4. Humidification

Humidification or addition of water to air is necessary in winter when air, because of its low temperature, has very low humidity. For ordinary conditions, humidification can be done by allowing the incoming air to pass through pans of water or wetted cloth strips. However, when large volumes of air is handled, humidification is accomplished by spray humidifiers. In the latter case it is essential to instal eliminator plates arranged in zig-zag manner so that fine water drops contained in humidified air are removed. Excess humidification should be avoided since it results in condensation on room surfaces.

5. Dehumidification

In this process certain reqiured amount of water is extracted from air. This is done in summer when the incoming air is cooled and dehumidified before the entry into the room. Its accomplished by (i) condensation, or by (ii) desiccation. In the former method, the temperature of air is first brought dowen below the dew point and then condensing out the required quantity of moisture from it ; the air is then reheated to the desired temperature with dry heat. In the desiccation method cither absorbants arc used or adsorbants are used. The absorbants, such as the solutions of salts of calcium or ammonia, possess the capacity to absorb excess moisture from air. The air is passed through the beds of small particles of these absorbants and is thus dehumidified. The adsorbants such as silica jels and activated alumina, allow moisture to stay on their surfaces. These absorbants can be reactivated by removing the collected moisture from their surfaces by heating.

6. Air circulation or distribution

This is one of the most essential requirement and the efficiency of the system depends largely on the air circulation or distribution system. The minimum fresh air requirements, as recommended by Indian Standard, arc given in Table 2.3. Air circulation is achieved by the following : (i) air pumps, (ii) air delivery system consisting of supply and return ducts, and (iii) air distribution system consisting of inlets and outlets.

(i) Air pumps

Air pumps may be of two types : (a) Axial flow, propeller or fan type ; and (b) Radial flow, centrifugal or blower type. Propeller type pumps are used to produce air at relatively low pressures. They

Unit 12 albert einstein

Albert Einstein, a well-known German physicist and mathematician, was born in Germany on March 14, 1879. His unusual ability in mathe­matics and physics began to show itself at a technical school in Zurich.² At the age of 21, after four years of university study, Albert Einstein got a job as a clerk in an office. But already in 1905 he made revolutionary discoveries in science. He published three papers in the field of physics and mathematics. In the first he explained the, photoelectric effect by means of Planck's³ quantum theory. The second paper developed a math­ematical theory of Brownian motion.⁴ He presented his third paper on "Special Theory of Relativity" to a physical journal. Einstein expressed his theory in the equation E = me , roughly that energy equals mass times the square of the speed of light.

All over the world scientists read the work with great surprise. Few physicists understood its' importance at that time. Everybody wanted to know as much as possible about the author. Which institute did he teach in? What laboratory did he do his research in?

Einstein's fame among scientists grew slowly but surely. For a few years he lived in Prague⁵ where he worked as a professor. When he came to Prague, he often told his students: "I will always try to help you. If you have a problem, come to me with it, we will solve it together."

He liked questions and answered them at once, for there were no simple or foolish questions for him. He spoke much with his students about scientific problems and his new ideas. His advice to students was, "Don't take easy problems."

In 1921 Einstein got the Nobel Prize in physics not for the theory of relativity but for a logical explanation of the photoelectric effect.

In 1922 he became a foreign member of the Russian Academy of Sciences for his outstanding contributions to physics and mathematics. On March 14, 1979 by UNESCO decision all people throughout the world celebrated the birth centenary of the great 20th century scientist.

.Words and Expressions to Be Learnt

age — возраст

among —среди

answer — отвечать

become (became; become) — становиться

century — век, столетие

come (came; come) — приходить

contribution — вклад

decision — решение

discovery — открытие

easy — легкий

equal — равняться

equation — уравнение

establish — устанавливать .

explain — объяснять

field — область, сфера

foreign — иностранный

get (got) — получать

help — помощь, помогать

job — работа

know (knew; known) — знать

make (made) — делать

often — часто

possible — возможный

question — вопрос

relativity — относительность

research — исследование

slowly — медленно

solve — решать (проблему)

speed — скорость

teach (taught) — учить, обучать

tell (told) — говорить, сказать

together — вместе

understand (understood) — понимать

by means of—посредством to be born — родиться