碳纤维红外板辐射特性及其农产品物料干燥试验

Infrared drying properties and drying experiment of carbon fiber for agricultural production

为将碳纤维红外板的辐射加热技术应用于农产品物料的干燥中,探究其辐射加热特性和干燥特点。在介绍其制作工艺的基础上,以碳纤维红外板作为辐射热源搭建干燥试验台,对胡萝卜块、苹果块、香蕉块、木耳等4种常见果蔬物料进行干燥。通过实时采集、检测干燥过程中物料内部温度、干燥室温度、相对湿度变化情况了解干燥进程;并对红外干燥过程中物料升温情况、物料厚度、辐射间距、干燥方式进行探讨。结果表明：1）碳纤维红外板可作为红外干燥热源,辐射功率1.1 k W/m2时,能发射1~30μm的中、长波红外线,且主要集中在5~15μm,红外板表面温度范围为84~92℃。辐射间距8 mm条件下,4种物料从水分比1干燥到水分比0.1时,耗时为270~300 min,且20 mm×20 mm×11 mm的胡萝卜片内部温度升高到60℃仅需20 min。2）胡萝卜片长宽20 mm×20 mm,厚度5~11 mm范围内,在干燥中期近似恒温段,物料中心温度随厚度的增加而增加。3）辐射间距为4~12 mm范围内,辐射间距越大,干燥时间越长。4）与普通热风干燥相比,红外—热风联合干燥可有效缩短40%干燥时间,能耗约为普通热风干燥的49.39%;干燥前期排湿、干燥过程较小的风速均有助于红外干燥的进行。综上所述,碳纤维红外板可作为干燥热源。研究结果可为碳纤维在干燥领域的实际应用提供理论依据。

Recently, infrared radiation heating has been widely applied in different thermal processing systems in food industry. It has several advantages such as high efficiency, low energy consumption, and high quality of dried products. In addition, the heating power generated from infrared radiation can penetrate into food materials. But the electric radiant infrared heater, such as ceramic infrared heater and gas-fired infrared radiator, has the some drawbacks e.g., large structure and high heating temperature, which lead to higher energy consumption of infrared drier. In order to explore the drying characteristics of carbon fiber and develop a new heating technology of infrared drying, the drying characteristics of banana slices, apple slices, carrot slices and agaric were investigated in a carbon fiber infrared heating. The material internal temperature, ambient temperature, ambient humidity of drying process were detected during drying process. Result indicated that： 1） Far-infrared waves in the rage of 1-30 μm could be launched by the carbon fiber heating board, and main infrared waves were concentrated in the rage of 5-15 μm. The surface temperature of carbon fiber board was in the range of 84-92℃. Fruits and vegetables could be quickly dried in this form of infrared drying. Under the radiation power of 1.1 kW /m2 and the radiation distance of 8 mm, the drying time of 3 kinds of fruit slices（20 mm×20 mm×11 mm） and agaric（approximately 6-8 g） was about 270-300 min; 2） Carrot slices with size of 20 mm×20 mm and 5-11 mm thickness were dried under the radiation power of 1.1 kW /m2. It was found that the internal temperature increased with the increase of the thickness. 3） Under the radiation power of 1.1 kW /m2, at the radiation distance of 4, 8 and 12 mm, the drying time of 11 mm thick carrot slices was 240, 320 and 450 min, respectively and the drying time increased with the increase of the radiation distance. The adjustment of the distance between the heat source and the material could enhance convection heat transfer, and the temperature of the medium inside the dryer could also be effective in decreasing the drying time without causing quality degradation. 4） Samples were dried in 5 modes： infrared drying, infrared ＋ dehumidification drying, infrared ＋ cold air drying, infrared ＋ hot air drying, hot air drying. The energy consumption of infrared drying of the carbon crystal fiber infrared plate was lower, and the energy consumption of the infrared ＋ cold air drying mode was only 7.68% of the traditional hot air drying at temperature of 55℃. ＂Infrared＋ hot air＂ drying could effectively shorten the drying time and reduce the energy consumption, which were 60% and 49.39% of the hot air drying at 55℃, respectively. In addition, reducing the humidity of drying chamber at the initial drying stage and keeping low air velocity could accelerate drying process. This phenomenon was probably due to the fact that with air velocity increasing, the cooling effect is enhanced, which can reduce the material＇s temperature. In summary, the carbon crystal fiber infrared plate can be used in fruits and vegetables drying as the heating source, which has the advantages of higher heating rate, compact radiation distance, lower energy consumption and simple structure. The findings of the current work provide theoretical basis for the practical application of carbon fiber heating infrared plate in drying.