With the summer heat becoming increasingly unbearable over the years due to climate change,the cooling load in the summertime has also been on the rise.Insulation(隔热) is currently the main solution for blocking heat from entering a building,but by applying an additional material that can delay heat penetration(渗透),it can prevent the indoor temperature from rising and in turn lower the cooling load of the building.
A research team in Korea has developed a new material for building walls that can help reduce the penetration of heat from the outside.The team directed by Dr.Sarng Woo Karng from KIST revealed that they have successfully done it through building walls by applying a phase change material(PCM).One of the most common types is paraffin oil,which is used to make candles.
A solid PCM absorbs heat as it transforms into a liquid phase,so by using a case to hold it when it is in a liquid phase without causing any leakage(渗漏),it is possible to apply them to a building wall to block heat from entering inside.
The problem,however,is that the PCM turns into liquid starting from the outermost layer,and the parts that are hot move upward,while the parts that are still relatively cool move downward.Thus,while the upper part may have completely melted,the lower part will have not,and as a result,heat will penetrate into the building through the area where the PCM is in a liquid phase.In the end,the PCM becomes ineffective in controlling the indoor temperature and is rendered useless.
Dr.Karng's team addressed the non-uniform phase change with bubble injections.Injecting bubbles into the bottom part of the PCM enabled uniform circulation(流动)of the PCM in a liquid phase.Dr.Karng said,"We expect that the insulating wall using the PCM bubble generator used in this study will contribute to reducing the amount of energy used to heat or cool a building.Insulation techniques using the PCM help reduce heat penetration,in combination with the building insulating material,and it can also be used as the outer walls of zero-energy buildings."
