Concept explainers
The temperature distribution in laser-irradiated materials is determined by the power, size, and shape of the laser beam, along with the properties of the material being irradiated. The beam shape is typically Gaussian, and the local beam irradiation flux (often referred to as the laser fluence) is
The x- and y-coordinates determine the location of interest on the surface of the irradiated material. Consider the case where the center of the beam is located at
A shape factor for Gaussian heating is S = 27112%, where
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Fundamentals of Heat and Mass Transfer
- 1.26 Repeat Problem 1.25 but assume that the surface of the storage vessel has an absorbance (equal to the emittance) of 0.1. Then determine the rate of evaporation of the liquid oxygen in kilograms per second and pounds per hour, assuming that convection can be neglected. The heat of vaporization of oxygen at –183°C is .arrow_forwardConsider a flat plate or a plane wall with a thickness L and a long cylinder of radius r0. Both of these are made of materials such that they can be treated as lumped capacitances (Bi0.1). Show that in each case, the characteristic length lc, defined lc=(V/As), can be approximated as (L/2) and (ro/2), respectively.arrow_forwardRepeat Problem 1.35 but assume that instead of surface temperatures, the given temperatures are those of the air on the left and right sides of the wall and that the convection heat transfer coefficients on the left and right surfaces are 6 and 10W/m2K, respectively.arrow_forward
- 3.A steam at 118°C is flowing inside a diameter of 40 mm, thickness of 10 mm ceramic pipe (k=1.52 W/mK). The pipe is insulated with 25 mm of insulator (k=0.064 W/m K). The convective coefficient for steam inside the pipe is h;=20.7 W/m²K and the convective coefficient for air outside the pipe is h.=0.07W/m²K. The air is at a temperature of 28°C ? (1)Calculate the heat loss per unit length of 1m of pipe (W)? (2)Repeat, using the overall U; based on the inside area A; ?arrow_forwardThe sun's intensity at the distance of the earth is 1370 W/m2W/m2. 30%% of this energy is reflected by water and clouds; 70%% is absorbed. What would be the earth's average temperature (in ∘C∘C) if the earth had no atmosphere? The emissivity of the surface is very close to 1. (The actual average temperature of the earth, about 15 ∘C∘C, is higher than your calculation because of the greenhouse effect.) Express your answer to two significant figures and include the appropriate units.arrow_forwardThe temperature of a experimental heated enclosure is being ramped up from 80 to 450°F at the rate of 20°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 6 s. ( a ) At t = 10 min, what is the difference between the actual temperature and the temperature indicated by the thermocouple? What is it at 60 min? ( b ) When the thermocouple indicates 450°F, the heater will begin to modulate and maintain the temperature at the desired 450°F. What is the actual oven temperature when the thermocouple first indicates 450°F?arrow_forward
- An electric heating system is installed in the ceiling of a room 5 m (length) × 5 m (width) ×2.5 m (height). The temperature of the ceiling is 315 K whereas under equilibrium conditions the walls are at 295 K. If the floor is non-sensitive to radiations and the emissivities of the ceiling and wall are 0.75 and 0.65, respectively. Calculate the radiant heat loss from the ceiling to the walls. The answer should be 1595 W. Please show steps in your solutionarrow_forwardA nuclear power station is situated in Coal Valley, which is a roughly rectangular valley that is 5 km long, 2 km wide, and 200 m deep. You have been asked to evaluate the effects of a worst-case scenario where the reactor housing fails, and radiation is released to the atmosphere. In your evaluation, you determine that 120 kg of Iodine-131 (a radioisotope that causes thyroid gland and liver damage) could be released into the atmosphere. Assuming the release of Iodine-131 was very rapid and all of it was uniformly distributed through the valley’s atmosphere with none escaping the valley, what would the concentration of Iodine-131 be in the valley’s air? Your answer should be expressed in units of ppm(v), and you may assume an atmospheric pressure of 1.0 atm and a temperature of 20oC. 2. Assuming the Iodine-131 concentration you calculated in part (a) is the initial concentration in the valley, you now want to determine the time it will take for the concentration to decrease to…arrow_forwarddiscuss the thermal conductivity of fruits and vegetables, including the different methods of measurement and their applications.arrow_forward
- The solar power striking Earth every day averages 168watts per square meter. The highest ever recorded electricalpower usage in New York City was 13,200 MW. A recordestablished in July of 2013. Considering that present technologyfor solar energy conversion is about 10% efficient,from how many square meters of land must sunlight becollected in order to provide this peak power? (For comparison,the total area of New York City is 830 km2.)arrow_forwardOptical properties of Enstatite - Becke line = - Wave plate = - Sign of elongation (Length fast vs. length slow) = - Extinction angle =arrow_forwardFish in lakes beside power plants, which use lake water for cooling, are subject to the danger of suffocation as a consequence of "thermal pollution", because _____________________. a. dissolved oxygen decreases as temperature of the lake waters increase b. dissolved oxygen increases in the lake waters c. gas solubility increases as temperature goes up d. the power plant noise disturbs the fisharrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning