Large Eddy Simulation of Hypersonic Turbulent Boundary Layers

The recent revival of interest in developing new hypersonic vehicles brings attention to the need for accurate prediction of hypersonic flows by computational methods. One of the challenges is prediction of aerothermodynamic loading over the surface of the vehicles. Reynolds Average Navier-Stokes (RANS) methods have not shown consistent accuracy in prediction of such flows. Therefore, new methods including Large Eddy Simulations (LES) should be investigated. In this paper, the LES method is used for prediction of the boundary layer over a flat plate. A new recycling-rescaling method is tested. The method uses total enthalpy and static pressure along with the velocity components to produce the best results for the Law of the Wall, turbulent statistics and turbulent Prandtl number.

To on-board MHD power generation

The electric power generation in on-board MHD generator is considered under conditions of vehicle’s flight in Earth atmosphere. The physical and computational model of on-board MHD power generation is presented. It is shown that electric power of order of 18 – 20 MW (or ∼ 100 W/cm3) can be extracted in ordinary Faraday-type segmented MHD generator. This high level of electric power is achieved at magnetic field about 0.3 – 0.4 tesla and constitutes nearly 9.5% of total enthalpy flux. The main factor limiting the rise of extracted power is a stall of flow due to MHD deceleration.

Axisymmetric Turbulent Methane Jet Propagation in a Co-Current Air Flow Under Combustion at a Finite Velocity

The paper introduces a numerical method for solving the problem of the axisymmetric methane jet propagation in an infinite co-current air flow. For modeling, we used the dimensionless equations of the turbulent boundary layer of reacting gases in the Mises coordinates. To close the Reynolds equation, a modified k - ε turbulence model was used. The k - ε model is considered a low Rhine turbulence model. Assuming that the intensities of convective and turbulent transfers of components are the same and using the stoichiometric ratios of the concentrations of components during combustion, we reduced five equations for the transfer and conservation of the mass of components to two equations for the relative excess concentration of the combustible gas. The concentrations of the components were determined from the solutions of these equations. By using relatively excessive velocities and total enthalpy, we reduced the boundary conditions for the three equations to a general form. To solve the problem in the Mises coordinates, we used a two-layer, six-point implicit finite-difference scheme, which provides the second order of accuracy of approximation in coordinates. The equations for the conservation and transfer of substances being non-linear, an iterative process was implemented. The influence of the radius of the fuel nozzle on the indices of the turbulent jet and flame was investigated. Findings of research show that in an endless co-current flow of fuel with a decrease in the radius of the nozzle, the rate of the chemical reaction and the maximum temperature in the calculation area decrease, and the amount of unburned part of the combustible gas increases

Swirling mean flow effects on locally reacting interstage liner

Sound transmission through a finite-lined section in a rigid annular duct with swirling and sheared mean flow is analyzed with a new mode-matching method based on the conservation of the total enthalpy and the mass flow, which does not reduce to the conservation of the pressure and the axial velocity when the swirl is non-zero. It relies on a new projection method based on the property of the Chebyshev polynomials and on the scattering matrix formalism to yield transmission losses. This new method is first validated against a finite elements method tool in the uniform axial flow case, and then provides a parametric study of the effect of swirl. At low azimuthal mode order [Formula: see text], the swirl amplifies the attenuation of the contra-rotating modes and makes the attenuation of the co-rotating modes decrease with a trend of a general shift of the transmission loss curve toward contra-rotating modes. A small rotation of the transmission loss curves at low [Formula: see text] is also generally observed. The boundary condition in the lined section has a small effect on the transmission loss, except close to the cut-on thresholds. Finally, the duct boundary-layer thickness has a significant effect on the cut-on modes and the transmission loss but not its profile.

Pengaruh Suhu dan Kelembaban Terhadap Rasio Kelembaban dan Entalpi (Studi Kasus: Gedung UNIFA Makassar)

Temperature affects humidity. The interaction of temperature and humidity also directly affects the health and well-being of humans. The relative humidity (RH) of the air is an indication of how much water vapor is in the air at a particular temperature compared with how much water vapor the air could actually hold at that temperature. Air at 100 % relative humidity holds the maximum amount of water possible at that particular temperature and is said to be saturated. Therefore, air at 50% relative humidity, regardless of temperature, is holding half of its total possible water capacity. In essence, cold air cannot hold as much water vapor as warm air. In a closed environment such as a display case, there will be a fixed amount of water vapor, referred to as the absolute humidity. If the temperature inside the case falls then the relative humidity will rise. If the temperature rises the relative humidity will fall. Such changes in relative humidity could be caused by many factors including direct sunlight, spotlights and air-conditioning failures. Research carried out by experimental studies that we can get the humidity ratio and specific enthalpy in a kind of rooms either using The Psychrometric Chart and The formula. The specific humidity or humidity ratio of an air sample is the ratio of the weight of water vapor contained in the sample compared to the weight of the dry air in the same sample. Enthalpy is the amount of heat (energy) in the air per unit mass. Enthalpy is the total amount of energy present in the air, both from air and water vapor contained therein. And, Specific enthalpy of moist air is defined as the total enthalpy of the dry air and the water vapor mixture - per unit mass of dry air. Keywords: Temperature; Relative Humidity; Humidity Ratio; Specific Enthalpy.

Performance Evaluation of Coupled Thermal Enhancement through Novel Wire-Wound Fins Design and Graphene Nano-Platelets in Shell-and-Tube Latent Heat Storage System

Technological development in latent heat storage (LHS) systems is essential for energy security and energy management for both renewable and non-renewable sources. In this article, numerical analyses on a shell-and-tube-based LHS system with coupled thermal enhancement through extended fins and nano-additives are conducted to propose optimal combinations for guaranteed higher discharging rate, enthalpy capacity and thermal distribution. Transient numerical simulations of fourteen scenarios with varied combinations are investigated in three-dimensional computational models. The shell-and-tube includes paraffin as phase change material (PCM), longitudinal, radial and wire-wound fins and graphene nano-platelets (GNP) as extended fins and nano-additives, respectively. The extended fins have demonstrated better effectiveness than nano-additives. For instance, the discharging durations for paraffin with longitudinal, radial and wire-wound fins are shortened by 88.76%, 95.13% and 96.44% as compared to 39.33% for paraffin with 2.5% GNP. The combined strengths of extended fins and nano-additives have indicated further enhancement in neutralising the insulative resistance and stratification of paraffin. However, the increase in volume fraction from 1% to 3% and 5% is rather detrimental to the total enthalpy capacity. Hence, the novel designed wire-wound fins with both base paraffin and paraffin with 1% GNP are proposed as optimal candidates owing to their significantly higher heat transfer potentials. The proposed novel designed configuration can retrieve 11.15 MJ of thermal enthalpy in 1.08 h as compared to 44.5 h for paraffin in a conventional shell-and-tube without fins. In addition, the proposed novel designed LHS systems have prolonged service life with zero maintenance and flexible scalability to meet both medium and large-scale energy storage demands.

Open Source Axial Compressor Mean-Line Design Tool for Supercritical Carbon Dioxide

This paper presents an open-source axial compressor design code developed for applications using Supercritical CO2 (S-CO2). Real property tables are generated using REFPROP (Reference Fluid Thermodynamic and Transport Properties Database) linked to MATLAB. These tables are created and are provided for S-CO2 and could be created for any fluid in the database. At this time, only a single-phase fluid has been implemented. The tables are imported into the mean-line code and are interpolated with cubic splines to calculate real properties based on two given properties. The mean-line code is written in Python to allow portability and convenient plotting capability. The inputs are simple ascii files with the overall compressor details, stage data, and an optional IGV file. The code uses the axial flow equations of continuity, energy, and angular momentum in addition to velocity triangles to calculate state properties at every station. A free vortex assumption at each between-blade row station is used to calculate information at hub, pitch, and tip. The input for each stage includes the Mach number and absolute flow angle at the rotor leading edge in addition to the total enthalpy rise across each rotor. Loss coefficients, solidity, aspect ratio and axial spacing are also specified for each blade row along with blockage to account for wakes, boundary layers, and bleed. A hub radius is also specified. These parameters allow for a complete set of realistic inputs for the design of axial compressors using S-CO2 as the working fluid. The output can be used to assess the design and is used as the start of higher fidelity design.

Preparation and non-isothermal cure kinetics study of epoxy resin nanocomposites with amine and epoxy functionalized magnetic nanoparticles

Amine-functionalized magnetic nanoparticles NiFe2O4@SiO2@Amine (AMNP), and epoxy functionalized magnetic nanoparticles, CuFe2O4@SiO2@Epoxy (EMNP) were synthesized in three steps. Homogeneous stable dispersion of AMNP and EMNP, at concentrations of 1, 5, 10, 15, 20 wt% in epoxy resin were prepared using stoichiometric amounts of 4,4’-diaminodiphenylsulfone (DDS) as a curing. The optimum ratio of AMNP and EMNP were found to be 5%, and these were investigated by the total enthalpy of the curing reaction using differential scanning calorimetry (DSC) thermograms at 10°C/min. The cure kinetics of epoxy resin-functional magnetic nanoparticles-DDS composites were studied using non-isothermal DSC thermograms at different heating rates (5, 10, 15, 20°C/min). The kinetic parameters of the curing process, such as activation energy ( Ea), pre-exponential factor ( A), and rate constant ( k) were determined using several non-isothermal kinetic methods: Kissinger-Akahira-Sunose (KAS), Kissinger, Straink, Flynn-Wall-Ozawa (OFW), and Bosewell. The kinetic curing values obtained with different kinetic methods are well-matched. The Ea values were calculated in the range of 59.80 to 65.94, 57.69 to 63.92, and 45.38 to 52.45 kJ.mol−1 for the DGEBA/DDS, DGEBA/DDS/AMNP, and DGEBA/DDS/EMNP systems respectively. Also, The A values, using the Kissinger method, were calculated to be in the range of 7.0 × 105, 4.0 × 105, and 0.2 × 105 S−1 for the DGEBA/DDS, DGEBA/DDS/AMNP, and DGEBA/DDS/EMNP systems respectively. The glass transition temperatures of cured resins were determined with DSC, and the surface morphology of the nanocomposites and also the dispersion of the nanoparticles were investigated using scanning electron microscopy (SEM).

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.