8 replies to this topic

[Art Montemayor]

Sam:

Your post doesn't reflect a background in absorption refrigeration training. What is UCF? – University of Central Florida (@ Orlando)? What doesn't jive is that if you are a Senior in Chemical Engineering (I'm assuming you are in ChE, since this is a ChE Forum), then you should have more Thermodynamics under your belt and already have accumulated 2 semesters of General Chemistry, 2 semesters of Organic Chemistry, 2 semesters of Physical Chemistry, and Quantitative & Qualitative courses as well as labs. Aqua Ammonia and its characteristics ought to be a piece of cake for you.

The reason I ask is to make sure I don't make any recommendations that you won't identify with. Maybe you are just a Mechanical Engineer, not a ChE – no matter, you should be familiar with what I am following up with:

• Get a copy of the ASHRAE Handbook – Fundamentals Volume. My copy is the 1985 Fundamentals and on Figure 32, "Enthalpy – Concentration Diagram for Ammonia – Water Solution", on page 17.68 you will find the enthalpy values you are seeking.
• Additionally, you will find a complete, typical absorption refrigeration example using aqua ammonia on page 1.24, example 6. If you haven't done an absorption cycle before, then this section should be a good primer and must reading and studying for you. If you are doing class work on the refrigeration systems, then you must obtain a good basis of knowledge regarding ASHRAE. I note that you already know about the NIST refrigerant database program, REFPROP. REFPROP costs US$200 and is really worth it if you are going to continue doing engineering work in the refrigeration field. The ASHRAE Handbook should be costing close to that also.
• Do not employ the pure ammonia and pure water database enthalpies for working on absorption systems. Use the above-noted chart or the REFPROP database for aqua ammonia.

I hope these comments help. Good Luck.

[Art Montemayor]

Sam:

Your apologies for posting here although you are an ME student fall on deaf ears. We engineers are all brothers – bonded together by the desire and ability to resolve problems for society. And Thermodynamics brings us even closer together in teaming up to whip those problems. You are certainly welcomed in all our Forums here and I would hope you keep coming back.

My personal feeling is that you are going to be glad you picked an absorption refrigeration system for a challenging problem. You not only will pick up a lot of valuable engineering knowledge from the experience, but you will get a unique insight into how to produce "cold" with heat. The cycle is neat and not many engineers are up to speed with it. By immersing yourself in it now, you will have a heads-up advantage over others when you venture out as a Professional.

Book costs are horrible for the engineering student today, and you should make every attempt to obtain the enthalpy values for aqua ammonia through your UCF technical library – assuming that you have a well-stocked inventory for engineers. Hopefully, you will find the ASHRAE Fundamentals volume of the 4-volume handbook. I believe the latest one is the 2002 – 2006 editions. If you don't find the ASHRAE handbook in your library, you may have to purchase the information.

ASHRAE, of course, sells the 4-volume handbook collection for over $250; this is steep and you don't need the 4 volumes just yet. The collection comes in a CD. Go to:

http://www.ashrae.or...ations/page/158
and
http://resourcecente...g/store/ashrae/

if you are interested.

I recommend you also go to:

http://resourcecente...oginid=13600265

where you can see that you can purchase the specific chapters within the Fundamentals volume for a lower cost:

2005 - Fundamentals Chapters as PDFs
F1 - Thermodynamics and Refrigeration Cycles (this has the theory and the example problem I mentioned). Price: $39.00 Member Price $39.00

F20 - Thermophysical Properties of Refrigerants (this has the aqua ammonia enthalpy properties)
Price: $49.00 Member Price $49.00

I recommend the F1 chapter because it covers the theory well and gives you the example problems resolved. If you haven't had a lot of exposure to vapor pressures and aqua ammonia before, it can come in very handy in understanding the basis and algorithm of resolving the design problem.

If you have problems with the above costs, let us know. I don't believe we can copy the aqua ammonia enthalpy curves and send you a copy that you may use for your calculations because ASHRAE has both the text and the illustrations fully protected by copyright. We would require their permission to do so. Perhaps someone on the Forum reading this has the values from another source that isn't copyrighted. Or perhaps you can give the exact points you need and we can furnish the values from our chart.

We certainly will try to help you out as much as we can – legally and honestly.
Good Luck.

[fahood]

Absorption Cycle is really an interesting cooling cycle as you produce cooling from heating I've done my thermo project on it if you need more assistance please let me know ...

hi all,

I'm doing my project in Vapour Absorption System. Where can i get the Temperature-pressure concentration diagram of Aqua-Ammonia Solution..?

[Qasim Hussain]

Respected Members
I am Student of Associate engineer in Mechanical Technology. Recently I started study on absorption refrigeration system using ammonia-water and hydrogen. This system has no moving part i-e pump or compressor. I want to calculate heat transfer in each section of refrigeration system generator, condenser, evaporator, absorber and also the working and flow calculation of bubble pump used in the system.
Currently I have problem to calculate the heat produce during absorption of ammonia in water. I required formula for this calculation and produce heat quantity during absorption of unit mass of ammonia in water at different temperatures (40 t0 45 c) and pressure (10 to 20 bar).
Please provide me chart, parameters related to my calculation. And also the working and flow calculation of bubble pump used in the system.I could not purchase ASHRAE Handbook, and also simulation software due to financial problems. I will be thank full to you for this kind.
Qasim Hussain