The interior wall of a large, commercial walk-in type meat freezer is covered under normal operating conditions with a 2-cm thick layer of ice. One day, a power outage cuts electricity to the refrigeration system of the freezer. Estimate the time required to melt this layer of ice if it has a mass density of
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Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
- Hi, can you help me to answer this question using the first law of thermodynamics formula to explain this event? On a hot summer day, a student turns his fan on when he leaves his room in themorning. When he returns in the evening will the room be warmer or cooler than theneighborouing rooms ? Explain your answer using the first law of thermodynamics.Assume ALL doors and windows are kept closed.arrow_forwardQ2/ A 4-m-internal-diameter spherical tank made of 1.75-cm-thick stainless steel (k 15 W/m °C) is used to store iced water at 0°C. The tank is located in a room whose temperature is 35°C. The walls of the room are also at 35°C. The outer surface of the tank is black, and heat transfer between the outer surface of the tank and the surroundings is by natural convection and radiation. The convection heat transfer coefficients at the inner and the outer surfaces of the tank are 80 W/m2 °C and 10 W/m2· °C, respectively. Determine (a) the rate of heat transfer to the iced water in the tank and (b) the amount of ice at 0°C that melts during a l-h period. The heat of fusion of water at atmospheric pressure is hif 334 kJ/kg.arrow_forwardHi, can you help me to answer this question using the first law of thermodynamics? On a hot summer day a student turns his fan on when he leaves his room in themorning. When he returns in the evening will the room be warmer or cooler than theneighborouing rooms ? Explain your answer using the first law of thermodynamics.Assume ALL doors and windows are kept closed.arrow_forward
- Ice water of 0°C is stored in a spherical container made of steel with an inner diameter of 3 m and a thickness of 1 cm. This container is located in a place where the external temperature is 25℃. The temperature of the entire container is assumed to be 0°C. If thermal resistance in the container is ignored, obtain (a) the heat transfer rate to ice water, and (b) the amount of ice that melts for 24 hours. The melting heat of ice at atmospheric pressure is 333.7 kJ/kg. The emissivity of the outer wall of the container is 0.75, and the convective thermoelectric transfer coefficient is 30 W/m2·K. The average temperature of the surrounding surface for radiation is 15℃. ***I would appreciate it if sir could write it in a way that I could read it well.**arrow_forwardA food product with 82% moisture content is being frozen. Estimate the specific heat of the product at -8°C when 82% of the water is in a frozen state. The specific heat of dry product solid is 2.5 kJ/(kg °C). Assume specific heat of water at -10°C is similar to specific heat of water at 0°C.arrow_forwardNewton's Law of Cooling - Differential Equations The rate at which a body cools is proportional to the difference in temperature between the body and its surroundings. If a body in air at 0°C will cool from 200°C to 100°C in 40 minutes, how many more minutes will it take the body to cool from 100°C to 50°C?arrow_forward
- A power station uses oil-fired boilers which are supplied with fuel from 4 cylindrical tanks, each with 12 m diameter and 11 m high. The calorific value of the oil is 38,039 kJ/kg and its relative density is 0.78. The output from the power station is 77 MW. Assuming the only 21% of the heat input is converted to into electrical energy output, how long will the boilers run (in days) on the oil in the tanks. Correct Answer: 4.7 ± 0.1arrow_forwardConsider a wall of 6-m x 2.8-m constructed by the following threelayers: plaster with a thickness of 1 cm (k = 0.36 W⁄m ∙ °C),brick with a thickness of 20 cm (k = 0.72 W⁄m ∙ °C) and wallcovering with a thickness of 2 cm (k = 1.4 W⁄m ∙ °C). Disregardthe effect of convection in the inner surface of the wall and considerthe inner temperature of the wall to be 23 °C. Consider thetemperature of the surroundings to be 8 °C. The heat transfer ratein this wall must be reduced by 90% by the installation of a layerof insulation. If heat transfer between the outer surface of the walland the surroundings is by natural convection (12 W m2 ⁄ ∙ °C)and radiation, and considering the outer wall to be black with atemperature of 9 °C, determine:a) The heat transfer rate without insulation.b) The thickness of the insulation if the material of the layer is polyurethane foam (k =0.025 W⁄m ∙ °C)c) The thickness of the insulation if the material of the layer is fiber glass (k = 0.036 W⁄m ∙ °C)arrow_forwardThe 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…arrow_forward
- A thermopane window consists of two glass panes, each 0.50 cm thick, with a 1.0-cm-thick sealed layer of air in between. (a) If the inside surface temperature is 22.1°C and the outside surface temperature is 0.0°C, determine the rate of energy transfer through 1.40 m² of the window. W (b) Compare your answer to (a) with the rate of energy transfer through 1.40 m² of a single 1.0-cm-thick pane of glass. Disregard surface air layers. (Find the rate of energy transfer.) kWarrow_forward6. A cylindrical electric heater of outside diameter D = 2.5 cm and length L= 2 m is immersed horizontally into a pool of mercury at 100°C. If the surface of the heater is maintained at an average temperature of 300°C, calculate the rate of heat transfer to the mercury.arrow_forwardConsider a double-paned window consisting of two panes of glass, each with a thickness of 0.500 cm and an area of 0.795 m2 , separated by a layer of air with a thickness of 1.50 cm. The temperature on one side of the window is 0.00 ∘C∘C; the temperature on the other side is 21.0 ∘C∘C. In addition, note that the thermal conductivity of glass is roughly 36 times greater than that of air. Approximate the heat transfer through this window by ignoring the glass. That is, calculate the heat flow per second through 1.50 cmcm of air with a temperature difference of 21.0 ∘C∘C. (The exact result for the complete window is 25.6 J/sJ/s .)arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning