An inexpensive food and beverage container is fabricated from 25-mm-thick polystyrene
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Fundamentals of Heat and Mass Transfer
- A square silicon chip 7mm7mm in size and 0.5-mm thick is mounted on a plastic substrate as shown in the sketch below. The top surface of the chip is cooled by a synthetic liquid flowing over it. Electronic circuits on the bottom of the chip generate heat at a rate of 5 W that must be transferred through the chip. Estimate the steady-state temperature difference between the front and back surfaces of the chip. The thermal conductivity of silicon is 150 W/m K. Problem 1.6arrow_forward1.4 To measure thermal conductivity, two similar 1-cm-thick specimens are placed in the apparatus shown in the accompanying sketch. Electric current is supplied to the guard heater, and a wattmeter shows that the power dissipation is 10 W. Thermocouples attached to the warmer and to the cooler surfaces show temperatures of 322 and 300 K, respectively. Calculate the thermal conductivity of the material at the mean temperature in W/m K. Problem 1.4arrow_forwardQ1/ The fumace wall consists of 120 mm wide refractory brick and 120 mm wide insulating fire brick separated by an air gap. The outside wall is covered with a 12 mm thickness of plaster. The inner surface of the wall is at 1090°C and the room temperature is 20°C. The heat transfer coefficient from the outside wall surface to the air in the room is 18 W/m2 °C, and the resistance to heat flow of the air gap is 0.16 °C /W. If the thermal conductivities of the refractory brick, insulating fire brick, and plaster are 1.6, 0.3 and 0.14 W/m. °C, respectively calculates: (i) Rate at which heat is lost per m of the wall surface; (ii) Each interface temperature.arrow_forward
- Question 1: A glass window of width W = 1 m and height H = 2m is 5 mm thick and has a thermal conductivity of kg =1.4 W/m.K. If the inner and outer surface temperatures of the glass are 15 °C and -20 C, respectively, on a cold winter day, what is the rate of heat loss through the glass? To reduce heat loss through windows, it is customary to use a double pane construction in which adjoining panes are separated by an air space. If the spacing is 10 mm and the glass surfaces in contact with the air have temperatures of (last two digit of your Registration number) °C and -15 °C, what is the rate of heat loss from a 1 mx2mwindow? The thermal conductivity of air is ka = 0.024 W/m.K.arrow_forwardThe rate at which energy must be dissipated away from single integrated circuits (computer chips) continues to increase as transitors continue to shrink in size and more and more computations are being completed in smaller and smaller volumes. The maximum chip temperature, however, has not changed much over time and remains around Tc = 75 °C. To increase the rate of dissipation of thermal energy away from a new chip, it is proposed to add a 5 x 5 array of copper pin fins to the chip. Each fin will be individually joined to the chip surface such that there is a minimal contact resistance between the fin and the chip. The diameter of the fins is df = 1 mm and the length is Lf = 15 mm. The chip is square, with a side length of W= 15 mm. It is so thin that it can be treated as having a single temperature. A dielectric liquid flows over the outer surface of the chip and around the fins, with a temperature of T»,f= 20 °C and a convection coefficient of hf = 1150 W/m²-K. The chip is joined to…arrow_forwardQ1/ The fumace wall consists of 120 mm wide Reftactory bricks Air gap Insulating fire bricks -Plaster refractory brick and 120 mm wide insulating fire brick separated by an air gap. The outside wall is covered with a 12 mm thickness of plaster. The inner surface of the wall is at 1090°C and the - 1090°C room temperature is 20°C. The heat transfer coefficient from the outside wall surface to the air in the room is 18 W/m² °C, and the resistance to heat flow of the air gap is 0.16 °C /W. If the thermal conductivities of the refractory brick, insulating fire brick, and plaster are 1.6, 0.3 and 0.14 W/m. °C, respectively calculates: (i) Rate at which heat is lost per m of the wall surface; (ii) Each interface temperature. -20°C - 120 mm 120 mm12 mmarrow_forward
- 1. Consider a 5-m-high, 8-m-long, and 0.22-m-thick wall whose representative cross section is as given in the Fig. The thermal conductivities of various materials used, in W/m-°C, are k = kr = 2, KB = 8,kc=20, KD = 15, and k = 35. The left and right surfaces of the wall are maintained at uniform temperatures of 300 °C and 100 °C, respectively. Assuming heat transfer through the wall to be one-dimensional, determine: (a) the rate of heat transfer through the wall; (b) the temperature at the point where the sections B, D, and E meet; and (c) the temperature drop across the section F. Disregard any contact resistances at the interfaces. 300°C 1 cm C A 4 cm B 4 cm 4 cm D C 6 cm 5 cm 6 cm E| F 10 cm 6 cm 100°C 8 marrow_forwardOne vessel having a carbon-steel wall of thickness 5 mm carrying saturated steam and water at 423K. The vessel is insulated with magnesia of thickness 50 mm. If the ambient air temperature is 321 K, determine the heat loss from the vessel. Given: i. thermal conductivity of carbon steel is 52 W/m.K ii. thermal conductivity of magnesia is 0.5 W/m.K iii. surface coefficient of insulation surface is 3 W/m2.Karrow_forwardPlease fats. The answer in the box is incorrectarrow_forward
- 2. A steam line is covered with two successive layers of insulation. The 1.6 in thick layer in contact with the pipe is asbestos which is covered with a 1.4 inch thickness of magnesia insulation. The internal pipe diameter is 3 in, the pipewall thickness is 0.40 in made from common brick. The steam temperature is 850ºF, and the internal surface film coefficient is 50 Btu/hr.ft².F, while the ambient outer temperature is 105°F and the outer surface film coefficient is 3.0 Btu/hr.ft².F. Calculate the following: a. value of U based upon the external area of the magnesia covering, Btu/hr.ft2.F b. heat loss from the steam for a length of 190 feet of pipe, Btu/hrarrow_forwardQuestion(2): The ceiling outer surface temperature of an oven is 60°C. If the oven is in an environment of 20 °C and the ceiling is 1 m wide and 2 m long. find the heat loss from the furnace ceiling surface. NOTE: Use the physical properties of the air at 40°C for the environment.arrow_forwardJohn is employed by a new food processing plant where eggs are to be boiled in large quantities to produce egg salad. John has been assigned the task of determining the minimum cooking time for the eggs, utilizing his vast knowledge of heat transfer. As a basis of calculation, he assumed that the eggs are perfect spheres with a diameter of 5 cm and uniform material properties (r =1000kg/m'; Cp = 3300 J/(kg K) and k=0.75 W/(m-K)). The eggs were taken from a cold storage room at 5°C and immediately put into pots of boiling water at 100°C. The convective heat transfer coefficient of the water is h = 1500 W/m°K. For health safety reasons, the plant requires that the entire egg must be at a temperature above 75°C for at least 20 seconds in order for the cooking process to be complete. a. What is the minimum time necessary to cook the egg to company specifications? b. In the testing lab, John forgot to remove a batch of eggs, and they remained in the cooking pot long enough to reach a…arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning