Hot Air Heating Research Articles

Chemical‐Free Approach for Z‐Isomerization of Lycopene in Tomato Powder: Hot Air and Superheated Steam Heating above the Melting Point of Lycopene

AbstractZ‐isomers of lycopene exhibit higher bioavailability and antioxidant capacity than those of the all‐E‐isomer. Therefore, it is important to develop an efficient and environmentally friendly procedure for Z‐isomerization. The current methods for Z‐isomerization of (all‐E)‐lycopene use toxic chemicals such as organic solvents and catalysts. This study is aimed to develop a chemical‐free method for Z‐isomerization of (all‐E)‐lycopene in tomato powder by hot air and superheated steam heating. The Z‐isomerization reaction is promoted by heating above the melting point of lycopene. When heated with superheated steam, the thermal decomposition of lycopene is suppressed compared to that when heated with hot air. When tomato powder is heated at 240 °C for 5 min by superheated steam, the total Z‐isomer content and remaining lycopene are 69.0% and 90.7%, respectively, while with hot air heating, the total Z‐isomer content and remaining lycopene are 69.9% and 68.0%, respectively. These results indicate that the thermal Z‐isomerization of lycopene occurs in the molten state and heating in a low oxygen atmosphere suppresses the thermal decomposition of lycopene.Practical Applications: Tomato powder rich in lycopene Z‐isomers is an important ingredient for the food and animal feed industries. Since Z‐isomers of lycopene are more soluble in solvents including ethanol which is a low‐toxicity and environmentally friendly solvent, the efficiency of lycopene extraction with ethanol can be improved by using the Z‐isomer‐rich tomato powder as a raw material. The obtained Z‐isomer‐rich extract has a high added value because the Z‐isomers have higher bioavailability and antioxidant capacity than those of the all‐E‐isomer. In addition, since lycopene Z‐isomers exhibit higher accumulation efficiency and better color improvement in hen egg yolks than those of the all‐E‐isomer, Z‐isomer‐rich tomato powder is an effective animal feed.

Gas radiative effects on gas-filled flat plate solar collectors

A standard thermal solar collector can be used for both hot water production and air heating purposes. Gas-filled solar collectors represent a new emerging design approach with enhanced characteristics. In this research, numerical modeling is utilized to study radiative effects of the participating gases on the performance of solar collectors. The coupled radiative–convective heat transfer in the solar collector is considered and the collector cavity is considered as a radiatively participating medium. The finite volume method has been adopted to solve the governing equations and discrete ordinates method is used for radiative transfer. After validating the model used in this study, it is used to obtain the heat transfer characteristics of a flat-plate solar collector with real solar conditions of the city of Kerman, Iran, in summer at a wide range of air absorption coefficients. According to the results, by increasing the absorption coefficient of the air, the temperature of the absorber plate is reduced and the air temperature is increased, but the increase of air temperature is much higher than the reduction of absorber temperature. Hence, it is concluded that it is possible to use participating gases in the solar air heaters to enhance the performance of the collector.

Comparative analysis of heating systems used in Orthodox churches

This work displays a numerical examination of the improvement of indoor atmosphere conditions inside an Orthodox church of Iasi. The objective consists in proposing a solution for reducing the risk of condensation for the case of the real heating system with hot air, used in Three Holy Hierarchs Monastery of Iasi. The solution was to use the local ventilation at towers, that generates air flow in these zones and evacuate humidity. This configuration was tested numerically and the results highlighted its effects. For comparison, the local ventilation was studied for two other heating solutions that are largely used in this type of buildings, underfloor heating and static heaters. The simulations demonstrated that the local ventilation represents a suitable solution when it is combined with the hot air heating.

Hot single-point incremental forming of glass-fiber-reinforced polymer (PA6GF47) supported by hot air

Glass-fiber-reinforced polymers (GFRP) are used in a wide range of applications, especially in the aerospace industry, in lightweight constructions and in the production of medical implants. The utilization of unautomated forming is more time-consuming and costly for recently applied processes in the production of medical implants. Consequently, there is a need for an alternative process to reduce the manufacturing costs and time while improving product quality. Therefore, a new forming method was proposed to form GFRP. This method utilizes single-point incremental forming assisted by hot air heating to form the GFRP of a thermoplastic base matrix polyamide 6. The GFRP sheet was sandwiched between combinations of two Teflon layers and metal sheets. The Teflon was applied to improve the forming behaviour of the GFRP. The metal sheets were used to protect the GFRP from friction exerted by the forming tool and to reduce the flow of the melted matrix polymer out of the woven fiber. As a result, conical profiles formed well till reaching a wall angle of 55°. Internal cracks and voids started to appear in the formed profile when reaching the wall angle of 50°. The results are presented regarding the investigation of the experimental process. The proposed method can easily be applied to form GFRP parts. Furthermore, it can be considered as a prototype process, especially in the production of aerospace parts medical implants.

Features of Gravitational Flow of Heated Air in an Exhaust Shaft Above a Multirow Finned Bank

The authors have carried out investigations into the introduction of hot-air heating systems in buildings and structures, and also the applicability of mixed convection in calorifers of recirculating air heaters. The heat transfer of two- and four-row staggered air-heater banks consisting of bimetallic finned tubes in mixed convection has been studied. Experimental investigations into the characteristics of a gravitational flow of heated air in an exhaust shaft above a heat-exchange bank in a mixed-convection regime have been presented. An increase of 1.5–3 times in the heat transfer in the mixed-convection regime compared to the heat transfer under conditions of free convection of the air has been established. The dynamics of motion of a geyser flow of heated air in the exhaust shaft above the heatexchange bank under gravity has been described. A decline of 20–50% in the heat transfer of staggered two- and four-row banks because of the presence of geyser air flows has been established. A method to diminish the adverse impact of geyser air flows on the heat transfer of the bank has been proposed.

Wheat bran stabilization and its effect on cookies quality

Wheat bran are widely used as a source of dietary fiber with enhanced health benefits. However, its hight application level in bakery products caused lower quality of these products (eg. reduced volume and increased hardness of product). Different mechanical, physical or chemical methods are used for modification of wheat bran physicochemical properties. Wheat bran obtained from two wheat variety was used to evaluate the effect of bran stabilization process on qualitative properties of baked goods. Stabilization was performed using hot air and microwave heating. Threated and unthreated wheat bran were blended with wheat flour at 5, 10 and 15% substitution level. Influence of bran addition on rheological properties was evaluated using Mixolab 2. Stabilized wheat bran increased water absorption up to 11.7% (hot air stabilization) and 11.9% (microwave stabilization), respectively. Hot air stabilization of wheat bran improved heat resistance of dough proteins during mixing and the stability of hot gel during heating. Stabilization process of wheat bran using both methods also increased the volume and spread ratio values of enriched cookies. Cookies incorporated with hot air treated bran were significantly softer than cookies contained raw bran. Sensory evaluation showed that addition of stabilized bran improved the shape and taste of cookies. Additionally, it was concluded that the most acceptable cookies were obtained at 5% addition level of bran stabilized using microwave heating.

Heat supported single point incremental forming of hybrid laminates for orthopedic applications

Abstract Ecofriendly composite fibers are increasingly applied as a substitutional material instead of the expensive carbon fibers. Within this context a hybrid laminate was developed combining an aluminum sheet with basalt fiber-reinforced thermoplastic polyamide 6 (BFRP). As a condition for the formability it is necessary to transform the polyamide matrix into a semi-fluidized state. Therefore, a single point incremental forming process supported with hot air heating was utilized to form the hybrid laminate into the desired shape. During the forming process the composite was inserted between two metal sheets and two Teflon layers which were used to improve the sliding of the hybrid laminate during the forming operation. Furthermore, the metal sheets were used to ensure an efficient processing and protect the hybrid laminate against wear caused by friction between the forming tool and the composite. In addition, the squeeze out of the melted polymer matrix out of the hybrid laminate was reduced. The results of the investigation of the experimental process parameters are presented. The proposed method offers the possibility to manufacture individual orthopedic products or prototypes of medical implants.

Modified atmosphere packaging pre-storage treatment for thermal control of E. coli ATCC 25922 in almond kernels assisted by radio frequency energy

The purposes of this study were to validate modified atmosphere packaging (MAP) pre-storage for reducing surviving populations and thermal resistance of E. coli ATCC 25922 in almond kernels. A 6 kW, 27.12 MHz radio frequency (RF) assisted hot air heating system was used to conduct thermal treatments of 1.5 kg MAP pre-storage samples. Surviving populations of E. coli ATCC 25922 in almond kernels with 8.0% wet basis were determined weekly for 12-week pre-storage and samples were removed at five different time intervals during thermal treatments to achieve at least 4-log reduction. The results showed that reduction levels of E. coli for MAP and regular atmosphere packaging (RAP) were 1.47 ± 0.08 and 0.61 ± 0.05 log CFU/g after 12-week pre-storage. The 4-log reduction time of E. coli in MAP was 18 ± 1 min holding after RF assisted heating to 75 ± 2 °C, reducing 40% pasteurization time as compared with RAP pre-storage. Fatty acid and peroxide values remained within acceptable range (FA < 0.6% and PV < 1.0 meq/kg), and color values of treated samples were not significantly (p > 0.05) different from those of untreated ones. MAP pre-storage assisted thermal treatments induced by RF energy may hold potential as an effective and environmentally friendly method to control E. coli ATCC 25922 in almond kernels.

Thermal analysis and optimization of a system for water harvesting from humid air using thermoelectric coolers

Condensation of water vapor available in atmospheric air can be considered as a solution for water scarcity problem. In this paper, a comprehensive thermodynamic analysis of water production from humid air using thermoelectric coolers (TECs) is presented. The system consists of a number of thermoelectric coolers, a fan to supply the required air flow circulation, two cold and hot air channels, heat sinks and solar cells for powering the thermoelectric coolers and fan. Effects of various design parameters are investigated and discussed. The proposed design is optimized to get the maximum effectiveness which is defined as the amount of produced water per unit of energy consumption. Sensitivity analysis is used to find the optimum number of TECs, length of the channels and performance of the system at different temperatures. The resulting system is capable of producing 26 ml of water within 1 h from the air with 75% relative humidity and the temperature of 318 K by consuming only 20 W of electrical power. In addition, the annual performance and optimization of this device in three southern cities of Iran are presented based on hourly meteorological data. Finally, comparison of the present system with other air water generators indicates that the proposed design is the most energy efficient system among similar devices especially in high relative humidity.

Impact of Process Temperature, Humidity, and Initial Product Moisture on Thermal Inactivation of Salmonella Enteritidis PT 30 on Pistachios during Hot-Air Heating

Some thermal processes, such as pistachio roasting, are not yet well characterized with respect to the impact of product and process variables on Salmonella lethality. This study aimed to quantify the effects of process temperature, humidity, and initial product water activity (aw), on Salmonella lethality for in-shell pistachios. In-shell pistachios were inoculated with Salmonella Enteritidis PT 30 (∼8.5 log CFU/g), equilibrated (0.45 or 0.65 aw), and heated without soaking ("dry") or after a pure-water or 27% NaCl brining pretreatment ("presoaked"). Inoculated pistachio samples (15 g) were heated in a laboratory-scale, moist-air convection oven at 104.4 or 118.3°C, humidities of ∼3, 15, or 30%, v/v (∼24.4, 54.4, or 69.4°C dew point), and air speed of 1.3 m/s. Salmonella survivors were quantified at six times during each treatment, targeting total reductions of ∼3 to 5 log. Survivor data were analyzed using analysis of variance to identify main effects (time, temperature, humidity, and initial aw) and two-term interactions with time. As expected, lethality increased ( P < 0.05) with temperature and humidity. For example, the time to achieve a 4-log reduction decreased 50 to 80% when humidity increased from ∼3 to 30%. When the dry and presoaked treatments were analyzed separately, initial product aw (0.45 versus 0.65 aw or 0.75 versus 0.95 aw) did not affect lethality ( P > 0.05). However, when comparing dry against presoaked treatments, the time to achieve a 4-log reduction decreased 55 to 85% ( P < 0.05) for presoaked pistachios subjected to the same temperature-humidity treatment. Salt had no effect ( P > 0.05) on lethality outcomes. These results, relative to initial aw, process humidity, brining, and salt effects on process lethality, are critically important and must be considered in the design and validation of thermal processes for Salmonella reduction in pistachio processing.

High-solids semi-continuous anaerobic digestion of corn silage in bag-type digester

AbstractThe aim of this paper is to discuss the usability of a newly designed partially stirred horizontal anaerobic bioreactor made from triple layer bag material Sioen B6070 and heated by circulating hot air. For verification of the possibility of processing typical agricultural fibrous substrate at relatively high solids content in this type of reactor, the semi-continuous mesophilic (40±3°C) anaerobic digestion of corn silage of KWS Atletico cultivar was conducted. The reactor with a total volume of 0.7 m3provided 0.5 m3working volume. Liquid slurry from the 1st stage of the agricultural biogas station Pustejov II was used as inoculum. The silage dosage was performed so that the reactor reached high methane production intensity at low volumetric production of the digestate for 120 days. The average organic loading reached 4.27 kgVSm−3d−1while the average hydraulic retention time decreased to 85 days. The dry biogas production intensity was 3.42 mN3m−3d−1with an average methane content of 52.5 vol%. The specific methane production from corn silage was 0.419 mN3kgVS−1. At the end of the test, the digestate contained 13–14 wt% of total solids (TS) and 82–85 wt% of volatile solids in TS. The bag-type digester with hot air heating can be used by small farmers where there is no viable biogas cogeneration.

Thermal inactivation of fungi in chestnuts by hot air assisted radio frequency treatments

Infestations with fungi in chestnuts are one of the major safety issues during process and storage, resulting in short shelf-life and high economic losses. The purpose of this research was to study possible applications of radio frequency (RF) treatments for pasteurization of chestnuts to replace chemical methods. Thermal lethal kinetic models of fungi isolated from spoilage chestnuts and parameters of the developed model were determined. A 6 kW, 27 MHz free-running oscillator RF system combined with hot air heating was used to validate the treatment parameters based on thermal lethal kinetic models of fungi. The results showed that four mycotoxigenic fungi dominated and were isolated at frequency of 58.31 ± 2.39% for Penicillium crustosum, 17.78 ± 5.00% for Penicilluim discolor, 15.66 ± 7.67% for Penicillium expansum, and 14.24 ± 6.71% for Penicillium glabrum from a total sample size of one hundred spoilage nuts. Modified Weibull distribution model (R2 = 0.939 to 0.999) had a better description of the inactivation behavior of Penicillium sp. than the first-order kinetic model (R2 = 0.829 to 0.993) and P. crustosum was the most heat resistant fungi in chestnuts. Heating chestnuts to 60 °C or higher using hot air assisted RF energy resulted in 4-log reductions of P. crustosum isolated from moldy chestnuts. Quality of chestnuts was not influenced by the hot air assisted RF treatments because no significant differences in moisture, firmness, and color were observed between thermal treatments and untreated controls. Meanwhile, RF treatments also help to inhibit the growth of fungi during accelerated shelf life storage. The RF treatments may provide a rapid and environmentally friendly method to replace chemical fungicide for pasteurizing chestnuts.

Evaluation of a heating block system for accurate temperature-time controlled pasteurization treatments on various foods

For simulating real pasteurization treatments using hot air, hot water, radio frequency and microwave heating, a unique experimental heating block system (HBS) was developed. The stability and uniformity of sample temperatures and heating rates in HBS were determined for studying the thermal resistance of food-borne pathogens. A computer simulation model was also developed to analyze the behavior of thermal process in HBS. The results showed that the required heating rates with various set-temperatures and holding times could be easily and precisely achieved in eight selected food materials. Thermocouple and thermal imaging data showed that the good sample heating uniformity in six cells of HBS was achieved. The real temperature-time histories obtained by radio frequency energy could be approximately done in HBS by setting a number of linear regression curves. The HBS can help in more precisely characterizing the heat resistance of pathogens in foods to further develop pasteurization processes. Keywords: thermal treatment, heating rate, heating uniformity, thermal resistance, simulation, heating block system (HBS) DOI: 10.25165/j.ijabe.20181103.3734 Citation: Kou X X, Li R, Hou L X, Cheng T, Zhou X, Wang S J. Evaluation of a heating block system for accurate temperature-time controlled pasteurization treatments on various foods. Int J Agric & Biol Eng, 2018; 11(3): 220–228.

운전자의 심리·생리 반응을 고려한 승용차 쾌적 난방 모드에 관한 연구

In this research, the psychological and physiological reactions of the driver were measured during winter to evaluate thermal comfort. The experiment was conducted using 3 different cases which are hot air heating, warm-wire seat heating and hot air & warm-wire seat heater operating simultaneously. With regard to psychological reaction, the warm-wire heating mode was the most preferred. The reason is that it is dry in other cases. With regard to EEG response, thermal comfort increased by 37% in warm air mode heating. In addition, when the warm-wire heating mode and the hot air & warm-wire heating mode were simultaneously operated, the thermal comfort continuously increased by between 17% and 20% for 20 minutes after boarding. Under the change of the autonomic nervous system, the thermal stress level increased by 23% after 15 minutes on board in the hot air heating mode and decreased continuously by 13% during the warm-wire seat heating mode. We recommended the hot air heating mode is only used for a short time to raise the inside temperature during the early boarding period and that warm-wire seat heating mode be actively utilized.

Classification of the hot air heat treatment degree of larch wood using a multivariate analysis of near-infrared spectroscopy

In this study, hot air heat treatments of larch (Larix kaempferi) wood specimens were conducted at various temperatures (160–220 °C) and times (1–12 h) to classify the degree of hot air heat treatment using near-infrared (NIR) spectroscopy. NIR reflectance spectra were acquired from specimen cross-sections and were then preprocessed using the standard normal variate. Hierarchical clustering analysis (HCA) using the complete linkage and squared Euclidean distance was conducted to classify the three degrees of heat treatment. A principal component score plot of the NIR spectra was well grouped by the HCA grouping result, and the first component reflected the cluster analysis grouping well. A partial least squares discriminant analysis was performed to develop the discriminant regression model of the three heat treatment degrees. The R2 and root mean square error of validation were 0.959 and 0.191, respectively. NIR is considered to be a good candidate to routinely measure the degree of hot air treatment for larch wood.

Experimental study on incremental sheet forming of magnesium alloy AZ31 with hot air heating

Products of tomorrow are characterized by environmental sustainability, individuality and economic feasibility. This trend also occurs in the field of sheet metal forming. Lightweight materials such as magnesium alloys are applied to reduce the weight and concluding the CO2 emissions of cars. They are characterized by a high specific strength and almost inexhaustible availability. Applying them in innovative forming technologies offers the chance for various new products. Flexible forming technologies such as single-point incremental forming (SPIF) have been newly developed to meet the requirements of decreasing lot sizes and a rising variety of products and design. The application of SPIF on magnesium alloys is considered to be an outstanding approach to obtain innovative sheet metal products. For this reason, SPIF of the magnesium alloy AZ31 with a hot air heating system is investigated experimentally. The mechanical properties are investigated as well as the initial microstructure and texture of the AZ31. An experimental setup is designed for SPIF using a hot air blower for heating of the AZ31 sheet. The setup is tested in order to obtain a homogeneous sheet temperature distribution. Forming trials are performed to determine the critical wall angle of a cone for temperatures up to 320 °C. During the experiments the occurring forming forces are investigated. Subsequently, an analysis is conducted of the sheet thickness distribution, the geometrical accuracy and the microstructure development.

Strain-Stress Formation and Deformation of Molded Materials by Drying-Induced Shrinkage

Drying-induced strain-stress and deformation was modeled for molded materials such as ceramics and foods. The transient three-dimensional problem of strain-stress and heat and moisture transfer was solved simultaneously by the finite element method. The behaviors of internal strain-stress formation and deformation are compared among three modes of hot air heating, intermittent heating and internal heating for a ceramic slab. The concepts of the mass transfer potential and a linear viscoelasticity were introduced to consider the different sorption isotherm for layered foods consisting of two ingredients and creep phenomenon. The tensile and compressive stresses fluctuate and fall remarkably during lower heating period when the slab is heated intermittently. In the internal heating mode, drying proceeds fastest as well as stress formation is maintained at the lowest level in the three modes. This effectiveness of the internal heating is investigated experimentally by employing the microwave heating as well. The combination of different foods influences significantly not only the drying characteristic but also the internal strain-stress generation. The drying behavior could be analyzed with a high accuracy even if only heat and moisture transfer were solved without strain-stress analysis. This fact results in that heat and mass transfer and strain-stress are not always necessary to be analyzed simultaneously for saving the CPU time.

Comparison of Heating Characteristics of Electric Heating Element Heater and Oil Hot Air Heater in Single Span Greenhouses

Comparison of Heating Characteristics of Electric Heating Element Heater and Oil Hot Air Heater in Single Span Greenhouses

Effect of offset-jets arrangement on leading edge hot-air heating effectiveness of engine inlet guide strut

An experimental investigation is conducted to study the effect of offset-jets arrangement on the conjugated heat transfer performance for a specifically wedge-shaped concave surface subjected to external cold flow and internal hot jet impingement. The external flow Reynolds number (Rec) defined on the base width of wedge-shaped concave surface is fixed as 54,000. The jet Reynolds number (Rej) is varied in the range of 7900–31,700. Four non-dimensional jet-hole offset distances (L/d) ranging from 0 to 2.5 and four non-dimensional jet-to-leading edge distances (H/d) ranging from 6 to 15 are considered respectively. In order to illustrate the effect of offset-jets arrangement on the flow and heat transfer features inside the wedge-shaped concave cavity, numerical simulations are also performed. The results show that the offset-jets arrangement generally has a significant impact on improving the overall heating effectiveness in the vicinity of concave wall leading edge due to the reduction of normal jet impinging distance and the formation of recirculation flow structure inside the concave cavity. In current study, L/d=1.5 is confirmed to be a superior offset-jets arrangement for achieving the highest specified area-averaged heating effectiveness. It is also noted that the effect of offset-jets arrangement on the leading edge hot-air heating effectiveness is tightly dependent on the normal jet-to-leading edge distance. Under H/d=15, the offset-jets distance has a weak effect of on the internal hot-jet impingement heat transfer. In this situation, the offset-jets arrangement has nearly no effect on improving the hot-jet heating effectiveness.

Evaluation of a hybrid system for a nearly zero energy greenhouse

Greenhouses are widely used in the World, especially in the Mediterranean climate, to provide suitable environment in cultivation of different agricultural crops. Significant amount of energy is necessary to produce, process and distribute these crops. Various systems, including steam or hot water radiation system and hot air heater system, are being used in greenhouse heating. A ground source heat pump system, generally seen as a favorable option since it can provide both heating and cooling energy, is considered for a greenhouse in this study. The aim of this study is to evaluate a renewable energy option for the required total energy need of a greenhouse. Grid connected solar photovoltaic panels are selected to assist a ground source heat pump, and generate sufficient electrical energy for lighting. In this way, a nearly zero energy greenhouse concept is foreseen for three different agricultural products. Monthly and annual heating, cooling and lighting energy load of the greenhouse for these agricultural products were computed. The monthly average electricity generation of 66 photovoltaic panels, which cover 50% of the southern face part of the asymmetric roof, was calculated. Annual photovoltaic electricity generation was found as 21510.4kWh. It was observed that photovoltaic electricity generation can meet 33.2–67.2% of greenhouse demand in summer operation months. Nevertheless, the coverage ratio, calculated by dividing the photovoltaic panels electricity generation to the electricity demand of the greenhouse (heating, cooling and lighting) for each crop, were very high in winter operation months. Yearly coverage ratio values were 95.7% for tomato, 86.8% for cucumber and 104.5% for lettuce. These high coverage ratio values justify the nearly zero energy concept for the considered greenhouse. Economic and environmental evaluation of the considered system were also accomplished. A simple payback time of the crop cultivations was computed between 7.0 and 7.4years. The energy payback time of the system was found to be 4.9years and the greenhouse gas payback time value of 5.7years and 2.6years were calculated, based on natural gas and coal based electricity generation, respectively.