Solution of Problems in Heat Transfer Transient Conduction or Unsteady Conduction 1st. Edition by Osama Mohammed Elmardi | 9783659668227 | 3659668222

Heat Transfer

Solution of Problems in Heat Transfer Transient Conduction or Unsteady Conduction

36 SOLVED PROBLEMS

Question: 7.14

Determining the Total Time Required for a Cylindrical Ingot to be heated to a Given Temperature A hot cylinder ingot of 50mm diameter and 200mm long is taken out from the furnace at 800°𝐶 and dipped in water till its temperature fall to 500°𝐶 . Then, it is directly exposed to air till its ...

Verified Answer:

Given:

r=\frac{50}{2}=25m m=0.025m;{ L}=200...

Question: 7.13

Calculation of the Time Taken to Boil an Egg An egg with mean diameter of 40mm and initially at 20°𝐶 is placed in a boiling water pan for 4 minutes and found to be boiled to the consumer’s taste. For how long should a similar egg for the same consumer be boiled when taken from a refrigerator at ...

Verified Answer:

Given:

r=\frac{40}{2}=20m m=0.02m;\;T_{o}=2...

Question: 7.12

Estimation of the Time Required to Cool a Decorative Plastic Film on Copper Sphere to a Given Temperature using Lumped Capacitance Theory The decorative plastic film on copper sphere 10mm in diameter is cured in an oven at 75°𝐶. After removal from oven, the sphere is exposed to an air stream at ...

Verified Answer:

{d=10m m=0.01m{\mathrm;\ T}_{o}=75^{\circ}C...

Question: 7.11

Determining the Time Required to Cool a Mild Steel Sphere, the Instantaneous Heat Transfer Rate, and the Total Energy Transfer A 15𝑚𝑚 diameter mild steel sphere (𝑘 = 4.2𝑤/𝑚°C is exposed to cooling air flow at 20°𝑐 resulting in the convective, coefficient ℎ = 120𝑤/m²° 𝐶. Determine the ...

Verified Answer:

Given:

r=\frac{15}{2}=7.5m m=0.0075m;\;k=42...

Question: 7.10

Determination of the Maximum Speed of a Cylindrical Ingot inside a Furnace A cylinder ingot 10𝑐𝑚 diameter and 30𝑐𝑚 long passes through a heat treatment furnace which is 6m in length. The ingot must reach a temperature of 800°𝐶 before it comes out of the furnace. The furnace gas is at 1250°𝐶 ...

Verified Answer:

\rm{d=10c m =0.1m; \ L=30cm=0.3m; \ Length ...

Question: 7.9

Calculation of the Initial Rate of Cooling of a Steel Ball A steel ball 50mm in diameter and at 900°𝐶 is placed in still atmosphere of 30°𝐶. Calculate the initial rate of cooling of the ball in °𝐶/𝑚𝑖𝑛, if the duration of cooling is 1 minute.Take: 𝜌 = 7800𝑘𝑔/m³; 𝑐𝑝 = 2𝑘𝑗/𝑘𝑔°𝐶 ...

Verified Answer:

Given:

r={\frac{50}{2}}=25m m=0.025m;\;T_{o...

Question: 7.8

Determination of the Heat Transfer Coefficient The heat transfer coefficients for flow of air at 28°𝐶 over a 12.5𝑚𝑚 diameter sphere are measured by observing the temperature – time history of a copper ball of the same dimension. The temperature of the copper ball (𝑐𝑝 = 0.4𝑘𝑗/𝑘𝑔 𝐾 and ...

Verified Answer:

Given:

\;T_{\infty}=28^{\circ}C;r({\mathrm{...

Question: 7.7

Determination of the Heat Transfer Coefficient An average convective heat transfer coefficient for flow of 90°𝐶 air over a plate is measured by observing the temperature – time history of a 40𝑚𝑚 thick copper slab (𝜌 = 9000𝑘𝑔/m³, 𝑐𝑝 = 0.38𝑘𝑗/𝑘𝑔°𝐶, 𝑘 = 370𝑤/𝑚°𝐶) exposed to 90°𝐶 ...

Verified Answer:

{\mathrm{Given}}\colon\;T_{\infty}=90^{\cir...

Question: 7.6

Determining the Temperature of a Solid Copper Sphere at a Given Time after the Immersion in a Well – Stirred Fluid A solid copper sphere of 10𝑐𝑚 diameter (𝜌 = 8954𝑘𝑔/m³, 𝑐𝑝 = 383𝐽/𝑘𝑔, 𝐾 = 386𝑤/𝑚𝐾) initially at a uniform temperature of 𝑇𝑜 = 250°𝐶, is suddenly immersed in a well ...

Verified Answer:

Given:

d=10c m = 0.1m; \ p=8954kg/m^{3}; \...

Question: 7.4

Calculation of the Time Required for the Plate to Reach a Given Temperature A 50𝑐𝑚 × 50𝑐𝑚 copper slab 6.25mm thick has a uniform temperature of 300°𝐶. Its temperature is suddenly lowered to 36°𝐶. Calculate the time required for the plate to reach the temperature of 108°𝐶. Take: ...

Verified Answer:

Surface area of plate (two sides),

A_{s}=\,...