Concept explainers
Quenching is the process of immersing a hot metal object in a bath for a specified time to improve properties such as hardness. A copper sphere 25 mm in diameter, initially at 300°C, is immersed in a bath at 0°C. Measurements of the sphere’s temperature versus time are shown here. Plot the data and find a functional description of the data.
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SYSTEM DYNAMICS CONNECT
- Using the information in Problem 1.22, estimate the ambient air temperature that could cause frostbite on a calm day on the ski slopes. 1.22 In order to prevent frostbite to skiers on chair lifts, the weather report at most ski areas gives both an air temperature and the wind-chill temperature. The air temperature is measured with a thermometer that is not affected by the wind. However, the rate of heat loss from the skier increases with wind velocity, and the wind-chill temperature is the temperature that would result in the same rate of heat loss in still air as occurs at the measured air temperature with the existing wind. Suppose that the inner temperature of a 3-mm-thick layer of skin with a thermal conductivity of 0.35W/mKis35C and the air temperature is 20C. Under calm ambient conditions the heat transfer coefficient at the outer skin surface is about 20W/m2K (see Table 1.4), but in a 40-mph wind it increases to 75W/m2K. If frostbite occurs when the skin temperature drops to about 10C, do you advise the skier to wear a face mask? What is the skin temperature drop due to the wind?arrow_forward1.22 In order to prevent frostbite to skiers on chair lifts, the weather report at most ski areas gives both an air temperature and the wind-chill temperature. The air temperature is measured with a thermometer that is not affected by the wind. However, the rate of heat loss from the skier increases with wind velocity, and the wind-chill temperature is the temperature that would result in the same rate of heat loss in still air as occurs at the measured air temperature with the existing wind. Suppose that the inner temperature of a 3-mm-thick layer of skin with a thermal conductivity of 0.35 W/m K is and the air temperature is . Under calm ambient conditions the heat transfer coefficient at the outer skin surface is about (see Table 1.4), but in a 40-mph wind it increases to . (a) If frostbite occurs when the skin temperature drops to about , do you advise the skier to wear a face mask? (b) What is the skin temperature drop due to the wind?arrow_forwardThe drag on an airplane wing in flight is known to be a function of the density of air (), the viscosity of air(), the free-stream velocity (U), a characteristic dimension of the wing (s), and the shear stress on the surface of the wing (s). Show that the dimensionless drag, sU2, can be expressed as a function of the Reynolds number, Us.arrow_forward
- The rate of heat flow per unit length q/L through a hollow cylinder of inside radius ri and outside radius ro is q/L=(AkT)/(rori) where A=2/(rori)/ln(ro/ri). Determine the percent error in the rate of heat flow if the arithmetic mean area (ro+ri) is used instead of the logarithmic mean area A for ratios of outside-to-inside diameters (Do/Dj) of 1.5, 2.0, and 3.0. Plot the results.arrow_forwardThe data below is from a passenger hot air balloon. The balloon is designed to lift 10-people (80 kg each person). The balloon consists of a basket, a burner- propane tank system. It will lift up when the cold air trapped inside warms up by the burner. Density of air inside the balloon is 99°C: 0.9486 kg/m³, density of air outside balloon is 20°C (ambient): 1.2041 kg/m³, Assume the balloon is a sphere shape, volume =(4/3)pi R3 Mass (kg) Balloon Basket Burner Propane tank 113.4 kg 63.5 kg 22.7 kg 183.7 kg a) Determine the minimum diameter of the balloon that would have a total lifting force to balance the weight of balloon, basket, burner, propane tank and 10 people? b) If the balloon is converted to survey the weather, it will be filled with hydrogen gas (H2). Assume the weight of the people (800kg) is now replaced by onboard equipment, what is minimum diameter needed to keep it afloat at 18km above the surface of the earth?arrow_forward1000 cm^3 of air at an initial pressure of 1.10 × 10^5 Pa and temperature of 300 K undergoes the following changes: heat the air at constant pressureuntil its temperature reaches 390 K and then compress the air isothermallyuntil it returns to the initial volume of 1000 cm3and finally allow the air to cool so that its final pressure is 1.10 × 10^5 Pa. i. Draw a P-V graph to represent the changes undergone by the air ii. Calculate the maximum volume of the air. iii. What is the maximum pressure of the air? iv. State how the net work done on the air for the whole process can bedeterminedarrow_forward
- The heat transfer between a solid body and a fluid medium is determined by the equation Q=h·A·(Ts-Tf). Here; Q is the amount of heat transferred, h is the heat transfer coefficient, A is the heat transfer surface area, Ts is the temperature of the surface and Tf is the temperature of the fluid. These parameters were measured as h=250±1.75 W/m2ºC, A=20±0.75 m2, Ts =100±0.75ºC and Tf =25±0.75ºC, including error levels. What is the total uncertainty in the amount of heat transferred, in ±%? a. 3.98 b. 4.07 c. 2.73 d. 2.95 e. 3.88arrow_forwardA grocery store sells 5-lb bags of mangoes. You purchase four bags over the course of a month and weigh the mangoes each time. You obtain the following measurement: Week 1 weight: 4.8 lb Week 2 weigh: 5.3 lb Week 3 weigh: 4.9 lb Week 4 weigh: 5.4 lb Does the measurement have random error? Does the measurement have systematic error?arrow_forwardA solid steel cube is stored in a freezer, where the temperature is −20.0 ̊C. While the cube is in the freezer, you measure its side length (L) to be 1.75050 meters. The cube is then placed outside for a long time, so that the temperature of the cube reaches the temperature of the air outside. As a result, the side length increases to 1.75170 meters due to thermal expansion. The coefficient of linear expansion for steel is 12.0×10−6 ̊C−1. (a) What is the temperature of the air outside? Give your answer in degrees Celsius ( ̊C). (b) What is the volume of the cube when its temperature is 20.0 ̊C? Give your answer in cubic meters (m3).arrow_forward
- Based on your equations for the above problem, solve for the extension of the spring (in meters) when the variables have values as follows: angle A is 74.79 degrees angle B is 44.36 degrees spring constant k is 123.77 N/m mass m2 is 2.52 kgarrow_forwardCalculate the pressure due to a column of 0.4 m of the following liquids (a) water (b) an oil of specific gravity 0.9 (c) mercury (d) a liquid of specific weight 46780 N/marrow_forwarda=2, b=1 A bullet is to be tested in the laboratory to determine the drag force on it. Dependent parameter the drag force D (Newton) depends on the velocity of the bullet V(m/s), the length of the bullet L(m), sound velocity c(m/s), density of fluid ρ (kg/m3) and dynamic viscosity µ(kg/ms). Solve the problem by making the necessary assumptions and drawing the schematic figure I-Determine the nondimensional p parameters using repeating variables ii-a bullet with a speed of 9a,b m/s in air may be modelled in a water tunnel with a test section velocity of 2ab cm/s. Determine the length of the model, if the length of the bullet is 5a,b mm. The air and water temperature is 20 oC degree at 1 atm. iii- if the drag force on the model is measured to be 2,ab N, then determine the expected drag force on the bullet. Comment on dynamic similarity equivalence?arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning