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An electronic device that internally generates 600 mW of heat has a maximum permissible operating temperature of
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Chapter 1 Solutions
Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
- Determine the rate of heat transfer per meter length to a light oil flowing through a 2.5-cm-ID, 60-cm-long copper tube at a velocity of 0.03 m/s. The oil enters the tube at 16C, and the tube is heated by steam condensing on its outer surface at atmospheric pressure with a heat transfer coefficient of 11.3 kW/m K. The properties of the oil at various temperatures are listed in the following table: Temperature, T(C) 15 30 40 65 100 (kg/m3) 912 912 896 880 864 c(kJ/kgK) 1.80 1.84 1.925 2.0 2.135 k(W/mK) 0.133 0.133 0.131 0.129 0.128 (kg/ms) 0.089 0.0414 0.023 0.00786 0.0033 Pr 1204 573 338 122 55arrow_forward3.16 A large, 2.54-cm.-thick copper plate is placed between two air streams. The heat transfer coefficient on one side is and on the other side is . If the temperature of both streams is suddenly changed from 38°C to 93°C, determine how long it takes for the copper plate to reach a temperature of 82°C.arrow_forwardA cooling system is to be designed for a food storage warehouse for keeping perishable foods cool prior to transportation to grocery stores. The warehouse has an effective surface area of 1860 m2 exposed to an ambient air temperature of 32C. The warehouse wall insulation (k=0.17W/(mK)) is 7.5 cm thick. Determine the rate at which heat must be removed (W) from the warehouse to maintain the food at 4C.arrow_forward
- A central heating system from a house consists of 50m of 15mm outside diameter copper pipe with a wall thickness of 1mm. This pipe is used to distribute water at a temperature of 70 degrees C. Calculate the rate of heat loss from the length of pipe if it is fitted with a 15mm radial thickness of insulation. Take the ambient air temperature to be 15 degrees C and the internal and external surface heat transfer coefficients to be 100 W/m².K and 8 W/m2.K respectively. The thermal conductivity of the copper is known to be 400 W/m.K and 0.05 W/m.K for the insulation. State your answer correct to three significant figures in Watts. Assume steady state radial heat transfer. Answer: Ensure that you consider the overall effects of radial heat transfer through conduction and convection. Additionally ensure that you consider the overall length of the copper pipe.arrow_forwardQUESTION 3: Warm air is blown over the inner surface of the windshield of an automobile to defrost ice accumulated on the outer surface. The windshield has a thickness of 5 mm and thermal conductivity of 1.4 W/m-K. The outside ambient temperature is -10°C and the convection heat transfer coefficient is 200 W/m²-K, while the ambient temperature inside the automobile is 25°C. Determine the value of the convection heat transfer coefficient for the warm air blowing over the inner surface of the windshield necessary to cause the accumulated ice to begin melting.arrow_forwardIn a food industry, pieces of meat with approximately 30 cm in diameter and 20 mm in thickness are stored in a industrial freezer and thawed by exposure to ambient air at 15°C with convective heat transfer coefficient equal to 10W/(m2.K). Consider a piece of meat that, when removed from the freezer, had a temperature of -12°C. For defrosting, the piece is hung on a "line", so that both larger surfaces are exposed to the ambient air. For frozen meat, the following properties can be assumed ρ=1090 kg/m3, cp=3.54 kJ/(kg.K), k=0.47 W/(m.K). Ask: (1) Indicating the control volume and the simplifications adopted, obtain the differential energy balance equation for the cooling the piece of meat and describe the conditions of outline and initial that apply to the process, justifying them; (2) Use the appropriate analytical solution to determine the time necessary for the complete defrosting of the part. The part is considered to be completely thawed when a minimum temperature of 5oC is reached…arrow_forward
- A transparent film will be glued onto an upper surface of a solid plate within a heated chamber. For common gluing, the temperature between the glue, a film and the solid board must be kept at 70 °C. The transparent film has a thickness of 1 mm and thermal conductivity 0.05 W/mK, while the solid board is 13 mm thick. thickness and thermal conductivity of 1.2 W / mK. Inside the climate chamber, the convection heat transfer coefficient is 70 W/m²K. The bottom surface of the solid plate is kept at 52 °C, determines the temperature inside the heated chamber and the temperature of the surface of the transparent film. Assume negligible thermal contact resistance.arrow_forwardA cold storage wall, whose components and dimensions are given below, is formed by connecting layers A, B, C, D, E and F in series and in parallel. The temperature of the outside air is 30 oC and the temperature of the inside of the warehouse is -4 oC. If the film heat transfer coefficient between the air in the warehouse and the E layer is 24 W/m2 oC and the film heat transfer coefficient between the outer surface of the flat wall (A and F layers surface) and the atmospheric air is 16 W/m2 oC; Calculate the heat transferred in a day. (KA= 0.17 W/m.K, kc 0.98 W/m.K) (kD= 0.21 W/m.K, KF= 0.58 W/m.K) XA=3cm B KBK= 0.024 W/m.K, KE=0.01 W/m.K, F C D E XB=14 cm Xc=Xp=8cm XE=10cm AF AC AD= A/3 h= 2 m 70 cmarrow_forwardCalculate the quantity of heat conducted per minute through a duralumin circular disc 119mm diameter and 22.65mm thick when the temperature drop across the thickness of the plate is 9.3°F take the coefficient of thermal conductivity of duralumin as 150 W/m-K. Answer: 22.833 kJ/minarrow_forward
- An aluminum fins 1.5 cm wide and 1 mm thick are placed on a 2.5 cm diameter tube to dissipate the heat . The tube surface temperature is 170 oC . Calculate the heat loss per fin for h= 130 W/m2 .oC for aluminum.arrow_forwardA plane wall (0.8 m x 0.6 m) at 10 oC is to be heated by attaching 7-cm-long, 3-mm-diameter pin fins (k=200 W/mK, ρ=5000 kg/m3) to it. nfin=200 fins are to be used in total. Temperature of the surrounding fluid is 100 oC, and the heat transfer coefficient on the surfaces is 35 W/m2K. Total (material + manufacturing) cost of the fins is 850 TL/kg. Fill the table below by neglecting heat transfer from the fin tips. nfin=? a) Fin efficiency b) Fin effectiveness c) Overall fin effectiveness d) Total cost of finsarrow_forward3. An industrial freezer is designed to operate with an internal air temperature of 18°C when the external air temperature is 29°C, and the internal and external heat transfer coefficients are 8 W/m²-K and 12 W/m²-K, respectively. The walls of the freezer are composite construction, comprising an inner layer of plastic (k = 0.33 W/m-K, and thickness of 10 mm), and an outer layer of stainless steel (k = 15 W/m- K, and thickness of 3 mm). Sandwiched between these two layers is a layer of insulation material with k = 0.07 W/m-K. Find the width (mm) of the insulation that is required to reduce the convective heat loss to 35 W/m².arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning