M. Torkian Boldaji; A. M. Borghaee; B. Beheshti; S. E. Hosseini
Abstract
Introduction Thermal processing has a huge impact on the textural attribute of the final food product and texture is a major factor contributing the overall quality of food. Ohmic heating is an advanced thermal processing method in which heat is internally generated within foods by passing an alternating ...
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Introduction Thermal processing has a huge impact on the textural attribute of the final food product and texture is a major factor contributing the overall quality of food. Ohmic heating is an advanced thermal processing method in which heat is internally generated within foods by passing an alternating electric current through them. Ohmic heating can volumetrically heat the entire mass of a food system, resulting in faster heating, better quality and less energy consumption than conventional thermal processing. Gradient voltage and electrode type have high effect on ohmic heating system. Materials and Methods In this study, the effect of voltage gradient and electrode type on moisture reduction time, a/b, ΔE color indexes and energy consumption were studied. For this purpose, four levels of voltage gradients (5, 7, 9 and 11 V cm-1) and four electrode types (Aluminum, Stainless steel, Brass and Graphite) was investigated by ohmic heating in tomato paste processing. Tomato used in this study was purchased from a local market. The whole tomatoes were washed, crushed and mixed in a way that a red less-viscous liquid obtained (Fig. 1). This liquid was considered as tomato samples in the remainder of the article. Ohmic cooking experiments were conducted in laboratory scale ohmic heating system consists of a power supply, a variable transformer, power analyzer, a microcomputer, digital scale (GF-6000) and thermometer (Dual inpur RTD 804U) (Fig. 3). The ohmic cell had a PTF cylinder with an inner diameter of 0.05 m, a length of 0.10 m and two electrodes on both side of the cell. A hole with 3 mm diameter to insert the thermocouple was created and two holes with 5 mm diameter was created on surface of cell. One of them was used for pouring tomato puree and other for exiting steam from cell. Temperature uniformity was checked during previous heating experiments by measuring the temperatures at different locations in the test cell. Ohmic heating was accomplished till the moisture content of the tomato samples reduced from initial moisture content of as 91(wet basis) to a safer level of 70 (wet basis). Moisture reduction time, a/b and ΔE color indexes, temperature and energy consumption were measured. Results and Discussion The results of the nonlinear mathematical model showed that the effect of different voltage gradient levels on moisture reduction time, ΔE parameters and energy consumption had a good agreement (α≤0.01) as well as voltage gradient had a significant effect on a/b color index (α≤0.05). Electrode type had significant effect on processing time, ΔE (α≤0.01), on energy consumption and a/b index (α≤0.05). Interaction of voltage gradient and electrode type was significant on processing time, energy consumption, a/b and ΔE (α≤0.05). In all electrodes by increasing the voltage gradient, processing time and energy consumption were reduced. For example by increasing the voltage gradient from 5 to 11 V cm-1, processing time and energy consumption were decreased on average 38% and 23%, respectively. Minimal processing time and minimal energy consumption were observed in 11 V cm-1 with graphite electrode that were 17 min and 203 kJ, respectively. As well as maximum processing time and maximum energy consumption were obtained in 5V cm-1 with aluminum electrode that were 105.21 min and 321 kJ, respectively. But maximum a/b parameter and minimal ΔE index were observed with stainless steel electrode in 11V cm-1. In determining the best electrode, in addition to the processing time and energy consumption, product quality is also an important parameter. However, graphite electrode has better performance in terms of time and energy consumption, but stainless steel electrode has better performance in term of product quality. Since the production of food, quality is an important parameter, and also the two electrodes graphite and steel are similar in terms of energy consumption and processing time, but stainless steel electrode is better in term of quality, so stainless steel electrode is selected for ohmic heating tomato paste. Conclusion Different voltage gradients and Electrode type have a significant effect on processing time, energy consumption, ΔE and a/b color indexes. Minimal processing time and minimal energy consumption were observed in 11 V cm-1 with graphite electrode that were 17 min and 203 kJ, respectively. But maximum a/b parameter and minimal ΔE index were observed with stainless steel electrode in 11V cm-1. Stainless steel electrode and 11 V cm-1 voltage gradient were the best condition for tomato paste processing by ohmic heating.
S. M. Ataei Ardestani; B. Beheshti; M. Sadeghi; S. Minaei
Abstract
Fluidized bed dryers have not yet been used for drying products such as mint leaves. This could be due to high porosity and low mechanical resistance resulting in poor quality of fluidization. Applying vibration has been recommended to overcome problems such as channeling and defluidization, and hence ...
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Fluidized bed dryers have not yet been used for drying products such as mint leaves. This could be due to high porosity and low mechanical resistance resulting in poor quality of fluidization. Applying vibration has been recommended to overcome problems such as channeling and defluidization, and hence improving the fluidization quality. In this research, a laboratory scale vibro-fluidized bed heat pump dryer was designed and constructed for drying mint leaves. The experiments were conducted at vibration frequency of 80 Hz and amplitude of 3 mm. The velocity and temperature of the inlet air was controlled by an automatic control system. Experiments were carried out at 40, 50 and 60 °C, and two methods: heat pump drying (HPD) and non-heat pump drying (NHPD). The results revealed that drying process primarily occurred in the falling rate period. Effective moisture diffusivity of the samples increased with increase in drying air temperature and varied from 4.26656×10-11 to 2.95872×10-10 m2 s-1 for the HPD method, and 3.71918×10-11 to 1.29196×10-10 m2 s-1 for the NHPD method and was within the reported range of 10-9 to 10-11 m2 s-1 for drying of food materials. The activation energy was determined to be 84 kJ mol-1 for the HPD and 54.34 kJ mol-1 for the NHPD, both have very good agreement with the results of other investigators. The coefficient of performance and specific moisture evaporation rate showed the acceptable performance of the heat pump system. Moreover, the energy consumption of the dryer for the NHPD method was more than the HPD method.
S. H. Hashemi Fard; M. Almassi; A. M. Borghaee; B. Beheshti
Abstract
The use of Bio-ethanol as an alternative diesel engine fuel is rapidly increasing. Bio-ethanol is mixed with diesel fuel at different ratios and used in CI and SI engines. Since vibrations have direct effects on users and engine components, for this reason analysis of vibration resulting from combustion ...
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The use of Bio-ethanol as an alternative diesel engine fuel is rapidly increasing. Bio-ethanol is mixed with diesel fuel at different ratios and used in CI and SI engines. Since vibrations have direct effects on users and engine components, for this reason analysis of vibration resulting from combustion in CI engines is very important. In this study, evaluation of vibration was performed for both diesel and ethanol blends. Commercial diesel fuel (D100), E2 (2% ethanol and 98% diesel fuel), E5, E10, E15 and E20 were used in a two-wheel MITSUBISHI tractor. The engine was tested in 1200, 1600, 2000 and 2400 rpm for all fuel blends, and also the effect of load was investigated for D100 and E10. Results showed that vibration is significantly affected by fuel blend. It was observed that E10 had the lowest vibration while E20 had the highest value. It was also observed that vibration increased as engine speed increased for all fuel blends. It was found that both axial and lateral vibrations affected significantly by load. The lateral vibrations decreased continuously with load rise , but the axial vibrations increased initially but started to follow a reverse trend.
