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Engineering

Mechanical Engineering

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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.

Chapter8: Natural Convection

Section: Chapter Questions

Problem 8.6P

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3.9 The heat transfer coefficients for the flow of 26.6°C air over a sphere of 1.25 cm in diameter are measured by observing the temperature-time history of a copper ball the same dimension. The temperature of the copper ball was measured by two thermocouples, one located in the center and the other near the surface. The two thermocouples registered, within the accuracy of the recording instruments, the same temperature at any given instant. In one test run, the initial temperature of the ball was 66°C, and the temperature decreased by 7°C in 1.15 min. Calculate the heat transfer coefficient for this case.
The TPD method measures temperature elevations in a tissue region during a heating pulse and its later temperature decay after the pulse. It is then using the Pennes bioheat equation to perform a curve fitting to determine the local blood perfusion rate. If the TPD probe is placed in the vicinity of very large blood vessel, will the TPD technique provide an accurate measurement of the local blood perfusion in the vicinity of this large blood vessel? Explain briefly. (Hint: Is the Pennes bioheat equation accurate surrounding a large blood vessel?)
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A J- type thermocouple is used to measure the temperature in a heating process. Sheath material used is SS316. The length of the sheath is 13mm and thickness is 0.3mm. Find the time constant of the sheath. Material QU(kg/m)s(J/Kg - °c) K(W/m-k) Platinum 21450 130 71.6 SS304 8030 500 21.4 SS316 7990 500 21.4 SS410 7750 460 24.9 Air 1.20 1005 0.025 MgO Powder 3580 877 26.8 Silicon compound3210 800 Time constant of the bare material is, T=
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A J- type thermocouple is used to measure the temperature in a heating process. Sheath material used is SS316. The length of the sheath is 10mm and thickness is 0.2mm. Find the time constant of the sheath. Material Q(kg/m3) s(J/Kg - oc) K(W/m-k) Platinum 21450 130 71.6 SS304 8030 500 21.4 SS316 7990 500 21.4 SS410 7750 460 24.9 Air 1.20 1005 0.025 MgO Powder 3580 877 26.8 Silicon compound 3210 800 3 Time constant of the bare material is, T= Answer
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Examples of external data I can use to support the claim that the consumers living within regions with hot climate will buy the stainless steel pan with digital thermometer reading that is powered by the heat generated while cooking and that sales will be higher in summer.
A plate-shaped glass wall with a thickness of 3 cm and a heat transfer coefficient of 2W / m.K has 30C air on the inside and 10C ambient air on the outside. The internal and external convulsion coefficients are 30 W / m ^ 2.K and Since it is 15W / m ^ 2.K,a.) The amount of heat in the unit area of the wall,b.) Calculate the inner and outer surface temperatures of the wall.
Let'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…