A rectangular forced air healing duct is suspended fromthe ceiling of a basement whose air and walls are at atemperature of
(a) For an uninsulated duct whose average surface temperature is 50°C, estimate the rate of heat loss from the duct. The surface emissivity and convectioncoefficient are approximately 0.5 and
(b) If heated air enters the duct at 58°C and a velocity of4 m/s and the heat loss corresponds to the result ofpart (a), what is the outlet temperature? The densityand specific heat of the air may be assumed to be
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Fundamentals of Heat and Mass Transfer
- 7.43 Liquid sodium is to be heated from 500 K to 600 K by passing it at a flow rate of 5.0 kg/s through a 5-cmID tube whose surface is maintained at 620 K. What length of tube is required?arrow_forward3.10 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_forwardWater at 340 K and a flow rate of 5 kg/s enters a black, thin-walled tube, which passes through a large furnace whose walls and air are at a temperature of 700 K. The diameter and length of the tube are 0.25 m and 8 m, respectively. Convection coefficients associated with water flow through the tube and airflow over the tube are 300 W/m²-K and 50 W/m².K, respectively. Water Tme= i m = 5 kg/s Tai K Tube, D = 0.25 m L = 8 m, ε = 1 Air T= 700 K -Furnace, Tur 700 K Write an expression for the linearized radiation coefficient corresponding to radiation exchange between the outer surface of the pipe and the furnace walls. Determine how to calculate this coefficient if the surface temperature of the tube is represented by the arithmetic mean of its inlet and outlet values. Use these expressions to determine the outlet temperature of the water, Tm,o, in K. Tmoarrow_forward
- Water at 310 K and a flow rate of 5 kg/s enters a black, thin-walled tube, which passes through a large furnace whose walls and air are at a temperature of 700 K. The diameter and length of the tube are 0.25 m and 8 m, respectively. Convection coefficients associated with water flow through the tube and airflow over the tube are 300 W/m²-K and 50 W/m².K, respectively. -Tube, D = 0.25 m L = 8 m, & = 1 Air T= 700 K Water m = 5 kg/s Imo m.i -Furnace, Tur 700 K = Write an expression for the linearized radiation coefficient corresponding to radiation exchange between the outer surface of the pipe and the furnace walls. Determine how to calculate this coefficient if the surface temperature of the tube is represented by the arithmetic mean of its inlet and outlet values. Use these expressions to determine the outlet temperature of the water, Tm,o, in K.arrow_forwardHot air flows with a mass rate of m = 0.060 kg/s through an uninsulated sheet metal duct of diameter D = 0.18 m, which is in the crawlspace of a house. The hot air enters at 120 C and, after a distance of L = 5 m, cools to 80 C. The heat transfer coefficient between the duct outer surface and the ambient air at T, = 0 C is known to be ho = 6 W/m2 K. a. Calculate the heat loss (W) from the duct over the length L. h. Determine the heat flux and the duct surface temperature at x= 1.arrow_forwardFor safety reasons, air 15cmx20 cm in contact not allowed circuit board, cold air through a 20cm long 0.2cmx14cm rectangular hole drilled inside will be cooled. From electronic parts mosque heat is transmitted from the thin layer of the card to the channel, where the air entering the channel at 15 ° C is removed. The heat flux on the upper surface of the channel can be regarded as uniform and other Heat transfer from surfaces can be neglected. If the velocity of the air inside the duct does not exceed 600m / min and the surface surface of the duct is fixed at 50 ° C, write on this circuit board. Total calculations of electronic parts to be placed.arrow_forward
- A 10-mm-inner-diameter pipe made of commercial steel is used to heat a liquid in an industrial process. The liquid enters the pipe with Ti=25°C, V=0.8 m/s. A uniform heat flux is maintained by an electric resistance heater wrapped arounf the outer surface of the pipe, so that the fluid exits at 75°C. Assuming fully developed flow and taking the average fluid properties to be ρ=1000 kg/m3, cp=4000 J/kg·K, µ=2x10-3 kg/m·s, k=0.48 W/m·K, and Pr=10, determine: The required surface heat flux , produced by the heater The surface temperature at the exit, Ts The pressure loss through the piper and the minimum power required to overcome the resistance to flow.arrow_forwardWhat is the length of tubing required to cool air from 80°C to 20°C via an isothermal tube maintained at 0°C? The tube diameter is 20 cm. Mean velocity of air is 4 m/s. Assume the flow to be fully-developed.arrow_forwardDry, compressed air at Tm,i whose surface is at T; = 25°C. Determine the thermal entry length, in m, the mean temperature of the air at the tube outlet, in K, the rate of heat transfer from the air to the tube wall, in W, and the power required to flow the air through the tube, in W. For these conditions the fully developed heat transfer coefficient is h = 3.58 W/m2-K. Evaluate the properties of air at 320 K 75°C, p = 10 atm, with a mass flow rate of m = 0.003 kg/s, enters a 32-mm-diameter, 5-m-long tube i Tmo = i K P = i q =arrow_forward
- Prove that the thermocouple will underestimate the temperature of airflow by more than 15% but less than 30% in a large air duct if the temperature of the hot air is 1367 K, duct-wall temperature is 533 K, emissivity of the thermocouple is 0.5, and the convection heat-transfer coefficient is 114 W/m2 -K.arrow_forwardT0 2-Water is heated as it flows through a square duct with side a=2 cm and the mean velocity through each is U = 3.2 cm/s. Duct is heated electrically by 2000 W/m2 into the water. Assuming that the water properties can be evaluated at 50◦C and that the flow is thermally fully developed: (a) Verify that the flow is laminar. (b) Calculate heat transfer coefficient (c) the mean temperature difference between the wall and the water stream. (d) Calculate the rate of temperature increase along the channel, (e) calculate pressure drop per unit lengtharrow_forwardAir at 1 atm and 27 C enters a rectangular duct that is 1 m long with a cross-sectional area that measures 4 mm x 16 mm as shown below. The mass flow rate of the air is 3 x 10* kg/s. A uniform heat flux of 600 W/m2 is imposed on all four sides of the duct surface. Evaluate air properties at the inlet temperature since the outlet temperature must be determined. 4 mm a. b. What is the outlet temperature of the air (K)? Ans. 379.8 K What is the temperature of the duct surface at the outlet (K)? (Hint:By taking advantage of the heat flux given the average temperature of the flow you can find)arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning