Consider the steam pipe of Example 1.2. The facilitiesmanager wants you to recommend methods for reducing the heat loss to the room, and two options are proposed. The first option would restrict air movementaround the outer surface of the pipe and thereby reducethe convection coefficient by a factor of two. The second option would coat the outer surface of the pipe witha low emissivity
(a) Which of the foregoing options would you recommend?
(b) To prepare for a presentation of your recommendation to management, generate a graph of the heatloss
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Fundamentals of Heat and Mass Transfer
- A long wire 0.7 mm in diameter with an emissivity of 0.9 is placed in a large quiescent air space at 270 K. If the wire is at 800 K, calculate the net rate of heat loss. Discuss your assumptions.arrow_forwardDescribe and compare the modes of heat loss through the single-pane and double-pane window assemblies shown in the sketch below.arrow_forwardA long, horizontal, cylindrical steel reactor, 1 m in diameter, has a surface temperature of 300ºC. The emissivity of the steel is 0.6, and the heat transfer coefficient for natural convection is 5 W m−2 K−1 . Heat is lost by convection to the air at 15ºC, and also by radiation to the surroundings, which can be considered to be a black body at 15ºC. a) Calculate the total heat loss per metre length of the reactor, and the proportions lost by convection and radiation b) The reactor is then insulated with a thin layer of insulation material to reduce the total heat loss to one-tenth of its original value. This causes the surface temperature of the steel to rise to 400ºC. The thermal conductivity of the insulation is 0.01 W m−1 K−1 , and its surface emissivity is 0.2. Show that the resulting surface temperature of the insulation is about 89ºC, and calculate the thickness of insulation required, stating any assumptions made. Specifically need help with part barrow_forward
- A long, horizontal, cylindrical steel reactor, 1 m in diameter, has a surface temperature of 300ºC. The emissivity of the steel is 0.6, and the heat transfer coefficient for natural convection is 5 W m−2 K−1 . Heat is lost by convection to the air at 15ºC, and also by radiation to the surroundings, which can be considered to be a black body at 15ºC. a) Calculate the total heat loss per metre length of the reactor, and the proportions lost by convection and radiation. b) The reactor is then insulated with a thin layer of insulation material to reduce the total heat loss to one-tenth of its original value. This causes the surface temperature of the steel to rise to 400ºC. The thermal conductivity of the insulation is 0.01 W m−1 K−1 , and its surface emissivity is 0.2. Show that the resulting surface temperature of the insulation is about 89ºC, and calculate the thickness of insulation required, stating any assumptions made. can you solve part b please?arrow_forwardPROBLEM 4: A black thermocouple is inside a chamber with black walls. If the air around the thermocouple is at 20°C, the walls are at 100-C, and the heat transfer coefficient between the thermocouple and the air is 75 W/m²K, what temperature will the thermocouple read?arrow_forwardThe basal metabolic rate isthe rate at which energy is produced in the body when a person is at rest.A 75 kg (165 lb) person of height 1.83 m (6 ft) has a body surface areaof approximately 2.0 m2. (a) What is the net amount of heat this personcould radiate per second into a room at 18°C (about 65°F) if his skin’ssurface temperature is 30°C? (At such temperatures, nearly all the heatis infrared radiation, for which the body’s emissivity is 1.0, regardless ofthe amount of pigment.) (b) Normally, 80% of the energy produced bymetabolism goes into heat, while the rest goes into things like pumpingblood and repairing cells. Also normally, a person at rest can get rid ofthis excess heat just through radiation. Use your answer to part (a) to findthis person’s basal metabolic rate.arrow_forward
- QUESTION 6 A simple solar collector in Figure Q1 is built by placing a 5 cm diameter clear plastic tube around a garden hose whose outer diameter is 1.6 cm. The hose is painted black to maximize solar absorption, and some plastic rings are used to keep the spacing between the hose and the clear plastic cover constant. During a clear day, the temperature of the hose is measured to be 65 °C, while the ambient air temperature is 26 °C. Determine the clear plastic tube temperature and the rate of heat loss from the water in the hose per meter of its length by natural convection. Solar radiation ||| 26°C Clear plastic tube Water Spacer Garden hose 65°C Figure Q1arrow_forward2. A heater is a thin vertical panel 1.0m long and 0.7m high and is used in a warehouse to keep workers warm. The heater has air circulating on each side. Assume the maximum temperature of the panel is 60°C (already above the board line that is safe for human hands to touch briefly without getting hurt). Assume the room air temperature is 18°C but the warehouse wall temperature is 5°C. Model the surface with an emittance of 0.9 and Vair = 1.57x105 m²/s. a. Determine the maximum power rating for the heater. b. Now if you run the heat by standing on its side (it will be 1.0 m high and 0.7 m long), determine the surface temperature. c. Compare case a and b and explain any differences you see.arrow_forwardAfter sunset, radiant energy can be sensed by a person standing near a brick wall, such walls frequently have surface temperatures around 44°C, and typical brick emissivity values are on the order of 0.92. What would be the radiant thermal flux per square foot from a brick wall at this temperature?arrow_forward
- A microwave dinner has the instructions listed below. In this problem, you will explain how following the instructions affect the heat transfer into the meal. (The meal starts off frozen, and is covered with a thin piece of plastic "film" or covering when it is taken out of the box. The vegetables are separate from the beef and potatoes.) Instructions1. Cut slit in film over vegetables.2. Microwave on high 4 minutes3. Turn back film from beef and potatoes. Stir beef and potatoes. Replace film. Return tray to microwave oven4. Microwave on high 3 minutes.5. Let stand 2 minutes in microwave oven., Stir beef and potatoes.a. How does each of the steps above (cut slit in film, stir beef and potatoes, etc) affect the heat transfer to the food? Make sure to consider conduction, convection, and radiation where appropriate. b. The instructions ask you to stir the beef and potatoes, but not the vegetables. From this, what can you tell about how each type of food receives and transfers heat?…arrow_forwardThe last portion asks you for "net radiant heat flux to the surface", meaning that positive net radiative heat flux means in and negative net radiative heat flux means out. This is opposite the typical sign convention - be aware of thisarrow_forwardThe fan circulates the warm air on the inside of the windshield to stop condensation of water vapor and allow for maximum visibility during wintertime (see images). You have been provided with some info. and are asked to pick from the bottom table, the right model number(s) that will satisfy the requirement.Your car is equipped with a fan blower setting that allow you to choose between speeds 0, 1, 2 and 3. Variation of the convection heat transfer coefficient is dependent upon multiple factors, including the size and theblower configuration.following image shows the parametersarrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning