Ma Chongfang

Experimental study of viscosity characteristics of hightemperature heat transfer molten salts

In this paper several kinds of high temperature molten salts were investigated experimentally on viscosity-temperature characteristics with high-temperature viscometer. The viscosities of the molten salts were measured and compared with those from references to verify the reliability of the viscometer and measuring methods, and a good agreement was observed from the comparisons. Then, two new high-temperature molten salts were made from the HITEC salt by some additives and the viscosity-temperature profiles of them were obtained by experiments. The results show that the new molten salts have much lower viscosities, thus suitable for reducing the flow resistance in transportation system of high-temperature solar thermal power generation.

Characteristics of pressure drop for single-phase and two-phase flow across sudden contraction in microtubes

Single-phase and gas-liquid two-phase pressure drops caused by a sudden contraction in microtubes were experimentally investigated at room temperature and atmospheric pressure, using nitrogen and water. The experimental results on pressure drop with a novel measurement method, the tiny gaps on the tubes, were used to characterize the sudden contraction pressure drop for tube diameters from 850 to 330 μm. The ranges of the gas and liquid superficial velocity were 2.55–322.08 and 0.98–9.78 m/s in the smaller tube respectively. In single-phase flow experiments, the contraction loss coefficients were larger than the experimental results from conventional tubes in the laminar flow. While in the turbulent flow, the contraction loss coefficients were slightly smaller than those from conventional tubes and predicted well by Kc=0.5×(1−σ2)0.75. In two-phase flow experiments, the slip flow model with a velocity slip ratio S=(ρL/ρG)1/3 showed a good prediction that reveals the occurrence of velocity slip. An empirical correlation for two-phase flow pressure drops caused by the sudden contraction was developed based on the proposed contraction loss coefficients correlation for single-phase flow and Martinelli factor.

Analysis and Optimization of the Power Cycle Based on the Cold Energy of Liquefied Natural Gas

Liquid natural gas (LNG) delivered by sea-ships contains considerable cryogenic energy which can be used for power generation before its evaporation and introduction into the system of pipe line. Electric power generation utilizing LNG cold energy is a major research direction. There are two kinds of LNG cold energy utilization in electric power generation, that is, independent thermal cycle with natural gas direct expansion and close-loop Rankin cycle. However, the efficiency of LNG cold energy utilization is low. Recently, many efforts have been dedicated to improve the efficiency of LNG cold energy utilization. Different optimizing process has been proposed to improve the utilization of LNG cold energy. However, the optimizing target and methods needed to be further decided. In this paper a new methodology combining the energy level analysis and the pinch analysis is determined. A so-called T-W-H diagram is introduced, where T is temperature, W states the energy level and H indicates the amount of energy. The proposed method can promise modifications quickly for improving a base cycle design. Utilizing this method to analysis the normal Rankin power cycle with LNG cold energy as heat sink, the results show that the thermodynamic imperfection in heat exchanger is the main position for improvement. Based on which two cascading power cycle with LNG cold energy recovery is proposed and the analytical results show that the longitudinal cascading cycle has the high performance than transverse cascading cycle. The simulating results showed that this new method is effective for improving thermodynamic cycle of power generation.

Experimental study of dynamic characteristicsof single screw expander with compressed air and water steam as workingfluid

The research and development of novel high-efficient devices used for thermal energy conversion of low-temperature heat source (blow 230°C) is of great significance for energy saving. Single screw expander is a novel expander with a lot of advantages, such as a good axial and redial force balance, a long working life which is twice of double screw, a high pressure ratio which is up to 15 for single stage, a highest volumetric efficiency which can reach 92%, 4% higher than that of double screw, a relatively high efficiency under part load condition, a simple structure, a lowest noise which is 10dB lower than the double screw, and an oil free lubrication. In this paper, an experimental system used for testing the performance of a single screw expander whose diameter is 117 mm was designed and established. The number of screw head is 6 and the number of star wheel teeth is 11. The compressed air and the water steam were used as the working fluid to experimentally study the dynamic characteristics of single screw expander. In the experiment, the inlet temperature, the outlet temperature, the inlet pressure, the outlet pressure, the flow rate of the working fluid, the torque, the speed, and the power of the single screw expander were measured. When compressed air was used as the working fluid, the valve is fully open and the outlet pressure of the air compressor is set to be 0.75–0.85 MPa. From the experimental results, it can be seen that the single screw expander has an optimal power output working condition when the speed is about 2500–3500 r/min, and an optimal temperature drop working condition when the speed is about 2180–2700 r/min. The maximum torque was 4.4 kW when the speed of expander reached 2700 r/min. The maximum inlet flow rate was 32.9 m3/h. The initial inlet temperature of the expander was 22.7°C, and the final inlet temperature is 28.7°C. The variation of the inlet temperature is due to the inadequate heat dissipation caused by the long-time running of the air compressor. The lowest outlet temperature of the single screw expander reached - 20°C. The maximum temperature drop between inlet and outlet of expander reached 45°C. The lowest gas consumption rate was 55.2 kg/(kW h), the highest reached 187 kg/(kW h), and the average was 77.5 kg/(kW h). The maximum total efficiency of expander reached 58.8% and the average was 45.8%. Moreover, the irreversible loss increases first and then decreases with the increase of speed and with the increase of expansion ratio. The highest irreversible loss reached when the speed was 1200 r/min and the expansion ratio was 6.2. With the increase of the speed, the outlet pressure gradually increased and the expansion ratio gradually decreased. The gas consumption rate of the single screw expander first increased and then decreased with the increase of the speed. When water steam was used as the working fluid, the maximum power of expander was up to 3.9 kW. The lowest gas consumption rate was 22.5 kg/(kW h), and the maximum total efficiency of expander reached 66%.

Experimental study on fouling characteristics of spiral-grooved tube and smooth tube

In this paper, we carried out some experiments on fouling characteristics of spiral grooved tubes and smooth tube in many kinds of experimental conditions and parameters of spiral grooved tubes. As compared with the smooth tube, the spiral groove tube has a good anti-fouling propertiy in higher hardness of water, higher cold-water inlet temperature and lower cold-water flow velocity. And we have found a kind of spiral grooved tube which has a good anti-fouling in a variety of conditions.

Thermaleconomic Analysis of Supercritical Compressed Air Energy System

In this paper, the economy of supercritical compressed air energy system is evaluated by using thermal economic method. Electricity price of input system to evaluate selects by the beijing municipal market price for peak and valley, and uses Engineering Equation Solver software to simulate. The results show that the electricity price of output is0.5153 RMB/kW„ªh, while electricity price of input system is0.3148 RMB/kW„ªh by 35 kV valley market price, there is obvious economic advantages compared to the peak market price. This system has no CO2 and other greenhouse gas emission comparing with the compressed air energy storage system, it can also reach the purpose of regulating network load and improve renewable energy power system efficiency, so it has significant environmental and economic advantages.