Post-harvest technologies
H. Rezaei; M. Sadeghi
Abstract
IntroductionDue to the disadvantages of using chemical materials as pretreatment before grape drying, the application of non-chemical methods that not only take the environmental issues into account but also increase the drying rate and improve the quality of the produced raisins is vitally important. ...
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IntroductionDue to the disadvantages of using chemical materials as pretreatment before grape drying, the application of non-chemical methods that not only take the environmental issues into account but also increase the drying rate and improve the quality of the produced raisins is vitally important. The high-humidity hot air impingement blanching (HHAIB) is one of the non-chemical methods that can be used as a suitable alternative for chemical pretreatment in grape drying. In this research, the design, construction, and evaluation of a high-humidity hot air impingement blanching system are discussed in terms of the drying kinetics of white seedless grapes. The results are compared against the control and chemical pretreatment.Materials and MethodsHigh-humidity hot air impingement blanching (HHAIB) systemThe HHAIB system is composed of the steam generator, steam transfer pipes, side channel pump, closing and opening valves, air recycling channel, electric air heater, hot-humid air transfer channel, pretreatment chamber, hot-humid air distribution chamber, nozzles, temperature and humidity sensors and controllers. The performance of the system depends on the humid air temperature, the output fluid velocity from the nozzle, the distance of the nozzles from the product surface, as well as the diameter and arrangement of the nozzles. In order to achieve optimal design of the nozzle array, the relationships existed for the heat transfer coefficient, air mass flow, and blowing power were considered.Application of the HHAIB pretreatment and evaluation of its effect on the grape drying processExperiments were conducted to investigate the effect of temperature and duration of HHAIB pretreatment on the kinetics of grape drying. A two-factor completely randomized factorial design with three replications was used to analyze the data.According to the studies, the air at temperatures of 90, 100, and 110°C, a velocity of 10 m s-1, and relative humidity in the range of 40-45% was applied to the product. Pretreatment durations of 30, 60, 90, 120, and 150 s were also considered. Experiments were conducted with three replicates and control treatment and acid pretreatment were used to compare the drying process. Due to the high quality of shade-dried raisins, this method was used to study the process.The effect of the pretreatment duration on the drying kinetics of white seedless grapes was assessed by observing variations in moisture ratio and drying rate over time, as well as determining the effective diffusivity of water.For the color evaluation of the produced raisins, chroma (C), hue angle H°, and total color difference (ΔE) parameters were calculated after measuring L*, a*, and b* values.Results and DiscussionThe comparison of the drying process among the control, chemical, and HHAIB showed the positive efficacy of HHAIB on the drying rate of grapes. Compared to fresh grapes, the increase in drying rate under the influence of HHAIB varied from 8% for a duration of 30 s at 90°C to 68% for a duration of 150 s at 110°C. The values of the diffusion coefficient of grapes for the HHAIB pretreatment at temperatures of 90, 100, and 110°C and durations of 30, 60, 90, 120, and 150 s, as well as for the control and chemical pretreatments were determined. The values of the coefficient changed from 2.28×10-10 m2 s-1 for 30 s of applying pretreatment at 90°C to 3.53×10-10 m2 s-1 for 150 s of applying the pretreatment at 110°C. The highest value of this coefficient (7.46×10-10 m2 s-1) was associated with the chemical pretreatment. The value of the diffusion coefficient increased with increasing temperature and duration of the HHAIB pretreatment. In general, this increase in the drying rate and the diffusion coefficient can be attributed to the effect of the HHAIB pretreatment on the texture and destruction of the cell wall, as well as the microcracks created on the skin of the grapes. Moreover, the findings reveal that, in comparison with the hot air temperature, the duration of the HHAIB pretreatment was more effective in enhancing the drying rate. Additionally, based on the color analysis, a temperature of 110°C and a duration range of 90-150 s were achieved as suitable conditions for applying pretreatment.ConclusionThe HHAIB pretreatment, which combines the benefits of hot air blanching with jet technology, affects the texture and skin of grapes, accelerates the drying process, and increases the quality of the produced raisins. However, the correct application of this pretreatment depends on the proper design of the system and appropriate conditions, including duration, temperature, and relative humidity. The results of drying kinetics showed that the drying rate increased with an increase in the temperature and duration of the pretreatment. The findings indicate that the HHAIB pretreatment could improve the color indices of the raisins, resulting in an increase in the drying rate and acceptable quality of the final product. This provides a basis for the use of HHAIB on larger and industrial scales.
H. Rezaei; A. Shanaghi
Abstract
Introduction Nowadays, enhancing the impact-resistant and wear-resistant properties of the parts and devices used in the agriculture is necessary to increase the efficiency and lifetime. Among of metals, mild steels due to their properties and low economic cost widely used in the manufacturing of agricultural ...
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Introduction Nowadays, enhancing the impact-resistant and wear-resistant properties of the parts and devices used in the agriculture is necessary to increase the efficiency and lifetime. Among of metals, mild steels due to their properties and low economic cost widely used in the manufacturing of agricultural equipment, but one of their problems is the low wear resistance. So, some methods such as carbon surface hardening, induction hardening, etc., were used to improve the tribological properties. Among of these methods, the nitriding process is an appropriate surface hardening process. In this process, liquid or gaseous of nitrogen atom is provided and then using the appropriate conditions such as heat treatment led to nitrogen atoms penetrate into the matrix structure. Materials and Methods Nine rebar samples of CK45 mild steel with a diameter of 20 mm and a height of 10 mm were prepared with a standard number 1.1191DIN. Firstly, the samples were grinded and polished by alumina powder with particle size of 1 to 3 microns. After cleaning the plasma chamber, samples were placed in the chamber, and the vacuum was created, then plasma nitriding treatment conditions were selected as shown in Table 1. Then phase properties, coating composition, structure and abrasion coating, investigated by using XRD, AFM, FESEM and pin on disc, respectively. Pin on disk wear tests were done according to the standard ASTM G99-90 by pins abrasive tungsten-cobalt with the spherical head (a radius of 5 mm) and under a load of 10 N in the slurry containing soft soil with 10% sand (silicon dioxide), a temperature of 31 °C, humidity 38% and linear velocity of 0.1 mm per seconds. Results and Discussion The curve of XRD, FESEM and AFM images clearly shows the formation of a completely homogenous layer nitride on the surface of the CK45 carbon steel, with a hardness of 810 Vickers and friction coefficient of 0.38. The X-ray diffraction curve indicate the formation of mixed phases ỳ + ε and ε at the surface, and also the presence of α- Fe is due to the passage of X-rays and reaching the CK45 carbon steel substrate. The presence of an unknown peak that was not detected by standard cards, can be related to the presence of nitride in the diffusion layer. According to the AFM, FESEM images and Debye Scherrer relationship, the average particle sizes are in the range of 40 to 70 nm, which formed highly uniform structure. The surface hardness profile shows that the highest hardness of compound layer ỳ + ε may be due the influence of nitrogen in the surface layer to create a complex between surface and Fe4N and Fe3N, which respectively contain more than 7.9% nitrogen, ε-phase and phase ỳ contain about 6% nitrogen. It is noteworthy that the low flexibility, hard and brittle properties of ε-phase leads to higher hardness and thickness of the compound layer that is about 10 microns. Then, increasing distance from the surface cause to present a diffusion layer, which can include nitrides alloy with iron nitride, the thickness of this layer is about 70 microns. It could be notable that the change in the slope of the graph was shown from 40 to 60 microns, it would due to the emergence of fine-grained alloy nitride in this area, which deposit at grain boundary and can be reduced mobility of slip systems and prevent their movement. Fracture energy of the mild steel and plasma nitriding treated mild steel are 57.5 and 57.3 J.cm-2, respectively, which reflects that the softness or flexibility behaviors of samples are similar. However, the abrasive wear mechanism of the silica-based minerals is the main cause of the degradation and the wear of parts and agricultural implements. According to the coefficient of friction behavior, the compound layer of composition as well as its supporting layer, diffusion layer, both resulting in improved abrasion resistance are as follows: • Increasing hardness, reducing the coefficient of friction and also preventing scratches on parts of the silica minerals. • Increasing adhesion of the coating by the diffusion layer leads to increase the tolerance, as well as tapering hard coating layer and substrate combination is resulting in increased longevity. Conclusion Plasma nitriding treated of CK45 mild steel at 450 °C cause to the formation of compound layer (ỳ+ ε) with a thickness of 10 micron and diffusion layer with a thickness of 70 microns. The quite smooth, homogeneous and fine grain structure of surface and also formation of compound layer and diffusion layer led to reduce the friction coefficient of the mild steel by nearly 52% along with the stagnation offracture energy of about 57.3 J.cm-2. In fact, the increasing hardness of the surface led to reduce its coefficient of friction and improve wear performance of parts.
