Ning Mei

Significantly reduced thermal diffusivity of free-standing two-layer graphene in graphene foam

We report on a thermal diffusivity study of suspended graphene foam (GF) using the transient electro-thermal technique. Our Raman study confirms the GF is composed of two-layer graphene. By measuring GF of different lengths, we are able to exclude the radiation effect. Using Schuetzs model, the intrinsic thermal diffusivity of the free-standing two-layer graphene is determined with a high accuracy without using knowledge of the porosity of the GF. The intrinsic thermal diffusivity of the two-layer graphene is determined at 1.16-2.22xa0×xa010(-4)xa0m(2)xa0s(-1). The corresponding intrinsic thermal conductivity is 182-349xa0Wxa0m(-1)xa0K(-1), about one order of magnitude lower than those reported for single-layer graphene. Extensive surface impurity defects, wrinkles and rough edges are observed under a scanning electron microscope for the studied GF. These structural defects induce substantial phonon scattering and explain the observed significant thermal conductivity reduction. Our thermal diffusivity characterization of GF provides an advanced way to look into the thermal transport capacity of free-standing graphene with high accuracy and ease of experimental implementation.

Thermal and Electrical Conduction in Ultrathin Metallic Films: 7 nm down to Sub‐Nanometer Thickness

For ultrathin metallic films (e.g., less than 5 nm), no knowledge is yet available on how electron scattering at surface and grain boundaries reduces the electrical and thermal transport. The thermal and electrical conduction of metallic films is characterized down to 0.6 nm average thickness. The electrical and thermal conductivities of 0.6 nm Ir film are reduced by 82% and 50% from the respective bulk values. The Lorenz number is measured as 7.08 × 10⁻⁸ W Ω K⁻², almost a twofold increase of the bulk value. The Mayadas-Shatzkes model is used to interpret the experimental results and reveals very strong electron reflection (>90%) at grain boundaries.

Theoretical and experimental studies of the transport process of micro-particles in static water

A theoretical model is established in this paper to investigate the micro-particle behavior in the static water. The forces acting on the micro-particles are analyzed to obtain a description of the micro-particle behavior in the static water. It is shown that the velocity of the micro-particles is a function of the diameter of the micro-particles, the density of the fluid and the micro-particles, the viscosity and the time. The micro-particle’s motion undergoes an accelerating period and a constant velocity period, and the acceleration period of small micro-particles is very short, its velocity is much smaller than that of larger ones. The net flux of a control-volume in the flow field is calculated combined with the Fick Law. It is shown that the transport coefficient is a function of the diameter of the micro-particles, the density of the fluid and the micro-particles, the viscosity and the temperature. The transport of smaller particles is more extended than the larger ones. The digital holography technology is applied to detect the micro-particle’s motion and the comparison between the theoretical solution and the experimental results is made, with a quantitative agreement between them.

Investigation on an ammonia supply system for flue gas denitrification of low-speed marine diesel

Low-speed marine diesel flue gas denitrification is in great demand in the ship transport industry. This research proposes an ammonia supply system which can be used for flue gas denitrification of low-speed marine diesel. In this proposed ammonia supply system, ammonium bicarbonate is selected as the ammonia carrier to produce ammonia and carbon dioxide by thermal decomposition. The diesel engine exhaust heat is used as the heating source for ammonium bicarbonate decomposition and ammonia gas desorption. As the ammonium bicarbonate decomposition is critical to the proper operation of this system, effects have been observed to reveal the performance of the thermal decomposition chamber in this paper. A visualization experiment for determination of the single-tube heat transfer coefficient and simulation of flow and heat transfer in two structures is conducted; the decomposition of ammonium bicarbonate is simulated by ASPEN PLUS. The results show that the single-tube heat transfer coefficient is 1052u2009Wu2009m2u2009°C−1; the thermal decomposition chamber fork-type structure gets a higher heat transfer compared with the row-type. With regard to the simulation of ammonium bicarbonate thermal decomposition, the ammonia production is significantly affected by the reaction temperature and the mass flow rate of the ammonium bicarbonate input.

Combustion characteristic of coal–ammonia composite

ABSTRACT In this article, the combustion characteristic of coal–ammonia composite is investigated. Raw coal and preheating modified coal are treated to absorb the ammonia. Four kinds of samples are made to conduct the thermal balance experiments. The results show that the content of ammonia in the coal–ammonia composite greatly affects its combustion characteristics. The coal–ammonia composite has a lower carbon emission than the raw coal when the same amount of heat is released. Besides, the performances of raw coal can also be improved by preheating treatment, but the coal–ammonia composite has better combustion performances with the same amount of calorific value.

Energy Grade Analysis of Liquefied Natural Gas Cold Energy Utilization

To increase the utilization efficiency of LNG cold energy, this paper analyzes LNG regasification process basing on energy-grade analysis. The result shows that comprehensive utilization both of doing work and heat transfer is the most efficient. Moreover, this paper proposes a chart to select a suitable cold energy utilizaiton way.

Theoretical Investigation of a Power Cycle Using Ammonia-Water as Working Fluid

A novel ammonia-water power cycle is proposed, which uses low-temperature heat sources such as oceanic-thermal, biomass as well as industrial waste heats. An ejector is introduced between the turbine and the absorber. The main emphasis is placed on the energy and exergy analysis to guide the thermodynamic improvement for the cycle; parametric analysis is conducted to investigate the effects of thermodynamic parameters on the cycle performances. The result shows that the thermal efficiency can reach to 5.31% and the exergitic efficiency varies between 13.3% and 24.4% under the given condition. In addition, the generator pressure, the deflation ratio variation and the turbine outlet depressurization made by ejector have significant effects on the performance of the power cycle.

Numerical and Experimental Study on Soot Accumulation on the Wall of Falling Fuel Film Micro-Combustor

Fluid flow contributes much to fuel-air mixture formation in a micro-combustor, the RNG k-e turbulence model was used to simulate the cold flow field of a falling fuel film microcombustor, and comparison was made between numerical result and experimental results. It is shown that the RNG k-e turbulence model translated the flow field of a complex structure micro-combustor and the soot accumulation on the wall of combustion chamber. The experimental results showed that soot accumulation occurs in vortex backflow area near the wall of combustion chamber and the numerical methods is helpful for understanding the way of soot accumulation in the wall of combustion chamber. Therefore, modifications on the flow field with different diameters and entrance direction of the air flow into the primary combustion chamber were made. The numerical simulation of flow distribution showed that the flow field of micro-combustor could be ideal for eliminated soot accumulation.Copyright