Chongfang Ma

Synergistic Effect of Nanophotocatalysis and Nonthermal Plasma on the Removal of Indoor HCHO

Photocatalysis is an effective method of air purification at the condition of a higher pollutant concentration. However, its wide application in indoor air cleaning is limited due to the low level of indoor air contaminants. Immobilizing the nanosized TiO2 particles on the surface of activated carbon filter (TiO2/AC film) could increase the photocatalytic reaction rate as a local high pollutant concentration can be formed on the surface of TiO2 by the adsorption of AC. However, the pollutant removal still decreased quickly with the increase in flow velocity, which results in a decrease in air treatment capacity. In order to improve the air treatment capacity by the photocatalytic oxidation (PCO) method, this paper used formaldehyde (HCHO) as a contaminant to study the effect of combination of PCO with nonthermal plasma technology (NTP) on the removal of HCHO. The experimental results show that HCHO removal is more effective with line-to-plate electrode discharge reactor; the HCHO removal and the reaction rate can be enhanced and the amount of air that needs to be cleaned can be improved. Meanwhile, the results show that there is the synergistic effect on the indoor air purification by the combination of PCO with NTP.

Experimental investigation of the influence of electric field on frost layer growth under natural convection condition

Abstract The influence of direct current (DC) electric field on the thickness and mass of frost on a cold vertical plate was investigated. The photos of frost layer growth were taken with and without the presence of electric field, and results showed that the electric filed has a strong influence on the frost thickness. The influences of cold plate temperature and ambient temperature on frost thickness and frost mass were also investigated under the natural convection condition with electric field. Experimental results demonstrated that the cold plate temperature has very strong effect on the frost layer thickness, but its influence on frost mass is minor; the influence or ambient temperature on the frost mass is more obvious than that on the frost thickness. *Supported by National Natural Science Foundation of China (Grant No. 50376001) and the Major State Basic Research Development Program of China (Grant No. G200026304)

Experimental Study on Anti-Fouling Performance in a Heat Exchanger with Low Voltage Electrolysis Treatment

An innovative physical method to control fouling in heat transfer equipment—low voltage electrolysis anti-fouling (LVEAF) technology—is introduced. The objective of the present study is to testify the effect of LVEAF treatment in forced convective system and identify the operating mechanism. A series of fouling tests were carried out with and without LVEAF treatment. During the experiments fouling resistance was monitored, and the properties of test liquid were measured, including hardness, alkalinity, electrical conductivity, and pH. The main results were as follows: (1) The fouling was effectively restrained to form on the heat exchanger surface if the circulating water was treated with LVEAF. The scale inhibition ratios exceeded 90% in most cases. (2) The LVEAF technology is an active anti-fouling technology with lower energy consumption. The properties of treated test liquid were changed. (3) Electrochemical reactions occur near the electrode due to the low current existence in the water when the LVEAF device is working. A lot of fouling deposits formed in the test liquid near the cathode or on the inner surface of the treatment unit, but did not deposit on the heat exchanger surface.

A study of coupled convective heat and mass transfer from thin water film to moist air flow

Convective evaporation of a thin water film is numerically studied to investigate the characteristics of friction, heat, and mass transfer in a laminar boundary-layer flow. A special attention has been paid to the problem of inversion vapor concentration. In the range of To= 300 -350 K and C 0 = 0-0.2, the skin friction at the interface does not change much comparing to the flat boundary flow of single phase. On the other hand, the sensible heat transfer and the mass transfer at the interface degrade obviously. 11% of degradation of sensible heat transfer is observed in the parameter range of the study. An inversion concentration is revealed in the numerical results. Below and above this inversion concentration the latent heat transfer changes in opposite ways with the temperature of free stream

Experimental Study on the Influence of Rotational Speed on the Performance of a Single-screw Expander with a 175 mm Screw Diameter

A single-screw expander has been designed and manufactured independently. Based on this prototype, testing system has been built and performance experiment has been made. In this article, compressed air was used as working fluid and performance test for the prototype was finished at conditions including different rotational speed and different inlet pressure. From the experimental data, it is shown that when inlet pressure less than 0.8MPa the output power increases with the increase of rotational speed because of not enough expansion; when inlet pressure more than 0.8MPa, the every biggest output power is appeared in the condition of rotational speed 2600 rpm. The test results also show that the total efficiency is influenced by rotational speed obviously, and the highest total efficiency of this machine is 69.64% in the condition of 3000 rpm and 15 bar.

Experimental Study on the Performance of the Single Screw Expander Prototype by Optimizing Configuration

Improving thermodynamic efficiency of prime movers is the key issue for efficient utilization of low temperature heat resources. Because of many good characteristics, the single screw expander is perhaps a good choice. Precisions in manufacture and assembly are very important factors to the performance of single screw expanders. In this paper, experimental results of the first single screw expander prototype made by ourselves was analyzed and reported for the first time. From the experimental data, the power output of the prototype was about 5kW, but the gas consumption rate was above 105kg/kWh, so the shaft efficiency was only 34% or so. The results indicated that internal leakage was very serious. Hence, the second single screw expander prototype was manufactured. The gap between gate rotor and shell of the new prototype was reduced. The gap is about 0.02mm. From the new experimental data, the mass flow rate was significantly decreased. However, the power output was only 1.4kW. So, the gas consumption rate was even more than the first prototype. The reason of bad experimental results may arise from the too large friction between screw, gate rotor and shell in the case of small gap. So, we manufactured the third single screw expander prototype, which is 0.04mm in gap. From the experimental data, the maximum power output was about 4.5kW, but the mass flow rate was decreased sharply. So the gas consumption rate was about 60kg/kWh, and the shaft efficiency was about 60%. The result indicated that the performance of the single screw expander was remarkable improved by optimizing its configuration.Copyright

Experimental Study on Thermal Performance of Mixed Nitrate and Carbonate Salts

Although molten salts have been used in large scale in the experimental or commercial solar thermal power plants, systematic studies on thermal performence of mixed-salts are lacking. Four eutectic nitrate salts with low melting point were choosed by the analysis of the TG curve and DSC curves with nine binary mixtures of salts with different mass ratio, the specific heat-temperature curve were obtained after further analysis of the DSC curve and experimental correlations were fitted. Potassium carbonate, lithium carbonate, sodium carbonate are mixed in accordance with the different proportions, 36 kinds of mixed molten salt are obtained. The data of melting point, decomposition temperature, specific heat, latent heat and use temperature range were obtained by the analysis of the TGA and DSC curves of 36 salts.Copyright

Comparative study of impact of compressor speed on system performance subject to micro-gravity

Vapor compression heat pump has good prospects in future large-scale spacecraft thermal control technology. Compressor is a key component in vapor compression heat pump. It is essential to study its adaptability under micro-gravity. In this paper, an experimental system was built up to test the performance of inverted compressor subjected to micro-gravity. The performance of compressor upright and inverted was compared. The influence of compressor speed on the performance of vapor compression heat pump was investigated. The results showed that the inverted compressor could be considered gravity-independent because of normal operation. Compressor discharge temperature and power increased with compressor speed. However, the COP(Coefficient of Performance) was less than that of compressor upright. The maximum COP obtained with upright and inverted compressor were 8.4 and 7.6, respectively. The experiment subject to micro-gravity of vapor compressor heat pump provides an experimental basis and lays foundation for future space applications.

Thermal performance study of a parabolic trough collectoer based on heat transfer oil

Based on the parabolic trough collector developed by ourselves, an experiment system is established to evaluate the thermal performance of the parabolic trough collector. Experiments on the thermal performance of the parabolic trough collector have been carried out at different thermal and fluid conditions. Experimental results show that peak efficiency of the parabolic trough collector exceeds 70% at a average thermal oil temperature of 305°C and is close to that level of the commrcialized EUROTRGH collectors, which implies that steel structure of the collector is good and error of the tracking and driving system is very low.

The Manufacture and Performance Test of a Mini-Type Single Screw Compressor

With the development of very large scale integration, the chip heat dissipation is a problem that needs to be solved urgently. Vapor compression refrigeration system is a valid method to cool the electric chip. However, a particular challenge is to make a small and efficient gas compressor. In this paper, a mini-type single screw compressor was manufactured in Beijing University of Technology and a corresponding performance test system was set up. Experimental results show that the heat created by the single screw compressor is higher, which led to an extreme high exhaust temperature. An effective solution is to introduce the low temperature refrigerant from the condenser to the compressor directly to cool down the compressor. Based on this procedure, the compressor performance was measured experimentally. It was found that the condensing temperature, compressor rotation speed and refrigerant charge can affect the compressor performance noticeably and every affective factor has an optimal value. According to the optimal results, the compressor refrigerating capacity of 2.03 kW and system coefficient of performance (COP) of 2.24 was achieved at the evaporating temperature of 5 °C and condensing temperature of 32 °C. Those results can be a baseline for the further performance enhancement of the single screw compressor and can be a valid method for the cooling of large scale integration.© 2012 ASME