Text B: equipment running time

Although refrigerating equipment capacities are normally given in Btu per hour, in refrigeration applications the total cooling load is usually calculated for a 24-hr period, that is in Btu per 24-hr. Then to determine the required Btu per hour capacity of the equipment,the total load for the 24-hr period is divided by the desired running time for the equipment, viz:

Required Btu/hr ₌ Total cooling load, Btu/24-h r

equipment capacity Desired running time

Because of the necessity for defrosting the evaporator at frequent intervals, it is not practical to design the refrigerating system in such a way that the equipment must operate continuously in order to handle the load. In most cases, the air passing over the cooling coil is chilled to a temperature below its dew point and moisture is condensed out of the air onto the surface of the cooling coil. When the temperature of the coil surface is above the freezing temperature of water, the moisture condensed out of the air drains off the coil into the condensate pan and leaves the space through the condensate drain. However, when the temperature of the cooling coil is below the freezing temperature of water, the moisture condensed out of the air freezes into ice and adheres to the surface of the coil, thereby causing "frost" to accumulate on the coil surface. Since frost accumulation on the coil surface tends to insulate the coil and reduce the coil's capacity, the frost must be melted off periodically by raising the surface temperature of the coil above the freezing point of water and maintaining it on this level until the frost has melted off the coil and left the space through the condensate drain.

No matter how the defrosting is accomplished, the defrosting requires a certain amount of time, during which the refrigerating effect of the system must be stopped.

Answer the questions:

1. What are the sources of heat which supply the load on refrigerating equipment?

2. How is the total cooling load in refrigeration applications calculated?

Lesson В

Translation Practice

Indefinite Personal and Impersonal Sentences Неозначено-особові та безособові речення

Речення, підметами яких виступають займенники it, one (без означення), they і ці займенники не можуть бути віднесені до раніш згаданих осіб або предметів, перекладаються на українську мову неозначено-особовими чи безособовими реченнями.

Наприклад:

It is never too late to learn (proverb)

Вчитися ніколи не пізно

One should take into consideration these instructions.

Ці інструкції слід взяти до уваги.

They say the weather will change in the nearest few days. Говорять, що погода зміниться у найближчі декілька днів.

Translate the following sentences into Ukrainian:

1. It should be fair to say that metal is the bread of industry.

2. One shouldn't think, however, that the students are interested only in lectures and seminars.

3. It is not certain,that this is in fact possible,even in principle.

4. It's frosty. It's going to snow.

5. One has to show one's identity card at the door here.

6. It's getting dark.

7. One must do one's best.

8. They say it is going to be a hot summer.

9. It looks like rain.

10. One should do morning exercises regularly.

Abbreviations.

Reading scientific and technical literature we find shortened words or phrases, which are formed by leaving out or substituting letters. They are called abbreviations.

Here are some abbreviations one can meet in texts on refrigerating and cryogenic engineering:

 

adpapparatus dew point ambambient atmatmosphere avg average bpboiling point BRABritish Refrigeration Association bt.boiling temperature BTUBritish thermal unit BtuhBritish thermal units per hour cop coefficient of performance db.dry bulb dbt.dry bulb temperature DE direct expansion dp(t)dew point (temperature) fpsfeet per second ftfoot gpmgallons per minute hphorse power hrhour in inch lb libra, pound mpmelting point mtdmean temperature difference psipound per square inch rhrelative humidity rpmrevolutions per minute RT refrigeration ton RV relief valve sp gr specific gravity sp htspecific heat vvelocity vap prfvaporproof wt weight

точка роси апарату навколишнє середовище атмосфера середнє значення точка кипіння   Британська Асоціація Холоду температура кипіння Британська теплова одиниця британських теплових одиниць на годину холодильний коефіцієнт, тепловий коефіцієнт кулька сухого термометра температура за сухим термометром безпосереднє охолодження точка роси (температура точки роси) футів на секунду фут галонів на хвилину кінська сила година дюйм фунт точка плавлення середня різниця температур фунтів на квадратний дюйм відносна вологість обертів на хвилину тона охолодження запобіжний клапан питома вага питома теплоємкість швидкість паронепроникний вага

Read the abbreviations and give their meaning: viz., lb., psi., rpm., rh., db., Btuh, ft., hr., bt., bp., hp., RT, BRA

Translate the text using a dictionary:

REFRIGERATING CAPACITY

The measure of the job done by a refrigerating machine is the rate of heat transfer to its evaporator or cold part, from the bodies or fluids which are being refrigerated. This rate of heat transfer will be called the refrigerating capacity.

1 Ton of Refrigeration = 12,000 Btu/h = 200 Btu/min

In terms of other units:

1 Ton of Refrigeration = 3516.85 W = 3023.95 kcal/h

Plant capacities in practice range from microwatts in very low temperature refrigerators to several megawatts in large plants.

The "Ton" is often used in general terms to indicate the order of size of a plant, e.g. a 100 Ton plant, or "fractional tonnage" plants (small commercial ones).

It also happens that at the temperature of evaporation and condensation used in air-conditioning, 1 Ton of refrigeration requires a power of about 1 horse-power, which gives a useful way of visualizing the size of a plant.

Other names for what is called refrigerating capacity above are also to be met, and one of these will be used from time to time, namely the refrigerating load. This also means the rate of heat transfer to the evaporator or cold part of the plant, but it places the emphasis on what the plant is asked to do rather than on what it can do. It will be said, for example, that the load is increased or decreased, that the temperature of the things being cooled, or the rate of heat transfer from them is increased or decreased. The refrigerating plant reacts to match the load, by an increase or decrease of the refrigerating capacity. This use of the word "load" is the same as its use in connection with engines. Applying load to an engine means making a demand for more power by increasing the torque, i.e. by attempting to stop the shaft turning. The engine reacts by giving more power, providing it is within its capacity to do so. At a steady state, with no acceleration, the power equals the load of course. But the difference of emphasis is clear: load is the demand which is made of the engine, power is what the engine gives.

Another term in use is refrigeration duty. It has at least two meanings. One is the same as refrigerating capacity, meaning the rate of heat transfer at a particular instant to the evaporator. Another meaning is the specified refrigerating capacity, i.e. what is asked for by the buyer of the plant, usually at a specified set of conditions. The conditions may be internal ones, such as evaporating and condensing temperatures, temperature of liquid at the expansion valve, and temperature of the vapour leaving the evaporator and entering the compressor. On the other hand, the conditions may be external ones: temperature of cooling water, rate of flow, temperature of cooled fluid and rate of flow, for example.

Finally, the term refrigerating effect is also in use, meaning either refrigerating capacity or the heat transfer to the evaporator associated with the passage of a certain amount of refrigerant.

 

 

Lesson C.

Speech Practice

AT AN OFFICE. В ОФІСІ.

a desk a drawer a swivel chair a desk set an intercom a desk lamp index cards, address cards stationery paper clips punch stapler (stapling machine) staple correcting paper correcting fluid for typing errors ink pencil sharpener fountain-pen felt tip pen ball-point pen adhesive tape dispenser desk diary file (document file)   filing cabinet   text liner, marker flip frame   eraser typewriter carbon paper flimsy patent pocket calculator   personal computer safe fax glue basket/bin for waste

/dro:/ /'swivl/ / ' t∫eə/     /'steipl/     /iŋk/   /'fauntin 'pen/   /'peitənt/     /'fæks/ /ɡLu:/

письмовий (робочий) стіл висувний ящик, шухляда обертаючийся стілець настільний письмовий комплект, набір переговорний пристрій настільна лампа картотека канцелярське приладдя скріпки діркопробивач зшивач скоба коректор для виправлення помилок при друкуванні чорнило точилка для олівців авторучка капілярна ручка кулькова ручка клейова стрічка настільний календар папка-швидкозшивач; підшиті документи висувні шухляди для зберігання папок маркер прозора обкладинка для документів, паперів гумка друкарська машинка копіювальний папір тонкий папір для копіювання патент кишеньковий калькулятор, мікрокалькулятор персональний комп'ютер сейф факс клей корзина для канцелярських відходів

Exercises: