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
- An electrical transmission line of 1.2-cm diameter carries a current of 200 amps and has a resistance of 310-4 ohm per meter of length. If the air around this line is at v, determine the surface temperature on a windy day, assuming a wind blows across the line at 33 km/h.arrow_forwardFor the Convective Heat Transfer experiment, describe the difference in the procedures: Natural or FreeConvection and Forced convection. What makes the FORCED convection experiment as FORCED? Explain which, in your consideration should give the higher heat transfer rate? And REASON why? Did your results support your consideration?arrow_forwardA steel plate has dimensions of 3 m by 1 m and is initially kept at a temperature of 30 degree Celsius. It is cooled by blowing air parallel to the 1 m edge at 9 km/hr. The temperature of the flowing air is maintained at 10 degree Celsius. Estimate the convection heat transfer rate from both sides of the plate.arrow_forward
- A thermocouple junction, which may be approximated as a sphere, is to be used for temperature measurement in a gas stream. The convection coefficient between the junction surface and the gas is h=400W/m².K, and the junction thermophysical properties are ĸ= 20W/m.°K, c= 400J/kg.°K and ρ=8500kg/m³. Determine the junction diameter needed for the thermocouple to have a time constant of 1s. If the junction is at 25°C and is placed in a gas stream that is at 200°C, how long will it take for the junction to reach 199°C?arrow_forwardA house located in the south of the country was built using windowsdoubles to reduce heat loss to the outside environment on very cold days. Consider that the house has 6 windows 80 cm high and 1.2 m wide, each consisting of 2 layers of glass (kv=1.4 W/(m.oC) 4 mm thick, separated from each other for a spacing of 10 mm filled with stagnant air (ka=0.024 W/(mK), we disregard natural convection effects) On a day when the interior of the house is kept at 22oC, with h=10 W/(m2. K) while the external environment is at 5oC with h=50 W/(m2.K), it is requested:(a) What is the rate of heat dissipation through the windows?(b) What are the temperatures on the glass surfaces inside and in theexterior of the house?(c) Which of the resistances is the limiting in the dissipation process ofheat?(d) Estimate the increase in dissipation rate if we consider that the natural air convection in the space between the windows is characterizedby a convective coefficient h=5 W/(m.K).(e) How the value obtained…arrow_forwardChips of width L _ 15 mm on a side are mounted to a substrate that is installed in an enclosure whose walls and air are maintained at a temperature of Tsur=T∞=25oC. The chips have an emissivity of ε=0.60 and a maximum allowable temperature of Ts=85oC. (a) If heat is rejected from the chips by radiation and natural convection, what is the maximum operating power of each chip? The convection coefficient may be approximated as h=11.7 W/m2K. (b) If a fan is used to maintain airflow through the enclosure and heat transfer is by only forced convection, with h=250 W/m2K, what is the maximum operating powerarrow_forward
- A transformer is to be cooled via forced air convection. To increase the effectiveness of thecooling, Alloy 1095 cast aluminum fins are attached to the top of the transformer overwhich air is blown (negligible thermal contact resistance between the transformer and thefins). The fins are 2 cm thick and 7 cm long and span the entire length of the transformer,and the transformer is 7 cm wide and 10 cm long. Air leaves the cooling fan at 25°C .a) Decide how to model the fins before performing any real analysis. Youare willing to accept some error in your analysis and so you will either model thefins as having adiabatic tips or being infinitely long. You expect the average convectioncoefficient over the heat transfer surfaces for this system to be around 50 W m2– K⁄ .Which tip condition should you use for the fins in your analysis? b) Modeling the transformer as being isothermal, determine the average convectioncoefficient over the heat transfer surfaces. Account for heat transfer from the…arrow_forwardA flat aluminum plate 8 m long and 1.5 m wide has a surface temperature of 180°C. For its cooling, air at 1 atm and speed of 10 m/s circulates at 20°C parallel to the length of the plate.a) Determine the rate of heat transfer by convection in steady state. b) In order to increase the heat dissipation from the plate, the engineers considered placing rectangular fins of the same material (Kaluminium = 200 W/m.K). The fins are 50 mm long and 0.5 mm thick and the placement density is 75 fins per unit length of the plate (the fins are equally spaced and span the entire width of the plate). The convective coefficient of the air over the plate resulting from the placement of fins is 10 W/m².K. Determine the heat transfer rate and percentage increase over part (a).arrow_forward2.2: Water at a temperature of T∞= 25°C flows over one ofthe surfaces of a steel wall (AISI 1010) whose temperatureis Ts,1= 40°C and thermal conductivity of steel is 671 w/m.k. The wall is 0.35 m thick, and itsother surface temperature is Ts,2= 100°C. For steadystateconditions what is the convection coefficient associatedwith the water flow?arrow_forward
- Air at 25 ° C blows over the hot steel plate whose surface temperature is maintained at 250 ° C. The plates are 70 cm x 40 cm in dimensions and 2.5 cm thick. The convection heat transfer coefficient on the upper surface is 20 W / (m² ° C). The thermal conductivity of steel is 45 W / (m ° C). Calculate the hourly heat loss from the plate surface. a. heat loss per hour = AnswerkJ. b. If the reverse side surface temperature is maintained, determine the hourly heat loss occurring = AnswerkJ.arrow_forwardpnts) Chips of width L _ 15 mm on a side are mounted to a substrate that is installed in an enclosure whose walls and air are maintained at a temperature of Tsur=T∞=25oC. The chips have an emissivity of ε=0.60 and a maximum allowable temperature of Ts=85oC. (a) If heat is rejected from the chips by radiation and natural convection, what is the maximum operating power of each chip? The convection coefficient may be approximated as h=11.7 W/m2K. (b) If a fan is used to maintain airflow through the enclosure and heat transfer is by only forced convection, with h=250 W/m2K, what is the maximum operating power?arrow_forwarda) What regions show the largest oceanic latent heat loss? b) What regions show the saltiest surface waters? c) What is the main factor affecting the two radiation heat flux terms? Name the two fluxes. d) What is the main factor affecting the two turbulent heat flux terms? Name the two fluxes.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning