Grammar: The Impersonal Construction. The Passive Voice

Word List:

1. injector	впрыскиватель, пушка
2. euterium	тяжелый водород
3. barrel	цилиндр, барабан
4. gradient	перепад
5. gun	пушка
6. decay	угасание, распад
7. pellet	пулька, шарик, дробинка
8. flange	фланец, кромка, борт

Tritium Pellet Injector Results

Many types of pellet injectors have been successfully used to produce and accelerate hydrogen and deuterium pellets for fusion experiments. However, no previous attempt has been made to produce tritium pellets. The properties of tritium, especially its radioactive decay, are quite different from those of the other hydrogen isotopes. Decay heating, the production of 3He and its effect on the physical properties of solid tritium, the need for tritium-compatible materials of construction, and use of double containment to prevent tritium release are all problems unique to tritium. Because of these differences, it is desirable to demonstrate the production and acceleration of tritium pellets.

Pneumatic guns produce pellets by direct condensation of hydrogen from the gas phase into the chamber or chambering mechanism of the gun. Because of their simplicity, they appear to be appropriate for initial tritium experiments. Milora and co-workers used a disk-shaped pellet carrier with pellet-size holes (1 and 1.6 mm in diameter) to transport pellets from a fill station to the barrel for firing. Pellets were formed at the fill station by direct condensation from the gas phase. Pellet length in this device was set by the thickness of the disk which sheared off any excess solid as it was rotated. Lafferranderie and co-workers later used an approach in which the pellet was frozen directly in the barrel in a position ready for firing; they referred to this approach as in situcondensation. A pellet-length copper section was sandwiched between two stainless-steel flanges in the barrel. Gas admitted from both ends of the barrel was frozen into a pellet ready for firing. This concept simplifies gun operation because it eliminates all moving parts inside the gun. However, since pellet length is not mechanically constrained, pellet size is more difficult to control. Pellets have a tendency to grow beyond the ends of the cooled section of the barrel. Lafferranderie attached heaters to the stainless-steel flanges near the pellet to increase the temperature gradient to the pellet and reduce its length.

Focused Practice

I. Answer the following questions:

1. What have many types of pellet injectors been used for?

2. Has any previous attempt been made to produce tritium pellets?

3. What property of tritium is quite different from that of the other hydrogen isotopes?

4. Why is it desirable to demonstrate the production and acceleration of tritium pellets?

5. How do pneumatic guns produce pellets?

6. What did Milora and co-workers use a disk-shaped pellet carrier with pellet-size holes for?

7. What approach did Lafferranderie and co-workers use?

II. Analyse the grammar structures underlined in the above text.

III. Speak on: Problems unique to tritium

Unit 7

Grammar: The Attribute

Word List:

1. vapour state	парообразное состояние
2. atmosphere	единица измерения давления
3. kPa	килопаскаль (единица измерения давления)
4. vapour compression refrigeration equipment	оборудование компрессионного охлаждения пара
5. boiling point	точка кипения
6. freezing point	точка замерзания
7. versus	в зависимости от

Fundamental Characteristics of a Fluid

The triple point, normal boiling point and critical point parameters are fundamental characteristics of a fluid. The triple point is the state at which three phases (solid, liquid and vapour) coexist; it is virtually identical with the more often reported freezing point. The normal boiling point is simply the temperature at which the vapour pressure of a fluid is one standard atmosphere (101.325 kPa, 14.696 psia). As the vapour pressures of nearly all fluids are approximately parallel when plotted as the logarithm of pressure versusinverse temperature, the normal boiling point is a rough predictor of the vapour pressure at all temperatures. The critical point is the state at which the properties of the saturated liquid and vapour become indistinguishable: coexisting liquid and vapour are possible only at temperatures and pressures below the critical point values.

These parameters, often in the absence of any other information, are frequently used in screening many different compounds to select a more limited set for further study. For many applications they define the temperature limits for the use of a particular fluid. Clearly a refrigerant cannot be used below the triple point temperature. For many refrigeration applications, operation at sub-atmospheric pressures is avoided and, thus, the normal boiling point is a more practical lower limit. Vapour compression refrigeration equipment transports heat through condensation and evaporation (i.e. two-phase) processes and thus the critical point represents an upper temperature and pressure limit. The critical point parameters are the essential inputs to estimation techniques based on the law of corresponding states, which is the observation that, when scaled by the critical parameters, the properties of nearly all fluids are similar.

Focused Practice

I. Answer the following questions:

1. What are fundamental characteristics of a fluid?

2. Which state do three phases coexist at?

3. What is the normal boiling point?

4. When are the vapour pressures of nearly all fluids approximately parallel?

5. What is the critical point?

6. What does vapour compression refrigeration equipment do?

II. Analyse the grammar structures underlined in the above text.

III. Speak on: The normal boiling point.

Unit 8

Grammar: The Gerund

Word List:

1. axial flow	осевое течение, поток
2. enhancement ratio	степень интенсификации (теплообмена)
3. film condensation	плёночная конденсация
4. fine wire	тонкая проволока
5. fins	пластины радиатора
6. pressure gradient	градиент давления, перепад давления
7. surface tension	поверхностное натяжение
8. thermal conductivity	теплопроводность
9. wire wrap	монтаж проводов накруткой
10. curvature	кривизна
11. heat transfer	теплоотдача
12. refrigerant	охладитель
13. momentum	количество движения

Enhancing Film Condensation Heat Transfer

Several workers have investigated the simple and cheap method of enhancing film condensation heat transfer by winding fine wire on the surface of a condenser tube. The wire wrap does not act in the same way as fins and the wire does not need to have high thermal conductivity. Enhancement is due to thinning of the film between the adjacent turns of the wire caused by the surface tension induced pressure gradient in the condensate. The pressure gradient results from the fact that the interface curvature is higher nearer the wire and gives rise to axial flow of condensate towards the wire.

The presence of the curvature term in the momentum balance for the condensate film leads to significant complication in the theory and no complete solution of the problem has been published to date. An approximate approach involved some empiricism backed by experiments for R11 and ethanol, and naturally the final result was in broad agreement with the data for these fluids. Later measurements for steam do not agree with the approximate theory. The approximate theory has recently been amended to include condensate retention. The theory then involves no empiricism and is in general agreement with the tem data. However, while giving results of the correct order of magnitude, the modified theory predicts a dependence on wire diameter that is opposite to that reported by the approximate approach. There is a report on the first stage of a research programme aimed at resolving these discrepancies. Further theoretical investigations and experiments using a refrigerant are in progress.

The report is given on new measurements for condensation of steam on a horizontal, water-cooled, wire-wrapped tube. The wire diameter and pitch of winding were systematically varied and heat-transfer measurements made for a range of coolant flow rates for each wire diameter and pitch. Data, in the form of heat flux and vapour-to-surface temperature difference were used to determine enhancement ratios (ratio of heat flux for wire-wrapped tube to that for a plain tube at the same vapour-to-surface temperature difference).

The problem of condensation on wire-wrapped tubes is not yet fully understood. Further light should be shed on the problem by the new data using a refrigerant as condensing fluid.

Focused Practice

I. Answer the following questions:

1. What method of enhancing film condensation heat transfer have several earlier workers investigated?

2. What is enhancement due to?

3. Where is the interface curvature higher?

4. What did an approximate approach involve?

5. Does the modified theory involve any empiricism?

6. What is the research programme aimed at?

7. Is the problem of condensation on wire-wrapped tubes fully understood?

II. Analyse the grammar structures underlined in the above text.

III. Speak on: The approximate approach and the modified theory.

Unit 9