Surface Temperatures Of Samples Research Articles

Effect of Bubbling on Ignition of PMMA Slab: Change in Thermo-Physical and Thermo-Radiative Properties

In semi-transparent polymers, ignition is not only dependent on conductive thermal transfer into the material but also on in-depth absorption of the radiation. The aim of this work was to investigate the influence of bubbling on the thermo-physical and thermo-radiative properties of PMMA and how it may affect its ignition. PMMA plates of varying thickness were exposed to the heat flux of two radiative sources with different emission spectra. Exposure was stopped after different periods of time to study bubbling kinetics and bubble size distribution by optical microscopy. Front and back surface temperatures of samples were recorded during heat exposure. The results indicate that the bubble size distribution is closely related to the temperature gradient within the sample. Steep thermal gradients lead to small-sized bubbles underneath the exposed surface, while weak thermal gradients generate a wider size distribution with in-depth bubbling. All thermo-physical quantities k, ρ and Cp were shown to decrease with increasing bubbling degree. Likewise, it was highlighted that bubbling modifies the thermo-radiative properties of PMMA, especially in the near-infrared range. Transmittance decreases while absorbance increases with a bubbling degree. The increase in the absorption coefficient was attributed to multiple scattering by bubbles that expand the pathway of radiation into the materials. It was concluded that changes in both the thermo-physical and thermo-radiative properties with bubbling were likely to account for the delay in ignition observed when using the near-infrared heating source.

Effect of Microwave Irradiation on Computed Tomography and Acoustic Emission Characteristics of Hard Rock

Microwave-induced fracturing of hard rock can be used to assist mechanical rock breakage and release stress on rock masses in deep underground engineering operations. This is significant to those aiming to improve the construction efficiency and safety of underground tunnelling and ore extraction operations. The research was devoted to exploring the computed tomography (CT) and acoustic emission (AE) characteristics of hard rock subjected to microwave irradiation. For this purpose, microwave irradiation tests at a given power for different irradiation times were conducted on basalt collected from Chifeng, China by utilising a multimode cavity working at a frequency of 2450 MHz. By applying an infrared camera, the temperature distribution on the surface of samples during microwave irradiation was measured. Three-dimensional (3-d) microscopic CT was conducted on samples treated, and not treated, with microwave irradiation to explore the crack propagation regimes in such samples. Based on CT value and P-wave velocities, the damage characteristics of microwave treatment on basalt samples were evaluated. Afterwards, uniaxial compression strength tests were conducted and AE information in the loading process of samples was collected. After conducting microwave irradiation, internal cracks of samples propagated to generate fracture surfaces and surface temperatures of samples were found to have been non-uniformly distributed. The longer the irradiation time, the higher the degree of crack propagation in samples; P-wave velocities both decreased with increasing irradiation duration. With increasing irradiation time, the brittle failure characteristics of basalt shown in the time-dependent change curve of stress on basalt were gradually weakened while ductile failure characteristics were gradually strengthened. The uniaxial compressive strength, corresponding AE energy and cumulative AE energy at peak strength all gradually decreased with increasing irradiation time. The failure stress, the level of stress drop, AE energy, and cumulative AE energy of basalt after different irradiation times reflected consistent fracturing characteristics of basalt, which were interactively validated.

Experimental, analytical and numerical investigation on auto-ignition of thermally intermediate PMMA imposed to linear time-increasing heat flux

Auto-ignition of finite thick PMMA (polymethyl methacrylate) subjected to linear time-increasing heat flux (HF) is experimentally investigated utilizing a heating apparatus capable of freely controlling the variation of the exposure. Ignition times, surface and in-depth temperatures of samples were recorded. Theoretical analysis, using critical temperature, and numerical simulations considering pyrolysis and thermal insulation layer were implemented to estimate the corresponding measurements. Approximate correlations are obtained based on the analysis and they are related to the ones in thermally thick cases. Results show that the thermal insulation layer and the pyrolysis in solid have limited and significant effects on surface temperature, respectively. 1 mm PMMA cannot be treated as thermally thin due to the large temperature gradient in solid. Appreciable sample distortion and thickness regression observed in thin sample tests are responsible for the large uncertainty of ignition time and non-ignition phenomenon. Thinner sample and larger increasing rate of HF would lead to higher surface temperature and shorter ignition time. Two stages separated by pyrolysis temperature are identified before ignition. The measured critical temperature is 695 ± 14.5 K, and a more reasonable uncertainty range, ±30 K, is suggested by numerically fitting the measured ignition times.

Seasonal and Diurnal Surface Temperatures of Urban Landscape Elements

In the context of the Urban Heat Island effect, landscape professionals need practical guidance to design for managing surface urban heat. The apparent surface temperatures of samples of 19 hard and soft landscape elements (LEs) found in Perth (Australia) were measured. Thermal images of LE samples on an oval were taken at a 1 m height. The study was conducted in two phases. Phase 1 LE surface temperatures relative to ambient (ΔT) were measured over one day in all four seasons. LEs were ranked by average ΔT, and maintained a similar order across seasons, with summer LEs the hottest. Some LEs were 30–44 °C above ambient in spring and autumn, so these seasons are also significant. Phase 2 repeated the summer test, but used only 14 larger LEs, which were well-coupled to the ground, i.e. more representative of in situ LEs. ΔT values were averaged over daytime and evening periods. Larger LEs were generally hotter than corresponding smaller LEs, with the effect more evident for heavier, denser LEs in the evenings. Future tests should be performed as per phase 2. Averaged measured values of grey pavers were the hottest, whilst ground-cover plants were the coolest. In the evening, grey pavers were also the hottest, whilst decking, soil and turf grass were the coolest. This data will help landscape professionals to assess and compare the thermal performance of different landscape designs, particularly when considering the time of use.

Experimental Investigation of the Effect Exerted by a Natural Fire on Wood Material

An experimental investigation of ignition of a wood material under the action of the forest fire front has been carried out in a laboratory to determine the conditions of ignition and combustion. The surface temperatures of samples were measured by means of thermocouples. The dependences have been derived showing the change of the surface temperature of samples exposed to the ground fire front.

Imaging analysis of biological soil crusts to understand surface heating properties in the Mojave Desert of California

Biological soil crusts (biocrusts) are composed of a combination of cyanobacteria, green algae, lichens, and mosses that can protect arid soil surfaces from erosive forces. The presence of biocrusts in desert regions is influenced by a complex interaction of climatic, edaphic, and topographic variables, but their distribution and coverage densities in southern California deserts are not precisely mapped. Visible satellite bands (red-green-blue; RGB) and infra-red image resolution are generally too coarse to distinguish between biocrusts and their interstitial sand substrates, limiting most remote sensing analysis of these soil biotic assemblages. The purpose of this study was to better understand the relationships between biocrust cover, surface coloration and roughness, and the thermal infra-red (TIR) emission properties of biocrusts to determine if new types of imaging of desert surfaces could be used to more accurately detect biocrust presence. Based on the results from megapixel digital photos and TIR imaging for nearly 130 different, well-developed biocrust surfaces in the Mojave and Lower Colorado Deserts of California, we designed laboratory heating experiments to test the effect of biocrust cover on the heating properties of sandy wash habitats. Biocrust samples collected from the field were subjected to artificial heating and cooling to simulate the Mojave Desert diurnal cycle. We used image segmentation algorithms to separate true-color biocrust images from their sandy substrates, and to map the heating and cooling patterns of these surfaces with different levels of biocrust coloration and roughness. The major findings of this study showed that biocrust patch images in the field had Red texture mean values between digital numbers of 95 and 131 with moderate positive tail shewness levels, indicative of a highly rugose surface of the biocrust cover. Such patches were also well-compacted overall, with moderate skewness toward negative tails. In controlled laboratory temperature experiments to simulate the desert diurnal cycle, surface wetting with a fine mist of water resulted in significantly lower peak surface temperatures of biocrust samples compared to dry biocrust heating results of the same crust and sand samples. The findings of this study can improve future mapping for lichen-dominated biocrust surfaces in the Mojave Desert.

Drying kinetics study of irregular fibril materials in a “differential” laboratory rotary dryer: Case study for cut tobacco

ABSTRACTRotary dryers are commonly used in the modern large-scale tobacco drying industry that consumes huge amounts of energy. In fact, rotary dryers are commonly used in chemical industry in general. It is difficult to investigate the drying behavior at industrial scale. A “differential” laboratory rotary dryer was therefore designed and tested. The large diameter of the industrial dryer was preserved, but the width was a section of the industrial dryer. The drying characteristics of cut tobacco from top leaves and bottom leaves with initial moisture contents (22.5 ± 1.0% on the wet basis) were studied in the “differential” dryer at air temperatures of 65, 85, 105, 125, and 145°C, respectively. The results show that increasing drying temperature accelerated the drying process, whereas the surface temperatures of the cut tobacco samples stayed in the temperature range of 48–71°C when their moisture contents were reduced to 12.0 ± 1.0% (wb). This 12.0% (wb) was required by commercial operations. Uniquely, the drying kinetics was captured using the reaction engineering approach (REA). Although different settings were applied, the model can be used to describe all the data well. The unique relationship between the normalized activation energy and the moisture content is approximated which is independent of the drying air temperature and the tobacco origin. The different drying behaviors for the cut tobacco from top leaves and bottom leaves can be attributed to their different equilibrium isotherms. Through controlling the drying time as predicted by REA model, the outlet moisture contents of cut tobacco from top leaves dried at 95°C/RH0.034/320 s and 115°C/RH0.017/250 s were shown to be 12.3 and 11.8% (wb), with the relative deviations of 2.5 and 1.7%, respectively, and these were within the industrial permissible range.

EFFECT OF GLASS BEAD AND ZEOLITE IN CONCRETE UNDER HIGH TEMPERATURE

The paper presents the impact of high temperature on concrete with glass bead and zeolite in its mixture. It is desired to reduce the concrete surface temperature when it is exposed to high temperature. In this study, different range of proportions of glass beads (%10, %20, %30) and zeolite (%10, %30) were added into the C30/37 strength class concrete as a fine aggregate and Portland cement, respectively. Surface temperatures of concrete samples were measured when concrete was under about 3000°C flame for a short time. It was determined that, using glass bead and zeolite together in concrete reduces surface temperature significantly under high temperature. The study presented herein provides important results on regulating concrete mixture if there is any risk to be exposed to high temperature. The study presented herein provides important results on regulating concrete mixture if there is any risk to be exposed to high temperature. The main research question is “Is it possible to reduce surface temperature of concrete when it is exposed to very high temperature by using glass bead and zeolite in concrete mixture”. 10 different types of concrete mixtures were designed to study the effects of concrete and zeolite on compressive strength and surface temperatures of concrete. It was determined that using glass bead as a fine aggregate and zeolite, significantly affects concrete surface temperature and temperature differences of both sides when concrete is exposed to very high temperature. Using glass bead and zeolite in concrete for fire resistance hasn’t been searched before. In this study it was determined that it is possible to get lower surface temperatures by using glass bead and zeolite in concrete mixture. The ideal proportion was %20 for glass bead and %30 for zeolite in the mixture to obtain lowest surface temperatures and meet the compressive strength requirements. These types of mixtures can also be examined for concrete pavements to get lower temperature gradients in summer and obtain less thermal cracking on concrete road.

Inactivation of Escherichia coli O157:H7 in Moisture‐Enhanced Nonintact Beef by Pan‐Broiling or Roasting with Various Cooking Appliances Set at Different Temperatures

This study evaluated inactivation of Escherichia coli O157:H7 in moisture-enhanced restructured nonintact beef cooked to 65 °C using different cooking appliances set at different temperatures. Batches (2 kg) of coarse-ground beef (approximately 5% fat) were mixed with an 8-strain composite (100 mL) of rifampicin-resistant E. coli O157:H7 (6.4 ± 0.1 log CFU/g) and a solution (100 mL) of sodium chloride plus sodium tripolyphosphate to yield concentrations (wt/wt) of 0.5% and 0.25%, respectively, in the final product. Beef portions of 2.54 cm thickness (15 cm dia) were prepared and were vacuum-packaged and frozen (-20 °C, 42 h). Partially thawed (-2.5 ± 1.0 °C) portions were pan-broiled (Presto electric skillet and Sanyo grill) or roasted (Oster toaster oven and Magic Chef kitchen oven) to 65 °C. The appliances were set at, and preheated before cooking to 149 or 204 °C (electric skillet), 149 or 218 °C (grill), 149 or 232 °C (toaster oven), and 149, 204, or 260 °C (kitchen oven). Temperatures of appliances and beef samples were monitored with thermocouples, and meat samples were analyzed for surviving microbial populations. In general, the higher the appliance temperature setting, the shorter the time needed to reach 65 °C, and the higher the edge and surface temperatures of the meat samples. Temperatures of 204 to 260 °C, regardless of appliance, resulted in greater (P < 0.05) pathogen reductions (3.3 to 5.5 log CFU/g) than those obtained at 149 °C (1.5 to 2.4 log CFU/g). The highest (P < 0.05) reduction (5.5 log CFU/g) was obtained in samples cooked in the kitchen oven set at 260 °C. The results should be useful to the food service industry for selection of effective nonintact beef cooking protocols, and for use in risk assessments for nonintact meat products. Practical Application: Results of this study should be useful for developing cooking recommendations to enhance the safety of nonintact beef products, and for use in risk assessments of such products.

Measurement of evaporated acrylamide during frying of potatoes: Effect of frying conditions and surface area-to-volume ratio

The amount of acrylamide lost through water vaporization during frying of potatoes was quantified in this study. Water vapor was condensed by a cold trap, and then analyzed for acrylamide content. Acrylamide content of potato samples was also determined. In order to assess the thermal effect on acrylamide formation, surface and internal temperatures of potato samples were measured during frying. Effect of frying oil temperature (150 °C, 170 °C, and 180 °C), time (1, 3, and 5 min) and surface area-to-volume ratio (strips, cubes, and discs) on both acrylamide level of potato samples and the evaporated acrylamide was investigated. The percentage ratio of the amount of acrylamide lost by evaporation ranged between 0.7 and 1.8 during frying of potato at temperatures ranging between 150 °C and 180 °C. Based on these results it is concluded that although a fraction of the acrylamide formed during frying is removed with vaporizing water, it appears to be insignificant. The results, on the other hand, indicated that air exposure to acrylamide could be a concern from the viewpoint of risk assessment for a group of people working on frying operations.

INFLUENCE OF ENDPOINT TEMPERATURE, HUMIDITY AND COLD STORAGE ON MECHANICAL AND SENSORY PROPERTIES OF SMOKED CHICKEN SAUSAGE

This study was conducted to evaluate the influence of relative humidity, endpoint temperature and period of cold storage on some mechanical and sensory properties of smoked chicken sausage. Weight changes, cooking losses and emulsifying capacity of the processed samples were determined. During heat processing and smoking, the internal temperature of samples increased more rapidly at a relative humidity of 70 or 80% than at 40%, due to the enhanced heat transfer coefficient of the condensing steam and the temperature differential between the surface and center temperatures of the sausage samples. Consequently, processing time was shorter, but the weight of samples increased by about 1.5% during the first 15 min of heat processing at 97C. As the relative humidity in the smokehouse increased from 40 to 80%, both the weight loss, emulsifying capacity, compression and penetration stresses decreased from 11.1 to 7.5%, 28.2 to 27.4 mL oil/100 mg protein, 2.14 to 1.68kg/cm2 and 1.36 to 1.15 kg/cm2, respectively, while the cooking losses decreased from 11.1 to 7.5% when the samples were held at an endpoint temperature of 70C for the same period. The cold storage results showed that both the compression and penetration stresses decreased as the period of storage increased or as the humidity in the smokehouse increased. The sensory scores indicated that all the sausage samples were acceptable within 4 weeks of frozen storage. Firmness and color scores decreased as humidity increased; however, as the period of storage increased, scores for firmness increased, and color, juiciness and flavor scores decreased.

On the role of oxygen in the horizontal flame spread of polypropylene

AbstractThe horizontal flame‐spreading behavior of slabs of uninhibited polypropylene (PP) and commercial polymethylmethacrylate (PMMA) is described, and the flame spread and mass vaporization rates are discussed. The quantities of peroxide and carbonyl moieties formed on the surface of PP beneath the flame front, determined by an iodometric procedure and by reaction with 2,4‐dinitrophenylhydrazine, are presented. A statistical analysis was performed to ascertain the significance of these quantities formed in four combustion environments, each differing in oxygen concentration. Flame and surface temperatures of the PP samples at each oxygen concentration as well as flame and surface temperatures of samples burned in 23% oxygen with an added external radiant heat source are presented. The data support the concept that surface oxidative reactions occur in the combustion of PP, that the quantity of oxidative products is related to the concentration of oxygen in the combustion environment, and the possible importance of these reactions in producing heat to propagate the flame is indicated. Comparison of PP and PMMA show that the two are quite dissimilar in flame‐spreading behavior.

Investigations on the Heating and drying of wood with infrared radiation

By means of a newly developed measuring device the temperature distribution on the surface and inside of dry samples of beech and spruce was determined at one-sided short and long wave infrared radiation in dependency on time and intensity of radiation and on the thickness of the wood. Furthermore, the surface temperatures of moist samples were measured as a function of moisture content. The results which are important for the practice of infrared radiation were plotted in diagrams from which e. g. the increase of the temperature at the radiated surface in dependence on thickness and species of the wood and on the duration and intensity of short and long wave infrared radiation can be read. The drying tests, made on wood samples of different thickness by means of one- and two-sided short and long wave infrared radiation, gave valuable information on the practical application of infrared wood drying.