An array of electrical heating elements is used in an air$-$duct heater as shown in the figure. Each element has a length of $200$ mm and a uniform surface temperature of $350^$C$.$ Atmospheric air enters the heater with a velocity of $8$ m $/$ s and a temperature of $25^$C$.$ Determine the total heat transfer rate and the temperature of the air leaving the heater. Neglect the change in air properties as a result of temperature change across the heater. Evaluate the air properties at an assumed mean temperature of $35^$C and $1$ atm. The total heat transfer rate is W$.$ The air properties at an assumed temperature of $35^$C are $[$ k$=\backslash$times $10^-2$ W $/$ m$$K; $\backslash$rho $=$ kg $/$ m$^3$; c$\_$p$=$ kJ $/$ kg$$K; $\backslash$mu $=\backslash$times $10^-5$ kg $/$ m$$s; Pr$=]$