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

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There is actually a commercial product based on zeolite/water adsorption available, also in Germany, namely self-cooling bear kegs. The user just turns a handle and waits for about ten minutes. Then he/she can serve 20 liters of cold beer to guests. The empty kegs are returned to the factory, recharged by heating, and filled with beer again. Air humidification/cooling and dehumidification/heating are being used to cool the bear glasses and recharge the empty kegs, respectively. Since its introduction in 2001, about 20,000 kegs are in regular use [105]. Thermochemical reactions have the potential to store up to 1 MWh.m -3 , depending of course upon the actual reaction [103]. However, they are more complex than other thermal energy storage systems, and still in the development phase, but they are also more flexible [98]. 2.4 Sensible heat energy storage (SHES) In sensible heat storage (SHES), temperature of the storage material varies with the amount of heat energy stored. SHES system utilizes the heat capacity (c) and the change in temperature ΔT of the material during charging and discharging processes. The amount of stored heat depends on specific heat of the medium, the temperature change, and the amount of storage material. T 2 Q m. c. dT (2.1) T 1 Most SHS use water, stone, iron, earth, or ceramic bricks as the thermal storage material, and air, water, or oil as the heat transfer fluid. The high heat capacity of water often makes water tanks logical choice for thermal energy storage systems that operate in a temperature needed for heating and cooling applications, but the low density of water requires large volumes. In desalination technology, water storage tanks are highly recommended for 24 hours operation of humidificationdehumidification solar desalination units [87]. The relatively low heat capacity of thermal storage materials such as rock and ceramics is somewhat offset by the large temperature difference possible by these materials and their relatively high densities [88]. 2.5 Latent heat energy storage (LHES) 2.5.1 Concept of Phase Change Energy Storage The latent heat storage (LHES) or phase change materials (PCM) absorb and release heat as it undergoes a change in phase from solid to solid, solid to liquid or 15
liquid to gas or reverse. The phase change involved takes place without a change in the temperature of the material itself. Figure (2.1) depicts the mechanisms of heat absorption and release in LHES materials. During the heat transfer to the solid phase, as long as the matrix structure is strong enough to stand the rising kinetic energy due to the higher oscillation amplitude of each element in the matrix; the matrix structures does not change and the change of internal energy can be monitored by a rise of temperature. Therefore, initially solid-liquid PCM perform like conventional storage materials; their temperature rises as they absorb heat, then change has yet a sensible component. At the melting point there is a change to the next higher level of entropy, the binding forces in the matrix are no longer strong enough to stand the risen kinetic energy of its elements. As the temperature of the PCM rises, their chemical bonds break up gradually as the material changes phase from solid to liquid. The phase change is a heat seeking (endothermic) process and therefore, the PCM absorbs large amount of heat without getting hotter, i.e. while storing heat, the temperature of the PCM stays nearly constant until the melting process is completed. (a) (b) Figure 2.1: Phase change behavior of solid-liquid latent heat storage systems; (a) melting at a sharp point, (b) melting over a temperature range The energy stored during the phase change process is called “latent heat” or “heat of fusion”. As the materials cool off (at night or on cloudy days) they subsequently release the stored heat while solidifying in the same fashion. The storage capacity of the LHES system with a PCM medium is defined by the following equation: Q T T 1 2 cs( Tm T1) mH m cl ( T2 Tm ) m T T m 16
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 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 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
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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
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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
Page 152 and 153:
Figure 6.2: Evolution of inlet and
Page 154 and 155:
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
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
Page 200 and 201:
[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
Page 218 and 219:
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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