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

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(solid–liquid) have a storage density in the order of 0.1 MWh/m 3 [103]. This study now focuses on solid/liquid phase change materials that have a characteristic melting temperature in the range 40-90 °C. 2.6 Classification of Phase Change Materials Phase change materials are classified into two main categories; organic compounds and inorganic (salts), figure (2.2a) shows a classification of existing materials which can be used for thermal energy storage. Figure (2.2b) gives an overview on different phase change storage materials and sorts them according to their melting temperature and latent heat of fusion. More detailed description of the properties of these materials are given below. (a) According to type of thermal energy storage media [93] (b) According to melting temperature and heat of fusion (ZAE Bayern) Figure 2.2: Classification of energy storage materials 19
As the thermal and chemical behaviour of each subgroup is greatly different, the properties of each subgroup are to be discussed in some detail. However, these PCM to be used in the design of thermal storage systems should exhibit certain desirable thermo physical, kinetic, and chemical properties, which are listed in frame (1). In addition, economic competitiveness and large-scale availability of these materials should be considered. 2.6.1 Organic Phase Change Materials Paraffins: Some of the more popular and easy to use products are various paraffin and these can be made with melting points between – 20 °C and 120 °C [103]. Paraffins are non-toxic, ecologically harmless, and chemically inert to nearly all materials, and this means that there will be no corrosion in energy storage systems. Paraffin waxes are normally mineral oil products of type C n H 2n+2 , which are a family of saturated hydrocarbons with very similar properties. Paraffins between C 5 and C 15 are liquids, and the rest are waxy solids. They consist of a mixture of mostly straightchain paraffins, or normal alkanes, their melting temperatures are strongly influenced by the length of the chain of the alkalis, and ranges between 23 and 67 °C [97]. Generally, the longer the average length of the chain, the higher the melting temperature and heat of fusion [96]. Numerous investigations show that paraffin waxes present many desirable characteristics of a PCM for heat storage purposes such as: (i) High heat of fusion, good self-nucleating properties, and no tendency of phase segregation on melting (ii) Chemically stable, safe, and non-reactive, good kinetic properties for the phase transition, therefore only a low or no supercooling effect (iii) Compatible with all metal containers and easily incorporated into heat storage systems. Care however should be taken when using plastic containers as paraffins have a tendency to infiltrate and soften some plastics [99] (iv) Easily available commercially from many manufacturers in various grades with reasonable prices However, the main drawbacks are equally addressed as: (i) Low thermal conductivity in solid state, which presents a problem when high heat transfer rates are required during the freezing cycle. Therefore, special considerations are required for the heat exchanger in order to overcome this problem. The most sound solutions to enhance the thermal conductivity of paraffins are to use finned containers and metallic fillers or through combination latent/sensible storage systems [100]. Aluminum honeycombs has been found to improve system performance [86]. (ii) In addition, pure paraffin waxes are very expensive therefore economics only permit the use of technical quality paraffin waxes, which do not have 20
Page 1: Technische Universität München In
Page 4 and 5: It is my pleasure to thank Prof. Th
Page 6 and 7: Contents List of figures ..........
Page 8 and 9: 5.3 Functional description ........
Page 10 and 11: List of Figures Figure 1.1: Cost br
Page 12 and 13: 78cm; Top: Evaporator, Bottom: Cond
Page 14 and 15: xii
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 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 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
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the air pressure drop ∆P per unit
Page 92 and 93:
evaporation rate per unit volume of
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where β t , β c , ρ ref , c ref
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the viscous transport and introduce
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liquid and solid phases, respective
Page 100 and 101:
4.2.3.3 Liquid and gas hold-ups Liq
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Several models and approaches for m
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where G=ρU d /ε g is the pore mas
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k k eff s 1 3 2 (4.55) This cor
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uncertainties associated with the f
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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
Page 118 and 119:
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
Page 136 and 137:
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
Page 172 and 173:
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
Page 220 and 221:
Appendix D D1. Cooling tower theory
Page 222 and 223:
A m w = the plan or cross sectiona
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