• Share
  • Email
  • Embed
  • Like
  • Save
  • Private Content
343 s k sukla
 

 

Statistics

Views

Total Views
176
Views on SlideShare
168
Embed Views
8

Actions

Likes
0
Downloads
8
Comments
0

1 Embed 8

http://www.ese.iitb.ac.in 8

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

    343 s k sukla 343 s k sukla Presentation Transcript

    • by Dr. S.K.Shukla Department of Mechanical Engineering Indian Institute of Technology, Banaras Hindu University Varanasi– 221005, India December 10, 2013 IIT Banaras Hindu University 1
    • Outline  Technology  Literature Options review of PCM Storage  Theoretical Analysis  Experimental  Results and discussion  Conclusions  Publications December 10, 2013 2
    • Solar Energy & Technology Advances December 10, 2013 Banaras Hindu University 3
    • Energy Storage in Solar Process system  The solar energy resource is suffering from some obstacles to become reliable and suitable energy resource. The main obstacle in the character of solar energy, it is intermittent energy or it dependent on time. To eliminate the mismatch between energy supply and energy demand, it is necessary to store the energy. Thus, the energy storage device plays an important role in conserving the energy and also enhances the system by reducing the losses energy. Thermal energy storage can provide the energy to system at any time. Therefore, the thermal energy storage is a vital role in any solar energy system. There are two methods in which solar thermal energy can be stored. This methods are : December 10, 2013 Banaras Hindu University 4
    • Sensible Heat Storage  Sensible heat storage is stored the heat by rising (increasing) the temperature of material and release it after the temperature of material is low. Also no change of phase is happen during the stored process. The amount of sensible heat storage depends on the ability of a material to store heat (heat capacity) and the mass of material. In equation form: 1   Cp is the specific heat of the material (kJ/kg oC), T1 is the initial temperature(oC) and T2 is the final temperature(oC). it is clear from eq. (1) the quantity of store also depends on the temperature change and in addition to Cp and m. several material such as stone, rock , water etc. have been used in storage system. December 10, 2013 Banaras Hindu University 5
    • Latent Heat Storage    This is the storage that it using phase change of material to absorb or release heat. This heat is named latent heat of material. Materials used for their thermal storage capacity as latent heat are called phase change materials (PCM’s). The term ‘’latent heat storage’’, as we generally understand it today, applies to the storage of heat as the latent heat of fusion in suitable substance that undergo melting of freezing at a desired temperature level (Beghi, 1982). The amount of the energy stored as latent heat by a material is in equation form 2    Where Ql is the quantity of stored latent heat (kJ), ‘m’ is the mass of material (kg) and λl is the latent heat of phase change. Thus is clear from eq. (2) the energy storage depend on ‘m’ and λ l. December 10, 2013 Banaras Hindu University 6
    • Comparison between Sensible and Latent Thermal Energy Storage  One of the important characteristics of a storage system is the length of time during which energy can be kept stored with acceptable losses. Another important characteristic of a storage system is its volumetric energy capacity, or the amount of energy stored per unit volume. The smaller the volume, the better is the storage system. Therefore, a good system should have a long storage time and a small volume per unit of stored energy (Ataer).  A general discussion on sensible heat storage and latent heat storage. However, sensible heat storage suffers a disadvantage in energy storage density. Comparison between the two methods of heat storage is revealed in Table 1. December 10, 2013 Banaras Hindu University 7
    • Table 1 Comparison between the different methods of heat storage (Hasnain, 1998) Property Rock Water Organic PCM Inorganic PCM Density, kg/m3 2240 1000 800 1600 4.2 2.0 2.0 Specific heat, kJ/kg 1.0 Latent heat, kJ/kg – – 190 230 Latent heat, kJ/m3 – – 152 368 67,000 16,000 5300 4350 30 16 6.6 2.7 15 4 1.25 1.0 11 6 2.5 1.0 Storage mass for 106 J, kg Storage volume for 106 J, m3 Relative storage mass Relative storage volume December 10, 2013 Banaras Hindu University 8
    • The main advantages of phase change storage in comparison to conventional water storage techniques are: Higher thermal energy storage capacity (smaller storages) than sensible energy Storage, at least if only small useful temperature differences can be achieved. Relatively constant temperature during charging and discharging. The CO and HC emissions can be reduced. December 10, 2013 Banaras Hindu University 9
    • Phase Change Material (PCM) Abhat (1983) gave a useful classification of the materials used for thermal energy storage, shown in fig. 3. The different applications of the phase change material as heat storage , also the property, the useful life of PCM and various experimental techniques was reviewed by (Abhat, 1983; Farid et al., 2004). December 10, 2013 Banaras Hindu University 10
    • Fig. 3. Classification of energy storage materials (Abhat, 1983) December 10, 2013 Banaras Hindu University 11
    • Thermo physical properties The Important characteristics of energy storage materials: Thermal properties: phase change temperature fitted to application, high change of enthalpy near temperature of use and high thermal conductivity in both liquid and solid phases (although not always).  Physical properties: low density variation, high density small or no subcooling.  Chemical properties: stability, no phase separation, compatibility with container materials Non-toxic, nonflammable and non-polluting.  Economic properties: cheap, abundant. December 10, 2013 Banaras Hindu University 12
    •  A comparison of the advantages and disadvantages of organic and inorganic materials is shown in Table 2(Luisa et al., 2005). Among the organic materials, fatty acids mostly used for storage system. Fatty acids have superior properties over many PCMs such as melting congruency, good chemical stability and nontoxicity. The exploited of fatty acids, such as Myristic Acid and Lauric Acid, as phase change materials, was studied by (Sarı and Kaygusuz, 2002; Sarı, 2003). Table 2: Comparison of organic and inorganic materials for heat storage. Organics Inorganics Advantages Advantages - No corrosives - Greater phase change enthalpy - Low or none under cooling - Chemical and thermal stability Disadvantages Disadvantages - Lower phase change enthalpy - Subcooling - Low thermal conductivity - Corrosion - In flammability - Phase separation Organic and inorganic materials stability - Phase segregation, lack of thermal December 10, 2013 Banaras Hindu University 13
    • Long term stability  The weak stability of PCM is caused due to two factors: poor stability of the material properties due to thermal cycling and corrosion between the PCM and the container. Stability of the PCM-container system The fatty acids investigated as PCMs have a good thermal stability as a function of latent heat and phase transition temperature range for an actual middle-term thermal energy storage utility(Sarı and Kaygusuz, 2003). Sari(2003) showed that the fatty acids had a good thermal reliability in view of the latent heat of fusion and melting temperature with respect to thermal cycling for thermal energy storage applications in the long term, some fatty acids of interest to low temperature latent heat thermal energy storage applications and are tabulated in Table 4.. Corrosion of the materials  Most organic PCMs are non-corrosive but inorganic which suffer from corrosive which can affect their phase change properties. Inorganic mainly include hydrate salts which is their tendency to cause corrosion in metal containers that are commonly used in thermal storage systems (Abhat, 1983). December 10, 2013 Banaras Hindu University 14
    • PCM selection By using fatty acid material summaries from a literature review (Sharmaet al., 2009) with materials from the manufacturers (National Chemicals ), which are available in market. Therefore the Lauric and Myristic acid was selected as a PCM for storage system . Table 3 Melting point and latent heat of fusion: fatty acids December 10, 2013 Banaras Hindu University 15
    • Myristic and Lauric acid Properties One of the major obstacles facing phase change material thermal storage design are the lack of readily available material property information. The Lauric acid and Myristic acid relate to the class of fatty acids that have superior properties such as melting congruency, good chemical stability and non-toxicity, good thermal reliability over many other PCMs [Sarı, 2003]. Therefore, lauric and myristic acid have been used as a latent heat storage material due to its low cost and easy availability. Table 4 summarizes the thermo-physical properties of Lauric and Myristic acid[Sharmaet al., 2004]used in the experimentation. The measurement of property of PCM was done by Netzsch Technologies India Pvt. Ltd., using the differential scanning calorimetry (DSC) technique as revealed in Figs. 4 and 5 for Lauric acid and Figs.6 and 7 for Myristic acid. December 10, 2013 Banaras Hindu University 16
    • Table 4: Thermo-physical properties of Myristic and Lauric acid S.No. Properties lauric acid myristic acid 1 Melting point 40-43.9 oC 2 Latent heat of fusion 180kJ/kg 50-54 ℃ 177.6kJ/kg 3 Thermal conductivity 0.16 Wm-1 oC -1 0.25 Wm-1℃-1 4 Specific heat solid liquid 5 2.1 kJkg-1 oC -1(@25 oC) 3 kJ kg-1 oC -1(@44oC) [Buddhi, et al., 1987] 1.7kJkg-1℃-1(@35oC) Density solid 1007 kg/m3 990 kg/m3 liquid 862 kg/m3 861 kg/m3 2.42kJkg-1℃-1(@70oC) December 10, 2013 Banaras Hindu University 17
    • Fig. 4. DSC curve for melting temperature and heat of fusion for Lauric acid. December 10, 2013 Fig. 5. DSC curve for specific heat of Lauric acid Banaras Hindu University 18
    • Fig. 6. DSC curve for melting temperature and heat of fusion for myristic acid. December 10, 2013 Fig. 7. DSC curve for specific heat of myristic acid. Banaras Hindu University 19
    • Theoretical Analysis In conventional solar still, solar radiation passes through the glass cover, then it is absorbed by the water basin and black plate of water basin, later on heat transfers from black plate to the other parts inside solar still using different modes of heat transfer such as, radiation, evaporation, condensation, conduction and convection. One of the important steps in thermal analysis is, it draws the system and assume the assumptions. A schematic diagram of solar still with and without PCM and thermal resistance networks are shown in fig.8. and fig. 9. December 10, 2013 Banaras Hindu University 20
    • Theoretical Analysis Mathematical Model The following assumptions have been made in order to write the energy balance equations ;  Solar still distillation unit is vapor-leakage proof.  The conduction of heat transfer mode is between PCM and basin liner.  The temperature gradient through PCM is negligible. It means Tpcm represents average temperature through the PCM chamber.  Temperature gradients in the water are neglected.  The heat conduction between PCM and liners is 1-D.  The experiments are carried out under atmospheric pressure.  Condensate is not a thermal resistance to heat flows through the glass cover, etc. December 10, 2013 Banaras Hindu University 21
    • Fig. 8. A schematic diagram of a single slope solar still without PCM (A) and thermal resistance network of the still part (B). December 10, 2013 Banaras Hindu University 22
    • Fig. 9. A schematic diagram of a single slope solar still with PCM (A) and thermal resistance network of the still elements for the charging (B) and discharging (C) modes. December 10, 2013 Banaras Hindu University 23
    • Passive solar still without PCM Energy balance for outer surface of glass cover kg/Lg (Tgin- Tgo) = h2 (Tgo- Ta ) 1 Energy balance for inner surface of glass cover αg' I(t) + h1 (Tw- Tgin )=kg/Lg (Tgin- Tgo ) 2 Energy balance for water mass α'w I(t) + h3 (Tb - Tw )=mw Cw dTw/dt + h1 (Tw - Tgin ) 3 Energy balance for basin liner α'b I(t) = h3 (Tb - Tw )+hb (Tb- Ta ) December 10, 2013 4 Banaras Hindu University 24
    •  From eq(1) and eq(2) will obtain the eq of Tgo  Tgo= ( kg/Lg Tgin+h2 Ta)/( h2 + kg/Lg )  From eq(5) and eq(2) will obtain the eq of Tgin  Tgin = (α'g I(t) +h1 Tw + Uga Ta )/(Uga+h1 )  From equation (4) can find Tb Tb= ( α'b I(t)+ h3 Tw +hbc Tpcm )/(h3+hb ) December 10, 2013 Banaras Hindu University 5 6 7 25
    •  From equation (6) and equation (7) and put both in equation (1) can find  dTw/dt + a Tw= f(t) 8  The solution of eq.(8) can be obtained using integration factor with boundary condition when t=0 that Tw = Two thus :  Tw =(f(t) /a ) * [1- exp(-a*t) ]+ Two exp(-a*t) 9 Where, f(t) is the average value of f(t) for time interval 0 to t. December 10, 2013 Banaras Hindu University 26
    • The still with the PCM charging mode        Energy balance for inner surface of glass cover αg' I(t) + h1 (Tw- Tgin )=kg/Lg (Tgin- Tgo ) 10 Energy balance for outer surface of glass cover kg/Lg (Tgin- Tgo) = h2 (Tgo- Ta ) 11 Energy balance for water mass α'w I(t) + h3 (Tb - Tw )=mw Cw dTw/dt + h1 (Tw - Tgin ) 12 Energy balance for basin liner December 10, 2013 Banaras Hindu University 27
    •  α'b I(t) = h3 (Tb - Tw )+hbc (Tb- Tpcm )  Energy balance for phase change material PCM  hbc (Tb- Tpcm ) =(Mequ/Ab )(dTpcm / dt)+hb (Tpcm- Ta ) 13 14 Where hb= kins/xins is the back loss coefficient and Mequ is the equivalent heat capacity of the PCM. Mequ = mpcm Cs,pcm for Tb<Tmt , Mequ = mpcm Ls,pcm for Tb<Tmt+δ , Mequ = mpcm Cl,pcm for Tb>Tmt   From Eqs. (10) , (11) and (13), Tgo ,Tgin and Tb are obtained as: Tgo= ( kg/Lg Tgin+h2 Ta)/( h2 + kg/Lg ) December 10, 2013 Banaras Hindu University 15 28
    •  From eq(5) and eq(1) will obtain the eq of Tgin  Tgin = (α'g I(t) +h1 Tw + Uga Ta )/(Uga+h1 ) 16  Tb= ( α'b I(t)+ h3 Tw +hbc Tpcm )/(h3+hb ) 17   Substituting eq (16) and eq(17) and using eq(12) to find Tw dTw/dt + ac Tw= fc(t) 18  Eq(18) was solving by using integral factor with boundary condition, when t=0 that Tw = Two  Tw =(fc(t) /ac )* (1- exp(-ac*t) )+ Two*exp(-ac*t)  To find Tpcm ,it can that from eq(17) and eq(14)  Tpcm = (fc1(t) /ac1) * (1- exp(-ac1*t) )+ Tpcm*exp(-ac1*t) December 10, 2013 Banaras Hindu University 19 20 29
    • The still with the PCM discharging mode For selected time interval Δt, the energy balance equation for the PCM may be written as : mpcm Lpcm/Ab ∆t =hbd (Tpcm- Tb )+hb (Tpcm- Ta ) 21  for Tpcm=Tmt hbd (Tpcm- Tb)+ hb (Tpcm- Ta) = (Mequ/ Ab )(dTpcm/ dt) for 22 Tpcm≠Tmt where Mequ = mpcm Cl,pcm for Tpcm > Tmt , Mequ = mpcmCs,pcm for Tpcm < Tmt , hbd = kpcm/xpcm that is the conductive heat transfer coefficient from the PCM to the basin liner.  Energy balance for inner surface of glass cover  h1 (Tw- Tgin )=kg/Lg (Tgin- Tgo ) December 10, 2013 23 Banaras Hindu University 30
    •  Energy balance for outer surface of glass cover kg/Lg (Tgin- Tgo) = h2 (Tgo- Ta )  24 Energy balance for water mass h3 (Tb - Tw )=mw Cw dTw/dt + h1 (Tw - Tgin )  Energy balance for basin liner h3 (Tb - Tw ) = hbd (Tpcm- Tb )  25 26 From eq(24) will obtain the eq of Tgo Tgo= ( kg/Lg Tgin+h2 Ta)/( h2 + kg/Lg ) Tgin = (h1 Tw + Uga Ta )/(Uga+h1 ) December 10, 2013 27 28 Banaras Hindu University 31
    • Tb= ( h3 Tw +hbd Tpcm )/(h3+hbd ) dTw/dt + ad Tw= fd(t)  29 30 by solving eq. (30)with boundary condition, when t=0 that Tw = Two Tw =(fd(t) /ad ) *(1- exp(-ad*t))+ Two*exp(-ad*t)  31 To find Tpcm will find from eq. (29) in eq. (22) Tpcm = (fd1(t) /ad1 )* (1- exp(-ad1*t) )+ Tpcm*exp(-ad1*t) December 10, 2013 Banaras Hindu University 32 32
    • Productivity and efficiency of the solar still  The hourly and daily productivity of solar still is : mewh=hew (Tw- Tgin )/ γ  33 Where ϒ is the latent heat of vaporization mewd = ∑_24 hr mewh  34 The instantaneous efficiency of system is: ηi = hew (Tw- Tgin )/(I (t) )*100 % December 10, 2013 35 Banaras Hindu University 33
    • Heat transfer coefficient of single slope passive solar stills  The performance of a solar still depends on the values of convective and evaporative heat transfer coefficients  h1=hcw + hew + hrw  h1 = Total heat transfer coefficient from water to glass cover, W/m2 oC  hcw = c kf * Rafn/d  hcw  hew = 16.273*10-3*( hcw * (pw - pgin)/(Tw - Tgin))  hew  hrw = εeff * σ* ((Tw + 273.15)2 - (Tgin + 273.15)2) *(Tw - Tgin + 546)  hrw  h2 = hca + hra = 5.7 + 3.8*v  h2  h3 = 0.54*kw* Raf1/4 /xc  h3 36 37 Convective heat transfer coefficient from water surface to the glass cover, W/m2 oC 38 Evaporative heat transfer coefficient from water surface to the glass cover, W/m2 oC Radiative heat transfer coefficient from water surface to the glass cover, 39 W/m2 oC 40 Convective heat transfer coefficient from glass to ambient, W/m2 oC 41 Convective heat transfer coefficient from basin liner to water, W/m2 oC December 10, 2013 Banaras Hindu University 34
    • Numerical Computation  The variation of the evaporative heat transfer coefficient with temperature is highly nonlinear(Sharma and Mullick, 1991). The nonlinearity in radiation energy and water diffusion terms makes the equations difficult to solve explicitly. An iteration method is used to obtain the final solution(YUNG, and LANSING, 1982). The classical method of optimization has been used to solve the problem. On the other hand, if the optimization involves the objective function that is not stated as explicit function of the design variables, we cannot solve it by using the classical analytical method. In such case we need to use the numerical method of optimization for solution. For this purpose Newton Raphson Method has been chosen(Rao, 2010). The iteration process starts with a guess for all values of dependent variables (Majumdar, 2005).Two programs of ‘C’ language have been developed to find the predicted theoretical values from equations 4-35, first one is to calculate parameters ‘c’ and ‘n’ to find h cw with the help of Tw and Tgin observed data. These value have been used with the second developed program to calculate the productivity of solar still with and without PCM. The program executed by using parameter design of solar still with and without PCM as shown in table 5. December 10, 2013 Banaras Hindu University 35
    • Table 5. Design parameters of solar still with and without PCM Sl.no. Parameter Values, units Sl.no. Parameter Values, units 1 Ab 1, [m2] 10 Rw 0.05 2 Ag 1.1, [m2] 11 εg 0.95 3 αb 0.95 12 εw 0.95 4 αg 0.05 13 mw 30-50, [kg] 5 αw 0.05 14 mpcm 10-30, [kg] 6 Rg 0.05 15 Lins 0.05, [m] 7 h2 5.7+ 3.8 v,[W m-1oC-1] 16 Lb 0.002 [m] 8 Kg 0.035, [W m-2oC-1] 17 Kb 43, [W m-2oC-1] 9 Lg 0.004, [m] December 10, 2013 Banaras Hindu University 36
    • Experimental procedure A photograph and schematic of both the single slope solar stills with and without PCM (SSWPCM and SSWOUTPCM) at indoor and outdoor condition is given in fig. 10. and fig. 11. Fig.12 explains cross-sectional schematic side views of SSWOUTPCM and SSWPCM. The basin is fabricated from black painted 2 mm thick mild steel having an area of 1 m2 each. A vertical gap beneath the horizontal portion of the basin liner is provided to upload and/or unload the PCM through a PVC pipe which takes care of the volumetric expansion of the melting PCM as well. The operational and melting temperature of PCM, in fact, governs the applicability of different types of PCMs. December 10, 2013 Banaras Hindu University 37
    • Fig. 10. Photograph SSWOUTPCM (left) and SSWPCM (right) for indoor condition December 10, 2013 Banaras Hindu University 38
    • Fig. 11. Photograph SSWOUTPCM (left) and SSWPCM (right) December 10, 2013 Banaras Hindu University 39
    • Fig. 12. Cross-sectional schematic side views of SSWOUTPCM (A),SSWPCM(B). December 10, 2013 Banaras Hindu University 40
    • Indoor instrument  Indoor condition that uses two variac transformers are employed to vary the delivered power to the systems. Two ammeters and two voltammeters are used to measure the current and voltage respectively (see Fig.13). A temperature scanner (Altop Industries Ltd, India Sn.1005164, model ADT 5003) with resolution 0.1 oC has been used to record the temperature with k-type thermocouples in solar stills. December 10, 2013 Banaras Hindu University 41
    • Fig. 13. Photograph of the variac transformers with voltmeters and ammeter Variac Temperatur e scanner Digital voltmeter Digital ammeter Digital temperature December 10, 2013 Banaras Hindu University 42
    • Outdoor instrument A temperature scanner (Altop Industries ltd, Sn.1005164, model ADT 5003) with resolution 0.1 oC and HTC DT-8811Infrared thermometer range: -20 oC – 450 oC Spectral response: 6-14 µm CE ASCO products had been used to record the temperature with k-type thermocouples in solar stills.The solar radiation measure by using the daystar meter Watts/m2 ASCO products, the wind speed was observed by HTC Instruments AVM-07 Anemometer vane probe CE. The variation of the typical observed ambient temperature and calculated solar radiation have been shown in Fig. 14. December 10, 2013 Banaras Hindu University 43
    • Figure 14. Photograph of the measurement instruments. Anemometer vane probe Temperatur e scanner Daystar meter Infrared Thermometer Digital temperature
    • Fig. 15. The location of thermocouples in A- Side view of solar still with PCM, B-the top view of PCM container. 1 7 2 10 3 y 4 5 z 6 7 10 11 9 8 8 x 11 6 9 z 1=Tgo,2=Tgin,3=Tv,4=Tw,5=Tb,6=Tpcm(X=0.25,Y=0.02,Z=0.25),7=Tpcm(X=0.75,Y=0.03,Z=0.25),8=T pcm (X=0.75,Y=0.01,Z=0.25),9=Tpcm(X=0.25,Y=0.04,Z=0.75),10=Tpcm(X=0.5,Y=0.005,Z=0.45),11= Tpcm(X=0.5,Y =0.04, Z=0.55), all dimensions are in meter. December 10, 2013 Banaras Hindu University 45
    • Experimental Uncertainty  The experimental method used is an indirect approach for estimating the convective  heat transfer coefficient based on the mass of distillate collected from still. It will therefore, have a considerable degree of experimental uncertainty.  An estimation of uncertainty (Nakra and Chaudhary, 1985) has been carried out separately for both the solar stills. Data of a particular measurement for a number of days have been taken and an estimate of individual uncertainties of the sample values has been calculated. An estimate of internal uncertainty (Ui) has then been found by 43    where σi is the standard deviation of the ith sample and N is the total number of  samples. The total uncertainty for single and new design solar stills has been calculated as 22 and 24%, respectively. December 10, 2013  Banaras Hindu University 46
    • Outline  Technology  Literature Options review of PCM Storage  Theoretical Analysis  Experimental  Results and discussion  Conclusions December 10, 2013 47
    • Indoor daily productivity  The daily productivity of PCM (30 kg) with three different water masses has been shown in Figure 16. It is observed that the overall productivity does not change significantly for 24 hours, but the day and night hours’ productivities differ significantly .Though the higher mass of PCM enhances the productivity during night hours, the quantum of the output is yet lower than that obtained during day hours. Therefore, the higher mass of PCM could not contribute significantly to the distillate output. December 10, 2013 Figure 16 Variation of hourly productivity due to SSWPCM Banaras Hindu University 48
    • Experiments on Solar Stills (Environmental Parameters) outdoor condition  The effect of environmental parameters outdoor condition on the productivity of still was seen by using two single sloped solar stills, each with basin area equal to 1 m2.  These two solar stills have identical design features except one without PCM and second with PCM (lauric acid). Hourly output and climatic parameters were determined for one complete year.  The productivity due to solar still without PCM has been shown in Figure 17 for the comparative purpose. It is observed that the PCM enhances the productivity of the system by 30 % due to PCM being acting as heat source under discharge mode during night. December 10, 2013 Banaras Hindu University 49
    • Fig. 17. Variation of daily productivity for solar still with and without PCM for 02 May 2011. 400 D a ily p rod u c tiv ity , m l 350 02 May 2011 SSWPCM SSWOUTPCM 300 mw = 50 kg mpcm = 30 kg 250 200 150 100 50 0 0 5 10 15 20 25 Time, hr December 10, 2013 Banaras Hindu University 50
    •  Figure 18 (A) shows that the productivity decreases with the increase in water mass during daytime, and it is due to the fact that higher quantity of water relatively needs more energy to raise its temperature before being evaporated. However, the productivity increases with the increasing water mass and PCM mass during night hours (see Figure 18 B) due to relatively larger storage of energy in PCM as latent heat and sensible heat in higher water mass, thus for 30 kg PCM the percentage of enhancement of productivity was 127% compare with solar still without PCM. December 10, 2013 Banaras Hindu University 51
    • Fig. 18B . Variation of on night productivity due to solar still with and without PCM for may 2011 Fig. 18A. Variation of daytime productivity due to solar still with and without PCM for may 2011 550 1500 500 mpcm=0 kg mpcm = 10 kg mpcm = 20 kg mpcm = 30 kg 450 1300 1200 mw = 30 kg 350 Productivity on night, ml Daytime productivity, ml 400 mw = 30 kg mw = 40 kg mw = 50 kg 1400 300 250 200 150 100 1100 1000 900 800 700 600 500 50 400 0 0 2 4 6 8 10 12 0 5 15 20 25 30 mpcm, kg Time, hr December 10, 2013 10 Banaras Hindu University 52
    • Effect of Solar Radiation   . Further the quantity of the solar radiation is very important reason to increase the day time productivity that it has been explained in table 6.In this table the solar radiation for 20 kg PCM was lower quantity than 10 kg ,therefore 10 kg of PCM was given more productivity, other reason the 10 kg absorbed low heat during day. Table 5 the day time productivity and solar radiation for 10 and 20 kg of PCM December 10, 2013 Table 6 the day time productivity and solar radiation for 10 and 20 kg of PCM Masses kg soalr radiation W/m2/day Pdt Ml/day mw = 40 mpcm = 10 5368 2625 mw = 40 mpcm = 20 4876 1703 Banaras Hindu University 53
    • Effect of Mass of water variation of total distillate productivity with time, for different water masses, has been plotted for 24 hrs duration (see fig. 19). The decreasing trend of the curve in fig. 19 reveals that the thicker water depth in solar still basin yields lower distillate productivity over 24 hours, and the reason relates to the conversion of major portion of energy to sensible heat due to higher heat capacity of water mass December 10, 2013 Fig. 19. Variation of daily productivity due to solar still with and without PCM during May 2011 5000 mw = 30 kg mw = 40 kg mw = 50 kg 4500 4000 D aily productiv ity, m l  The 3500 3000 2500 2000 1500 1000 0 5 Banaras Hindu University 10 15 20 25 30 mpcm, kg 54
    • The comparing of the productivity of present work with other researchers. productivity of the solar still without PCM has also been compared see Figure 20 with the data of (Dev and Tiwari 2009) and (Dwivedi and Tiwari 2009). The observed data show the similar trend, however, the reason for the difference in the productivity may be attributed to the difference in the climatic conditions of two cities of INDIA: Varanasi and New Delhi. December 10, 2013 Figure 20. Variation daily productivity for different type of solar still at same solar radiation 600 productivity, m l  The 100 pres ent work s olar s till , mw=40 kg(0.04 m)) Dev. & Tiwari s olar s till,mw=40 kg(0.04 m)) Dwived & Tiwari s olar s till,mw=10 kg(0.01 m)) 10 0 2 Banaras Hindu University 4 6 8 10 12 Time, hr 55
    • The variation of the instantaneous efficiency The variation of the instantaneous efficiency for solar stills, with and without PCM, has also been plotted in Figure 21. It is observed that the instantaneous efficiency for solar still with PCM is always higher than that due to traditional still; however, the increasing trend of both the curves with time indicates that the instantaneous efficiency keeps increasing due to increased temperature difference between basin water and ambience. December 10, 2013 Fig. 21 . Variation of instantaneous efficiency for SWPCM when mpcm=10 kg during May 2011 50 45 mpcm=10 kg, mw = 50 kg mpcm=10 kg, mw = 40 kg mpcm=10 kg, mw = 30 kg 40 ins tantanous effic iency %  35 30 25 20 15 10 5 0 1 2 Banaras Hindu University 3 4 Time, 5 6 7 hr 56
    • Experiments on solar stills with different Phase Change Materials (PCM) used as storage medium  The performance of a single slope solar still with Lauric acid (99% purity) and Myristc acid (99.2%) as PCM has been investigated for different masses during summer climatic conditions of Varanasi, India, (25 o 19` N,83o 00` E) to collect output data for the new design of solar still. The experiments were performed at roof top of Renewable Energy Laboratory, Mechanical Engineering Department, Institute of Technology, Banaras Hindu University, Varanasi, India. On the basis of collected data exergy analysis has been done to calculate the energy and exergy efficiencies for solar still system integrated with phase change materials. The experimentation started at 7:00 AM everyday during 30 April to 10 May 2011 on the experimental setup of solar still integrated with Lauric acid (SSWLA) and during 12 May to 22 May on solar still integrated with Myristic acid ( SSWMA),(see Table 7). The temperatures of the outer and the inner surface of glass cover; basin liner, water basin and PCM were recorded at the time interval of one hour till 6:00 P.M. The values of solar radiation, and distillate productivity were also recorded simultaneously December 10, 2013 Banaras Hindu University 57
    • Table 7 Meteorological data of SSWLA and SSWMA Date I(t) pdt SSWLA pon pd SSWMA pdt pon W/m Date ml/m hr ml/m hr ml/m2 hr I(t)n pd W/m ml/m hr ml/m hr ml/m hr 10-05-2011 5411 2652 1185 3837 12 -05 -2011 5372 1925 1300 3225 09-05-2011 5368 2625 950 3575 14 -05 -2011 5044 2235 820 3055 08-05-2011 5413 2980 750 3730 15-05 -2011 5275 2375 860 3235 06-05-2011 5344 2440 800 3240 17-05 -2011 4616 2185 910 3095 05-05-2011 4876 1723 900 2623 18-05 -2011 4616 1515 1050 2565 04-05-2011 4572 1713 1100 2813 19-05 -2011 5429 1885 970 2855 02-05-2011 5128 2200 1480 3680 21-05-2011 5341 1930 1090 3020 01-50-2011 4736 1600 1110 2710 22-05-2011 5258 1810 1190 3000 30-4-2011 4788 1775 875 2650 23-05-2011 5865 2340 880 3220 2 mw = 50 kg 2 2 2 2 2 2 mpcm = 10 kg mw = 40 kg mpcm = 10 kg mw = 30 kg mpcm = 10 kg mw = 30 kg mpcm = 20 kg mw = 40 kg mpcm = 20 kg mw = 50 kg mpcm = 20 kg mw = 50 kg mpcm = 30 kg mw = 40 kg mpcm = 30 kg mw = 30 kg mpcm = 30 kg December 10, 2013 Banaras Hindu University 58
    • Day time productivity for SSWLA and SSWMA December 10, 2013 Fig.22. Variation of day time productivity for SSWLA and SSWMA for mw=30 kg and mpcm=10 kg 600 SSWLA SSWMA 500 mw = 30 kg mpcm = 10 kg 400 2 The experimental results are plotted, to show the variation of day time productivity for the SSWLA and SSWMA with 10 kg of mass of PCM with different masses of water (30-50 kg.). The result are shown in Fig. 22, 23 and 24. These figures reveals that the daytime productivity of SSWLA is more than the SSWMA. It is due to fact that Lauric Acid works better and both the PCM act as storage material as well as insulation for the base. Pdt, m l/m hr  300 200 100 0 0 2 Banaras Hindu University 4 6 8 10 12 Time, hr 59
    • Fig.24 Variation of day time productivity for SSWLA and SSWMA for mw=50 kg and mpcm=10 kg Fig.23 Variation of day time productivity for SSWLA and SSWMA for mw=40 kg and mpcm=10 kg 500 SSWLA SSWMA 600 mw = 40 kg mpcm = 10 kg mw = 50 kg mpcm = 10 kg 300 2 Pdt, m l/m hr 400 2 Pdt, m l/m hr 500 SSWITHLA SSWITHMA 400 300 200 200 100 100 0 0 0 2 4 6 8 10 12 0 2 Time, hr December 10, 2013 4 6 8 10 12 Time, hr Banaras Hindu University 60
    • Night time productivity for SSWLA and SSWMA The latent heat stored in PCM during the daytime charging is utilized by discharging in night to assist the evaporation process by heating the water basin. The two system were tested during night to know the performance of these systems. The recorded data of the productivity during night with different PCM’s mass for two systems is shown in fig.25. Fig.25. Productivity during night with different PCMmasses for SSWLA and SSWMA 1800 1600 1400 SSWLA SSWMA mw = 50 kg May 2011 1200 Pon, m l  1000 800 600 400 200 0 10 20 30 mpcm, kg December 10, 2013 Banaras Hindu University 61
    • Night time productivity  The Productivity for SSWMA in night for 10 kg of PCM is little higher than SSWLA But with change of mass of water from 10 kg to 20 kg and 30 kg, the SSWLA produce more distillate output in spite of the fact that input solar energy for SSWMA is larger than SSWLA, as shown in Table 8.The reason for higher productivity with lower input energy is attributed to fast melting of Lauric acid as compared to the myristic acid due to its low melting point. December 10, 2013 Table 8 Night productivity of SSWLA and SSWMA with the total solar energy incident on them. SSWLA SSWMA Mass I(t) Pon I(t) Pon (In kg) (W/m2) (ml/m2 hr) (W/m2) (ml/m2 hr) mw=50 kg 4572 1100 5429 970 5128 1480 5341 1090 mpcm = 20 kg mw=50 kg mpcm = 30 kg Banaras Hindu University 62
    • The melting of lauric acid and myristic acid The melting of PCM is important factor to examine the heat energy storage. This energy can heat the water at night during discharge process. Figures (26-27) represent the variation of temperatures in SSWLA and SSWMA for different mass of water. Fig. 28. represent the location of thermocouple inside the system December 10, 2013 Banaras Hindu University 63
    • Fig. 27. Evolution of temperature at Points 8 Fig. 26. Evolution of temperature at Points 8 and and 10 with time for MA. 10 with time for LA. 52 50 48 Liquid LA 46 full molten LA 42 o Tem perature, C o Tem pera ture , C 44 40 s tart molten LA 38 36 s olid LA point10 (y=0.005 m) point8 (y=0.01 m) 34 32 30 mw = 40 kg mpcm = 10 kg 28 26 0 5 10 15 20 25 Fig. 28. The location of thermocouples in side view of solar still with PCM. full molten MA Liquid MA s tart molten MA Solid MA point10 (y=0.005 m) point8 (y=0.01 m) mw = 40 kg mpcm = 10 kg 0 1 Time, hr 56 54 52 50 48 46 44 42 40 38 36 34 32 30 28 26 24 22 20 5 10 15 20 25 Time, hr 2 3 y 4 5 z 6 December 10, 2013 7 10 11 9 8 Banaras Hindu University 64
    • Energy and exergy Efficiency of Solar Still Systems The values of energy and exergy Efficiency of Solar Still Systems are depicted in Figs. 29 and 30. It is clear from the figures that the energy efficiency for SSWLA is better than SSWMA. This is due to the fact that solar still integrated with Lauric Acid utilizes more stored heat for a larger duration and lower heat lost due its melting characteristics. Fig. 29. Energy and exergy efficiency for SSWLA for mw=30 kg and mpcm=10 kg 40 SSWLA 30 Energy Exergy mw=30 kg, mpcm = 10 kg 30 mw =30 kg, mpcm = 10 kg 25 Effic ie n c y (%) 25 SSWMA 35 Energy Exergy 35 Efficiency (%) Fig. 30. Energy and exergy efficiency for SSWMA for mw=30 kg and mpcm=10 kg 20 15 10 20 15 10 5 5 0 0 1 2 3 4 5 6 1 2 4 5 6 Time, hr Time, hr December 10, 2013 3 Banaras Hindu University 65
    • New Design of Solar Still (NDSS) December 10, 2013 Banaras Hindu University 66
    •  The aim of the present study was to develop a new design of solar still (NDSS) that increases the amount of distilled water in a solar still. To verify the performance of the new design, a single slope passive solar still with PCM (lauric acid) integrated with an external condenser was used. The condenser was connected at its upper and lower parts of the back of the still. Thermal performances of CSS and NDSS were compared in typical sunny and partially cloudy days. Furthermore, the effect of the mass of water basin and mass of PCM on total productivity of the NDSS and CSS were investigated through 5 to 18 of June, 2012. December 10, 2013 Banaras Hindu University 67
    • New design solar still  Schematic diagram and photograph of the new design single slope solar still are shown in Figs. 31a and 31b, respectively. The new design solar still and conventional solar still were designed based on the optimum inclination through the year for Varanasi city in India. The major components of this solar distillation system were evaporator, condenser and PCM chamber units. The two sides and back walls are covered with aluminium sheet plate, so these walls serve as the internal reflectors. This solar still forms three basins with saline water. Basin 1 was in the evaporator unit while basins 2 and 3 were stacked inside the condenser unit to recover heat from the first effect (Fig. 25a). Basin 1 of (1 m x 1 m) of the test still (AR = 1) was constructed from mild steel sheet (0.002 m thick), painted black on the inner surface to optimize absorption of solar radiation. Basin liners 2 and 3 were made from iron sheet (0.0015 m thick) but they were not painted to reduce resistance to heat conduction. Basin 2 includes stepped basin with 5 steps, with area of 0.3 m2. December 10, 2013 Banaras Hindu University 68
    •  While basin 3 was inclined at 12o to enable distillate flow downward into the collection channels. The fins were added in basin 1 of NDSS to decrease the preheating time required for evaporating the still basin water. While using fins in the solar still, the area of the absorber plate increased. Hence, absorber plate temperature and saline water temperature increased.  As the temperature difference between water and glass increases, productivity increased. In this work, five circular fins with height and diameter 35 mm, 155 mm, respectively were used. Slender shaped fins were welded on the upper of PCM’s chamber.  The solar radiation passes through the glass cover to heat saline water in basin 1 (first effect). Then, vapour from the first effect flows upward and condenses when it gets into contact with the inner side of the glass cover at lower temperature while part of the vapour flows into the condensing chamber to heat water in basin 2 (second effect) and basin 3 (third effect). The transfer of water vapour from the still to the condenser could be done through one or more of the following mass transfer modes: diffusion, purging, and natural circulation. December 10, 2013 Banaras Hindu University 69
    • Fig. 31a. Schematic diagram of new design solar still. December 10, 2013 Banaras Hindu University 70
    • Fig. 31b. Photograph of new design solar still. Slot 1 Slot 2 Reflector Fins Reflector December 10, 2013 Banaras Hindu University 71
    • Result and discussion of NDSS 50 1000 C) 45 o 900 Ta Solar radiation 9-June-2012 800 700 600 40 500 400 35 300 200 30 100 2 December 10, 2013 Fig. 32 Daily variation of ambient temperature and solar intensity Solar radiation , W/m An experimental study during 5th June 2012 to 18th June 2012 days were carried out to compare the thermal performance of NDSS and CSS. The mass water 10,15,20 and 30 kg are used for basin1. The mass water of basin2 and basin3 is 4 and 7.4 kg respectively. The mass of PCM is varies between 10 to 30 kg for NDSS. The mass water 10, 15, 20 and 30 kg are used for the CSS. Fig. 32 shows the solar intensity and the hourly yield produced on 9th June 2012. Ambient Temperature (  0 25 -100 -200 20 0 6:00 Am 5 Banaras Hindu University 10 15 20 25 Time (hr) 72
    • Temperature of system components o C) Fig.33 shows the variation of the observed Fig.33. Variation of experimental temperature of glass cover (Tgc), saline water temperature of saline water in basin1 of (Twb1), condenser cover (Tco,NDSS), glass cover CSS and NDSS on 9th June 2012. (Tgc,CSS), saline water (Tw,CSS) on a 9th June 75 Twb1,NDSS 2012. It is observed that the values of Tgc for Tgo,NDSS 70 th 9 June 2012 Tco,NDSS the CSS (Tgc,CSS) are higher than those of the 65 Tw,CSS NDSS (Tgc,NDSS) from about 10:00 hr to 18:00 60 Tgo,CSS 55 hr, with maximum values of Tgc,CSS=57 oC and 50 Tgc,NDSS= 50 oC. In addition, the temperature 45 of water in basin for the CSS (Tw,CSS) is 40 higher than that of the NDSS (Twb1,NDSS) from 35 about 8:00 hr to 13:00 hr. But after that the 30 temperature of water in basin for the CSS 25 (Tw,CSS) is lower than that of the NDSS 20 (Twb1,NDSS). It should be mentioned that part -2 0 2 4 6 8 10 12 14 16 18 20 22 24 6:00 Am of the heat from the evaporator basin flows Time (hr) into the condenser chamber by purging, diffusion and circulation which would tend to lower the glazing temperature of the NDSS (El-Bahi and Inan, 1999; Fath and Elsherbiny, 1993; A. Madhlopa and Banaras Hindu University Johnstone, 2009). December 10, 2013 Temperature (  26 73
    • Sunny and Entirely cloudy day  An experimental study in sunny and partially cloudy 8th June 2012 and entirely cloudy 7th June 2012 days were carried out to compare the thermal performance of NDSS and CSS. Fig. 33a and b illustrates the daily productivity of NDSS and CSS in typical sunny and cloudy days, respectively. The mass water of CSS is 20 kg, but for NDSS water masses are 20 kg, 4.3 kg and 7.4 kg for basin1, basin2 and basin3 respectively.  Fig. 33a indicates that hourly productivity in NDSS at morning is higher because NDSS has more area of water surface evaporation. But when the height of solar radiation about 9am to 11am the CSS is reading are higher than NDSS because, some of the absorbed solar energy is used to increase the PCM temperature and the solid fins of basin1, the absorber temperature is higher than the PCM and this trend is inverted in the low solar radiation intensity. It is clear from Figures 29a and 29b that the hourly productivity at night is significant for NDSS because of using the stored energy. Total productivity for NDSS and CSS is 5710 and 4295 ml/m2 day for sunny day (8th June 2012) and 1675 and 1095 ml/m2 day for entirely cloudy day (7th June 2012), respectively. It is also observed that there is a significant difference in the total productivity for the sunny day and entirely cloudy day. December 10, 2013 Banaras Hindu University 74
    • Fig. 33. Variations of hourly productivity with time for NDSS and CSS (a) typical sunny day, 8th June 2012 and (b) entirely cloudy day 7th June 2012. a b 1000 160 2 600 400 200 0 NDSS CSS mw=20 kg 140 mpcm=10 kg 180 Daily productivity (ml/m hr) Sunny and partially cloudy day 8th June 2012 mw=20 kg mpcm=10 kg 2 Daily productivity (ml/m hr) 800 200 NDSS CSS Entirely cloudy day 7th June 2012 120 100 80 60 40 20 0 -20 0 6:00 AM 5 December 10, 2013 10 15 Time (hr) 20 25 0 6:00 Am 5 10 15 20 25 Time (hr) Banaras Hindu University 75
    • Daytime productivity  Figures (40-43) is reveals the variation of the daytime productivity with variation the mass of the mass of water 10, 15, 20 and 30 kg for basin1 in the NDSS and for the basin of CSS with 10 kg of PCM. The daytime productivity of CSS is higher than NDSS with 10 kg of water (see fig. 29). The reason of this higher readings of CSS is because the little mass of water (2 cm depth of basin water), thus water immediately is heated and evaporated. But with NDSS the system is gradually heated; part of vapour will circulate inside the integrated condenser. These higher readings of CSS get reduced with mass of 15,20 and 30 kg, see figures 41, 42 and 43. Figure 42 shows higher performance of NDSS. Furthermore NDSS yields better results in all figures after 2 pm . December 10, 2013 Banaras Hindu University 76
    • Fig.40. The daytime productivity of NDSS and CSS for mw,b1=10 kg , mpcm=10 kg and mw =10 kg Fig.41. The daytime productivity of NDSS and CSS for mw,b1=15 kg , mpcm=10 kg and mw =15 kg 800 NDSS, mw,b1 = 15 kg CSS, mw = 10 kg 2 Daytime productivity (ml/m hr) 600 800 NDSS, mw,b1 = 10 kg 2 Daytime productivity (ml/m hr) 700 500 mpcm=10 kg 400 300 200 100 mpcm=10 kg 400 200 0 0 0 6:00 AM CSS, mw = 15 kg 600 2 4 6 Time (hr) December 10, 2013 8 10 12 0 6:00 AM 2 4 Banaras Hindu University 6 8 10 12 Time (hr) 77
    • Fig.42. The daytime productivity of NDSS and CSS for mw,b1=20 kg , mpcm=10 kg and mw =20 kg Fig.43. The daytime productivity of NDSS and CSS for mw,b1=30 kg , mpcm=10 kg and mw =30 kg 1000 600 NDSS, mw,b1 = 20 kg NDSS, mw,b1 = 30 kg Daytime productivity (ml/m hr) CSS, mw = 20 kg 600 400 200 0 0 6:00 AM 500 CSS, mw = 30 kg mpcm=10 kg 2 mpcm=10 kg 2 Daytime productivity (ml/m hr) 800 400 300 200 100 0 2 4 December 10, 2013 6 Time (hr) 8 10 12 0 6:00 AM 2 4 Banaras Hindu University 6 8 10 12 Time (hr) 78
    • Variation of daytime productivity with altered mass of PCM December 10, 2013 Fig. 44. Variation of daytime productivity of NDSS for mpcm =10, 20 and 30 kg with mw=10 kg 700 mpcm=10 kg 600 2 Figures 44, 45 and 46 present variations of the daytime productivities with mpcm for different masses of basin1 water mw,b1 for NDSS . Assessment of Figures indicated that daytime productivity increases with time. Also the productivity of NDSS of mpcm = 10 kg with mw,b1 = 20 kg is higher value as shown in figures. The reason may be that when the mass of PCM increases, the energy absorbed from basin liner by the PCM increases. Another reason may be the diffusion, purging and circulation inside the integrated condenser increase the convection , evaporating and condensation of vapor water, with the help of the cooler temperature of integrated condenser. The low glass temperature will increase the condensation of water vapor. Daytime productivity (ml/m hr)  500 mpcm=20 kg mpcm=30 kg mw,b1=10 kg 400 300 200 100 0 0 6:00 Am 2 4 Banaras Hindu University 6 8 10 12 Time (hr) 79
    • Fig. 45. Variation of daytime productivity of NDSS for mpcm =10, 20 and 30 kg with mw=15 kg Fig. 46. Variation of daytime productivity of NDSS for mpcm =10, 20 and 30 kg with mw=20 kg 1000 mpcm=10 kg mpcm=10 kg 800 mpcm=20 kg mpcm=30 kg mw,b1=15 kg 400 200 0 0 6:00 Am mpcm=20 kg mpcm=30 kg 2 600 Daytime productivity (ml/m hr) 2 Daytime productivity (ml/m hr) 800 600 mw,b1=20 kg 400 200 0 2 4 December 10, 2013 6 Time (hr) 8 10 12 0 6:00 Am 2 4 Banaras Hindu University 6 8 10 12 Time (hr) 80
    • Variation of productivity on night with altered mass of PCM The key point of using PCM is to increase the productivity at night. Fig. 42 depicts the influence of adding mass of PCM on the productivity during night time; Productivity increases with the increase of the mass of PCM. The fluctuation in curves is because the difference in the solar radiation and the cloudy day. Fig. 42. The productivity on night of NDSS and CSS for mpcm =10, 20 and 30 kg with mw=10, 15 and 20 kg 1400 1200 2 Productivity on night (ml/ m day)  NDSS, mw,b1 = 20 kg CSS, mw=20 kg NDSS, mw,b1 = 15 kg CSS, mw=15 kg NDSS, mw,b1 = 10 kg CSS, mw=10 kg 1000 800 600 400 200 0 10 15 20 25 30 mpcm (kg) December 10, 2013 Banaras Hindu University 81
    •  Table 9 depicts the productivity of 10, 20 and 30 kg of PCM with 20 kg of water. The difference in productivity for 30 kg PCM with 10 kg PCM is nearly 193 ml/m2 kg. This value if we compared with the daytime productivity of NDSS that has 20 kg of basin1 water with 10 kg of PCM. But the daytime productivity of NDSS that has 20 kg of basin1 water with 10 kg of PCM is greater 2.339 kg/m2 day compared with 20 kg of basin1 water with 30 kg of PCM. Thus 10 kg of PCM is suitable for storage system. However the price of 30 kg of PCM is costly if compared with 10 kg of PCM. December 10, 2013 Table 9 the daytime and on night productivity of NDSS of 10, 20 and 30 kg of PCM with 20 kg of water Mass of Mass of Productivit Daytime PCM water y on night, Productivit kg kg kg/m2 day y on kg/m2 day 10 20 887 4.823 20 20 980 3.132 30 20 1080 2.484 Banaras Hindu University 82
    • Variation of Daily productivity with altered mass of PCM The December 10, 2013 Fig. 43. Variation of Daily productivity of NDSS with CSS for mw,b1=10 kg , mpcm=10, 20 and 30 kg and mw =10 kg. 4400 NDSS, mw,b1= 10 kg 4200 2 Daily productivity (ml/ m day) daily productivity is represented in figures 43, 44and 45. It is clear that the highest productivity within 20 kg of water basin1 with 10 kg of PCM (see fig.37). CSS, mw = 10 kg 4000 3800 3600 3400 3200 10 Banaras Hindu University 15 20 25 30 mpcm (kg) 83
    • Fig. 44. Variation of Daily productivity of NDSS with CSS for mw,b1=15 kg , mpcm=10, 20 and 30 kg and mw =15 kg. Fig. 45. Variation of Daily productivity of NDSS with CSS for mw,b1=20 kg , mpcm=10, 20 and 30 kg and mw =20 kg. 6000 4400 NDSS, mw,b1= 15 kg 2 CSS, mw = 15 kg 3800 3600 3400 3200 3000 NDSS, mw,b1= 20 kg 5500 Daily productivity (ml/ m day) 4000 2 Daily productivity (ml/ m day) 4200 CSS, mw = 20 kg 5000 4500 4000 3500 2800 2600 3000 10 15 20 25 30 10 15 mpcm (kg) December 10, 2013 20 25 30 mpcm (kg) Banaras Hindu University 84
    • In order to have a comparison, amounts of total productivity of the designed stills and other still configurations are provided in Table 10. Table 10 the Comparison is between total productivity of the designed still with other still Configurations. Still type Date Productivity (kg/m2 day) Designed NDSS (present work) 08/06/2012 5.71 Designed still with LHTESS (Tabrizi et al., 2010) . 23/05/2009 4.85 Designed still with a separate condenser (Amos Madhlopa, 2009). 2009 4.59 Inclined type with black fleece (Aybar et al., 2005) May, 2004 2.995 Basin type only (Velmurugan et al., 2008) 16/08/2006 1.88 Basin type with sponge (Velmurugan, et al., 2008) 13/08/2006 2.26 Basin type with wick (Velmurugan, et al., 2008) 06/04/2006 4.07 Basin type with fin (Velmurugan, et al., 2008) 28/08/2006 2.81 December 10, 2013 Banaras Hindu University 85
    • Conclusion •The integrated PCM with conventional solar still enhances 30-35 % productivity. •By using SSWPCM the losses of heat to surrounding reduces. •By considering the inner glass cover temperature, there is reasonable agreement between the experimental and theoretical/ predicted values. •It was found that the high-est productivity rate is at the least water depth. •The productivity at night increased significantly with increased PCM. •From the above studies, it is seen that when the temperature difference between night time ambient temperature and melting point of PCM is higher than 3oC, it attains lower rates for complete solidification of PCM within available night time hours. But in case, if it is lower than 3oC then it will not solidify completely in both the cases. December 10, 2013 Banaras Hindu University 86
    •       Productivity of solar still integrated with Lauric acid is 22% more than the solar still integrated with Myristic acid. The energy efficiencies for solar still integrated with Lauric acid and Myristic acid are found to be 39.6% and 34.4% where as exergy efficiencies values are 0.29% and 0.74% respectively The cost of using Lauric acid is less than using Myristic acid for the same amount of productivity due to market costs of these two materials. Using integrated condenser reduces the glass temperature. The saline water in basin1 and basin 2 is also heated and evaporated to increase the productivity of the solar still because the temperature of integrated condenser is lower than evaporator. The shielded condenser keeps the outer wall of condenser cool. To get benefit from circulation of the water vapor inside integrated condenser, the stepped basin 2 is housed in the condenser from left and right side and free from the other side to let the mixture to circulate. The daily productivity of NDSS is slightly higher than the CSS. The productivity is found to be 5.71 kg/m2 day for NDSS and 4.295 kg/m2 day for CSS. Thus, NDSS is favored for sunny and partially cloudy days due to the higher productivity. The productivity during night time of NDSS is mostly higher than the CSS over all days of experimentation. This increase is due to the increase of the mass of PCM. Thus it is necessary to consider using it in solar still system. Furthermore, the transferred heat from the PCM to the saline water during discharge process is enough to produce high amount of distillated water because of the decrease in operating temperature which is compared with low ambient temperature at night condition. December 10, 2013 Banaras Hindu University 87
    • Stepped Solar Still December 10, 2013 88
    • LIST OF PUBLICATIONS (a) Papers in journals Al-Hamadani, A. A. F. and Shukla, S. K., Water Distillation Using Solar Energy System with Lauric Acid as Storage Medium. International Journal of Energy Engineering, 1(1), 1-8, 2011. Al-Hamadani, A. A. F. and Shukla, S. K., Modelling of Solar Distillation System with Phase Change Material (PCM) Storage Medium, paper accepted at the Thermal Science, 2012. Al-Hamadani, A. A. F. and Shukla, S. K., Experimental Investigation and Thermodynamic Performance Analysis of a Solar Distillation System with PCM Storage: Energy and Exergy Analysis, paper communicated with International Journal of Ambient Energy, 2012. (b) Conferences Papers Al-Hamadani, A. A. F. and Shukla, S. K. (2011), Thermal Modelling of Solar Stills Using PCM as Storage Medium, ASME-ES Fuel Cell 2011 conference Washington D.C. USA, August 7-10, 2011. Al-Hamadani, A. A. F. and Shukla, Performance of Single Slope Solar Still with Solar Protected Condenser, Finned Absorber Plate Finned Phase Change Material Container, paper accepted in 11th International Conference on Sustainable Energy Technologies (SET-2012). December 10, 2013 Banaras Hindu University 89
    • International Journal of Energy Engineering December 10, 2013 Banaras Hindu University 90
    • Thermal Science international Scientific Journal December 10, 2013 Banaras Hindu University 91
    • International Journal of Ambient Energy December 10, 2013 Banaras Hindu University 92
    • International Journal of Ambient Energy December 10, 2013 Banaras Hindu University 93
    • ASME 2011 5th International Conference on Energy Sustainability & 9th Fuel Cell Science, Engineering and Technology Conference. December 10, 2013 Banaras Hindu University 94
    • ASME 2011 5th International Conference on Energy Sustainability & 9th Fuel Cell Science, Engineering and Technology Conference. December 10, 2013 Banaras Hindu University 95
    • ASME 2011 5th International Conference on Energy Sustainability & 9th Fuel Cell Science, Engineering and Technology Conference. December 10, 2013 Banaras Hindu University 96
    • 11th International Conference on Sustainable Energy technologies December 10, 2013 Banaras Hindu University 97
    • 11th International Conference on Sustainable Energy Technologies December 10, 2013 Banaras Hindu University 98
    • Journal of the Energy Institute December 10, 2013 Banaras Hindu University 99
    • December 10, 2013 Banaras Hindu University 100