Heat Transfer Law Of Soil-finned Tube Interface And It's Effects On Output Of Thermoelectric Power Generation Devices

How to power wireless sensors in forest is such an enormous problem that it restricts the application of the internet of things to forestry badly.A solution idea is to use the temperature difference between air and forest soil to generate electricity to power those sensors,based on the Seebeck effect.This paper focus on the heat transfer law of soil-finned tube interface and it's effects on output of thermoelectric power generation devices,so a simulation model for soil-finned tube has been set up and designed and built a experiment platform for forestry soil temperature difference thermoelectric power generation system,than field experiments were carried out.To efficiently harvest environmental micro-energy from shallow soil,simulated analysis,theoretical arithmetic and experimental verification are performed to explore the spatiotemporal rule of heat transfer on a soil/finned tube interface.Simulations are carried out for 36 types of different working conditions,and the empirical formulas for temperature and heat flux are obtained.The temperature and heat flux can be calculated using the formulas if the soil temperature,soil moisture content and finned tube initial temperature are known.The simulations also show that the highest heat flux can reach approximately 0.30 mW/mm2,approximately 1 507.96 mW of energy can be harvested through the finned tube.Theoretical arithmetic indicates that the heat transfer rate of the copper finned tube is 76.77%higher than that of the bare tube,the effect is clear.Results also show that the finned tube should be placed where the soil moisture is greater than 30%to get more heat from soil.An experiment platform was designed and built.Using heating cable to heat soil so that the temperature of soil is higher than the air's,an experiment of forest soil thermoelectric power generation based on the Seebeck effect was carried out to verify the feasibility of powering forestry sensors.The results showed that it gets about 3.5 mW of electrical power output when the temperature difference is about 10?.The paper puts forward a relational model between soil-air temperature difference and electrical power output by introducing temperature difference deliver coefficient ? and lag coefficient ?,PR=1.459×10-3(??TS-A-?)2,by which we can calculate electrical power output.Field experiments were carried out in Beijng and Harbin for 9 months,the temperature difference between soil and air reached 13.8? and 28?,the maximum power out put reached 2.3 mW and 3.7 mW,energy about 1 181.952 J and 5 209.92 J could be harvested during the generation period.