Zheng Youqu

Experimental study on a potable thermoelectric power generating stove

Electricity is not available everywhere, and a significant portion of people still lives without electricity. Available commercial potable thermoelectric power generating stoves are rare. In order to obtain electrical energy in off-grid areas and in special conditions (earthquake, hurricane, tidal wave, military field, etc.), a potable thermoelectric power generating stove with eight thermoelectric modules was designed. The starting-up performance, temperature level, power load feature and thermoelectric efficiency were tested experimentally using thermocouples, electronic load and corresponding data acquisition systems. Biomass fuel, e.g. dry branches and withered-grasses, can be used in the thermoelectric power generating stove. The weight and the dimensions of the stove are 2.5 kg and 0.25 m×0.2 m×0.044 m (after folded), respectively. No battery is embedded inside, and the stove can producing electricity continuously in case of fire up. The fans for the heat sink are self-starting within 2 min after fire up, and electrical energy can be extracted from the stove to the outside electric equipment subsequently. Tested results found that a maximum output power of 2.45 W at 12.2 V can be obtained after self-powered fans for the heat sink when the load resistance lies between 50 Ω and 70 Ω . The system will fail to produce electricity when the load resistance is smaller than 40 Ω , while the output power decreases when the load resistance continues to increase from 70 Ω . In case a voltage converter with a conversion efficiency of 84% was adopted to maintain a 5.0 V output voltage, a maximum output power of 2.06 W was recorded when the load resistance is 12 Ω . Smaller load resistance will cause system failure, and larger load resistance results in less power output. The thermoelectric efficiency was found to be about 2.1% for the present stove based on experimental measurements and one dimensional Fourier law approximation. On the other hand, it is found that the working temperature difference is about 66°C, indicating that a large potential to increase the power output exists, and convective heat transfer enhancing methods for the heat sink should be a possible solution. This study reveals that the heat management is the key principle in the thermoelectric power generating technology. The zero energy consumption design of the heat end, the temperature controlling strategy for the heat end, the total heat capacity of the heat sink for the fan self-starting, the electrical power load selection for the cold end are the key parameters to extract electrical energy from the system. Comparisons were made between present results and tested data of a commercial potable thermoelectric power generating stove, and analysis and discussions were made. The tested commercial one has a weight of 0.934 kg, and producing a maximum output power of 1.07 W continuously when the load resistance is 5 Ω under the working temperature difference of about 72°C. It is showed that the ratio of output power to weight of the present potable thermoelectric power generating stove is 1.0 W/kg, while the commercial stove is 1.14 W/kg. The ratio of output power to volume for the present stove is 936 W/m3, while the commercial one is 540 W/m3.

Lattice Boltzmann Simulation for Complex Flow in a Solar Wall

In this letter, we present a lattice Boltzmann simulation for complex flow in a solar wall system which includes porous media flow and heat transfer, specifically for solar energy utilization through an unglazed transpired solar air collector (UTC). Besides the lattice Boltzmann equation (LBE) for time evolution of particle distribution function for fluid field, we introduce an analogy, LBE for time evolution of distribution function for temperature. Both temperature fields of fluid (air) and solid (porous media) are modeled. We study the effects of fan velocity, solar radiation intensity, porosity, etc. on the thermal performance of the UTC. In general, our simulation results are in good agreement with what in literature. With the current system setting, both fan velocity and solar radiation intensity have significant effect on the thermal performance of the UTC. However, it is shown that the porosity has negligible effect on the heat collector indicating the current system setting might not be realistic. Further examinations of thermal performance in different UTC systems are ongoing. The results are expected to present in near future.

Simultaneous Recovery of Porosity (Porosity Seed) and Total Heat Transmission in Fibrous Porous Materials

We present an inverse analysis of the conductive and radiative heat transfer problem in fibrous porous materials. The porosity and total heat transmission are simultaneously recovered in the finite-volume method and genetic algorithm scheme for both uniform and nonuniform porosity distributions. We solve the heat transfer equations directly to obtain the total heat transmission that defines the objective function to be minimized in the inverse analysis. The results show that the combined scheme is an effective tool for the inverse analysis of fibrous porous materials.