- 2 days ago
This video will help you understand
what is reboiler
what is pool boiling
what is film boiling
its significance
what is reboiler
what is pool boiling
what is film boiling
its significance
Category
📚
LearningTranscript
00:00hi friends welcome to our channel concept engineering flux
00:04in today's video we are going to understand reboilers and in the reboilers the basis like
00:10what is the pool boiling and flow boiling so let's start
00:16disclaimer for our channel and the content you shown in this videos
00:24before going to the reboilers we need to understand few basics
00:28so there is a difference between evaporation and the boiling so because we are today focusing on
00:33the boiling basically evaporation is a surface phenomena it so happens on the liquid surface
00:39only however the boiling happens throughout the liquid through the liquid volume you can say
00:46also evaporation can happen on at any temperature however the boiling happens at the boiling
00:53temperature you can say or any specific temperature or you can call it as a boiling point
00:58similarly the vapor pressure is lower than the atmospheric pressure in case of evaporation
01:04however in case of boiling the vapor pressure is equal to the atmospheric pressure so these are
01:09the basic difference between evaporation and boiling but evaporator when we see the evaporator
01:14evaporator the shell and tube evaporator may may will have a boiling also it's not it it's called as
01:22evaporator but it happens the boiling also happen nucleate boiling happen on the surface
01:30so what is boiling boiling is the phase transition in which the liquid is converted into the vapor
01:37at solid surface so when you have any tube so liquid get vaporized on any surface or interface between
01:45the solid solid means the tube wall and the temperature of the solid surface so the temperature
01:52on this solid surface or the tube surface whatever we are using is always higher than the saturation
01:57temperature of the liquid so if it is in the any exchanger so this outside liquid
02:04the temperature of this wall is always higher than your saturation temperature of this saturation
02:08temperature is that when the liquid and vapors are at equilibrium and when we give additional
02:15heat it will get into convert it into vapor and if you condense cooling it then it will get condensed
02:20the vapor will get condensed that is the saturation condition and the there are there are two types of
02:26boiling first is the pool boiling pool boiling you can understand by a simple example when you are keeping a
02:33uh water bucket and heating through a heating rod or coil heater then this is called the pool
02:40boiling so because why uh the water inside the bucket is not moving uh basically it refers to heating
02:47surface submerged in the relatively stagnant pool of liquid so this is stagnant pool of liquid
02:51and there is no motion no movement of the liquid so that's called the pool boiling and there is a
02:59flow
02:59boiling flow boiling flow boiling is the phenomena where the uh that the the fluid is uh forcefully
03:05passes through these tubes and when it passes through the tubes it get the heating and uh it creates a
03:12basically a uh flow boiling involves the motion and creates the flow regime that in this when the flow
03:18boiling is there you will find the flow regime so so suppose this is a tube if you uh maybe
03:24the saturated
03:24liquid from starts from here and it started boiling here here and then it will be get vaporized then
03:30uh completely vapor can form when it's go from this side to this side so because you are getting
03:36heating from all the sides uh and in the pool boiling generally vapors are at the saturation temperature
03:43only however in the flow boiling it can be super heated also so this is the basic difference between the
03:50pool boiling and the flow boiling pool boiling uh in this we'll see the how the pool boiling happens
04:00what what mechanism happen on the surface of the uh surface of the tube and how the bubble formations
04:07and nucleate sites are getting formed so as we understand the pool boiling is is the relatively
04:13stagnant liquid will be there and there is no movement of the molecules caused molecule movement only
04:18caused by the density and there is no force movement of the liquid and the bubbles we'll see how the
04:25bubbles are getting forms and how it it get heated or what how the boiling mechanical mechanism happens
04:32agitation is caused by only by the bubbles so bubbles are forming so that's why we are seeing the
04:37bubble formation at the nucleate site so what is the nucleate site uh the example of pool boiling
04:42basically it's a cattle type reboiler this is this is the good example of the pool boiling because
04:48the liquid is completely filled and heat source is passing through these tubes uh so uh the all the
04:55all the times tubes are submerged in it and the what are the bubbles forms on the tube surfaces travel
05:00through this liquid and comes out of this vapor and there is a vapor space available in the cattle
05:05type of reboiler that will be your vapor out so how bubble formations and nucleate site forms
05:12uh as you may aware that all the tubes it if any tubes is smooth also it but it will
05:19have some
05:20grooves or on some uneven surface so when liquid uh comes in contact with that grooves or liquid
05:27or that uh gaps the surface is never too smooth so first it gets uh heated and the first bubble
05:36starts at the
05:37uh at the uh that curved curved area or the uneven area and then that bubble starts from there and
05:45it's it's getting little bigger because of the uh self it's taking heat from all the three sides of the
05:52that surface and then the first bubble just get traveled through the this is the liquid this is the
06:01whole liquid or liquid pool and that bubble gets started up uh for understanding uh generally surface is
06:09not like this type of rectangle it may be any type of any zigzag so bubble will form here and
06:14it start
06:15traveling into the liquid surface so we'll see how what happens then once liquid surface this bubble starts
06:21if this liquid is saturated or superheated uh what is the impact on that bubble and how the boiling happens
06:31so as we understand that the bubbles are formed in the notch or or the gaps in of the uh
06:37the surface
06:37of the tube so when the first bubbles uh form and when it travels in the liquid and if the
06:43liquid is
06:44uh below the saturation temperature if this liquid is below the saturation temperature
06:50saturation temperature means when the more heat is given it will be formed in the vapor so saturation
06:55temperature i believe everybody understand so if it is below saturation temperature then this water
06:59the bubble forms it's when it travels to that uh liquid which is below the saturation what will
07:06happen the heat get loosed in the uh that bubble loses the heat in the surrounding liquid and and and
07:15and uh it start decreasing in the size because it's uh the vapors are getting um you know must be
07:21condensing on the liquid interface so that's why it's starting reducing its size and it get dissolved or
07:28uh that bubble therefore decreasing in size and eventually it's collapse in the this liquid and
07:34then this liquid by water the heat or the vapor is having the vapor is losing their heat to this
07:39liquid
07:39and the whole liquid is started uh going towards like saturation temperature once this type of
07:46phenomena happens continuously it will come into the saturation this is suppose this is a figure one
07:52one and in figure two when the boiling is already started and this phenomena already happened the
07:58bubble started and get collapsed and after sometimes when the bubble forms and the bubble uh when
08:04this liquid is achieved to the saturation temperature then the bubble forms that bubble just
08:12there is only very small temperature difference because this liquid came at at the saturation temperature already
08:17now when this uh liquid comes at the saturation temperature these bubbles are not uh losing any
08:25heat to the surrounding liquid so the and the and the pressure of the vapor bubble is uh some of
08:31the
08:31pressure of above the liquid surface and the pressure due to the static and uh liquid above the bubble uh
08:38the pressure above the liquid is quite low and static head will be therefore significantly part of the total
08:44pressure of the bubble so that's why this bubble is increasing in the size because this liquid is
08:48already saturated liquid so it this bubbles is also getting heat and it's it started uh the the liquid
08:55come in the contact of this uh bubble is uh getting vaporized so this bubble started forming bigger and
09:03bigger and when it come out of your uh liquid pull it will gives you the vapor so this way
09:10this uh bubble
09:11journey happens from nucleate side to the vapor based on the pool boiling mechanism we can conclude that the
09:22pool boiling depends on tube surface the and the fluid surface tension latent heat of the fluid and the delta
09:31temperature between the uh surface and the fluid then surface decrease in surface tension will increase the
09:40boiling increasing delta t will increase the boiling to the some extent but excessive excessive increasing
09:47temperature will promote flame boiling and which is not good for the heat exchanger so one question
09:54if the cattle type reboiler circulation rate increase by 25 percent what will be the increase in heat
10:00transfer coefficient why we this question asked because uh cattle type reboiler is depending on the pool
10:06boiling so what is the impact of increasing the flow rate to 25 percent if you want to know the
10:12answer
10:12watch our last slide in this in this video
10:18different stages of boiling if you see this curve this shows you the different steps uh stages happens
10:26in the boiling when the boiling happens so first a to b basically it's a natural convection happens in the
10:32liquid so natural convection happens suppose this is a tube surface when it heated above the saturation
10:39temperature of the liquid the convection happens the movement of the liquid hot liquid goes up
10:45and cold liquid moves this is the simple convection happen this is the first steps of boiling
10:53then in uh second phase mixed boiling and just nucleation uh what we see in the nucleation have
11:00uh started that just getting started that is called the mixed boiling and the convection
11:05then c to d this section is the nucleate boiling where the nucleates if you see this is a surface
11:14and you can see the bubbles are started and traveling in the liquid surface then
11:23then d to e it's a nucleate boiling with high heat flux so high heat flux means when the surface
11:30temperature is now high because uh if you see if there is a two pass or three pass then uh
11:36at the
11:36out towards outlet where the uh liquid start out or vapor start out and if you have two phase to
11:44feed or hot steam coming from this side so this is the more heat will be on this uh liquid
11:50surface
11:51or solid surface so this heat flux means the temperature between difference between the your liquid
11:56and your metal temperature or your wall temperature of the uh tube so nucleate boiling happens at the
12:04highest heat flux so see you can see the bubbles are quickly forming and moving in the liquid the next
12:11step it comes as a peak heat flux this e is called as a peak heat flux so peak heat
12:17flux means the
12:17difference between the wall temperature and the liquid is highest here in this region so that is called the
12:24uh heat flux and uh your boiling happens uh quickly uh and moving the bubbles are moving the next phase
12:33comes is the e to f is a unstable boiling or transition boiling so when now your heat flux is
12:39high and uh
12:40and after the highest heat flux it's it's a transition boiling means now there is a vapor layer started or
12:47film started forming on the tube surface and uh bubbles are also forming
12:54so thin flame just started so it is unstable sometimes uh flame will be there sometimes
13:00directly bubbles are forming from the notch or the gap and the last stage is f to g where the
13:08complete your
13:09uh you will have a flame complete the uh film boiling so film boiling means there is a
13:15fine layer of uh vapor will form over the tube surface and the heat transfer the conduction happens
13:22through this vapor only so that's why it's not preferable and it will give your low heat
13:27transfers so why this happens when your heat flux increases again you will have a very high temperature
13:33on the tube wall and the bubbles are forming above the vapor that vapor film so that's called the
13:43uh film boiling and then h will be the again the highest heat flux with the film boiling so basically
13:52low heat transfer due to vapor and vapor insulation because see when the surface will form a vapor uh a
14:00layer of vapor and then the boiling start on this so it will use that uh it's act as an
14:05insulation it
14:06gives a less heat transfer you know the vapor having a less heat transfer coefficient so this is a
14:11the the so when this happen film volume is happened there is a risk of material failure or by overheating
14:16because one side is a very high uh heating material the tube surface which is very high temperature
14:22and you have a like a insulation thing so and heat is not dissipated from this uh tube so then
14:29there is a
14:29chance of uh failure of the tube by overheating so then that's why film film boiling should be avoided
14:36hence it should it should be uh usually avoided in the uh during the um heat exchanger so when how
14:44you
14:44will find that the film boiling is happening or not you have to see your cell side and tube side
14:48properties
14:49in the thermal design so there you can find that you can you will find one uh one section of
14:55the
14:55film boiling nucleate boiling so if you find a number in the film boiling it means the film boiling is
15:00happening in your exchanger so in that case you have to avoid it you have to see how we can
15:05avoid it
15:05by reducing the temperature of the hot fluid or there are multiple methods that we can see in the letter
15:15after the pool boiling the flow boiling however the reason remains same in the flow boiling and the
15:20tube boiling there is a some few difference the flow boiling occurs when the temperature of heating
15:25surface is significantly higher than the saturation temperature of the liquid and creates the stable
15:30blanketing of vapor that acts as an insulator and preventing the liquid to launching the surface
15:37so the the day-to-day example of flow boiling is when you on a hot pan if you put
15:44a few droplets of
15:45water it just started dancing so that happening because there is a there is a thin layer of film happen
15:53on the surface of the pan and the water droplets above it so that's why this you can see and
16:01when
16:02this flame boiling happen in the horizontal tube because you can have a vertical exchanger as well
16:09as the horizontal exchanger so when it happens on the horizontal tube and the heating source comes from
16:17this counter current so if you see the single phase liquid will be here at the start of the tube
16:23because
16:24we are going in this way then there is a bubble formation happens on the surface
16:30this is inside boiling is happening not the outside flow boiling happens generally on the inside as we
16:35seen in the first exchanger the tube the you will forcefully flow will be flow from the tubes and it's
16:44happen on the inside and the outside you will be the heating media so the in the first bubble bubbles
16:49are
16:50getting formed then because of the bugs there is a plug flow happens then when the actually i i
16:56understood that you all are know that this slug flow wave flow otherwise we will we'll cover in the
17:02next slide on that so then the plug flow started in that tube when it moves liquid started moving
17:10then slug flow and then you will find the vapors are already started forming and the liquid layer
17:16started reducing in the tubes so then it's called a wavy flow and then it is a you can say
17:24some there
17:24are some surface happens where the annulary you will find the dry zone there is no liquid in this section
17:31because of the flow so flow is moving like this then this is a wet surface again this is a
17:36dry surface here
17:36and that this surface tube is getting dry so and after this section you will find the complete vapors
17:44in the tube or you can say vapors are getting super heated also during its movement towards the
17:50horizontally so if you see the thin layer of liquid will be there so this is this is the if
17:58means the
17:58stages in the flow boiling in the horizontal pipe
18:06boiling starts in the vertical tube the heat source coming from the top and the liquid goes from the
18:12bottom inside the tube so and when the it's getting gaining heat it suppress the saturation temperature
18:18of the liquid and at which the of the point comes when the sub cooling boiling happens so here the
18:24liquid
18:24is in sub cool conditions and the very fine bubbles are started forming where the bubbles of the
18:31nucleate grow and and in the thermal boundary layer and condense in the sub cool core so which we seen
18:37in the our first figure where the bubble just forms and it get disappeared in the liquid because of the
18:43sub cooling effect further up to the tube when the liquid bulb reaches to the saturation temperature so
18:49somewhere here it reaches to the saturation temperature and the bubbles flow bubbly flow gets
18:56started from here and then bubbly flow then the it comes to the slug flow or the churn flow and
19:03then
19:03finally it goes in the annular regime when the most of the liquid gets saturated temperature and now
19:10after getting the further heated from the source it's almost the annular flow forms and the vapors are
19:16formed in the between and then the second this this the section comes on the tube where the
19:22it's dry it's completely vapor forms and and you will find the single phase of vapors are traveling
19:27from the top of the tube so this way this flow boiling happens in the vertical tube
19:37flow boiling in the shell side so when when you are heating any liquid on the shell side by passing
19:42the
19:43uh heat source to the tubes then it happens like uh if the if the sub cool liquid coming from
19:49the bottom
19:51it started heating uh from the bottom and flows upward until the wall temperature surpasses the
19:58this wall temperature of the tube surpasses the saturation temperature so bubble forms and it get
20:03dissolved still till this liquid achieves the shell side liquid achieves the saturation temperature
20:09and then once the wall temperature above the saturation temperature the uh the boiling sub cool boiling
20:16starts and the bubble starts forming and the bubbly flow will be there so this region comes under the
20:23bubbly flow and then these bubbles when the multiple bubbles start forming it goes as a bubble jet flow
20:29on the shell side so you will find the bubbles are uh try to move uh between this two between
20:35the tube so
20:36in this case you should you should understand you should keep the pitch instead of triangular it should be the
20:42square pitch should be better because it will give you path to the vapor to flow instead of triangular
20:48pitch otherwise it will again uh hit the tubes so uh sometimes this we have to see by which
20:57service we are using you have to select the uh pitch also then when uh when this rapid departure
21:05sequence of the bubbles of the bubbles happens uh and it collects to the uh other bubbles and form the
21:11bigger bubbles then this characteristic is called as the uh churning flow chugging flow so it it will forms
21:18and it will uh uh forming bigger and there is small bubbles also the that flows called as chugging flow
21:26then uh it when it further moves there is almost vapor form and there is a uh the tubes will
21:33have a thin layer
21:34of liquid uh this is this uh this is this region is called as the like tube will be weighted
21:40with the
21:41liquid because it's it's getting some uh that vapor uh touch to this and getting some liquid on this so
21:48there will be liquid all the time to form the vapors on this surface and then uh when it that
21:55that's
21:55called the spray type of flow region and then and the fire but here the heat flux remains the critical
22:03it comes heat flux will be almost at the critical stage and then uh the liquid goes uh further above
22:11will be the it will be basically the complete full vapors on this section if you see the heat transfer
22:18regime in this case so convection heat transfers between the liquid sub cooling boiling will happen
22:23then saturated nucleate boiling will happen when the bubbles are started forming and collapsing
22:28then sliding bubble evaporation happens and the convection through the liquid flame happens
22:33and the heat transfer these are the heat transfer regimes happen in the when the shell boiling
22:38shell flow boiling uh shell side there is a boiling on the shell side
22:47based on the flow boiling mechanism we can understood that the flow
22:51boiling is depending on same same parameters as pool boiling like surface phenomena and the
22:58surface tension including that it is depending on the flow velocity and liquid vapor ratios it
23:06depends on this also and the only part of the flow boiling coefficient is affected by the velocity
23:11so because the other part is already uh comes under the pool boiling so major part is pool boiling and
23:17then the convection heat transfer also will take care takes place in the flow boiling and the regimes are
23:23also important so heat transfer coefficient cannot be predicted by simple scaling method for the flow
23:30boiling so there are simple uh scaling methods are used to predict the heat transfer coefficient which
23:38is mostly used the details bolter's law and but this method will not be used for the uh flow uh
23:45flow
23:45boiling because there is a it's depending on vapor liquid ratio and other properties
23:54so impact of pressure on the heat flux or the boiling so when uh when the saturation temperature uh
24:03and the pressure increases the enthalpy of enthalpy of the change decreases
24:08and uh eventually it becomes the zero so when you increase the pressure
24:12of any system your um saturation temperature is also getting increases and when uh saturation temperature
24:20increases uh your enthalpy of phase change getting decreased
24:28and then uh so that's why enthalpy of the change determines how much heat flux is required so
24:34so so uh when it decreases with the higher pressure uh you will come to know that enthalpy of phase
24:40change
24:41required it will be reduced therefore higher pressure and this uh and the smaller amount of heat
24:45requires to uh boil or get the boiling so when suppose this is the this is the delta t or
24:54you can say temperature
24:55difference required this side x side is the temperature difference required uh for the boiling and this is the heat
25:03flux
25:05difference so suppose if you uh if you have a 1.5 bar of pressure of of your liquid then
25:14you you need a 20 bar of delta p
25:18to heat that liquid
25:22when you increase the temperature to 4 bar you can see the delta p between the temperatures are reduced to
25:2910
25:2910 degree 10 degree fahrenheit kelvin or anything you can consider when it increased to 8 bar it further reduced
25:37when it increased to 29 bar you can say uh that um and this is the heat flux so same
25:44heat flux suppose there is a 20
25:46uh this is the 20 000 uh watt per uh meter square um thermal flux so if the it required
25:56a 20 k
25:57when the pressure is uh when the pressure is only 1.5 but when you increase the pressure but to
26:05the 4 bar the flux
26:07reduces to uh it reduces the temperature delta is reduces to 10 degree and when it increased to
26:1429 you need a very low delta temperature delta for the same 20 000 uh watt per uh meter square
26:23so for the uh same heat flux it's almost like a one uh degree delta is required so that is
26:30the impact of
26:30pressure on the boiling just to understand the flow patterns in a vertical tube the first is the bubbly
26:39flow so bubbly flow is the regime uh in the gas disappears in the form of district bubble so there
26:45are small district bubbles which continuously in the liquid phase and these shapes and size of the bubble may
26:51vary but it will be smaller than your tube diameter so that is called the bubbly flow to understand
26:58properly slug flow is the increasing in the uh gas fraction and the bubbles collates and collapse to
27:05form a larger bubbles so multiple bubbles forms together and it's a large bubble form and these
27:11characteristics uh it's like a semi spherical nose or um it's it's similar to the bullet and referred as the
27:21uh teller bubbles and successively bubbles are separated by the liquid slug which uh may include
27:29in the smaller entity and the uh in this case the the bullet shape is bubbled have thin flim some
27:36places
27:37and the liquid between them the channel and the wall which may downwards due to the force of the gravity
27:44so this liquid may fall uh down but finally overall flow will be remains on the up only then the
27:50churn
27:51flow the further increasing in velocity the flow becomes unstable and the liquid travels up and down in
28:00oscillation uh oscillation fashion and although the net flow remains on the up only but if it goes upward and
28:08downwards and uh in this case basically uh the churn flow may be developed such that the flow passes
28:16directly to from the slug flow to the annular flow also sometimes then uh annular flow uh it's it's uh
28:25it's
28:25a bulk of liquid flows uh as a thin flim uh on the wall and with the gas as a
28:34continuous phase from the
28:35uh center of the tube so this is the annular flow and uh wispy annular flow when the flow rate
28:42is increased
28:43further uh the interrupted droplets uh coagulated to form a large lumps here also in the liquid there is
28:51already a lot of uh bubbles are formed and uh the vapors are flowing from the center so this is
29:00called
29:00the width annular flow for the vertical pipes the flow pattern in horizontal tubes it's almost same
29:09but however in the bubbly flow when it forms it forms on the half section of the or you can
29:15say
29:15top section of the pipe so bubbles are disappear and continues in the liquid where the concentration
29:20on the upper of the of the tubes because of the Beyonce effect basically similarly plug flow open
29:26when these bubbles are getting coagulated together and forming a big bigger bubble but that also
29:31almost on the uh half side of the uh on the top half side of the horizontal group so because
29:38it's
29:38horizontal group the the pattern slightly get changed the starified uh flow is the uh the the liquid
29:46and the gas velocity there are completely separation so liquid flows from the top and sorry the vapor flows
29:53from the top and liquid is in from the uh on the annular surface at the bottom uh the gas
30:00on the top
30:00and liquid at the bottom separates the undisturbed horizontal surface so this happens in the horizontal
30:05tube only then um there is a annular flow which is the similar to the vertical flow when the both
30:15side
30:16you will find the thin flame of the liquid and the vapors from from the middle the slug flow is
30:22that
30:22you will find the liquid moves up and down in the uh your uh tube and the wavy flow also
30:32you can find
30:33the liquid surface moves in the wave form so that's it's called the wave form that is also on the
30:38bottom part of the uh tube so when you see the horizontal tube so liquid movement is on the bottom
30:45of the half of the tube and the vapor movement in the top half of the tube so that's where
30:50this flow
30:51pattern distinct between the horizontal tube and the horizontal tube and the vertical tubes
30:58based on the flow regimes or flow pattern we can understood that the flow uh we should prevent the
31:04slug flow in the piping and heat exchanger because it will lead to mechanical stresses and noise in the
31:09piping so slug flow is to be avoided and it will also lead to unsteady flow pressure fluctuation in
31:16heat exchanger also heat transfer is poor in the mist regime hence it should be avoided if possible mist
31:23regime but it it will not be avoided in the flow boiling so slug flow is unavoidable in thermosypon
31:31reboiler also the mist flow is unavoidable in thermosypon reboiler and there is a one rule 25 33
31:41three percent rule for a vaporization rule for thermosypon reboiler so all these three points
31:46we are going to see in detail in our next lecture of thermosypon reboiler
31:54so blue boiling versus a flow boiling versus the pool boiling so basically pool boiling happens in the
32:01gravity or the because of the buoyancy and the flow boiling need an external source or a pressure
32:06which can be a thermosypon reboiler or it's a force reboiler will be comes under the flow boiling
32:11then there is a no movement of the liquid the water the movement happen it is because of the bubbles
32:17that is the natural movement or buoyancy movement but the movement of the liquid happens high because
32:22of the pressure difference or by the external force it occurs the bubbles and form the vapor mat on the
32:31surface it occurs it can occurs the dry out also and the liquid film on the will be disappear on
32:38the tube so
32:39in the flow boiling we see that maybe you will have a dry surface on the two internal tubes but
32:46in the
32:48in the pool boiling you will not find that you need dry surface
32:54generally vapors lose at the saturation temperature when it's a pool boiling and vapors can be super
32:58heated when is a force boiling so when you have a go to for the you need a very high
33:02temperature or the
33:04higher vapor than the saturation temperature then you can go for the flow boiling
33:10how to enhance the boiling so to enhance the boiling enhancing the surface
33:14abundant surface uh to form the nucleates
33:18which is initiated initially the boiling at very low wall superheat with respect to the plane surface so
33:24when you have a high uh window of surface then you can uh boiling can be enhanced uh such low
33:31fins if
33:32you use a low fin tubes it will give you two to three uh 3.5 times the higher surface
33:37area with the
33:37similar the plane size when you in the two if you instead of using plane tubes if you use the
33:42low fin
33:43tubes then you will get a higher area of around two to uh three point three five uh three point
33:48five times
33:50and also if you put some enhancing mint in that so like internals or um internal or any this so
33:57that
33:58will give you the high ratio around four to ten times than the plane surface there is one additional
34:03way if you put a porous coating or a coagulation ribs uh start insert twisted tape or micro fins
34:12uh in the exchanger this will uh this will enhance your uh boiling
34:23to answer to our question that recirculation rate increased by 25 percent what is the increase in
34:28heat transfer coefficient in cattle type reboiler basically if we understood the cattle type basically
34:36we understood to the pool boiling pool boiling the cattle type is the best example of the pool
34:41boiling and the bundle is submerged in the large cell and primarily heat transfer is by the
34:48nuclear boiling and not by convection hence increasing 20 percent flow rate will not increase the overall
34:55rate because the additional whatever the fluid comes it will be overflow through the internal wear
35:02so as you know this is our
35:06tube inside and this is the thermosyphon like this and there is a wear
35:12so fluid will be overflow through the wear only
35:18however in the force circulation unit it may increase by 12 to 15 percent when you increase the
35:23flow rate but in cattle type it will it will less than one um one percent increased so it is
35:30negligible
35:31so increasing the flow rate in uh cattle type reboiler will not increase your heat transfer coefficient
35:40so thank you very much write your question and comment i will be happy to answer it
35:47you can reach us on conceptengineering2025 at gmail.com
35:53links and links for the other sessions are given in this description
35:58description
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