Experimental Determination of Effective Heat Conductivities of Highly Porous Media

摘要

Ceramic foams are utilized in several applications, including the recently developed porous medium burner technology because of their high porosity and good temeprature resistance.However, there is a lack of knowledge of an improtant property for this application, namely the effective heat conductivity. Models for the effective heat conductivity exist only for packed beds so far. THis paper presents experimental investigations on the effective heat conductivity of ceramic foams. An apparatus was built and emasurements of the temperature profiles under steady-state conditions in the porous media were carried out. An inverse method was used to estimate the effective heat conductivity. By guessing the reaial and axial effective heat conductivities, the temperature profiles in porous media wee solved under local thermal equilibrium assumption using a finite-volume code. The best combination of radial and axial effective heat conductivities was found when the minimal error based on the least-squares methd between the measured and two-dimensionally simulated temperture fields were reached. For validation purposesd, investigations of two kinds of sphere packings were carried out, and the results showed fairly gogod agreement wit existing models of effective heat conductivity in packed beds. Different types of ceramic foams were investiaged. As the results show, the effectiveheat conductivities increase with increase in temperature. The aixal effective heat conductivity also increases iwt increasing velocity. SiC foam is promising because of the high heat conductivity of its solid matrix. With the measured effectiv eheat conductivities, a numeridal simulation of the heat transfer in porous media burners was performed. Results for different porous media are presented.