 I thought I would discuss absorption refrigeration I have got some numbers these numbers are from I forget which book I took it from but these are numbers from basically I will put the picture down and put the numbers in now we have I am going to discuss this was omitted earlier when I discussed refrigeration we discussed vapor compression but we did not discuss absorption. I postpone this because we needed to discuss solutions enthalpy concentration variations in vapor compression you have a throttle valve in which the liquid refrigerant is throttle and comes out at very low temperature you have liquid here comes out at a lower pressure this is p high this is p low this passes through a heat exchanger which absorbs heat from the surroundings thereby cooling it and this is vapor here this is still liquid and this is vapor this vapor is then compressed I think it is you do some work on it W s dot I have some liquid at some m dot some flow rate this compressed liquid is then cooled in a heat exchanger where heat is removed and this is a vapor compression refrigeration in absorption refrigeration this part of the cycle remains the same this part with absorption refrigeration exactly like in vapor compression refrigeration you have a pure liquid that comes in here at this stage this is compressed this is still vapor this vapor is cooled and condensed in this liquid at some rate m dot is throttled to a lower pressure so this pressure is p high it works between two pressures so on the thermodynamic diagram pure fluid diagram the process looks like this you want to label these points a before throttling b c and d so a before throttling b c and d in absorption refrigeration what you do is just turn the same thing around it is this part is the same I still have the throttling part I have another heat exchanger this part is common then this in this case usually the refrigerant is a fluorohedrocarbon or a variation various refrigerants now R103A and so on some refrigerant I have what you do is take in this case it is usually ammonia I will put down some numbers I have got the numbers from the ammonia diagram I put the numbers here for example typically this point is what have I called it here I think I will relabel these things b is your throttle heat exchanger what these equivalent numbers are this before this is I have called this c if you do not mind let us change some of these labels alone because for absorption refrigeration I have got this notation this is c after the after throttling it is d and before the throttling it is c it is b wait a minute yeah it is c and then before this this is b and this is a that means the corresponding points here before c and d this is cd then throttling then heat exchanger d this is evaporation d to a and a to b bc d a is common to the absorption refrigeration so I label these points this is b this is c then I have d after this this is a here I have an absorber this is usually ammonia ammonia comes out of the it is after throttling this is the place where the heat is picked up this is cooling this is high pressure this is low pressure so these two pressures this pressure and this pressure are determined this is p high this is p low these are determined by the thermodynamic properties of ammonia and the temperatures you want for example in absorption refrigeration typically it is large industrial applications to try to keep this at 10 degrees c at 10 degrees f and the other one will be room temperature 80 degrees roughly so the corresponding saturation pressures are the saturation pressures of ammonia corresponding to those temperatures so those two are fixed so this part is still the same a bc d a is the same instead of using a compressor you do it slightly differently compressing a gas requires much more energy than pumping a liquid and also you take advantage of enthalpy changes during absorption what I have here is a liquid is water in this ammonia comes in it is absorbed here so a concentrated solution of ammonia will be taken out here this is got all numbers so I want to keep the labels the same this is g and this is typically this is a centrifugal pump so it is shown in flow sheets and this is pumped up to what is called a regenerator from the regenerator it comes down I will put down some concentrations and we will describe the whole process because I have some work here and describe the whole process again this is absorber this is regenerator and what comes out here is ammonia negligible amount of water so this part of the cycle right hand side is the same as the upper part of this cycle except instead of the refrigerant I have ammonia instead of R103104 etc use ammonia as the refrigerant this part I will put down some numbers to give you a feel this is works between 10 and 70 degrees F so this is at 10 degrees F this is at 70 degrees F the corresponding high pressure will be saturation pressure of ammonia at 70 degrees F this is the saturation pressure of ammonia at 10 degrees F and I will put some numbers down directly at this the regenerator this thing is at 175 degrees F within parenthesis I will put down enthalpy values I will tell you where I got them from one chart is coming to you now this part is pure ammonia so you just have to take the pH chart and read the enthalpies on it just I have these numbers I have read I have just put it down here and this one is 70 degrees 70 is that the outlet and then this is 122 is the enthalpy all the enthalpies are in BTU per pound refrigeration industry still works primarily in British units then I have throttling the temperature here is F and the enthalpy is 122 it is enthalpy this here after the heat has been absorbed it is this is just evaporation so it is still at 10 degrees F but the enthalpy 613 that represents a latent heat of evaporation of ammonia when you go through then after absorption what you get is a saturation this temperature is 70 degrees F it is heated essentially in the absorber the temperature goes up to 70 degrees F with an enthalpy of minus 25 in the same in the concentration as 46.5 percent ammonia this is by weight of ammonia this is pumped in the condition here the enthalpy here is minus 24.7 from minus 25 to minus 24.7 that is all it takes to pump a liquid in the regenerator outlet this is E this is 175 degrees F and 35.7% by weight of ammonia that is all I need so this is 10 this is 175 this is the liquid coming back this is water with 3735.7% this absorbs more ammonia and the concentration of ammonia increases to 46.5% these temperatures this 10 degrees in 175 depending on the amount of each substance you go to get a final temperature of what 70 degrees F this is pumped here in the ammonia that comes out here is 175 degrees finally comes to I suppose 70 degrees is what I should put down when I say high pressure it is at 70 corresponding to the temperature is 70 only here at the outlet similarly it is not 10 in the heat exchangers low pressure is at 10 degrees I think that is all I need then I have some numbers here okay for the absorption part I have given you a chart there as chart is from I think it is dowboards thermodynamics book but it is also available in Perry more comprehensive chart is available in chemical engineers handbook should realize when you look at enthalpy this is absorption and essentially by heating it you are reducing the solubility so you are removing the ammonia from there the big difference between that and this looks much more complicated but you have a compression huge compressor for gases here for the vapor phase here you have only a pump which is much more rugged and the work for pumping a liquid is much less than the work required for compressing a gas from here to here so you are hopefully you have less this thing and because the pump maintenance is trivial this part of it these are only stationary devices this part of it is maintained easily for large scale refrigeration even now this is what is used now let me do the calculations for this part I have got a table of numbers but let me explain if you have a concentration a solution the enthalpy of a solution of ammonia in water typically would be simply I use x1 h1 or I should use small h1 plus x2 h2 plus delta h of mixing this is measured in a typical chart like this will assume h1 equal to this is pure say this is ammonia let us say this is water 2 is water these charts are prepared so when you mix charts you have to be careful h1 at some reference temperature equal to 0 similarly h2 it could be a completely different reference temperature equal to 0 I will call this reference T1 reference T2 but if you take differences between two points in the chart your enthalpy differences are what you will use but when you use it in conjunction with a pure ammonia chart you have to make sure that in the ammonia chart also the enthalpy has the same reference value. So this part of the data you will get from a pure ammonia chart this part of the data this side left side you get from enthalpy concentration diagrams actually the part of the diagram that you will use here is very very small part of this whole diagram I have given you you first of all you will use only the saturated liquid part of it it is a function of temperature it should actually strictly be a function of pressure as well but the properties of the condensed phase are negligibly dependent on pressure. So really pressure would not come into this thing so you will find there is a saturated liquid curve you take 60 degrees for example curve the 60 goes out take 100 for example at 100 degrees F this saturated liquid has a concentration of 0.7 right 0.7 in this case this is mass fraction so it is 70% by weight of ammonia for ammonia water system these two are approximately the same because the molecular weights are 17 and 18 so mole fraction and mass fraction would not be very different but anyway about 70% is the saturated solution represents a saturated solution of ammonia and water by weight so in this case you have in the absorber when the ammonia comes out here this is in the case of the thing what you do is simply your this is your refrigerator in the refrigerator there is a coil to which of a the heat is absorbed from the outside so the temperature outside is maintained at 10 degrees actually in practice if this is 10 this temperature outside will be about 12 or 13 degrees you will have some differential actually 5 degrees F typically so 15 degrees will be the refrigeration temperature so this will pick up the heat and this is essentially isobaric it is just at one pressure it is evaporation so this is pure vapor ammonia which is bubbled through water this absorber design is important they will have various devices for making sure that the ammonia is mixed well with the liquid so what you get out of it is a saturated solution of ammonia at the temperature that you have that comes out of this balance at 70 degrees you can read the saturation temperature here you know gas solubilities will decrease as the temperature goes up so here let us assume that read this as the saturation concentration I will double check on that but the thing the nature of the graph is correct there will be lines representing the saturated liquid and you should be able to read the saturation temperature from that at this solubility point I think there is a shift in numbers there but you will find differences will probably be the same come back to it so at 70 degrees F 46.5 is the concentration of ammonia and you pump this up here essentially you have to provide heating this there will be a heater here where you supply heat this thing will be heated to 175 degrees as is shown 175 degrees this is the solubility I will put down these numbers this is solubility at 175 at 70 degrees F is 46.5 percent by weight of ammonia and at 175 degrees F this is 35.7 so I have some numbers to be calculated this quantity the quantity that is flowing here is x I have to get my notation right where I just put down numbers here yeah this this circulation rate is m dot everywhere here it is m dot this is x and this is y that is the question is what are x and y given this these are the conditions that are given the user specifies 10 degrees here and 70 degrees here because this is when you lose heat to the air to the atmosphere so if this is if the outside temperature 80 degrees F you will get about 70 here and similarly if you keep this at 10 you probably get even 20 15 or 20 degrees inside the refrigerator so these are user specifications this determines the pressure automatically this temperature determines the pressure this temperature determines the low pressure in this case the pressures are also given this pressure at 70 it is 128 and 38 this is 128 pounds per square inch absolute and low pressure is 38 pounds per square inch absolute these are this whole thing is from the ammonia chart so working between two pressures 38 PSA and 128 PSA now this part is what you have to design you have an absorber and a regenerator and what you are asked is what are x and y and of course the total m dot this enthalpy that you pick up from the refrigerator is fixed per unit mass of ammonia because it comes from this chart here this is the amount that you pick up you are looking at after throttling you are looking at this part right HA-HD is the enthalpy per pound that is picked up so your total refrigeration demand divided by this will give you m dot so this this m dot is fixed again in the design of the refrigeration unit so let me put down this chart you can verify this my suggestion is I am sorry that this chart turned out to be the wrong one please look at perry handbook of chem have you ever looked at this book you cannot graduate without looking at the book it is called handbook of chemical engineers and it is still finally the book you refer to when you actually go to industry and do any design the thing is it is fairly boring but if you are life dependent on it becomes terribly interesting because if your boss says design this and if you do not design it in one week you lose your job that one week you will read perry like nobody's business and you will have great value for it how wonderful in this book is what information is actually everyone of us gets used to one edition I have got used to the fourth edition but a lot of the data is the same in subsequent editions also a lot of it is thermo chemical data I do not know if this is available actually I am so outdated in terms of ICT that I do not know if this is available online I have to double check I have not it is available online should be biologically so you can look it up in your own thing then the chart will appear and I have got this I took it from the fourth edition I do not know why anybody would want to steal a fourth edition from me but let me I will check who has it this is okay the basis here is enthalpy H of ammonia you know I told you about the reference the basis in the H ammonia enthalpy of pure ammonia saturated liquid at minus 40 degrees F is equal to 0 we can check that here if you look at this is mass fraction of ammonia if you look at mass fraction equal to 1 you get the enthalpies at saturated liquid at minus 40 degrees this is given you saturated actually you cannot see it in this 160 goes in steps of 40 so you can sort of extrapolate I still cannot it seems in this case the enthalpy comes to below 0 right on the chart on the x y axis 0 is actually does not correspond to saturated liquid in any temperature but it corresponds to something like just below the saturated liquid at 100 degrees something but 140 degrees so there is a translation of numbers here so this chart does not give you these numbers but let me put down the chart table here I am going to say state this is C D A G F I should have made a I can make a Xerox copy of this or I will print it out for you because I have scribbled all over it this is 70 degrees F 10 and 10 then 70 again and 175 70 twice 175 175 and double check this the pressure here is 128 38 38 this is PSIA and then 128 38 3 times the rest is 128 then the enthalpy here this is 122 122 then 613 minus 25 minus 24.7 we have two more 80 and 696 then weight percent is 3 or 100 percent this is pure ammonia when you begin the solutions G is 46.5 and then last two or this is where is B B is 100 percent again and before B this is 35.7 okay and then the flow rate for these three it is m dot and then for G this is X as I have marked there then it is X again F is also X then this is Y and again m dot do all the calculations per ton of refrigeration this you starting here at C this is m dot at 70 degrees F at 128 PSIA and enthalpy of 122 enthalpy remains the same across the throttling process you still have 122 but the temperature is 10 degrees and the pressure here is 38 PSIA then passes through the refrigeration refrigerator where it picks up the heat and the enthalpy at A is 613 so if you want the m dot let us say 1 ton of refrigeration you know this is 200 BTU per minute or 12000 BTU per hour divided by your enthalpy at A minus enthalpy at D this is 613 minus 122 okay this is your m dot got this tell me what the value is but I have done this it is just H C minus H B I made a mistake here circulation rate is determined here and tell me this value you have to work this number out if you made some mistakes no this is all right this comes to 24.4 pounds per hour correct this is okay H A minus H B but 524 is all right 24.4 this is your evaporator this is your condenser so you calculate your condenser heat load Q C dot is simply this 24.4 into the difference enthalpy between C and B that is 696 and 122 this will be as far as system is concerned there it is losing heat there will be a minus sign this comes to 14 minus 14000 BTU per hour then if you do a balance around the absorber this is the calculation that you do to calculate these quantities you need to know how much of water has to be used in circulation you will get m is equal to x plus y or m dot is equal to x plus y and not m dot sorry m dot plus y is equal to x y is coming in m dot is coming in m dot plus y is equal to x and then m dot into H A enthalpy at A plus y into enthalpy at E the energy balance is equal to x into enthalpy at G now m dot is known and all these enthalpies are known you can play around with these temperatures if you like but these are just happen this 70 is prescribed you can play around with 175 you can go up or down 10 degrees 15 degrees and so on point is to get a significant difference in the solubility 46.5 is that difference is what will give you the difference in the enthalpy of absorption you get essentially these are heat effects in absorption and D absorption if you like I have solved this you can double check these numbers you get 145.4 for x this comes to 145.4 and your y is 121 your pump work W s dot is between see this is adiabatic pumping W s dot is simply delta H minus delta H so enthalpy 24.7 minus 25 so you get 0.3 in this is your this is your enthalpy per pound into 24.4 which is m dot comes to 72 something the matter here is 24.4.3 is the enthalpy difference that is correct but it should be multiplied by x that is the mistake you are right x is 145.4 you are right that comes to 46 you can with numbers this is your BTU per hour whereas your vapor compression if you are done vapor compression you would have to take it from this enthalpy of 613 to 696 directly and 613 to 696 is what so compare CF W s dot for vapor compression 1696 minus 613 which is 83 but into m dot only this case m dot is 24.4 it comes to 2229 that is the difference usually used in large installations basically ammonia is toxic for use in homes so it is only industrial this thing where safety can be guaranteed that they use this absorption refrigeration very large devices but you can see the big difference in the work required any questions basically I just go through this this part of it is identical so there is nothing to discuss here it is identical with your vapor compression refrigeration it is fairly trivial this is the only part that you replace you go through absorption process at the end of the absorption you look at the enthalpies here a enthalpies you go from 613 now I am looking at a to g I have gone to an enthalpy of minus 25 here and then I go through a regeneration goes from effectively g I do not have a label for this is this f we have called it f I have an f there yeah that is g to f is a negligible thermodynamic change but f splits into two streams at 175 there so from f you going to e f to e enthalpy changes from 24 point minus 24.7 to 80 there is heat addition here I do not have to put a coil here there is heat addition here and heat removal Q regenerator this is heat removal here Q absorber that those numbers also have calculated absorber comes to write it here Q absorber is 28297 Q regenerator is 30279 these are big numbers remember this is what you have fixed Q evaporator is fixed this is one term this is this 12000 BTU per hour you are comparing vapor compression with absorption refrigeration for the same refrigeration load so you are going to buy two more heat exchange essentially what people do in practice is these two streams are heat exchanged this is what in chemical industry that is what makes it so confusing this is the process but in practice you have this going up you are going to add heat here you are going this is coming out at 70 degrees this is coming down at 175 degrees and you want to cool it so what you will do is heat exchange these two streams you will have one stream will be the in the shell side one stream will be in the tube side of a heat exchanger and so instead of 175 you will come down here at 160 or 150 and there will be a corresponding rise in temperature here so this load will go down this heat removed will be less this kind of optimization is done all the time in chemical industry that is why when you go to an actual chemical industry you think it is it looks like a large number of pipes connected to a few equipment does not look like equipment with pipes attached to it the number of pipes are so large in the final is alone you will have about 1000 kilometers of piping typically I will stop there