Collision of gas molecules

In situations where the surrounding fluid behaves as a non-continuum fluid, for example at very high temperatures and/or at low pressures, it is possible for Nu to be less than 2. A gas begins to exhibit non-continuum behaviour when the mean free path between collisions of gas molecules or atoms with each other is greater than about 1/100 of the characteristic size of the surface considered. The molecules or atoms are then sufficiently far apart on average for the gas to begin to lose the character of a homogeneous or continuum fluid which is normally assumed in the majority of heat transfer or fluid... 

The rate of collision of gas molecules is given by gas kinetic theory. Molecules have an average kinetic energy given by the expression... 

EXAM PLE 9.6 Rate of Atomic Collisions as a Function of Pressure. Assuming 1019 atoms per square meter as a reasonable estimate of the density of atoms at a solid surface, estimate the time that elapses between collisions of gas molecules at 10 6 torr and 25°C with surface atoms. Use the kinetic molecular theory result that relates collision frequency to gas pressure through the relationship Z = 1/4 vNIV, for which the mean velocity of the molecules v = (BRTI-kM) 12 and NIV is the number density of molecules in the gas phase and equals pNJRT. Repeat the calculation at 10 8 and 10 10 torr. 

An attempt was made by Daniel Bernoulli (1738) to explain Boyle s law on tlie basis of what later became known as the kinetic theory of gases. Bernoulli introduced tlie concept that the pressure of a gas results from the collisions of gas molecules within tlie walls of the gas container. This established a connection between the numbers of gas molecules present and their kinetic energy present at any given temperature. 

The inhalation airflow comes to a rest in the alveolar region. In still air, the collision of gas molecules with each other results in Brownian motion. The same happens with sufficiently small particles (which can be seen when the dust particles in a nonventilated room are hit by a sunbeam). For very small or ultrafine particles (when the particle size is similar to the mean free path length of the air molecules), the motion is not determined by the flow alone but also by the random walk called diffusion. The diffusion process is always associated with a net mass transport of particles from a region of high particle concentration to regions of lower concentration in accordance with the laws of statistical... 

Deposition by diffusion is the main mechanism for particles smaller than 0.5 pm, and is important in bronchioles, alveoli, and bronchial bifurcations. Aerosol particles are displaced by a random collision of gas molecules this results in particle collision with the airway walls [24]. Deposition by diffusion increases with the decrease in particle size, and breath-holding following inhalation was also found to increase this deposition [25]. 

Pressure is defined as force per unit area. The pressure exerted by a gas comes from the forces exerted by collisions of gas molecules with the walls of the container. Since the mass of the walls of the container is much larger than the mass of each particle, the assumption of elastic collisions implies that the velocity component perpendicular to the wall is exactly reversed, and the other two components are unaffected as discussed in Section 7.1. 

The thermocouple pressure gauge is a bimetallic pressure gauge (range 10 mbar to 10 3 mbar), invented by Voege in 1906115 it measures the temperature between the "hot" junction and a reference cold junction, as affected by collisions of gas molecules and concomitant heat loss from the wire. 

When the size of the pores is much smaller than the molecular mean free paths in the gas mixture, collisions of gas molecules with the pore wall are more frequent than inter-molecular collisions. This type of gas transport is also known as Knudsen diffusion. In this case each molecule acts independently of all the others and each component in a mixture behaves as though it were present alone. The movement of each molecule can be conveniently pictured as a random walk between the walls of pores. This leads to the following expression for the molar flux of species A ... 

Consider a 1.0-L container of neon gas at STR Will the average kinetic energy, root mean square velocity, frequency of collisions of gas molecules with each other, frequency of collisions of gas molecules with the walls of the container, and energy of impact of gas molecules with the container increase, decrease, or remain the same under each of the following conditions ... 

In most commercial freeze drying processes, chamber pressure, shelf temperature, and time are the only controllable process parameters. Product temperature is not directly controlled. It is the balance between heat and mass transfer that determines the product temperature. Obviously, shelf temperature is important in determining the heat transfer and product temperature. However, because much of the heat is transferred through the gas phase (i.e., collisions of gas molecules with the hot shelf surface and the cold vial bottom), heat transfer as well as mass transfer Eq. (1) is determined, in part, by the chamber pressure. Therefore, product temperature is determined by shelf temperature, chamber pressure, the heat transfer characteristics of the vials, and the mass transfer characteristics of the product and semistoppered vials. 

The relative collision rates can be calculated from the kinetic theory of gases. Both values should strictly include a term to take account of the entropy and energy of viscous flow, which depends, according to the Eyring theory, on the structure of the liquid and on the work required to form a hole in the liquid for the diffusing molecule to move into (see Section III). The rate of collision of gas molecules with a surface, Zs, is given by ... 

Let s call Z the rate of collisions of gas molecules with a section of wall of area A. A full mathematical calculation of Z requires integral calculus and solid geometry. We present instead some simple physical arguments to show how this rate depends on the properties of the gas. 

In the kinetic-molecular theory pressure is viewed as the result of collisions of gas molecules with the walls of the container. As each molecule strikes a wall, it exerts a small impulse. The pressure is the total force thus exerted on the walls divided by the area of the walls. The total force on the walls (and thus the pressure) is proportional to two factors (1) the... 

Which of the following statements is correct (a) Heat is produced by the collision of gas molecules against one another, (b) When a gas is heated, the molecules collide with one another more often. 

Adsorption is localized and takes place only through collision of gas molecules with vacant sites. 

E25.1(b) The number of collisions of gas molecules per unit surface area is... 

During the collision of the adsorbed gas atom with the surface, it exchanges kinetic or translational energy T with the vibrational modes of the surface atoms. The type of energy transfer that takes place in this circumstance is often called the T F, energy exchange. During the collision of gas molecules with the surface. 

Pressure inside container comes from collisions of gas molecules with container walls... 

The increased pressure creates more collisions of gas molecules with the solvent surface. These more frequent collisions create more opportunities for the gas to dissolve in the solvent Champagne, sparkling waters, Coca-Cola, and Pepsi are examples. 

The same is true for / Reverse [Products]. In other words, Forward[Reactants] and /cReverse[Products] have the same units as Ra, which leads to our equating them. Thus, Ra in the forward reaction direction must be a function of reactant concentration while in the reverse reaction direction it must be a function of product concentration. The kinetic theory of gases also indicates that the collision of gas molecules and their resultant reaction with each other depends upon the concentration of each component gas. ... 

But the rate of collision of gas molecules with a surface is a familiar result of the kinetic theory of gases the number of molecules striking a unit of surface area per unit time is proportional to the mean molecular velocity v and to the number density c of molecules in the gas ... 

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