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Question 43939

posted 10 months ago

A sphere with a temperature of 100°C and a diameter of 10 cm is exposed to a 5 m/s-stream of air at 500°C. Using the properties below, determine the convectiveheat transfer
\text { Kinematic Viscosity }=7.65 \times 10^{-5} \mathrm{~m}^{2} / \mathrm{s}
\text { Thermal conductivity }=0.0549 \mathrm{~W} /(\mathrm{m}-\mathrm{K})
\text { Prandtl number }=0.72

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Question 44263

posted 10 months ago

2. Pin fins are to specified for use in a industrial cooling application. The fines will be subject to a gas incross flow at V=10m/s. The cylindrical fin has a diameter of D=15mm, and the cross-sectional area isthe same for each configuration shown in the sketch.
For fins of equal length, which fin has the largest heat transfer rate? Assume the gas properties are those of air atT=350K. Use correlations in Table 7.3 from the book.

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Question 44262

posted 10 months ago

1. An electric air heater consists of a horizontal array of thin metal strips that are each 10mm long. Each strip is 0.2m wide, and 25 strips are arranged side by side, forming a continuous and smooth surface over which the air flow. During operation, each strip is maintained at 500C and the air is at 25C.
a) At 2.5m/s air flow, what is the rate of heat transfer from the first strip? The fifth strip? The tenthstrip? All the strips (average)?
b) For air velocities of 2, 5, and 10 m/s, determine the heat transfer for all the locations of part (a).Represent your results in tabular or bar graph.
c) Repeat part (b), but under conditions for which the flow is fully turbulent over the entire array strips.

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Question 44264

posted 10 months ago

3. Fluid enters a tube with a flow rate of 0.015kg/s and an inlet temperature of 20C. The tube, which has a length of 6m and a diameter of 15mm, has a surface temperature of 30C. Determine the heat transfer rate assuming the fluid is water.

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Question 44564

posted 10 months ago

Water in the blue cavity flows in a loop and is being continuously heated by the heat load of 1kW. 40 degrees Celsius water is passed through the orange tube to cool the cavity. Both the cavity and pipe have the same flow rate of201/min. what is the temperature of water flowing out of the orange pipe.
Inner diameter of pipe12mm
Outer diameter of pipe14mmLonath of pino
Length of pipe = 1m%
Blue cavity is a 30mm by 30mm box with length 1m

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Question 44633

posted 10 months ago

Problem 3: The hot and cold inlet temperatures to a concentric tube heat exchanger are Tnj=200°C,Tai=100°C, respectively. The outlet temperatures are The=110°C and Tco=125°C.
(a) Is the heat exchanger operating in a parallel flow or in a counter flow configuration? Sketch the temperatures through the heat exchanger using a diagram similar to Figure 11.7 or 11.8.
(b) What is the heat exchanger effectiveness, ɛ? What is the NTU? Phase change does not occur in either fluid. Partial Ans: NTU=2.75 (may need to use Fig. 11.10 or 11.11 as appropriate).
(c) If the hot fluid is ammonia gas at a flowrate of 0.2 kg/s, what is the overall heat transfer in the heat exchanger? Ans: 42.4 kW

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Question 44632

posted 10 months ago

Problem 2: A flat plate made of copper (length=10 cm, thickness=1 cm, width=6cm) is in an oven, such that its initial temperature is uniform at 127°C. The plate is then moved to a cooling area, where the quiescent air temperature is 27°C.
(a) If the plate is held such that its longest dimension (length) is vertical, what is the average convective heat transfer coefficient over the plate immediately after it is moved to the cooling area? Ans: 7.45 W/m?-K
(b) Assuming that the convective heat transfer coefficient does not change significantly over time, how long might it take for the plate to cool to 45°C? Ans: 53 min
(c) If the surfaces around the plate in the cooling area are large and at a constant temperature of 27°C,would radiation heat transfer be potentially significant in this problem? Assume that the copper emissivity is equivalent to a stably oxidized surface at 600K (see Table A.11), and evaluate the radiation heat flux at the start of the cooling. Compare to the convection heat flux at the start of cooling.

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Question 44631

posted 10 months ago

Problem 1: A thin-walled metallic tube of length 1 m and inside diameter 3 mm has water flowing through it at a mass flow rate of 0.01 kg/s and a mean inlet temperature of 97°C. Assume that the average temperature for property evaluation for all parts of this problem is 325K.
(b) If air blows around the pipe (perpendicular to the pipe axis) with a velocity of 10 m/s and a freestream temperature of 27°C, what is the outlet temperature of the water? (Hint: review the last part of Ch. 8.3.3;you can neglect the conduction resistance of the pipe wall and assume that because it is so thin, the inner diameter and outer diameter are essentially the same). Is this result surprising to you? Why do you think it is so different from part (a)? Partial Ans: 94.3°C
(a) What is the outlet temperature of the water in the tube if the tube surface temperature can be maintained constant at 27°C? Ans: 33.7°C

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Question 44685

posted 10 months ago

2. Generate a plot of the temperature distribution (0/0p) for the adiabatic tip conditions. Use a plotting program of choice (ex. Excel, matlab, gnuplot, etc). Assume a rectangular fin with the following cross-section. See Table 3.4 in the book for the equations. The fin material i sAluminum Alloy 2024-T6.

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Question 44686

posted 10 months ago

3. A pin fin is constructed as shown in the figure below of pure copper (look up value of copper).Determine the (a) fin efficiency, (b) fin resistance, (c) fin effectiveness, and (d) heat rate of the fin assuming adiabatic tip. Use table 3.5 from the book. Convert the fin into a straight rectangular fin with the same surface area and diameter (t=D) and length (L=L) as the pin fin.Repeat calculations and compare answers. Which fin design is most effective?

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