Investigating the Effect of the Magnetic Field Generated by the Helmholtz Coil on Water Evaporation Rate in a Hot Air Convection Dryer

Articles in Press

Document Type : Research Article

Authors

• H. Mohammadinezhad
• M. H. Aghkhani
• H. Sadrnia

Department of Biosystems Engineering, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran

10.22067/jam.2025.91869.1337

Abstract

Introduction
Water is a very important component of many food products and determines their physical properties, texture, sensory quality, and rate of chemical and microbiological reactions. Magnetic fields, as an emerging technological tool, have recently received increasing attention in the food industry due to their strong permeability and non-contact nature. Studies have shown that magnetic fields weaken hydrogen bonds. Researchers reported that when the magnetic field strength increases, the refractive index of water increases by approximately 0.1%. Magnetic fields can also weaken the van der Waals bonds between water molecules. A similar type of magnet was used in another study for a magnetic field of 6 Tesla. They did not evaluate the evaporation rate, but rather some other properties using the air flow contact angle, and suggested that the magnetization of pure water requires air and the relative motion of the water against the magnetic flux. Previous experiments were conducted at room temperature. The effects of magnetic fields on water samples have been studied from various aspects and are still of interest to researchers in this field. The direction of air flow relative to the magnetic field gradient also affects the evaporation rate. However, some experiments are not well-defined, and their repetition will not be easily feasible. Therefore, a review of the literature on the effects of magnetic fields on water properties shows that there is still no coherent view on the mechanism of the effects of such fields. In this study, we focused on studying the effect of a static electromagnetic field with predefined intensities on the water evaporation rate, fields from 30 to 130 mT and a temperature range between 30, 50, and 70 °C with forced air movement at a uniform speed, and the continuous presence of samples in the electromagnetic field, which, to our knowledge, has not been reported before. To this end, the objectives of this study include: (1) quantitative determination of the evaporation rate as a function of the applied magnetic field; (2) finding the energy contribution to the evaporation rate in the presence of a magnetic field.
Materials and Methods
To create a magnetic field, two copper coils with a wire gauge of 1.25 mm, a core diameter of 110 mm, and 2500 turns were used. To measure the level of magnetism, the PHYWE Tesla meter with an accuracy of 10 microteslas and measurement range of 20 to 2000 mT, made in Germany, was used. To measure the weight of the samples at the desired intervals, the AND digital scale model GF6000 with a weighing capacity of 6000 grams and an accuracy of 0.01 grams, made in Japan, was used. For each of the tests, 40 milliliters of Type II distilled water were used in accordance with ASTM D1193 and ISO 3696 standards, with a conductivity of 0.1 μS.cm^-1. Initially, to ensure uniform testing conditions, the device was operated for 15 minutes, after which the samples were placed in petri dishes with a diameter of 90 millimeters and a height of 11 millimeters at a constant temperature of 20 degrees Celsius and prepared for testing. After preparing the samples and the device, the prepared samples were placed inside the device and removed at 15-minute intervals for a duration of 120 minutes, then weighed using a scale with an accuracy of 0.01 grams. This process was carried out separately for each treatment, and the data were collected. The evaporation rate of the sample per unit time was calculated using the unit of milligrams per minute and the trend line equation. The slope of the obtained lines indicated the evaporation rate values. All the trend lines obtained had a coefficient of determination (i.e., linear correlation degree) equal to or greater than 0.99. We chose the magnetic field range of 30 to 130 mT because the working range of the magnetic field generator in the device fell within this range. The experiments were conducted using a factorial test based on a completely randomized design with two replications. The first factor was the intensity of the electromagnetic field at four levels: 0, 30, 60, and 130 mT; the second factor was temperature at three levels: 30, 50, and 70 degrees Celsius; and the third factor was time at eight levels: 15 to 120 minutes. The means were compared at the 5% significance level using Duncan's test. For this purpose, SAS software version 9.2 was used, and Excel 2016 was used for plotting the graphs.
Results and Discussions
The samples were placed in the field generated by the Helmholtz coil, and the results confirmed the effect of the magnetic field on the water evaporation rate. It was demonstrated in a study that, although increasing temperature and decreasing humidity are the dominant factors affecting the rate of water evaporation, a stationary magnetic field with decreasing temperature has an increasing effect on the evaporation rate. This finding contradicts the results of the present study, where the experimental data indicate an increased impact of the magnetic field with rising temperature levels. Considering the results of the analysis of variance, all factors along with their two-way and three-way interactions were significant at the one percent level.
Based on Duncan's multiple range test, for duration, magnetic intensity, and temperature, with the increase in each factor level, the weighted evaporation values of the samples significantly decreased compared to the previous factor level. All the trend lines obtained had a coefficient of determination (i.e., linear correlation degree) equal to or greater than 0.99. The slope of the line equation between weight and time is equal to the evaporation rate (R). From the evaporation rates obtained from experimental data, it is clear that the correlation with temperature is not linear, but rather an exponential function as:
The above model can behave like a linear model. The parameter estimates of the model were obtained using the SPSS software as:
The final model can be expressed in the following form:
At a temperature of 30 degrees Celsius, the energy consumption decreased by 11.4 kJ with the increase of magnetic levels. At temperatures of 50 and 70 degrees Celsius, the reduction in energy consumption with the application of a magnetic field was observed to be 48.3 and 45.2 kJ per gram, respectively. These results demonstrate the effect of magnetism on optimizing energy consumption at different temperature levels, with 50 degrees Celsius and a magnetic field intensity of 130 mT being the optimal conditions in terms of energy consumption.
Conclusion
In this study, a statistical approach was used to investigate the rate of water evaporation under different magnetic fields and temperatures over a specified period. The results indicated that the magnetic field, like temperature, affects water evaporation, and as the field increased, the rate of water evaporation also rose. Specifically, the evaporation rates in the treatments at 30, 50, and 70 degrees Celsius after 120 minutes without applying the magnetic field were 43.7%, 53.3%, and 66.5% of the initial weight of the sample, respectively. After applying the magnetic field from 0 to 130 mT, the evaporation rates were reported as 59.6%, 82.8%, and 94.7% of the initial sample weight, respectively, indicating an increase in the evaporation rate with the application of the magnetic field. Finally, a model was proposed that accurately predicts this trend and can be utilized. The analysis of the energy consumption results for each treatment also showed that the magnetic field can influence the total energy consumption for water evaporation and optimize energy use, with reductions of 14.6% at 30 degrees Celsius, 26.55% at 50 degrees Celsius, and 22.5% at 70 degrees Celsius.
Acknowledgments
The present study pertains to research project number 60993 approved by Ferdowsi University of Mashhad, and it acknowledges the efforts of Dr. Mohammad Farkhari (Associate Professor of Plant Breeding at the University of Agricultural Sciences and Natural Resources of Khuzestan) and Dr. Omid Doosti Irani, alumnus of the Biosystems Engineering Department at Ferdowsi University of Mashhad.

Keywords

• Energy consumption
• Magnetic field
• Temperature
• Water evaporation

Main Subjects

• Post-harvest technologies

©2025 The author(s). This is an open access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0).

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