Preparation Of Cs_0.33WO₃-Paraffin Wax Composites And Optimization Of Their Solar Energy Capture And Storage Abilities

Cesium tungsten bronze(Cs_0.33WO₃)has a wide band gap?².6 eV?and can keep a high visible transparency.At the same time,free electrons are introduced into the cesium ion embedded in the material,which makes the Cs_0.33WO₃ have local plasma resonance absorption and small pole absorption.Therefore,cesium tungsten bronze(Cs_0.33WO₃)can selectively shield near infrared?NIR?light while keeping a high visible transparency,which can effectively inhibit the solar thermal gain and air-conditioning energy consumption of buildings.Cs_0.33WO₃ shows high photo-thermal conversion efficiency?⁷3%?,the absorption of solar energy is converted into thermal energy efficiently.The intensive secondary thermal radiation is produced by the Cs_0.33WO₃/SiO₂ coating.Phase change of materials?PCMs?collect or release heat in the process of phase change,and use the latent heat of phase change materials to achieve energy storage.They can solve the contradiction between energy supply and demand in time and space,effectively improve energy utilization efficiency.And the PCMs can achieve the goal of energy saving and emission reduction.This characteristic of phase change material is applied to building envelope.The PCMs collect solar energy under strong sunlight irradiation,and then release the harvested energy back to keep a more comfortable indoor temperature.And the PCMs wouldn't need extra energy.The PCM is a real environment friendly.In this study,we design two forms of Cs_0.33WO₃-paraffin wax composite materials.In the composite materials,Cs_0.33WO₃ can convert NIR during the day into heat,existing heat into phase change materials.At night,the phase change materials releases the heat.These two functional materials can not only solve the problem of Cs_0.33WO₃ overheating,but also efficiently capture and utilize solar energy.The main results this study are as follows:?1?We design a new energy-efficient composite window by integrating NIR-shielding Cs_0.33WO₃ with phase change materials?PCMs,paraffin wax in our case?.In the composite window,the hexagonal-phase Cs_0.33WO₃ is prepared by a solid state reaction method,and then coated onto commercial float glass as Cs_0.33WO₃/SiO₂ composite films via a sol-gel process.Afterwards,a home-made double-plane window of a float glass and a Cs_0.33WO₃/SiO₂ coating glass is filled by molten commercial paraffin wax to obtain the composite window.The Cs_0.33WO₃ component of the window can reduce solar heat gain buildings.Meanwhile,the paraffin wax component can accumulate the Cs_0.33WO₃-converted thermal energy by phase transition?i.e.,molting with large endothermic latent heat of fusion?,thereby depressing temperature increment and secondary thermal radiation of the Cs_0.33WO₃ layer.When the ambient temperature drops low enough,the paraffin wax can gradually release back the stored thermal energy into surroundings by a reverse phase transition process?solidifying?.Therefore,this Cs_0.33WO₃-paraffin wax composite window should be very effective to keep stable and comfortable indoor temperature for buildings.Performed on a home-made house model,the Cs_0.33WO₃-paraffin wax composite window can depress indoor temperature variation from 24.2 down to7.3?,compared with a bare window glass.This window is expected to improve energy efficiency of buildings locating in areas with high day-night or cross-season temperature fluctuations between.?2?Furthermore,the photo-thermal conversion of Cs_0.33WO₃ and the phase change energy storage of paraffin wax are uniformly compounded to improve the heat transfer efficiency.As this Cs_0.33WO₃-paraffin wax composite is a solid-liquid phase change material,it is imperative to encapsulate it.Therefore,porous wood was obtained by processing the nature wood,and the Cs_0.33WO₃-paraffin wax composite material was filled in the porous wood,and finally the composited wood was sealed with polyurethane?PU?.Putting a certain amount of nature woods and the composite woods placed indoor in the model house respectively and measured temperature of inner room,with the nature woods temperature changes within the range of 27.2?,?white wood,24.5??,and equipped with the sample A indoor temperature in the range of17.8??sample B,13.5??.The composite wood is not limited to the windows.It can be more widely used in indoor furniture,in order to maintain a comfortable indoor temperature.