A plane wall with constant properties is initially at a uniform temperature
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Fundamentals of Heat and Mass Transfer
- (Q4) A 4m x 6m wall consists of 4 glass windows of 2m x 1.5m dimensions. The wall has thickness of 0.13m and a thermal conductivity of 0.5 W/m.K, while the glass windows are 6 mm thick with a thermal conductivity of 1.228 W/m.K. The values of intemal and external surface conductance for the wall (including glass) are 7.8 W/m? K and 34.4 W/m².K, respectively. The intemal and extemal temperatures are 22° C and 42°C, respectively. Calculate the total heat transfer rate through the wall. What percentage of this heat transfer is through the windows?arrow_forwardHow long should it take to boil an egg? Model the egg as a sphere with radius of 2.3 cm that has properties similar to water with a density of = 1000 kg/m3 and thermal conductivity of k = 0.606 Watts/(mC) and specific heat of c = 4182 J/(kg C). Suppose that an egg is fully cooked when the temperature at the center reaches 70 C. Initially the egg is taken out of the fridge at 4 C and placed in the boiling water at 100 C. Since the egg shell is very thin assume that it quickly reaches a temperature of 100 C. The protein in the egg effectively immobilizes the water so the heat conduction is purely conduction (no convection). Plot the temperature of the egg over time and use the data tooltip in MATLAB to make your conclusion on the time it takes to cook the egg in minutes.arrow_forwardThe initial temperature of a 50 cm long silver wire is 50 °C. The circumference of the wire in question is completely insulated, but both ends are kept at a temperature of 0 °C (zero degrees Celsius). Obtain the heat conduction along the wire as a function of time and position and, taking a single term in the solution, determine how many degrees Celsius the temperature in the middle of the rod will be after 7 minutes. (For silver wire, α=1.70 cm2/s.)arrow_forward
- Radioactive wastes are packarrow_forwardA hot water pipe is 100 mm in diameter and 80 m long. This pipe is insulated in two layers. First layer is 25 mm thick, thermal conductivity is 0.12 W/m C material, second layer is 45 mm thick It is made of material with a thermal conductivity of 0.05 W/m C. T1, T2 and T3 are the surface temperatures in the pipe. One With the acceptance of heat transfer in dimensional and continuous conditions, transfer from the pipe in case T1= 600 OC and T3= 35 C Find the amount of heat released and the temperature T2. 2.tabaka 1.tabaka 100 mm T₁ T₂ T3arrow_forwardA plane wall of thickness 2L=40 mm and thermal conductivity k=5 W/m·K experiences uniform volumetric heat generation at a rate q, while convection heat transfer occurs at both of its surfaces (x=-L, +L), each of which is exposed to a fluid of temperature T=20 °C. Under steady-state conditions, the temperature distribution in the wall is of the form T(x) = a+bx+cx² where a = 82.0 °C, b=-210 °C/m, c = -2x10 °C/m², and x is in meters. The origin of the x- coordinate is at the midplane of the wall. -L x -L (a) Determine the surface heat fluxes, qx(-L) and qx(+L). (b) What is the volumetric rate of heat generation & in the wall? (c) What is the convection heat transfer coefficient for the surfaces at x = +L? (d) Obtain an expression for the heat flux distribution q (as a function of x). Is the heat flux zero at any location? (e) If the source of the heat generation is suddenly deactivated (i. e. q = 0), what temperature will the wall eventually reach with q = 0?arrow_forward
- A certain material has a thickness of 30 cm and a thermal conductivity of 0.04 W/m- °C. At a particular instant in time, the temperature distribution with x, the distance from the left face, is T = 150x ^ 2 - 30x , where x is in meters. Calculate the heat-flow rates atx x = 0 and x = 30 cm . Is the solid heating up or cooling down?arrow_forward= Consider a large plane wall of thickness L=0.3 m, thermal conductivity k = 2.5 W/m.K, and surface area A = 12 m². The left side of the wall at x=0 is subjected to a net heat flux of ɖo = 700 W/m² while the temperature at that surface is measured to be T₁ = 80°C. Assuming constant thermal conductivity and no heat generation in the wall, (a) express the differential equation and the boundary equations for steady one- dimensional heat conduction through the wall, (b) obtain a relation for the variation of the temperature in the wall by solving the differential equation, and (c) evaluate the temperature of the right surface of the wall at x=L. Ti до L Xarrow_forwardPLEASE HELP ANSWER THIS THERMODYNAMICS PRACTICE QUESTION THANK YOUarrow_forward
- Example: . A steel ball [c-0.46 kJ/kg C, k-35 W/m. C] 5.0 cm in diameter and initially at a uniform temperature of 450°C is suddenly placed in a controlled environment in which the temperature is maintained at 100°C. The convection heat-transfer coefficient is 10 W/m². C. Calculate the time required for the ball to attain a temperature of 150°C. Solution: We anticipate that the lumped-capacity method will apply because of the low value of h and high value of k.We can check by using Equation (3.9): hLc B₁ = k 3 Lc = T 0.025 =-= = 0.00833 A₂ 4mr² 3 3 hle 10-0.00833 B₁ = = = 0.0023 < 0.1 k 35 The lumped system capacitance method is valid and can used. Therefore, may can use equation 3.4: t= pvc In 0₁ hAs 0 92 HEAT TRANSFER t = pvc In pvc Ti-Too hAs T-Too T = 150 °C, p = 7800 kg/m³. Too-100 °C, h=10 w/m².C. T₁-450 °C, c-460 J/kg. "C. pvc In Ti-Too t = hAs T-Too t= Pr³c In Ti-Too h4r² T-T t= 1 In Ti-To pre 3h T-T V -= = 7800+0.025-460 In 3.10 450-100 150-100 = 5818.3 s= 1.62 h 6arrow_forwardSolve fast and correctly. Handwritten answer please.arrow_forwardThree (3) bricks, specifically A, B, and C were arranged horizontally in such a way that it can be illustrated as a sandwich panel. Consider the system to be in series and in the order of Brick A, Brick B and Brick C. The outside surface temperature of Brick A is 1,500℃ and 150 ℃ for the outside surface of Brick C. The thermal conductivities for Brick A, Brick B and Brick C, are 2 ?/? °? , 0.50 ?/? °? , 60 ?/? °?. The thickness of Brick A and Brick C are 50 cm and 22 cm. The rate of heat transfer per unit area is 1,000 ?/?2 . Determine the following: The thickness of Brick B in the unit of mm. Assume that all the conditions were retain except that the thickness of Brick B was increased to 800 mm, what is the new value for the rate of heat transfer per unit area in ???/ℎ? . ??2 please explain the principles to solve thisarrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning