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A technique for measuring convection heat transfer coefficients involves bonding one surface of a thin metallic foil to an insulating material and exposing the other surface to the fluid flow conditions of interest.
By passing an electric current through the foil, heat is dissipated uniformly within the foil and the corresponding flux,
With water flow over the surface, the foil temperature measurement yields
- Determine the convection coefficient. What error would be incurred by assuming all of the dissipated power to be transferred to the water by convection? If, instead, air flows over the surface and the temperature measurement yields
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Chapter 3 Solutions
Fundamentals of Heat and Mass Transfer
- 1.4 To measure thermal conductivity, two similar 1-cm-thick specimens are placed in the apparatus shown in the accompanying sketch. Electric current is supplied to the guard heater, and a wattmeter shows that the power dissipation is 10 W. Thermocouples attached to the warmer and to the cooler surfaces show temperatures of 322 and 300 K, respectively. Calculate the thermal conductivity of the material at the mean temperature in W/m K. Problem 1.4arrow_forward1.15 A thermocouple (0.8-mm-diameter wire) used to measure the temperature of the quiescent gas in a furnace gives a reading of . It is known, however, that the rate of radiant heat flow per meter length from the hotter furnace walls to the thermocouple wire is 1.1 W/m and the convection heat transfer coefficient between the wire and the gas is K. With this information, estimate the true gas temperature. State your assumptions and indicate the equations used.arrow_forward10.3 A light oil flows through a copper tube of 2.6-cm ID and 3.2-cm OD. Air flows perpendicular over the exterior of the tube as shown in the following sketch. The convection heat transfer coefficient for the oil is and for the air is . Calculate the overall heat transfer coefficient based on the outside area of the tube (a) considering the thermal resistance of the tube and (b) neglecting the resistance of the tube.arrow_forward
- 2.2: Water at a temperature of T∞= 25°C flows over one ofthe surfaces of a steel wall (AISI 1010) whose temperatureis Ts,1= 40°C and thermal conductivity of steel is 671 w/m.k. The wall is 0.35 m thick, and itsother surface temperature is Ts,2= 100°C. For steadystateconditions what is the convection coefficient associatedwith the water flow?arrow_forwardQ/ Steam flowing through a long, thin-walled pipe maintains the pipe wall at a uniform temperature of 500 K. The pipe is covered with an insulation blanket comprised of two different materials, A and B. The interface between the two materials may be assumed to have an infinite contact resistance, and the entire outer surface is exposed to air for which Too = 300 K and h =25 W/m2, K. Calculate the total heat loss from the pipe and What are %3D the outer surface temperatures Ts,2(A) and Ts,2(B)? n- 50 mm 2- 100 mm T 2A) -k - 2 W/m-K T5, 218) -kg = 0.25 W/m-K T1- 500 Karrow_forwardEXAMPLE 3 Steam at a temperature of 300 °C flows through a steal pipe, k= 14.9 W/m.K of 60 mm inside diameter and 80 mm outside diameter. The convection coefficient between the steam and the inner surface of the pipe is 500 W/m? K, while that between the outer surface of the pipe and the surroundings is 25 W/m2 .K the temperature of the surroundings air is 25 C. -What is the heat loss per unit length of pipe?arrow_forward
- (B) In order to measure the convection heat transfer coefficients one of the common methods involve bonding one surface of a thin metallic foil to an insulating material and exposing the other surface to the fluid flow conditions of interest. T, h Foil (Pelec T) Foam Insulation (k) Figure1: Heat transfer direction By passing an electric current through the foil, heat is dissipated uniformly within the foil and the corresponding flux (P elec) may be inferred from related voltage and current measurements. Consider conditions for which T0 = Tb = 25°C, Pelec = 2000 W/m2, L = 7 mm, and k = 0.05 W/m.K. (1) With water flow over the surface, the foil temperature measurement yields Ts = 30°C. Determine the convection heat transfer coefficient for both cases below. The foil has an emissivity of 0.15 and is exposed to large surroundings at 25°C. (2) On the other hand, if air flows over the surface and the temperature measurement yields Ts = 120°C, how the convection heat transfer coefficient will…arrow_forwardIf the length of the cylinder is 50 m, calculate the overall heat loss and the temperature profile at each interface. Please write the solution legibly.arrow_forwardc) A steel pipe of 100 mm bore, and 10 mm bore thickness, carrying dry saturated steam at 28 bars, is insulated with a 40 mm layer of moulded insulation. This insulation in turn is insulated with a 60 mm layer of felt. The atmospheric temperature is 15 °C. Calculate: (i) the rate of heat loss by the steam per metre pipe length. (ii) the temperature of the outside Dimensions in mm surface.zzzzzzz h₂-15 W/m²K Steel k₁=50 W/mK AVALEHT Ø100 1₂ " Steam 28 bar h-550 W/m²K, Inner heat transfer coefficient = 550 W/m² K Outer heat transfer coefficient = 15 W/m² K Thermal conductivity of steel = 50 W/m K Thermal conductivity of felt = 0.07 W/m K Moulded insulation Felt Moulded insulation K₂=0.09 W/mK Thermal conductivity of moulded insulation = 0.09 W/m 40 10. A 60 15°C Felt K₁=0.07 W/mK zzzzzzzzarrow_forward
- Calculate the overall heat loss and the temperature profile for each interface if the length of the cylinder is 50 m.Please write your answers legibly.arrow_forwardNuclear fuel rods. A typical nuclear fuel rod contains circular uranium oxide (UO2) fuel pellets 10 mm in diameter and 5-mm thick stacked in a column to a length of 4 m inside a thin zirconium alloy tube, as shown below. The pellets generate heat uniformly throughout their volume due to nuclear fission, with a power density a (i.e., the heat power produced per unit volume of the pellet) that depends on their 235U enrichment. This heats up the water in the reactor to produce steam to drive the turbine. Assuming that the rim of the fuel pellet is maintained at a constant temperature Trim due to water cooling, show that the steady-state temperature profile T(r), where r is the radial distance from the centre of the pellet and fuel rod, 4. P(R? -r²; is given by: T(r) = Tim + 4k where k is the thermal conductivity of the pellet and R is its radius. partial stacked column of fuel pellets in rodarrow_forwardLet's say a 3.0 gram copper wafer is dropped from a height of 50.0 meters. If 60% of the potential energy lost in the drop could be converted to thermal energy used to heat the copper from an initial temperature of 25 degrees celsius, what would the final temperature of the copper wafer? Would the answer be different if the wafer has a mass greater than 3 grams? Note: the specific heat of copper is 387 J/(kg*K). The temperature is between 25.8 and 26.0 degrees celsius, yes the bigger the mass the greater the energy. O The temperature is between 25.6 and 25.8 celsius, answer does not depend on mass. O The temperature is between 25.0 and 25.2 celsius, answer does not depend on mass. O The temperature is 25.5 and of course the more mass something has the greater energy will be needed to raise the temperature. The temperature is 26.2 and if the mass is doubled so will be the change in temperature. O The temperature is 25.9 degrees celsius and the answer does not depend on mass. O The…arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning
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