then conducted as temperature remained at 23 °C but the relative humidity changed to 35%, 65% and 80%, respectively, in order to know if the diffusion properties are the same or change with varying relative humidity. The results from the wet cup and dry cup tests under different relative humidity conditions were non-linear and different. These results indicate vapour-permeable membranes behave differently when exposed to different relative humidity conditions. In conclusion, this research demonstrates that the current vapour resistivity test method is inadequate, hence the need to establish more detailed diffusion resistivity properties in different humidity ranges that represent conditions experienced within a building’s external envelope.

Electrothermal Desiccant Regeneration Technique for Air Dehumidification

Adsorption dehumidification and drying equipment is essential general equipment for domestic and industrial use. The most commonly used type in industry is the compressed air adsorption dryer. The analysis results show that the heat loss of the traditional heat air regeneration system of the compressor dryer is 39.4%, and the exhaust waste heat is 32.4%. The actual use of heat energy for desiccant regeneration is only 28.2%. Therefore, this study uses an innovative electrothermal adsorbent unit (ETAU) to regenerate the desiccant. By directly heating the adsorbent, heat loss can be effectively improved. On the other hand, the composite arrangement of zeolite and activated alumina is used. The inlet compressed air is firstly treated by the activated alumina, which has a high adsorption capacity in the high relative humidity condition, then a zeolite is used as a second part to make the dew point reach –40 °C. In the regeneration step, the airflow direction is reversed, whereby the zeolite is regenerated by the ETAU, and the waste heat of the exhaust air is used to regenerate the activated alumina, which reduces the temperature of the exhaust air. Compared with the traditional heat air compressed air system, the two technologies can save about 27% energy in total.

Enhanced Photo-Assisted Acetone Gas Sensor and Efficient Photocatalytic Degradation Using Fe-Doped Hexagonal and Monoclinic WO3 Phase−Junction

The development of WO3-based gas sensors for analysis of acetone in exhaled breath is significant for noninvasive diagnosis of diabetes. A series of Fe-doped hexagonal and monoclinic WO3 phase−junction (Fe−h/m−WO3) sensors were synthesized by the hydrothermal calcination method, and the influences of operating temperature and light irradiation on the response were studied. Under light emitting diode (LED) illumination, Fe−h/m−WO3 exhibited higher responses to acetone than those of the undoped WO3-based sensors at an operating temperature of 260 °C with 90% relative humidity, and good linearity between response and acetone concentration (0.5 to 2.5 ppm) was achieved under the 90% relative humidity condition. Meanwhile, the optimal Fe−h/m−WO3 sensor exhibited high selectivity and stability for a duration of three months. The excellent sensing performance of Fe−h/m−WO3 was attributed to the formation of phase−junction and Fe doping, and these were beneficial for the separation of photon−generated carriers and oxygen adsorption on the WO3 surface, promoting the generation of superoxide radicals, which was demonstrated by electron paramagnetic resonance and photocurrent tests. Additionally, the Fe−doped WO3 phase−junction sample also showed good photocatalytic performance for rhodamine B degradation. This study may provide some insights into rational design of new types of gas sensors and offer an alternative for noninvasive diagnosis of diabetes.

Integrated adsorption and photocatalytic degradation of VOCs using a TiO2/diatomite composite: effects of relative humidity and reaction atmosphere

The optimal relative humidity condition for VOC degradation is related to the length of the carbon chain of VOCs.

The Sensitivity of Temperature to Tachyhydrite Formation: Evidence from Evaporation Experiments of Simulated Brines Based on Compositions of Fluid Inclusions in Halite

An average of concentrations of Na+, Mg2+, Ca2+, K+, and Cl– in fluid inclusions, from the Khorat Plateau evaporite primary halite, was employed. The evaporation–crystallization sequence and paths were obtained under various temperature conditions for the quinary system, Na+, K+, Mg2+, Ca2+//Cl–-H2O. The results showed (1) a halite, sylvite, and carnallite stage at 25°C; (2) a halite, sylvite, carnallite, and bischofite stage at 35°C; and (3) a halite, sylvite, carnallite, bischofite, and tachyhydrite stage at 50°C. These results indicated that (1) a hot state is favorable for tachyhydrite formation, (2) tachyhydrite occurs in the late evaporation stage, and (3) the stability field of tachyhydrite increases with increasing temperature. The crystallization paths were plotted by the application of Jänecke phase diagram at 25°C, 35°C, and 50°C involving the system Na+, K+, Mg2+, Ca2+//Cl–-H2O. The crystallization sequence predicted on the Jänecke phase diagram showed a good agreement with the experimental crystallization sequences and paths. Tachyhydrite precipitate more easily from a high Ca concentration solution during the late evaporation stage with increasing temperature under the same relative humidity condition. The evaporite mineral succession in the Khorat Plateau, Sergipe, and Congo basins agrees well with the mineral precipitation sequences predicted from their own fluid inclusions in halite. This is confirmed by the simulation of the Jänecke phase diagram at 50°C involving the system Na+, K+, Mg2+, Ca2+//Cl–-H2O. The precipitation of tachyhydrite was sensitive to the temperature, and that the thermal resource may originate from a temperature profile in the solar pond. This study presented a simulated approach that can help in understanding similar cases that studies the sensitivity of temperature to salt formation.

Sensing Characteristics of Smart Microsensor Systems for Measuring Relative Humidity in Pressurized Air

The detailed experimental investigation of the performance of a commercially available smart humidity sensor used for the measurement of relative humidity at elevated pressures (0.1–2 MPa) is reported. A dedicated set-up was developed for generating defined humidities in pressurized air. The measurements reveal that the pressure coefficient of the sensor deviation at a given relative humidity condition cannot be attributed solely to the enhancement factor of the humid air. For such microsensors, an additional sensor-specific pressure compensation factor was determined which is significant for precise measurements in applications with pressurized air.