Heat Transfer calc on Falling Film Evap type on Tube Icemaker

[llewelyn]

hi guys,... this is my second attempt to ask for help,unfortunately,no one commented on the my previous thread..cry..hop you can help me on this one cos im really a complete newbie....:(

im planning to design an NH3 tube ice maker system,now,my primary problem is the evaporator design,im thinkin bout the so-called falling film type wherein water is circulated again and again on the vertical tubes,but im stuck on the film coefficient calculations knowing that it continually changes as ice films are formed on the tube walls....anyone can help me figure out any method for this case????or any relation/empirical formula???it really takes me confused considering the fact that it involves a two-phse heat and mass flow,right???please i need ur help and expert knowledge guys.....

also,if ever,im looking for the second option of using brine and tube-shaped cans instead of the falling film system.....is it any good as a replacement?????

hoping for your help.....:confused::confused:

[US Iceman]

I doubt you will find any easy or fast answers to this question.

If the ice maker is a scraped surface heat exchanger and a falling film also for the refrigerant. The ice thickness is essentially fixed by the scraper blade. This thickness becomes one of your heat transfer resistances. Just like the cylinder wall of the evaporator.

If you do a search on Google you might find some help on the falling film equations. I'm looking for the same thing myself for a different reason.

[Josip]

Hi, llewelyn :)

Please check this:

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V4R-4DWVXN0-2&_user=10&_coverDate=05%2F01%2F2005&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=02b9f6b569e8deb2f0930e3b29e4d98f

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V1Y-4MMPNPW-2&_user=5769509&_coverDate=08%2F31%2F2007&_rdoc=36&_fmt=summary&_orig=browse&_srch=doc-info(%23toc%235687%232007%23999729988%23650377%23FLA%23display%23Volume)&_cdi=5687&_sort=d&_docanchor=&_ct=48&_acct=C000050221&_version=1&_urlVersion=0&_userid=5769509&md5=d29860816dc58357901e2629df192fd7


Best regards, Josip :)

[llewelyn]

@Mr. josip,
Sir,thanks for the links,checkin 'em out now,hope to find them useful.....thank you
<edit><my bad,seems the articles are'nt free....>

@Mr. Iceman
Sir,i did a lot of googling but still cant find a closer case like mine...anyway,this heat exchanger im talkin bout is harvested thru hot gas defrost instead of scraping....moreover,the refrigerant is not of the falling film setup,only the refrigerated water....

[iv attached an image for a clearer description:]

it shows thhat for some period of time,a film of water passes thru the inner surface of the tube, this thin film solidifies and ice is formed,then when water is
recirculated again,another layer of icefilm is added on the first layer until a volume of ice finally fills up the whole tubespace...this is then the
harvesting is done thru hot gas defrost.

hmmmmm.....i really cant devise relations and empirical equations till now...all i know that this involves some damn complicated two-phase transient heat transfer....

[Dan]

Vogt machines come to mind. Have you looked at their design and sizing?