Pulsed IR Heating of Thermoplastic Sheets for Thermoforming Applications

This study presents the pulsed heating strategy as an advancement of the current state of the art in industry towards the theoretically fastest method of heating a thermoplastic sheet. Experimental temperature measurements are combined with an explicit finite difference numerical model to describe the pulsed heating method and indicate its added value in IR heating of thermoplastic sheets. Different process settings are evaluated and indicate the effect of the applied heat flux and the time interval tOFF during pulsed heating. When switched off, the residual heating of the heater elements is able to partially compensate for the convective heat losses at the surface of the sheet. This results in a more uniform temperature distribution through thickness without slowing down the overall heating process. The study shows that this effect is lost when the time interval in which the heater element is switched off, increases. Applying pulsed heating opens up a large processing window to control the through-thickness temperature difference. When the total amount of applied thermal energy is taken into account, pulsed heating is able to increase the overall heating rate and simultaneously keep the temperature difference through thickness limited.

Resistive-IR Hybrid Heating in FDM Printing

FDM printing is based on resistance to heat of the polymer filament, which starts in a viscous state and is extruded from nozzle to the printing area. The printing area is hot around 70°C for a better adherence of the deposited polymer and for slow cooling of it. The later deposited layers will experience faster cooling and the characteristics of the polymer will suffer light changes. The paper aims to present the results of a preliminary research regarding the double source successive heating and double source hybrid heating of the extruded polymer in FDM process. There were used two distinct heat sources, the resistive source mounted in the extrusion nozzle and IR lamp heat source placed in the printing chamber. The first heating, which acts during the extrusion process, is a hybrid heating and it is developed inside the extrusion nozzle (hot-end); it is given by the resistive heat source by the IR lamp. After the extrusion, during the deposition process and after the deposition process, the heating of the polymer continues due to the IR lamp. The difference between the printing with IR heating and without IR heating was monitored. A decreasing of about 5-8% of the material stiffness was noticed when the IR lamp was introduced. The material became more viscous and the bonding of the successive layers was improved. DSC analysis has been performed in both cases: with and without IR heat source. The evolution of the elastic modulus proved a decreasing of the plasticity during the simple printing process. The decreasing was less (at least by about 25%) when used IR heat source. The elongation viscosity was analysed and its values were decreasing while the temperature was increasing that took place. The decreasing was produced by the reduction of the elasticity, when the chain branches were decreasing their length. The decreasing is more pronounced while the increasing of the temperature. A low difference (of about 2-5%) was observed to the mechanical characteristics after tensile tests.

Fast Pyrolysis of Cellulose by Infrared Heating

The fast pyrolysis of cellulose produces levoglucosan (LG), but secondary pyrolysis reactions tend to reduce the yield. The present study assessed the fast pyrolysis of cellulose by infrared (IR) heating under nitrogen flow. Because the nitrogen was not efficiently heated, gaseous LG was immediately cooled, resulting in a maximum yield of 52.7% under optimized conditions. Slow nitrogen flow and a high IR power level provided a greater gas yield by raising the temperature of the cellulose, and the formation of CO could be used as an indicator of the gasification of LG. Glycolaldehyde (GA) was the major byproduct, and the GA yield remained relatively constant under all conditions. Accordingly, GA was not a secondary product from the LG but was likely produced from the reducing ends of cellulose and other intermediate carbohydrates. The pyrolysis of cellulose proceeded within a narrow region of carbonized material that absorbed IR radiation more efficiently. The bulk of each cellulose sample could be decomposed in spite of this heterogeneous process by maintaining fast pyrolysis conditions for a sufficient length of time. This technique is a superior approach to LG production compared with other fast pyrolysis methods based on heat conduction.

One-step synthesis, characterization and properties of novel hybrid electromagnetic nanomaterials based on polydiphenylamine and Co–Fe particles in the absence and presence of single-walled carbon nanotubes

In a self-organizing system within one stage under IR heating conditions, hybrid nanomaterials are formed with a structure that contains bimetallic Co–Fe particles, free or immobilized on the SWCNT surface, dispersed in the polymer PDPA matrix.

Innovative Infrared Heating Technologies for Food and Agricultural Processing

Food and agricultural industries have an increasing need to develop and adopt novel and sustainable processing technologies with high processing and energy efficiency and less water usage and waste-water generation while, at the same time, delivering safe, high-quality processed food and agricultural products. The use of infrared (IR) radiation heating for food and agricultural processing represents a novel approach for various food thermal processing operations, including drying, blanching, disinfestation, disinfection, and stabilization. Relevant attributes of IR heating technology include high heat delivery rate, lack of need for a heating medium, reduced processing time, improved energy efficiency, and enhanced product quality and safety with a minimal environmental footprint. The author and his research team recently conducted systematic and innovative research on IR heating for food and agricultural product processing, which resulted in an advancement in the scientific knowledge of IR heating in food science and engineering and the development and commercialization of a series of patented processing technologies. The novel IR heating technologies improved food healthfulness, quality, and safety while saving energy and water. The focus of this article is the review of several innovative IR heating-based processing technologies that were developed, including IR dry-peeling, dry-blanching, and dehydration technologies for fruits and vegetables; IR heating technology for drying and roasting of tree nuts; and effective IR heating for simultaneously achieving multiple goals in rice postharvest processing.

Deterrence of Aspergillus Flavus Regrowth and Aflatoxin Accumulation on Shelled Corn Using Infrared Heat Treatments

HighlightsInfrared heating was used to deactivate Aspergillus flavus.Treating samples for 150 s at the 3.24 kW/m2 intensity resulted in complete deactivation of A. flavus.Adding a tempering step at 70°C for 4 h significantly increased deactivation of A. flavus.Corn treated at IR intensity =3.24 kW/m2 showed no potential for A. flavus regrowth or aflatoxin persistence.The study demonstrated a non-chemical approach to deactivate mycotoxigenic fungi on corn.Abstract.The objectives of this study were to determine the suitable combinations of infrared (IR) heating duration and intensity, followed by tempering treatments to maximize the deactivation of aflatoxin-producing mold spores, specifically Aspergillus flavus (A. flavus). Corn samples at moisture content of 24% wet basis were inoculated with spore suspension of A. flavus and incubated to allow microbial attachment on the kernels. Corn samples were then heated using IR energy and then tempered for 4 h. Following the treatments, the samples were placed in conditions favorable for mold regrowth. Treatments of non-tempered samples for 210 s at the lowest intensity (1.27 kW/m2) resulted in A. flavus load reductions of 5.9 Log CFU/g. Treatments of non-tempered samples at the medium (3.24 kW/m2) and highest intensity (6.9 kW/m2) for 210 s resulted in complete deactivation of A. flavus. No fungal regrowth or aflatoxin persistence was observed on samples treated for 210 s at the lowest, medium, and highest IR intensities. Keywords: Aflatoxins, Aspergillus flavus, Infrared heating, Shelled corn, Tempering.

Effects of Infrared Radiation on Eggplant (Solanum melongena L.) Greenhouse Cultivation and Fruits’ Phenolic Profile

The implementation of Infrared (IR) radiation in heated greenhouses possesses the advantage of high directional control and focused compensation of energy losses, appropriate for creating local microclimate conditions in highly energy-consuming systems, such as greenhouses. Moreover, it can efficiently maintain favorable environmental conditions at the plant canopy. The present study studies the application of Infrared (IR) heating in an experimental greenhouse with eggplant (Solanum melongena L.) cultivation. The experimental results are presented from a full cultivation period inside two identical, small scale experimental greenhouses, with IR and forced air heating system, respectively. The effects of IR heating over plant growth parameters, including the yield of the fruits as well as the total phenolic content and the antioxidant profile of eggplants fruits’ extracts are measured and discussed. The results indicate a greater uniformity production in the IR heating greenhouse in terms of antioxidant and radical scavenging activities, as well as the total phenolic content. Moreover, the phenolic profile of eggplant fruits from both greenhouses revealed the existence of numerous bioactive compounds, some of which were only characteristic of the eggplant fruits from IR heated greenhouses.