Chapter 8, Problem 8.13P

Number 3A 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 1.2W/(m K), and the initial freezing temperature is -2.5°C. After 11 hours in the freezing medium -40°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= answer in W/(m²K)

(B) Cylindrical Water cans (diameter 6.5cm and length 15cm) are to be cooled from initial temperature of 20°C by placing theme in a cooler with ambient temperature of 1˚C. Compare the initial cooling rates when the cans are laid horizontally to when the cans are laid vertically. Take v = 15.55x10 m²/s, k=0.024 W/mK and Pr-0.7. Nu = 0.53 Ra¹ for horizontal orientation Nu = 0.59 Ra¹/4 for vertical orientation

Cylindrical Water cans (diameter 6.5cm and length 15cm) are to be cooled from initial temperature of 20' C by placing theme in a cooler with ambient temperature of 1 C. Compare the initial cooling rates when the cans are laid horizontally to when the cans are laid vertically. Take v= 15.55x10" m/s, k=0.024 W/mK and Pr-0.7. Nu = 0.53RA for horizontal orientation Nu = 0.59 Ra for vertical orientation 1/4

Thermodynamics problem. A membrane type electrical heater of 20,000 w/m? capacity is sandwiched between an Insulation of 25 mm thickness with thermal conductivity of 0.029 W/m-K and a metal plate with k = 12.6 W/m-K of thickness 15 mm. The convection coefficient is 150 W/m2-K. The surroundings are at 5°C. Determine the surface temperature of the heater and the flow on either side.

Electronic components are attached under a thin square plate and the all the energy dissipated by components is removed by water flow over the top surface. The plate length is 0.18 m and the thermophysical properties of water may be approximated as: k = 0.620 W/mK, Pr = 5.2, ν = 0.96x10-6 m2/s Water flow velocity is 1.5 m/s and the amount of dissipated energy (q’’) from the components can be estimated as uniformly distributed heat flux of 80000 W/m2. One approach to analyze this problem is to assume the plate has an isothermal temperature as a boundary condition. Calculate the average isothermal plate temperature in °C for the given conditions blank If the boundary layer is ‘tripped’ and the flow over the plate is completely turbulent; what will be the average isothermal plate temperature in °C for this case?

Required information Air flows in a pipe under fully developed conditions with an average velocity of 1.25 m/s and a temperature of 24°C. The pipe's inner diameter is 4 cm, and its length is 4 m. The first half of the pipe is kept at a constant wall temperature of 100°C. The second half of the pipe is subjected to a constant heat flux of 200 W. The properties of air at 80°C are p = 0.9994 kg/m³, k = 0.02953 W/m-K, v= 2.097 x 10-5 m²/s, cp=1008 J/kg-K, and Pr = 0.7154. NOTE: This is a multi-part question. Once an answer is submitted, you will be unable to return to this part. Air 1.25 m/s 2m T, = 100°C D = 4 cm 2 m g, = 200 W Determine the wall temperature at the exit of the tube. The wall temperature at the exit of the tube is 282 * °C.

The free convection heat transfer coefficient on a thin hot vertical plate suspended in still air can be determined from observations of the change in plate temperature with time as it cools. Assuming the plate is isothermal and radiation exchange with its surroundings is negligible, evaluate the convection coefficient at the instant of time when the plate temperature is Tplate = 277 °C and the change in plate temperature with time (dT/dt) is −0.022 K/s. The ambient air temperature is Tinf = 28°C and the plate measures 0.7 × 0.7 m with a mass of 5.56 kg and a specific heat of 2,780 J/kg · K.