Thermal Analysis of a Clay Pot Utilized for Cooling Water and Storing Vegetables/ Fruits

ABSTRACT

In addition to supplying cooled water, clay pots can also be used to store fruits, vegetables, and even medicines that need to be kept at a moderate temperature. The authors recommended storing perishable things submerged inside the clay pot filled with water in locally accessible polythene bags. In the present paper, a mathematical model to determine the preservation temperature has been developed and validated for the climate of Raipur, Chhattisgarh, India. The convective coefficient between the pot and the surrounding air has been determined. Experiments were performed by loading a pot with apples/tomatoes. It is seen that with a load up to 10 W, the preservation temperature is between 20 and 25°C during summer for the climate of Raipur. The cost of cooling water and storing product is Rs 0.11/kWh (US$0.00146/kWh). The load test reveals that apples can be stored inside for about 8–9 days, whereas tomatoes can be stored up to 7 days inside the pot.

KEYWORDS:

• Clay pot
• convective heat transfer coefficient
• economic analysis
• heat and mass transfer
• water storage

Nomenclature

$c_w$	=	Specific heat of water $\mathit{JK}{{\mathit{g}}^{-1}}^{\mathit{o}}{C}^{-1}$
$c_{\mathit{pa}}$	=	Specific heat of air (constant pressure) $\mathit{JK}{g}^{-1\mathit{o}}{C}^{-1}$
$D_{\mathit{ab}}$	=	Mass diffusivity ${\mathrm{m}}^2/\mathrm{s}$
$h_c$	=	Convective coefficient between pot and surrounding $\mathit{W}/m^2\mathit{K}$
$h_r$	=	Radiative coefficient between pot and surrounding $\mathit{W}/m^2\mathit{K}$
L	=	Latent heat of vaporization $\mathit{kJ}/\mathit{kg}$
$\mathit{M}{{\mathit{ }}^{\mathrm{\prime }}}_{\mathit{w}}$	=	Molar water mass $\mathit{kJ}/\mathit{mol}$
$M_a$	=	Molar mass of air $\mathit{kJ}/\mathit{mol}$
$M_w$	=	Mass of water stored in the pot $\mathit{kg}$
$\stackrel{.}{m_m}$	=	Mass of make-up water added to clay pot per second $\mathit{kg}/\mathit{s}$
$P_a$	=	Saturated water vapor pressure in air $\mathit{N}{m}^{-2}$
$P_w$	=	Saturated water vapor pressure in air at the temperature of water $\mathit{N}{m}^{-2}$
$P_T$	=	Total pressure of air-vapor mixture $\mathit{N}{m}^{-2}$
$\stackrel{.}{Q_c}$	=	Convective heat transfer rate $\mathit{W}$
$\stackrel{.}{Q_e}$	=	Evaporative heat transfer rate from water to air $\mathit{W}$
$\stackrel{.}{Q_r}$	=	Radiative heat rate given to water $\mathit{W}$
$\stackrel{.}{Q_m}$	=	Rate of heat given by make-up water $\mathit{W}$
$\stackrel{.}{Q_L}$	=	Heating load given by product stored $\mathit{W}$
$T_w$	=	Water temperature stored in pot ${\hspace{0.17em}}_{\hspace{0.17em}}^o\mathit{C}$
$T_a$	=	Temperature of surrounding air ${\hspace{0.17em}}_{\hspace{0.17em}}^o\mathit{C}$
$T_o$	=	Temperature of water stored outside pot ${\hspace{0.17em}}_{\hspace{0.17em}}^o\mathit{C}$
v	=	Velocity of air $\mathit{m}/\mathit{s}$
Greek letters	=
${\alpha }^{\prime }$	=	Thermal diffusivity $m^2/\mathit{s}$
${\rho }_a$	=	Density of air $\mathit{kg}/m^3$
$\mathit{\gamma }$	=	Relative humidity of air

Disclosure statement

No potential conflict of interest was reported by the authors.