An overhead 25-m-long, uninsulated industrial steampipe of 100-mm diameter is routed through a buildingwhose walls and air are at 25°C. Pressurized steammaintains a pipe surface temperature of 150°C, and thecoefficient associated with natural Convection is
(a) What is the rate of heat loss from the steam line?
(b) If the steam is generated in a gas-fired boiler operating at an efficiency of
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Fundamentals of Heat and Mass Transfer
- 3.10 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_forward300°C steam flows in a stainless-steel (ss.) pipe with thermal conductivity of 50 W/m.K. The pipe has internal diameter (ID) of 40 cm, and outer diameter (OD) of 42 cm. The pipe is placed in another ss. pipe with ID and OD 44 cm and 44.2 cm, respectively. The gap between the pipes is filled with steel air (use air properties at 160°C from appendix). The convection heat transfer coefficient at the inner and the outer surfaces of the pipe is hi = 40 W/m?. K and h2= 15 W/m2. K. Determine the rate of heat loss if the length of the pipe %3D is 10 m. Also determine the temperature at inside, intermediate and outer surfaces.arrow_forwardA food product with 80% moisture content in a 5 cm diameter can wants to be frozen. The density of the product is 1000 kg / m³, the thermal conductivity is 1.0 W / (m K), and the initial freezing temperature is -2.25 ° C. After 10 hours in the freezing medium -35 ° C, the product temperature becomes -10 ° C. Estimate the convection heat transfer coefficient of the freezing medium. Assume the can as an infinite cylinder. h = Answer W / (m² K).arrow_forward
- A food product with 80% moisture content in a 5 cm diameter can wants to be frozen. The density of the product is 1000 kg / m cubic, the thermal conductivity is 1.0 W / (m K), and the initial freezing temperature is -1.75 ° C. After 10 hours in -25 ° C freezing medium, the product temperature becomes -10 ° C. Estimate the convection heat transfer coefficient of the freezing medium. Assume the can as an infinite cylinderarrow_forwardA steel sphere (AISI 1010), 100 mm in diameter, is coated with a dielectric material layer of thickness 1.75 mm and thermal conductivity 0.04 W/m.K. The coated sphere is initially at a uniform temperature of 500°C and is suddenly quenched in a large oil bath for which T = 100°C and h = 3000 W/m².K. Estimate the time, in h, required for the coated sphere temperature to reach 150°C. Hint: Neglect the effect of energy storage in the dielectric material, since its thermal capacitance (pc)is small compared to that of the steel sphere. t = harrow_forwardA silicon chip is encapsulated so that, under steady-state conditions, all the power dissipated by it is transferred by convection for a fluid current with h=1000 W/(m2.K) and Tꚙ=25oC. An aluminum plate (k=237 W/(mK)), 2 mm thick, is placed on the chip surface, the contact resistance on the chip/aluminum interface is 0.5x10-4 (m2.K)/W. If the chip area is 100 mm2 and the maximum allowable temperature is 85 oC, what is the maximum allowable power dissipation on the chip?arrow_forward
- Q1:(a) Define convection and its types. Either free or forced convection is good by considering an example. (b)Explain, motorcycle engine is either considered as free or forced convection. Justify your answer.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_forwardNeed answer ASAP! Thank you Water at 5°C is being used to cool apples from an initial temperature of 25° to 10°C. Thewater flow over the surface of the apple creates a convective heat-transfer coefficientof 10 W/(m2-K). Assume the apple can be described as a sphere with an 8 cm diameterand the geometric center is to be reduced to 10°C. The apple properties include thermalconductivity of 0.4 W/(m-K), specific heat of 3.950 kJ/(kg-K), and density of 940 kg/m3 a. Determine the time that the apples must be exposed to the water.b. If the apple is submerged only for 2 hours, what will be its center temperature?arrow_forward
- A 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_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/m, 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/m?K. Calculate the time (in seconds) required for its surface temperature to drop 90°C.arrow_forwardH.W. Q1: Consider a hot automotive engine, which can be approximated as 0.40m wide, and 0.8m long rectangular block. The bottom surface of the block is at a temperature of 80°C and has an emissivity of 0.95. The ambient air is at 20°C, and the road surface is at 25°C. Determine the rate of heat transfer from the bottom surface of the engine block by convection and radiation as the car travels at a velocity of 80 km/h. Assume, the flow to be turbulent over the entire surface because of the constant agitation of the engine block. k = 0.02735 W/m.°C v=1.798×10* m²/s Air properties at Tf= 50 °C: Pr = 0.7228 Answer: Qcony = 1363 W, Qrad = 132 W, Qotal = 1495 w Hint: Use the correlations (equations) of average Reynold number (ReL). L = 0.8 m Engine block Air V, = 80 km/h T. = 20°C T; = 80°C ɛ = 0.95arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning