Abstract: Abstract: The tunnel dryers with direct blowing are widely applied to dry agricultural products in Chinese rural area. While in practice, the existing single fan blowing designs were found to cause a non-uniform gas velocity distribution inside the tunnel, which results in a non-homogeneous drying quality of the dried product. To address this problem, a multiple fans blowing design concept was proposed in this paper and its feasibility was evaluated by using the computational fluid dynamics (CFD) modeling method.In this paper, the CFD model was developed to simulate the cold flow field inside the tunnel dryer and thus the drying process was ignored at the present stage. The self-developed CFD model consisted of governing equations and suitable boundary conditions. The governing equations comprised of the mass, momentum conservation ones, the K-epison turbulent ones. The boundary conditions were set according to the actual operation conditions of the tunnel dryer and included the velocity inlet, pressure outlet, and non-slip boundary ones. The mathematical model was solved using a commercial CFD software-Fluent 6.3.The flow field inside an industrial tunnel dryer with a single fan blowing used for the drying of cowpeas was measured experimentally and simulated using the above CFD model. The CFD simulation results were compared with the experimental data to validate the CFD model. Both the simulation and experimental results showed that a strong, hot air inlet jet with a velocity of 9 m/s was formed under the air flow rate of 6 300 m3/h. The strong air jet would diffuse completely after 10 m of the whole dryer length of 15 m, causing a big non-uniform gas velocity distribution inside the tunnel dryer.Aiming to reduce the strong air jet forming in the single fan blowing design, four, six, and nine fans blowing designs were proposed and their gas velocity distributions were also simulated using the CFD model. It was found that when keeping the air flow rate of 6 300 m3/h, the complete diffusion distance of the inlet air jet was 3 m for the nine fans case, 4 m for the six fans case, and 6 m for the four fans case. Compared with the 10 m diffusion distance in the single fan case, the diffusion distance was shortened largely in the six and nine fans designs and the gas velocity distribution inside the tunnel dryer was also improved. The reduction in the diffusion distance was a result of the reduced air jet velocity due to the increased fan numbers.Simulation results showed that the air inlet jet diffused fast in the dryer width direction, then in the length direction, and finally in the height direction. The compact material structure hinders the through flow between the material layers and thus, the gas diffusion in the dryer height direction was inhibited. For example, in the case of four fans design, the diffusion distance was about 6 meters at the middle height (Z=0 m), 7 meters at Z=0.5 m. At the top part of the dryer where Z=1 meter, air velocity was small.Comparison of the four, six, and nine fans designs showed that the nine fans case could achieve the most uniform gas inlet velocity distribution and homogeneous flow field inside the tunnel dryer, but the six fans design was more cost-effective. The results obtained in this work provide a reference for the optimization design of the air inlet structure of the tunnel dryers.