1. The optimal parameters of geothermal energy based on supercritical CO2
David T.W. Lin, 郭智惠, Bo-Yen Shih
Institute of Mechatronic System Engineering, National University of Tainan, Taiwan, R.O.C
Abstract:
The purpose of this study is to find optimal operating condition which can be obtained the best heat extraction in horizontal tube of supercritical CO2. In this study, the heat transfer model conjugated with the Brinkman’s law is used to obtain the thermal behavior in the porous medium. Optimization methods based on the Nelder-Mead of COMSOL non-gradient method to solve and apply to establish the optimal material parameters. The results show that the proposed operating condition is suitable for heat extraction of the enhanced geothermal system. Actual simulation for reservoir of heat extraction in particle size1.54mm & 2.03mm, results can be seen improved it after the optimization.
INTRODUCTION
Experimental apparatus
The heat transfer characteristics of supercritical CO2 in a horizontal tube were investigated experimentally. Figure 1 shows the experimental system, which included a compressed CO2 cylinder, a cooling water bath, a high pressure CO2 pump, a pre-heater, a test section, heating unit, cooler, differential pressure transmitter, heater and measurement systems, a computer, and a data acquisition system (YOKOGAWA MA100).
Figure 1. Schematic of experimental apparatus.
Simulation modeling
In this model, a 3D model combined with free and porous media flow model and heat transfer model is established by finite element method – COMSOL multiphasics package. The length, outer-diameter and inner-diameter are mm, 27.54mm and 14.76mm, respectively. The material of tube is stainless steel. The properties of supercritical carbon dioxide are interpolation functions based on data from the National Institute of Standards and Technology (NIST) standard reference database 69. The schematic diagram of this model is shown in Figure 2.
Figure 2. The schematic diagram of test tube.
RESULTS AND DISCUSSION
The comparison with the experimental data process, we can see that the simulation data obviously lower, but it can clearly see a similar phenomenon, the most important is the experimental error for the actual reasons.
After optimization, we can see more clearly the changes around. The optimal result show that the result are occurred in 12.5(MPa) at 20(ml/min), and the corresponding heat extraction are (W) and (W) as shown figure 4.
Comparison
(a)Particle size 1.54mm (b)Particle size 2.03mm
Figure 3. The comparison between experiment with simulation
Optimization
Figure 4. The results of optimization
CONCLUSIONS
This study is to find optimal operating condition of the heat extraction of supercritical CO2 in the geothermal reservoir. This study can improving the heat extraction and reduces the cost of actual test of enhanced geothermal system. We hope that these results can bring better operating condition for heat extraction and contribution to geothermal energy.