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Old 22nd June 2008, 23:24   #106
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Default Physics behind the fogging

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Originally Posted by svsantosh View Post
Fellow CS friend, you got it completely wrong, you need to set the AC to CHILL full speed and then set it to windscreen speed max. science behind this is since the air is already warm inside the car because of your breath's air and the rain makes the outside quite cool, the diff in temp creates the fog, so to match the outside temp you need to chill the inside air. Let me know after your next drive in the rains...

chk my thread, got a new accessory...
Hi svsantosh, since you are talking physics and that's my bread and butter and interests me most, so let me give a brief scientific explanation of the formation of mist inside the car. Your explanation in terms of difference in temperature is not fully correct : powerful hot, dry air can remove mist though it repeats the initial condition(analogy : loo). It requires some explanation in terms of physics.

But first, let me say that physics is an experimental science. I already had an experimental result with me which I quoted earlier: in US, be it torrential rain or sleet, the heater saved my day not the AC. It doesn't mean that the AC was not able to remove the mist from the windscreen but the heater was much more effective. So by blowing hot and dry powerful current of air, I was able to remove the mist efficiently. This is a fact upon which I relied very much and applied the same here in India.

Now let me come to the explanation. The formation of mist on inside the windscreen is due to two facts : (i) humidity and (ii) condensation. If one is able to stop/reduce either of the two, mist will not form. The moisture content of air depends crucially on two factors : (a) temperature and (b) pressure. Cold air has high pressure and it can hold very less amount of moisture. Warm air has low pressure and it can contain a lot of moisture. The moisture content is measured in terms of relative humidity. The warm condition of air is formed due to direct radiation from the sun and indirect radiation from the surface. I am not taking into account hot current of air since such blow can reduce the relative humidity very efficiently.

When it is raining cats and dogs outside, the inside and outside temperature of a car without anybody sitting inside, are almost the same, the inside being a little warmer. Not only that, the relative humidity is almost same, viz. it's 100% outside and say, 99% inside. When a person enters and locks the car, he/she starts breathing inside the car and emits water vapor. The relative humidity of the inside air quickly reaches the maximum : 100%. The air inside the car can not take moisture any further since it is already saturated at that given temperature. The extra water molecule(in vapor phase) must leave the air. Then it looks for some colder surface with large surface area where it can condense and make a phase transition to liquid water. The coldest material closer to the person in front row, are the windscreen and window glass panes. The process of condensation needs some "nucleus" which is provided by either dust particles or rough surface of the glass. These conditions are easily met by the windscreen, so the mist starts forming immediately.

How does the AC help? AC starts blowing cold and high pressure air; this air must be colder than the air in contact with the windscreen. So the colder air from the AC will get warmed by the windscreen. As fresh supply of colder air gets warmed up, it's moisture carrying capacity will increase. Hence it sucks up more moisture from the windscreen. Even after the air inside the car becomes fully saturated, no vapor can condense on the windscreen so long as the screen remains warmer than the air -- on warmer windscreen, vapor will not be able to condense. This is exactly the reason why in US using AC was not so effective, since there the cold air blown by the AC was not colder than the outside temperature when it was raining or we were having sleets. In India, it will never happen. The AC will always be able to produce colder air than the outside, so the screen remains warmer.

How does the hot and dry current of air help? Hot current of air has low humidity, so it can absorb a lot of moisture. The best example is the loo blowing in northern parts of India during summer, or the hair dryer used in day to day life. So if I blow such hot, dry air against the windscreen, it will absorb the moisture pretty fast off the screen. However, by doing this we get a hotter inside and a cold windscreen. So it is likely to fog up again unless the blower is sufficiently powerful to provide a very dry and hot air, so that it warms the screen enough and no vapor can condense upon it.

The process of drying by hot air is actually faster than defogging by cold air. Suppose it is raining outside and the temp. is around 27C. Suppose the AC is producing air with temp. 16C. So it can get warmed up to 27C and can hold water vapor earmarked for temp. at 27C. However, if the heater produces air current with temp. 35C, it can absorb almost 8-10 times the moisture, since the equation relating the saturation water vapor pressure and temperature is not linear.

This is not the end of the story. I briefly said that final stage of mist formation is due to condensation which requires rough edges. The windscreen, though loks smooth at the macroscopic scale, it is very rough even at a few thousand times the atomic scale. This is sufficient for condensation to take place. However, by using solution like RainX, one can smooth out those rough edges and no condensation can take place. This is why RainX is mainly applied outside the windscreen during rainy season, so that no water can stick to the glasses.

I have learned my lesson through experiments with both hot dry air and colder air from AC in India: it's better either to use the hot, dry air first to soak off the mist and then quickly switch to the colder air so that the initial condition is not repeated. Otherwise one can simply use AC though it will take slightly longer time. Another solution is to use solution like RainX which stops moisture formation by prohibiting condensation.
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Old 22nd June 2008, 23:45   #107
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I thought the de misting capablities of the air from the AC was due to its lesser relative humidity ( I believe the Air from the AC is passed through a dehumidifier, besides being cooled- the heater air , on the other hand is just heated). But for me too much AC led to condensation on the outside- had to turn on the wipers/ wind up/down the windows to remove that !

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Old 23rd June 2008, 09:25   #108
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I thought the de misting capablities of the air from the AC was due to its lesser relative humidity ( I believe the Air from the AC is passed through a dehumidifier, besides being cooled- the heater air , on the other hand is just heated).
Yes, you are absolutely right greenhorn. Both the cold air and heated air have low relative humidities but their mechanism to soak off the moisture are completely different. Hot, dry air can absorb moisture because at the temperature it can hold more moisture whereas cold air though being low on humidities can't directly absorb the moisture since the temperature doesn't allow it to do so. It must become warm in the neighborhood of the windscreen and then it can absorb moisture.

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But for me too much AC led to condensation on the outside- had to turn on the wipers/ wind up/down the windows to remove that !
Thank you for this data! I was expecting this when I was writing the explanation; yesterday I saw it while driving for a brief period. And now your experience also supports it. Don't use the AC with the windscreen outlet; use it with other outlets where cold air is sent only inside the car. And yes, rolling down the windows helps a lot. I could not do it as it was raining heavily.
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Old 23rd June 2008, 10:47   #109
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Don't use the AC with the windscreen outlet; use it with other outlets where cold air is sent only inside the car. And yes, rolling down the windows helps a lot. I could not do it as it was raining heavily.
hi crosscap, good to hear you are putting some miles in your car, your explanation was great. And referring to the above point - while on a drive in a Optra in HUMID Chennai last year, FULL AC On, I noticed there was a GREAT amount of condensation outside on ALL GLASS;s - read - windscreen, 4 windows and 1 rear windscreen. And hold on to the best part - The moment I stepped out of the car the next second my SPECTACLES Misted UP Completely inside. It was so funny - any explanation for that?

And the USA experience you had was informative too - I will try the HOT air trick next time it rains while I am driving. PS - Can you draw a parallel between Heater demisting in USA conditions and AC demisting in Indian conditions? Meaning in USA its mostly COLD rains (outside) so hot inside helps - Indian rains are mostly Humid related (so cool inside helps)- Is my thinking right?

---PS --- Did you get a chance to refill the petrol tank, I almost convinced my colleague to buy a CS GLS---
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Old 23rd June 2008, 11:35   #110
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Hi Guys,

I have been using my car AC always with the vents directed to face level and never change the position of that switch.

AC is effective against the mist that would form inside the car. For the mist outside the car, I reduce the thermostat and is effective. In fact, except for the initial cooling, my thermostat is never on the maximum and the blower is adjusted as and when needed.

It was tough with my Indica DLE as it did not have separate temperature controlas it was not HVAC.
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Old 23rd June 2008, 12:36   #111
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hi crosscap, good to hear you are putting some miles in your car, your explanation was great.
Thank you for your compliments.

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And referring to the above point - while on a drive in a Optra in HUMID Chennai last year, FULL AC On, I noticed there was a GREAT amount of condensation outside on ALL GLASS;s - read - windscreen, 4 windows and 1 rear windscreen.
Okay, I have explained this part before. Like greenhorn, your experience supports the explanation I put forward.

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And hold on to the best part - The moment I stepped out of the car the next second my SPECTACLES Misted UP Completely inside. It was so funny - any explanation for that?
This is expected as I said earlier. I think when you came out of your car, the AC was on. So your specs temperature was qquite low compared to outside temperature. The outside air was almost over-saturated with vapor i.e. its relative humidity was almost 100%; the water vapor is much more prone to condense. When it comes in contact with colder body like the glasses, it immediately condenses upon it. The situation is exactly similar to the problem we started with. Another familiar example of this phenomena is this one: when we put a glass full of ice-cold water, vapor starts condensing on the outside wall of the glass.

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And the USA experience you had was informative too - I will try the HOT air trick next time it rains while I am driving. PS - Can you draw a parallel between Heater demisting in USA conditions and AC demisting in Indian conditions? Meaning in USA its mostly COLD rains (outside) so hot inside helps - Indian rains are mostly Humid related (so cool inside helps)- Is my thinking right?
You are bang on target. In US, generically the outside remains colder even when we turn on AC. So this will not improve the situation much. In India, the outside temp. will hardly be above the inside temperature(with AC on) except in the mountains.

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---PS --- Did you get a chance to refill the petrol tank, I almost convinced my colleague to buy a CS GLS---
No, not yet. It will take some time before I refill. Soon my oil gauge is going to hit the halfway mark. Then I can give you a rough estimate. Anyway, tell him that it's great car to have. I recommend it whole heartedly. However FE matters much nowadays with the petrol spiraling up within few months.
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Old 23rd June 2008, 12:44   #112
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Hi Guys,

I have been using my car AC always with the vents directed to face level and never change the position of that switch.
Precisely. This is what I recommended in my earlier post.

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AC is effective against the mist that would form inside the car. For the mist outside the car, I reduce the thermostat and is effective. In fact, except for the initial cooling, my thermostat is never on the maximum and the blower is adjusted as and when needed.
This is a very helpful piece of information. This will help reduce the moisture formation outside the glass. Otherwise the situation will be like this : we have a system(car's inside) full of cold fluid(air) in a very humid environment. This is exactly similar to a glass full of cold water kept in a moist atmosphere. And we all know where the moisture forms -- it's outside the glass. So in our case, the moisture will start forming outside the glass. Controlling the inside temp. with thermostat will try to minimize this effect.
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Old 23rd June 2008, 14:02   #113
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Hi,

> Controlling the inside temp. with thermostat will try to minimize this effect.

It is also better for getting better mileage.
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Old 2nd July 2008, 00:19   #114
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Default Seatbelt warning sign in the dashboard

Today I noticed one thing: the dashboard in my indigo cs has a provision for seatbelt warning sign. By default it deactivated. However, I think the same dashboard cluster is used in all the models of indigo. This is confirmed by looking at this post of bouncer's indigo XL :

http://www.team-bhp.com/forum/test-d...tml#post884839

Does anybody have any idea how can I activate the seatbelt warning sign? What additional stuff do I have to install?
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Old 2nd July 2008, 07:37   #115
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I suppose you can ask the T.A.S.S folks , since they will have the parts

do you really need it ? the sensors arent fool proof, and i dont get the door closed alarm even if the doors arent closed properly. I'd prefer visual confirmation
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Old 2nd July 2008, 12:27   #116
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LOL - cross cap if you notice your dash has got lot more warning LED's meant for european exports and the XL range - but not all of them are activated or connected to a sensor - as green says - stick to visual - it helps.

PS - FE? still surprised you are driving in one tank ful?
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Old 2nd July 2008, 22:43   #117
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I suppose you can ask the T.A.S.S folks , since they will have the parts
Okay.

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do you really need it ?
I somehow got used to it. However, I can live without it now. But when I found that it's deactivated by default, again my alter ego started talking to me: "if you have it, why don't you activate it?"

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the sensors arent fool proof, and i dont get the door closed alarm even if the doors arent closed properly. I'd prefer visual confirmation
The Minda central lock that I installed works in this way : it locks all the door within 5 seconds after entering the car if I don't put the ignition key in its slot. If I put the ignition key within the slot withing 5 secs. after entering the car, it will autolock after 5 secs. the engine starts. Now, if somehow some passenger doesn't close any of the 4 doors properly, it will not autolock. So I am careful and detect that autolocking didn't occur, I can say that one of the doors didn't close properly. I was successful every time it ocuured. However, I can not pinpoint which of the doors isn't locked properly.

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LOL - cross cap if you notice your dash has got lot more warning LED's meant for european exports and the XL range - but not all of them are activated or connected to a sensor...
Quite true. However, dash being the same, it will just require few tweaks.

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PS - FE? still surprised you are driving in one tank full?
Yes, that's right. I had been able to drive only within the city. For last two weeks, we are having heavy downpour. I didn't have time to drive on highways. I am going to hit the halfway mark soon. So that will give me a rough estimate. I am afraid, the preliminary guess points out to the fact the FE number might be low (with AC on all the time and on an average the car runs mstly on 3rd gear). Maybe, it's due to my driving habit. One additional factor which hamper the calculation is that the pump owners in Allahabad are not at all trustworthy and they cheat a lot. Let's hope for the best.

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Old 3rd July 2008, 07:32   #118
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>>>>>>>>>>Quite true. However, dash being the same, it will just require few tweaks.<<<<

crosscap - no tweaks, i think you need real back breaking alterations and wiring work to the main harness.most of these LED;s need sensors and its not worth the pain considering the fuse boxes provided in indian cars dont have anymore provisions or wiring to hold the add on wires load. All said - let me know if something works.
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Old 8th July 2008, 19:42   #119
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Default A burning smell

First, I would like to say that there is nothing wrong with the car. There was some human errors and I just want to clarify few things from you.

Today my father took my car for a spin. He was driving only after 40 years. Earlier he used to drive jeeps when he was doing service in army. He applied all his repertoire about jeeps on the sweet little indigo cs. So he pressed the gas pedal quite hard sometimes and the engine speed touched 3000 rpm several number of times while the car was almost idle. While making a 180 degree turn, he pressed the gas pedal and clutch very hard. After making the turn, we got a burning smell inside the car. The AC was on all the time. I was a bit nervous and perplexed. So much so that I could not recognise the kind of the smell. However, it seems to be smell of burnt oil. I am not sure whether it's a smell of a burning rubber. If so, can it be from the burnt clutch plate? The dashboard didn't show any irregularities. If there is some damage to the clutch plate will it show up in the dashboard malfunction display? Or, is it just from over-burnt oil and hence nothing to worry.

It would be nice to get your feedback on this issue.
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Old 8th July 2008, 19:48   #120
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yup, sounds like burnt clutch. got in once when i had to do a vigourous half clutch revving while on an incline, and once again when i was ripping and mis-timed my clutch release and acceleration

It wont show up anywhere , except for the smell. It is bad for the clutch, but as long as you dont do it regularly, shouldn't be too much of a problem
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