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

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Evaporator Condenser Figure 5.8: Average inlet and outlet liquid and gas temperatures for experiment case (1), Left: Evaporator, Right: Condenser 5.5.2 Comparison between conductive and non conductive packing Overall comparative distillate output for the two packing types under similar boundary conditions for an operation period of two hours after reaching steady state are shown in figure (5.10). For the higher level of packing height as shown in figure (5.10a), the positive impact of conductive packing (PCM beads) on the productivity can be seen more clearly in the first and fourth cases of boundary conditions (i.e. first and fourth case from the left hand side on figure 5.10 or as listed in table 5.2). Both of them have a higher inlet water temperature (83 ºC). The first set has higher inlet mass flow rate of water (500 l/h) to the evaporator, and higher air velocity (0.55 m/s) while the fourth set has the lower levels of both inlet water mass flow (250 l/h) and air velocity (0.23 m/s) in the system as pointed out earlier. In the first case, there are both good direct contact diffusion and MEHH in the PCM system, which results in 14.5% higher distillate rate than the empty packing system. The fourth case of boundary conditions (case of low water mass flow rate, low air velocity, and high inlet water temperature) is more interesting. We can not see 117 --
any effect of PCM at the lower packing height as shwon in figure (5.10b), while the PCM system productivity enhancement reaches its maximum value amongst all several sets of experiments at the higher level of packing height. Figure 5.9: Evolution of productivity and GOR for PCM and Empty balls packing elements In this case, direct contact diffusion is drastically damped due to the lower levels of both inlet water mass flow (less wetted and interfacial areas, see equations 4.46 and 4.47) and air velocity (i.e. less mass transfer coefficient at the interface, see equation 4.49). The PCM system acheives 42.9% higher distillate rate than the empty packing system. When decreasing the packing height by 50% as in figure (5.10b) for both first and fourth sets of boundary conditions, the difference in productivity between PCM and empty packing systems nearly vanishes since the number of PCM layers (i.e. the number of effects) is also decreased by 50%, which hinders the MEHH. The second set of boundary conditions is another example of the trade-off between the direct latent and sensible heat transfer at different interfaces. At the high packing heigt, lowering inlet hot water mass flow rate to 250 l/h has a negative impact on the PCM compared to the empty packing system due to the cooling effect in the lower part of the bed, which has been illustrated qualitatively in figures (5.4) and (5.5). This negative impact turns out to be positive at the lower packing height under same conditions, where the cooling effect is avoided by lowering the packing height. In contrast, GOR values are nearly the same 118 --
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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
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distillate rate. The system was not
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were; EnviPac Gr.1, 32 mm, and VFF
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Figure 2.15: Height versus air temp
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The performance of the condenser is
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Klausner and Mei [136] described a
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The impact of the collector cost ca
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exchanger and energy storage in one
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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
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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
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 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 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
Page 160 and 161: 7 Parameters Analysis of the Evapor
Page 162 and 163: Figure 7.1: Effect of packing size
Page 164 and 165: e 0.45 kPa under natural convection
Page 166 and 167: 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
Page 178 and 179: 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
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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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