Three electric resistance heaters of length
(a) If the heaters are activated, each dissipating
(b) If the natural convection coefficient ¡s given by an expression of the form
(c) If the heaters are inadvertently activated when the tank is empty, the natural convection coefficient associated with heat transfer to the ambient air at
also 300 K and the emissivity of the heater surface is
Want to see the full answer?
Check out a sample textbook solutionChapter 1 Solutions
Fundamentals of Heat and Mass Transfer
- In the figure, the cylindrical capacitor, connected to a constant voltage source Vo= 80 V, rests with its edges on the surface of the water of density ρ=1000 kg/m3 . The distance d=0.4 cm between the condenser armatures is much smaller than its radius half. Find the height "h" at which the water level is established between the reinforcements of the condenser. Neglect capillary phenomena. (k=9•109N•m2/C2,κ=81,g=9.8m/2)arrow_forwardWater flows along a tube of diameter d = 6 mm with a velocity w = 0.4 m/s. The temperature of the tube wall t = 50°C. What should the length of the tube be to ensure a water outlet temperature tr2 = 20°C at a water inlet temperature twi = 10°C?arrow_forward8. A coal fired steam boiler uses 3000 kg of coal per hour. Air required for combustion is 15.5 kg ofcoal at barometric pressure of 98.2 KPa. The flue gas has temperature of 285 degree Celsiusand an average molecular weight of 30. Assuming an ash loss of 11% and allowable gas velocityof 7.5 meters per second. Find the diameter of the chimney 9. The gas density is 0.75 kg per cubic meters and air density is of 1.15 kg per cubic meter. If thedriving pressure is 0.25 KPA. Determine the height of the chimney. 10. A powerplant situated at an altitude having an ambient air of 96.53 KPa and 23.88 degreeCelsius. Flue gases at a rate of 5.0 kg per second enter the stack at 200 degree Celsius andleaves at 160 degree Celsius. The flue gases gravimetric analysis are 18% CO2, 7% O2 and 75%N2. Calculate the height of the stack necessary for a driving pressure of 0.20 KPaKindly answer all please. Thank youarrow_forward
- Imagine a plate 0.1 m long by 0.1 m wide at a temperature of 80 °C. Water is passed over its surface at a speed of 0.1 m/s and 40°C. Calculate the heat dissipated by the plate. Assume the following properties of water at 60 °C: k= 0.651 W/mK, Pr=3.02 y v = 0.478 x 10-6 m²/s.arrow_forwardWater with density ρ = 998 kg/m3, is flowing at steady mass flow rate through a uniform-diameter pipe. The entrance pressure of the fluid is 68.9 kPa in the pipe, which connects to a pump, which supplies 155.4 J/kg of fluid flowing in the pipe. The exit pipe from the pump is the same diameter as the inlet pipe. The exit section of the pipe is 3.05 m higher than the entrance, and the exit pressure is 137.8 kPa. The Reynolds number in the pipe is above 4,000 in this system. Calculate the frictional loss in the pipe system.arrow_forwardThe compressed air requirements of a textile factory are met by a large compressor that draws in 0.6 m3/s air at atmospheric conditions of 20°C and 1 bar (100 kPa) and consumes 300 kW electric power when operating. Air is compressed to a gage pressure of 8 bar (absolute pressure of 900 kPa), and compressed air is transported to the production area through a 15-cm-internal-diameter, 83-m-long, plastic (smooth) pipes with a surface roughness of 0.15 mm. The average temperature of compressed air in the pipe is 60°C. The compressed air line has 8 elbows with a loss coefficient of 0.6 each. In order to reduce the head losses in the piping and thus the power wasted, someone suggests doubling the diameter of the 83-m-long compressed air pipes. Calculating the reduction in wasted power, and determine if this is a worthwhile idea. Considering the cost of replacement, does this proposal make sense to you?arrow_forward
- Hot water, k=48 W/m. It flows along the cast iron pipe, which is oC, at a speed of 1.4 m/s. The inner and outer diameter of the pipe are 3.0 and 3.5 cm, respectively. The pipe is located in a 15 m section of a basement floor with a temperature of 15 oC. If the water temperature drops from 70 OC to 67 OC when passing through the basement, and the film heat transfer coefficient on the inner surface of the pipe is 400 W/m2. If oC is, calculate the convective heat transfer coefficient on the outer surface of the pipe and the heat that will be transferred.arrow_forwardLiquid bismuth flows at a rate of 4.5 kg/s through a 5.0-cm-diameter stainless-steel tube. The bismuth enters at 415◦C and is heated to 440◦C as it passes through the tube. If a constant heat flux is maintained along the tube and the tube wall is at a temperature 20◦C higher than the bismuth bulk temperature, calculate the length of tube required to effect the heat transfearrow_forwardA computer cooled by a fan contains eight printed circuit boards (PCBs), each dissipating 10 W of power. The height of the PCBs is 12 cm and the length is 18 cm. The clearance between the tips of the components on the PCB and the back surface of the adjacent PCB is 0.3 cm. The cooling air is supplied by a 10-W fan mounted at the inlet. If the temperature rise of air as it flows through the case of the computer is not to exceed 10°C, determine (a) the flow rate of the air that the fan needs to deliver, (b) the fraction of the temperature rise of air that is due to the heat generated by the fan and its motor, and (c) the highest allowable inlet air temperature if the surface temperature of the components is not to exceed 70°C anywhere in the system. As a first approximation, assume flow is fully developed in the channel. Evaluate properties of air at a bulk mean temperature of 25°C. Is this a good assumption?arrow_forward
- A long 8-cm diameter vertical steam pipe whose external surface temperature is 90 degrees C passes through some open area that is not protected against the wind blows. Determine the rate of heat loss from the pipe per unit length when the air is at 1 atm, 7 degrees Celsius and the wind is blowing across the pipe at a velocity of 50 km/h. From Table A-1:Thermal conductivity, k = 0.0275 W/m degrees Celsius ,viscosity, v = 1.77 x 10^-5 m^2/sPrandtl no. Pr = 0.71arrow_forward3. An unknown gas moving at a constant speed of 164 m/s enters a tube of constant crosssectional area at a rate of 3.00kg/s. Assuming the critical pressure and temperature are 767kPa and 140oC respectively for a given static condition at the entrance to the tube. Assumingthe ratio of specific heat and gas constant of the unknown gas to be 1.289 and 0.1889 kJ/kg Krespectively.Determinea) the static pressure, temperature and density at the entrance to the tubeb) stagnation temperature and pressurec) the Mach number of the gas at the entrance to the tubed) the cross sectional area of the tubee) the critical speedf) determine the unknown gas?arrow_forwardWhat is the value of the heat transfer coefficient for air at 37 ° C flowing at 5 m / s perpendicular to a 10 cm x 10 cm square pipe at 93 ° C? h = 23kcal / hm ^ 2 ° C around this valuearrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning