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ME 304 HW problems

# ME 304 HW problems - 8.22 Engine oil is heated by ﬂowing...

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Unformatted text preview: 8.22 Engine oil is heated by ﬂowing through a circular tube of diameter D = 50 mm and length L = 25 m and whose surface is maintained at [50°C. (a) if the ﬂow rate and inlet temperature of the oil are 0.5 kgrs and 20°C, what is the outlet temperature Ens? What is the total heat transfer rate a for the tube? lleiFor ﬂow rates in the range 0.5 Eric 5 2.0 kgls. compute and plot the 1.tariations of Tm and q with iii. For what ﬂow ratelis) are q and T maximized“? ”It” Explain your results. 8.21 In the ﬁnal stages of production. a pharmaceutical is sterilized by heating it from 25 to ?5°C as it moves at 0.2 rats through a straight thin-walled stainless steel tube of l2.?-rttttt diameter. A uniform heat ﬂux is maintained by an electric resistance heater wrapped around the outer surface of the tube. If the tube is ID at long, what is the required heat ﬂux? if ﬂuid enters the tube with a fully developed velocity proﬁle and a uniform temperature proﬁle. what is the surface temperature at the tube exit and at a distance of 0.5 in from the entrance? Fluid prop- erties may be approximated as p = 1000 kglrn’. on = 4000 ”kg K. p. I 2 X 10"1L kgfs'm. l: = 0.8 Wlm-K. and Pr = ID. E3.31 To cool a summer home without using a vapor- compression refrigeration cycle. air is routed through a plastic pipe (k=0.15W!m*K, D;=0.15 n1, Dn= OJ? m) that is submerged in an adjoining body of water. The water temperature is nominally at Tm = l?“C, and a convection coefﬁcient of ha er 1500 “Jim: - K is main- tained at the outer surface of the pipe. If air from the home enters the pipe at a temperature of T,“ = 29°C and a volumetric ﬂow rate of VI. = 0.025 mus. what pipe length L is needed to provide a discharge temperature of Tm = 21°C? What is the fan power required to more the air through this length of pipe if its inner surface is smooth? EEshaust gases from a wire processing oven are dis- charged into a tall stack. and the gas and stack surface temperatures at the outlet of the stack must he esti- mated. Knowledge of the outlet gas temperature T“ is hateful for predicting lhe dispersion of efﬂuents in the thermal plume, while knowledge of the outlet stack sur— ﬁce temperature 1'1...p indicates whether condensation of the gas products will occur. The thin-walled. cylindrical stack is 0.5 m in diameter and on m high. The crimust gas ﬂow rate is (1.5 kgt‘s. and the inlet temperature is 600T. "I'liemal plume 7 Height, 5 m l Building [a] Consider conditions for which the ambient air tern- perature and wind velocity are 4°C and 5 We. respectively. Approximating the ﬂiemtophvsical properties of the gas as those ot auraaspltede air, esti- mate the tastiet gas and stack surface temperaturea for the given conditions. @ IThe gas outlet temperature is sensitive to variations in the ambient air temperature and wind velocity. For T, = —25°Ci 5°C. and 35°C, compute and plot the gas outlet temperature as a function of wind velocity for2 5. V 5 ll} mfs. 8.80 You have been asked to perform a feasibility study on the design of a blood warmer to be used during the transfusion of blood to a patient. This exchanger is to heat blood taken from the bank at |0°C to 3?°C at a ﬂow rate of 200 mlfmin. The blood passes through a rectangular cross-section tube. 6.4 mm by 1.6 111111. which is sandwiched between two plates held at a con— stant temperature of 40°C. Plate - Tube at 40°C T Uniform temperature plates I 1.5 mm *4 bi- + 5.4 mm Front viewI ‘ {with one plate removed] Tube —— {a} Compute the length of the tubing required to achieve the desired outlet conditions at the speci- ﬁed ﬂow rate. Assume the ﬂow is fully developed and the blood has the same properties as water. (b) Assess your assumptions and indicate whether your analysis over" or underestimates the necessary length. 8.9!] Consider a concentric tube annulus for which the inner and outer diameters are 25 and 50 mm. Water enters the annular region at 0.04 kgr’s and 25°C. It the inner tube wall is heated electrically at a rate (per unit length} of q’ = 4000 me, while the outer tube wall is insulated, how long must the tubes be for the water to ac ’ outlet temperature of 85°C? What is the innertu face temperature at the outlet. where fully de conditions ma}r be assumed? ...
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ME 304 HW problems - 8.22 Engine oil is heated by ﬂowing...

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