Micro Channels
Welcome to the course heat exchangers fundamentals and design analysis. If you recall we have started learning and the micro heat exchangers and for micro heat exchangers it is important to know that how heat transfer takes place, convective heat transfer takes place through micro passages or microchannels. So we have spent some time we have taken some example and I have felt that the fluid flow particularly as close to that size passages to micro passages that is healing and that has got some difference with similar kind of floor situation but that takes place through conventional sized conventionalized channel let's proceed with thatwe have done that there could be depending on what cell number we can have conventional flow or continuous flow we can have continue improving with slip condition at 1 there could be transitional floor and there could be free money please let’s say the Nazi number is such that they mention is such that they’re still not same number we aren’t getting the conventional flow only back within the channel there will be there will not be much difference in the flow phenomena compared to a large side channel butdefinition August around r is equal to Reynolds number is equal to 2102 manufacturing of this microchannel quantity Mercedes are still down here that are so that that is onethen what happens that brightness is uniformly distributed over the surface area but in case of microchannel devices could be very non-isa tropically distributed over the surface areas to FX what we will find that there could be orderly transition to there could be an army transition from laminate to carpet and due to this early transition what will have that turbulent flow gives good mixing and good heat transfer so there could be a tendency of highway or rather improvement of heat transfer in case of Michael Jackson we used to have 40 channelwhat do different ranges of Reynolds number we we had these two coalition phone number for calculation of interest calculation ofmorning to go through all this quotation needed before getting a good reference book or handbook or technical paper one can pick up the school what are you like to stress upon which is very important that even in the continuum label or even in the continual Riverside mall then we can have a difference in heat transfer between the small side channel and a lot so we should need to have different sets of correlation this is important to do with these letters crossword when we are considering gas flow through narrow passages think of water or let us look into what are the effect of gas property should number that can be defined by the gas properties like here we have got that same number the basic definition is from the molecular free path and the scale length of the system or problem we are considering show me people that is one important parameter of lesson number lesson number is important when dealing with microscopic calculation which depends on gas property should have given by this formula to Lambda is equal to me you into to her by her under root 2 is the dynamic viscosity room is the density of gas constant is the temperature you see then the mean free path that is different for different gases it should be and we have we have a belated here helium hydrogen and nitrogen moleculeready to 0.068 and .0662 across these two are small compared to hydrogen or helium is like a school to another respect changing dimension in micrometre for different types of flu for gases at one atmosphere 244 different kind of flu I have define towards the beginning of the school year at the beginning of this topic that is continuum floor continuum floor with sleep down there then transitional floor and free molecule air flow for different gases we have given the channel dimension in millimetre it is greater than 67 micrometres then it is continuing to 67 micro micro and .007 micro metre then it is free I like to remind you once again for this food different kind of Laura jeans we have different kind of physical laws for the first case we are familiar with the laws that let’s say we are solving a momentum balance problem situation will be used for continuum but again we have to consider like women Technic are we can have the Monte Carlo method next club information he kind of has been described and diameter has been given in mm or microwave conventional channel to 200 microwave 200 200 metre to micrometre micrometre micrometre micrometre 21 micrometres one micrometre 2.1 micrometre and molecule and nanochannels that maybe point one micrometre and less so you see that people for convenience they have name the channels this is not the recycle sign there could be some difference and this is for gastro some people say that we should follow the same kind of classification for liquid flow or flow for two-faced way but some people say no for liquid fluid flow or flow through of multiphase mixture to face mixture we should have different classification but it needs an idea what we can consider as unconventional channel microchannel transitional channel latest go to another informationlet me tell you these different kind of passages are procedures are seen in microchannel design architecture in micro it’s because most of the we will come to the suspect and but that is not critical an example of should not be cut back circular messages and not possible but they’re real let'show we are making this channel is that on one where we have made this kind of depression and in another way for we have this kind ofthis is how the micro channels are formed and even with this method we can create some sort of a microchannel hit scenes or hitting or microchannel heat exchanger and this particular slide explains why we get different kind of channel geometry because the manufacturing method is completely different approach this is not the only manufacturing method that’s why we get different kind of micro channels micro channels of here we are giving a taxonomy of microfabrication technology microwave making my channels and they can be used for microlet me tell you by Benson somewhere and I like to stress upon the point that I have the microchip exchanges are becoming more important areas of application day-by-day we are finding more application the manufacturing or publication of micro channel that is also an active field of research and different new techniques are being given conventional techniques of traditional techniques we see that let’s go to the conventional method which has been mentioned as shop techniques meaning and showing you need to discharge ultrasonic waterjet cutting these are some of the Matrix these are some of the methods which are used for making micro channel meaningand with Millie particularly micro meaning and meaning kind of a thing what we will get we will get channels of probably we will week we will be convenient conveniently I mean one can conveniently and conveniently make a rectangular channel but the channel did not be always very straight channel we can have GTR or serpentine channel we can have been since it rained eternal truth that is possible with micro mini particularly in milling type of operation planning operation women can have a chat history channel’s one can help with sun circular saw one can have stayed channel with diamond cutter one can have one can create channels physical methods by which one can do and there is another method one can make channels of units and also the whole design if thereso this is one way particularly for manufacturing metal Inc microchannels Michael katsidis this is if there is another manufacturing technique which is used for manufacturing component but for other component these processes that is printed circuit board the way we can make microchannels small channels without serpentine features we can make it then stereo lithography is one method by which we can make it then electroforming molding design method by which we can make it how many also used for making microchannel folding method can be done in a small changes can be made out of Silicon I need is made out of silicon because we have to have is a very important feature for having reliable skin of education and for that we had to have micro Channel in electronic as a silicon wafer show the technique on based are can be classified as bulk surface and surface on a system-on-chip then bank that can be done by a chemical etching and dryer plug wire on silicon wafer if we have to have this passage is to generate heating process can be done chemical processes then we can then we can have micro molding and micro stamping process etc then what kind of other week and plus I already have all but metal processing can be done by this modern-day all processes are there Dennis and then assembly packaging and you can have many different kind of done and then the new designwe can have it says I cannot discuss YouTube video of time in details but only the processing a very large number of passages are very large number of geometry small fishes that can be made and that can be used for my Chris will be transferred and microscope heat exchanger fabricationbecause these techniques some of these techniques are cutting-edge techniques new techniques techniques which are under development but they are very important if the micro-scale heat exchangers are to be made with please I come to an end of today’s lecture what we will do we will we have some idea regarding the micro-scale heat transfer and micro passages microchannels how they are fabricated. We will take it forward and then ultimately, very quickly with we will end with some idea regarding micro heat exchangers. Thank you.