Study On The Construction Strategy Of Indoor Local Space Wet Environment Of Buildings In Qinghai-tibet Plateau

The indoor air in the buildings on the Qinghai-Tibet Plateau is extremely dry in winter,with the lowest relative humidity of 3%to 5%.The human body will have symptoms such as chapped skin,dry eyes,nostril bleeding and throat injury in the low-humidity environment,which seriously affects the health of people on the plateau.At present,centralized humidification and humidifier local humidification are mainly used to improve the indoor wet environment,and centralized humidification is mainly used to improve the wet environment level of the whole building space.For buildings with larger space,local humidification is an effective way to ensure moisture demand.However,due to the low air pressure in the Qinghai-Tibet Plateau,the air density decreases and the diffusion rate of wet components in the air increases,resulting in the different diffusion trajectory of wet components and the effective range of humidification compared with those under air pressure.Therefore,it is very important to analyze the influencing factors of indoor local wet environment in buildings on the Qinghai-Tibet Plateau,and then put forward the strategy of creating local wet environment.In this paper,a mathematical model of the flow and diffusion of wet components was established for the construction of a humid environment in a building under low air pressure.Through analysis,the characteristics of air physical parameters,water vapor diffusion coefficient and droplet evaporation rate varying with pressure were obtained.the parameters such as blowing sensation,moisture content and response time were used as the evaluation indexes of humidification effectiveness.Steam humidification and gas-liquid two-phase mixed humidification（water vapor and liquid droplets）were used to calculate the effects of moisture source outlet form,humidification height,humidification angle,humidification velocity,humidity concentration,gas-liquid ratio,droplet size and humidity temperature on the moisture diffusion law and the distribution characteristics of velocity field and humidity field in the local space of the building.The main conclusions are as follows:Part1:Steam humidification（the target area is 1.2～3.5m in length,1.6m in width and 1～1.2m in height from the outlet of the moisture source,and the effective humidification area is the range containing the target area in the local space.）（1）The strip,circular and square wet source outlet forms（the total area of the wet source outlet is the same,but the circular and square wet source outlets are divided into three）have little influence on the humidity distribution in the target area,but have a great influence on the velocity distribution.Under the condition of meeting the humidity requirements of the target area,the circular and square wet source outlet form will lead to the blowing feeling in the target area,and the strip wet source outlet form can meet the requirements of air flow velocity.（2）Considering the influence of initial jet inertia force and water vapor floating lift on the diffusion trajectory of wet components,the humidity delivery height of 0.9～1.1m and the humidity delivery angle of horizontal or downward 15°can meet the requirements of wet environment in the target area.For horizontal humidification,the humidification height decreased from 1.1m to 0.9m,and the effective humidification area increased by28.6%.（3）When the wet environment requirements of the target area are met,the humidification concentration is 8g/kg_dry,the humidification speed increases from 0.4m/s to 0.6m/s,the diffusion rate of wet components is accelerated,the response time is shortened by 39.4%,and the effective humidification area is reduced by 250%.When the humidification rate is 0.4m/s,the humidification concentration increases from 8g/kg_dryto10g/kg_dry,the response time is shortened by 6.2%,and the effective humidification area is reduced by 14.3%.（4）When creating a local wet environment by steam humidification,it is recommended to use the strip wet source outlet,the humidification height 1m,the humidification angle downward 15°,the humidification concentration 8～10g/kg_dry and the humidification speed 0.4～0.5m/s.Part2:Gas-liquid two-phase mixed humidification（the target area is 1.2～3.5m in length,1.6m in width and 0.5～1.2m in height from the outlet of the moisture source,and the effective humidification area is the range of the target area in the local space.）（1）When the gas-liquid two-phase horizontal moisture supply is carried out,the droplets are affected by gravity and inertia force,and the wet component trajectory will shift downwards.When the moisture delivery height is too low,the wet component concentration near the ground will be too high,resulting in moisture accumulation.When the humidification height increased from 0.9m to 1.1m,the effective humidification area increased by 14.3%,and the response time was shortened by 15.5%.（2）When the droplet size is 1E-5m and the humidification temperature is 18℃,the gas-liquid ratio increases from 1:1 to 3:1,the diffusion rate of the wet component at the outlet of the wet source increases,but the effective humidification area decreases by55.6%.When the gas-liquid ratio is 1:1 and the humidification temperature is 18℃,the droplet size decreases from 2E-5m to 5E-6m and when the gas-liquid ratio is 1:1 and the droplet size is 2E-5m,the humidification temperature increases from 18℃to 26℃.Under the above two conditions,the droplet evaporation rate increases,and the effective humidification area increases by 11.1%and decreases by 87.5%,respectively.（3）For horizontal moisture supply through gas-liquid two-phase mixing,it is recommended to use the humidity delivery height of 1.1m,droplet size of 5E-6m～1E-5m,gas-liquid ratio of 1:1～2:1,and moisture delivery temperature of 18℃～26℃.In this paper,the effects of outlet form of wet source,humidity supply height,humidity supply angle,air supply parameters,humidity concentration and gas-liquid ratio on the airflow distribution and humidity distribution in the local space of the building are studied under the condition of low pressure on the plateau.The suitable wet source moisture supply parameters for creating wet environment are put forward initially,which provides a reference for the construction of indoor local space wet environment in plateau buildings.