Ionut Voicu

Earth-based materials are promising candidates for balancing thermal performance, hygrothermal regulation, and environmental sustainability. The objective of this study is to evaluate and compare the hygrothermal behavior of two earthen materials, structural cob and lightweight insulating earth, against conventional reference concrete, taking into account not only their insulating properties but also their ability to regulate coupled heat and moisture transfers. Experimental tests show a significantly higher hygroscopic buffering capacity for earth-based materials, with an MBV of 2.23 g/(m²∙%RH) for the structural material and 1.21 g/(m²∙%RH) for the insulation material, compared to less than 0.5 g/(m²∙%RH) for concrete. The sorption isotherms confirm distinct water storage behaviors, with an average sensitivity to relative humidity of 10.47% for the insulation material, compared to 3.8% for concrete and 2.25% for the structural material, in addition to an average reduction of 26% in the adsorption capacity between 23 °C and 45 °C for both earthen materials. Coupled heat–moisture simulations in COMSOL quantitatively demonstrate the hygrothermal superiority of bio-based materials over conventional concrete, as concrete promotes interstitial moisture accumulation due to its low vapor permeability. The parametric sensitivity analysis highlights the effect of hygrothermal properties, where diffusivity controls transport kinetics and sorption governs water storage, while thermal conductivity modulates the spatial redistribution of thermo-hygric fields. The next and final step made it possible to link the phenomena observed at the material scale to the actual energy performance of the building, confirming the potential of the double-wall cob + lightweight earth system to reduce heating and cooling requirements and maintain stable indoor comfort, where the annual heating demand is reduced by approximately 24% compared to the conventional prototype.

Biosourced materials made of a combination of raw earth and fibers are attracting increasing interest for low-carbon construction due to their reduced environmental impact and good thermal and hygric performance. This study investigates several soil–fiber composites selected and formulated at different densities to assess their thermal conductivity, enabling the selection of two complementary materials: a structural earthen mix and a lightweight insulating mix. Experimental measurements were taken under controlled conditions and used to characterize heat and moisture fluxes, and numerical calculations were carried out to evaluate the performance of single and double-layer wall configurations. The results showed that an increase in thermal gradients accelerates vapor migration and alters the internal distribution of moisture. The evaluation of wall configurations demonstrated that placing the earthen insulating layer externally optimizes thermal fluxes and eliminates condensation risks at the interface between materials, while internal insulation can be sensitive to hygrothermal gradients and prone to moisture accumulation. The combined experimental–numerical approach provides new insights into high-performance designs of bio-based earthen envelopes, establishing guidelines for minimizing moisture-related risks in low-carbon building systems.

This paper highlights the impact of environmental conditions on cob buildings. Different factors such as wall thickness, material permeability and interactions between moisture and heat fluxes can all have significant effects on the performance and durability of cob buildings. An experimental and modeling-based study was conducted on the hygrothermal characterization of cob building materials, which were obtained by mixing earth and fibers. Two types of cob materials that can be used as insulation and to form structural materials in buildings were tested. The effect of outside temperature on adsorption isotherms was investigated for both materials. The experimental data were fitted using the GAB model, after which a new correlation of water content correlation was proposed. Three specific configurations were investigated in which cob material was subjected to moisture transfer and a zero, positive or negative temperature gradient. Based on the resulting measurements, a high coupling effect between heat and moisture transfer inside the structural material was analyzed. A comparison of the experimental and modeling results demonstrated the satisfactory correlation and reliability of the developed model. Simulations were carried out for various wall thicknesses, in order to assess the effect of heat and moisture transfer on water content. The three scenarios were simulated and distributions of water content inside the walls were determined. The results show that the wall thickness of cob buildings and the direction of heat and moisture fluxes affect water content distribution in the structure. A greater thickness of the cob wall leads to higher water content, but this relationship reverses when the heat and moisture fluxes move in the same direction.

Supercapacitors (SCs) are electrical energy storage devices which have the peculiarity of storing more electrical energy than capacitors and supply it at higher power outputs than batteries. This, together with the fact that the SCs have high cyclability and long-term stability, make them very attractive devices for electrical energy storage. Thermal transfer around a novel arrangement of a module of five rows of SCs is approached in this paper. A mixed aligned/staggered configuration is studied, aiming to explore a new possibility that can improve heat transfer more than other configurations studied before in the literature. The maximum SC current rate current is 84 A and the maximum temperature is 65 °C. The module undergoes charge and discharge cycles. The current tests are performed up to 50 A for natural convection and up to 70 A in forced convection. For the natural convection case, the SC located in the center of module is the most critical from the temperature point of view and the temperature evolution shows the necessity of a cooling system. The relative temperature reaches 27 °C for 50 A and the permanent regime cannot be reached with a current greater than 50 A. Thereafter, the impact of position and current on the temperature of SCs in forced convection is examined. The airflow mean air velocity is 0.69 m/s. The temperature of the SCs located on the third and fourth row are very close. However, the last row is the least cooled. This low temperature rise can be explained by the change from an aligned to a staggered arrangement between these rows. Compared to the natural convection case, a significant decrease is observed for the relative temperatures. The difference between the highest and lowest temperature augmentation also decrease but remain high. The temperature difference becomes greater than 5 °C if continuous current exceeds 39 A. CFD numerical simulation is performed for steady state at maximum experimental current rate in order to better understand the thermal and flow behavior. Numerical and experimental results are in good agreement, with a temperature deviation of less than 10%.

This paper is focused on a problem that may appear in the technological process inside a waste water plant and may disturb the normal water treatment technology. It is a sedimentation process that could appear between the screenings and the grit removals because of low velocity values of the flow. This sedimentation process just before the access area to the grit removals has to be avoided in order to ensure the normal water flow rate. In this paper we have envisaged the possibility to modify the structure of the water flow in order to avoid low velocity values that could increase the sedimentation process. The free surface flow structure will be modified by introducing new wall structures to create new water paths at normal velocities and to avoid low velocities areas. The study is a numerical one using CFD tools. First of all the numerical calculus was directed to point out the areas where the flow velocity is low and the sedimentation could appear and secondly the new system configurations are tested in order to prove the new free surface flow structure. The need of validate the numerical results is also considered in the article.