11.10 The following set of data are produced by a temperature-measuring device (first order) that is suddenly immersed into a mixture of ice and liquid water. Initially, the device is in ambient air (20°C). Determine the time constant of this temperature-measuring device. Time (s) Temperature (°C) 0.1 0.5 1 2 3 16.7 8.1 3.3 0.6 0.1

11.10 The following set of data are produced by a temperature-measuring device (first order) that is suddenly immersed into a mixture of ice and liquid water. Initially, the device is in ambient air (20°C). Determine the time constant of this temperature-measuring device. Time (s) Temperature (°C) 0.1 0.5 1 2 3 16.7 8.1 3.3 0.6 0.1

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.22P: 1.22 In order to prevent frostbite to skiers on chair lifts, the weather report at most ski areas...

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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?
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Give True or False for the following: 1.In liquids and gases, heat transmission is caused by conduction and convection 2.The surface geometry is the important factor in convection heat transfer 3. The heat transfer by conduction from heated surface to the adjacent layer of fluid, 4. The heat transfer is increased in the fin when &> 1 5.The unit of the thermal diffusivity is m²/s 6. Temperature change between the materials interfaces is attributed to the thermal contact resistance 7. A material that has a low heat capacity will have a large thermal diffusivity. 8. Heat conduction flowing from one side to other depends directly on thickness 9.Fin efficiency is the ratio of the fin heat dissipation with that of no fin 10.The critical radius is represented the ratio of the convicted heat transfer to the thermal conductivity
Q2/ A thermometer initially at a temperature of 20°C is suddenly plunged into a liquid bath maintained at 150°C. After time interval of 3 seconds, the thermometer indicated a temperature of 95°C. Determine: a. The time constant of the thermometer. b. The indicated temperature after 5 time constants.
The temperature of an experimental heated enclosure is being ramped up from 80 to 450°F at the rate of 19°F/min. A thermocouple, embedded in a Thermowell for protection, is being used to monitor the oven temperature. The thermocouple has a time constant of 84 s. At t = 10 min, what is the difference between the actual temperature and the temperature indicated by the thermocouple? Final answer in whole number. Please show your complete solution and write readable.
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Consider an introductory thermodynamics class experiment used to demonstrate phase change phenomena. A beaker of water is heated, and its temperature measured over time to establish the temperature at which boiling occurs. The results, shown in the Figure below, are for three separate tests conducted on different days by different student groups using the same equipment and method. Why might the data from three seemingly identical tests show different results? Temperature (°C) 101 100 99 98 97 96 95 94 1 2 3 4 Time (min) 5 Boiling region 100.3 100.1 99.8 Boiling point results Test 1 (762 mm Hg) Test 2 (754 mm Hg) Test 3 (767 mm Hg) 6 7
TRUE OR FALSE 4.) Bioyield is considered an elastic state and is located within the proportional limit 5.) The difference in the effect of temperature on viscosity of liquids and gases is related to the difference in their density. 6.) The parallel method of thermal conductivity calculation is based on the weighted harmonic mean of the components
After the sinking of RMS Titanic, US operated the International Ice patrol with the purpose of monitoring the presence and movements of icebergs in the Atlantic and Arctic oceans. Once, they observed a unique tabular iceberg in a form of a rectangle (250 km x 50 km x 300 m). How many years would it take to melt the iceberg solely by heat from the sun if the ice absorbs a mean of 98 J/m2 -s, 12.5 hrs per day? Note: the exposed area for heating is 250 km x 50 km and the density is 920 kg/m3 . This is my solution.
4- A thermometer having a time constant of 0.4 min. is placed in a temperature bath and after the thermometer comes to equilibrium with the bath, the temperature of the bath is increased linearly with time at the rate of 2 deg.C min. what is the difference between the indicated temperature and bath temperature after : (a) 2 min. (b) 20 min.
Example 3.4 measured by observing the temperature-time history of a copper ball of the same dimension. The temperature of the copper ball (c = 0.4 kJ/kg K, p = 8850 kg/m³) was measured by two thermocouples, one located in the centre, the other near the surface. Both of the thermocouples registered within the accuracy of the recording instruments the same temperature at a given instant. In one test the initial temperature of the ball was 65°C and in 1.15 min the temperature decreased by 11°C. Calculate the heat transfer coefficient for this case. The heat transfer coefficients for the flow of air at 28°C over a 12.5 mm diameter sphere are