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

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to 550 kWh/m 3 of distilled water and 4 to 12 l/m 2 .day of solar collector area, as reported by Narayan et al [149]. GOR is directly proportional to heat and mass transfer effectiveness in the evaporator and condenser or both the temperature drop of hot water in the evaporator (ΔT hw ) and temperature rise of feed seawater in the condenser (ΔT cw ) and inversely to the temperature jump in the solar collector (ΔT coll ). When the HDH system works efficiently, both the temperature drop in the evaporator and temperature rise through the condenser become high, which reduces the required temperature jump in the collector, i.e. the required energy input to produce same amount of distillate. The heat and mass transfer rates in the evaporator and condenser depend on the following parameters, see the finite element illustration in figure (2.5): 1. heat and mass transfer coefficients 2. gas-liquid contact area 3. driving forces for heat and mass transfer (i.e. temperature difference ΔT, and water vapor concentration difference ΔC) Liquid film T l C l Gas film Q T g The driving force for heat transfer is the temperature difference between the liquid film and the bulk of the carrier gas. For mass transfer, it is due to the difference in water vapor pressure (or vapor concentration C) on the liquid film surface and partial pressure of water vapor in the bulk gas. The gas liquid contact area is a function of the geometric configuration of the exchanger, packing shape and size, and liquid and gas flow rates. Packing surface Bulk liquid m v Liquid-gas interface C g Bulk gas Figure 2.5: Finite element at the liquidair interface in direct contact heat and mass exchangers 2.8.3 Lumped model analysis In this section a simplified lumped model of a HDH system as shown in Figure (2.4) will be developed to explain how it works. Such a framework might help in interpretation and making sense of literature results, which will be presented in the following parts of this chapter. 31
2.8.3.1 Heat and mass balances Applying thermodynamic laws on the evaporator, condenser, and solar heater as shown in figure (2.4) and assuming no heat losses in the HDH cycle, the heat and mass balances can be written as: Humidifier Mass balance: m sw m a wa 1 m b m a wa 2 (2.5) Heat balance: m sw hsw 2 m a ha 1 m b hsw 1 m a ha 2 (2.6) Where the subscripts a, b, 1, and 2 stand for air, brine or blow down, bottom and top of the evaporator/condenser respectively, while w a2 and w a1 are the moisture contents of the air entering and leaving the condenser respectively. Dehumidifier Mass balance: m m w w dist a a2 a1 (2.7) 2 (2.8) 3 Heat balance: ma ha ha 1 msw hcw4 hcw mdist hdist where the subscript “dist” stands for distilled water, while h cw3 and h cw4 are the enthalpies of the cooling seawater water entering and leaving the condenser respectively. Solar heater Heat balance: The useful energy obtained from the collector can be written in the form: Q m c T I A (2.9) in sw sw coll T coll coll Where I T represents the solar global irradiation intensity (W/m 2 ), A coll is the collector area (m 2 ), and coll is the collector thermal efficiency. Based on various commercial collectors performance data, the efficiency is assumed to be represented as: coll T4 T 0.75 0.025 I amb (2.10) 32
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 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 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
Page 84 and 85: The two-energy equation models whic
Page 86 and 87: solid-liquid phase change inside th
Page 88 and 89: assumed by conduction in both axial
Page 90 and 91: 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
Page 96 and 97: the viscous transport and introduce
Page 98 and 99: 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
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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
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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
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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
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[48] Crone S., Bergins C., and Stra
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[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
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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