Chapter 2, Problem 2.21P

What is the approximate temperature difference between a hot plate and the surrounding air if the heat flux from the plate is 800 W/m2? Assume that the air is flowing past the surface with a velocity of 5 m/s giving a heat transfer coefficient of 20 W/(m2K).

In a meat processing plant, 4 cm-diameter spherical meat balls (k=0.45 W/m-K and α=0.91×10-7 m²/s) that are initially at 25 °C are to be cooled by passing them through a refrigeration room at -10 °C. The heat transfer coefficient in the cold room is 22.5 W/m²-K. If surface of the meat balls is to be cooled to 3 °C, determine how long the meat balls should be kept in the refrigeration room. What will be the center temperature of the meat balls at the end of the process?

A 5-cm-external-diameter, 10-m-long hot-water pipe at 80 deg C is losing heat to the surrounding air at 5 deg C by natural convection with a heat transfer coefficient of 25 W/m^2.K. Determine the rate of heat loss from the pipe by natural convection (6m)

You are using a silver spoon to stir water that just started boiling so that you can achieve a more even heat distribution in your water. The spoon is partially immersed in boiling water and a thermometer in your kitchen reads 27 °C. The handle of the spoon has a cross section of 2mm × 1cm and extends 15 cm in the air from the free surface of the water. The heat transfer coefficient at the exposed surfaces of the spoon handle is 3 W/m2 ×K. Part A : Determine the temperature difference across the exposed surface of the spoon handle. Follow the problem-solving guide on the front page. At the minimum, your analysis should answer the following questions providing detailed justifications: -What are the modes of heat transfer that the spoon is exposed to? -Is this a time dependent or steady state problem? Why or why not? -Is this a 1-D, 2-D or 3-D problem? Why or why not? - What is the thermal conductivity of the material? - The heat transfer coefficient is a function of many variables.…

A pipe in a manufacturing plant is transporting superheated vapor at a mass flow rate of 0.3 kg/s. The pipe is 10 m long and has an inner diameter of 5 cm and a wall thickness of 6 mm. The pipe has a thermal conductivity of 17 W/m·K, and the inner pipe surface is at a uniform temperature of 120°C. The temperature drop between the inlet and exit of the pipe is 7°C, and the constant pressure specific heat of vapor is 2190 J/kg·°C. If the air temperature in the manufacturing plant is 25°C, determine the heat transfer coefficient as a result of convection between the outer pipe surface and the surrounding air.

During a picnic on a hot summer day, the only available drinks were those at the ambient temperature of 90°F. In an effort to cool a 12-fluid-oz drink in a can, which is 5 in high and has a diameter of 2.5 in, a person grabs the can and starts shaking it in the iced water of the chest at 32°F. The temperature of the drink can be assumed to be uniform at all times, and the heat transfer coefficient between the iced water and the aluminum can is 30 Btu/h·ft2·°F. Using the properties of water for the drink, estimate how long it will take for the canned drink to cool to 40°F.

A 5 m long section of a steam pipe whose outer diameter is 10 cm passes through an open space at 30°C. The average temperature of the outer surface of the pipe is measured to be 150°C, and the average heat transfer coefficient on that surface is determined to be 180 W/m^2.k. Determine (a) the rate of heat loss through convection from the steam pipe and (b) the annual cost of this energy loss if steam is generated in a natural gas furnace, and the price of natural gas is 0.05 Rs/Kwh, consider a 250 working-day year.

A person puts a few apples into the freezer at 215°C tocool them quickly for guests who are about to arrive. Initially,the apples are at a uniform temperature of 20°C, and the heattransfer coefficient on the surfaces is 8 W/m2·K. Treating theapples as 9-cm-diameter spheres and taking their properties tobe r = 840 kg/m3, cp = 3.81 kJ/kg·K, k = 0.418 W/m·K, anda = 1.3 * 1027 m2/s, determine the center and surface temperaturesof the apples in 1 h. Also, determine the amount ofheat transfer from each apple. Solve this problem using analyticalone-term approximation method (not the Heisler charts).

A person puts a few apples into the freezer at 15°C cool them quickly for guestswho are about to arrive. Initially, the apples are at a uniform temperature of 20°C,and the heat transfer coefficient on the surfaces is 8 W/m2·K. Treating the apples as9-cm-diameter spheres and taking their properties to be 840 kg/m3, Cp 3.81 kJ/kg·K, k = 0.418 W/m·K, and α =10-7 m2/s, determine the center and surface temperatures of the apples in 1 h. Also, determine the amount of heat transfer from each apple. Solve this problem using analytical one-term approximation method (notthe Heisler charts). Answer: Center: 11.2 ℃, Surface: 2.7 ℃, heat transfer: 17.2 kJ