Example

Ex$\mathrm{.}1$: Calculate the overall loss coefficient for a flat$-$plate collector with two glass covers. The following data is given: $($a$)$ size of the absorber plate: $1\mathrm{.}90m0\mathrm{.}90m,($b$)$ spacing between plate and first glass cover: $5cm,($c$)$ spacing between first and second glass cover: $5cm,($d$)$ plate emissivity : $0\mathrm{.}90,($e$)$ glass cover emissivity: $0\mathrm{.}85,($f$)$ collector tilt: $23,($g$)$ Mean plate temperature: $73C,($h$)$ Ambient air temperature: $25C,($i$)$ wind speed : $2\mathrm{.}7\frac{m}{s},($j$)$ Back insulation thickness: $10cm,($k$)$ side insulation thickness: $5cm,($I$)$ thermal conductivity of insulation: $0\mathrm{.}07\frac{W}{m}-K.$ Use the appropriate correlation from the correlation Table$-1.$ The properties of air is given in Table$-2.$

Table$-1$ Correlation table

$=1+1\mathrm{.}446[1-\frac{1708}{Racos}]$ for $1708$