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

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1 2 (4.62) d1 capp c2 c1 c2 1 H m dT (4.63) k k k k (4.64) 1 2 1 2 In equation (4.63), c app denotes the specific apparent heat capacity and ΔH m the specific latent heat for change from phase 2 to phase 1, which are determined according to the specific enthalpies of phases 1 and 2, respectively. If the phase transition takes place instantaneously at a fixed temperature, then a mathematical function such as: T t U T (4.65) 1 is representative of the volumetric fraction of the phase 1, where U is a step function whose value is zero when T
fixed temperature by a gradual change over a small temperature interval should be acceptable if (2∆T t )/ (T i -T s ) < 0.1. Through the use of Equation (4.63), the transient model is applicable anywhere in the storage medium. This model removes the necessity of tracking the moving phase change boundary and generally simplifies the numerical solution. 4.5 Macro-dynamic performance analysis of the HDH system 4.5.1 Cooling tower performance In comparison with the two phase flow in the PCM-packed columns (i.e. the evaporator and condenser), the energy balance for a conventional cooling tower which is packed with nonconductive media doesn’t include the solid sub-domain. Thus, this results in two energy balance equations for both liquid and gas phases instead of three for the case of PCM packing. Though the cooling tower theory is basically different from the developed mathematical modeling approach, it is indeed useful for defining and identifying the crucial indicative parameters for addressing the system performance. Since operation and design theory of evaporative coolers and direct contact condensers is closely related, these parameters can serve both of them. The practical theory of cooling towers operation was, perhaps, first developed by Merkel [54]. This theory has been presented and discussed in detail throughout numerous heat and mass transfer textbooks as the basis of most cooling tower analysis and design rating. Appendix (D) covers the theoretical development and analysis of Merkel’s equation, which is extremely important to develop a common understanding of the performance measures in the subsequent discussions. 4.5.2 Humidifier efficiency The performance of a humidification column can be evaluated by Braun's [58] effectiveness model for a counter flow cooling tower. This model was based on Merkel's assumptions which neglect the effect of the water loss due to evaporation and set the Lewis number to unity. Braun defines air-side effectiveness, ζ a as the ratio of the actual heat transfer to the maximum possible air-side heat transfer that would occur if the exiting air stream were saturated at the temperature of the inlet hot water (i.e., h a2 = h s,w2 with reference to figure (4.1) for the present study); Qg, actual Q evap (4.69) Qg,max imum mg h g, actual s, w2 hg1 evap where h s,w2 is the saturated air enthalpy at inlet water conditions, and h a1 is the enthalpy of the inlet air. Analogously to a dry counter flow heat exchanger, Braun 92
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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
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The enthalpy and humidity of the sa
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Air mass flow rate [kg/h] GOR [-] 1
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On the other hand, the efficiency o
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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
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 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
Page 152 and 153: Figure 6.2: Evolution of inlet and
Page 154 and 155: Figure 6.4: Evolution of inlet and
Page 156 and 157: temperature is at its maximum level
Page 158 and 159: 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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