Research On The Natural Ventilation Of Bulk Grain Carried On Board Under Marine Environment

Recent decades have seen quite a few accidences in the carriage of bulk grain by sea. Although it is difficult to determine the causes of these accidents, improper ventilation is commonly belived one of the key contributing factors.Only analyzing the inward nature of grain such as moisture content and percentage of broken beans, percentage of foreign materials and insects etc. is not enough, the influence to cargo hold of every marine meteorologic factor is also needed to be considered for the question of ventilation of bulk grain carried by sea. However, the writings about the question from the point of view of the influence of marine environment are limited, and the research is definitely difficult. Grain is colloid, porous and can breathe, and the temperature of every spot in cargo hold change with time incessantly after bulk grain loading in hold. The change of whole temperature field in cargo hold belongs to porous natural convection in unsteady heat conduction status, which has not been widely used in field of grain sea transportation. The change of temperature field of cargo hold need to be studied for avoiding the grain damage, or estimating the time of damage occurred. Nevertheless, lots of initial conditions when sailing and boundary conditions during the voyage are required for setting up the temperature field model of cargo hold and analyzing the change in it. The initial condition are, such as, grain natural, status and grain temperature when loading the cargo, air temperature, relative humidity , solar radiation, apparent wind direction and velocity, and water temperature, etc. Boundary condition are, such as, the change of solar radiation, apparent wind direction and velocity, water temperature, time to ventilate, time elapsed, air temperature and relative humidity when carrying ventilation, etc. The data is still not enough yet for the research because the data of solar radiation should be real time, however, most of the research on it is about daily mean change, although most of the initial condition can be obtained. Research has been made in this paper with the following achievement based on the basic theory of heat transfer knowledge:â—†Typical bulk grain cargo hold has been partitioned into few areas for making sure the main area influenced by marine meteorologic factor;â—†Throw analysis on the every marine meteorologic factors for calculating which factor can affect the cargo hold badly, and provide relevant measures to minimize the influence;â—†Analyze the distribution of temperature and moisture in bulk grain cargo hold,and provide the a new way to measure them;â—†Provide the way to improve the efficiecy of ventilation and the way to set the ventilator combined with the structure of the ventilator of modern bulk grain cargo ship;â—†Provide a practical way to conduct ventilation according to psychrometric chart.