An electrically heated plate 15cm high and 10cm wide is maintained at 140°C. Estimate the rate of heat dissipation from both sides of the plate in an atmospheric at 20° C, if the radiation heat transfer co-efficient is 8.72W /m² -K. For air at the mean temperature of 80°C; Take kinematic viscosity= 21.09x10 m² /s, Pr 0.692, and k = 0.0305 W/m-K.
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- 7.43 Liquid sodium is to be heated from 500 K to 600 K by passing it at a flow rate of 5.0 kg/s through a 5-cmID tube whose surface is maintained at 620 K. What length of tube is required?Q3/Condensing steam at 1 atm is used to maintain a vertical plate 20 cm high and 3.0 m wide at a constant temperature of 100°C. The plate is exposed to room air at 20°C. What flow rate of air will result from this heating process? What is the total heating supplied to the room air? Ans. 0.0034 kg/s, 278WA composite wall constructed of 2.5cm of steel (k-60.5 W/m-K) and 5.0 cm of aluminum (k177W/m-K) separates two liquids. The liquid on the steel side has a film coefficient of 15W/m²-K and a temperature of 400degC. The liquid on the steel side has a film coefficient of 30W/m² and a temperature of 100degC. Assume steady state conditions, what is the temperature at the steel-aluminum interface in deg C
- BThe heat transfer from a 2-m-diameter sphere to a 25 °C air stream over a time interval of one hour is 3000 kJ. Estimate the surface temperature of the sphere if the heat transfer coefficient is 10 W/m²K.During air cooling of oranges, grapefruit, andtangelos, the heat transfer coefficient for combined convection,radiation, and evaporation for air velocities of0.11 < V < 0.33 m/s is determined experimentally and isexpressed as h = 5.05 kair Re1/3/D, where the diameter Dis the characteristic length. Oranges are cooled by refrigeratedair at 5°C and 1 atm at a velocity of 0.3 m/s. Determine(a) the initial rate of heat transfer from a 7-cm-diameterorange initially at 15°C with a thermal conductivity of0.50 W/m·K, (b) the value of the initial temperature gradientinside the orange at the surface, and (c) the value of theNusselt number.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.
- A 10 cm thick and 1 m wide long steel plate is immersed in an oil bath at T0 = 40 ° C when the temperature is Ti = 240 ° C. According to the heat transfer coefficient between the plate and oil h = 600 W / m2K and p = 7833 kg / m3 for steel, cp = 465 J / kgK, k = 43 W / mK, α = 1.2x10-5m2 / s (a) after how long the core temperature of the steel plate becomes 100 ° C (b) What is the temperature within 3 cm from the surface of the steel plate (c) What will be the amount of heat transferred to the unit length plate during this time?Example: 0.5 kg of water per minute is heated from 20° to 40°C when passed through a tube of 2.5 cm diameter steel pipe. The pipe surface temperature is maintained at 110°C by condensing steam on its surface. Find out the length of the pipe required. The properties of water at mean temperature of 70°C are given below: p = 978 kg/m² k= 0.575 W/m. K Cp = 4200 J/kg. K v = 0.415 x 10-6 m²/secA 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=0.690
- 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.7. Air at 600 K, 1 atm is flowing across a flat plate kept at 300 K with a convection coefficient of 91 W/m2 K. If the Stanton number at this condition of flow is 0.039. what is the velocity of the air? Express your answer in m/s.The defroster of an automobile functions by discharging warm air on the inner surface of the windshield. To prevent condensation of water vapor on the surface, the temperature of the air and the surface convection coefficient (T¡,¡ ) must be large enough to maintain a surface temperature T, that is at least as high as the dewpoint (Ts,i ≥ Tdp). Step 1 00,0¹ kg 8 - 0 Consider a windshield of length L = 800 mm and thickness t = 6 mm and driving conditions for which the vehicle moves at a velocity of V = 70 mph in ambient air at T%0,0 = 0°C. From laboratory experiments performed on a model of the vehicle, the average convection coefficient on the outer surface of the windshield is known to be correlated by an expression of the form 1/3 Nu₁ = 0.037 Re8 Pr¹/³, where Re₁ = VL/v. Air properties may be approximated as k = 0.023 W/m·K, v = 12.5 × 10-6 m²/s, and Pr = 0.71. If Tdp = = 10°C and Ti 50°C, what is the smallest value of the inside convection coefficient required to prevent…