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Definition of key parametres of a stream of a cement-air mix in an unloading pipe

In installations for cement swapping by pneumochamber pumps the most energy conserving mode of transportation by streams with high concentration of a material and low speeds [73, 107] is realised.

In such streams volume concentration of a material can reach the values close to a bulk condition

Where β0 - concentration of a material in a bulk condition (β0 ≈0,6).

Such high concentration of a material arise on an entrance point in tsementoprovod [28]. Further in process of acceleration of movement of a material its concentration decreases to level β = (0,15 — 0,25). Mass expenses of air and cement in tsementoprovode are defined by parities

Where F - a cross area of the pipeline, air and cement density, kg/m3; uв, uм - their speeds averaged on a cross area of a pipe, km/s.

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Loading tsementoprovoda a material is characterised by its valid or instant mass concentration equal to the relation of mass of a material to mass of air in any excreted piece of the pipeline

Size μdявляется the local characteristic of a stream of a cement aeromix which varies lengthways tsementoprovoda. Pneumotransport installation is characterised as a whole by the account concentration of a material equal to the relation of mass expenses of cement and air

At μ ≥ concentration of cement is considered 10 kg/kg high, and at μ ≥ 60 kg/kg in tsementoprovode are established a material dense bed.

Key parametres of a stream of a cement aeromix, speed of phases, concentration of particles and other indicators continuously vary as in time, and lengthways tsementoprovoda, therefore at the description of process of pneumotransportation the speeds of phases led to a cross-section of a pump chamber or the pipeline always more fictitious, as a material being in an aeromix are often used leads to reduction of live sectional view tsementoprovoda.

Indicators of efficiency of pneumotransport process is the load per area unit on a cross-section tsementoprovoda

And also the specific expense of a pressure air on transportation

gdeobemnyj the expense of air led by the normal

To conditions, m3/with.

Prominent feature of two-phase streams is advancing movement of a bearing air stream concerning material particles.

The relation of speed of a transporting air stream to speed of cement particles, i.e. sliding factor can be estimated by means of the following empirical dependence [94]

In tsementoprovode it is necessary to consider as the top limit of speed of air critical speed, at which particles do not drop out on a pipeline bottom. Resulted, and size it is possible to estimate its value by means of the parity received empirical by [94]

At use of pneumochamber pumps reliably transporting airspeed excluding blockages tsementoprovoda, as a rule, below critical, but its size steals up by practical consideration.

Course of processes of pneumotransportation of cement appreciably depends on properties of the most transporting agent - a pressure air.

Pressure air parametres are connected among themselves by the equation of a condition of ideal gas [1, 3]

Where P - pressure of air, the Pas; V - the volume occupied with air, м3; m - air mass, kg; T - air thermodynamic temperature, To (T=273+t°C); R - a specific gas constant of air, R = 287,3Dzh/KG-to.

From the equation (2.37) dependence of density of air on pressure and temperature follows

Under normal conditions (Р0 = 1 atm = 101325 Pases, t =20°C, T = 293) air density r = 1,2 kg/m3, and in capacity of the pneumochamber pump (R = 0,6 MPa, t =140°C) reach r = 5,12 kg/m3.

Viscosity of air with temperature increase increases. Dependence of factor of dynamic viscosity ot looks like temperature [3]

The factor of kinematic viscosity of air depends not only on temperature, but also from pressure

Reduction of the volume expense of air to a standard conditions can be executed under the formula

Where - pressure in the chamber, temperature and the volume expense

Air in a service conditions.

Operating pressure Ppвключает in itself and atmospheric (normal) pressure

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Where Ph - normal pressure, the Pas; Риз6 - a superpressure, the Pas.

Speed of the expiration of an air stream through a restrained layer of the disperse environment makes from 10 to 50 % of speed of a sound in air With which is defined by a parity

Where to - an adiabatic curve indicator, to =1,405; R - pressure of an air phase, the Pas; r - density of an air phase, kg/m3. For the streams expiring in cement from nozzles aeratsionnogo the devices of the pneumochamber pump, speed of the expiration can accept values from 40 to 90 km/s. At such speeds in thickness of cement near to nozzles there are the torches (cavities) filled gazovzvesju with the maintenance of air ε = 0,9-0,98. The length of streams torches can be estimated by means of an empirical parity [94]

Where Q - the volume expense of a stream, m3/with.

In process of attenuation of streams their speed decreases, it can be defined

Where U0 - speed of the expiration of a stream, km/s; D0 - diameter of a nozzle, m.

The cement-air mix (psevdoozhizhennyj a layer), obrazuemaja aeratsionnym the device in the bottom working area of a pump chamber, is forced by a pressure air in an unloading pipe in the form of pulsing gazodispersnogo a stream in which clots (stoppers) of strongly concentrated mix move air bubbles in which the material is in a sort gazovzvesi.

At transition to horizontal lots tsementoprovoda cement partially drops out on a bottom and moves in a wave mode or timber connectors. Strongly

The expressed heterogeneity of streams of the cement aeromix created by pneumochamber pumps, excludes possibility of application for their calculation of the methods developed for calculation of pneumotransport in the weighed (aerosol) condition.

2.3

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A source: Gavrilenko Andrey Vladimirovich. IMPROVEMENT OF MULTIPLACE AERATION DEVICE IN THE PNEUMO CHAMBER PUMP. Thesis for the degree of candidate of technical sciences.Belgorod - 2017. 2017

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