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

More documents

Recommendations

Info

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
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 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
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
Page 164 and 165:
e 0.45 kPa under natural convection
Page 166 and 167:
aspect ratio under constant bed vol
Page 168 and 169:
Figure 7.7: Effect of inlet hot wat
Page 170 and 171:
well as the time required to reach
Page 172 and 173:
Figure 7.10: Effect of packing medi
Page 174 and 175:
40°C respectively. This gives flex
Page 176 and 177:
the condensate rate, productivity f
Page 178 and 179:
esult, rather than PCM media which
Page 180 and 181:
Figure 7.18: Effect of PCM thermal
Page 182 and 183:
8 Optimization of HDH plant In this
Page 184 and 185:
The MATLAB model describes how the
Page 186 and 187:
less steep than that of the distill
Page 188 and 189:
8.3.4 Effect of hot water flow rate
Page 190 and 191:
storage materials and thus it can h
Page 192 and 193:
for latent heat storage would be ob
Page 194 and 195:
When T m becomes sufficiently highe
Page 196 and 197:
9 Summary and conclusions 9.1 Summa
Page 198 and 199:
productivities at any cooling water
Page 200 and 201:
[13] Vafai K., Sozen M. An investig
Page 202 and 203:
[48] Crone S., Bergins C., and Stra
Page 204 and 205:
[79] Tiwari G.N. and Yadav Y.P. (78
Page 206 and 207:
[109] Mehling H., Hiebler S. and Zi
Page 208 and 209:
[139] Belessiotis V, Delyannis E (2
Page 210 and 211:
Appendices Appendix A A1. PCM Therm
Page 212 and 213:
A3. Constants and Thermo-physical p
Page 214 and 215:
From the above correlation, the con
Page 216 and 217:
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
show all

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

Create successful ePaper yourself

Delete template?

Save as template?