Determine the time needed to decrease the temperature of a solid cylinder from 40 C to 35 C if the ambient temperature is equal to 31 C. The cylinder has a length equals to 0.9 m and diameter equals to 100 mm. The heat convective coefficient is equal to 9 W/m^2.K. The cylinder has a conductivity equals to 2 W/m.K, a density equals to 1200 kg/m^3 and its Cp is equal to 4.700 kJ/kgK.
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- A plane wall 15 cm thick has a thermal conductivity given by the relation k=2.0+0.0005T[W/mK] where T is in kelvin. If one surface of this wall is maintained at 150C and the other at 50C, determine the rate of heat transfer per square meter. Sketch the temperature distribution through the wall.Discuss the modes of heat transfer that determine the equilibrium temperature of the space shuttle Endeavour when it is in orbit. What happens when it reenters the earths atmosphere?1.10 A heat flux meter at the outer (cold) wall of a concrete building indicates that the heat loss through a wall of 10-cm thickness is . If a thermocouple at the inner surface of the wall indicates a temperature of 22°C while another at the outer surface shows 6°C, calculate the thermal conductivity of the concrete and compare your result with the value in Appendix 2, Table 11.
- Consider 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 80002 kilograms of gas with a molecular weight of 28 is closed and equipped with an electrical resistor. located in a rigid tank. This system has a fixed resistance of 10 amps and a voltage of 12 volts for 10 minutes. is implemented. When thermal equilibrium is reached, it measures that the temperature of the gas rises by 40.3°C. shows. It is estimated that the heat transfer to the environment occurs as 20 W. With the help of the measured data and assuming the ideal gas behavior, the gas's Determine the average value of the specific heat Cp in kJ/(kg K).Thermistors are semiconductors used for measuring temperature. The electri- cal resistance of a thermistor changes with temperature. One model for the et- fect of temperature on a specific thermistor is R = 2,252e4000(-36.16), where R is the resistance in ohms and T is the temperature in K. You can verify that this thermistor has a resistance of 2,252 at 25°C = 298.16 K. For the data below, calculate the correlation coefficient for the model and decide whether the model fits the data well or not. Temperature (°C) Resistance (N) 7,850 10 4,400 2,900 20 1,500 30 1,000 40
- 6. a. The heat flux applied to the walls of the biomass combustion furnace is 20 W/m2. The furnace walls have a thickness of 10 mm and a thermal conductivity of 12 W/m.K. If the wall surface temperature is measured to be 50oC on the left and 30oC on the right, prove that conduction heat transfer occurs at a steady state!b. Heating the iron cylinder on the bottom side is done by placing the iron on the hotplate. This iron has a length of 20 cm. The surface temperature of the hotplate is set at 300oC while the top side of the iron is in contact with the still outside air. To reach the desired hotplate temperature, it takes 5 minutes. Then it takes 15 minutes to measure the temperature of the upper side of the iron cylinder at 300oC. Show 3 proofs that heat transfer occurs transientlyConsider 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. T2 L Determine the heat flux, in kW/m?, and the unknown quantity for each case. T1 (°C) T2(°C) dT/dx(K/m) 9 (kW/m?) Case 1 50 -20 i i 2 -30 -10 i 70 i 160 i 40 -80 i 5 i 30 200 iDetermine the time needed to decrease the temperature of a solid cylinder from 40 C to 35 C if the ambient temperature is equal to 31 C. The cylinder has a length equals to 0.9 m and diameter equals to 100 mm. The heat convective coefficient is equal to 1.3 W/m^2.K. The cylinder has a conductivity equals to 2 W/m.K, a density equals to 1200 kg/m^3 and its Cp is equal to 4.700 kJ/kgK. Select one: a. 83325 s O b. 10500s O c. 45360 s O d. 30050 s
- The time evolution of the temperature of an object follows the Newton's cooling laws dT dx = -k(T - Ts), where the term k = 2.2 (1/s) is the heat transfer constant, and Tg = 25.6° C is the ambient temperature. The initial temperature of the object at time t = = 0 is T(t = 0) = 200°C. °C Use the Euler's method, and a time step of h=0.2s, calculate: When t = = 0.2s, T = °C When t 1s, T =Consider steady-state conditions for one-dimensional conduction in a plane wall having a thermal conductivity k = 40 W/m-K and a thickness L = 0.4 m, with no internal heat generation. -T2 L Determine the heat flux, in kW/m2, and the unknown quantity for each case. Case T1(°C) T2(°C) dT/dx(K/m) 9% (kW/m²) 1 50 -20 i i -30 -10 i i 3 70 i 160 i 4 i 40 -80 i i 30 200 i LOA hot fluid (60° C) flows inside an copper tube with 1.7 cm OD and 1.5 cm ID. The inside of the pipe has a heat transfer coefficient of 130 W/m2-K. The tube is exposed to a room with air and surrounding walls of 23° C. The heat transfer coefficent between the outside of the walls and the room air is 15 W/m2 K. Draw an equivalent circuit diagram of the heat transfer, and quantify the resistance to heat flow by each of the two convective processes, conduction in the tube, and radiation between the outside of the tube and the room walls. Are any of the resistances negligible to the overall heat transfer, and if so, which ones?