Consider the conditions of Problem 6.7, for which a heat transfer experiment yielded the prescribed distribution of the local convection coefficient,
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Fundamentals of Heat and Mass Transfer
- A manufacturing plant produces an efluent as a waste product. As part of a waste heat recovery system, they want to use this for internal heating and cooling. The effluent is flown through a system where its temperature remains at 303.15 K. A 0.06-m diameter pipe carrying hot water and 0.04-m diameter pipe carrying cold air is passed through this effluent chamber. It can be assumed that the surface temperature of these air and water pipes are same as the effluent temperature. Water comes in at 328.15 K and exits at 308.15 K. The air comes in at 268.15 K and exits at 298.15 K. The mass flow rate of water and air is respectively, 1 kg/s and 0.01 kg/s. Determine the length of the water and air pipes in the system. Convert all calculations to C.arrow_forward8.2 From its definition and from the property values in Appendix 2, Table 13, calculate the coefficient of thermal expansion, , for saturated water at 403 K. Then compare your results with the value in the table.arrow_forwardI need the answer as soon as possiblearrow_forward
- Calculate the time taken for a 7 um radius cloud droplet to grow via condensation into a 3500 um rain droplet. Assume a super-saturation of 1.55%, a water vapour density of 3 g m-3, and a water vapour diffusion coefficient in dry air of D=24 x10-6 m2 S -1 PLEASE SHOW CALCULATIONarrow_forward10A.5. Free convection velocity. (a) Verify the expression for the average velocity in the upward-moving stream in Eq. 10.9-16. (b) Evaluate 3 for the conditions given below. (c) What is the average velocity in the upward-moving stream in the system described in Fig. 10.9-1 for air flowing under these conditions? Pressure Temperature of the heated wall Temperature of the cooled wall Spacing between the walls Answer: 2.3 cm/s T3=0°F. Wall 1 atm 100°C 20°C 0.6 cm -T₂ = 61°F Surface temperatures -T₁ = 69°F of plastic panel Plastic panel has thermal conductivity k = 0.075 Btu/hr. ft. °F (average value between T₁ and T₂) -0.502" Fig. 10A.6. Determination of the thermal resistance of a wall. Problems 321arrow_forwardAn open tank, 6 mm in diameter, contains 1 mm deep layer of benzene (Mol wt = 78) at its bottom. The vapour pressure of benzene in the tank is 13.15 kN/m2 and its diffusion takes place through a stagnant air film 2.5 mm thick, At the operating temperature of 20°C, the diffusivity of benzene in the tank is 8.0 x 10-6 m2/s. If the benzene has a density of 880 kg/m³, calculate the time taken for the entire benzene to evaporate. Take atmospheric pressure as 101.3 kN/m² and neglect any resistance to diffusion of benzene beyond the air film. %3Darrow_forward
- 2. Calculate the free convection heat transfer coefficient for a plate 6 ft high and 8 ft wide at 120 °F that is exposed to nitrogen at 60 °F. (see attached) 3. Constant Flux Application. Air at 1 atm and 300 °C is cooled as it flows at a velocity of 5.0 m/s through a tube with a diameter of 2.54 cm. Calculate the heat transfer coefficient if a constant heat flux condition is maintained at the wall and the wall temperature is 20 °C above the temperature along the entire length of the tube. (See attached)arrow_forwardHandwrite pleasearrow_forwardA thermocouple is initially at temperature of T; and it is used to measure the temperature of air (Tair). It would take a while for the temperature of the thermocouple junction to approach Tair. The thermocouple junction can be approximated by a copper sphere of 0.5 mm in diameter. Using the lumped system analysis (chapter 5, undergraduate heat transfer textbook), derive an expression for T(t) (it should look like: (T(t)-Tair )/(Ti-Tair) = e, where T; is the initial temperature of the thermocouple, and Tair is the air temperature). Calculate the time constant 7 (assuming the convection heat transfer coefficient h=5 W/m²K). Use the thermal properties of copper from your undergraduate textbook or any other books. Usually t=3t is used as the response time of the thermocouple with 5% measuring error. Explain why? If the thermocouple size is increased to 5 mm in diameter, what is the response time?arrow_forward
- Problem#6* A preheater involves the use of condensing steam at 100°C on the inside of a bank of tubes to heat air that enters at 1 atmosphere and 15°C. The air moves at 8 m/s in cross flow over the tubes. Each tube is 2 m long and has an outside diameter of 5 mm. The bank consists of 196 tubes in a square, aligned array in which the distance between tube centers is 15 mm. What is the temperature of the air after passing through the tubes. Also, what is the pressure drop associated with the air flow?arrow_forwardSmall potato balls of 0.5 cm radius (can be approximated as a sphere) baked in the oven and initially at a uniform temperature of 160°C. Assume, potatoes have a density of 650 kg/m³, specific heat of 3400 J/kgK and conductivity of 1 W/mK. You want to eat potatoes quickly without burning your tongue so that you have decided to cool them down with forced convection. Air h, T. hot potato initially Air temperature is 20'C and the convective heat transfer coefficient is 140 W/m²K. Calculate the time (in seconds) required for its surface temperature to drop 90°C. Round the value you calculated and write it as an integer!! For example, if you find 8.2, write is as 8. Answer:arrow_forwardThe main body of plenum is a steel vessel of diameter 0.1meters has two semicircle domed ends. During operation is will contain mix of fuel and air at approximately 250OC. The wall of the vessel is 0.03meters thick and the plenum is 0.45meters long. Estimate the rate of heat loss from the vessel when the outside air temperature is 45OC. The thermal conductivity of steel is 45 W/m K and the surface heat transfer coefficient on the air side is 8 W/m2 . On the inside it is 65W/m2 . If it was possible to clad the plenum calculate the reduction in the rate of heat loss. Assume the lagging would be 5mm thick and has a thermal conductivity of 0.05 W/m.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning