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

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were; EnviPac Gr.1, 32 mm, and VFF plastic Pall-Rings 25 mm. Based on a parametrical study, Lex [143] summarized the results and design recommendations in table (2.1). Figure 2.13: Representation of multi effect of heating and humidification by Chafik [155] on the psychometric chart Figure 2.14: Specific water cost produced by the solar HDH desalination unit by Chafik [155] 43
The optimal value of feed water temperature was recommended as 85°C which also was confirmed in numerous preliminary tests for yielding optimal evaporation ratio at reduced calcination and gypsum formation effects. This range of water temperatures would enable using economical materials like polymers in construction of the units. As secondary effect the costs stay low. The following figures (2.15) and (2.16) show temperature and evaporation rate dependency over the filling height of 300 mm for EnviPac at different brine temperatures, different inlet air temperatures, and a mass flow of 360 l/h. The dashed line delineates the evaporator outlet air temperature, hence temperature levels decrease over the evaporator outlet. Local temperature minima at a filling height of 200 mm depicts a local maximum in evaporation. Air develops a mass flow of 0,05 kg/s with an entrance relative humidity of 25 % and an outlet relative humidity of 95 %. Table 2.1: Design parameters range of AQUASOL II [143] Parameter Range Height of packing (H) 300 mm Interfacial area main factor to increase vapor production Distribution system nozzles Brine inlet temperature 85 °C For the temperature range given in this application a height of 300 mm was found to be ideal under natural draft operation. The irrigated area is variable and can be used as parameter to increase the humidity ratio in the exit air and hence its velocity. Indeed, the problem of pressure loss is evident and is leading to an optimum in filling height. The diagram in figure (2.16) shows the evaporation rate [l/h] at different filling heights with EnviPac filling material. It can be shown, that in this case, an optimum is achieved at 300 mm. These results reveal that free convection air flow in HDH units is very sensitive to the permeability of the bed. However, optimal filling height under forced convection with the same packing material would be significantly higher than with natural convection discussed above, as pressure loss may not be one of the main governing factors in the overall heat and mass balance. It was reported that the distribution system was the main problem of the evaporation over the packed bed. The shower heads didn’t show good results, the nozzles had good results in front of uniform irrigation. Against fouling and crystallization out of sea water they won’t have a satisfying comportment in continuous use. The gutter distribution would have better properties in this point, but its fabrication cost was high. The realized distribution was irrigation by nozzles. 44
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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
Page 12 and 13: 78cm; Top: Evaporator, Bottom: Cond
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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 50 and 51: 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 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
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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
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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
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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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