| The relative humidity of indoor air during the heating season in the Qinghai-Tibetan Plateau can be as low as 5%.Dry air leads to rough and chapped skin,damage to the respiratory tract,weakens human immunity and affects the health and comfort of personnel.At present,small humidifiers or atomising nozzles are usually used for local humidification in civil buildings.When the centralised humidification system is used to regulate the indoor humidity,the humidification parameters are usually obtained at atmospheric pressure.However,the Qinghai-Tibet Plateau has low air pressure,low air density,and the diffusion resistance of wet components in the air is different from that under normal pressure.At present,there is a lack of relevant research on the characteristics of indoor air flow and humidity distribution when the plateau buildings are centrally supplied with humidity.Therefore,research into creating a humid environment through the centralised humidification system in the Plateau buildings has become very important.In this paper,the variation law of thermal and humidity parameters related to the evaporation of wet air and water mist with pressure is first analysed,and the mathematical model of air flow and heat and mass transfer in the central humidification room under the condition of low pressure is established.Two humidification modes of water vapour humidification and vapor-liquid two-phase humidification are adopted respectively.The effects of air flow structure,humidification speed,humidification air relative humidity,water mist mass flow rate and vapor-liquid ratio on the room velocity field and humidity field were investigated.The suitable humidity delivery parameters required to meet the indoor wet environmental conditions have been obtained,and the main conclusions are as follows:(1)When water-vapor is used for humidification:(1)The particle size of water mist mainly affects the evaporation rate of water mist,when the particle size exceeds 50μm,it causes local moisture accumulation,with particle sizes ranging from 5 to 20μm has little effect on the process of creating a humid indoor environment,so an intermediate value of 10μm is selected as the particle size of water mist.(2)The humidity delivery speed mainly affects the magnitude of the velocity value in the velocity field and the equilibrium time of the humidity field.As the humidity delivery speed increases from 1m/s to 5m/s,the equilibrium time of the humidity field decreases from about 2200 s to about 370 s.The relative humidity of the humid air mainly affects the unevenness coefficient and the relative humidity value during the formation of the humidity field.At t=200s,the relative humidity of the humid air increases from 30% to 60%,and the maximum relative humidity difference of the humidity field increases from 0.4% to 1.1%.(3)The suitable air distribution and humidity supply parameters are: strip up and down return air vents,horizontal humidity supply,humidity supply speed less than 2m/s,and humidity supply air relative humidity should be between 25% and 60%.(2)When vapor-liquid two-phase humidification is adopted:(1)The particle size of water mist mainly affects the evaporation rate of water mist.When the particle size exceeds 50μm,it will cause wet accumulation in local areas.When the particle size is between 5 and 20μm,it has little effect on the indoor wet environment construction process,so the intermediate value of 10μm is chosen as the particle size of water mist.(2)The effect of humidification rate on the creation of a humid environment is basically the same as that of steam humidification.At the same humidity supply speed,the equilibrium time of the humidity field is slightly slower than that of steam humidification.When the humidity supply speed is between 2m/s and 5m/s,the equilibrium time is about 340 s to 1100 s.The mass flow rate of water mist mainly affects the non-uniformity coefficient and moisture content during the formation of the indoor humidity field.Under different combinations of humidity supply velocity and water mist mass flow rate,the achievable indoor moisture content value ranges from 1.5 to 6.4g/kg(d.a).(3)The humidification temperature mainly affects the change of the indoor temperature field.In order to compensate the indoor temperature decrease caused by water mist evaporation,the lowest humidification temperature range is 19.7℃ ～ 25.2℃under different humidification speed and water mist mass flow combination.(4)The vapor-liquid ratio has a great influence on the uneven coefficient of humidity field and the equilibrium time.When the humidification velocity is 1.6m/s,the mass flow rate of water mist is 0.001kg/s,and the vapor-liquid ratio is 0.5 ～ 2,the maximum difference of room humidity increases from 0.03g/kg(d.a.)to 0.1g/kg(d.a).When t=200s,The equilibrium time increased from 1211 s to 1273 s.(5)By using an orthogonal design scheme to optimise the design of different humidity delivery rates,water mist mass flow rates and vapor-liquid ratios,the optimum range of values for humidity delivery rates,water mist mass flow rates and vapor-liquid ratios was obtained when the comfortable indoor temperature and relative humidity range was between 25% and 60%.When the humidity supply rate was between 1 and 2m/s and the water mist mass flow rate was 0.0006 kg/s,the vapor-liquid mass ratio range was 4.73 to 7.54;when the water mist mass flow rate was 0.0010 kg/s,the vapor-liquid mass ratio range was 2.44 to 4.08;when the water mist mass flow rate was0.0014 kg/s,the vapor-liquid mass ratio range was 1.46 to 2.63.This paper analyses the influence of air distribution form and humidity transmission parameters on indoor wet environment under low pressure conditions by using two humidity transmission modes,i.e,vapor humidity transmission and vapor-liquid two-phase humidity transmission,and obtains appropriate humidity transmission parameters,which provides a theoretical basis and reference for centralized indoor humidity transmission under plateau low pressure area conditions. |
PDF Full Text Request