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Cal Poly Pomona CHE 425 - Problem Set #1

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CHE425: Problem set #11) Run the program Microplant as an Expert Troubleshooter and turn in the last display ofthe program.You need to copy the Microplant folder from the CHE425 distribution folder into your H:drive or your flash drive. Open the Microplant folder and double click on Microplant.exe torun the program. Turn in the last page of the program with performance number.2) 1 Ethylene glycol and water, at 60 and 10°C, respectively, enter a shell-and-tube heat exchanger for which the total heat transfer area is 15 m2.With ethylene glycol and water flow rates of 2 and 5 kg/s, respectively,the overall heat transfer coefficient is 800 W/m2K. Ethylene glycol: cp =2474 J/kgK, water: cp = 4186 J/kgK.(a) Determine the rate of heat transfer and the fluid outlet temperatures.(b) Assuming all other conditions to remain the same, plot the effectiveness and fluid outlet temperatures as a function of the flow rate of ethylene glycol for 0.5  hm&  5 kg/s. Use Matlab and put your name onthe graph using the Title command.Ans.q = 2.0213×105 W, Tc,o = 19.66oC, Th,o = 19.15oC11 Incropera and DeWitt, Fundamentals of Heat and Mass Transfer, Wiley, 6th ed., 20073) The compartment heater of an automobile exchanges heat between warm radiator fluidand cooler outside air. The flow rate of water is large compared to the air, and theeffectiveness,, of the heater is known to depend on the flow rate of air according to therelation,   0.2airm-&.a) If the fan is switch to high and airm& is doubled, determine the percentage increase in theheat added to the car, if the fluid inlet temperatures remain the same.b) For the low-speed fan conditions, the heater warms outdoor air from 0 to 30oC. When thefan is turned to medium, the air flow rate increases 50% and the heat transfer increases 20%.Find the new outlet temperature.Ans.a) Heat rate increased by 74%, b) Tco = 24oC4. Estimate the temperature of saturated steam that is required in the shell of a new (i.e. noscale deposit) single-pass shell-and-tube heat exchanger when water on the tube side, foreither the new design or the original design that included scale formation, is heated from 21to 65.5oC at a flow rate of 15.75 kg/s. The exchanger contains 60 steel tubes, each with aninside diameter of 0.0186 m and an outside diameter of 0.0254 m. The unit is designed withsufficient tube area to permit the heating of the water as specified. In the original design, anhd of 8250 W/m2K was used to allow for scaling on the water side of the tube. The film∙coefficient for the steam was taken as 11,400 W/m2K, and the temperature of the saturated∙steam required to account for the heating of the water was found to be 153.3oC. No scalingfactor for the shell side was used in the original design, and it can be neglected in the newdesign.Data: cp,w = 4179 J/kgK, w = 0.00063 Pas, w = 991 kg/m3, kw = 0.641 W/mK, ksteel = 45W/mK. The inside heat transfer coefficient can be estimated fromhi = wikD(0.023)Re0.8Pr1/3Ans. 125.5oC5. A heat exchanger is to be constructed by forming copper tubing into a coil and placing thelatter inside an insulated steel shell. In this exchanger, water will flow inside the tubing, and ahydrocarbon vapor at a rate of 0.226 kg/s will be condensing on the outside surface of thetubing. The inside and outside diameters of the tube are 0.0127 and 0.0152 m, respectively.Inlet and exit temperatures for the water are 10 and 32oC, respectively. The heat ofcondensation of the hydrocarbon at a condensing temperature of 88oC is 335 kJ/kg, and theheat transfer coefficient for the condensing vapor is 1420 W/m2K. Heat losses from theshell may be neglected. What length of copper tubing will be required to accomplish thedesired heat transfer?Data: cp,w = 4151 J/kgK, w = 0.000994 Pas, w = 997 kg/m3, kw = 0.61 W/mK, kcopper =385 W/mK. The inside heat transfer coefficient can be estimated fromhi = wikD(0.023)Re0.8Pr1/3Ans. 18.5 m6. A shell-and-tube heat exchanger with two tube passes is to heat 20,000 kg/h of water from25 to 84oC by hot engine oil flowing through the shell. The oil makes a single shell pass,entering at 160oC and leaving at 94oC, with a heat transfer coefficient of 500 W/m2K. Theheat exchanger contains 150 steel tubes of 22.9-mm inside diameter and 25.4-mm outsidediameter. The inside heat transfer coefficient is 3210 W/m2K. Neglecting foulingcoefficients, determine the required tube length.Data: Water: Cp = 4182 J/kgK, density = 998.1 kg/m3Steel: k = 40 W/mKAns. 4.37 m7. A concentric tube heat exchanger uses water (Cp = 4178 J/kgK), which is available at15oC to cool ethylene glycol (Cp = 2650 J/kgK) from 100 to 60oC. The water flow rate is0.5 kg/s and glycol flow rate is each 1.0 kg/s. Determine the effectiveness of the exchanger.Ans.


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