00:00Hi friends welcome to our channel concept engineering flux focus on fundamentals
00:05in today's session we will try to understand why TRV is required on the cooling water
00:11cooling water line for any exchangers any cooler which is using cooling water why we put a TRV on
00:17it so let's start so basically what is thermal expansion you know there is a there are some
00:26molecules for any fluid it's generally having some pattern so before heating it's it's remains
00:34in its normal state if it is a liquid or gas depending gas remains some molecules are be
00:40or atoms are remain away but when we heat it these molecules get more space or you can say it's
00:48increase its distance between two molecules so it's get expands so that's why after
00:56heating there will be expansion in the any fluid so there are three types of thermal expansion
01:05linear expansion the linear is a simpler expansion when the length of any pipe or any metal get
01:14increased because of the thermal increase but that is the linear length increase suppose you have a
01:20pipe long run pipe if you if this line passing the hot material it it wants to try to expand
01:29but if it is
01:30a straight and you do not have any um if it is not having any space to expand then it
01:35can be
01:36break or damage so to avoid that we generally provide the expansion loop which we have seen maybe
01:44in various units like this or there is a 3d expansion loop also like going up and then like this
01:51coming
01:52down and then horizontal as well or we can use the expansion bellows so this way linear expansion can
01:58take care and the formula is increasing in delta length is it can be a beta or any uh you
02:05can say
02:06linear expansion coefficient and this is a change in length and that is this is the delta temperature for
02:12that and the second type of thermal expansion is the area expansion where you can this you can see in
02:19tube
02:19sheets or flanges the formula is remain same so suppose this is a tube sheet if this while
02:30exchanging of the heat if the tube should get heated because of the one side material is too much hot
02:35then this holes or the tube sheets holes may get expands this is called the area expansion so generally
02:45when you heat the the the diameter of your you can say tube holes will increase not decrease it will
02:53get
02:53increased with the thermal expansion so third is the volumetric volume expansion in the thermal expansion type
03:05other than the earlier three earlier two so suppose this is an exchanger a cooling water exchanger where
03:12the cooling water is flowing through the tube sides and you will find that there is a trv in the
03:19outlet of
03:19this cooling water outlet line we will see why this is required and a hot fluid is flowing from the
03:27shell
03:27side and going out so suppose if the operators close this inlet and outlet walls of the cooling water side
03:38then liquid your cooling water is get trapped inside the volume of this exchanger only and it cannot go
03:47anywhere but however the hot fluid is still continually heating or passing through this exchanger then
03:58this cooling water which is trapped inside this tubes or in under this exchanger it start absorbing the
04:06temperature and it increases its temperature but it cannot expand because it does not have any space
04:13but the volume expansion is that which it's required some space to be increased and because if it is not
04:21able to increase it starting getting pressurized also how we will see with one example how this will get
04:27pressurized but for the general understanding if one degree temperature also increase in this exchanger
04:36or you can say cooling water suppose cooling water is at 25 degrees C
04:40and because of getting the heat for a shorter time and temperature increase by one degree centigrade
04:48it can almost increase your pressure by 50 to 100 psi which is mean around
04:563 to 5 bar something 3 to 5 bar or 3 to 6 bar depending on what is your inlet
05:03temperature and the
05:05one degree of expansion above it so that's why this this trv is very important in the cooling water
05:12circuit so let's understand with one example
05:17so we have this our cooling water our exchanger where the cooling water flowing through the
05:22tube sides and we have this trv at the outlet of the cooling water and the hot fluid flowing from
05:28the shell
05:29suppose this cooling water is at 25 degrees centigrade
05:34and someone has closed this inlet and outlet wall of the cooling water system however the
05:40hot process is still passing and the and the temperature increase because of this
05:48absorption of heat from the hot fluid to cooling water is 1 degree centigrade
05:53so then volumetric expansion coefficient you can say beta at 25 degrees centigrade is 2.41 to the power 10
06:04to
06:04the power minus 4 per degree centigrade or it can be maybe 2.5 or some around it it will
06:10be little bit
06:10different for different books or from some different lectures but this volume expansion coefficient means
06:18water expands about 0.257 percentage per degree centigrade rise in temperature so water expansion
06:28is only this much and isothermal expansion is 4.5 10 to the power minus 5 per bar means this
06:41is you can say
06:41compressibility of your fluid or your cooling water means if you increase the pressure by 100 bar of this
06:50water the volume change in volume or reduction in volume is only 0.046 percentage means which is negligible
07:01so to calculate how much pressure is increasing because of increasing in 1 degree temperature
07:09the delta p can be calculated based on the beta by k into the delta t so in our case
07:18delta beta is 2.41 10 to the power 4 and k is 4.52 to 10 to the power
07:244 and 1 is your increasing in
07:26temperature or you can say 1 degree is the delta t so when you solve this this equation you will
07:34find
07:35that your delta p is increasing by 5.33 bar so you can understand that by increasing the temperature from
07:4425 to 26 degrees centigrade only 1 degree centigrade temperature your pressure in this cooling water
07:51system or circuit or circuit will increase by almost 5 bar suppose this temperature increase by 5 degree
08:00and your because your hot fluid is continuously running and your temperature increases by 5 degree
08:07so your outlet temperature is now become 30 degree centigrade then at 30 degree centigrade your
08:15volumetric expansion coefficient change to 2.7 to the power 10.4 per degree centigrade okay so when you solve
08:24again just put here 2.73 in 10 to the power 4 and because the isothermal expansion almost remains constant
08:32so you can take this value same value then you come to know that your temperature increased or sorry
08:38the pressure increase is almost 29 bar or you can say exactly as 28.55 bar so definitely your cooling
08:47water
08:47system is not designed for 28.55 bar is maximumly designed for 6 or 7 bar design temperature and it's
08:55hard
08:55to test and other things maybe if it is 150 rating it can go up to 17 or 18 bar
09:00but definitely not the 28 bar so
09:04if you put temperature increase by only 5 degree it can increase your pressure very high so that's why
09:11your cooling water system should have this trv always in the line so thank you very much write your question
09:22and comment i will be happy to answer it you can reach us on conceptengineering2025 at gmail.com
09:33links and links for the other sessions are given in this description
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