Analysis and Optimization of the Airflow Field in a Head-air Heat Pump Dryer Based on Fluent

doi:10.13304/j.nykjdb.2023.0203

Abstract

Abstract:

As the main energy-saving drying equipment for fruit and vegetable products at present， the uniformity of the internal flow field is very important to the efficiency and quality of drying. In this paper， the internal flow field of top-wind heat pump drying oven was optimized using the research method of Fluent dynamic grid numerical simulation optimization and experimental verification， which improved the inter-layer uniformity and drying efficiency of the flow field. Based on the structural characteristics of the headwind drying box， a controllable moving air deflector mechanism was innovatively designed， and 3 schemes including uniform motion， segmented uniform motion and uniform + stagnation compound motion were compared. The simulation results showed that the uniform + stagnation compound motion scheme had the best interlayer uniformity of flow field. After optimization， the uneven coefficient of air volume distribution between layers was as low as 7.02%， and the effectiveness of the optimization scheme was verified by the experiment of green plum drying. The standard deviation of water content of each layer after optimization was 0.01. The system provided reference for the flow field design and structure optimization of the top-wind heat pump drying oven.

Key words: top-air drying ovens, fluent, dynamic grid, structural optimization, flow field uniformity

摘要：

热泵干燥箱作为当前主要的果蔬类产品的节能干燥设备，其内部流场的均匀性对干燥效率与品质至关重要。针对顶风式热泵干燥箱内部流场层间不均匀性问题，采用Fluent动网格数值仿真方法对其内部流场进行优化，提升了流场层间均匀性及干燥效率。基于顶风式干燥箱的结构特点，创新性设计了可控移动导风板机构，并针对该机构匀速运动、分段匀速运动、匀速+停滞复合运动3种方案进行了对比，结果表明，匀速+停滞复合运动方案的流场层间均匀性最佳，经优化后的层间风量分布不均匀系数低至7.02%，并通过青梅烘干实验验证了该优化方案的有效性，优化后的各层青梅含水率标准差为0.01。该系统可为顶风式热泵干燥箱流场设计和结构优化提供借鉴。

关键词: 顶风式干燥箱, Fluent, 动网格, 结构优化, 流场均匀性

CLC Number:

S226.6

Zimin CHEN, Jiangting MO, Guangsheng CHEN, Xiaoxuan GUO, Xianwen ZHU. Analysis and Optimization of the Airflow Field in a Head-air Heat Pump Dryer Based on Fluent[J]. Journal of Agricultural Science and Technology, 2024, 26(10): 135-144.

陈子民, 莫江婷, 陈广生, 郭小璇, 朱贤文. 基于Fluent的顶风式热泵干燥箱气流场分析及优化[J]. 中国农业科技导报, 2024, 26(10): 135-144.

Figures/Tables 16

Fig. 1 Device of the top air heat pump drying oven

Fig. 2 Simplified model for drying oven simulation

Fig. 3 Location of wind speed measurement points

Table 1 Numerical model boundary setting

边界Boundary	边界类型Type of boundary	参数设置Parameter setting
进风口Inlet	速度入口Velocity inlet	风速 Velocity/（m $∙$ s^-1）	2.12，3.21
出风口Outlet	压力出口Pressure outlet	表压 Pressure/Pa	0
物料架Material racks	壁面Wall	滑移 Slip
气流Airflow	流体区域Fluid	空气密度 Air density/（kg $∙$ m^-3）	1.225

Table 1 Numerical model boundary setting

边界Boundary	边界类型Type of boundary	参数设置Parameter setting
进风口Inlet	速度入口Velocity inlet	风速 Velocity/（m $∙$ s^-1）	2.12，3.21
出风口Outlet	压力出口Pressure outlet	表压 Pressure/Pa	0
物料架Material racks	壁面Wall	滑移 Slip
气流Airflow	流体区域Fluid	空气密度 Air density/（kg $∙$ m^-3）	1.225

Fig. 4 Global grid ma

Fig. 5 Grid independence verification

Fig. 6 Top-air drying ovens with moving air guides

Fig. 7 Flow of structural optimization simulation calculation

Fig. 8 Wind velocity cloud at x=2.8 m section

Fig. 9 Velocity vector diagram at x=2.8 m section

Fig. 10 Wind speed diagram for each level of the material rack

Fig. 11 Air volume at each level of the uniform motion of the air guideNote：Dashed line shows the average air volume.

Fig. 12 Air volume at each level of the uniform motion of the air guide in sectionsNote：Dashed line shows the average air volume.

Fig. 13 Uniform + stagnant motion velocity cloud

Fig. 14 Air volume at each level of the guide plate with uniform + stagnant motionNote：The dashed line is the average air volume.

Table 2 Water content of dried plums

层 Layer	初重 Primary weight/kg	末重 End weight/kg	末含水率 Final water content/%	误差 Error/%
1	4.648	2.980	25.13	4.03
2	4.745	3.023	24.66	2.06
3	4.783	2.993	23.29	-3.58
4	4.759	3.043	24.93	3.20
5	4.772	2.993	23.47	-2.85
6	4.761	3.023	24.40	1.01
7	4.710	2.973	23.96	-0.84
8	4.726	3.013	24.71	2.28
9	4.839	3.043	23.67	-2.02
10	4.777	3.023	24.15	-0.04
11	4.802	3.026	23.83	-1.37
12	4.789	3.057	24.80	2.67
13	4.835	3.045	23.78	-1.55
14	4.784	3.003	23.53	-2.59
15	4.795	3.052	24.59	1.77
16	4.738	2.978	23.63	-2.18

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