Particulate Fouling Effect on Heat Exchanger Performance

Transcription

1 Tishreen University Jurnal fr Research and Scientific Studies - Engineering Sciences Series Vl. ( ) N. ( ) Particulate Fuling Effect n Heat Exchanger Perfrmance Dr. Rabie Habib (Received / /. Accepted / / ) ABSTRACT The previus wrk prves that there is n reliable crrelatin t predict particulate fuling effect n heat exchangers perfrmance. The main bjective f this wrk is t develp a semi-empirical mdel fr heat exchanger fuling.. The available experimental data are analyzed and then used t establish the prpsed mdel. This mdel accunts fr the effects f flw cnditins n fuling. Resistance t predict the design, peratin and perfrmance parameters f plate type heat exchangers. It is fund that the exchanger effectiveness decrease by t due t fuling f the present cnditins. Als, the predicted pressure drp with fuling is higher than that f the clean fluids by t fr the same cnditins. Therefre, extra pwer and initial perating csts are needed. The present mdel can be used t dcument the design parameters f plate type, duble pipe, and similar heat exchangers. Keywrds: predictins, particulate fuling, heat exchanger perfrmance, heat transfer * Assistant Prfessr, Department f Mechatrnic Engineering, Faculty f Mechanical & Electrical Engineering, Tishreen University, Lattakia, Syria.

2 Tishreen University Jurnal fr Research and Scientific Studies - Engineering Sciences Series Vl. ( ) N. ( )

3 Tishreen University Jurnal. Eng. Sciences Series NOMECLATURE: C b : bulk particle cncentratin, ppm q : initial heat heat flux, kw/m R f : fuling resistance, (m.k)/kw * R f : asympttic fuling resistance, (m.k)/kw R * f,c : asympttic fuling resistance in terms f particle cncentratin, (m.k)/k W R * f,q : asympttic fuling resistance in terms f heat flux, (m.k)/kw R * f,u : asympttic fuling resistance in terms f flw average velcity, (m.k)/kw t : time, s U : verall heat transfer cefficient f fuled fliud, kw/(m. K) U : verall heat transfer cefficient f clean fliud, kw/(m. K) u : fuled flw average velcity, m/s u : clean flw average velcity, m/s : time cnstant, /min c : time cnstant in terms f particle cncentratin, /s q : time cnstant in terms f heat flux, /s u : time cnstant in terms f flw average velcity, /s p : pressure drp f fuled flw, Pa p : pressure drp f clean flw, Pa : exchanger effectiveness fr fuled flw, dimensinless : exchanger effectiveness fr clean flw, dimensinless X : fuled fluid (fr cmpsitin see Muller-Steinhagen and Middlis, ) INTRODUCTION: Fuling is cnsidered ne f the mst imprtant prblems in many engineering applicatins, especially in heat transfer equipment. Fuling f such equipment is defined as the depsitin f unwanted materials n heat transfer surfaces. Such depsit causes degradatin in thermal and hydraulic perfrmance f the equipment. Therefre, predictin f fuling (especially particulate fuling) is necessary fr design, peratin and perfrmance f heat exchangers. Particulate fuling is studied experimentally in several engineering applicatins. The experimental data f such investigatins are quite useful t understand this imprtant phenmenn. Fr example, Blchl and Muller-Steinhagen ( ) studied the influence f particulate fuling in a vertical annular test sectin. Btt and Bemrse ( ) measured the effect f particulate fuling in the gas side f finned tube heat exchangers. Chamra and Webb ( ) investigated particulate fuling in plain and enhanced tubes. Freeman et al.,

4 measured particulate fuling n the uter surface f finned and rugh tubes in duble pipe heat exchangers. Kim and Webb ( ) and ( ) studied the effect f rughness n particulate fuling. Middis and Muller-Steinhagen, investigated the effect f particulate fuling f smth, artificially rughened and crrugated heat transfer surfaces f plate type heat exchangers. Muller-Steinhagen and Middis ( ) studied the effect f particulate fuling n plate heat exchangers. Muller-Steinhagen and Blchl, ( ) investigated the effect f particulate fuling in annular heat exchangers. Muller-Steinhagen et al. ( ) and ( ) studied the effect f particulate fuling during biling and sensible heat transfer. Smerscales et al ( ) investigated the effect f particulate fuling n heat transfer f internally enhanced tubes. The water quality effect n particulate fuling was studied by Warkinsn ( ). Webb and Chamra ( ) perfrmed particulate fuling tests in enhanced and plain tubes while Webb and Kim ( ) investigated the effect f particulate fuling in cmmercial tubes. Zhang et al. ( ) and ( ) measured particulate fuling n plate finned-tube autmtive heat exchangers in rder t enhance the heat transfer rate. The first theretical significant attempt t derive a general fuling mdel was by Kern and Seatn ( ). They bserved that the experimental data f fuling curves fllw a typical pattern after an initial perid f fast fuling build-up. They als bserved that the fuling resistance tends t remain cnstant. Watkinsn and Epstein, ( ) and ( ) extended the mdel f Kern and Seatn ( ) by incrprating a sticking prbability in their depsitin mdel. Recently, Chamra and Webb ( ) and ( ) mdeled the liquid side particulate fuling in enhanced and plain tubes. The remval rate f particulate fuling was mdeled by Epstein ( ). Gudmundssn ( ) identified three main depsitin regimes, namely diffusin, inertia and impactin. Kim and Webb ( ) mdeled particulate fuling f water in tubes having tw-dimensinal rughness. Pinheir ( ) summarized particulate fuling mdels f the nce thrugh heat exchangers. The gal f this wrk is t develp a semi-empirical mdel t predict the effects f the actual perating cnditins n particulate fuling f plate type heat exchangers since there is n reliable r generalized mdel is available. The available experimental results are first assessed, analyzed and then used t develp the present mdel. This mdel incrprates the effect f time, flw velcity, particle cncentratin and heat flux n the design, peratin and perfrmance f plate type heat exchangers. The mdel can als d the same predictins fr duble pipe heat exchangers. The develped mdel can be used as a fast and inexpensive tl t dcument the details f particulate fuling effect n plate type, duble pipe and the similar heat exchangers. Materials and Methds: Kern and Seatn ( ) described the behavir f fuling resistance, R f experimental data by the fllwing mdel

5 Tishreen University Jurnal. Eng. Sciences Series R f * t R (1 e ) ( ) f where, R * f : asympttic fuling resistance, t is the time and is the time cnstsnt. Pinheir, summarized the prpsed dependence f R * f and n fuled flw average velcity, u, f several investigatrs. His summary shws that R * f is prprtinal t /u r /u r /u and is prprtinal t u r u based n theretical studies. Muller- Steinhagen and Middis, suggested that R * f is prprtinal t u based n their experimental study using plate type heat exchanger. The present mdel is the same as that f Kern and Satn ( ) and nly expressins fr R * f and f equatin ( ) are btained frm the experimental data f Muller-Steinhagen and Middis ( ) shwn in Figs t fr plate type heat exchangers. These data are fr a fuled fluid X (fr cmpsitin see Muller-Steinhagen and Middis ( ) and water as the clean fluid. These experimental data are assessed and analyzed first and then used t develp the required expressins. The asympttic fuling resistance, R, and time cnstant, u, in terms f the flw average velcity, u, are btaind frm the experimental data shwn in Fig. * f,u * R f, u a a1u a u ( ) and u b b1u b u ( ) * In the same way, The asympttic fuling resistance, R f,c, and the time cnstant, c, as a functin f bulk particle cncentratin. C b, are btained frm experimental data shwn in Fige. as: * R f, c a a1c b a C b ( ) and b b C b C ( ) c 1 b Similarly, the asympttic fuling resistance, b R * f,q as:, and the time cnstant, q, as functin f the initial heat flux, q, are btained frm the experimental data shwn in Fig. * R f, q a a1q a q ( ) and b b q b q ( ) q 1 The cnstants a, a, a, b, b and b f the abve equatins are given in Tables I and II. The general expressins f R * f and in terms f clean flw average velcity, bulk as

6 particle cncentratin and initial heat flux is develped frm the crrelatins ( ) thrugh ( ) using the experimental data shwn in Figs, and as * * * * * * * Rf c c1rf,u crf,u c3rf,c c4rf,c c5rf, q c6rf,q ( ) and e e e e e e e ( ) 1 u u 3 c 4 c 5 q 6 q The cnstants c, c, c, c, c, c, c, e, e, e, e, e, e, and e are given in Table III. The develped mdel cvers a wide range f the actual perating cnditins and can be used fr plate type, duble pipe and the similar heat exchangers. RESULTS AND DISCUSSION: The semi-empirical mdel develped fr particulate fuling is used t predict the perfrmance, design and peratin parameters f plate type and duble pipe heat exchangers. The mdel predictins cver a wide range f the actual perating cnditins, namely the time, flw velcity, bulk particle cncentratin and initial heat flux. The experimental data in Figs., and are used t develp the present mdel. These data are fr different flw average velcity, bulk particle cncentratin and initial heat flux. The predictin f the present mdel fr such perating cnditins are als shwn in these figures. Cmparisn with Previus Results: The predictins f the present mdel are cmpared with the available experimental data. Figure shws the cmparisn f predictins against the experimental data f Muller-Steinhagen and Muddis ( ) and Muller-Steinhagen et al. ( ) fr plate type heat exchangers. This figure shws the variatin f the asympttic fuling resistance versus the flw average velcity and bulk particle cncentratin. It is seen that the asympttic fuling resistance increases with bulk particle cncentratin and decreases with flw average velcity. It is clear that the present mdel predicts the experimental data with gd agreement. Figure shws the cmparisn between the present predictin and experimental data f Muller-Steinhagen and Muddis, ( ) fr plate type heat exchangers. It is seen that the predicted dimensinless verall heat transfer cefficient is als in gd agreement with experimental data. Fr duble pipe heat exchangers, the present mdel predictins are cmpared with the experimental results f Blchl and Muller-Steinhagen ( ) in Fig.. This figure shws the variatin f fuling resistance versus time and bulk particle cncentratin. It is clear frm this figure that bth the experimental and predictin data fllw an expnential behavir until they asymptte t certain values. The rate f fuling, dr f /dt, is seen t be smaller than that f plate type heat exchangers and lager than that f duble pipe heat exchangers. This is due t higher remval rate f depsited fuling in case f rund pipes. It is seen frm this figure that the mdel ver predicts the experimental data. This is because the flw near the crners f the flw area in case f plate type exchangers allws

7 Tishreen University Jurnal. Eng. Sciences Series mre fuling depsitin cmpared with that in rund pipes. The mre fuling depsitin near the crners is due t the decreased flw average velcity and secndary flw there. Therefre, the present mdel can be used as a quick and cheap tl t dcument the predictins f such heat exchangers and the similar nes. In the fllwing sectin, the effect f time, flw average velcity, bulk particle cncentratin and initial heat flux are investigated fr plate type heat exchangers Effect f Time: The variatin f experimental and predicted data f fuling resistance with time is shwn in Figs., and fr different flw average velcity, particle cncentratin and heat flux. It seen that the fuling resistance f bth data increases with time expnentially until it asympttes t a certain value. It is seen frm these Figs. and that the rate f fuling, dr f /dt, increases as the flw average velcity decreases r as the particle cncentratin increases. The variatin f predicted heat exchanger effectiveness rati,, and dimensinless pressure drp, p/p, versus time is shwn in Figs. and fr different flw velcities ( t m/s). Fr cnstant velcity, the effectiveness decreases expnentially with time and asympttes t a cnstant value as seen in Fig.. The predicted dimensinless pressure drp increases expnentially with time until it asympttes t a cnstant value fr a specific velcity. The decrease f effectiveness rati results frm the increase f fuling accumulatin f depsitin with time, which increases the thermal resistance fr heat transfer. The increase f pressure drp is due t the increase f fuling thickness, which results in higher flw average velcity fr the same flw rate. As well, the depsitin f fuling increases the surface rughness. Similar behavir f predictins fr different particle cncentratins and heat fluxes is shwn in Figs. t. Effect f Flw Velcity: The effect f flw average velcity n bth the experimental and predicted fuling resistance is shwn in Fig.. It is clear frm Fig. and that the asympttic fuling resistance f bth data increases as the flw average velcity decreases. As well, the rate f fuling, dr f /dt, in the starting perid increases with the flw average velcity. The variatin f exchanger effectiveness and pressure drp ratis with time is shwn in Figs. and respectively. This is fr initial heat flux and bulk particle cncentratin f kw/m and ppm respectively and fr different flw average velcities ( t m/s). It is clear frm these figures that the predictins decrease r increase expnentially. The asympttic effectiveness rati decreases as the flw average velcity decreases. The asympttic values f is in the range f t fr the shwn range f flw average velcity. The mre decrease in is due t the mre depsitin and the less remval f fuling by lwer flw average velcity, which increases the heat transfer thermal resistance. On the ther hand, the asympttic pressure drp rati increases as the flw average velcity decreases. The net increase in pressure drp r decrease in exchanger effectiveness shwn in Figs. and is cntrlled by the depsited fulant rughness, depsitin rate, remval rate and flw average velcity. The asympttic values

8 f pressure drp rati are in the range f t fr the shwn average velcity range. This means that an extra pumping pwer f abut t is needed fr fuled flw circulatin under the present flw cnditins cmpared with nn fuling (clean) flw. This adds an extra initial cst t the pumping system and als increases the perating cst due t extra pwer cnsumptin. Effect f Particle Cncentratin: The effect f bulk particle cncentratin n bth experimental and predicted fuling resistance shwn in Fig.. It is clear frm Figs. and that the asympttic fuling resistance f bth data increases as the bulk particle cncentratin increases and the rate f fuling, dr f /dt, in the starting perid increase as the bulk particle cncentratin increases. The change f exchanger effectiveness and pressure drp ratis with time and bulk particle cncentratin is shwn in Figs. and fr an initial heat flux and flw average velcity f kw/m and m/s respectively. The behavir f predictins and discussin are the same as fr Figs. and t sme degree with ne exceptin. As the bulk particle cncentratin decreases, the asympttic effectiveness rati increases while the asympttic pressure drp rati decreases. The asympttic effectiveness and pressure drp ratis are in the range f t and t respectively fr bulk particle cncentratin in the range f t ppm and fr the present perating cnditins. Effect f Heat Flux: The effect f initial heat flux n bth experimental and predicted fuling resistance is shwn in Fig.. It is clear that the asympttic fuling resistance increase with initial heat flux t a certain value and then decreases again. It is clear frm Figs. t that the effect f initial heat flux n fuling is small cmpared with the effect f flw velcity and particle cncentratin. The behavir f exchanger effectiveness and pressure drp ratis with time and initial heat flux are displayed in Figs. and fr a bulk particle cncentratin and flw average velcity f ppm and m/s respectively. Again, the variatin seen in these figures is expnential behavir either decreasing r increasing fr cnstant initial heat flux. It is clear that the asympttic effectiveness rati decreases as the initial heat flux increases until it reaches a minimum value at a heat flux f kw/m and then increases again. This behavir is cnfirmed experimentally by Muller-Steinhagen and Muddis ( ). Fr the present flw cnditins and initial heat flux range f t kw/m, the asympttic effectiveness rati is in the range f t. On the ther hand, the asympttic pressure drp rati increases t a maximum value (at kw/m ) and then decreases again with the increase f initial heat flux. The asympttic pressure drp rati values are in the range f t fr the same perating cnditins. It is clear frm these figures that the effect f initial heat flux ( increase in and extra pumping pwer) is small

9 Tishreen University Jurnal. Eng. Sciences Series cmpared with the effect f flw average velcity ( and respectively) and bulk particle cncentratin ( and respectively). SUMMARY AND CONCLOSSIONS: The available fuling experimental data are first assessed and analyzed. These data are then used t develp a semi-empirical mdel fr particulate fuling in plate type heat exchangers. Expressins f the asympttic fuling resistance and time cnstant are btained. One expressin fr fuling is in terms f flw average velcity alne. The ther is in terms f bulk particle cncentratin alne while the third is in terms f the initial heat flux alne. Three similar expressins are develped fr the time cnstant. A general expressin fr fuling resistance is btained using the develped crrelatins and the used experimental data in terms f flw average velcity, bulk particle cncentratin and initial heat flux. A similar expressin is als btained fr the time cnstant. The develped mdel is used t predict the effect f fuling n the heat exchanger design, peratin and perfrmance parameters. This mdel can be used as a quick and cheap tl t predict the fuling effects n heat exchangers and als leads t a better understanding f this imprtant phenmenn. The present results shwed that bth the fuling rate at the beginning f peratin after cleaning and the asympttic fuling resistance increase as the flw average velcity decreases r as the bulk particle cncentratin increases. As well, the rate f fuling decreases as the peratin time increases fr cnstant flw average velcity r bulk particle cncentratin. The present predictins and experimental data shw that the effect f initial heat flux n fuling resistance is small cmpared with that f average velcity r bulk particle cncentratin. Mrever, the present predictins shw gd agreement with the experimental data f plate type and duble pipe heat exchangers. The present results fr exchanger effectiveness decreases with time at the beginning f peratin since previus cleaning while the pressure drp increases fr cnstant flw average velcity r bulk particle cncentratin r initial heat flux. The asympttic effectiveness rati decreases as the flw average velcity decreases r as the bulk particle cncentratin increases. On the ther hand, the asympttic pressure drp rati decreases as the flw average velcity decreases r as the bulk particle cncentratin increases. The predicted results shw a decrease in the exchanger effectiveness in the range f t cmpared with the data f clean fluids under the cnsidered perating cnditins. As well, the present results shw an increase in pressure drp in the range f t ver that needed fr cleaned fluids fr the same cnditins. Therefre, an extra pumping pwer f t is need fr the circulatin system due t fuling and this adds an extra initial and perating csts t the pumping system. The predicted results suggest the use f the present mdel t dcument the design, peratin and perfrmance parameters f plate type, duble pipe and similar heat exchangers. REFERENCES:

10 . BLOCHL, R. AND MULLER-STEINHAGEN, H., Influence f Particle Size and Particle/Fluid Cmbinatin n Particulate Fuling in Heat Exchangers, Can. J. Chem. Eng., Vl.,.. BOTT, T.R. AND BEMROSE, C.R., Particulate Fuling n the Gas-Side f Finned Tube Heat Exchangers, in Fuling f Heat Exchanger Equipment, (Edited by J.M. Chenweth and M. Impagliazz), ASMS Symp., New Yrk, HTD-Vl.,.. CHAMRA, L.M. AND WEBB, R.L., Effect f Particle Size and Size Distributin n Particulate Fuling in Enhanced Tubes, J. Enhanced Heat Transfer, Vl., N.,.. CHAMRA, L.M. AND WEBB, R.L., Mdeling Liquid-Side Particulate Fuling in Enhanced Tubes, Int. J. Heat & Mass Transfer, Vl., N.,,. CHAMRA, L.M. AND WEBB, R.L., Mdeling Liquid-Side Particulate Fuling in Plain Tubes, Int. Cnf. Energy Research & Develpment, Kuwait, Vl.,.. EPSTEIN, N., Particulate Fuling f Heat Transfer Surfaces: Mechanisms and Mdels, in Fuling Science and Technlgy, (Edited by L.F. Mel, T.R. Btt and C.A. Pinheir), Kluwer Academic,.. FREEMAN, W.B., MIDDIS, J. AND MULLER-STEINHAGEN, H.M., Influence f Augmented Surfaces and f Surface Finish n Particulate Fuling in Duble Pipe Heat Exchangers, J. Chem. Eng. Prcess, Vl.,.. GUDMUNDSSON, J.S., Particulate Fuling, In Fuling f Heat Transfer Equipment, (Edited by E.F.C., Smerscales and J.G. Knudsen), Hemisphere Crp., Washingtn, D. C.,.. KERN, D.Q. AND SEATON, R.A., A Theretical Analysis f Thermal Surface Fuling, J. Brit. Chem. Eng., Vl.,.. KIM, N.H. AND WEBB, R.L., Particulate Fuling in Tubes Having Arc-Shaped Tw-Dimensinal Rughness by a Flwing Suspensin f Aluminum Oxide in Water, Prc. th Int. Heat Transfer Cnf., Vl.,.. KIM, N. AND WEBB, R.L., Particulate Fuling f Water in Tubes Having a Tw- Dimensinal Rughness Gemetry, Int. J. Heat Mass Transfer, Vl., N.,.. MIDDIS, J., AND MULLER-STEINHAGEN, H.M., Particulate Fuling in Heat Exchangers with Enhanced Surfaces, th Australian Chem. Eng. Cnf., Vl.,.. MULLER-STEINHAGEN, H.M. AND MIDDIS, J., Particulate Fuling in Plate Heat Exchangers, J. Heat Transfer Eng., Vl., N.,.. MULLER-STEINHAGEN, H.M. AND BLOCHL, R., Particulate Fuling in Heat Exchangers, Prc. IPENZ Cnf., New Plymuth, New Zealand,.. MULLER-STEINHAGEN, H.M., REIF, F., EPSTEIN, N. AND WATKINSON, th A.P., Particulate Fuling During Biling and Nn-Biling Heat Transfer, Prc. Int. Heat Transfer Cnf., San Francisc, Vl.,.

11 Tishreen University Jurnal. Eng. Sciences Series. MULLER-STEINHAGEN, H.M., REIF, F., EPSTEIN, N. AND WATKINSON, A.P., Influence f Operating Cnditins n Particulate Fuling, Can. J. Chem. Eng., Vl.,.. PINHEIRO, J.R.S., Fuling f Heat Transfer Surface, in Design and Operatin f Heat Exchangers, (Edited by J.G. Cllier, J. Tabrek and N. Afgan), McGraw-Hill Bk Cmpany Inc., New Yrk,.. SOMERSCALES, E.F.C., PONTEDURO, A.F. AND BERGLES, A. E., Particulate Fuling f Heat Transfer Tubes Enhanced n Their Inner Surfaces, in Fuling and Enhancement Interactins, (Edited by T.J. Rabas and J.M. Chenweth), ASME, HTD- Vl.,.. WATKINSON, A.P., Water Quality Effects n Fuling frm Hard Waters, in Heat Exchangers, Thery and Practice, (Edited by J.Y. Wen and M. Yasu), Hemisphere Crp., Washingtn, D. C.,.. WATKINSON, A.P. AND EPSTEIN, N., Particulate Fuling f Sensible Heat Exchangers, Prc. th Int. Heat Transfer Cnf., Paris-Versailles, Vl.,.. WATKINSON, A.P. AND EPSTEIN, N., Particulate Fuling f Sensible Heat Exchanger, in Design and Operatin f Heat Exchangers, (Edited by J.G. Cllier, J. Tabrek and N. Afgan), McGraw-Hill Bk Cmpany Inc.,.. WEBB, R.L. AND CHAMRA, L.M., On-Line Cleaning f Particulate Fuling in Enhanced Tubes, in Fuling and Enhancement Interactins, (Edited by T.J. Rabas and J.M. Chenweth), ASME, HTD-Vl.,.. WEBB, R.L. AND KIM, N.H., Particulate Fuling f Internally-Ribbed Tubes, in Heat Transfer Equipment Fundamentals, Design, Applicatins and Operating Prblems, (Edited by R.K. Shah), ASME, HTD-Vl.,.. ZHANG, G., BOTT, T.R. AND BEMROSE, C.R., Finned Tube Heat Exchanger Fuling by Particles, Prc. th Int. Heat Transfer Cnf., Jerusalem, Vl.,.. ZHANG, G., BOTT, T.R. AND BEMROSE, C.R., Reducing Particle Depsitin in Air-Cled Heat Exchangers, J. Heat Transfer Eng., Vl., N.,.

12 TABLE I: CONSTANTS OF FOULING RESISTANCE EXPRESSIONS Equatin ( ) ( ) ( ) Cnstants a * a * * a * * TABLE II: CONSTANTS OF TIME CONSTANT EXPRESSIONS. Cnstants Equatin ( ) ( ) ( ) b b * * b * TABLE III: CONSTANTS OF THE GENERAL EXPRESSIONS ( ) & ( ) c c e e c * e c c c c e e e e

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16 q = 40 kw/m C b = 400 ppm Present Exp. f Muller-Steinhagen and Middis, 1989 U/U Time, min Fig.5. Cmparisn f predictins with experimental data f plate heat exchanger q = 16 kw/m u = 0.33 m /s present Exp. f Blchl and Muller-Steinhagen, 1990 R f, (m K)/kW ppm Time, min Fig. 6. Cmparisn f predictins with experimental data f duble pipe heat exchanger.

17 Tishreen University Jurnal. Eng. Sciences Series q = 40 kw/m C b = 400 ppm m/s Time, min Fig.7. Variatin f predicted exchanger effectiveness with time and flw velcity m/s p/ p q = 40 kw/m C b = 400 ppm Time, min Fig. 8. Variatin f predicted p/ p with time and flw velcity.

18 q = 40 kw/m u = 0.4 m/s ppm Time, min Fig. 9. Variatin f predicted exchanger effectiveness with time and particle cncentratin ppm 800 P/ P u = 0.4 m/s q = 40kW/m Time, min Fig.10. Variatin f predicted p/ p with time and particle cncentratin.

19 Tishreen University Jurnal. Eng. Sciences Series C b =400 ppm u = 0.4 m/s 0 kw/m Time, min Fig. 11. Variatin f predicted exchanger effectiveness with time and heat flux p/ p kw/m 1.1 C b = 400 ppm u = 0.4 m/s Time, min Fig. 1. Variatin f predicted p/ p with time and heat flux.

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