The heat flux, q, is 6000 W/m² at the surface of an electrical heater. The heater temperature is 120°C when it is cooled by air at 70°C. What is the average convective heat transfer coefficient, h? What will the heater temperature be if the power is reduced so that q is 2000 W/m²?

The heat flux, q, is 6000 W/m² at the surface of an electrical heater. The heater temperature is 120°C when it is cooled by air at 70°C. What is the average convective heat transfer coefficient, h? What will the heater temperature be if the power is reduced so that q is 2000 W/m²?

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.

Chapter3: Transient Heat Conduction

Section: Chapter Questions

Problem 3.14P: 3.14 A thin-wall cylindrical vessel (1 m in diameter) is filled to a depth of 1.2 m with water at an...

See similar textbooks

Similar questions

2.30 An electrical heater capable of generating 10,000 W is to be designed. The heating element is to be a stainless steel wire having an electrical resistivity of ohm-centimeter. The operating temperature of the stainless steel is to be no more than 1260°C. The heat transfer coefficient at the outer surface is expected to be no less than in a medium whose maximum temperature is 93°C. A transformer capable of delivering current at 9 and 12 V is available. Determine a suitable size for the wire, the current required, and discuss what effect a reduction in the heat transfer coefficient would have. (Hint: Demonstrate first that the temperature drop between the center and the surface of the wire is independent of the wire diameter, and determine its value.)
3.14 A thin-wall cylindrical vessel (1 m in diameter) is filled to a depth of 1.2 m with water at an initial temperature of 15°C. The water is well stirred by a mechanical agitator. Estimate the time required to heat the water to 50°C if the tank is suddenly immersed in oil at 105°C. The overall heat transfer coefficient between the oil and the water is , and the effective heat transfer surface is .
1. For a steam pipe with a given diameter of 10 cm covered by two (2) layers of insulation. The first insulation has a thickness of 4 cm and a coefficient of thermal conductivity of 0.08 W/m.K. and the second insulation has a thickness of 3 cm and a thermal conductivity of 0.15 W/m.K. The steam main conveys steam at a pressure of 1.70 MPa with 25°C superheat. Outside temperature is 27°C. The pipe is 30 meters in length. (tsat @ 1.70 MPa = 204°C). Determine the following: a) The heat loss in KW b) Explain the concepts/principles that were considered and the factors that affected the condition of the above mentioned items (a & b).
3. A 3 in O.D. aluminum tube (k=133 BTU/h ft°F) has 16 longitudinal fins spaced around its outside surface as shown below. The fins are .06 in thick and extend 2 in from the outside surface of the tube. If the outside surface of the tube wall is at 200F, the surrounding air is at 70°F and the convective heat transfer coefficient is 15 BTU/h ft°F, determine the percent increase in heat transfer for the finned pipe over that for the unfinned pipe. Note: longitudinal fins are rectangular fins that extend along the length of the tube. Figure shows view looking down the tube
Blowtorch is used to connect the two pipes together. Length of the pipe section shown is 150 cm with an inner diameter of 85 cm. The thickness of the pipe wall is 4 mm. The conductivity of the pipe section is 167 W/m^2K. Environment has a temperature of 30 C and convective heat transfer coefficient of 28 WI(mC), find the required heat transfer to join the pipe sections at 220 C? HINT: Assume that the welding section is the base plate and the pipe is 1D extended surface (fin) symmetric about the torch melting line. Heat transfer happens by conduction along the pipe thickness in horizontal direction and by convection to the environment. Length thickness Torch melting line
The thermal conductivities of wood is kwood = 0.1W/(m°C)and air is kair = 0.0234W/(m°C). Part A If the temperature of the room is 20°C and outside is 10°C, find the rate of heat flow for a wall of wood with area = 10 m² and thickness of 5cm. O 60 W O 304 W O 34 W O 200 W O 100 W Submit Request Answer Part B The wall of wood with thickness of 5cm is now replaced with two layers of wood and a gap of air between the wood. Each layer of wood has a 2.5cm thickness and the gap is 1cm. The rate of heat flow will, decreases. increases. stay the same. Submit Request Answer Part C The temperature in the air gap will be, O 20°C, between 10°C and 20°C, O 10°C,
A steel tube (k = 15 W/m.K) 3 m long carries a refrigerated liquid at 5°C. The inner diameter of the tube is 4 cm and the thickness is 1.5 cm. The convection heat transfer coefficient inside the tube is 80 W/m.K. The fluid receives heat from the external environment, which is at 28°C with a convection heat transfer coefficient of 20 W/m .K. To reduce the gain, it is studied to add a layer of insulating foam to the tube with a thickness of 5 cm and thermal conductivity k = 0.08 W/m.K. The placement of insulation pays off financially if the heat transfer rate is reduced by at least 30% and if the external surface temperature is above 15°C. Ignoring the effects of radiation, verify that these conditions are met.
Item 1 1 of 5 II Review Part A A flow-through electric water heater has a 22 kW electric heater inside an insulated 2.0-cm-diameter pipe so that water flowing through the pipe will have good thermal contact with the heater. Assume that all the heat energy is transferred to the water. Suppose the inlet water temperature is 12°C and the flow rate is 8.0 L/min (about that of a standard shower head). What is the outlet temperature? Express your answer in degrees Celsius. ? Tout = °C Submit Request Answer Provide Feedback Next >
A bare fuel rod has a diameter of 0.373 in and length of 12 ft. The volumetric heat generation rate for this rod is q ′′′ = 10,000 kW/ft3 . The heat produced by the rod is removed by water used as the coolant, at 2250 psia and 575 F. Find the heat transfer coefficient between the bare fuel rod and the coolant. The fuel rod surface temperature is 675 F. [Ans.: h = 2651 Btu/h·ft2 ·F].
1 - A square chip, with side w = 5 mm, operates under isothermal conditions.The chip is positioned on a substrate so that its side and bottom surfaces are thermally insulated, while its top surface is exposed to theflow of a refrigerant at T∞ = 15°C. From reliability considerations, the chip temperature cannot exceed T = 85°C. The refrigerant being air, with a convection heat transfer coefficientcorresponding h = 200 W/(m2K), what is the maximum allowable power for the chip? Since the coolant is a dielectric liquid for which h = 3000 W/(m²K), what is the maximum allowed power?
Problem-1: Superheated steam at an average temperature 200°C is transported through a steel pipe (k = 50 W/m-K, D₁ = 8.0 cm, D₁ = 6.0 cm, and L=20.0 m). The pipe is insulated with a 4-cm thick layer of gypsum plaster (k = 0.5 W/m K). The insulated pipe is placed horizontally inside a warehouse where the average air temperature is 10°C. The steam and the air heat transfer coefficients are estimated to be 800 and 200 W/m2.K, respectively. Calculate (a) the daily rate of heat transfer from the superheated steam and (b) the temperature on the outside surface of the gypsum plaster insulation.
Blowtorch is used to connect the two pipes together. Length of the pipe section shown is 80 cm with an inner diameter of 70 cm. The thickness of the pipe wall is 3 mm. The conductivity of the pipe section is 177 W/m^2K. Environment has a temperature of 25 C and convective heat transfer coefficient of 20 W/(mC) , find the required heat transfer to join the pipe sections at 220 C? HINT: Assume that the welding section is the base plate and the pipe is 1D extended surface (fin) symmetric about the torch melting line. Heat transfer happens by conduction along the pipe thickness in horizontal direction and by convection to the environment. Length thickness Torch melting line