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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+MASS TRANSFER:FUND.+APPL.
- The heat transfer rate from hot air by convection at 100C flowing over one side of a flat plate with dimensions 0.1m0.5m is determined to be 125 W when the surface of the plate is kept at 30C. What is the average convection heat transfer coefficient between the plate and the air?arrow_forward3.10 A spherical shell satellite (3-m-OD, 1.25-cm-thick stainless steel walls) re-enters the atmosphere from outer space. If its original temperature is 38°C, the effective average temperature of the atmosphere is 1093°C, and the effective heat transfer coefficient is , estimate the temperature of the shell after reentry, assuming the time of reentry is 10 min and the interior of the shell is evacuated.arrow_forward2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from one side of an electronic device 1 m wide and 1 m tall. The fins are to be rectangular in cross section, 2.5 cm long and 0.25 cm thick, as shown in the figure. There are to be 100 fins per meter. The convection heat transfer coefficient, both for the wall and the fins, is estimated to be K. With this information determine the percent increase in the rate of heat transfer of the finned wall compared to the bare wall.arrow_forward
- Indirect Cooling With Liquid Nitrogen. You are designing a system to cool an insulated silver plate of dimensions 2.00 cm × 2.00 cm x 0.40 cm. One end of a thermally insulated copper wire (diameter D = 2.70 mm and length L = 12.0 cm) is dipped into a vat of liquid nitrogen (T = 77.2 K), and the other end is attached to the bottom of the silver plate. (a) If the silver plate starts at room temperature (73.0°F), what is the initial rate of heat flow between the plate and the liquid nitrogen reservoir? (b) Assuming the rate of heat flow calculated in part (a), estimate the temperature of the silver plate after 30.0 seconds.arrow_forwardAir is flowing through a 20 m long pipe of 20 cm diameter at a rate of 0.8 kg/s. The inlet air temperature is 40 deg C; the entire pipe wall is held at a constant temperature of 90 deg C. Estimate the air temperature at the outlet as well as the heat transfer rate for the entire length of the pipe. Properties are: 1.038 kg/m3; 1009 J/(kg-K); 2.042E-05 Pa-s; 0.0293 W/(m-K).arrow_forwardThe temperature of an air stream flowing is measured by a copper – constantanthermocouple which may be approximated as a cylinder of 1.7 mm diameter. Initiallythe junction and air at a temperature of 25 oC. The air temperature suddenly changesto and is maintained at 215 oC. The thermal junction properties are: ρ = 8750 kg/m3; Cp = 380 J/kgoC; k(thermocouple) = 28W/moC; h = 145 W/m2-oC. a. Determine the time required for the thermocouple to indicate temperature of 165oC. Also, determine the thermal time constant and the temperature indicated bythe thermocouple at that instant.b. Discuss the stability of this thermocouple to measure unsteady state temperatureof a fluid when the temperature variation in the fluid has a time period of 3.6 s.arrow_forward
- Indirect Cooling With Liquid Nitrogen. You are designing a system to cool an insulated silver plate of dimensions 2.00 cm × 2.00 cm × 0.60 cm. One end of a thermally insulated copper wire (diameter D = 2.70 mm and length L = 18.0 cm) is dipped into a vat of liquid nitrogen (T = 77.2 K), and the other end is attached to the bottom of the silver plate.(a) If the silver plate starts at room temperature (65.0 °F), what is the initial rate of heat flow between the plate and the liquid nitrogen reservoir?(b) Assuming the rate of heat flow calculated in part (a), estimate the temperature of the silver plate after 30.0 seconds.arrow_forwardQuestion 1: The exterior wall of a building consists of 100 mm thick face brick (k = 0.9 W/m∙K), 40 mm thick polystyrene insulating board (k = 0.036 W/m∙K), 125 mm thick concrete block (k = 1.8 W/m∙K) and 15 mm thick interior gypsum board (k = 0.18 W/m∙K). The inside and outside convective heat transfer coefficients are 6.5 W/m2∙K and 22.5 W/m2∙K, respectively. The outside air temperature is -5°C and the inside air temperature is 20°C. The wall is 3 m high and 15 m long. Calculate the rate of heat loss (in W) through the wall. Follow-up question to Question 1, calculate the temperature (in °C) of the interior surface of the wall. Follow-up question to Question 1, calculate the temperature (in °C) of the exterior surface of the wall. Note: Round the answers to 2 decimal places.arrow_forwardA glass door is used on a fireplace to reduce exfiltration of room air through the chimney. The door, 0.70m high and 1.00m wide, reaches a uniform temperature of 232oC. If the room air temperature is 23oC, estimate the rate of heat transfer to the room air due to convection. Air properties: k=0.0338W/m-K ν=26.4x10-6 m2/s Pr=0.690arrow_forward
- The temperature of a gas stream is to be measured by a thermocouple whose junction can be approximated as a 1.2-mm-diameter sphere. The properties of the junction are k = 35 W/m °C, ρ= 8500 kg/m3 ,and Cp = 320 J/kg °C, and the heat transfer coefficient between the junction and the gas is h = 65 W/m2 °C. Determine how long it will take for the thermocouple to read %95 of the initial temperature difference.arrow_forwardA small copper wire with a diameter of 0.792 mm and initially at 366.5 K is suddenly immersed in a liquid held constant at 311 K. The convection coefficient h = 85.2 W/m2 · K. The physical properties can be assumed constant and are k = 374 W/m · K, cp = 0.389 kJ/kg · K, and ρ = 8890 kg/m3. Determine the time in seconds for the average temperature of the wire to drop to 338.8 K (one-half the initial temperature difference). Do the same but for h=11.36W/m2·K. Forpart(b),calculate the total amount of heat removed for a wire 1.0 m long.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning