During a picnic on a hot summer day, the only available drinks were those at the ambient temperature of 90°F. In an effort to cool a 1 2-fluid-oz drink in a can, which is 5 in high and has a diameter of 2.5 in. a person grabs the can and starts shaking it in the iced page 311 water of the chest at 32°F. The temperature of the drink can be assumed to be uniform at all times, and the heat transfer coefficient between the iced water and the aluminum can is 30 Bta1rfi2°F. Using the properties of water for the drink, estimate how long it vi11 take for the canned drink to cool to 40°F. Solve this problem using lumped system analysis. Is the lumped system analysis applicable to this problem? Why?
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Heat and Mass Transfer: Fundamentals and Applications
- Measuring the temperature of very cold substances can be challenging. Here is one way of measuring the temperature of liquid nitrogen. A 50g flake of aluminum is submerged in liquid nitrogen and left immersed until it is in thermal equilibrium. The flake is then removed and placed in a well-insulated container with 500ml of water at 30°C. When water and flake attain thermal equilibrium, the temperature of the water is found to be 25°C. What was the temperature of the liquid nitrogen?arrow_forwardIce 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_forward
- 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_forwardConsider a house that has a floor space of 15m x 12m and an average height of 2.7 m at 150m elevation where the standard atmospheric pressure is 84.1 kPa (shown in figure below). Initially the house is at a uniform temperature of 10°C. Now the electric heater is turned on, and the heater runs until the air temperature in the house rises to an average value of 21°C. Determine the amount of energy transferred to the air assuming (a) the house is air-tight and thus no air escapes during the heating process and (b) some air escapes through the cracks as the heated air in the house expands at constant pressure. Also determine the cost of this heat for each case if the cost of electricity in that area is $0.080/kWharrow_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
- A father and son conducted the following simple experiment on a hot dog which measured 12.5 cm in length and 2.2 cm in diameter. They inserted one food thermometer into the midpoint of the hot dog and another one was placed just under the skin of the hot dog. The temperatures of the thermometers were monitored until both thermometers read 20°C, which is the ambient temperature. The hot dog was then placed in 94°C boiling water and after exactly 2 min they recorded the center temperature and the skin temperature of the hot dog to be 59°C and 88°C, respectively. Assuming the following properties for the hot dog: r = 980 kg/m3 and cp = 3900 J/kg·K and using transient temperature charts, determine (a) the thermal diffusivity of the hot dog, (b) the thermal conductivity of the hot dog, and (c) the convection heat transfer coefficient.arrow_forwardIt 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 95°Carrow_forwardA 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.arrow_forward
- What is a quasi-equilibrium process? What is its importance in engineering?arrow_forwardThe outer wall consists of a 30 cm thick brick wall which is covered by a layer of styrofoam. How thick is the styrofoam layer if the temperature at the boundary between the brick and styrofoam is 0 °C. External the temperature is −15°C and the indoor temperature is 23°C.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_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage LearningRefrigeration and Air Conditioning Technology (Mi...Mechanical EngineeringISBN:9781305578296Author:John Tomczyk, Eugene Silberstein, Bill Whitman, Bill JohnsonPublisher:Cengage Learning