哺乳动物毛被传热性能及其影响因素

Heat transfer property of mammal pelage and its influencing factors

毛被能够加强或减弱动物向周围环境的热量散失,毛被的形态结构和颜色是传热性能的决定因素,其传热过程往往是传导、对流和辐射3个过程的耦合。以往研究发现环境因子中,风可增加机体向环境中的散热速率,且散失量与风速正相关,动物通过调节在风场中的姿态来适应不同风向。动物体与环境间的温差是影响散热速率的另一因素,不同环境中的动物通过改变毛被结构来适应温差变化。毛被含水率上升会引起导热和蒸发冷却作用加强,动物通过行为或毛被结构变化来调节毛被含水率。毛色决定毛被吸收和反射热辐射的能力。毛被传热性能直接把动物的生理特点与环境因子关联起来,这对揭示动物的适应、进化机制都具有重要意义。同时提出,毛被结构和传热性能的研究还有助于仿生学意义的挖掘。因此,今后应重点在毛被结构和物理性能、研究技术与方法以及毛被生物学和仿生学意义等方面开展研究。

Animals living in thermally stressful environments exhibit morphological,physiological and behavioral adjustments to regulate the thermal balance.The insulation of pelage can retard or enhance heat loss.Pelage structure and color are factors that contribute to regulation of heat transfer.We review the heat transfer properties of mammalian pelage and the factors that influence rates of transfer.Heat transfer through pelage occurs as a result of thermal transduction,convection and radiation.Each of these processes is affected by wind,temperature,moisture and solar radiation.Wind has a strong influence on convection.When hair is separated or compressed by wind,the thermal insulation of pelage is lower than in still air.Wind speed is positively correlated with the amount of heat loss.At high wind speeds,the relationship between hydrodynamic parameters and heat loss cannot be accurately defined.However,thermal conductance can be estimated from cooling curves in still air adjusted for different wind speeds.Body orientation relative to wind direction also affects the heat loss rate due to the direction of hair growth： animals facing toward the wind have lower insulation than back to the wind.The differential between an animal′s body temperature and the surrounding air temperature is another influencing factor,heat loss increases with increasing differentials.Animals show higher sensitivity to temperature change when hair is lacking.Animals adapt to environmental temperatures through evolutionary changes in their pelage structure that avoid the need for increased energy expenditure.In cold environments well-insulated mammals have more latitude in habitat selection and behavior than do poorly insulated mammals.Moisture also affects thermal conduction of pelage.Increasing pelage humidity increase the heat loss by thermal conductive and evaporative cooling.Because water has a thermal coefficient 23.1 times higher than air,wet pelage loses heat about 3 times faster than dry pelage.Apart from this,the distribution pattern,quantity,and secretion capacity of sweat glands are additional factors influencing pelage insulation.Animals optimize their pelage humidity through behavioral regulation and pelage structure.Solar radiation can compensate animal body heat loss.Pelage color determines the capacity for absorbance and reflection of radiant heat,with darker pelage absorbing more solar heat but with lower penetrability than lighter pelage.Solar heat gain is a potentially important factor in the energy budget of diurnal mammals.This may be significant for mammals feeding on poor quality food with low energy density and variable availability.In conclusion,heat transfer capability directly links animal physiology with environmental factors,which is important for understanding the mechanisms of adaptation and evolution.Variations in heat transfer of pelage suggest that knowledge of pelage structure and physiological properties may also facilitate bionic exploration.We recommend continued research concentration on the structure and physiology of pelage and development of supporting technology,especially on bionic significance and applications.