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

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summarized in figure (1.2). Thermal technologies (or distillation) are based on liquid-vapor phase change due to addition of heat to drive the process. In the distillation process, seawater is heated to evaporate the water partially and the generated vapor is then condensed back into fresh water, leaving behind high concentrated salts in the waste brine. Evaporation heat is retained by the generated vapor as latent heat. When the vapor is condensed, it releases its latent heat, which can either be used to preheat feed seawater or evaporate water in a next stage. This process produces highly purified fresh water of better quality than the membrane processes. Distillation processes are divided into mainly three methods, multiple effect distillation (MED), multistage flash (MSF), and vapor compression (VC) as well as solar distillation techniques (e.g. basin-type solar distillers and HDH technique). Figure 1.2: Overview and energy classification of desalination processes In membrane technologies, the separation is realized by selectively passing fresh water or salt ions through semi-permeable membranes. The former process is called reverse osmosis (RO) where the separation is realized by applying high pressure difference on the membrane to outbalance the osmotic pressure. The later is called electro dialysis (ED) where an electrolytic charge difference on a pair of separation membranes is used as the driving force. In such processes no phase change takes place and, therefore, the energy consumption is lower than that of thermal processes for producing the same amount of fresh water. Other types such as micro and nano filtration membranes are used for water quality improvement and wastewater treatment. 3
1.3.1 Energy requirements and water cost Desalination processes, require mainly either low temperature steam or sensible heat for thermal distillation processes and electrical power for membrane systems. Electrical power is also necessary in thermal desalination plants for driving mechanical components such as pumps. The majority of desalination plants acquire their electric power requirements either directly from a public grid or from co-located power plant. The flow diagram of energy, water, and money for desalination process is illustrated in figure (1.3). Traditionally, fossil fuels such as oil and gas have been the major energy sources. However, sustainability of this resource in the long term is a vital issue to be addressed in view of the limited fossil fuels, prices volatility, and their negative impact on the global environment. Sustainability assurance of energy and water supply in the long term is prompting consideration of alternative renewable energy sources for seawater desalination. Figure 1.3: Flow scheme of energy, water, and money; adopted from [158] The theoretical absolute minimum energy required for water desalination is about 0.8 kWh/m 3 (≈2.88 kJ/kg) of water produced, depending solely on feed water salinity regardless of the technology and configuration of the desalination scheme [70]. This value represents the reversible, isothermal work for any steady state separation process. This figure is practically unrealistic not only because it assumes complete reversibility of all operations, but also because it would involve pumping an infinite amount of feed water and the pumping work would then be infinity [71]. The practically minimum energy consumption to produce fresh water is approximately 5 kWh/m 3 for RO as a membrane process and 50 kWh/ m 3 for MED as a distillation process. 4
Page 1: Technische Universität München In
Page 4 and 5: It is my pleasure to thank Prof. Th
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 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
Page 60 and 61: distillate rate. The system was not
Page 62 and 63: were; EnviPac Gr.1, 32 mm, and VFF
Page 64 and 65: Figure 2.15: Height versus air temp
Page 66 and 67: 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
Page 72 and 73:
exchanger and energy storage in one
Page 74 and 75:
3 Scope of the Study This chapter p
Page 76 and 77:
packing where it gets in direct con
Page 78 and 79:
In fact there is a tradeoff between
Page 80 and 81:
The energy flow between all and eac
Page 82 and 83:
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
Page 88 and 89:
assumed by conduction in both axial
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the air pressure drop ∆P per unit
Page 92 and 93:
evaporation rate per unit volume of
Page 94 and 95:
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
Page 100 and 101:
4.2.3.3 Liquid and gas hold-ups Liq
Page 102 and 103:
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
Page 110 and 111:
1 2 (4.62) d1 capp c2 c1 c2 1
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[58] evaluated the cooling tower ai
Page 114 and 115:
1 exp NTU 1 C r, cond cond (4
Page 116 and 117:
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
Page 130 and 131:
In the last two cases, the inlet ho
Page 132 and 133:
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
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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
Page 154 and 155:
Figure 6.4: Evolution of inlet and
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temperature is at its maximum level
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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
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e 0.45 kPa under natural convection
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aspect ratio under constant bed vol
Page 168 and 169:
Figure 7.7: Effect of inlet hot wat
Page 170 and 171:
well as the time required to reach
Page 172 and 173:
Figure 7.10: Effect of packing medi
Page 174 and 175:
40°C respectively. This gives flex
Page 176 and 177:
the condensate rate, productivity f
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esult, rather than PCM media which
Page 180 and 181:
Figure 7.18: Effect of PCM thermal
Page 182 and 183:
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
Page 192 and 193:
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
Page 214 and 215:
From the above correlation, the con
Page 216 and 217:
The Ergun analogy factor J h repres
Page 218 and 219:
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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