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In an experiment, the temperature of a hot gas stream is to be measured by a thermocouple with a spherical junction. Due to the nature of this experiment, the response time of the thermocouple to register 99 percent of the initial temperature difference must be within 5 s. The properties of the thermocouple junction are
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Heat and Mass Transfer: Fundamentals and Applications
- 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.arrow_forwardA 2 cm thick steel slab heated to 5250 C is held in air stream having a mean temperature of 25° C. determine the time interval when the slab temperature would not depart from the mean value of 25° C by more than 0.50 C at any point in the slab when Boit Number = Bi = 0.0078, Fourier number = Fo = 0.127 T 885 sec 6907 sec 6973 sec 9573 secarrow_forwardAnswer this ASAP The diameter of the tube is 25 mm. The specific heat of water is 4.18 kJ/kg.°C. The overall heat transfer coefficient is 0.7 kW/m².°C. 1. Schematic of temperature distribution 2.ΔTLMTD 3.Actual heat transfer rate 4.Cmin 5.Maximum heat transfer ratearrow_forward
- Nonearrow_forwardQ1/ Consider a large plane wall of thickness L=0.03 m. The wall surface at x =0 is insulated, while the surface at x =L is maintained at a temperature of 30°C. The thermal conductivity of the wall is k=25 W/m °C, and heat is generated in the wall at a rate of g = 9oe0.5x/L W/m³ Where g, = 8 x 10 W /m². Assuming steady one-dimensional heat transfer, (a) express the differential equation and the boundary conditions for heat conduction through the wall, (b) obtain a relation for the variation of temperature in the wall by solving the differential equation, and (c) determine the temperature of the insulated surface of the wall.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_forward
- Q1. A 50 meter long cast iron pipe with outer diameter of 10 cm passes in an open space of 288 K temperature. The outer surface of the pipe temperature is 423 K and the combined heat transfer coefficient on the outer surface of the pipe is 25 W/m? K. Considering and stating the necessary assumptions determine, (a) The rate of heat loss from the pipe (b) The energy lost per year if the cost of the fuel is 0.52 $/therm ( 1 therm = 105,500 kJ) (c) The thickness of the insulation if 98% of the energy loss is planned to be saved. Consider the conduction coefficient of the insulation is 0.035 W/mK. Tair = 288 K 423 K Steam 50 m Fiberglass insulation Figure Q1.arrow_forwardA J- type thermocouple is used to measure the temperature in a heating process. The length of the bare material is 120mm and thickness is 1.5mm. Find the time constant of the bare material. уре of Thermo-Material K ( Q W/m- (kg/m3) k) IS |(J/Kg- oc) couple J Iron- Constantan 46 8535 345 K Kromel- Alumel 35 8738 380 IT Copper- Constantan 160 8902 316 Cromel - Contantan 33 8825 336 Nicrocil- Nisil 34 8702 376 Pt(30%)Rhodium - 19 15718 56 Pt(6%)Rhodium Platinum(13%)Rodium, 55 16628 99 - Platinum Platinum(10%)Rodium 52.9 16745 99 Platinum Time constant of the bare material is, T=arrow_forwardA thermal system having a cylindrical form contains a sequence of cylindrical layers is used to cool hot gases. The thermal properties of the system materials are as follows : k = 231 W/m.K, c = 1033 J/kg.K and the density = 2702 kg/m^3. The gases to be cooled has a temperature equals to 500 C. Determine the temperature of the system that corresponds to 10 % of the maximum possible heat transfer between the gas and the system. Consider that the system has a characteristic length equals to 0.03 m. The heat convective coefficient is equal to 50 W/m^2.K. The initial temperature of the system is equal to 20 C. Select one: О а. 370 К O b. 489 K С. 341 К d. 410 Karrow_forward
- Mechanical servicesarrow_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_forwardConsider steady-state conditions for one-dimensional conduction in a plane wall having a thermal conductivity k = 40 W/m-K and a thickness L = 0.3 m, with no internal heat generation. T1 -T2 L Determine the heat flux, in kW/m?, and the unknown quantity for each case. Case T1(°C) T2(°C) dT/dx(K/m) q (kW/m?) 1 50 -20 -233.333 9333.32 2 -30 -10 66.667 75466.67 3 70 117.85 160 6400 4 63.85 40 -80 3200 5 -30.15 30 200 8000arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning