3 replies to this topic

[04_che_uet]

I am Chemical engineering student . in my final year project I am designing cooling tower . I have calculated cooling tower height, number of transfer units. Mechanical design is also a requirment of final year project .

I need help on mechanical designn of cooling tower . If anyone can guide me that . When some one asks for a cooling tower's mechanical design .. What specifications is he asking for?

- Which parts of cooling tower fall in mechanical design ?
- any book which can help me?

[Art Montemayor]

Before I address your questions, I am going to quote something that should be read and studied by all chemical engineering students – and especially all those chemical engineering instructors who lack practical experience or are naïve in their imagination of what constitutes the way that a process engineer designs a real chemical process or plant out in industry. It is unfortunate that this subject is repeated over and over again in this Student Forum, and for that reason I am taking the time to detail out the explanations to my responses. The following is taken from the 1966 book, “Strategy in Process Engineering”, by Dale F. Rudd and Charles C. Watson (University of Wisconsin):

“The Purchase of Talent and Time
One would not attempt to redesign the wheel, and one does not feel any sense of shame in taking advantage of such existing technology. In the same sense, one often does not attempt or design established processes and techniques which are available elsewhere on a business basis by purchase or license.

This is an essential difference in the art practiced in process engineering and the art practiced in graphics, music, and literature, where the use of the ideas of others is frowned upon. Not only is such a purchase of the ideas of others acceptable in engineering - indeed, it is often incumbent to recommend this.

The experienced engineer develops over the years a deep respect for any device that works. This fosters the attitude that if a device can be purchased to do a given task, purchase is usually the proper choice over designing the device from scratch. In this choice, one takes advantage of the bitter and painful development experiences in which the manufacturer has invested, pays only a small portion of the development cost (this being shared by all the purchasers), and above all has the device available almost without delay and usually with a guarantee of expert service and maintenance. The purchase of a design or device is, in effect, the purchase of time and talent.

Not only does the engineer save time and money by specifying standard units of manufactured equipment (such as pumps, blowers, heat exchangers, controllers, etc.), he sill often consider the advantage of securing completely engineered “packaged” units (which in themselves are small processes) to serve as component parts of his system. While the supplier of such processes as inert gas generators, refrigeration units, etc., may contract to deliver the complete physical unit, sometimes compactly skid mounted, in other cases he may furnish only the design, usually with a license to build and operate, and sometimes with a guarantee of performance and a service contract.”

I have designed and built cooling water towers – but only because I found myself in very special conditions. I did this in my early years when I was working in affiliated companies located in under-developed countries and which were under a very limited amount of financial support in construction and maintenance costs. I did this because I had no other option: there was no hard currency for imports and no local resources or help. Today, these conditions no longer prevail in those countries where there are universities teaching Chemical Engineering. Countries that have these universities certainly have the resources to import the technology – or develop it.

In the case of Cooling Water Towers, the realistic and actual technology is not to be found in text books. Corporations are founded on the basis of this technology and they are not about to share this information freely with others without an equitable payment or reward. Simultaneous heat and mass transfer certainly is taught and can be found in text books. One can use this basic chemical engineering Unit Operation and apply it to building a water cooling tower. I did, and it worked – but in rather small sizes, around 300 to 500 gpm of cooling water circulation. They were probably grossly over-sized, because I couldn't tolerate a failure. Today, I would specify the cooling water tower and buy the complete, engineered package from a proven supplier like Marley.

I believe the assignment of a complete, mechanical design of such a specialized piece of engineered equipment such as a cooling tower is a sign of naivety on the part of any engineering instructor and demonstrates ignorance in practical engineering. No such design from a student could ever qualify as being the subject of scrutiny by an instructor unless that instructor was experienced in the design and construction of such equipment – which I dare to say is not the case of a university instructor.

It will be next to impossible for you to find any detailed mechanical design information on cooling towers. You are going to to have to use your ingenuity and try to put together what you believe you can expect to work – but giving it your best, educated effort. Your instructors are going to have a harder task in judging whether your design will work or not – since I am sure they never built one before themselves.

[bushtie]

In response to Art Montemayors comments, I can confirm that you CAN find mechanichal engineering details in text, not for cooling towers persay but steps are outlined for reactors. You will find detailed calculations of mechanical design of process equipment in Coulson and Richardson Volume 6. There is a whole chapter dedicated to the subject (chapter 13). There are no exact examples of a cooling tower unfortunately in your case, but there are the equations for vessel thickness etc outlined.

As a chemical engineer, we are not expected to do the whole process as that is what Mechanical Engineers are there for, but it is our job to give the basic data needed to help mech engineers. This will help you do this. I am surprised your lecturers have not pointed this book out to you as they are very popular volumes.

[djack77494]

This topic has been visited frequently on these forums and the conclusion of all experienced engineers is well summarized in the quote Art has referenced. Do NOT try to reinvent complex processes for which readily available commercial options are available. The cost of these attempts will be repeated failures and redesigns at far greater expense than if one just purchased the technology to begin with. There are many facets of licensed technology that are not apparent to the uninitiated, and you risk a lot by assuming that you can recognize and avoid the hidden hazards of process development. There is a good reason that these technologies are licensed. If anyone could design these systems, then everyone would. Much of the required know-how has come from the school of hard knocks, and you don't want to go there.