2-1. Temperature Response in Cooling a Wire. A small copper wire with a diameter of0.792 mm and initially at 366.5 K is suddenly immersed in a liquid held constant at311 K. The convection coefficient h 85.2 W/m K. The physical properties can beassumed constant and are k =374 W/m K, c, = 0.389 kJ/kg K, and p = 8890 kg/m2.(a) Determine the time in seconds for the average temperature of the wire todrop to 338.8 K (one-half the initial temperature difference).(b) Do the same but for h 11.36 W/m2 K(c) For part (b), calculate the total amount of heat removed for a wire 1.0 mрu (Along.(a) t 5.66 sAns.the Smou hire is lonsasbumeNhere rraolius, here radliusyinder hitu xChapter 14Principles of Unsteady-State Heat Transfer

Answered: 2-1. Temperature Response in Cooling a…

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

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The thermal conductivity of a sheet of rigid, extruded insulation is reported to be k = 0.029 W/m-K. The measured temperature difference across a 25-mm-thick sheet of the material is T – T2 = 12°C. (a) What is the heat flux through a 3 m x 3 m sheet of the insulation, in W/m2? (b) What is the rate of heat transfer through the sheet of insulation, in W? (c) What is the thermal resistance of the sheet due to conduction, in K/W?
Q: A large plane wall of thickness (L= 0.3 m), thermal conductivity (k = 40 W/m-°C), and surface area 0.4 m2. The left side of the wall is maintained at a constant temperature of 70°C while the right side loses heat to the surrounding air with heat flux q' expressed by: 1200k q = k+20L A- Find a relation to determine the variation of temperature in the wall. B- Determine the rate of heat transfer through the wall. C- Determine the temperature at the right side of the wall. wall T1= 70 °C L= 0.3m
Steel is sequentially heated and cooled to relieve stresses and to make it less brittle. Consider a 100 mm thick plate that is initially at a uniform temperature of 300 °C and is heated on both sides in a gas fired furnace for which To 700 °C and h=500 W/m². K. How long will it take the coldest spot to reach 550 °C in the plate? Materials properties are given in this graph. == = Steel plate: 11 T₁ = 300°C T(0,t) = 550°C L = 50 mm Combustion gases p=7800 kg/m3 Cp = 500 J/kg-K k = 45 W/m-K T∞ = 700°C h = 500 W/m²-K
#m 3 E D C F3 $ 4 R F Ac = 1m² V Too,1=1 K h₁ = 1 W/m²K (5) Consider a wall (as shown above) of thickness L=1 m and thermal conductivity k-1 W/m-K. The left (x=0) and the right (x=1 m) surfaces of the wall are subject to convection with a convectional heat transfer coefficient h = 1 W/m²K and an ambient temperature T.= 1 K. Heat generation inside the wall is q=1W/m³. You may assume 1-D heat transfer, steady state condition, and neglect any thermal contact resistance. Find T(x). 44 % 5 Q Search F5 T G T₁ B x=0 * A 6 q=1 W/m³ k= 1W/mK L=1m F6 Y H F7 & 7 T₂ x= 1 m U N Top 2 = 1 K h₂=1 W/m²K PrtScn F8 8 Home M F9 ( 9 K End F10 0 L PgUp
Q1: Consider a large plane wall of thickness L = 0.4 m, thermal conductivity k=2.3 W/m °C, and surface area A= 20 m2. The left side of the wall at x= 0 is subjected of T1 = 80°C. while the right side losses heated by convection to the surrounding air at T-15 °C with a heat transfer coefficient of h=24 W/m2 C. Assuming constant thermal conductivity and no heat generation in the wall, (a) express the differential equation and the boundary conditions for steady one-dimensional heat conduction through the wall, (b) obtain a relation for the variation of temperature in the wall by solving the differential equation, and (c) evaluate the rate of heat transfer through the wall Ans : (c) 6030 W
Q2- Water flows inside a steel pipe with an ID of 2.5 cm. The wall thickness is 2 mm, and the convection coefficient on the inside is 100 Wm? C. The convection coefficient on the outside is 10 W/n C. The pipe is covered with a layer of asbestos. 1-determine the thickness of the asbestos layer at the critical insulation radius of the pipe. 2-calculate the change percent of heat transfer with and without the insulation. 3-commet on your results,
I need the answer as soon as possible
Shown below is an insulated copper block that receives energy at a rate of 100 W from anembedded resistor. If the block has a volume of 10-3 m3and an initial temperature of 20oC, howlong would it take, in minutes, for the temperature to reach 60oC? Copper has a specific heatcapacity ccu = 0:385 kJ/ kg.K and a density of cu = 8930 kg/m3.
Q2: A 2.5 -mm-diameter electrical wire is insulated by a 2-mm-thick rubberized sheath (* = 0.11 W/m K), and the wire/sheath interface. The convection heat transfer coefficient of the outer surface of the sheath is 10 W/m² K, and the temperature of the ambient air is 20 C. If the temperature of the insulation may not exceed 50 C, what is the maximum allowable electrical power that may be dissipated per unit length of the conductor? What is the critical radius of the insulation?
Suppose that the 10 cm thick concrete wall of a commercial building measures 30 mby 4 m. The energy impinging on the surface is 700 Wm-2. Under these conditionsthe external air temperature is 25ºC, and the internal and external surfacetemperatures of the concrete wall are 17ºC and 40ºC, respectively.(a) State and briefly describe the three heat transfer mechanisms.[30%](b) Calculate the net amount of thermal energy radiated by the wall.[40%](c) State your assumptions and briefly discuss their effect on the relativesizes of the heat transfer mechanisms.[30%]Data for Question A3.Heat transfer coefficient of air at 25ºC = 5 Wm-2K-1Thermal conductivity of concrete = 1.2 Wm-1K-1Emissivity of concrete = 0.85Stefan’s constant = 5.7 x 10-8 Wm-2K-4
Question 1: In your own words, write down the differences between thermodynamic and heat transfer. (3 Marks) Question 2: Estimate the heat loss per square metre of surface through a brick wall 0.5 m thick when the inner surface is at 400 K and the outside surface is at 300 K. The thermal conductivity of the brick may be taken as 0.7 W/mK. (2 Marks) Question 3: A furnace is constructed with 0.20 m of firebrick, 0.10 m of insulating brick, and 0.20 m of building brick. The inside temperature is 1200 K and the outside temperature is 330 K. If the thermal conductivities are as shown in the figure below, estimate the heat loss per unit area. (5 Marks) 1200 K 330 K Fire brick X=0.20 m Insulating brick x=0.10 m Ordinary brick X=0.20 m k = 1.4 k = 0.21 k = 0.7 (WimK)
1- A solid infinitely long cylinder, radius 2 cm, has uniform internal heat generation. The temperature distribution in the cylinder is T(r) = = 256 – 8.6 x 104 r² where r is in meters, T in °C and the thermal conductivity of the cylinder material is 16 W/ m °C. Determine: (a) The temperature at the centerline. (b) The surface temperature. (c) The heat flux at the surface. (d) The rate of heat transfer to the surrounding per unit meter of cylinder length.

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