Thesis (MScEng)--University of Stellenbosch, 2008. / ENGLISH ABSTRACT: The performance of a natural draught wet-cooling tower can be improved by reducing the
average drop size in the rain zone. In this thesis, the effect of installing different horizontal
grids below the fill on drop size in the rain zone is investigated experimentally and
theoretically. A specially designed horizontal grid consisting of evenly spaced slats and a grid
made from expanded metal sheeting are tested. Drop size distribution measurements are taken
below different cooling tower fills to determine the respective Sauter mean drop sizes and also
below different configurations of splash grids to determine the reduction in drop size. Drop
break-up through a grid of horizontally placed slats is modelled and compared to measured
data to determine the optimum configuration in terms of spacing between the grid and fill, slat
width and slat spacing. A cross flow rain zone is modelled under different air and water flow
combinations with CFD for two distributions that represent the rain with and without splash
grids and the results are compared. The Merkel transfer characteristic for all the flow
conditions using both distributions are determined using a Lagrangian, Merkel, Poppe and e-
NTU method in order to quantify the increase in rain zone Merkel number. Pressure drop over
the cross flow rain zone is also determined and compared for the two distributions under
considerations. / AFRIKAANSE OPSOMMING: Die verkoelingsvermoë van ‘n reënsone van ‘n natuurlike trek nat koeltoring kan verbeter
word deur die verkleining van die gemiddelde druppelgrootte. In hierdie tesis word die effek
wat horisontale roosters op die druppelgrootte het, wanneer dit onder die pakking geïnstalleer
is, eksperimenteel en teoreties ondersoek. ‘n Spesiaal ontwerpte rooster bestaande uit
horisontaal gepakte latte en ‘n gerolde metaal rooster word onderskeidelik vir hierdie doel
gebruik. Druppelgrootte metings word geneem onder verskillende koeltoring
pakkingsmateriaal om die Sauter gemiddelde diameter te bepaal, asook onder die verskillende
rooster opstellings om die verkleinde druppelgrootte te bepaal wat die rooster veroorsaak.
Druppelopbreking deur ‘n laag horisontaal gepakte latte word gemodelleer en vergelyk met
gemete data om sodoende die beste kombinasie tussen die afstand onder die
pakkingsmateriaal, latwydte en latspasiëring te bepaal. ‘n Kruisvloei reënsone word
gemodelleer met CFD onder verkillende lug- en watervoeikombinasies vir twee
druppelverdelings wat die reënsone met en sonder roosters verteenwoordig. Die Merkel
oordragskoëffisiënt vir die twee verdelings word bereken en vergelyk deur van ‘n Lagrange- ,
Merkel- , Poppe- en e-NTU metode gebruik te maak om sodoende die verbetering in reënsone
Merkelgetal te kwantifiseer. Drukvalle oor die reënsone word ook bereken en vergelyk vir die
twee verdelings wat beskou is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/21441 |
| Date | 03 1900 |
| Creators | Terblanche, Riaan |
| Contributors | Reuter, H. C. R., Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xix, 141 leaves : ill. |
| Rights | Stellenbosch University |
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