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

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1.3.2 Selection criteria of desalination technology The right selection of desalination technology depends on several factors and, to a great extent, can be considered as case specific. The most influential aspects are the type of feed water, the required quality of produced water, the plant capacity, the local available energy source and its cost, and the availability of skilled human resources. Table (1.1) compares between the main streams of commercial desalination technologies in common use worldwide. Membrane processes, mainly reverse osmosis (RO), is currently the predominant technology due to its low specific energy consumption compared to thermal processes. However, membrane technologies are less tolerant to source water turbidity, require highly skilled personnel for operation and maintenance, and have comparatively high operation and maintenance costs. Moreover, membrane technologies are very sensitive to feed water quality and therefore require intensive feed water pretreatment. Thermal desalination technologies are, by default, more technically adopted to be integrated with thermal power plants for cogeneration of electricity and water. Table 1.1: Characteristics for various desalination Technologies [72] Even though currently practiced desalination of brackish or seawater may be economically efficient in large scale facilities, it is less suitable for the decentralised water supply, as it is needed for small communities in remote developing regions. Thus, desalting processes, which are appropriate for decentralised use, should be technically simple in order to reduce capital and maintenance costs and to provide an application which can be operated without specialised knowledge. It is also highly desired to operate these units by renewable energies, especially solar systems since solar energy is often abundantly available in water-scarce regions. 5
1.3.3 Coupling desalination plants with power plants Since thermal desalination technologies utilize heat energy as the main driving force, co-location with power plants is an attractive option for cogeneration of water and power at competitive economies. Co-location of power plants and thermal desalination plants has been considered the most desirable setup since it provides many advantages over the displaced plants: better overall thermal efficiency due to recovery and utilization of latent heat of condensation in the power plant as an energy source for the desalination plant cost saving through common use of infrastructure for both plants (e.g. the intake and outfall, and using the power plant condenser as a brine heater of the desalination plant) minimizes energy transportation losses and costs, better land use, and less man power is required for operation and maintenance of both plants Moreover, conventional electrical power production requires a sustainable source of water, while desalination technology requires a substantial power supply. This mutual interdependency implies that the sustainable solutions should be found in the autonomous systems which simultaneously produce both electrical power and desalinated water within the same scheme. 1.3.4 Coupling renewable energies with desalination technologies Renewable energy (RE) technologies such as solar thermal, photovoltaic (PV), wind energy, and biomass have reached a level of maturity that makes them reliable sources of energy for driving desalination processes. It is agreed that the economic feasibility of the desalination industry will depend greatly on technology development of renewable energies [73]. Recently, considerable attention has been given to the use of renewable energies for desalination plants, especially in remote areas and islands. Coupling renewable energy systems with the desalination technologies takes place at an interface between both of them, where the energy generated by the RE system is utilized by the desalination plant. This energy can be in different forms such as thermal energy, electricity or shaft power. Owing to the variety of desalination processes and required form of power, there are a number of coupling schemes with power generation systems. Plausible couplings are depicted in the form of a tree in figure (1.4). However, the two common features which characterize RE sources are the intermittence and continuous variation in intensity over time. In other words, RE systems are characterized by a transient behaviour and time mismatch between the demand and availability of energy supply. These handicaps require either some form 6
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 22 and 23: summarized in figure (1.2). Thermal
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
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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
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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
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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
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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
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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
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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
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9 Summary and conclusions 9.1 Summa
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productivities at any cooling water
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[13] Vafai K., Sozen M. An investig
Page 202 and 203:
[48] Crone S., Bergins C., and Stra
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[79] Tiwari G.N. and Yadav Y.P. (78
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[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
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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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