A spherical ball (15 cm in diameter) with a density of 1000 kg/m³, specific heat capacity of 4180 J/kg-K and thermal conductivity of 0.62 W/m-K is removed from an oven at a uniform temperature of 150 °C. The ball is then left to cool down in steady air at 10 °C. Calculate the heat transfer coefficient for this process and the time for the surface of the ball to drop to 20 °C. Use the following equation to solve this problem (characteristic dimension of the sphere is the diameter). 0.589 · Ra* Nu = 2+ 0.469 16 Pr
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- The boiling temperature of nitrogen at atmospheric pressure at sea level (1 atm) is -196°C. Therefore, nitrogen is commonly used in low temperature scientific studies since the temperature of liquid nitrogen in a tank open to the atmosphere will remain constant at -196°C until the liquid nitrogen in the tank is depleted. Any heat transfer to the tank will result in the evaporation of some liquid nitrogen, which has a heat of vaporization of 198 kJ/kg and a density of 810 kg/m3 at 1 atm. Consider a 3-m-diameter spherical tank initially filled with liquid nitrogen at 1 atm and 196°C. The tank is exposed to 22°C ambient air with a heat transfer coefficient of 22 W/m2 · °C. The temperature of the thin-shelled spherical tank is observed to be almost the same as the temperature of the nitrogen inside. Disregarding any radiation heat exchange, determine the rate of evaporation of the liquid nitrogen in the tank as a result of the heat transfer from the ambient air in kg/sec. Answer in…The boiling temperature of nitrogen at atmospheric pressure at sea level (1 atm pressure) is -196 °C. Therefore, nitrogen is commonly used in low-temperature scientific studies since the temperature of liquid nitrogen in a tank open to the atmosphere will remain constant at -196 °C until it is depleted. Any heat transfer to the tank will result in the evaporation of some liquid nitrogen, which has a heat of vaporization of 198 kJ/kg and a density of 810 kg/m3 at 1 atm. Consider a 3-m-diameter spherical tank that is initially filled with liquid nitrogen at 1 atm and -196 °C. The tank is exposed to ambient air at 15° C, with a combined convection and radiation heat transfer coefficient of 35 W/m2⋅K. The temperature of the thin-shelled spherical tank is observed to be almost the same as the temperature of the nitrogen inside. Determine the rate of evaporation (in kg/s) of the liquid nitrogen in the tank as a result of the heat transfer from the ambient air if the tank is insulated with…Ground turkey was made into me at balls and refrigerated at 2 ° C before being deep fried. The diameter of each meat ball is 9cm. To make sure that the meat balls are safe to be consumed, they must be cooked over 70 ° C. Assume that the cooking oil is at a constant temperature of 180 ° C and has a heat transfer coefficient of 50 W/(m 2 ∙ K). The conductivity and specific heat of the ground turkey are approximated at 2 W/( m∙K ) and 4 kJ/( kg ∙ K) respectively. The density of the ground turkey is 500kg/ m 3 . a) During the deep- frying process, do you anticipate that each meat ball has a uniform temperature distribution throughout its volume? Please show calculation to support your answer (5 pts) . b) Please calculate the minimum time required for cooking (1 5 p ts). c) When served, what are the surface and center temperatures of each meat ball ( 15 pts).
- Water hardening process of 2 m long and 0.05 m diameter steel bars will be carried out. The steel bar, which is heated up to 900 °C in the oven, is cooled to an average temperature of 100 °C in a water bath. The water bath is kept at a uniform temperature of 30 °C and the heat transfer coefficient between the water and the rod surface is 325 W/m2K. Accordingly, calculate the time required for the steel bar to cool to 100°C in the water bath. (Steel bar p=7832 kg/m3, cp=434 J/kgK, k=63.9 W/mK)A food product wants to be produced in a small round shape (pellet) by freezing it in a water blast freezer freezer. Air freezer operates at a temperature of -40 ° C. The initial product temperature is 25 ° C. The pellet has a diameter of 0.5 cm, and a density of 980 kg / m³. The initial freezing temperature is -2.5 ° C. The latent heat of freezing of the product is 280 kJ / kg. The thermal conductivity of the frozen product is 1.9 W / (m ° C). The convective heat transfer coefficient is 50 W / (m² K). Calculate the freeze time.A food product wants to be produced in a small round shape (pellet) by freezing it in a water blast freezer freezer. Air freezer operates at a temperature of -35 ° C. The initial product temperature is 25 ° C. The pellet has a diameter of 0.5 cm, and a density of 980 kg / m³. The initial freezing temperature is -2.5 ° C. The latent heat of freezing of the product is 280 kJ / kg. The thermal conductivity of the frozen product is 1.9 W / (m ° C). The convective heat transfer coefficient is 50 W / (m² K). Calculate the freeze time. t f = hour.
- BThe heat transfer from a 2-m-diameter sphere to a 25 °C air stream over a time interval of one hour is 3000 kJ. Estimate the surface temperature of the sphere if the heat transfer coefficient is 10 W/m²K.[2] Consider a 1.2-m-high and 2-m-wide double-pane window consisting of two 3-mm-thick layers of glass (k = 0.78 W/m °C) separated by a 12-mm-wide stagnant air space (k = 0.026 W/m- °C). Determine the steady rate of heat transfer through this double-pane window and the temperature of its inner surface for a day during which the room is maintained at 24°C while the temperature of the outdoors is -5°C. Take the convection heat transfer coefficients on the inner and outer surfaces of the window to be h1 = 10 W/m2.°C and h2 = 25 W/m2.°C, and disregard any heat transfer by radiation. Glass 3 12 3 mm Frame a.) Steady rate of heat transfer. А. 318 W B. 214 W C. 114 W D. 321 W b.) Temperature of its inner surface. A. 25°C B. 17.5°C С. 15°С D. 19.2°CConvection 2. For a boiling process such as shown in Figure below, the ambient temperature Tin Newton's law of cooling is replaced by the saturation temperature of the fluid Tsat. Consider a situation where the heat flux from the hot plate is q=20 x 105 W/m². If the fluid is water at atmospheric pressure and the convection heat transfer coefficient is hw=20 x 103 W/m2 K, determine the upper surface temperature of the plate, Ts, w. In an effort to minimize the surface temperature, a technician proposes replacing the water with a dielectric fluid whose saturation temperature is Teat, d=52 °C. If the heat transfer coefficient associated with the dielectric fluid is h = 3 x 103 W/m2 K, will the technician's plan work?
- A food product with 73% moisture content in a 10 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 -2.25 ° C. After 15 hours in the freezing medium -35 ° 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).A food product wants to be produced in a small round shape (pellet) by freezing it in a water blast freezer freezer. Air freezer operates at a temperature of -35 ° C. The initial product temperature is 25 ° C. The pellet has a diameter of 1.2 cm, and a density of 980 kg / m³. The initial freezing temperature is -2.5 ° C. The latent heat of freezing of the product is 280 kJ / kg. The thermal conductivity of the frozen product is 1.9 W / (m ° C). The convective heat transfer coefficient is 40 W / (m² K). Calculate the freeze time. t f = Answerhour.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.