Development Of The New Thermophysical Properties Measurement System And Research Of Thermophysical Properties Of Dimethyl Ether

For the petroleum resource is less and less in the earth, how to find or develop new alternative fuels, especially clean fuels, becomes an urgent problem to each country now. After lately ten and more years research, it has been found that alcohols, ethers and esters are potential clean alternative fuels. Especially, recent investigations indicated that, dimethyl ether and its mixtures have been shown to have excellent properties as a diesel fuel and have a future as a replacement for engine obtained from fossil reserves. Obviously, it will be benefit to preserve the petroleum resources, reduce the harmful discharge, and alleviate the environment pollution and energy crisis. At present, more and more researchers begin to carry out the research in this field. In hence, the thermophysical properties of these materials are very important and indispensability in these applications. But now, the experimental data of these materials especially with high precision is rare and difficult to find in literatures.The primary purpose of this work is to provide the urgent need experimental data and computation equations of thermophysical properties for the clean alternative fuels research, especially for the research that dimethyl ether is used as the diesel fuel. The second is to develop a new thermophysical properties measurement system with the up-to-date automatic measurement technology. The final purpose is to accumulate the experience and foundation for the research of thermophysical properties of clean fuels and other working fluids. The following is the mainly results obtained in this work: 1. A new thermophysical properties measurement system including the special software has been developed in this work. It consists of a temperature measurement system (range: -80~300℃, the temperature uncertainty less than±1mK), a pressure measurement system (range: 0~6.9 MPa, the accuracy better than 0.01%), oil thermostat bath (range: ambient temperature ~ 300℃, the temperature stability less than±3mK/15min), water thermostat bath (range: ambient temperature ~ 85℃, the temperature stability less than±1mK/15min), alcohol thermostat bath (range: -60 ~ 50℃, the temperature stability less than±5mK/15min, range: -80 ~ -40℃, the temperature stability less than±15mK/15min), vacuum system, mixture make-up system and etc. The software used to measure the temperature and pressure and control the thermostat baths and refrigeration system has been developed with the virtual instrument technology. With the new experimental system, the PVTx properties of fluids could be measured automatically. In order to improve the performance of the thermostat baths, a new quasi-two-dimension Fuzzy-PID control algorithm for temperature is developed and realized.2. A new criterion for determining critical parameters of fluids was provided in this work. After the critical opalescence phenomenon was studied systematically with dimethyl ether and HFC152a (1,1-difluoroethane), we found, there are some shortages and faults in the classical method to determine the critical parameters. Based on the above research, the new criterion is provided, and the critical parameters, co-existence curve and critical exponentβof dimethyl ether have been determined. The critical temperature of HFC152a was also measured. Compared to the classical method, the new method has high resolution and better repeatability.3. In this work, the apparatus used to measure critical parameters, vapor pressure, saturated liquid and vapor density, the Burnett apparatus used to measure the PVT properties; the apparatus used to measure the surface tension and the sealed capillary viscometer are revised and improved. Finally, thermophysical properties of dimethyl ether, including the critical parameters, vapor pressure, saturated vapor and liquid density, PVT property, surface tension, and saturate liquid viscosity, are studied systematically. It just provides the urgent need data to the dimethyl ether automobile research.4. In provide that the"Pressure Zero Temperature Point"exists, with the corresponding state method, a new vapor pressure equation is established in this work. After the detail test with a few decade substances, it's found that the new equation provides accuracy comparable with that of the Wagner vapor equation which is recognized as the best vapor equation at present, and better than that of Xiang equation. Furthermore, it reflects physical properties of the substance and only three adjustable parameters. The new equation also has a great advantage over all of the previous vapor pressure equations including Wagner and Xiang equations in that it can be used to extrapolate extraordinarily from the usual range in which data are available both to the critical point and to the triple point.5. A new method to determine the intermolecular potential parameter, including square well, Lennard-Jones, Kihara and etc, was developed with the relationships of the second virial coefficient, the second acoustical virial coefficient and the intermolecular potential function. With the new method, we've determined the intermolecular potential parameters of a few simple fluids and refrigerants. Compared with the typical method, the new method has more accuracy and dependability. In this work, the research of the parallel molecular dynamic simulation in the cluster of workstations is also carried out, and it's found that the atom-decomposition algorithm is more suitable than the spatial-decomposition algorithm for the small-scale cluster, especially the long-range intermolecular force can't be ignored.