Q1/ A heating system is to be designed to keep the wings of an aircraft cruising at a velocity of 900 km/h above freezing temperatures during flight at 12,200-m altitude where the standard atmospheric conditions are 55.4°C and 18.8 kPa. Approximating the wing as a cylinder the elliptical cross section whose minor axis is 30 cm and disregarding radiation, determine the average convection heat transfer coefficient on the wing surface and the average rate of heat transfer per unit surface area.
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- 1.67 In beauty salons and in homes, a ubiquitous device is the hairdryer. The front end of a typical hairdryer is idealized as a thin-walled cylindrical duct with a 6-cm diameter with a fan at the inlet that blows air over an electric heating coil as schematically shown in the figure. The design of this appliance requires two power settings, with which the air blown over the electric heating coil is heated from the ambient temperature of to an outlet temperature of and with exit air velocities of 1.0 m/s and 1.5 m/s. Estimate the electric power required for the heating coil to meet these conditions, assuming that heat loss from the outside of the dryer duct is neglected.The interior wall of a large, commercial walk-in type meat freezer is covered under normal operating conditions with a 2-cm thick layer of ice. One day, a power outage cuts electricity to the refrigeration system of the freezer. Estimate the time required to melt this layer of ice if it has a mass density of 700kg/m3 and a latent heat of fusion of 334 kJ/kg. Consider the air temperature inside the freezer to be 20C with a heat transfer coefficient of 2W/m2K for convection from the freezer surface to air, and clearly state the assumptions made in your calculations.H.W1 Consider a person standing in a room. Determine the total rate of heat transfer from this person if the exposed surface area and temperature are 1.6m² and 29°C, respectively. Assume that the convection heat transfer coefficient is 6W/m².K and the emissivity of a person is 0.95. The air temperature in the room is maintained at 22°C at all times of the year. In summer, the wall and ceiling temperatures are observed to be 25°C, while in winter, they are 10°C. Ans: Qrotal =104.4 W In Summer Qrotal =231.3 W In Winter
- An electric motor is to be connected by a horizontal steel shaft (k 42.56 W/m.K), 25 mm in diameter to an impeller of a pump, circulating liquid metal at a temperature of 540°C. If the temperature of electric motor is limited to a maximum value of 52°C with the ambient air at 27°C and heat transfer coefficient of 40.7 W/m2.K, what length of shaft should be specified between the motor and pump? Steel shaft8,000 kilograms of dressed poultry are blast-frozen on hand trucks each day (24 hrs) in a freezing tunnel. The poultry is to precooled to 7°C before entering the freezer where it is frozen and its temperature is lowered to -20°C for storage. The specific heat of poultry above and below freezing are 3.18 and 1.55 kJ/kg-°C, respectively. The latent heat is 246 kJ/kg and the freezing temperature is -2.75°C. Neglecting the heat load from the hand trucks, determine the amount of heat needed to be removed from the dressed poultry in kW.A long rod of AISI 4130 steel initially at a uniform temperature of 400°C issuddenly exposed to 20°C air, where the heat transfer coefficient is 15 W/m2∙K. The rod has a diameter of 4.8 cm. How long after being exposed to the 20°C airwill the steel rod reach a temperature of 60°C? The properties of the rod arep = 7840 kg/m3, Cp = 460 J/kg.K and k = 43 W
- Heat Transfer (Third year) 2020- 2021 Homework 01-03-2021 By Dr. Basil Noori Merzah one-dimensional heat transfer and disregarding radiation, determine the rate of heat transfer through the wall. Q4/ Steam at T01-320°C flows in a cast iron pipe (k=80W/m. C) whose inner and outer diameters are D,=5cm, and D,-5.5cm, respectively. The pipe is covered with 3 cm thick glass wool insulation with k=0.05W/m. C. Heat is lost to the surroundings at T2-5°C by natural convection and radiation, with a combined heat transfer coefficient to be h,=18W/m."C. Taking the heat transfer coefficient inside the pipe to be 2 0 h,-60W/m. C, determine the rate of heat loss from the steam per unit length of the pipe. Also determine the temperature drops across the pipe shell and the insulation. Q5/ Determine the overall heat transfer coefficient U based on the outer surface of a D=2.5cm, and D =3.34 cm steel pipe (k=54.0W/m. C) for the following conditions: inside and outside heat transfer coefficients are…For internal forced convection, friction factor f can be found by using either the Moody charts, the Colebrook equation, the Haaland relation or the EES software. State an advantage and a disadvantage of finding the friction factor using the Moody charts.a) A turbine blade 6 cm long and having a cross sectional area 4.65 cm and perimeter 12 cm is made of stainless steel (k=23.3 Wim K). The temperature at the root is 500 C. The blade is exposed to a hot gas at 870 °C. The heat transfer coefficient between the blade surface and gas is 442 W/im K. Determine the temperature distribution and rate of beat flow at the root of the blade, Assume the tip of the blade to be insulated. b) The hot combustion gases of a fumace are separated from the ambient air and its surounding, which are at 20°C, by a brick wall 0.5 m thick. The brick has a themal conductivity of 5 W/mk and a surface emissivity of 0.6. Under steady-state conditions an Page no.1 of 1 outer surface temperature of 120°C is measured Free convection heat transter to the air adjoining the surface is characterized by a convection coefficient of 15 Wim K What is the brick inner surface temperature
- 43% uo 7:52 * ZAIN IQ I. sheet No.3.pdf Homework 01-03 -2021 one-dimensional heat transfer and disregarding radiation, determine the rate of heat transfer through the wall. Q4/ Steam at Te1-320°C flows in a cast iron pipe (k=80W/m.°C) whose inner and outer diameters are D =5cm, and D=5.5cm, respectively. The pipe is covered with 3 cm thick glass wool insulation with k=0.05W/m.°C. Heat is lost to the surroundings at T02=5°C_by natural convection and radiation, with a combined heat transfer coefficient to be h,=18W/m.C. Taking the heat transfer coefficient inside the pipe to be h,=60W/m.C, determine the rate of heat loss from the steam per unit length of the pipe. Also determine the temperature drops across the pipe shell and the insulation. 05/ Determine the overall heat transfer coefficient U based on the outer surface of a D=2.5cm, and D=3.34 cm steel pipe (k=54.0W/m.°C) for the following conditions: inside and outside heat transfer coefficients are 1200W/m."C. and 2000W/m."C…This problem is for us to practice convection coefficient calculation for internal flow. You will have to design a water heating system that will heat up water flowing at 1 kg/s from 10°C to 40°C. You have to chose from two heated ducts - (a) one with rectangular cross-section of 0.6 mx1.2 m and (b) the other with 15 cm diameter circular pipe. Both ducts are maintained at a constant temperature of 60°C. Assuming that the flow is fully devloped in both cases, compare the length required for the two ducts to reach the deasired water temperature. Comment on whether the fully-developed assumption is justifiable in both cases.bb) Hot air at 60 °C leaving the furnace of a house enters a 12 m long section of a sheet metal duct of rectangular cross section 20 cm x 20 cm at an average velocity of 4 m/s. The thermal resistance of the duct is negligible, and the outer surface of the duct, whose emissivity is 0.3, is exposed to the cold air at 10 °C in the basement, with a convection heat transfer coeff basement to be at 10 °C also, det leave the basemeņt and 6) the rate of heat loss from the hot air in the duct to the basement. (2622 W, 45.1 C) y of 10 W/m².°C. Taking the walls of the ine (a) the temperature at which the hot air will Hma