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

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1 exp NTU 1 C r, cond cond (4.74) 1 Cr, cond If the heat capacity flow of the gas phase is lesser than that of the liquid phase, then: C C C m C min g s, cond r, cond (4.75) Cmax mcw cw h h s, w4 s, w3 s, cond (4.76) T w4 Tw3 where h s,w3 and h s,w4 are the enthalpies of saturated air at inlet and exit water conditions respectively. The maximum heat and mass transfer and humidity change would be achieved when air is cooled down to the inlet cooling water temperature. In this idealized situation, the partial vapor pressure of the air at the outlet is equal to the saturation pressure of the liquid solution at the inlet of the column. 4.5.4 Productivity factor (PF) This factor is a measure of how much condensation rate can be gained per unit mass transfer potential (K i A) in the evaporator or condenser. It is defined as [62]: PF M d M d 1 (4.77) K A M NTU i a where M d and M a are the distillate rate and air mass flow rate (kg.s -1 ) respectively, K i is the mean value for the overall mass transfer coefficient between water and air based on the enthalpy difference (kg.m -2 .s -1 ), and A is the mass transfer surface area associated with K i in m 2 . 4.5.5 Efficiency of the solar collector The instantaneous overall energy balance of the solar water heater (which comprises a solar flat plate collector (FPC) and a thermal buffer) is an important consideration in the numerical prediction of the HDH system’s thermal performance. The performance of the FPC is estimated using an empirical relation available in the literature [59] as a function of the inlet water temperature to the collector T 7 , the incident global solar irradiation I incident, and the ambient temperature and: 95
T T amb col 0.60 0.0078 7 (4.78) Iincident The above efficiency includes the heat losses through the connecting pipes and the flow mal-distribution in the collector absorber due to low water flow rate used [2]. The FPC efficiencies available in the market nowadays are usually higher than those given by equation (4.78). However, this might provide conservative values of fresh water production, especially as this equation was developed under the climatic conditions of Jordan in the Middle East. Like any kind of energy conversion devices, the efficiency of a solar collector resembles the ratio between the rate of thermal energy extracted by the working medium (usable output heat) Q u and the incident solar irradiation I incident (W.m -2 ) crossing the aperture area (A col ) of the collector: Q Q u u col (4.79) Q IincidentAcol in, col The rate of input thermal energy through the solar collector determines the inlet temperature to the thermal buffer T w8 (i.e. the outlet water temperature from the FPC) under transient conditions: Q in, col col col incident hw w w8 w7 A I M c T T (4.80) 4.5.6 Energy balance on heat exchangers For both heat exchangers involved in the HDH process as depicted in figure 1 (i.e. the brine heater and water cooler in the condenser closed cycle) the energy balance calculations follow the same approach as Polifke and Kopitz [60]. In both cases a countercurrent regime is chosen due to its high effectiveness. In fact the brine heater has a direct influence on the recovery rate of latent heat of condensation while the water cooler has a high influence on the condenser performance. Moreover, the two heat exchangers implicitly have mutual influences on each other. In the brine heater, the margin between the outlet hot stream temperature and the outlet cold stream temperature (T w9 -T w7 ) is assumed to be 3K for simplification. For the water cooler, the temperature of the fresh cold water at the top of the condenser is not allowed to be more than (T amb +3)K. Thus, the design of the heat exchangers is confined in determining the maximum heat transfer surface area on yearly basis under transient operation conditions: 96
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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
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 110 and 111: 1 2 (4.62) d1 capp c2 c1 c2 1
Page 112 and 113: [58] evaluated the cooling tower ai
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
Page 160 and 161: 7 Parameters Analysis of the Evapor
Page 162 and 163: 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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