Field Experiment And Numerical Simulation Of Conductive Concrete Sheet For Indoor Heating

With the improvement of living standard,comfort of live become more and more important.Heating engineering is the important method for most people to pass the cold winter.The recent research shows that the radiant heating floor is the most comfortable system,based on the analysis of indoor flow field and human body temperature field.Most commonly used radiant heating floor are: cable,electrothermal film and hot water pipe,in which hot water pipe will cause seriously heating loss and occupy lots of building space;cable and electrothermal film is laid under the decorative layer,and the entire decorative layer would be destroyed when heating system needs to be mended,consequently cause huge waste.The development and application of conductive concrete on snow melting,deicing and indoor heating is rapid due to its good electric heating performance.But the thick of indoor-heating conductive concrete plate researchers use are commonly 50 mm,which not only reduce indoor net height,but also increase dead load of floor.However,reducing the thick of conductive concrete plate cause the difficulties of manufacture process.And the conductive materials in conductive concrete sheet(CCS,relative thin conductive concrete plate)easily disperse uneven,and it will cause uneven temperature rising.But there is a blank of research targeting CCS.In addition,existing research pays more attention to modification of the conductive concrete material itself than the actual engineering system.In this paper,20 mm CCS were fabricated with conductive materials,steel fiber and graphite.The factors effecting conductive performance of CCS were discussed,including space between electrodes,arrangement form of electrodes,silica fume and conductive material mix ratio.Based on the previous results,the CCSs with best electric heating performance were fabricated for indoor-heating field test which include temperature field of CCS and indoor space test.Based on the date of field test,the numerical simulation of the electric heating performance of CCS was carried out by Fluent software,and the result of simulation was compared with the field test results to analyze the thermal parameter of CCS.The main results are as follows:(1)The influence of space and arrangement form of electrodes on the resistivity and heating rate of CCS was analyzed.Experimental results showed that CCS with different electrode-space has approximate resistivity.Thus,in further numerical simulation,the CCS can be assumed as homogeneous conductive material.The heating rate of U-D CCS(electrode arrangement form is up-down)is 181.9 times that of L-R CCS(electrode arrangement form is left-right),it is concluded that electrode laying as up-down is optimized arrangement form.(2)The effects of silica fume on the strength,resistivity and electric heating performance of CCS were discussed,and microscopic test was carried out to analyze the mechanism of the effect.The results showed that 10% content of silica fume can improve the interface bonding of cement,consequently improve the strength of CCS.Though EDS(energy dispersive spectrometer),it was found that graphite particles are surrounded by the hydration products of silica fume which block the transition of the C atoms,and cause the increase of resistivity,consequently reduce the thermal efficiency of CCS.On the other hand,silica fume can reduce at least 3.01% of the maximum temperature difference of the sheet surface,so silica fume can improve temperature uniform of CCS during electric heating process.(3)According to the results of the preliminary test,CCS with 2.5% steel fiber and 6% graphite was fabricated for indoor heating test due to extraordinary electric heating performance.Indoor heating system was designed including 3×3 heating plate,temperature control switch and insurance tube.Whole indoor-heating system can realize temperature intelligent control to insurance the safety and inspect fault of system conveniently.The experimental results showed the effectiveness of the heating system.And the energy consumption of the heating system is 0.68 yuan per square meter per day,which is equal to the energy consumption of cables heating system.The indoor heating system in this paper can provide reference scheme to the engineering application of CCS,which has important practical value.(4)Based on the experimental data of indoor heating test,Fluent software was used to model heating system and simulate the heating process.The model and parameters of heating system were adjusted to make simulation data close to experimental data.The adjusted model can be used to predict the temperature distribution in the room with CCS heating system which was fabricated with different conductive material content.This model also can be used to calculate the mixing ratio of CCS when the required heating power is provided.