Heat Transfer

Questions & Answers

A counter-flow heat exchanger with inlet fluid temperature at 120°C and leaves at temperature 310°C. Hot side inlet temperature is 500°C, outlet temperature is 400°C, find the LMTD.


1. Using saturated liquid water at 100°C is being proposed to cool a heated wire. The wire may be operated at either 80°C, 120°C, 150°C, or 700°C. Which temperature, out of these four options, would you suggest would be the best operating conditions? Note that the wire may degrade beyond a temperature of 750°C, and that there are small fluctuations that exist in the wire's operating temperature/heat generation. Explain your choice of ideal operating condition and why the other options would not be ideal.


Shell-and-Tube Heat Exchnager With Hot and Cold Water The undergraduate laborartory uses


3. Insulation of a steam pipe for safety of the students In a chemical engineering lab, the students are working with a steam engine that is fed by steam pipes. One of the students reaches over to make an adjustment and burns herself by bumping her arm on the exposed steam pipe. This prompts the lab coordinator to buy foam to cover the steam pipes, but first he needs to calculate how thick the foam needs to be. The lab coordinator measures the outside of the bare pipe, which has an outer diameter of 10 cm and is 2 m tall, to be 106°C. The lab coordinator also knows that the pipe is stainless steel, and the conductivity is 17.3 W/m-K. There needs to be at least enough insulation that the outside temperature is 50°C or less. The lab is uncomfortably warm at 27°C, so a fan is positioned next to the steam engine and blows air at 7 m/s. The steam inside the pipe is at 107°C and is flowing at 10 m/s. Use Appendix I in Welty et al. for all physical properties of liquids and gases. A. How thick does the insulation have to be if expanded polyethylene foam, which has a conductivity of 0.3 W/m-K, is used? Hint: Excel Solver is your friend! B. What is the inner diameter of the steam pipe?


Consider a very long rectangular fin of thickness 5.6 mm. Its base temperature is 173°C The convection heat transfer coefficient and the temperature of the surrounding are 58 W/m2 K and 33°C, respectively. If the temperature at a distance of 6 8 cm from the base is 95°C, calculate the thermal conductivity of the fin


A cylindrical pin fin of diameter 1.0 cm and length of 2 cm with negligible heat loss from the tip has an efficiency of 0.88. the effectiveness of this fin is:


Two finned surfaces with very long fins are identical, EXCEPT that the convection heat transfer coefficient for the first finned surface is TWICE that of the second one. What statement below is accurate for the efficiency and effectiveness of the first finned surface relative to the second one?


An infinite circular fin of diameter D is attached to wall with surface temperature of 393°C. The thermal conductivity of the fin is 424 W/m K The fin is exposed to an ambient air condition of 20°C and 205 W/m2K. The rate of heat transfer loss from the fin is 277 W Find the diameter of the fin, in Cm.


A 1.6-cm-diameter, very long cylindrical fin made of aluminum (k-156 W/m.K) is attached to a surface at 117°C. The surface is exposed to ambient air at 22 °C with a heat transfer coefficient of 19 W/m².K. Determine the rate of heat transfer from the fin in (W)


AL=2.6-cm-long, W-2.4-mm width, and t-1.0-mm thickness rectangular fin is manufactured from metal of K-401 W/m.K and is attached to a surface. The fin efficiency is 64%. Determine the effectiveness of this single fin. Use, respectively, the following equations for surface and cross-sectional areas:


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