Study On Heat Transfer Model Of Hand And Thermal Comfort Improvement Through Local Heating

Working in a cold environment is more dangerous than doing the same type of work in a warmer climate.Physical strength and cognitive performance are closely related to body insulation.Hands are one of the most commonly used body parts in the human body and are the most effective means of performing complex tasks because they are capable of performing special tasks that require dexterity,maneuverability and tactile sensitivity.As a result,they are more likely to be exposed to cold conditions.When human hands are exposed to low temperature for a long time,the function of different tissues of the hands will be decreased due to cold,which will also increase the probability of accidents.In order to maintain hand performance and reduce the risk of accidents,hands should be thermally comfortable as much as possible.In this study,a hand heat transfer model was established,which included the heat conduction between the hand tissues,the heat generated by blood flow,the metabolic heat production within the bone core and soft tissue,and the heat source term for local heating of the hand with heating gloves.Because heat exchange between tissue and capillary network is difficult to measure,this term is not considered.The heat transfer model not only simplifies the hand model,but also takes into account the hand heating scene,which is more practical.The effectiveness of the model was verified by experiments and Fluent simulation.A comparative experiment was set up between the cold environment(8±1℃)and the comfortable environment(21±1℃),and the changing trend and rule of the skin temperature of the hand in the cold environment were analyzed and summarized,which deepened the understanding of the hand temperature regulation mechanism.At the same time,Fluent simulated the temperature distribution of the whole hand in a cold environment,verified the effectiveness of the simulation results by comparing with the limited experimental data,and analyzed the thermal physiology of the whole hand according to the simulation results.The model also considered gloves with heat sources and investigated the improvement of thermal comfort of human hands by local heating through the installation of insulation layers in the model.In order to improve the thermal comfort of hands,on the basis of the bare hand working condition(8±1℃)in a cold environment,the experiments of wearing gloves,heating first gear with gloves,heating second gear with gloves and heating third gear with gloves were added,These experiments provide data reference for the subsequent basic research on the improvement of thermal comfort of hands in cold environment.When the hand reaches thermal balance,a balance equation is established to estimate the heating power of gloves in a cold environment(8±1℃),and to predict the heating power of gloves required to achieve thermal comfort in cold environment.The empirical formula is summarized to provide a practical reference for life."Cold-induced vasodilation" was also observed in the experiment,that is,when the finger end is exposed to cold environment for a long time,the blood flow to the finger end will temporarily increase after the temperature is low to a certain value,resulting in an increase in the fingertip temperature.The phenomenon is also a way for the body to protect itself and is thought to reduce the risk of local frostbite.Vasoconstriction and vasodilation alter blood flow to the hands and other limbs to control heat loss from the skin to the environment.The purpose of this study is to improve the hand movement flexibility limitation and increased accident risk caused by freezing in the work,life and study of human hands in a cold environment.On the basis of improving the thermal comfort of hands,this study also aims to get rid of the bulky and inconvenient traditional gloves.The wearable local heating gloves adopted in the experiment can be used indoors.By heating human hands directly,the working time of air conditioning in winter can be reduced and the indoor air temperature required for heating can be reduced.It can also be used outdoors,such as the field tent that cannot be connected to the power supply at all times,and the electric car,which is also more convenient to use.While reducing energy consumption,it also provides a new idea to keep the cold part of the human body--hands warm,which can alleviate the contradiction between the energy consumption of the air conditioning system and the comfort requirement of the human body.