چكيده به لاتين
Accurate measurement of gas flow is a basic need in many industries, especially in domestic use. Diaphragm gas meters are currently used to measure domestic gas consumption, which is a very old and inaccurate technology. In recent years, the use of micro-thermal flowmeters or thermal MEMS flowmeters has been growing due to its small size, low power consumption and good accuracy. However, the micro-flowmeters need to be optimized for sensitivity in change of flow rates and power consumption. The aim of this project is CFD simulation of this type of flowmeter to predict performance and optimize its geometry. Based on previous studies, the best geometry for measurement of domestic gas consumption was chosen, and the geometry of the heater and the microchannel of this flowmeter were optimized by Comsol software. Unlike previous works in simulation of this flowmeters, it acted exactly like experimental samples by converting electricity into heat in the heater and obtaining the output of the flowmeter as voltage. Results were obtained with an error of 4.8% compared to the experimental data. In this project, the effect of height and width of the channel, and the geometric dimensions of the heater on the flowmeter performance were investigated using the Design Expert software. According to the results, as the channel height decreases, the sensitivity of the flowmeter increases in the high flowrates, but in the low flow rates it is almost constant and also the power consumption is constant in all flow rates. As the channel width and length of the heater increase, the the flowmeter sensitivity and power consumption decreases in all flowrates, but the rate of change in power consumption is greater than the rate of change in the flowmeter sensitivity. As the cross-section of the heater increases, the flowmeter sensitivity and power consumption increases. Now, with optimizing of dimensions by Design Expert software, three flowmeters with different dimensions are provided, which have sensitivities of 0.0030, 0.0106 and 0.0152 mV/(ml/min). They can work 13, 3.5 and 1.1 years, respectively by use of two batteries with each capacity of 750 mA. In the second part of the project, in order to use this flowmeter in the gas pipes used in the houses, a system was designed that simultaneously covers the capacity of G4 and G6 flowmeters. The system consists of a bypass path (micro channel) to which the flowmeter is connected. By CFD simulation, the ratio of flow distribution between the bypass path and the main path in the range of 0.025 to 10 cubic meters per hour and in the range of 0.025 Up to 3.4 cubic meters per hour was obtained second order polynomial and linearly respectively.
Keywords: Gas micro-thermal flowmeter, thermal MEMS flowmeter, Micro heater, Micro channel
