Coffee beans are roasted by floating them with a column of hot air at 250°c. if the beans start at 22°c and are done when they reach 200°c, how long does this process takewith average convection of h =20 w/m2°c? assume the coffee beans have typical volume and surface areas of 44 mm3 and 66 mm2 respectively, a conductivity of 0.184 w/m°c, specific heat of 2.564 kj/kg °c and a density of 552 kg/m3. assume that the beans are relatively dry at the start of this process and evaporative losses can be neglected.