China
Africa
Explore chapters and articles related to this topic
Unstructured Mesh
Published in George Qin, Computational Fluid Dynamics for Mechanical Engineering, 2021
We have a Dirichlet condition at the north boundary and Neumann conditions at the west and south boundaries: (∇T)⋅n→=q/k in which the thermal conductivity of air k=0.026W/(m⋅K). Notice that n→ is the unit normal pointing to the outside of the flow domain so we do not have the negative sign before the temperature gradient. At the east boundary we assume a vanishing temperature gradient: (∇T)⋅n→=0
Hydrogeologic Principles
Published in Stephen M. Testa, Geological Aspects of Hazardous Waste Management, 2020
For vapors and gases, the driving force is a pressure gradient in the gas, often resulting from changes in temperature in different regions of the subsurface. Mixtures of gases can behave more or less ideally, and each gas can be described by its partial pressure (i.e., the pressure that the gas would exert if it alone occupied the total space of the mixture). Therefore, all the individual partial pressures of each gas in a gas mixture add up to the actual pressure of the whole mixture. Partial pressures are very sensitive to temperature. A common reference pressure for gases is the atmospheric pressure at sea level, called an atmosphere (atm), which is equal to approximately 14.5 psi. This is the basal pressure generated by a column of air the height of the atmosphere at sea level, a column of mercury 760 mm high, or a column of water 1020 cm high. Ordinary air is 78% nitrogen, 21% oxygen, and 0.03% carbon dioxide, with the rest argon and some trace gases. The partial pressures for each gas are, therefore, PN2 = 0.78 atm, Po2 = 0.21 atm, and Pco2 = 0.0003 atm. Alternatively, pressure can be given in the mass of gas per volume of air (g/cm3).
Compressible Flow in Nozzles
Published in V. Babu, Fundamentals of Engineering Thermodynamics, 2019
It is well known from high school physics that sound (pressure waves) propagates in any medium with a speed which depends on the bulk compressibility. The less compressible the medium, the higher the speed of sound. Thus, speed of sound is a convenient reference speed, when flow is involved. Speed of sound in air under normal atmospheric conditions is 330 m/s. The implications of this when there is flow are as follows. Let us say that we are considering the flow of air around an automobile travelling at 120 kph (about 33 m/s). This speed is 1/10th of the speed of sound. In other words, compared with 120 kph, sound waves travel 10 times faster. Since the speed of sound appears to be high compared with the highest velocity in the flow field, the medium behaves as though it were incompressible. As the flow velocity becomes comparable to the speed of sound, compressibility effects become more prominent. In reality, the speed of sound itself can vary from one point to another in the flow field and so the velocity at each point has to be compared with the speed of sound at that point. This ratio is called the Mach number, after Ernst Mach who made pioneering contributions in the study of the propagation of sound waves. Thus, the Mach number at a point in the flow can be written as () M=Va
Design and Life Cycle Assessment of small-scale medical waste incinerator equipped with Porous Radiant Burner for remote areas
Published in Indian Chemical Engineer, 2022
Arun Kumar Mahalingam, Sofia Rani Shaik, Lav Kumar Kaushik, Muthukumar Palanisamy, Pratul Chandra Kalita
In this section, the design volume of the chambers (both primary and secondary chambers) and heat requirement in the secondary chamber are calculated using simple stoichiometric equations and, mass and heat balance analysis [5]. The following assumptions are made for simplifying the calculations: The inlet temperature of the medical waste, air and fuel is assumed to be 15.5°C.Composition of air is considered to be 23% Oxygen and 77% Nitrogen by weight.The air humidity ratio is assumed to be 0.0132 kg H2O/kg of dry air (at relative humidity: 60% and dry bulb temperature: 27°C).Volume of 1 kmole ideal gas is equal to 22.4 m3 (at 0°C and 101.3 kPa).The retention time of volatile gases in the secondary chamber and the temperature of the secondary chamber are considered to be 2 s and 1050°C.
Drying and Atterberg limits of Cochin marine clay
Published in International Journal of Geotechnical Engineering, 2020
Amal Azad Sahib, Retnamony G. Robinson
To verify the role of shrinkage stresses upon drying, suction values were measured in Cochin marine clay specimens using Dew point Potentiameter (WP4) that employs the chilled mirror hygrometer. The device is used as a rapid means of determining the total suction of unsaturated soils (Leong, Tripathy, and Rahardjo 2003; Vikas and Singh 2005). The specimens were filled in slurry state (about 1.5 times liquid limit) in a mould of 35 mm diameter and 7 mm height. The soil sample was placed in a sealed chamber containing a mirror with a detector of condensation. The dew-point is the temperature to which the air must be cooled so that the water vapour in the air condenses to liquid water. At the dew-point, the water vapour present in the air is just sufficient to saturate it. When equilibrium prevails, the relative humidity of the air in the chamber is equal to the relative humidity of the soil sample. Relative humidity is calculated as the ratio of the saturated vapour pressure of water at the dew-point to the saturated vapour pressure of water at the air temperature. This ratio can be substituted in the following thermodynamic equation to calculate the total suction pressure.
Estimation of swirl velocity of gas in Ranque-Hilsch vortex tube using a combined thermal and species separation model
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Mihir Chatterjee, Sulekha Mukhopadhyay, Pallippattu Krishnan Vijayan
Therefore for a given mixture of two different species present in fixed ratio the physical parameters are constant and the value of swirl velocity depends on operating parameters like feed flow rate, cold mass fraction and gas temperature. For the present work air as a binary mixture of oxygen and nitrogen has been considered. Air is a mixture of several gases, where the two most dominant components in dry air are 21 volume% oxygen and 78 vol% nitrogen. Oxygen has a molar mass of 15.9994 kg/mol and nitrogen has a molar mass of 14.0067 kg/mol. As both oxygen and nitrogen are di-atomic the molar mass of these molecules are 32 kg/mol and 28 kg/mol respectively. Hence oxygen is the heavier species for this binary mixture and difference in molecular weight of these two gases, ΔM is 4 kg/mol. Now the average molar mass of the gas mixture can be calculated by adding the product of mole fractions of each gas with its molar mass. Thus calculated, the mean molecular weight of air as a binary mixture of oxygen and nitrogen, Mm is 28.97 kg/mol. Mole fraction of the lighter component i.e. nitrogen in the gas mixture, N is taken as 0.78. A value of 1.76 × 10–5 m2/s for the diffusivity ( of gaseous oxygen into air at STP (Standard Temperature and Pressure) is given by (Cussler 1997). This value is used in the present calculation. Variation of air density with temperature can be calculated using the following corelation where ρ is in kg/m3 and temperature T is in K. Equation (24) is from neutrium website ().