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

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Several models and approaches for mass transfer coefficients on both the gas and liquid sides are presented by Wagner et al. [40]. Various approaches and models for determination of the wetted and effective interfacial areas for mass transfer presented by Kister [32] and Gandhidasan [41] were preliminary examined and compared against each other. One particular problem to address here is the significant discrepancies between the predicted values of mass transfer coefficients between various approaches and models. It is observed that many researchers have used Onda et al. [35] model to describe the liquid-gas interfacial areas and mass transfer coefficient in distillation columns. Klausner et al. [45] have already developed a detailed heat and mass transfer analysis for a HDH system called the diffusion driven desalination (DDD) process. They extensively tested Onda et al. [35] correlations and used it to evaluate the mass transfer coefficients on the liquid and gas sides. They reported that excellent results were obtained against experimentation measurements [47]; thus the same approach will be applied here. Nevertheless, Klausner and Mei [45-46] modified Onda et al. [35] model described by equations (4.46-4.47) by introducing a constant of 2.2 instead of 1.45 for calculating the wetted interfacial area in the (DDD) system. They argued that the model underestimates the wetted surface area of the packing and this was the reason behind this modification in equation (4.47). The model is based on the concept of wetted packing area as a geometric parameter in determining the Reynolds number for the liquid as opposed to the interfacial area. a a e c exp 1.45 l 0.75 0.1 0.2 0. 05 1 Rel Wel Frl (4.46) a w a c exp 2.2 L 0.75 0.5 0.2 0. 05 1 Re LA WeL Fr L (4.47) Therefore, this modification could be even more crucial for the present analysis due to the existence of conductive packing media or a solid phase in the energy and mass balances. However, their predicted performance using this modified correlation is always higher than their experimental measurements in terms of the outlet air humidity content, outlet water temperature, and outlet air temperature. In the original model, Onda et al. [35] assumed the wetted area was equal to the effective interfacial area. The total wetted surface area in the irrigated column is expected to be greater than the effective area for mass transfer due to existence of static liquid holdup which contributes little to heat and mass transfer. This finding has been ascertained during the course of preliminary calculations of the effective 83
interfacial area, when Onda model results nearly coincide with that of the conservative model of Shi and Mersmann [34]. Another important finding that has been discovered in the course of the present analysis is that the predicted wetted area by the modified Onda et al.’s correlation nearly coincides with that of Wagner et al. [40]. Based on these findings, the original and modified Onda et al.’s correlations will be used for describing the effective interfacial area and total wetted surface area in the column, respectively. 4.2.3.5 Liquid-gas heat and mass transport coefficients Following the methodology of Klausner et al. [45], Individual mass transfer coefficients for liquid and gas sides are evaluated using Onda et al.’s [35] correlations. Applying analogy between heat and mass transfer, the individual and overall heat transfer coefficients at the gas-liquid interface have been formulated based on the two resistance theory [45] as follows:. K l 2 / 3 1/ 3 0.5 L lg lD l 0.0051 ( ad p) a wl l l 0.4 (4.48) K g G C ag 0.7 g gD g 1/ 3 ( ad ) 2 p aD g 5.23 C 2 d d p p 0.015 0.015 (4.49) Where K l and K g are mass transfer coefficients on the liquid and gas sides respectively. Using analogy between heat and mass transfer, the heat transfer coefficients on each side (U l and U g ) and the overall heat transfer coefficient h lg are computed as follows [45]: U U l g L / 1/ 2 lc plkl Dl ( ) 1 /3 / 2/ 3 gcpg kg Dg 1 1 U U 1 K (4.50) K (4.51) g U h (4.52) gl l g A general empirical correlation for the condensation mass transfer coefficient at the gas-solid interface (i.e. condensation on dry PCM patches), which was originally developed by Sun and Besant [50] to calculate the adsorption rate of water vapor in a desiccant bed of silica gel particles, has been modified and introduced heuristically in the present model: k gs 0.048Re 0.3 g M g P ( / D a G g g g ) 2 / 3 (4.53) 84
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Technische Universität München In
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It is my pleasure to thank Prof. Th
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Contents List of figures ..........
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5.3 Functional description ........
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List of Figures Figure 1.1: Cost br
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78cm; Top: Evaporator, Bottom: Cond
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xii
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m Mass flow rate; [kg.s -1 ] m eva
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ed c coll cond cw d d e or eff evap
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1 Introduction The first part of th
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summarized in figure (1.2). Thermal
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1.3.2 Selection criteria of desalin
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of energy storage or hybridization
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Desalination development focuses on
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Introduction of the indirect type s
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2 Literature Survey 2.1 Introductio
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There is actually a commercial prod
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Q m H c ( T T1) c ( T 2 T ) (2.2)
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(solid-liquid) have a storage densi
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(iii) a sharp melting temperature.
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melt and freeze without segregation
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However, the stored heat is less va
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parameters on the heat transfer and
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categories. The first category is b
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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
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 104 and 105: where G=ρU d /ε g is the pore mas
Page 106 and 107: k k eff s 1 3 2 (4.55) This cor
Page 108 and 109: uncertainties associated with the f
Page 110 and 111: 1 2 (4.62) d1 capp c2 c1 c2 1
Page 112 and 113: [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
Page 120 and 121: that form the study logical foundat
Page 122 and 123: 5 Experimental Analysis This chapte
Page 124 and 125: 5.2 Measuring Techniques K-type the
Page 126 and 127: The product condensed water was mea
Page 128 and 129: 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
Page 138 and 139: within the inaccuracy margins. The
Page 140 and 141: The last two cases of boundary cond
Page 142 and 143: natural air flow in the system. In
Page 144 and 145: 6 Model Implementation and Validati
Page 146 and 147: x t u x u 0 0 , (6.5) and for a s
Page 148 and 149: Next time step validation were the
Page 150 and 151: 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
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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
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Equation (C.7) represents an overal
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Appendix D D1. Cooling tower theory
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A m w = the plan or cross sectiona
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