Prometheus stole fire from the gods which made Zeus very angry and he demanded that Prometheus return it to the gods 1:00. Then, to punish Prometheus’s further, Zeus issued the following set of orders to his infinite number of demons: “Demon #1, if Prometheus is alive at 2:00, kill him. Demon #2, if Prometheus is alive at 1:30, kill him. Demon #3, if Prometheus is alive at 1:15, kill him . . .” and so on, telling each subsequent demon to kill at half the time previously mandated.
But Prometheus is dead by 2:00, and the council of gods is not happy. They say: “Zeus, we’ll let you off the hook if you tell us which of your demons did this.” Zeus replies: “But none of my demons are guilty. Consider any one of them, and realize that he certainly could not have done it, for an infinite number of demons preceded him. Therefore it was none of mine.” So here’s the problem: Prometheus is dead, and yet for him to be so requires that there must be some first demon to have killed him, of which there is not. That is, he is dead and by the hands of no killer.
THROUGHPUT
(The first problem was: “What is it about an airliner’s air conditioner that makes it work so trashily on the ground but perfectly in flight?”) In flight, the outside temperature is in the range of -30° C and the ram air used in the heat exchangers is at this temperature. But on the ground the surrounding temperature is about 50° to 60° higher. Consequently, ram air is 50 to 60 degrees hotter This has a two pronged effect, the first being that the heat exchangers cannot cool the bleed air to the same degree as when the aircraft is at high altitude because of the higher outside temperature. Secondly, as the heat energy extracted is reused in the system until the efficiency drops. The two effects are cumulative and the air in the cabin gets warmer over time. --- Balagopalan Nair K, balagopalannair@gmail.com
The engines itself is used as a power source for operating the A/C while in flight. While on ground, the Auxiliary Power Unit (APU) is used. The APU is a micro-turbine engine that serves two purposes - to deliver bleed air to the main engines for air pressure start and to drive an electric generator (which in turn charges the aircraft’s batteries and supply the main electrical bus with power for electronics and ancillary systems - including the air-conditioning unit pressure pump).
Some APU’s are not capable of supplying enough power via the APU generator to start or run the A/C unit while parked on the tarmac because they were never intended for this use. -- Saifuddin S F Khomosi, Dubai(The second one was: “What you probably weren’t aware of is that most fan technicians can make it reverse normal direction and turn clockwise too. And that if you did that in winter at a slow speed it would actually feel comfortable. Why?”)
The ceiling fan when rotating normally anticlock pushes air downwards. This cools by forced convection. In winter if the direction is reversed the fan blows air upwards which makes the hotter air at the ceiling push downwards. This keeps us warmer. -- Raghavendra Rao Hebbani, rao.raghavendrah@gmail.com
In winter, we should set fans to move clockwise at a low speed to pull cool air up. This pushes the warm air on top downward making you feel comfortable. Ideally speaking the blades of the CF ought to be flipped upside down to improve the air-throw upward in winter. -- Ajit Quark, 1topquark@gmail.com
In winter, ceiling fans should rotate clockwise at a low speed to enable pulling cool air up.
The gentle updraft pushes warm air, which naturally rises to the ceiling, down along the walls and back the floor. This makes a room feel warmer. However, this does not work if your ceiling (and hence the fan) is very high -- for example, in a cathedral. -- Anand Sinha, sinha.anand.iim@gmail.com
Cold air is denser than warm air. Therefore, during winter it settles at the floor level. This forces hot air upwards. A reverse ceiling fan brings this warm air back, thus helping us to feel noticeably warmer. K.Narayana Murty, k_n_murty@yahoo.com
BUT GOOGLE THIS NOW
There are three clocks with all telling different times -- 11:55, 12:25 and 1:05. Each of them is a different number of minutes out compared to the actual time and, on an average, they are 30 minutes out. What is the actual time?
Sharma is a scriptwriter and former editor of Science Today magazine.
(mukul.mindsport@gmail.com)