Thermal And Moisture Analysis And Optimizing For Tobacco Leaf Flue-curing With Heat Pump Technology

Tobacco baking needs to consume large amounts of energy. As a result of the limitation of productivity development, coal barn is used to most of the tobacco baking in our country. Coal as baking heat source, directly heating the barn,there is no heat recovery, and has the condition of low heat efficiency, high coal consumption and pollution, and fossil fuels is unsustainable. In recent years our country vigorously develops the clean energy to replace traditional fossil fuels, it will transform the curing barn accordingly so as to form a new mode of sustainable development. Compared with coal-fired boiler, the use of heat pump as a heat source has a more obvious advantage. It belongs to high quality clean energy, and has the advantage of high control precision, saving work time and energy and environmental protection. In recent years, the use of heat pump technology with heat recovery unit to baked dry crops has received the widespread attention, it not only can effective recovery of waste heat, increase the energy utilization, also can reduce the curing cost, protect the environment.At present, there has a lot of comparative analysis research of system performance of heat pump and coal barn applied to flue-cured tobacco, it proved that using heat pump as a heat source is feasible and economic, But the research of using numerical calculation technology to obtain the distribution of flow field in the barn was rare. Intensive curing barn has large amount of tobacco, and the task of flue-cured tobacco cycle is heavy. If not understand all the distribution of flow field inside the barn, it cannot be sure about the baking performance of heat pump barn and it will affect the application of heat pump curing barn. Although the internal structure of the porous media still has a very obvious complexity and randomness, it makes that all kinds of porous media have large errors. In the study of large scale for porous media, through reasonable assumption, it has been found that more reasonable use of mathematical formula to describe its various parameters. The development of computational fluid dynamics makes it possible to introduce the use of numerical calculation technique to the study of baking.Therefore, with the trend of further research of the porous medium drying process, and combining with computational fluid dynamics and the commercial simulation software(FLUENT), the heat pump baking process of tobacco leaf curing barn was studied in this paper. This study obtained the distribution of temperature field, velocity field and concentration field inside the barn, and by changing the external conditions to get better baking process control with minimum cost and improve the tobacco baking quality. So as to provide the theoretical basis and technical support of the popularization and application of heat pump barn in different regions.Tobacco leaf in intensive curing barn in can be regarded as porous media with uniform distribution, and the baking process has the transfer of quality and heat at the same time. Hot air direct contact with the wet tobacco leaves constantly when baking tobacco. The water in the leaves expel from the drain outlet. The overall quality of the tobacco curing barn is closely related with the conditions of temperature and humidity, wind speed and other barn. In this paper, the process of flue-cured tobacco in Wushan, Chongqing County was studied by numerical calculation and practical test. The main research contents are as follows:(1) Unlike traditional coal burning barn, an alternative better approach using the heat pump technology for tobacco drying process is proposed in this study. Based on the theory of heat and mass transfer in porous medium, a numerical model is established using a widely accepted computational fluid dynamics(CFD) package, Ansys-Fluent, and different drying process boundary conditions and physical properties are considered with reasonable hypothesis. Numerical results such as the distribution of the temperature, humidity and velocity field in the curing barn are provided. This method is also applicable to other similar baking properties of porous media which could provide the calculation for the practical application of project reference.(2) On-site measurements are conducted based on an actual curing barn in Chongqing. Through comparing the distribution of the key parameters in the tobacco leaf flue-curing process with our numerical simulation, good agreements are found. Since the numerical simulation can enrich our understanding of thermal and moisture environment within the curing barn, the approach prosed in this study can be applied in future engineering projects for better drying process control of porous medium, such as tobacco leaf curing.(3) On the basis of the existing baking properties and the selection of wind turbine, the effect of external conditions on hot-air drying of tobacco leaves was studied by changing the wall heat preservation performance and circulating air volume.