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

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The energy flow between all and each pair of phases plays the major role in plotting the system behavior under each specific boundary and geometrical conditions. These particular characteristics have to be seen as the basic concept proposed in the present study for improving the performance of the HDH cycle. The main advantages of integrating a conductive packing media in the HDH cycle can be summarized in the following points: • High heat and mass transfer surface area per unit volume • Self establishment of MEHH and MECC locally • Air collector is not required • Extension of the external heat storage capacity 3.4 Concept of Multi-Effects of Cooling and Condensation (MECC) In the suggested PCM condenser, the physical phenomenon of direct contact condensation is characterized by the transport of heat and mass through the gas (i.e. humid air)-liquid interface as well as across the dry patches at the gas-PCM (or gas-solid) interface along the packing height. Due to continuous cooling of PCM elements by the subcooled liquid layer, supplementary cooling and condensation take place at the gas-solid interface simultaneously with that at the gas-liquid interface; as a result, heat and mass transfer rates are enhanced. Since axial stratification occurs entirely in all involved phases, the phase temperature is a function of distance and hence the PCM temperature profile plays an important role in the condenser performance. However, unlike the evaporator, the gas phase remains saturated at local temperatures throughout the MECC process since the condensation process takes place at both gas-liquid and gas-solid interfaces. 3.5 Study objectives and methodology In order to solve the problems discussed in the literature concerning the continuous operation of the solar-driven HDH plants round the clock and the problems associated with achieving the MEHH as explained above, investigation of an innovative solution shall be the main task of the present work. Here, in both evaporator and condenser, a porous package of spherical filling material shall be applied yielding similar flow behaviour. In order to guarantee an enhanced thermal performance, the new system consequently is using internal heat exchangers as filling material for evaporator and condenser. These materials for the first time will be integrated in a thermal desalination process. In the framework of the present study, a new evaporator and condenser technology for solar humid air distillation incorporating conductive media such as PCM storages shall be examined. 61
The major objective of this study is to examine the innovative approach for locally creating MEHH and MECC and to determine the technical and economic feasibility of applying conductive components in HDH cycle and PCM storage in solar desalination plants under both steady state and transient operation conditions. The study follows two main parallel lines through conducting comprehensive experimental analysis and numerical investigations on the PCM-supported HDH system. The main goals and scope of work to achieve the objectives of the study is as follows: A mixed micro-macro balance transient simulation model will be established and validated against experimental measurements using COMSOL Multiphysics and MATLAB for solving fluid flow and heat and mass transfer phenomena in one spatial dimension for different components in such a loop. The model is desired to be fairly general and simple, yet sufficiently accurate to be applied as a design and optimization tool for HDH plants integrated with different types of thermal storage systems. The thermal behavior of the new evaporator and condenser technology in the closed air loop distillation unit incorporating conductive packing under steady state conditions shall be discussed and analyzed both experimentally and numerically. Influence of using PCM and Non-PCM packing candidates on the plant performance has to be compiled and an optimal solution has to be integrated into the process. Effect of various influencing independent parameters on individual components and HDH plant performance and productivity will be investigated. The dynamic performance of the humid air distillation unit integrated with the PCM-thermal storage and solar flat plate collector will be discussed and analyzed. Comparative performance of HDH system is focused and clearly documented using PCM and water as a thermal storage media in the external thermal storage over a wide range of operation conditions. The overall analysis will be performed under real varying weather conditions over one year for a selected geographical location in Egypt. Special attention shall be paid to the heat recovery mechanisms and optimum coupling of the external thermal storage with the HDH cycle. Finally the numerical simulation model will be used to optimize the design characteristics of a small-scale HDH module with a production capacity of 1 m 3 /day. 62
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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
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 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 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 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
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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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