Molecular dynamics simulations are conducted to study the motion of carbon nanotube-based nanobearings powered by temperature difference. When a temperature difference exists between stator nanotubes, the rotor nanotubes acquire a higher temperature, which arises from the interaction between phonon currents and nanotubes. The thermal driving force increases with the increase in temperature difference between the stators, an increase that is nearly proportional to the temperature difference. Confined by the minimum energy track, the (5, 5)@(10, 10) nanotube bearings only translate along the axis direction but without successive rotation.

In this paper, a simple yet efficient performance comparison method is proposed based on the assumptions of constant properties and identical frontal area. For this method, no correlations are required, and a small number of discrete data are sufficient. To illustrate the feasibility of the proposed approach, a new slotted fin with 4 mm tubes is designed to replace the original louvered fin with tubes of 7 mm. The orthogonal design method is adopted in the fin design to reduce the number of computational cases significantly, and yet a nearly optimum combination of major geometric factors can still be obtained. The reasonable parametric combination of 3 global parameters is obtained by analyzing the numerical results of 16 plain plate fins. Based on this result, 3 new slotted fins with different fin pitches are studied. The slotted fin with a fin pitch of 1.4 mm is recommended after considering the heat transfer, comprehensive performance, and cost of material and operation. The result shows that compared with the original louvered fin, the recommended fin not only increases the heat transfer rate by 2.2%, 22.5%, and 13.7% under an identical flow rate, identical pressure drop, and identical pumping power constraint, respectively, but also saves approximately 36% of the copper tube materials.

A coal-fired power unit frequently operates under unsteady conditions; thus, in order to acquire scientific energy analysis of the unit, thermodynamic analysis of a single-phase heated surface in a boiler under such conditions requires investigation. Processes are analyzed, and distributions of energy and exergy are qualitatively revealed. Models for energy analysis, entropy analysis, and exergy analysis of control volumes and irreversible heat transfer processes are established. Taking the low-temperature superheater of a 610 t/h-boiler as an example, the distribution of energy, entropy production, and exergy is depicted quantitatively, and the results are analyzed.

Experiments were conducted to study the effects of enhanced surfaces on heat transfer performance during water spray cooling in non-boiling regime. The surface enhancement is straight fin. The structures were machined on the top surface of heated copper blocks with a cross-sectional area of 10 mm×10 mm. The spray was performed using Unijet full cone nozzles with a volumetric flux of 0.044–0.053 m³/(m²·s) and a nozzle height of 17 mm. It is found that the heat transfer is obviously enhanced for straight fin surfaces relative to the flat surface. However, the increment decreases as the fin height increases. For flat surface and enhanced surfaces with a fin height of 0.1 mm and 0.2 mm, as the coolant flux increases, the heat flux increases as well. However, for finned surface with a height of 0.4 mm, the heat flux is not sensitive to the coolant volumetric flux. Changed film thickness and the form of water/surface interaction due to an enhanced surface structure (different fin height) are the main reasons for changing of the local heat transfer coefficient.

This paper presents a numerical simulation of the performance of a meso-scale Wankel compressor and discusses the factors affecting its miniaturization. The discussion is related to the effect of leakage and friction on the design limit (cooling capacity and dimension) of the meso Wankel compressor. In the simulation, the main leakage comes from the gaps between the rotor and the endplates as well as between the seal apex and the cylinder. The largest friction originates from the clearance among the end face of the eccentric shaft, the end faces of the rotor, and the endplates. The decreasing cooling capacity of the meso Wankel compressor increases the proportion of leakage to displacement and causes the coefficient of performance COP and the mechanical efficiency to decrease. The rational design cooling capacity limit for the meso-scale Wankel compressor is approximately 4 W.

High methanol-to-oil ratio is required to obtain a high conversion of oil for the production of biodiesel with supercritical methanol. Recovering the methanol of a stream issuing from a transesterification supercritical reactor by flash distillation instead of evaporation was analyzed. The one-stage and two-stage flash distillation processes were presented and compared. The difference of the recovery percentage of methanol of the above two flash processes is less than 0.5% and the methanol concentration in the vapor for the one-stage process decreases rapidly when feed temperature increases. The process in which the product of transesterification of soybean oil with supercritical methanol is cooled to an appropriate temperature (about 240°C) first and then flashed was put forward. The effect of cooling temperature, feed pressure and flash pressure on methanol concentration and recovery percentage was investigated. According to this study, when the feed pressure range is 15–30 MPa, the flash pressure equals 0.4 MPa, and cooling temperature range is 240°C–250°C, the recovery percentage of methanol is not less than 85%, and the concentration of the vapor in mass fraction of methanol is approximately 99%. Thus, the vapor leaving the flash tank can be directly circulated to the transesterification reactor.

In the solar tower power plant, the receiver is one of the main components of efficient concentrating solar collector systems. In the design of the receiver, the heat flux distribution in the cavity should be considered first. In this study, a numerical simulation using the Monte Carlo Method has been conducted on the heat flux distribution in the cavity receiver, which consists of six lateral faces and floor and roof planes, with an aperture of 2.0 m×2.0 m on the front face. The mathematics and physical models of a single solar ray’s launching, reflection, and absorption were proposed. By tracing every solar ray, the distribution of heat flux density in the cavity receiver was obtained. The numerical results show that the solar flux distribution on the absorbing panels is similar to that of CESA-I’s. When the reradiation from walls was considered, the detailed heat flux distributions were issued, in which 49.10% of the total incident energy was absorbed by the central panels, 47.02% by the side panels, and 3.88% was overflowed from the aperture. Regarding the peak heat flux, the value of up to 1196.406 kW/m² was obtained in the center of absorbing panels. These results provide necessary data for the structure design of cavity receiver and the local thermal stress analysis for boiling and superheated panels.

The combustion and emission characteristics of a turbo-charged, common rail diesel engine fuelled with diesel-biodiesel-DEE blends were investigated. The study reports that the brake-specific fuel consumption of diesel-biodiesel-DEE blends increases with increase of oxygenated fuel fractions in the blends. Brake thermal efficiency shows little variation when operating on different diesel-biodiesel-DEE blends. At a low load, the NO_x emission of the diesel-biodiesel-DEE blends exhibits little variation in comparison with the biodiesel fraction. The NO_x emission slightly increases with increase in the biodiesel fraction in diesel-biodiesel-DEE blends at medium load. However, the NO_x emission increases remarkably with increase of the biodiesel fraction at high load. Particle mass concentration decreases significantly with increase of the oxygenated-fuels fraction at all engine speeds and loads; particle number concentration decreases remarkably with increase of the oxygenated-fuels fraction. HC and CO emissions decrease with increasing oxygenated-fuels fraction in these blends.

Segregation always occurs in a circulating fluidized bed (CFB) because of the wide distribution of particle size and density of the bed material. Terminal velocity has a significant influence on solids segregation; thus, it is convenient to describe the segregation tendency using single particle terminal velocity u_t. This paper proposes a segregation model in CFB boilers based on the Cell Model. In each cell along the riser, varied-sized particles have different tendencies toward segregation; finer particles are carried out more easily, while coarser ones tend to sink into the cell. It is assumed that the average terminal velocity ut ˉ, corresponding to the mean particle size in the cell, has a segregation index of x = 1.0 as the reference point. The segregation index of particles with higher terminal velocity is lower than 1.0, while that for finer particles is larger than 1.0. The empirical formulae of segregation parameters, namely x₀ and k₁, are derived by optimizing experimental data in published literature. The test result of ash size distribution in a 220 t/h CFB boiler validates the reasonableness of the model.

The temperature field of an axisymmetric ethylene diffusion flame is measured using laser holographic interferometry. Temperature field inversion is completed with the aid of components distribution divided from numerical simulation of combustion and air components assumption. Error analysis of key steps is conducted using the theoretical formula of interference temperature measurement and characteristic structure of fringes obtained from optical simulation. Based on the calculation and analysis, air components assumption will not cause significant error in the low temperature region but will result in high error in the high temperature region. Moreover, the small error in environmental temperature measurement transfer to a high temperature range will expand more than tenfold. Results of temperature measurement using air components assumption relative to combustion simulation require the greatest amendment amounting to seven percent.