Heat Transfer of Turbulent Gaseous Flow in Microtubes with Constant Wall Temperature

Experiments were conducted with nitrogen gas flow in two microtubes with constant wall temperature, made of stainless-steel and copper with diameters of 524 and 537 micrometers, to measure the total temperature at the inlet and outlet and quantitively determine the heat transfer rates. The temperature differences between the inlet and the wall were maintained at 3, 5 and 10 K by circulating water around the inlet and the wall. The stagnation pressures were controlled such that the flow with atmospheric back pressure reached Reynolds numbers as high as 26000. To measure the total temperature, a polystyrene tube with thermally insulated exterior wall containing six plastic baffles, was attached to the outlet. Heat transfer rates were obtained from the gas enthalpy difference by using the pressures and the total temperatures measured at the inlet and outlet. Heat transfer rates were also compared with those obtained from the ideal gas enthalpy using the measured total temperatures and from the Nusselt number for incompressible flow. It was found that the measured total temperature at the microtube outlet was higher than the wall temperature. Also, the heat transfer rates calculated from the total temperature difference were higher than the values obtained from the incompressible flow theory.

High-pressure new phase of AgN3

The structural evolutionary behaviors of AgN3 have been studied by using the particle swarm optimization structure search method combined with the density functional theory. One stable high-pressure metal polymeric phase with the [Formula: see text] space group is suggested. The enthalpy difference analysis indicates that the Ibam-AgN3 phase will transfer to the I4/mcm-AgN3 phase at 4.7 GPa and then to the [Formula: see text]-AgN3 phase at 24 GPa. The [Formula: see text]-AgN3 structure is composed of armchair–antiarmchair N-chain, in which all the N atoms are sp2 hybridization. The inherent stability of the armchair–antiarmchair chain and the anion–cation interaction between the N-chain and Ag atom induce a high stability of the [Formula: see text]-AgN3 phase, which can be captured at ambient conditions and hold its stable structure up to 1400 K. The exhibited high energy density (1.88 KJ/g) and prominent detonation properties ([Formula: see text] Km/s; [Formula: see text] GPa) of the [Formula: see text]-AgN3 phase make it a potentially high energy density material.

Effects of Thermal Water Upwelling on Microclimate Change in the High Geo-Temperature Roadway

Deep-circling thermal water upwelling and trickling to high geo-temperature roadway obviously alter the microclimate in mines, which brings difficulty to the prediction of airflow temperature and humidity. This is the basis of air-conditioning cooling load calculation. The heat and mass transfer between trickling water and airflow is rather complicated. Moreover, humid air exhibits the accumulation effect of heat and humidity in the long-distance flow process. In this paper, an apparatus was designed and developed to explore the influence of thermal water trickling on the airflow thermal parameters of a section of roadway (1L–39L, in which 1L–9L is the trickling section). The results show the following (1) With the rise of trickling water temperature, the total enthalpy difference of dry air in the roadway increases within a small range and that of humid air goes up nonlinearly. Besides, the increase of trickling water flow rate has an insignificant effect on the sensible heat of the airflow, while it plays a notable role in increasing the latent heat of the airflow. (2) High trickling water temperature results in a higher growth rate of humidity ratio at 19L than those at 29L and 39L in the early stage of thermal water trickling. Meanwhile, sensible heat exchange, which becomes strong after thermal water trickles for over 30 min, complicates the enthalpy difference variation rates of wet air at the three measuring points. (3) The three measuring points in the 19L–39L section all display a process of enthalpy growth with time. In the case of point 39L, the enthalpy difference of humid air surges sharply when the trickling water temperature is 80 ° C or the flow rate is 200 ml/min. The research results boast some reference value for thermal water management and microclimate change forecasting after the airflow passes through a trickling roadway.

Performance degradation analysis of combined cycle power plant under high ambient temperature

The mechanism of performance degradation of a natural gas combined cycle (NGCC) power plant under high ambient temperature is studied by analysing the performance characteristics and thermal properties of the working fluids. Real operating data under typical seasonal conditions are collected and studied. The results reveal that the power output of the NGCC system decreases by 22.6 %, and the energy efficiency decreases from 57.28 % to 56.3 % when the ambient temperature increases from 5-35?C. GT total power output and ST power output decrease by 17.0 % and 16.2 %, respectively, as ambient temperature increases from 5-35 0C. The enthalpy difference of the flue gas between the turbine inlet and outlet change slightly with varying ambient temperature. The fuel and air input decrease by 16.0 % and 16.2 %, respectively, as ambient temperature increases from 5-35?C. By analysing the calculated results, the decrement in air and fuel input d is considered as the immediate cause of system power output reduction. The proportion of power consumed by AC reaches 50.4 % at 35?C. This is considered to be caused by air compressor idle.

Impedance Modelling of All-Solid-State Thin Film Batteries: Influence of the Reaction Kinetics

Understanding the effect of material properties on the interface impedance is crucial for high energy all-solid-state thin film lithium-ion battery design. Nevertheless, reaction kinetics determined by the free enthalpy difference...

Digitizing “The NBS Tables of Chemical Thermodynamic Properties: Selected Values for Inorganic and C1 and C2 Organic Substances in SI Units”

The NBS Tables of Chemical Thermodynamic Properties is a collection of thermodynamic properties, published in book form, consisting of 103 tables with 14 330 critically evaluated species. The tables were originally published as a series of NBS Technical Notes As a result of this work, the data is now available in a more accessible spreadsheet format. Enthalpy of formation, ΔfH°, Gibbs energy of formation, ΔfG°, entropy, S°, heat capacity at constant pressure, Cp°, all at 298.15 K, and the enthalpy difference, [H°(298) – H°(0)] are provided where known. Within this collection of data, there are no values given for transuranic elements, Np to Lr (Tables 77–87).

Modelling the enthalpy change and transition temperature dependence of the metal–insulator transition in pure and doped vanadium dioxide

We show that a non-collinear spin density GGA+U functional calculation can describe the enthalpy difference (latent heat) of ΔE0 = −44.2 meV per formula unit, similar to the experimental value, between the paramagnetic rutile and the M1 phases of VO2.

The Energy Storage Properties of Refrigerants (R170, R134a, R143a, and R152a) in Mof-5 Nanoparticles: A Molecular Simulation Approach

The thermophysical properties of refrigerant can be modified via adding solid materials to it. In this paper, molecular simulations and thermodynamic calculations were employed to investigate the adsorption and energy storage of ethane (R170), 1,1,1,2-tetrafluoroethane (R134a), 1,1,1-trifluoroethane (R143a), and 1,1-difluoroethane (R152a) in metal organic framework (MOF)-5 nanoparticles. The results show that the fluorine atom in the refrigerants will strengthen the adsorption of refrigerants in MOF-5. However, the fluorine-free refrigerant, R170, owns larger enthalpy difference of desorption than the other refrigerants with fluorine under high pressure. The thermal energy storage capacity of the refrigerant/MOF-5 mixture is larger than that of the pure refrigerant at low pressure. Also, the negative enhancement of the energy storage property of the mixture is found in some cases when the refrigerant experiences phase transition.