Research On The Fluid Flow And Heat Transfer Characteristics Of The Multi-channel Cylider Dryer On Energy-saving Type

In the traditional drying process of the steam dryer,the steam will be condensed and formed water ring inside of the dryer, while the conductivity of condensate is only 1/87 of the dryer wall's thermal conductivity, the thermal resistance of the condensate layer is a considerable proportion of the total thermal resistance, it largely reduces the heat transfer coefficient of the dryer. While the dryer rotate at high speed, the common used siphon can not effectively drain off the condensate water. In this paper, a new multi-channel cylinder dryer will effectively solve this problem. The idea of designing new multi-port dryer is to form small port in dryer wall. Steam passed to cylinder is limited in small port, at the meantime, condensate flowed out with the high pressure steam .Multi-channel cylinder dryer as a new type of energy-saving dryer for paper drying, the research of the fluid flow and heat transfer characteristics within the channel is the foundation to the design of multi-channel cylinder dryer, This paper through the research methods of theoretical analysis and numerical simulation, establish the mathematical model of fluid flow and heat transfer in the channel of multi-channel cylinder dryer and the hydrodynamic model of numerical simulation. Simulate the fluid flow pattern, pressure drop and wall heat transfer in the multi-channel, Through theoretical analysis and numerical simulation to optimize the structure design of the multi-channel cylinder dryer.The main results of this study and the main contribution to the performance as the following aspects:(1) Establish a mathematical model of the fluid flow in the multi-channel dryer. The steam flow in the channel is gas-liquid two-phase flow, the flow mathematical model can be divided into homogeneous flow model and the sub-phase flow model according to the different flow patterns (2) Establish a mathematical model of the steam condensate for heat transfer in the multi-channel dryer. Model based on dimensionless number—the flow pattern number of criteria to determine the fluid flow in the channel is shear control or gravity control, and establish a formula of liquid phase heat transfer coefficient and gas phase heat transfer coefficient, meanwhile describe calculation method in detail of flow pressure drop in the process of the fluid flow in the channel.(3) Use numerical simulation software FLUENT's VOF(Volume of Fluid) model in the two-phase flow to simulate the fluid flow in the channel of multi-channel cylinder dryer. The simulation results show that the flow pattern in the channel of multi-channel cylinder dryer stay the same with the Mandhane flow pattern diagram, analyze the pressure drop of the channel we can know that the minimum pressure drop happens while the flow pattern is annular flow or loop mist flow in the channel, it is benefit to heat transfer. analyze the heat transfer process of the new multi-channel cylinder dryer, and found single-inlet steam of the dryer for the heat transfer process is possible to make the the phenomenon of the temperature differential. The multi-channel cylinder dryer have higher heat transfer coefficient than the traditional dryer according to predecessor's experiment, it is proven to be a energy-saving dryer.(4) Design a new type of double-inlet multi-channel cylinder dryer through the numerical simulation of the fluid flow and heat transfer, and use FLUENT to simulate the heat transfer of the double-inlet multi-channel cylinder dryer .Simulation results show that it is effective for double-inlet multi-channel cylinder dryer to improve the uniformity of the dryer's surface temperature.