A vertical array of circuit boards is immersed in quiescent ambient air at
Want to see the full answer?
Check out a sample textbook solutionChapter 9 Solutions
Fundamentals of Heat and Mass Transfer
Additional Engineering Textbook Solutions
Introduction to Heat Transfer
Fundamentals of Aerodynamics
Engineering Mechanics: Statics
Applied Fluid Mechanics (7th Edition)
Fluid Mechanics Fundamentals And Applications
Machine Tool Practices (10th Edition)
- The interior of a refrigerator whose dimensions are 0.05 x 0.05 dam base area and 1.25 m high, must be kept at 4 °C. The refrigerator walls are constructed of two steel sheets (k= 35 kcal/h.m.°C) 3 mm thick, with 65 mm of material insulation (k=0.213 kcal/h.m.°C) between them. The film coefficient of the inner surface is 10 kcal/h.m².°C, while on the external surface it varies from 8 to 12.5 kcal/h.m².°C. Calculate: a) The power (in HP) of the refrigerator motor so that the heat flux removed from the inside the refrigerator maintain the specified temperature, in a kitchen whose temperature can vary from 21 to 36 °C; b) The temperatures of the inner and outer surfaces of the wall. Given 1 HP = 641.2 Kcal/harrow_forwardA food product with 80% moisture content in a 7 cm diameter can wants to be frozen. product density is 1000 kg / m³ thermal conductivity is 1.0 W / (m K) and initial freezing temperature is -2.25 degrees Celsius after 8 hours in freezing medium -35 degrees Celsius Temperature to -10 degrees Celsius estimate convection heat transfer coefficient freezing medium assume the can as an infinite cylinder h =arrow_forwardA long wire of diameter D = 2 mm is submerged in an oil bath of temperature T∞ = 23°C. The wire has an electrical resistance per unit length of Re′=0.01 Ω/m. If a current of I = 180 A flows through the wire and the convection coefficient is h = 529 W/m2 · K, what is the steady-state temperature of the wire? From the time the current is applied, how long does it take for the wire to reach a temperature that is within 2°C of the steady-state value? The properties of the wire are ρ = 2,334 kg/m3, c = 537 J/kg · K, and k = 43 W/m · K.arrow_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_forwardWhat’s the correct answer for this please ?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_forward
- Q6: A large vertical plate 6.1 m high and 1.22 m wide is maintained at s constant temperature of 57:C and exposed to atmospheric air at 4-C. Caleulate the heat lost by the plate. Answers: Qarrow_forwardAluminum balls are heated up to 580 K and then exposed to air at 283 K to cool down with an average heat transfer coefficient of 25 W/m2·K. The balls are 3 cm in diameter. Find the temperature at r = 0.5 cm after 75 seconds of exposure. Is the lumped capacitance an acceptable solution here? [Ans.: 329 K].arrow_forwardPlease fats. The answer in the box is incorrectarrow_forward
- t = 30 + 0.9563 (62.2- 30) = 60.79°C (Ans.) Example 4.14. A very thin glass walled 3 mm diameter mercury thermometer is placed in a stream of air, where heat transfer coefficient is 55 W/m2°C, for measuring the unsteady temperature of air. Consider cylindrical thermometer bulb to consist of mercury only for which k and a = 0.0166 m2/h. Calculate the time required for the temperature change to reach half its final or, %3D 8.8 W/m C %3D value.arrow_forwardheat and mass transfer An uninsulated steam pipe of 100-mm diameter is routed through a building whose walls and air are at 27°C. Pressurized steam maintains a pipe surface temperature of 147°C, and the coefficient associated with natural convection is h =10 W/m2.K. The surface emissivity is ɛ= 0.8. What is the rate of heat loss per unit length from the steam line?arrow_forwardA spacecraft radioisotope thermoelectric generator (RTG) contains a cylindrical nuclear element, pictured below. The nuclear element generates q̇g = 200 kW/m3. The RTG is surrounded by eight (N = 8) identical rectangular fins. Each fin’s height (H), length (L), and thickness (t) are given in the picture. The fins are directly machined from a stainless steel cladding of inner and outer radii r1 and r2, respectively. The stainless steel has thermal conductivity of k = 18 W/m·K. Assume that the RTG is in a well-ventilated lab, where the convection heat transfer coefficient is h = 20 W/m2·K and the surrounding temperature is T = 20°C. Ignore effects of thermal radiation. (a) Calculate the fin efficiency of a single rectangular fin, f. (b) Calculate the overall fin efficiency of the entire eight fin array, Obtain the maximum temperature in the stainless steel cladding, T(r1).arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning