Research On Heat/mass Transfer Characteristics Of A Hardy-plant Stem

The research of heat and mass transfer of plant has been carried out on heat and mass transfer inside and between plant and environment upon leaf and root. With Common Camellia stem as research object, oriented analysis is first conducted with flow in the axial direction and mass transfer in the radial direction. The conventional research methods of “ theoretical modeling- simulation- experimental verification ”are adopted.The physical parameters and temperature field within the stem are determined under different environment temperature, as well as the series thermal resistance analysis theory has been applied to the heat resistance of every section inside stem;Research results and conclusions are as following:(1) The specific heat capacity distribution relationship in Common Camellia stem shows the following overall performance: the specific heat capacity of sapwood is bigger than the bark region, both of the above are bigger than the heartwood, the specific heat capacity of bark reaches the maximum at-1℃;(2) The thermal conductivity appears abrupt at 4℃, the values of thermal conductivity are small;(3) The average temperature of stem is higher than the atmospheric in the daytime;the temperature inside stem close to the outside atmosphere temperature in the night;The stem is greatly influenced by the ambient atmospheric temperature, and there is lag;(4) The heat flow distribution inside the stem of Common Camellia in axial direction shows reversible and good temperature uniformity characteristics;(5) The maximum temperature in the radial direction appears in the region of sapwood in the daytime, while in the night, the maximum temperature is in pith;(6) A significant difference exists with thermal conductivity of various parts inside stem at different atmospheric temperature in summer. The thermal resistance of sapwood is the smallest, the heartwood is smaller followed by the bark which maximize.Thermodynamics methods have been applied to measure the heat distribution andthe flow rate of Common Camellia stem can be calculated, as well as the environmental factors which effecting plant stem flow rate, analysis of the influences about light intensity, air temperature and soil temperature on the stem flow rate was given, the results show that:(1) The variation curve of stem flow rate keep the same trend with ambient temperature and light intensity as a multimodal form with a time-lag; The stem flow rate change with the soil temperature takes the form of “ unimodal curve ”;(2) The stem flow velocity changes with the soil temperature takes the form of “unimodal curve ”, The higher and lower soil temperature play an inhibitory effect on the flow rate;(3) The light intensity, ambient temperature and soil temperature increases can improve the stem flow rate Common Camellia, when the ambient temperature increases, the stem flow rate of Common Camellia increases more obviously, followed by the light intensity.In order to validate the accuracy of plant transport empirical correlations, a three-dimensional physical model of Common Camellia stem was established and the mathematical equations on heat and mass transfer inside porous media were deduced,to simulate the temperature distribution and fluid flows in certain circumstances. The results show that:(1) In the environmental conditions of winter, the impact of flow on temperature field is greater than the atmospheric temperature changes, the high thermal resistance of bark structure act as an good cold resistance;(2) In the axial direction, the stem temperature decreases from the bottom(T1>T2>T3); In the radial direction, showing the highest temperature appear in the portion of sapwood;(3) The flow rate inside stem is slow, the distribution of flow velocity is symmetrical; The flow rate near the wall is close to zero; At the inlet and outlet, there are fluctuations of the flow direction; The overall flow direction is parallel to the outer wall in a steady flow region.