Advantages and Disadvantages of Using Carbon Fiber Heating Tubes for Drying Fruits and Vegetables, and Necessary Parameter Adjustments

The article “Common Drying Methods for Fruits and Vegetables in Industrial Production and Their Pros and Cons” mentions the use of carbon fiber heating tubes for infrared radiation heating and drying. This method boasts several advantages such as shorter drying times, lower energy consumption per unit, and improved quality of dried products. Today, we will share more detailed research findings on infrared radiation drying of fruits and vegetables.

Let’s first list some of the international research findings on infrared or far-infrared drying. Nowak’s study on apple slice drying showed that, under the same drying conditions, infrared drying reduced drying time by 50% compared to hot air drying. Sandu reported that, at a hot air temperature of 250 degrees Celsius, the heat flux of convective drying is 0.9-2.0KW/m2, while the heat flux of radiation heating is 4.5-12KW/m2. Therien’s research also found that the heat flux of infrared drying is 6-10 times higher than that of hot air drying, confirming that infrared radiation heating is significantly more efficient.

Furthermore, many scholars have found that infrared drying, or a combination of infrared and other drying technologies, can greatly reduce drying times and energy consumption for other agricultural products. Afzal’s research showed that combining far-infrared drying with convective drying reduced the drying time for barley by 60% and decreased electricity consumption by 40%-70%. Paakkonen found that drying rosemary from a moisture content of 60%-70% to 8% took 24 hours with hot air drying, but only 3 hours with infrared drying.

In addition to enhancing energy utilization and drying efficiency, studies have also shown that combining infrared or far-infrared drying with hot air drying or convective drying can improve the quality of agricultural products, such as higher nutrient retention, better color appearance, and rehydration properties. Saki’s research on the drying of carrots and pumpkins showed that infrared drying had lower losses of vitamin C, β-carotene, and flavor substances. Paakkonen’s study on rosemary showed that the retention of vitamin E in products dried by infrared was twice that of those dried by hot air. Gabel’s comparative study on the drying of onion slices by infrared and hot air found that infrared dried onion slices retained better color and flavor substances.

However, infrared or far-infrared drying is not without its drawbacks. Its radiation performance has much lower penetration compared to microwaves, and the penetration capability depends on the wavelength of the infrared light; shorter wavelengths have stronger penetration and vice versa. However, the absorption bands of the baked materials are mostly in the medium to long wavelength range, presenting a contradiction. Thus, to further improve overall drying efficiency, infrared drying needs to be combined with other drying technologies. Additionally, some scholars have used intermittent infrared drying methods to mitigate the issue of weak penetration in infrared drying, marking a breakthrough and progress in the field of drying thicker materials.

In industrial applications of infrared drying, it is necessary to first verify the appropriate distance between the material being dried and the product. If the distance is too close, it can lead to uneven drying and local charring in later stages; if too far, it reduces the absorption of infrared radiation energy. Furthermore, the overall drying rate and the final drying endpoint must be validated during the baking stage. These parameters require continuous accumulation by enterprises to perfect the infrared drying parameters for various products. Thus, selecting the right carbon fiber heating tubes, appropriate drying parameters, and pre-processing techniques for agricultural products is crucial for achieving high-quality products. These factors need to be guided by the theory of infrared drying and further refined through practical application and improvement.

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