"The answer is blowin' in the wind" - case study of a perforated roof screen

A recently-completed building was fitted with a roof screen fabricated from perforated sheet metal panels having "U"-shaped upturned flanges. When wind impinges on the panels, complex tone clusters are generated, leading to complaints from the occupants. The unusual character of the tonal spectrum is reminiscent of a film sound effect intended to simulate a hovering extraterrestrial spacecraft. After some preliminary (but inconclusive) field investigations, it was decided to test samples of the perforated panel in a large commercial wind tunnel where the speed and angle of the airstream could be controlled. Tones generated in the tunnel were found to occur in groups or clusters - these are most pronounced when the airstream's angle of incidence is close to grazing. Gradually increasing airspeed caused the frequency of the tones to "jump" from one cluster to the next higher cluster. The physical principles of the tone-generating mechanism are not fully understood; however, it appears that structural resonances in the panel flanges are excited by air flowing over the perforate. Some form of a positive structural-acoustical feedback loop is involved since a) the frequencies within each tone cluster are quite stable and, b) damping the panel flanges extinguishes the tones.

Mechanical behavior of toilet paper perforation

Perforation is used in multilayer tissue products, such as toilet and kitchen papers, as part of the converting process. Perforation facilitates the detachment of consecutive sheets by the user. The compromise between the strength required to detach a perforated sheet and the strength required to break a sheet affects the perforation efficiency. In this work, the mechanical behaviors of 15 commercial papers from different European producers were studied. A morphological analysis of the materials was performed, followed by the determination of their perforation efficiency (through tensile tests). A qualitative analysis of the cuts quality, along with a quantitative analysis of the same cuts dimensions was performed through an optical system. Finally, the stress concentration in the holes and the influence of the cuts distance were analyzed using a finite element model implemented in Abaqus/Standard finite element software. The results showed that a cut distance of 2.0 mm should not be used in these types of papers, and the perforation efficiency increased with the cut distance, regardless of the number of plies in the toilet paper. The stress concentration factor was also determined to have a limit value of 0.11. Papers above this limit value tear at the perforation line, as desired.

Thermal analysis of a solar hybrid dehydrator designed for uniform multi-product drying

Thermal analysis was performed for a vertical cabinet solar hybrid dryer having a salient feature of perforated sheet along its entire height to achieve uniform drying. The dryer was integrated with a solar collector and gas burner for hybrid heating source. Experiments were performed using tomato at 55°C with solar, gas, and dual (solar-gas) heating sources. Energy analysis showed that rates of energy utilization were found in ranges of 2.7-12.5 kW (dual), 3-13 kW (gas), 2.9-12 kW (solar) and energy ratios were 13-56% (dual), 14-58% (gas), 12-50% (solar). Exergy analysis showed that exergy losses were 2.1-5.0 kJ/kg (dual), 2.1-5.3 kJ/kg (gas) 1.5-4.2 kJ/kg (solar) while exergy efficiencies found 33-70% (dual), 30-75% (gas), 20-69% (solar). Based on higher values of exergetic factor and improvement potential rate (IP), it was found that optimization of heating source especially those consisting solar collector and heat exchanger (IP 1.93 kW) is required. The specific energies for the removal of product moisture and to dry the product were found 2.42, 2.72, 2.58 MJ/kg of water and 18.8, 21.2, 20.15 MJ/kg dried product for drying processes conducted under solar, gas, and dual (solar-gas) heating sources respectively. For design optimization, a complete algorithm has been prepared for complete drying systems in terms of available energy and losses.

Efficient Lipid Bilayer Formation by Dipping Lipid-Loaded Microperforated Sheet in Aqueous Solution

This paper describes a method for a bilayer lipid membrane (BLM) formation using a perforated sheet along with an open chamber. Microscopic observation of the formed membrane showed a typical droplet interface bilayer. We proved that the formed membrane was a BLM based on electrical measurements of the membrane protein α-hemolysin, which produces nanopores in BLMs. Unlike the conventional approach for BLM formation based on the droplet contact method, this method provides aqueous surfaces with no organic solvent coating layer. Hence, this method is suitable for producing BLMs that facilitate the direct addition of chemicals into the aqueous phase.

Development of New Mash Filters for Craft Beer Brewing

Introduction. New innovative technologies make food industry more effective. The present paper introduces a new method of hopped wort production based on novel mash filters. Study objects and methods. The research featured two new designs of mash filters. The study of the mashing process involved malt, hops, drinking water, and beer wort. The research included generally accepted methods of physicochemical and sensory research. Results and discussion. Both models differed from the traditional design. Mash filter I had a cylindrical filtration vat at its bottom with filters in the lower and upper parts of the vat. A pump was installed on the outer side of the steam jacket to produce forced circulation of the liquid medium flow through the vat. The steam jacket was covered with Corundum Classic superfine liquid thermal insulation. Mash filter II had a filtration bottom made of perforated sheet and provided intensive liquid circulation. It also had a regulated mixer that moved the mash, which significantly improved the mashing process. After the mashing, the mash passed through the filtration bottom, separating the liquid phase from the solid phase. The crushed material was discharged through a hatch in bottom. The physicochemical and sensory profiles of the obtained beer wort and beer samples complied with State Standard 30060-93 “Beer. Methods for determination of organoleptic indices and product’s volume”. Mash filter II produced beer wort of higher quality and improved the sensory properties of the finished product. This model proved more effective in extracting proteins and digestible sugars during amylolysis due to a better mixing and circulation of liquid medium flow during the wort preparation. Conclusion. The new modified mash filter made it possible to reduce the brewing time by 28.6%. Not only was it more user friendly, but it also was less heat and electricity consuming. In addition, it reduced the production area as it combined the stages of mashing and filtering.