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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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.
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
A thermocouple is used to measure the temperature T1. The thermocouple reference junction labeled 2 is at a temperature of 20°C. The voltage output is measured using a potentiometer and found to be 4.686 mV. What is T1 in degrees RK: if the temperature values are not in the table, you have to use interpolation. Select one: O a. 98 O b. 118 O c. 105 O d. 108 Previous page Next page
Newton's Law of cooling states that the rate at which heat is lost by a heated body is proportional to the difference in temperature between the body and the surrounding medium. Match the following statements/phrases with the corresponding item in the drop down box. Choices in the box 1. In accordance with the stated law obove, we have the equation? 2. If a thermometer is taken outdoors where the temperoture is 5 deg C, from a room in which the temperature is 20 deg C and the reading drops 10 deg C in one minute, the working equation is? 3. In the obove problem, separoting the variables and integrating will result to? 4. In the obove problem, how long, in minutes, after its removal from the room will the reading be 6 deg C? 5. In the obove problem, ofter 30 seconds, whot will be the thermometer reading? 5.2 dT(body temp)/dt = k(Temp of medium - 5) dr(body temp)/dt = k(Temp of body - Temp of medium) Temp of body = Cenkt +5 2.5 13.7 dr(body temp)/dt = k(Temp of medium - Temp of body)…
You are analyzing the following (not necessarily well designed) process: At the start of the process, there two fluid streams, one containing species ‘A’ at a concentration of 2mol/l (Stream 1) and one containing species ‘B’ at a concentration of 3mol/l (Stream 2). Each stream has a control valve near the start of the process. Stream 1 has a temperature of 90°C and Stream 2 has a temperature of 70°C. The two streams enter a motorized mixer. A single stream exits the mixer (Stream 3). Stream 3 then enters a stirred tank reactor where nA+mB⟶C. The exit stream (Stream 4) enters a fluid separator. Out of the separator are two streams, one containing species ‘A’ and ‘B’ (Stream 5) and the other containing species ‘C’ at concentration of 1.5mol/l (Stream 6). Stream 5 goes back into the mixer. Stream 6 goes through a pump and another control valve. This stream is then cooled in a shell and tube heat exchanger using a cooled water stream that is at a temperature of 15°C. The outlet flow, now…
The left side of this equation tells how much energy Q the cylinder gives to the water while it cools. The right side of this equation tells how much energy Q the water and aluminum cup absorb from the cylinder to warm up. Because it is the same energy, they are equal. What is known in this equation? Mcyl 411.7 g, malum 46.5 g, malum+water = 175 g Can you find: mwater =? g Twater = Talum = 20°C (water and cup of room temperature) 90°C, T; = 35°C (hot cylinder and cool "cylinder+cup+water" temperatures) Tcyl kCal Calum = 0.22, Cwater 1 (specific heat of water and aluminum, measured in units kg-°C What are we looking for is Ccul - How we find it? Plug all the numbers into the equation (1), Ccul will be one unknown which you can calculate from the equation. Important, convert all the masses from grams to kilograms! After you find Ccyl, compare it to known value for the copper 0.093(our cylinder is made out of copper). |Ceyl -0.093| % : · 100% 0.093
A chamber of unknown volume is filled with an unknown amount of ideal gas. A cylinder with an open bottom and calibrated volume is connected to the chamber and is closed with a movable piston. A gas pressure sensor is also mounted on the chamber as shown in the figure. The whole experimental setup is kept at a constant temperature of 300 K. Doris moves the piston from mark 0 to mark 200 mL in steps of 50 mL and records the corresponding pressure in the chamber (see the table below). She moves the piston very slowly and waits several minutes before recording the pressure values. VCyl(mL) P(105N/m2)) 0 4.35 50 3.85 100 3.50 150 3.15 200 2.90 Determine the volume of the chamber using Doris's data in the table. (Note: This is a problem that requires linearization of data.) Determine the number of moles of gas. (Note: This is a problem that requires linearization of data.)
A picture window has dimensions 2.3 m x 1.4 m and is made of glass 5.6 mm thick. On a winter day the outside temperature is -18.0 °C while the inside temperature is 19.0 °C. The thermal conductivity of glass is 0.84 J/(s-m-°C) and the thermal conductivity of paper is 0.05 J/(s-m-°C). Determine the following.
23. The surface tension of water in contact with air is given as 0.0725 N/m. The pressure outside the droplet of 20. Determine the bulk modulus of elasticity of a fluid which is compressed in a cylinder from a volume a 0.009 m at 70 Ncn pressure to a volume of 0.0085 m' at 270 N/cm pressure. [Ans. 3.6 x 10° N/em1 21. The surface tension of water in contact with air at 20°C is given as 0.0716 N/m. The pressure inside droplet of water is to be 0.0147 N/cm greater than the outside pressure, calculate the diameter of droplet of water. 22. Find the surface tension in a soap bubble of 30 mm diameter when the inside pressure is 1.962 N/m* above [Ans. 1.94 mm) atmosphere. (Ans. 0.00735 Nm] water of diameter 0.02 mm is atmospheric 10.32 . Calculate the pressure within the droplet of cm water. [Ans. 11.77 N/em']
Liquid nitrogen has a density of 0.808 g/mL and boils at 77 K. Researchers often purchase liquid nitrogen in insulated 175-L tanks. The liquid vaporizes quickly to gaseous nitrogen (which has a density of 1.15 g/L at room temperature and atmospheric pressure) when the liquid is removed from the tank. Suppose that all 175 L of liquid nitrogen in a tank accidentally vaporized in a lab that measured 10.00m x 10.00m x 2.50m. What maximum fraction of the air in the room could be displaced by the gaseous nitrogen?