Unveiling the potential of concentric tubular solar stills (CTSS) through comprehensive thermodynamic modeling and analysis

ABSTRACT

The present research work delves into the thermodynamic modeling and analysis of concentric tubular solar stills (CTSS) using a rigorous mathematical approach. The primary objective is to gain a comprehensive understanding of the system’s behavior by formulating and analyzing various crucial parameters. These parameters include the basin water temperature, inner and outer glass cover temperatures, heat transfer coefficients, heat loss coefficients, thermal efficiency, exergy efficiency, hourly yield, and cumulative yield. The study is specifically conducted under the environmental conditions of Nagpur city (21.1458° N, 79.0882° E), India, in the month of May 2022. By selecting this location, the present study ensures that their findings are contextually relevant and applicable to the local conditions. To facilitate the computation of results and generate informative visualizations, MATLAB code has been developed. This code allows for efficient analysis, processing, and presentation of the obtained data, enabling a comprehensive interpretation of the research findings. Results of the study indicate that hourly yield, considering only bottom losses, is 5.071 $kg/m^2$ and 3.012 $kg/m^2$ when water and air are used as cooling mediums, respectively. However, when all losses are taken into account, the hourly yield decreases to 4.575 $kg/m^2$ and 2.555 $kg/m^2$ for water and air as cooling mediums, respectively. The percentage error when water and air are used as the cooling medium by considering bottom losses is 1.05 and 3.06, while considering all losses, the error is 10.73 and 18.26.

KEYWORDS:

• Concentric tubular solar still
• thermal modeling
• thermal desalination
• thermodynamic analysis
• exergy analysis

Nomenclatures

$\alpha =$ Absorbtivity	=	$M_e=$ Total yield kg/m2
$q_y=$ Amount of energy produced due to temperature difference (W/m2)	=	$\tau =$Transmissivity
$A_b=$ Area of basin$(m^2$)	=	n = Number of years
$h_{bottom}=$Bottom loss coefficient (W/m2.K)	=	i = interest rate
$\beta =$ Coefficient of thermal expansion (1/oC)	=	Wcost = Water cost
$\rho =$ Density (kg/m3)	=	Tcost = Total cost
$\mu =$Dynamic viscosity (kg/m.sec)	=	Fcost = Fixed cost
$h_{fg}=$ Enthalapy of vapourization (kJ/kg)	=	Ccost = Capital cost
$h_{f,b,1}=$Front and back loss coefficient from basin (W/m2.K)	=	ASV = Average salvage value
$Gr=$Grashoff number	=	S = Salvage value
$h$= Heat transfer coefficient (W/m2.K)	=	SF = Sinking fund factor
$h_{L,1}=$ Heat loss coefficient from 1st glass cover to ambient (W/m2.K)	=	A = Amortization factor
$h_{L,2}=$ Heat loss coefficient from 2nd glass cover to ambient (W/m2.K)	=	MOcost = Maintenance operational cost
$h_{eff}=$ Heat transfer coefficient between the glass cover and cooling medium(W/m2.K)	=	Abbreviations
$h_{total}$ = Heat transfer coefficient from water surface to glass cover (W/m2.K)	=	CTSS = Concentric tubular solar still
$m=$Hourly yield kg/m2	=	TSS = Tubular solar still
$M=$ Total yield kg/m2	=	PCM = Phase change material
$M_w$ = Mass of water (kg)	=	NPCM = Nano phase change material
$Pr=$ Prandtl number	=	CPC = Compound parabolic concentrators
W = working days	=	ATSS = Active tubular solar still
R = Reflectivity	=	TSS = Tubular solar still
$R_1=$ Reflectivity of 1stglass	=	Subscripts
$R_2$ = Reflectivity of 2ndglass	=	1 = first glass cover
$h_{s,1}=$ Side loss coefficient from basin (W/m2.K)	=	2 = second glass cover
Cp = Specific heat (kJ/kg.K)	=	$a=$Ambient
$\sigma =$Stefan Boltzmann constant (W/m2.K4)	=	$b$ = basin
$T=$Temperature oC	=	$c=$ Convective
k = Thermal conductivity (W/m.k)	=	$e=$ Evaporative
${\eta }_T=$ Thermal efficiency	=	$f=$front
${\eta }_{exr}$ = Exergy efficiency	=	$g$ = glass
$l=$ Thickness $\left(m\right)$	=	$g_i$ = inner glass
L = Litre	=	$g_o=$ Outer Glass
$t$ = Time (second)	=	$ins=$ Insulation
$r=$Radiative	=

Acknowledgements

This work is supported by the National Institute of Technology Raipur, which has given unlimited time for reading books and both online and offline research papers.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

Sunil Pal

Sunil Pal, formerly a PG scholar at the National Institute of Technology, Raipur, specialized in thermal engineering. His research interests include thermal modeling analysis of solar-based thermal systems and CFD analysis. Currently, he is pursuing a Ph.D. at the Indian Institute of Technology, Bombay.

Satish Kumar Dewangan

Dr. Satish Kumar Dewangan, an Associate Professor at the National Institute of Technology, Raipur, has published more than 50 research papers in the field of “CFD applications in solar thermal and other energy systems, CFD applications in oil-well drilling and multiphase flow systems, and rheology analysis of slurry and other complex fluids.” Currently, he is actively engaged in multiple projects related to these fields.