Study On The Effect Of Air Distribution On Cabin Sleeping Environment

Small and micro cabin sleeping space is widely used in various industries due to its advantages of strong adaptability,small footprint,convenience,economy,and low carbon,such as capsule hotel sleeping cabins,outdoor camping cabins,farmhouse breeding cabins,etc.In the process of creating a cabin-type sleeping environment,mechanical air supply is often used to improve the cabin environment to meet the requirements of thermal comfort and air quality.However,different from the traditional building sleeping environment,due to the limited space of the sleeping cabin,there are three problems in improving the cabin environment by means of air supply:1.The full development of the air supply jet is restricted by the narrow space;2.Due to the limited position of the air supply outlet,it is very easy to feel blowing when the personnel in the cabin are close to the air supply inlet;3.The cabin space is highly enclosed,and the density of heat sources and pollution sources is relatively large,which easily leads to accumulation of heat and pollutants.In view of the above situation,from the perspective of creating good air quality and personnel thermal comfort in the sleep cabin,this study compared and analyzed the air distribution in the sleeping cabin under three air supply modes:mixed air supply,attached jet air supply and collision jet air supply,so as to find the most suitable form of airflow organization.The research process can be divided into 3 steps:1.The effective CFD method after grid independence verification and model verification is used to obtain the velocity distribution in the sleeping cabin under the three air supply modes.Then,an equal-scale experimental platform is built to verify the accuracy of the CFD simulation results with the experimental results;2.The air supply speed and air supply temperature parameters are changed,to compare and analyze the influence of air supply parameters on the distribution characteristics of air distribution in the cabin under different air supply modes;3.Compile the UDF program of air quality and sleep comfort based on the characteristics of actual sleep physiological parameters.After loading the source FLUENT custom UDM and UDS files for further in-depth research,the effect of different air distribution on the improvement of cabin ambient air quality and personnel thermal comfort is quantitatively analyzed.The following main conclusions are obtained through the above research:（1）The comparison between the experimental results and the numerical simulation results shows that the results calculated by the Realizable k-εturbulence model are the closest to the actual situation.Therefore,this turbulence model is used to study the air flow characteristics in the cabin-type sleeping environment.The results show that:in the environment,the effect of the air supply jet on the cabin environment is amplified,and different air supply modes directly determine the distribution of air flow in the cabin;The mixed air supply jet has the fastest response to the air flow distribution in the cabin,and the flow and diffusion mechanism of the fresh air jet in the cabin also changes under the two new air supply modes of the attached jet air supply and the collision jet air supply;The influence of the three air supply modes on the airflow distribution of the head position of the supine human body in the cabin are as follows:mixed air supply>collision jet air supply>attachment jet air supply.（2）The results of separately exploring the influence of air supply parameters on the flow field in the sleeping cabin show that:The velocity distribution in the cabin responds rapidly to the changes of the air supply parameters,and the influence of the air supply temperature difference on the flow field in the cabin is much smaller than that of the air supply speed;In the attached jet air supply mode,the wind speed at the head position of the personnel accounts for the largest proportion in the range of 0.08-0.2 m/s,and the air supply speed of collision jet should be less than 0.3 m/s.（3）Comparing the evaluation indicators of thermal comfort in the cabin under the three air supply modes,it is found that:In the mixed air supply mode,the basic PMV in the cabin is maintained between 0.2 and 0.9,which is a neutral and partial heat environment;The attached jet air supply mode can reduce the PMV by about 0.3 and keep the DR value below 5%under the same air supply volume;The high momentum of the collision jet air supply leads to a strong blowing feeling.In practical application,special attention should be paid to the relationship between the size of the air supply port and the spatial layout in the small and microsleep cabin.（4）The research results on air quality show that:In the mixed air supply mode,the air supply volume should not be less than 30 L/s to ensure that the CO₂concentration in the head area is less than 500ppm.The air supply jet can easily form of a dead angle at the head of the supine person,resulting in a high air age value;The two air supply modes of the attached jet and the collision jet can efficiently send fresh air to the head position of the personnel in the cabin（at the source of CO₂ pollution）.Appropriate reduction of ventilation can still ensure the CO₂ concentration at a low level.Finally,after synthesizing a variety of thermal comfort and air quality evaluation indicators,it is believed that the attached jet air supply mode has the best performance in improving the comprehensive performance of the cabin sleep environment,followed by the collision jet air supply mode,and the mixed air supply mode is the worst.