Heat loss analysis: An approach toward the revival of parabolic dish type solar cooker

ABSTRACT

Present work investigates a noble approach toward the heat loss analysis of parabolic dish type solar cooker. Various experiments have been done on cooking pot to get the input parameter for calculation purposes. Cooking pot was kept at the focus of a parabolic dish type concentrator and repeated experiments have been done to measure solar radiation intensity (direct and Indirect) using a pyrometer, temperature at the focus of parabolic dish using a thermocouple and air velocity using hot wire anemometer to investigate the heat losses from the cooking pot. In the present article, a numerical approach has been performed to define the new parameter called performance index of the cooking pot which decides how the useful energy of working fluid inside the cooking pot approaches concentration ratio of the parabolic dish type solar cooker. The present analysis shows that the performance index varies from 15.45 to 17.66 and efficiency varies from 85.83% to 98.10% with the time of the day.

KEYWORDS:

• Concentration ratio
• efficiency
• heat loss coefficient
• parabolic dish concentrator
• performance index
• solar radiation intensity

Acknowledgment

The authors gratefully acknowledge the MHRD New Delhi for financial support for conducting this study.

Nomenclature

$C_o=$ Optical concentration ratio

$C_g=$Geometrical concentration ratio

$I_d=$Intensity of radiation falling on dish concentrator

$I_c=$Intensity of radiation falling on cooker

$A_d=$Area of dish collector

$A_a=$Area of section of cooker containing air (steam)

$A_c=$Area of cooker

$A_{top}=$Area of top surface of cooker

$Q_R=$Heat received by receiver (cooker)

$Q_f=$Heat received by cooking fluid

$Q_{ra}=$Heat transfer from receiver to air (steam) in cooking pot

$Q_{rs}=$Heat transfer due to radiation from side (cylindrical surface)

$Q_{loss}=$Heat lost from cooker

$m_r=$ Mass of the receiver (cooker)

$m_a=$ Mass of air in cooker

$C_R=$ Specific heat capacity of receiver

$T_R=$Temperature of receiver

$t=$Time

${\alpha }_R=$Absorptivity of receiving surface

$Q_d=$Heat collected by dish concentrator

$Q_b=$Heat lost from bottom of cooker

${\rho }_d=$Reflectivity of dish surface

$F_s=$ Shading factor for the cooker

${\eta }_d=$ Optical efficiency of dish concentrator

$A_s=$Cylindrical surface area of cooking pot (cooker)

$T_a=$Temperature of air (steam) above fluid in cooker

$Q_{fa}=$Heat transfer between fluid to air (steam) above fluid in cooker

$m_f=$ Mass of fluid in cooking pot (cooker)

$C_f=$ Specific heat capacity of fluid

$T_f=$Temperature of fluid

$T_r=$Temperature of receiver (cooker)

$Q_{top}=$Heat lost from top surface of cooker

$C_a=$ Specific heat capacity of air in cooker

$T_{amb}=$ Ambient temperature

$x_t=$Thickness of cooker

$K_t=$Thermal conductivity of cooker material

V= Wind velocity

$\sigma =$Stefan Boltzmann constant

${\epsilon }_{bm}=$Emissivity of black matt paint

${\epsilon }_{al}=$Emissivity of aluminum

$T_{sky}=$ Sky temperature

$R_c=$ Radius of cooking pot

$L_c=$ Length of cooking pot

$A_b=$ Base area of cooking pot (cooker)

$h_a=$Heat transfer coefficient of air above fluid in cooker

$h_{cs}=$ Convection heat transfer coefficient for cylindrical (side) surface

$h_{cb}=$ Convection heat transfer coefficient for bottom surface of cooker

$h_{ct}=$ Convection heat transfer coefficient for top surface of cooker

$h_{rs}=$ Radiation heat transfer coefficient for cylindrical (side) surface

$h_{rb}=$ Radiation heat transfer coefficient for bottom surface

$h_{rt}=$ Radiation heat transfer coefficient for top surface