Small potato balls of 0.5 cm radius (can be approximated as a sphere) baked in the oven and initially at a uniform temperature of 160°C. Assume, potatoes have a density of 650 kg/m³, specific heat of 3400 J/kgK and conductivity of 1 W/mK. You want to eat potatoes quickly without burning your tongue so that you have decided to cool them down with forced convection. Air h, T. hot potato initially @ T Air temperature is 20°c and the convective heat transfer coefficient is 140 W/m²K. Calculate the time (in seconds) required for its surface temperature to drop 90°C. Round the value you calculated and write it as an integer!!! For example, if you find 8.2, write is as 8..

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A food product with 73% moisture content in a 7 cm diameter can wants to be frozen. The density of the product is 970 kg / m³, the thermal conductivity is 1.2 W / (m K), and the initial freezing temperature is -2 ° C. After 11 hours in the freezing medium -30 ° C, the product temperature becomes -10 ° C. Estimate the convection heat transfer coefficient of the freezing medium. Assume the can as an infinite cylinder. h = W / (m² K).

The thermal boundary layer in heat transfer exists whenever there is a difference between the temperatures of the fluid and the outside environment. For fluid flow, how does a boundary layer form?A. Because common surfaces are not smooth, the flow is hindered, and boundary layers are formed.B. The disturbances on the streamlines in high Reynolds number flow produces boundary layer.C. The existence of walls or “boundaries” that keep the fluid inside (or outside) creates the boundary layer.D. Velocity profiles are inherently approaching no-slip condition because of the resistance of the walls.