Processes

Surface defects are frequently observed in calendered polyvinyl chloride (PVC) films. Their evaluation in production environments is typically qualitative and operator dependent. Using the common gas entrapment defects as the test case, the present study develops a four-step image-processing workflow that converts scanned film images into pixel intensity matrices and groups defect pixels using density-based clustering (DBSCAN). The procedure provides quantitative measures of defect count, size, and spatial distribution without manual labeling. The effects of roll gap, calendering speed, upstream mixing time, and plasticizer type were examined under controlled conditions. Larger roll gaps and higher speeds reduced degassing efficiency and increased both defect number and defect area. Short mixing times led to incomplete gelation and higher defect frequency. Among the tested plasticizers, TOTM produced the lowest defect counts, followed by DEHP and ESBO. Design-of-experiments analysis ranked parameter sensitivity and identified operating ranges that limit defect formation. The method provides a practical basis for routine surface inspection and supports process adjustment using measurable defect metrics rather than visual judgment alone.

This study investigates the impact of ethanol as a co-solvent in hydrothermal carbonization (HTC) of sewage sludge, a process referred to here as ethanothermal or solvothermal carbonization. Experiments were conducted at 180 °C, 200 °C, 220 °C, and 240 °C, comparing two sets of conditions: one using water (S/W) and the other using ethanol (S/E) as the reaction medium. The focus was placed on the composition of the aqueous phase, particularly the formation of volatile fatty acids (VFAs). Ethanol-assisted experiments consistently produced more alkaline process water (pH 7.6–8.2) compared to water-based runs. COD values in S/W samples ranged from 9358 mg/L to 19,756 mg/L, indicating significant organic loading. Hydrochar derived from the ethanol experiments exhibited higher energy content, with a peak high heating value (HHV) of 21.9 MJ/kg at 240 °C, compared to 19.9 MJ/kg in S/W samples. VFA concentrations were also enhanced under ethanothermal conditions, especially at lower temperatures: formic acid (30.4–34.8 mg/L), acetic acid (8.7–9.6 mg/L), and propionic acid (10.8–14.6 mg/L). These results demonstrate ethanol’s potential to enhance both the yield and quality of liquid and solid products in HTC of sewage sludge.

The paper presents an experimental comparison between a standard evacuated tube solar collector and a collector featuring a modified internal manifold architecture with an integrated metal-foam heat-exchange chamber. Both collectors have an identical geometric volume of the heat-exchange region, ensuring that the measured differences in performance are exclusively attributable to changes in the internal design of the manifold. The experimental validation comprised five measurements conducted at two mass flow rate levels, 60 and 120 kg·h⁻¹, under real outdoor operating conditions. The evaluation was based on time-resolved performance data and included instantaneous, cumulative, and dynamic indicators, such as energy yield, volumetric energy density, performance stability, dynamic sensitivity, and energy inertia. The results show that the solar collector with the modified manifold consistently achieves a higher energy yield, higher volumetric efficiency, and lower dynamic sensitivity than the standard collector. These benefits are obtained at the cost of increased pressure losses, indicating a trade-off between energy performance and hydraulic demand under real operating conditions.