IOP Cnference Series: Materials Science and Engineering PAPER OPEN ACCESS Investigatin f the effect f packing lcatin n perfrmance f clsed wet cling twer based n exergy analysis T cite this article: S M Qasim and M J Hayder 2016 IOP Cnf. Ser.: Mater. Sci. Eng. 145 032009 View the article nline fr updates and enhancements. This cntent was dwnladed frm IP address 46.3.205.38 n 23/11/2017 at 02:02
MdTech Internatinal Cnference - Mdern Technlgies in Industrial Engineering IV IOP Publishing IOP Cnf. Series: Materials Science and Engineering 145 (2016) 032009 di:10.1088/1757-899x/145/3/032009 Investigatin f the effect f packing lcatin n perfrmance f clsed wet cling twer based n exergy analysis S M Qasim 1 and M J Hayder 1 1 AL- Mustansiriya University Cllege f Engineering Iraq Baghdad E-mail: qasim602006@yah.cm Abstract. In this paper, the effect f packing lcatin n thermal perfrmance f Clsed Wet Cling Twer (CWCT) based n exergy analysis has been studied. The experimental study incrprates design, manufacture and testing f a mdified cunter flw frced draft CWCT prttype. The mdificatin based n additin packing t the cnventinal CWCT. The variatin f spray water temperature, air dry bulb temperature, air wet bulb temperature, enthalpy and relative humidity f air fr different psitin alng the twer are measured experimentally. Applying the exergy destructin methd fr the cling twer; exergy destructin, exergy efficiency, exergy f water and air were calculated fr tw cases: CWCT with packing belw the heat exchanger and CWCT with packing abve the heat exchanger. It is highly imprtant t analyze the exergy alng the cling twer height. Therefre, the exergy analysis f different elements alng the height f the twer is carried ut. Results shw that the ttal exergy destructin f mdified CWCT is higher when the heat exchanger is lcated abve the packing at the highest pint f the twer. 1. Intrductin Many studies have been made n the perfrmance f cling twer in view f exergy analysis. Qureshi and Zubair [1] presented theretically a thermdynamic analysis f cunter flw wet cling twers and evaprative heat exchangers using bth the first and secnd law f thermdynamics. By applying an exergy balance n each f the systems, the variatin f secnd- law efficiency as well as exergy destructin as a functin f varius input parameters such as inlet AWBT & inlet water temperature has been identified. Mani and Rajagpal. (2008), [2] frmed a scientific mdel taking int accunt mass and heat transfer t find the utlet cnditins f air and water in cunter flw pen type cling twer. Their mdel has been slved using iterative methd. Energy and exergy analysis infers that inlet AWBT was fund t be mst vital parameter than inlet water temperature. Thy shwed that at lwer inlet AWBT, the utlet temperature decreases which leads t higher water apprach temperature and exergy destructin by decreases the secnd law efficiency. Ramkumar and Ragupath.(2014), [3] investigated thermal perfrmance f pen type mechanical draft cunter flw cling twer with expanded wire mesh packing. Exergy analysis has been applied t study the cling twer ptential f perfrmance using the psychmetric gun technique. Abdul Hadi (2015), [4] Derivative Merkel thery fr a cunter flw induced draught cling twer with a few rearrangements. The verseeing mathematical statement was settled by an iterative strategy. The twer was islated int 100 even cmpnents. Mass, energy and exergy equalizatins were assessed fr every cmpnent utilizing Engineering Equatin Slver (EES) prgramming. Cntent frm this wrk may be used under the terms f the Creative Cmmns Attributin 3.0 licence. Any further distributin f this wrk must maintain attributin t the authr(s) and the title f the wrk, jurnal citatin and DOI. Published under licence by IOP Publishing Ltd 1
MdTech Internatinal Cnference - Mdern Technlgies in Industrial Engineering IV IOP Publishing IOP Cnf. Series: Materials Science and Engineering 145 (2016) 032009 di:10.1088/1757-899x/145/3/032009 2. General infrmatin A mdified CWCT was designed and cnstructed in which different perating parameters culd be varied and tested in the labratries f Envirnmental Engineering Department f Al-Mustansiriya University Cllege f Engineering. The general arrangement f the equipment is shwn in figure 1. Figure 1.a. Phtgraphic picture fr experimental apparatus (lateral view). Figure 1.b. Phtgraphic picture fr experimental apparatus (frnt view). The twer fabricated frm galvanized steel sheet cnnected tgether by screws and nuts as a rectangular bx f external dimensins (700 mm 400 mm 2300 mm). As exists in every frced cling, the test sectin cnsists f three znes: spray, fill and rain zne. Fill zne at 1000 mm height and characterized as cnsisting f three places fr sliding remvable drawer rectangular bxes at the same dimensins, manufacturing fr packing and heat exchangers t ensure change the lcatins and types f heat exchangers and height f packing t study the influence f all these additins n the perfrmance f the twer. The rectangular drawer made f galvanized steel with dimensins f 420 mm in width, 760 mm in depth and 280 mm in height. Air frm the atmsphere, enters the single stage centrifugal blwer at a rate which is cntrlled by the butterfly valve. The fan discharges int the PVC pipe and the entrance duct befre entering the packed clumn. As the air flws thrugh the packing and heat exchanger, its misture cntent increases and the water in the heat exchanger are cled. Ht water is pumped frm the lad tank thrugh the cntrl valve and a water flw meter t the heat exchanger placed inside the test sectin f twer. Plain tube heat exchanger was designed and manufactured fr the present wrk. The tubes were fixed hrizntally in test sectin inside supprted frame f rectangular drawer.cling water mves thrugh the tubes while the spray water and air mve ver the tubes in perpendicular directin. The tubes are arrayed in staggered arrangement with tube pitch f 3D (pitch ver diameter f 3).The specificatin f heat exchangers shws in table 1. Table 1. Physical dimensins f heat exchanger. Heat exchanger cnfiguratin Value Unit Length (L 1 ) 690 mm Height (L 2 ) 166 mm Width (L 3 ) 381 mm Number f tubes fr cil 30 - Vertical tube spacing (X L ) 24 mm Hrizntal tube spacing (X T ) 80 mm Tube per rw 5 - Outside tube diameter 15.88 mm Ttal heat transfer area 1032691.77 mm 2 2
MdTech Internatinal Cnference - Mdern Technlgies in Industrial Engineering IV IOP Publishing IOP Cnf. Series: Materials Science and Engineering 145 (2016) 032009 di:10.1088/1757-899x/145/3/032009 Thermcuples type K inserted befre and after the cler cil t measured cling water temperature. T measure the spray water temperatures at intermediate lcatins inside test sectin, especially channels have been manufacturing t insert thermcuples thrugh hles. These hles are clsed by rubber stppers thrugh which thermcuples are inserted t measure the temperature prfile. The variatins f air dry bulb temperature and relative humidity alng the test sectin as well as the inlet and utlet f the twer were measured by humidity meter, which cmbined temperature/humidity sensr. The humidity meter mdel TH-305 has a (main factin) temperature and relative humidity measurement range C and 20 t 95% respectively. The sensr prbe handle is placed directly in the air stream and cnnected t display. 3. Exergy Analysis In this study, the exergy analysis f the CWCT based n the Exergy Destructin Methd (EDM) was carried ut in the simplified system shwn in figure 2. Fr steady state cnditins, neglecting the effect f kinetic and ptential energy, an exergy balance is frmulated fr all cmpnents f the CWCT were presented in figure 2. Exergy f water can be btained by Bejan as flws [5]: w w h h T S S fw f fw Figure 2. Exergy balance f the cling twer. m R T ln Ø (1) Neglected the mechanical exergy f water cmparing with chemical exergy, s the exergy f water fr ideal gas law, equatin (6) becmes [6]: T w mw CPw T T TC Pw ln RvT ln Ø (2) T The ttal exergy in the psychmetric prcess such as in the cling twer perating mechanism, n the bases f dray air and water vapur as an ideal gas when neglecting the change f pressure thrugh the cling twer can thus be generally represented presented in Bejan [5]: g v a T 11.608 C Pa CPv T T T RaT 1 1.608 ln 1.608 ln ln (3) T 11.608 Exergy destructin represents by the difference between exergy change f water and f air. 0 (4) in ut D 3
MdTech Internatinal Cnference - Mdern Technlgies in Industrial Engineering IV IOP Publishing IOP Cnf. Series: Materials Science and Engineering 145 (2016) 032009 di:10.1088/1757-899x/145/3/032009 The exergy destructin can be determined by: d (5) a, in sw, in cw, in w, makeup a, ut sw, ut cw, ut The exergy efficiency (secnd lw efficiency), which is measured f irreversibility lsses in a given prcess is define as [1]: d Ex 1 air (6) 4. Results and discussins The effect f packing lcatin (fr CWCT with packing) n the exergy analysis will be discussed. figures 3 t 6 illustrated variatin in: exergy destructin, exergy efficiency, water exergy change and air exergy change with cling water flw rate fr tw cases: CWCT with packing under heat exchanger and CWCT with packing abve the heat exchanger fr 560 mm packing height fr heat exchanger. The impact f cling water flw rate n exergy destructin fr different packing lcatins is illustrated in figure 3. Frm this figure, it is stated that the exergy destructin increments with the increment f cling water flw rate fr bth cases. In cmparisn t lcatin f packing added t CWCT, it was bserved that adding packing t CWCT displays higher exergy destructin when lcated the heat exchanger at the highest pint f the twer than the lwer lcatin. This is generally expected as a result f increasing cling range fr this case. In ther wrds, the exergy destructin increases due t the increasing cntrast between inlet and utlet temperatures f cling water. Exergy efficiency as a functin f cling water flw rate fr varius packing lcatins is illustrated in figure 4. Frm this figure, it can be watched that the exergy efficiency diminishes when cling water flw rate was expanded fr bth cases f added packing. On the ther hand, it was bserved that the exergy efficiency f CWCT with packing under heat exchanger btained higher values than the CWCT with packing abve the heat exchanger. in Figure 3. Mesh Variatin f exergy destructin with cling water flw rate fr different lcatins f packing. Figure 4. Variatin f exergy efficiency with cling water flw rate fr different lcatins f packing. The relatinship between the ttal exergy changes f water with cling water flw rate fr different packing psitins is illustrated in figure 5. It is indicated that the ttal exergy change f water is prprtinal t the cling water flw rate. Als, it culd be seen that the ttal exergy change f water 4
MdTech Internatinal Cnference - Mdern Technlgies in Industrial Engineering IV IOP Publishing IOP Cnf. Series: Materials Science and Engineering 145 (2016) 032009 di:10.1088/1757-899x/145/3/032009 fr CWCT with packing under the heat exchanger higher than the ttal exergy change f CWCT with packing abve the heat exchanger. Figure 6 demnstrates the relatinship between the ttal exergy change f air and cling water flw rate fr different packing psitins. It culd be clearly seen that the ttal exergy change f air increments slightly with the increment f cling water flw rate fr bth packing psitins. Therefre, it is nticed that the ttal exergy change f air fr CWCT with packing under the heat exchanger higher than that fr CWCT with packing abve the heat exchanger. Figure 5. Variatin f exergy change f water with cling water flw rate fr different lcatins f packing. Figure 6. Variatin f exergy change f air with cling water flw rate fr different lcatins f packing. The exergy analyses f the different cmpnents alng the height f the twer are carried ut and the distributin f exergy alng the twer height frm up t dwn demnstrated in table 2. It is indicated that in bth cases the exergy destructin is higher in the base area and bit by bit diminishes twards the highest pint f the twer; cnsequently least exergy destructin is seen at the highest pint f the twer. As indicated frm this table, since the system generates entrpy, water absrbs mre exergy than f the air; the exergy f water decreases frm the upper part t its lwer part, while the exergy f air increases frm the lwer part t its upper part. This can be clarified by the way that water temperature diminishes frm highest pint t base f the twer as a cnsequence f supplying is exergy t the air. Table 2. Exergy distributin alng the twer height. Cmpnent D frm upper E X water E X air E X air(cnv) E X air(evap) (kw) (kw) (kw) (kw) (kw) CWCT with packing under the heat exchanger 1 132.0737 265.3732 133.2995 0.7992 132.5003 2 146.776 332.57 185.794-4.0178 189.8118 3 167.242 195.5013 28.2593 2.3233 26.0035 CWCT with packing abve the heat exchanger 1 40.9153 160.9044 119.989 2.0651 117.924 2 63.6694 171.2916 107.6222 1.4786 106.1437 3 257.4054 330.702 73.2966-1.1035 74.4001 5
MdTech Internatinal Cnference - Mdern Technlgies in Industrial Engineering IV IOP Publishing IOP Cnf. Series: Materials Science and Engineering 145 (2016) 032009 di:10.1088/1757-899x/145/3/032009 5. Cnclusins In the present paper, experiments were cnducted t determine the effect f packing lcatin n thermal perfrmance f CWCT based n exergy analysis. It is cncluded that the exergy destructin f CWCT with packing under the heat exchanger higher is than that fr the CWCT with packing abve the heat exchanger. Therefre, fr bth cases, maximum exergy destructin inside the twer ccurs at the bttm f the twer. Exergy efficiency behaviur is inversely prprtinal with the behaviur f the exergy destructin. Exergy change f the water is mre than twice the exergy change f the air. Als, exergy f air due t evapratin mre dminated functin in the air exergy due t cnvectin. Exergy f air due t an evapratin mre dminated functin in the air exergy due t a cnvectin. This is because the exergy f air due t cnvectin depends n the dry bulb temp and exergy f air due t evapratin depends f humidity rati f wet air. References [1] Qureshi B A and Zubair S M 2007 Secnd-lw Based perfrmance evaluatin f cling twers and evaprative heat exchangers Internatinal Jurnal f Thermal Sciences 46 pp 188-198 [2] Saravanan M and Saravanan R 2008 Energy and exergy f cunter flw wet cling twer Thermal Sciences 12(2) pp 69-78 [3] Ramakrishnan R and Aeumugam R 2014 Thermal perfrmance investigatin f mechanical draft cling twer using psychmetric gun technique Heat transfer Engineering 35(14-15) pp 1344-1353 [4] Khalifa A H N 2015 Thermal and exergy analysis f cunter flw induced draught cling twer Internatinal Jurnal f Current Engineering and Technlgy 5(4) [5] Bejan A 1997 Advanced Engineering Thermdynamics 2nd ed. (Singapre: J. Wiley) [6] Niksiar A and Rahimi A 2009 Energy and exergy analysis fr ccurrent gas spray cling systems based n the results f mathematical mdeling and simulatin Energy 34 pp 14-21 Nmenclature A=ttal heat transfer area, m2 Cp=specific heat at cnstant pressure, kj/kg C D=tube diameter, m d =exergy destructin, kw Elss m =mass flw rate, kg/s Q=vlume flw rate, l/min T=temperature, C Greek Symbls ρ=density,kg/m3 Φ=relative humidity, % ω= humidity rati, kg/kgdry air Ex =exergy efficiency, % Subscripts a=air cw=cling water in=inlet ut=utlet sw=spray water 6