4. Choose the right statement:
1). Positive-displacement pumps may be either a reciprocating type or … .
a)centrifugal,
b) a rotary type,
c) fluid.
2). A centrifugal pump can deliver a … volume of fluid with varying head for a constant speed.
a) minimal,
b) variable,
c) constant.
3). The efficiency for well-maintained pumps should be at least … per cent.
a). 70
b) 100
c) 95.
5. Fill in the gaps.
1. The centrifugal pumps have the disadvantages: that their output is effected by changes in pressure on the delivery side and they are not suitable for (1) liquids.
2. Unlike the centrifugal pumps, piston and plunger pumps are (2).
3. Plunger pumps are generally used for (3).
1).a) cold, b) viscous c) hot.
2) a) well equipped machines, b) good machines, c) constant output machines.
3)a) high pressures, b) low pressures, c) high temperature.
6. Complete the sentences.
a) spinning, h)qualities, f)handled, e)casing, g) runs, d) fluid-impellent, , b)reciprocating, c)driven, j) selection i) required.
Pumps of various kinds are 1)____ everywhere. The conditions that will influence the 2)____ of the type of the pump are: the type of liquid to be 3)____; that is its viscosity; cleanliness, temperature and so on. Pumps may be divided into four major classifications: piston pumps or 4)____pumps. These pumps are 5)____by engines or electrical motors; centrifugal pumps driven by steam turbines or electric motors; 6)____ pumps which are not mechanically operated but are fluid-pressure operated . The centrifugal pumps is one of the simplest types. It consists of an impeller 7)____ in a circular 8)____. It is cheap, occupies very little space, 9)____ for long periods takes little attention and possesses other good 10)____.
7. Group the synonyms.
a) drive, b) fluid, c) work, l) housing, e) operate, f) damage, h) ruin, i) liquid, j) run, d) quantity, g) delivery, k) amount.
Unit 12
1. Learn the notions and their definitions.
Conduction the transfer of heat by molecular action.
Convection turbulent transfer, the transfer of heat by a mixing process.
Radiation the transfer of heat by emission and absorption of energy without physical contact.
Heat-transfer cofficient a method of calculating film coefficient.
Steam The invisible vapor into which water is changed when it is heated to the boiling point.
Boiler A vessel in which water is boiled to produce steam.
Condense To return to a liquid state, as when steam reverts to water. The process is condensation and a device that causes the process to take place is a condenser.
Vacuum A space devoid of matter. Vacuums are partial, not complete.
Valve A device that opens or closes to control the flow of liquids or gases.
Evaporation the operation of concentrating a solution by boiling away the solvent.
Text 1
1. Read, translate and retell the text.
Industrial Heat-Exchange Equipment Heat-Exchangers. Principles of Unit Operations
A).Two mechanisms of heat transfer have already been established:
Molecular ─ the transfer of heat by molecular action; this is referred to as conduction. Turbulent ─ the transfer of heat by a mixing process; this is usually referred to as convection. It has been established that these two mechanisms can occur simultaneously or individually.
B).A third mechanism of heat transfer which is common but which has not
yet been discussed is radiation, which is the transfer of heat by emission and absorption of energy without physical contact. Unlike conduction or convection, which depend upon physical contact for thermal-energy transfer, radiation depends upon electromagnetic waves as a means for transferring thermal energy from a hot source to a low-temperature sink. Radiation may occur simultaneously with, or independent of, the other two mechanisms of transfer.
The one characteristic common to most heat exchangers is the transfer
of heat from a hot phase to a cold phase with the two phases being
separated by a solid boundary.
C). Heat-Transfer Coefficients. A method of calculating film coefficients was proposed by Wilson for condensing vapors. It is based on the over-all resistance (I / UA) being equal to the sum of the individual resistances,
ΣR +¹/UA = Rc + Rc + Rd = RL
where Rc = condensate resistance Rw = wall resistance Rd = scale or dirt resistance RL = liquid-side resistance
Slope = 1/C2
D). Double-Pipe Heat Exchangers. The simplest type of heat exchanger is the double-pipe heat exchanger as the basis for others. The double-pipe heat exchanger is essentially two concentric pipes with one fluid flowing through the center pipe while the other fluid moves cocurrently or countercurrently in the annular space. The length of each section is usually limited to standard pipe lengths, so that, if an appreciable heat-transfer surface is required, banks of sections are frequently used. If the required area is too large, a double-pipe exchanger is not recommended. The use of a double-pipe heat exchanger is not limited to liquid-liquid heat exchange but may also be used for gas-liquid exchange and for gas-to-gas exchange. Materials of construction may vary, depending upon the fluids being handled. Either fluid may be moved through the tube or annulus at relatively high velocities, thereby aiding in the heat-transfer process.
E). Shell-and-Tube Exchangers. When the required heat-transfer surface is large, the recommended type of exchanger is the shell-and-tube variety. In this type of heater or cooler, large heat-transfer surface can be achieved economically and practically by placing tubes in a bundle; the ends of the tubes are mounted in a tube sheet. This is very commonly accomplished by expanding the end of the tube into a close-fitting hole in the tube sheet by a process called "rolling." The resultant tube bundle is then enclosed by a cylindrical casing (the shell), through which the second fluid flows around and through the tube handle.