1411-5565

DEWAN REDAKSI

Ketua penyunting

Nurchayatr

Wakil Ketua penyunting

tGNK yudhyadi

Penyunting petaksana

^.Humalro Sardahulri Wahyu ltiriasto

Tata Usaha

Anrta Wulansari

Jurnarreknrk R*''yrs/l terbrt 2 (dua) karisetahirn pada butan Junr dan Desember

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ISSN

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VOLUME 14 NOMOR 2, Desember 2413

DAFTAR ISI

EDITORIAL

. Sifat Mekanik Komposit Pet-Serabut Kelapa-Tempurung Kelapa/ResinPoliester Tak Jenuh {Mechanical properties of PET-coconut fibre-coconutshell/U nsatu rated Polyesfer Resrn)( Nasmi Herlina Sari, Sugiman, Sujita, Emmy Dyah S. ). Pembuatan Dan Uji Briket Biomassa Dari Buah Nyamplung (Production andtesting of brbmass briquette of nyamplung fruit)(Hendry Sakke Tira, Abdurrahman)

. Pengaruh Pendidihan Di Upsfream Loop Terhadap Ketidak Stabilan DariAliranMendidih Di Dalam Saluran lMikro (Effecfs of Boiling in the Upstream Loop onlnstability of Flow Boiling in a Microchannef)(Mirmanto)

. Studi Tingkat Produktivitas lndustri Mikro Kecil Untuk Meningkatkan DayaSaing lndustri (Studi kasus: Di Kabupaten Lombok Barat) (Study ofProductivity of Small and Micro Scale Export Oriented Products lndustry toimprove its competitiveness (case study: in West Lombok Regency-NTB)(Suartika, Alit Triadi, Yudhyadi, Okariawan, Wijana)

o Analisa Kinerja Sistem Ofcdm I PSK Berbasis Wavelet Dan BerbasisFft(Pertormance analysis of 8 PSK OFCDM sysfem Based on Wavelet andBased on FFT )(Sudi mariyanto Al Sasongko,l Made BudiSuksmadana, Parlinawati)

o Analisis Hidrograf Satuan Untuk Daerah Aliran Sungai Berbentuk Bulu (UnifHydrograph Analyses for Fury Watershed)(Humairo Saidah, Muhamad Ulwan, Nurun Ainuddin)

o Kiflerja Jaringan lrigasi Berdasarkan Kerapatan Bangunan Dan KerumitanJaringan Pada Daerah lrigasi Tolo Tangga (Pertormance Of lrrigation NetworkEased on Network Complexity At Tolo Tangga lnigation Network Area)(Salehudin, M. Birgus Budianto, L. Wirahman W., RajabiMubarak)

. Tinjauan Kuat Acuan Kayu Lokal Berdasarkan Atas Pemilahan SecaraMekanik (Review Of Reference Wood Sfrong Local Sorting Based On TheMechanicaf(AryaniRofaida)

r Evaluasi Awal Potensi Likuifaksi Di Kota Mataram (lnitial Evaluation ofLiquefaction Potentialin The Mataram City)(Muhajirah, Agung Prabowo, lsya Ashari)

o Evaluasi Kelayakan Tarif Angkutan Penyeberangan Di Kawasan TamanWisata Alam Laut Gili Matra Kecamatan Pemenang Kabupaten Lombok Utara(Feasibility Study of Transport Rafres in Natural Park Marine Tourism Gili MatraSab-drsfncf of Pemenang North Lombok Regency)(Rohani)

fis - 124

. Kewajiban Perusahaan Memberikan Cuti Hamil Atau Melahirkan Terhadap 168 - 173Tenaga Kerja Wanita (The Liability Of Company to Give an Off Duty OfWomen Labor That Pregnant Or Has Giving Birth )(Nurun Ainuddin)

ISSN:1411-5565

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106- 114

121 - 128

129 -',134

135 - 140

141 - 145

146 -'156

157 - 167

Jumal REKAYASA, Volume 14 No 2, Desem er 2013

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---'ml Teknik REKAyASA, Volume t4 No 2 Desember 2013

PENGARUH PENDIDTHAN DI UPSTREAM LOOP TERHADAP KETIDAK

STABTLAN DARI ALIRAI.I MENDIDIH DI DALAM SALURAN MIKRO

Effects of Boiting in the tJpstream Loop on tnstability of Flow Boiling ina Microchannel

MirmantoJurusan Teknik Mesin Fakultas Teknik Universitas Mataram

Jtn. Majapahit No.62 Mataram Nusa Tenggara Barat Kode Pos: 83125

Teip. (0370) 636087;636126; ext 128 Fax (0370) 636087:ABSTRAK

caper ini menyajikan flukuasitekanan dan aliran batik di dalam saturan tunggal pada alira.n air

mendidih dan- pengaruh pendidihan pada upstream loop terhada-P flaktuasi tekanan. Saluran

iunggalfersebuf tiftuat dai tembaga dengan diameter hidtolik 619 pm 97ry 9a.1ian0 40 mm'

uniik menguXur fluktuasi tekanan Ai aatam saluran, empat transducer PCC24 di pasang pada

saluran aingan jarak antar sensor I mm. Dua sensor tekanan iuga dipasang pada sisi

nasukan din ketuaran. Atiran batik di observasi dengan metode perbedaan tekanan. Jika

petuedaan tekanan bemilai negatif, ada kemungkinan aliran balk sesaaf teriadi. Hasil penelitian

nenunjukan hahwa fluktuasi-tekanan dan aliran batik disebabkan oleh aktivitas gelembung

;,rng *ur"ul, tumbuh dan meninggalkan saluran secara peiodik. Pendidihan di bagian'ge,iipaan

sebetum seksi uji dapat-ienyebabkan aliran tidak stabil. Aliran balik dapat terjadi

ketika gelembung membaigkitkan tekaian sesaaf yang lebih besar dari pada tekanan di stst

masukan.

Kabkunci: saluran mikro, ftuffiuasi tekanan, aliran balik dan kerugian tekanan.

ABSIRACT

This paper presenfs pressure fluctuation and flow reversal in a metallic single channel duingflow

'boiling of de-ionized water and effecfs of boiling in the upstream loop on pressure

ffuctuations. The channel was made of a copper with a hydraulic diameter of 619 pm and a

6ngtn of 40 mm. To measure pressure fluctuations inside the channel, four inexpensive

dtff-erential pressure fransducers PCC24 were inserted into the channel with an inter'axial

disfance of I mm. Two pressurc sensors were also mounted on the channel, but they were in

the intet and outtet plenums. The two pressure sensors were used for measuring inlet and outlet

pressures. A flow reversal was observed using a pressure difference method. When a pressure

difference between two pressure tappings has a negative value, there is a possibility that a

temporary flow reversaloccurs. fnd resutts showed ihat prcssure ftuctuation and flow reversal

were due to activities of bubble which was appeaing, growing, departing and leaving from the

channel periodicatty. Boiling in the upstream loop could cause an unstable flow. The flow

reversal could occur when the bubbte generated a temporary pressure which was bigger than

the inlet prcssure.

Keyword: microchannel, pressure fluctuation, flow reversal and pressure drop.

106

llirmonto..........Penguruh pedidihon

Di l/pstreon Loop

INTRODUCTIONpressure fl

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--.l-E -erqt( REXIyASA, Volurne 14 No 2 Desember 2013

:-oesec trte superheated liquid released its

=r€. ener(ry to vapour phase through a1r-ale bubble interface during short time.::T€ffior€, an increased sharp pressure in:€ .€pour caused the fluid traveling in bothl:..:st'eam and upstream directions.

From open literature above, in7'e.al. pressure fluctuation and flow-=,ei'sal are due to activities of bubble3-arr$ inside the channel. However, there is-?- nteraction or a relationship between:r?ssure fluctuation-flow reversal and an-:stream compressibility. The upstream

=rnpressibility may influence or support the:-essure fluctuation and flow reversal, in:errns of magnitude and live time. ln this;aper. author presents differences between)ressure fluctuations and flow reversals'esutted in the experiments with boiling in:1e upstream loop (case A) and withoutrciling in the upstream loop (case B). The:olective of this work is to know the effectscf boiling in' the upstream loop on thepressure fluctuation and flow reversal.

Nomenclature:

: area

: channel length: pressure; power from power supply.: useful heat.: heat loss to the sunoundings.: heat flux

difference

Subscript:ht : heated1,2,3,4 : location measured from the inlet.

(8mm, 16mm,24mm and 32mm)in : inletout : outlet

EXPERIMENTAL SET UP ANDPROCEDURES

The experimentalfacility or flow loopis shown in Fig. 1. The loop consists of amain boiler tank, gear pump, Coriolisflowmeter, rotameter, two preheaters, and atest module (test section).

Deionized water with a PH of 6.8was used as the working fluid and drawnfrom the main boiler and flowed through outthe loop. To remove any particles in theworking fluid, two filters (1 mm and 1 pm)were fitted to the loop. The temperatures ofworking fluid were measured in the inlet andoutlet plenums of microchannel using K typethermocouples with a seated diameter of 0.5mm and a length of 150 mm. A Coriolisflowmeter with an uncertainty of t0.6 g/minwas installed in the loop and used torneasure the mass flow rate.

All thermocouples were calibratedusing a cpnstant temperature bath against aplatinum resistance precision thermometerwith an accuracy of 0.025 K. The uncertaintyof thermocouples was t0.2 K.

All local pressures were measuredusing inexpensive pressure transducersmodel PCC24 calibrated against adeadweight tester with an uncertainty of !0.2kPa.

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Jrrml Teknik REKAyASA, Volume 14 No 2 Des€rnber 2013

DATA REDUCTIONParameters used in the data

reduction are summarized in this section.Total power supplied to the channel is noted

as P* and given by

P. =VI (1)

where Z is the voltage and ,I is the current.

Total heat flux, qn is calculated as follows:

Q=P,-Qw"tn =(z.H +w)t

(2)

(3)

(4)

(5)

ttr€

, Q lt-Quu' Ah, QH +W )L

where 4 is the net power (net heat), F/ is

the channel deplh, W is the channel weight,

Z is the channel length and lr, is the heat

transfer area. Heat loss (Q,",,) was

determined from single-phase experirnentsusing energy balance and approximately6.8% of net heat. Therefore, Eq. (4) can berearranged as

,,- Q - 0.932V1-

' A^, (z.n +w)L

Pressure droP is the differencebetween inlet pressure and outlet pressureand expressed as:

LP = P,n - Po* (6)

where pi, and poa are measured intet andoutlet pressures. However, pressures in the

inlet and outlet channel ends were not

known since there was no pressure sensorat the end of upstream and downstrearn ofthe channel. Pressure drop is used forpredicting the flow reversal in this study.When the value of Pressure droP isnegative, it indicates that in the channelthere is a temporary flow reversal orreversed flow, Chang et al. (2007). Thereveresed flow between each pressuresensor inside the channel can be predicted

using a difference pressure value betweeneach sensor as given bY

Mt=pr-pz (7)

Lp, = Pt - Pt (8)

Lp-, = Pt - Pc (9)

where p1, Pz, Ps, pa w€re measured directly.

ln this work, there are two cases that areexamined: (1) flow boiling with boiling in thepreheater/upstream loop (case A) and (2)

flow boiling without boiling in the upstreamloop (case B).

RESULTS AND DISGUSSIONAs reported by Zu et al. (2009), flow

reversal can only happen when there is acompressible volume in the upstream loop.

Figure 3 depicts that pressure drop

fluctuation for case A is bigger than that forcase B. However, a flow reversal doeshappens regularly for case A, butoccasionally for case B. This indicates thatthe effect of boiling in the upstream loop issignificant. Nevertheless, without boiling in

the upstream looP, see case B' anoccasionally and temporary flow reversaloccurs.

-

G = 1S60 kgftnk, Ii * BAC , y = {21 ft{ttlrrf, Case A

-

G - 1068 kgtmrc, ?i - E8'c , { - Azl kllll/m", case B

Figure 3. Pressure drop fluctuation wlth and without bolllng in the up6tresm loop

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--.rnal Teknik REKAyASA, Volume lrt No 2 Desernber 2013

Flgure 6. Efiecr of hest flux oo prersure drop fluctuationurithout boiling h the prsheaer.

This might be due to existing trapped gas oranother upstream compressible volumesource. The maximum pressure dropfluctuation amplitude (peak to peak) for caseA is around 10 kPa, while for case B isaround 8.4 kPa. The minimum value of -2.2kPa is obtained for case A and -0.4 kPa forcase B. Hence, the biggest fluctuation isobserved for case A in which boiling in theupstream loop presents. The different valuesof pressure fluctuation for case A and B aredue to the boiling in the preheater. Thus,boiling in the upstream loop affects pressureand pressure drop fluctuations.

What does happen in single-phaseflow when boiling in the upstream loopexists? Figure 4 indicates that pressure dropfluctuation for both cases is small and thedifference of pressure fluctuation for bothcases is not big. lt is around 1.5 kPa (peakto peak). Hence, the influence of boiling inthe upstream loop for single-phase flow isnot significant. However, at a low mass flux,the effect of boiling in the upstream loop issignificant. Figure 5 shows the effect ofboiling in the upstream loop at a low massflux. For case A, the amplitude of pressuredrop is approximately 1.75 kPa, whilst for

case B is around 1 kPa. Thus, boiling in theupstream loop is not suitable to demonstratethe effect of upstream compressibility,especially at a low mass flux,

Figure 6 presents the effect of heatflux on pressure drop fluctuation at the samemass flux without boiling in the preheater. Ata low heat flux, see Fig. 6a, a flow reversalwas observed, it was indicated by a negativevalue of pressure drop. This was due to nearthe onset of flow boiling and a low pressuredrop. Near the onset of flow boiling, lessbubble nucleation was generated. Thiscreated a temporary/periodically boiling witha high pressure build up. This was alsoaffected by the fact that at low heat flux, thepressure drop generated was still low. As aresult, the inlet pressure was low and couldbe defeated by bubble pressures inside thechannel during boiling. At a high heat flux,see Fig. 6b, a flow reversal was notdetected. This was owing to a high pressuredropfinlet pressure. Moreover, at a high heatflux, there were many bubbles generatedand continue boiling occurred with highfrequencies. Therefore, an intermittent flow(two-phase flow and liquid flow) did notoccur. lf it was guessed that the upstream

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--r'-c -eknik REKAyASA, Volume 14 No 2 Desember 2013

different heat flux, lnt. J. Heat MassTransfer 47, pp. 3631 -3641.:- , erU. G., Zhang, W., Li, e., Wang, B.,2009. Seed bubble stabilizes ftowand heat transfer in parattetmicrochannels, lnt. J. MultiphaseFlow 35, pp. 773-790.

I-:-i i., Koo, J.M., Ashegi, M., Goodson,K.E., Santiago, .,.G., 2OO2,Measurement and modeling of twophase flow in nnicrochannel withnearly constant heat flux boundarycondition, J. Microelctromech, Syst.11(1), pp. 72-17.

Zu, Y.Q., Gedupudi, S., yan, y.y.,Karayiannis, T.G., Kenning, D.B.R.,20t2, Numerical simulation andexperimental obseruation ofconfined bubble growth during flowboiling in a microchannel with arectangular cross secf,bn of hQhaspect ratio, Proc. lnternationalASME conference, lCNMM2009,South Korea.

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