In a power plant, pipes transporting superheated vapor are very common. In a certain plant, superheated vapor is flowing at a rate of 0.3 kg/s inside a 5 cm diameter pipe of 10 m length. The air in the plant is maintained at 20oC while the surface temperature of the pipe is 100oC. If the temperature drop between the inlet and exit of the pipe is 30oC and the specific heat capacity of the vapor is 2190 kJ/kg.K, determine the convective heat transfer coefficient at the pipe surface. If necessary, how could this coefficient be increased?

In a power plant, pipes transporting superheated vapor are very common. In a certain plant, superheated vapor is flowing at a rate of 0.3 kg/s inside a 5 cm diameter pipe of 10 m length. The air in the plant is maintained at 20oC while the surface temperature of the pipe is 100oC. If the temperature drop between the inlet and exit of the pipe is 30oC and the specific heat capacity of the vapor is 2190 kJ/kg.K, determine the convective heat transfer coefficient at the pipe surface. If necessary, how could this coefficient be increased?

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter7: Forced Convection Inside Tubes And Ducts

Section: Chapter Questions

Problem 7.4P

See similar textbooks

Similar questions

Water is to be heated from 15°C to 65°C as it flows through a 3-cm-internaldiameter 5-m-long tube . The tube is equipped with an electric resistance heater that provides uniform heating throughout the surface of the tube. The outer surface of the heater is well insulated, so that in steady operation all the heat generated in the heater is transferred to the water in the tube. If the system is to provide hot water at a rate of 10 L/min, determine the power rating of the resistance heater. Also, estimate the inner surface temperature of the tube at the exit.
The chilling room of a meat plant is 15 m × 18 m × 5.5 m in size and has a capacity of 350 beef carcasses. The power consumed by the fans and the lights in the chilling room are 22 and 2 kW, respectively, and the room gains heat through its envelope at a rate of 14 kW. The average mass of beef carcasses is 220 kg. The carcasses enter the chilling room at 35C, after they are washed to facilitate evaporative cooling, and are cooled to 16°C in 12 h. The air enters the chilling room at 2.2°C and leaves at 0.5°C. Determine (a) the refrigeration load of the chilling room and (b) the volume flow rate of air. The average specific heats of beef carcasses and air are 3.14 and 1.0 kJ/kg · °C, respectively, and the density of air can be taken to be 1.28 kg/m3 .
Consider an air solar collector that is 1 m wide and 5 m longand has a constant spacing of 3 cm between the glass cover andthe collector plate. Air enters the collector at 30°C at a rate of0.15 m3/s through the 1-m-wide edge and flows along the 5-mlong passage way. If the average temperatures of the glasscover and the collector plate are 20°C and 60°C, respectively,determine (a) the net rate of heat transfer to the air in thecollector and (b) the temperature rise of air as it flows throughthe collector.
Air enters a 20-cm-diameter 12-m-long underwater duct at 50°C and 1 atm at a mean velocity of 7 m/s, and is cooled by the water outside. If the average heat transfer coefficient is 85 W/m2 °C and the tube temperature is nearly equal to the water temperature of 5°C, determine the exit temperature of air and the rate of heat transfer
Air at 60°C leaves a furnace and passes through a 12-m long, 20-cm × 20-cm square duct at an average velocity of 4 m/s. If the duct has a constant surface temperature of 33°C, determine the exit temperature of the air and the rate of heat transfer.
An average man has a body surface area of 1.8 m2 and a skin temperature of 33°C. The convection heat transfer coefficient for a clothed person walking in still air is expressed as h = 8.6V 0.53 for 0.5 < V < 2 m/s, where V is the walking velocity in m/s. Assuming the average surface temperature of the clothed person to be 30°C, determine the rate of heat loss from an average man walking in still air at 10°C by convection at a walking velocity of (a) 0.5 m/s, (b) 1.0 m/s, (c) 1.5 m/s, and (d) 2.0 m/s.
The blades of a wind turbine turn a large shaft at a relatively slow speed. The rotational speed is increased by a gearbox that has an efficiency of 0.93. In turn, the gearbox output shaft drives an electric generator with an efficiency of 0.95. The cylindrical nacelle, which houses the gearbox, generator, and associated equipment, is of length L = 6 m and diameter D = 3 m. If the turbine produces P = 2.5 MW of electrical power, and the air and surroundings temperatures are T = 25 oC and Tsur = 20 oC, respectively, determine the minimum possible operating temperature inside the nacelle. The emissivity of the nacelle is 0.83, and the convective heat transfer coefficient is h = 35 W/m2 .K. The surface of the nacelle that is adjacent to the blade hub can be considered to be adiabatic, and solar irradiation may be neglected. Use Fin or N number of fins to reduce the Ts of the nacelle less than 143 oC
The cross section of the rectangular duct of the heating system is 15 cm x 20 cm (figure shown below), with 6-m-long section of an air heating system of a house passes through an unheated space in the basement. Hot air enters the duct at 100 kPa and 60°C at an average velocity of 6 m/s. The temperature of the air in the duct drops to 54°C as a result of heat loss to the cool space in the basement. Determine the rate of heat loss from the air in the duct to the basement under steady conditions. Also, determine the cost of this heat loss per hour if the house is heated by a natural gas furnace that has an efficiency of 80 percent, and the cost of the natural gas in that area is $0.70/therm (1 therm = 100,000 Btu = 105,500 kJ).
Consider steady heat transfer between two parallel plates at a constant temperature
The components of an electronic system dissipating 180 W are located in a 1-m-long horizontal duct whose cross section is 16 cm * 16 cm. The components in the duct are cooled by forced air, which enters at 27°C at a rate of 0.65 m3/min. Assuming 85 percent of the heat generated inside is transferred to air flowing through the duct and the remaining 15 percent is lost through the outer surfaces of the duct, determine (a) the exit temperature of air and (b) the highest component surface temperature in the duct. As a first approximation assume flow is fully developed in the channel. Evaluate properties of air at a bulk mean temperature of 35°C. Is this a good assumption?
In many manufacturing plants, individuals areoften working around high-temperature surfaces.Exposed hot surfaces that can cause thermal burns on humanskin are considered hazards in the workplace. Metallic surfacesabove 70° C can instantly damage skin that touches them.Consider an AISI 1010 carbon steel strip (? = 7832 kg/ m 3 )2 mm thick and 3 cm wide that is conveyed into a chamber tobe cooled at a constant speed of 1 m/s. The steel strip entersthe cooling chamber at 597° C. Determine the rate at whichheat needs to be removed so that the steel strip exits the chamberat 47° C . Discuss how the conveyance speed can affect therequired rate of heat removal.
Metal plates (k = 150 W/m·K, ρ= 2800 kg/m3, and cp = 900 J/kg·K) with a thickness of 2 cm exiting an oven are conveyed through a 10-m long cooling chamber at a speed of 4 cm/s, as shown in the figure. The plates enter the cooling chamber at an initial temperature of 500°C. The air temperature in the cooling chamber is 15°C, and the plates are cooled with blowing air and the convection heat transfer coefficient is given as a function of the air velocity h(V) = 33V0.8, where h is in W/m2·K and V is in m/s. To prevent any hazard to workers handling the plates, it is necessary to design the cooling process such that the plates exit the cooling chamber at a relatively safe temperature of 50°C or less. Determine the air velocity V and the heat transfer coefficient h such that the temperature of the plates exiting the cooling chamber is at 50C.