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!)
- A 20-cm diameter copper ball is to be heated from 110°C to an average temperature of 170°C in 90 minutes. Taking the average density and specific heat of copper in this temperature range to be p=8950 kg/m and Cp=0.395 kJ/kg • °C, respectively, determine the total amount of heat transfer to the copper ball in kj (Area of sphere: TID2; Volume of sphere=TTD/6)? A 88.64 kJ B 886.4 kl 78.84 kJ D 788.4 kJarrow_forwardHi, 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_forwardIn a double-glazed window, the panes of glass are separated by 1.0 cm and the space is filled with a gas with thermal conductivity 24 mW K−1 m−1. What is the rate of transfer of heat by conduction from the warm room (28 °C) to the cold exterior (−15 °C) through a window of area 1.0 m2? You may assume that one pane of glass is at the same temperature as the inside and the other as the outside. What power of heater is required to make good the loss of heat?arrow_forward
- In determining the average rate of heating of a tank of 20% sugar syrup, thetemperature at the beginning was 20°C and it took 30 min to heat to 80°C. Thevolume of the sugar syrup was 50 ft3 and its density 66.9 lb/ft3. The specific heat ofthe sugar syrup is 0.9 Btu lb-1°F-1.(a) Convert the specific heat to kJ kg-1°C-1.(b) Determine the rate of heating, that is the heat energy transferred in unit time, in SI units (kJ s-1)arrow_forwardA computer room located on the second floor of a five-story office building is 10m by 7 m. The exterior wall is 3.5 m high and 10 m long; it is a metal curtain wall (steel backed with 10 mm of insulating board), 75 mm of glass-fiber insulation, and 16 mm of gypsum board. Single-glazed windows make up 30 percent of the exterior wall. The computer and lights in the room operate 24 h/d and have a combined heat release to the space of 2 kw. The indoor temperature is 20 C. (a) If the building is located in Columbus, Ohio, determine the heating load at winter design conditions. (b) What would be the load if the windows were double-glazed?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_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_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_forwardA 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_forward
- Consider 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_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_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_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning