Consider two identical rooms,one with a refrigerator in it and the other without one .if all the doors and windows are closed will the room that contains the refrigerator be cooler or warmer than the other room? why?
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Consider two identical rooms,one with a refrigerator in it and the other without one .if all the doors and windows are closed will the room that contains the refrigerator be cooler or warmer than the other room? why?
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- Calculate the amount of energy required to heat the air in a house 30 by 50 by 40 feet from 10 to 70°F. The density of air is about 0.080 lbs/ft3, and its specific heat at constant pressure is about 0.24 BTU/lb-°F1. It is commonly recommended that hot foods be cooled first to room temperature by simply waiting a while before they are put into the refrigerator to save energy. Despite this common sense recommendation, a person keeps cooking a large pan of stew twice a week and putting the pan into the refrigerator while it is still hot, thinking that the money saved is probably too little. The average mass of the pan and its contents is 5-kg. The average temperature of the kitchen is 20°C, and the average temperature of the food is 95°C when it is taken off the stove. The refrigerated space is maintained at 3°C, and the average specific heat of the food and the pan can be taken to be 3.9 kJ/kg-K. If the refrigerator has a coefficient of performance of 1.2 and the cost of electricity is Php 21.59 per kW-hr. Determine how much will be saved a year by waiting for the food to cool to room temperature before putting it into the refrigerator. Ans: Php 170.66 20°C Hot food 5°CConsider hotdog being cooked in boiling water in a pan. Would the heat transfer be modeled as one-dimensional or two-dimensional? Would the heat transfer be steady or transient? Explain.
- Hi, 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.A 12-by-12 in. open pan containing water at 140 °F is placed in the exact center of a 16-by-20 ft room having a ceiling temperature of 75°F. If the distance from the water surface to the ceiling is 10 ft and the ceiling is painted with an oil paint, what is the net radiant-heat exchange between the water surface and the ceiling?On a mild Saturday morning while people are working inside, the furnace keeps the temperature inside the building at 23°C. At noon the furnace is turned off, and the people go home. The temperature outside is a constant 14°C for the rest of the afternoon. If the time constant for the building is 3 hr, when will the temperature inside the building reach 19°C? If some windows are left open and the time constant drops to 2 hr, when will the temperature inside reach 19°C? If the time constant for the building is 3 hr, the temperature inside the building will reach 19°C about hr after noon. (Round to the nearest tenth as needed.) If the time constant for the building drops to 2 hr, the temperature inside the building will reach 19°C about (Round to the nearest tenth as needed.) hr after noon. C
- Room 4 mx 6 mx6m Fan FIGURE P1-31 A student living in a 4-m × 6-m X 6-m dormitory room turns his 150-W fan on before she leaves her room on a summer day hoping that the room will be cooler when she comes back in the evening. Assuming all the doors and win- dows are tightly closed and disregarding any heat transfer through the walls and the windows, determine the temperature in the room when she comes back 10 hours later. Use specific heat values at room temperature and assume the room to be at 100 kPa and 15°C in the morning when she leaves.I just took a water bottle out of my refrigerator (0₁ = 3°C) and placed it on the kitchen counter. The environment is at 0₂ = 20 °C. The overall heat transfer coefficient between the bottle and the environment is 2 W/K and the heat capacity of the bottle and its contents is 3 kJ/K. Over what time periods would you consider the bottle to be an adiabatic system? A diather- Colar mal system?A student living in a 4-m x 6-m x 6-m dormitory room turns his 150-W fan on before she leaves her room on a summer day hoping that the room will be cooler when she comes back in the evening. Assuming all the doors and windows are tightly closed and disregarding any heat transfer through the walls and the windows, determine the temperature in the room when she comes back 10 hours later. Use specific heat values at room temperature and assume the room to be at 100 kPa and 15°C in the morning when she leaves.
- In an electrically heated home, the temperature of the ground in contact with a concrete basement wall is 13.8 oC. The temperature at the inside surface of the wall is 18.4 oC. The wall is 0.13 m thick and has an area of 6.8 m2. Assume that one kilowatt hour of electrical energy costs $0.10. How many hours are required for one dollar's worth of energy to be conducted through the wall?What is the difference between internal heat generation and heat transfer in any direction. Thank you6. 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.