A food product with 73% moisture content is being frozen in a 7 cm-diameter can. The product density is 970 kg/m³, the thermal conductivity is 1.2 W/(m K), and the initial freezing temperature is -2.5°C. After 11 hour in the -40°C freezing medium, the product temperature is -10°C. Estimate the convective heat-transfer coefficient for the freezing medium. Assume the can has infinite height. a. h = ... W/m² K

A food product with 73% moisture content is being frozen in a 7 cm-diameter can. The product density is 970 kg/m³, the thermal conductivity is 1.2 W/(m K), and the initial freezing temperature is -2.5°C. After 11 hour in the -40°C freezing medium, the product temperature is -10°C. Estimate the convective heat-transfer coefficient for the freezing medium. Assume the can has infinite height. a. h = ... W/m² K

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter8: Natural Convection

Section: Chapter Questions

Problem 8.13P

See similar textbooks

Similar questions

An electrical transmission line of 1.2-cm diameter carries a current of 200 amps and has a resistance of 310-4 ohm per meter of length. If the air around this line is at v, determine the surface temperature on a windy day, assuming a wind blows across the line at 33 km/h.
3.10 A spherical shell satellite (3-m-OD, 1.25-cm-thick stainless steel walls) re-enters the atmosphere from outer space. If its original temperature is 38°C, the effective average temperature of the atmosphere is 1093°C, and the effective heat transfer coefficient is , estimate the temperature of the shell after reentry, assuming the time of reentry is 10 min and the interior of the shell is evacuated.
Partially-frozen ice cream is being placed in a package before completion of the freezing process. The package has dimensions of 8 cm by 10 cm by 20 cm and is placed in air- blast freezing with convective heat coefficient of 50 W/(m2 K) for freezing. The product temperature is -5°C when placed in the package, and the air temperature is -25°C. The product density is 700 kg/m3, the thermal conductivity (frozen) is 1.2 W/(m K), and the specific heat of the frozen product is 1.9 kJ/(kg K). If the latent heat to be removed during blast freezing is 100 kJ/kg, estimate the freezing time.
Consider a 50-cm-diameter and 95-cm-long hot water tank. The tank is placed on the roof of a house. The water inside the tank is heated to 80°C by a flat-plate solar collector during the day. The tank is then exposed to windy air at 18°C with an average velocity of 40 km/h during the night. Estimate the temperature of the tank after a 45-min period. Assume the tank surface to be at the same temperature as the water inside, and the heat transfer coefficient on the top and bottom surfaces to be the same as that on the side surface. Evaluate the air properties at 50°C.
Air is flowing in parallel over the upper surface of a flat plate with a length of 4m. The first half of the plate length, from the leading edge, has a constant surface temperature of 50 degrees Celsius. The second half of the plate length is subjected to a uniform heat flux of 86 W/m2. The air has a free stream velocity and temperature of 2 m/s and 10 degrees Celsius, respectively. Determine the local convection heat transfer coefficients at 1 m and 3 m from the leading edge. Evaluate the air properties at a film temperature of 30 degrees Celsius. Is the film temperature Tf=30 degrees Celsius applicable at x = 3 m?
A thermocouple junction, which may be approximated as a sphere, is to be used for temperature measurement in a gas stream. The convection coefficient between the junction surface and the gas is h=400W/m².K, and the junction thermophysical properties are ĸ= 20W/m.°K, c= 400J/kg.°K and ρ=8500kg/m³. Determine the junction diameter needed for the thermocouple to have a time constant of 1s. If the junction is at 25°C and is placed in a gas stream that is at 200°C, how long will it take for the junction to reach 199°C?
. Castor oil at 36 °C flows over a 6 m long and 1 m wide heated plate at 0.06 m/s. For a surfacetemperature of 96 °C, determine (i) the thermal boundary layer thickness at the end of the plate,(ii) the local heat transfer coefficient at the end of the plate, and (iii) the rate of heat transfer fromthe entire plate
In presence of an external flow when will the convective heat transfer be dominated by free convection and not by the forced convection due to the external flow? Gr ≫ Re². Gr ≪ Re. Gr ≫ Re. Gr ≪ Re For ideal gases, the specific heat capacity at constant pressure, thermal conductivity, dynamic viscosity, and Prandtl number are independent of pressure. How will the ratio of thicknesses of velocity boundary layer and thermal boundary layer change if pressure is increased from 1 atm to 5 atm for the flow of an ideal gas over a flat plate? It will decrease by a factor of 5. It will remain the same. It will increase by a factor of 5. We need to know the actual fluid properties to tell.
How can we use the transient temperature charts when the surface temperature of the geometry is specified instead of the temperature of the surrounding medium and the convection heat transfer coefficient?
Illustrate the concept of convection in heat transfer operation and also differentiate forced convection and natural convection with suitable examples. Why thermal conductivity of liquid decreases whereas that of gas increases by increasing temperature?
The author and his then 6-year-old son have conducted the following experiment to determine the thermal conductivity of a hot dog. They first boiled water in a large pan and measured the temperature of the boiling water to be 94°C, which is not surprising, since they live at an elevation of about 1650 m in Reno, Nevada. They then took a hot dog that is 12.5 cm long and 2.2 cm in diameter and inserted a thermocouple into the midpoint of the hot dog and another thermocouple just under the skin. They waited until both thermocouples read 20°C, which is the ambient temperature. They then dropped the hot dog into boiling water and observed the changes in both temperatures. Exactly 2 min after the hot dog was dropped into the boiling water, they recorded the center and the surface temperatures to be 59°C and 88°C, respectively. The density of the hot dog can be taken to be 980 kg/m3, which is slightly less than the density of water, since the hot dog was observed to be floating in water while…
A fabricated food, in the form of small spherical pellets, is to be frozen in an air-blast freezer. The air-blast freezer isoperating with air at -40°C. The initial product temperatureis 25°C. The pellets have a diameter of 0.5 cm, and the density of the product is 980 kg/m3. The initial freezing temperature is -2.5°C. The latent heat of fusion for this product is 280 kJ/kg. The thermal conductivity of the frozen productis 1.9 W/(m°C). The convective heat transfer coefficient is 50 W/(m2 °C). Calculate the freezing time.