Specific heat of air at constant volume

He began by heating the air with the piston in a fixed position. Thus the volume of air heated was kept constant. The amount of heat (in Btu) needed to heat a fixed weight of air, under constant volume conditions, he called Cy. This is now called the specific heat of air at constant volume. 

Carl Friedrich Mohr (Coblenz, 4 November 1806-Bonn, 28 September 1879), at first an apothecary in Coblenz then associate professor of pharmacy in Bonn, published many papers and a book on pharmacy, describing new apparatus. Mohr was one of the pioneers of volumetric analysis. He also wrote on the mechanical theory of heat and chemical afimity. He sa rs in (i) heat is no longer a substance, but is rather an oscillatory motion of the smallest parts (rather like Davy s theory) he used (like Mayer in 1842) the name E aft for energy, and said heat is a form of it. He pointed out the relation of the difference of the specific heats of air at constant volume and pressure to this nature of heat, but did not (as Mayer did) calculate the mechanical Equivalent of heat from it. He is an obscure writer and his later claims to have anticipated Clausius are unfounded, but he anticipated some of Mayer s ideas. He acted... 

Hence, Sensible heat = Air-mass flow rate (q , kg s ) x Specific heat capacity of humid air at constant volume (c ), which is 1.012 kj kg K. ... 

The specific heats of diamond and graphite are reduced to 19 and Tx() respectively between the ordinary temperature and the boiling-point of liquid hydrogen the specific heats of the substances between the temperatures of liquid air and liquid hydrogen are in fact less than those of any other substances, even less than that of a gas at constant volume. 

The specific heat at constant volume (i.e., CL.) is a measure of the amount of heat we put into the air, trapped inside the cylinder. All this heat goes to increasing the temperature of the trapped air by 1°F. None of the heat goes into compression work, because the piston remains fixed. 

The specific heat at constant volume and at constant pressure and Cp, the universal gas constant, R, and the ratio of specific heats, y, are related hy y = CpfCy, and R = Cp — c. For ambient air, Cp = kJ/kg K and a = 1.4. Four additional equations obtained from conservation of mass and energy for each layer are required to complete the equation set. The differential equations for mass in each layer are... 

A proposed air standard piston ylinder arrangement cycle consists of an isentropic compression process, a constant-volume heat addition process, an isentropic expansion process, and a constant-pressure heat-rejection process. The compression ratio (V1/V2) during the isentropic compression process is 8.5. At the beginning of the compression process, P=100kPa and r=300 K. The constant-volume specific heat addition is 1400kJ/kg. Assume constant specific heats at 25°C. 

T(r,t) is the spatial and temporal temperature distribution, I)th the thermal diffusivity, p the density, cp the specific heat at constant pressure, and Q(r,t) the local heat production per volume. A general solution of Eq. (12) with the appropriate boundary conditions, including thermal conductivity of the cell windows and heat transition to the ambient air, can be a challenging task. The whole problem is simplified, since the experiment is set up in such a way that it only... 

A gas cylinder containing air discharges to atmosphere through a valve whose characteristics may be considered similar to those of a sharp-edged orifice. If the pressure in the cylinder is initially 350 kN/m2, by how much will the pressure have fallen when the flowrate has decreased to one-quarter of its initial value The flow through the valve may be taken as isentropic and the expansion in the cylinder as isothermal. The ratio of the specific heats at constant pressure and constant volume is 1.4. 

When spraying solutions of substances of low molecular weight, a first drying step occurs above the solubility limit of the solute, and the drop reduces in size until the solubility limit is reached. For this first step, which is usually called the first or constant rate period (CRP), the drying velocity, that is, the solvent mass evaporated per unit time, is given by the vapor pressure of the solution at the drop surface, p s, and the vapor pressure in the vicinity of the particle, pv.oo. The vapor pressure at the surface depends - assuming a well-mixed state within the droplet - on the drop temperature and on the water activity within the solution. The surface temperature remains low in the CRP as the solvent, due to its heat of evaporation Ah uses up the sensible heat (expressed by the specific heat capacity Cp of the air-vapor mixture) transferred to the particle by the gas in a hot atmosphere. The particle surface temperature Ts is more or less close to the wet bulb temperature of pure water, depending on the water activity in the case of dissolved matter (see Eq. 5.44 in Volume 1 of this series). The dependence of the vapor pressure of the solvent on the surface temperature Ts may be expressed by the Antoine or Clausius-Clapeyron equation, as... 

The variable volume chemical fume hood controls the volume of air drawn into the hood as a function of sash position, while maintaining the face velocity of the air at a constant rate, within the specifications required. These types of chemical fume hoods are more energy efficient than the standard or bypass hoods because they minimize costs incurred by laboratory heating and cooling. 

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