Heat is transferred by radiation and convection between the inner surface of the nacelle of the wind turbine of Example 1.3 and the outer surfaces of the gearbox and generator. The convection heat flux associated with the gearbox and the generator may be described by
Want to see the full answer?
Check out a sample textbook solutionChapter 1 Solutions
Introduction to Heat Transfer
- To determine the thermal conductivity of a structural material, a large 15-cm-thick slab of the material is subjected to a uniform heat flux of 2500 W/m2 while thermocouples embedded in the wall at 2.5 cm. intervals are read over a period of time. After the system had reached equilibrium, an operator recorded the thermocouple readings shown below for two different environmental conditions: Distance from the Surface (cm) Temperature (C) Test 1 0 40 5 65 10 97 15 132 Test 2 0 95 5 130 10 168 15 208 From these data, determine an approximate expression for the thermal conductivity as a function of temperature between 40 and 208C.arrow_forwardA plane wall 15 cm thick has a thermal conductivity given by the relation k=2.0+0.0005T[W/mK] where T is in kelvin. If one surface of this wall is maintained at 150C and the other at 50C, determine the rate of heat transfer per square meter. Sketch the temperature distribution through the wall.arrow_forwardAn electric heater producing 260 W of heat is used to warm up a room containing 7 m3 of air. If we assume the room is perfectly sealed and there is no heat loss through the room boundaries, such that all of the heater output goes into increasing the air temperature, how long will it take to heat up the air in the room from 5.0 °C to 24.1 °C? Give your answer to the nearest minute and assume that the specific volume (v = 0.85 m3/kg) and specific heat capacity at constant volume (cv = 1.005 kJ/(kg K)) remain constant throughout the heating process.arrow_forward
- In a piping system at sea level, a liquid of relative density 1.5 flows through a pipe 8 cm in diameter.diameter at 1.2 m/s. Fifteen meters above the pipe diameter is reduced to 5 cm, Assume that the temperature of thefluid in the process remains at 30°C, producing a heat loss of 25 N-m/kg. Determine the pressure change in the thermodynamic process.arrow_forward1. A room has a pine ceiling (k = 0.12 WI(m-Cº) ] that measures 3.0 m x 4.0 m 2.0 cm. On a cold day, the temperature inside the room is 20°C, and the temperature in the attic above is 8°C. If 6.0 cm of glass wool insulation ( k = 0.042 WI(m.Cº) ] were put in above the ceiling, how much energy would be saved in one hour? 2. 2.0-kg block moving with an initial speed of 5 m/s slides on a rough table and is stopped by the force of friction. Assuming that the table and air remain at 24°C, calculate the entropy change of the universe.arrow_forwardExample 2: Double-pane window, each window have: Height = 0.8 m Width 1.5 m Thickness = 4 mm k (glass) = 0.78 W/m.K separation between two glasses (air) = 10 mm k (air) = 0.026 W/m.K Temperature of inner surface = 20°C Temperature of outer surface = -10°C Convection heat transfer coefficient on the inner surface h1= 10 W/m2·°C Convection heat transfer coefficient on the outer surface h2= 40 W/m2·°C Determine the heat transfer through the window?arrow_forward
- According to the U.S. Geological survey, the volume of water in oceans, seas, and bays is 1.41 ✕ 1018 m3. The average concentration of naturally occurring uranium in seawater is 3.15 ✕ 10−6 kg/m3. If 0.670% of naturally occurring uranium is the fissionable isotope U-235 and each fission reaction yields 200 MeV, estimate the amount of time the uranium in the seawater on the planet could meet the planet's energy needs at an average usage of 1.94 ✕ 1013 J/s.arrow_forwardIn the United States, energy for household heating is generally sold using English units, e.g., therm, gal, and cord. A house in Wisconsin uses 1200 therms of thermal energy during the heating season. Calculate the cost of fuel if the furnace uses (a) natural gas with an efficiency of 70%; (b) No. 2 fuel oil, efficiency 65%; (c) kerosene, efficiency 99.9% (unvented); and (d) wood with l5% moisture with an efficiency of 50%. Use the data in Tables 2.2, 2.7, and 2.13. The efficiencies are based on the HHV. Assume the cost of natural gas is $8/MBtu, the cost of No. 2 fuel oil is $3/gal, the cost of kerosene is $3.50/gal, and the cost of wood is $100/cord. Assume the bulk density of cord wood is 30 lbm/ft3 .arrow_forwardIn a differential equation, the unknown variable is also known as ___________arrow_forward
- A spaceship has crashed into an ocean on an unknown planet with radius 6.42 * 10 ^ 6 * m and mass 5.82 * 10 ^ 24 The atmospheric pressure at sea level is 202.0 kPa and the ocean has density of 0.817 * 10^ 3 kg/m3 . If the spacecraft can withstand external pressure of 3 atm how deep will the craft sink before being crushed?arrow_forward5. A pot plant falls off the balcony of an apartment. The balcony is 20 m above the ground and the pot plant has a mass of 2 kg. After falling a distance of 2 m from the balcony, the pot plant has a velocity of 6,26 m·s-1. Ignore the effect of air resistance. *  Your answerarrow_forward40. Water flows through a pipe of varying cross-section and varying elevation at the rate of 22.2m3/min. At one section of the pipe 3 m from the ground, the radius of the pipe is 36 cm and the pressure is 12 N/cm^2.What is the pressure at a section where the radius of the pipe is 18cm and is 0.7 m from the ground level?A. 136 123 N/m2 B. 50 N/cm2 C. 750 000 N/m2 D. 12 N/cm2arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning