A sample of porous sheet material of mineral origin is dried from both sides by cross circulation of air in a laboratory drier. The sample was $3$ m and $6$mm thick and edges were sealed. The air velocity is $3$ m$\text{'}$s$.$ DBT and WBT of air were $52\backslash$deg C and $21\backslash$deg C respectively: There was no radiation effect. Constant rate drying was $7\mathrm{.}5*10\text{'}$ kg$/$s until critical moisture content of $15\%($on wet basis$)$ was obtainod. In the talling rate period, rate of drying fell linearly with moisture content until the sample was dry. The dry weight of the sheet was $1\mathrm{.}8$ kg$.$ Estimate the time needed for drying similar shects$1\mathrm{.}2$ mx $1\mathrm{.}2$ m $*12$ mm thick from both sides from $25\%$ to$2\%$ moisture on wet basis using air at a DBT of $66\backslash$deg C but of the same absolute humidity and a linear velocity of $5$ m$/$s$.$ Assume the critical moisture content remains the same,