Experimental and Numerical Analysis of a PCM-Supported ...

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It is my pleasure to thank Prof. Thomas Sattelmayer, Head of the Lehrstul für Thermodynamik, TUM and all the administrative and supporting staff, who were abundantly helpful and offered invaluable assistance, and great hospitality. I would like to express my deep thanking to my colleague, Dipl.-Eng. Burkhard Seifert for his support and valuable discussions during the course of the study. This research project is co-funded by the Middle East Desalination Research Center (MEDRC) through the Ph.D. scholarship grant number 05-AS-003, and TUM, Germany. The financial support of MEDRC and TUM is gratefully acknowledged and appreciated. I’m fully indebted to my great parents for their unconditional loving and support throughout my whole life. I cherish the support in all life situations and friendship of my brothers and sister; Gamal, Usama, and Walaa. I am heartily thankful to Dr-Eng. Jürgen Blumenberg and his wife; Mrs. Gaby. Their great friendship and close social relationships made my family stay in Germany very pleasant. Thanks for never letting us feel that there was a long distance between us and our dear friends and families in our home country; Egypt. Last but not least, I owe my deepest gratitude to my lovely wife Abear for her patience, providing a supportive environment for me, and taking over major responsibilities of our kids. The long trip would have been very harsh and I could not have achieved as much as I did without her enduring support. Finally I can not describe how appreciative I’m to my three kids; my daughter Salma, my son Noureldin, and my little daughter Manar. The innocent smiley faces were always motivating and triggering my advancement. Whatever I achieve will be dedicated to make your future bright. München, September 2011 Abdel Hakim Hassabou ii
Abstract This work discusses the results of experimental and theoretical studies on a humidification-dehumidification (HDH) water desalination system equipped with phase change material (PCM) as a packing media in all its main components. The PCM-supported HDH system consists of an evaporator and condenser comprised by two cylindrical direct-contact packed beds filled with spherical PCM packing elements. Moreover, a solar collector and an external PCM thermal storage are used to drive the HDH plant. The external PCM thermal storage is used to guarantee continuous operation of the plant day and night round the clock under the transient behaviour of solar irradiation. The objective of using PCM elements in the evaporator and condenser was for heat storage as a back up during cloudy hours or for part-time night operation. During analysis of steady state conditions, it was discovered that the PCM packing media seem to enhance their thermal performance through locally establishing multipleeffects of heating/humidification (MEHH) and cooling/dehumidification (MECD) while air passing through the successive packing layers in the evaporator and condenser respectively. The multiple-effect phenomena are attributed solely to existence of conductive packing media, which act as heat and mass exchangers. Thus, the focus of the study lies on the thermal conductivity rather than the thermal capacity or solidliquid phase change processes of the packing in the two columns. The major aim of this study is to examine systematically the effect of MEHH and MECD at enhanced thermal conductivity of the filling material and to determine the technical and economic feasibility of applying these concepts in HDH desalination plants under steady state operation conditions. Transient simulation models for the individual components in the HDH system have been established and validated against experimental measurements. Using both experiment and simulation, a detailed heat and mass transfer analysis for the performance of the evaporator and condenser over a wide range of operation conditions under steady state has been performed using different types of packing materials. Furthermore, a yearly parametric analysis for the whole HDH plant has been performed under real weather conditions for two locations in Egypt. The overall performance analysis focuses on the optimum operation conditions of the HDH system, with optimum conductive filling material, with and without external PCM thermal buffer. Special attention is paid to the effect of climatic conditions and comparison between PCM and water as storage media in the external thermal storage. iii
Page 1: Technische Universität München In
Page 6 and 7: Contents List of figures ..........
Page 8 and 9: 5.3 Functional description ........
Page 10 and 11: List of Figures Figure 1.1: Cost br
Page 12 and 13: 78cm; Top: Evaporator, Bottom: Cond
Page 14 and 15: xii
Page 16 and 17: m Mass flow rate; [kg.s -1 ] m eva
Page 18 and 19: ed c coll cond cw d d e or eff evap
Page 20 and 21: 1 Introduction The first part of th
Page 22 and 23: summarized in figure (1.2). Thermal
Page 24 and 25: 1.3.2 Selection criteria of desalin
Page 26 and 27: of energy storage or hybridization
Page 28 and 29: Desalination development focuses on
Page 30 and 31: Introduction of the indirect type s
Page 32 and 33: 2 Literature Survey 2.1 Introductio
Page 34 and 35: There is actually a commercial prod
Page 36 and 37: Q m H c ( T T1) c ( T 2 T ) (2.2)
Page 38 and 39: (solid-liquid) have a storage densi
Page 40 and 41: (iii) a sharp melting temperature.
Page 42 and 43: melt and freeze without segregation
Page 44 and 45: However, the stored heat is less va
Page 46 and 47: parameters on the heat transfer and
Page 48 and 49: categories. The first category is b
Page 50 and 51: to 550 kWh/m 3 of distilled water a
Page 52 and 53: The enthalpy and humidity of the sa
Page 54 and 55:
Air mass flow rate [kg/h] GOR [-] 1
Page 56 and 57:
On the other hand, the efficiency o
Page 58 and 59:
2.8.4.2 Effect of air to water mass
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distillate rate. The system was not
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were; EnviPac Gr.1, 32 mm, and VFF
Page 64 and 65:
Figure 2.15: Height versus air temp
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The performance of the condenser is
Page 68 and 69:
Klausner and Mei [136] described a
Page 70 and 71:
The impact of the collector cost ca
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exchanger and energy storage in one
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3 Scope of the Study This chapter p
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packing where it gets in direct con
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In fact there is a tradeoff between
Page 80 and 81:
The energy flow between all and eac
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4 Theoretical Analysis and Modeling
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The two-energy equation models whic
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solid-liquid phase change inside th
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assumed by conduction in both axial
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the air pressure drop ∆P per unit
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evaporation rate per unit volume of
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where β t , β c , ρ ref , c ref
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the viscous transport and introduce
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liquid and solid phases, respective
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4.2.3.3 Liquid and gas hold-ups Liq
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Several models and approaches for m
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where G=ρU d /ε g is the pore mas
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k k eff s 1 3 2 (4.55) This cor
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uncertainties associated with the f
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1 2 (4.62) d1 capp c2 c1 c2 1
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[58] evaluated the cooling tower ai
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1 exp NTU 1 C r, cond cond (4
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A HE QHE U T HE LM (4.81) Where Q
Page 118 and 119:
c M f b (4.86) M b S S f where r
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that form the study logical foundat
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5 Experimental Analysis This chapte
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5.2 Measuring Techniques K-type the
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The product condensed water was mea
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operating limits. In light of the l
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In the last two cases, the inlet ho
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performance and its threshold value
Page 134 and 135:
It could be interpreted that this p
Page 136 and 137:
Evaporator Condenser Figure 5.8: Av
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within the inaccuracy margins. The
Page 140 and 141:
The last two cases of boundary cond
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natural air flow in the system. In
Page 144 and 145:
6 Model Implementation and Validati
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x t u x u 0 0 , (6.5) and for a s
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Next time step validation were the
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The evaporator and condenser both w
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Figure 6.2: Evolution of inlet and
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Figure 6.4: Evolution of inlet and
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temperature is at its maximum level
Page 158 and 159:
Bottom Top Figure 6.7: Evolution of
Page 160 and 161:
7 Parameters Analysis of the Evapor
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Figure 7.1: Effect of packing size
Page 164 and 165:
e 0.45 kPa under natural convection
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aspect ratio under constant bed vol
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Figure 7.7: Effect of inlet hot wat
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well as the time required to reach
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Figure 7.10: Effect of packing medi
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40°C respectively. This gives flex
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the condensate rate, productivity f
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esult, rather than PCM media which
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Figure 7.18: Effect of PCM thermal
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8 Optimization of HDH plant In this
Page 184 and 185:
The MATLAB model describes how the
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less steep than that of the distill
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8.3.4 Effect of hot water flow rate
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storage materials and thus it can h
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for latent heat storage would be ob
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When T m becomes sufficiently highe
Page 196 and 197:
9 Summary and conclusions 9.1 Summa
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productivities at any cooling water
Page 200 and 201:
[13] Vafai K., Sozen M. An investig
Page 202 and 203:
[48] Crone S., Bergins C., and Stra
Page 204 and 205:
[79] Tiwari G.N. and Yadav Y.P. (78
Page 206 and 207:
[109] Mehling H., Hiebler S. and Zi
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[139] Belessiotis V, Delyannis E (2
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Appendices Appendix A A1. PCM Therm
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A3. Constants and Thermo-physical p
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From the above correlation, the con
Page 216 and 217:
The Ergun analogy factor J h repres
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Equation (C.7) represents an overal
Page 220 and 221:
Appendix D D1. Cooling tower theory
Page 222 and 223:
A m w = the plan or cross sectiona
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