| China is the largest tea producing country in the world and has a long history of tea culture.Green tea contains a variety of active ingredients,such as tea polyphenols,free amino acids,caffeine,flavonoids,etc.These active ingredients make tea have a variety of health care functions,and if storage and transportation methods are not appropriate,it is very easy to change its composition,resulting in significant changes in tea quality.A large number of studies have shown that among the existing preservation methods,low-temperature refrigeration is the most advanced and effective method,and a dedicated tea cold store is the best way to preserve the famous tea.The method of combining numerical simulation and experimental test was used to investigate the influence of air duct structure and deflector device on the temperature and humidity field distribution characteristics in the shelf-type cold store in this study.And optimize the air duct opening methods,causeless air duct width and opening rate through orthogonal experimental design to obtain the air duct structure with more uniform temperature and humidity field distribution in the cold store.The airflow organization evaluation index was introduced to evaluate the uniformity of temperature and humidity field distribution and the effectiveness of energy utilization,and the significant degree of influence of each factor on the evaluation index was investigated by the extreme difference analysis method and the analysis of variance method to determine the optimal air duct structure and the coupling of the deflector.The numerical simulation results were in good agreement with the experimental test results,and the following research conclusions were obtained.（1）For the shelf-type refrigerator without an air duct structure and a deflector,there were obvious uneven temperature and humidity distribution and overheating problems in the local space.There was a "cooling blind area" at the upper right of the cold store,and the temperature of tea leaves was as high as 5.1℃.The fluctuation range of relative humidity was from 37% to 45%,and the maximum difference was 8%.The distribution of air distribution was extremely unreasonable.（2）The air duct structure had a great influence on the distribution characteristics of the temperature and humidity field in the cold store.The results of variance analysis and range analysis were basically consistent,and the effect of air duct opening methods was highly significant.The numerical simulation results show that there was no significant difference in the effect on temperature and humidity when the opening method was uniform opening and partition opening,and the uniformity of temperature and humidity field distribution was improved compared with the structure without air duct structure.The effects of the unevenness coefficient and the energy utilization coefficient were highly significant.Under the combined effect of the dimensionless air duct width and the opening ratio,a relatively uniform temperature and humidity field distribution could be obtained inside the cold store.When the opening form was the lower centralized opening,the problems of uneven temperature and humidity distribution and overheating of the local space were exacerbated.（3）The dimensionless air duct width directly determined the internal pressure of the air duct,which in turn affected the outflow angle of the air supply airflow,which had a significant impact on the flow state of the flow field near the air duct outlet.The range analysis showed that with the increase of the dimensionless air duct width,the temperature unevenness coefficient and the relative humidity unevenness coefficient showed a downward trend,the temperature and humidity distribution uniformity increases.And when the dimensionless air duct width was set as 0.5,the energy utilization coefficient reached the maximum value of 1.42.（4）The opening rate of the air duct played a decisive role in the air volume sent into the cold storage per unit time,which in turn affected the distribution of the airflow in the cold store.The simulation results showed that with the increasing of the opening rate,the temperature unevenness coefficient gradually decreased to a minimum of 0.124,the energy utilization coefficient gradually increased to a maximum value of 1.43.And the relative humidity unevenness coefficient appeared at an inflection point when the opening rate was set as 10.8%,and the minimum value was 0.022.（5）Under the additional optimized parameter combination conditions,the unevenness coefficients of temperature and humidity reached the minimum,which were 0.09 and 0.016,respectively.The temperature and humidity distribution was relatively uniform and reasonable,and the energy utilization coefficient reached the maximum value of 1.68,and the efficiency of energy utilization was significantly improved.（6）On the basis of the air duct structure,a deflector was added for drainage.The angle and dimensionless distance of the deflector had great differences in the influence of the air supply and drainage.When the air supply angle was set as 30° and 45°,there was no significant difference in the airflow distribution in the cold store.When the angle of the deflector was set as 60°,it caused the "short circuit of cold airflow",and the uniformity of temperature and humidity distribution was relatively unreasonable.（7）The dimensionless distance of different deflectors directly affected the air volume sent into the cold storage through the air outlet.When the dimensionless distance was set as0.90 and 0.86,the unevenness coefficient of temperature and humidity and the energy utilization coefficient have little difference.When the dimensionless distance was set as0.82,the temperature and humidity unevenness coefficient increases significantly,and the energy utilization coefficient decreases significantly.When the dimensionless distance was set as increased stepwise from bottom to top,the temperature unevenness coefficient reached a minimum value of 0.06,the relative humidity unevenness coefficient reached a minimum value of 0.012,and the energy utilization coefficient reached a maximum value of 1.83,which was the optimal air duct structure coupled with the deflector.（8）According to the research results of this subject,the combination of the air duct structure and the deflector device had become the optimal coupling method of the air duct structure and the deflector within the scope of the research object.A 45° deflector was added on the basis that the air duct opening method was non-uniform opening with a wide upper and a narrow lower,the opening rate was set as 11.8%,and the dimensionless air duct width was set as 0.5,which could support for solving the problem of temperature field non-uniformity in the actual use of shelf-type tea cold store. |
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