Che425: Problem set #1 1 Run the program Microplant

Download 34.28 Kb.

Date	20.05.2018
Size	34.28 Kb.
	#50173

CHE425: Problem set #1
1) Run the program Microplant as an Expert Troubleshooter and turn in the last display of the 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 to run 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: c_p = 2474 J/kgK, water: c_p = 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 

 5 kg/s. Use Matlab and put your name on the graph using the Title command.

Ans.

q = 2.0213×10⁵ W, T_c,o = 19.66^oC, T_h,o = 19.15^oC

3) The compartment heater of an automobile exchanges heat between warm radiator fluid and cooler outside air. The flow rate of water is large compared to the air, and the effectiveness,, of the heater is known to depend on the flow rate of air according to the relation,  

a) If the fan is switch to high and is doubled, determine the percentage increase in the heat 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 30^oC. When the fan 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) T_co = 24^oC
4. Estimate the temperature of saturated steam that is required in the shell of a new (i.e. no scale deposit) single-pass shell-and-tube heat exchanger when water on the tube side, for either the new design or the original design that included scale formation, is heated from 21 to 65.5^oC at a flow rate of 15.75 kg/s. The exchanger contains 60 steel tubes, each with an inside diameter of 0.0186 m and an outside diameter of 0.0254 m. The unit is designed with sufficient tube area to permit the heating of the water as specified. In the original design, an h_d of 8250 W/m²∙K 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/m²∙K, and the temperature of the saturated steam required to account for the heating of the water was found to be 153.3^oC. No scaling factor for the shell side was used in the original design, and it can be neglected in the new design.

Data: c_p,w = 4179 J/kgK, _w = 0.00063 Pas, _w = 991 kg/m³, k_w = 0.641 W/mK, k_steel = 45 W/mK. The inside heat transfer coefficient can be estimated from

h_i =

(0.023)Re^0.8Pr^1/3

Ans. 125.5^oC
5. A heat exchanger is to be constructed by forming copper tubing into a coil and placing the latter inside an insulated steel shell. In this exchanger, water will flow inside the tubing, and a hydrocarbon vapor at a rate of 0.226 kg/s will be condensing on the outside surface of the tubing. 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 32^oC, respectively. The heat of condensation of the hydrocarbon at a condensing temperature of 88^oC is 335 kJ/kg, and the heat transfer coefficient for the condensing vapor is 1420 W/m²K. Heat losses from the shell may be neglected. What length of copper tubing will be required to accomplish the desired heat transfer?

Data: c_p,w = 4151 J/kgK, _w = 0.000994 Pas, _w = 997 kg/m³, k_w = 0.61 W/mK, k_copper = 385 W/mK. The inside heat transfer coefficient can be estimated from

h_i =

(0.023)Re^0.8Pr^1/3

Ans. 18.5 m
6. A shell-and-tube heat exchanger with two tube passes is to heat 20,000 kg/h of water from 25 to 84^oC by hot engine oil flowing through the shell. The oil makes a single shell pass, entering at 160^oC and leaving at 94^oC, with a heat transfer coefficient of 500 W/m²K. The heat exchanger contains 150 steel tubes of 22.9-mm inside diameter and 25.4-mm outside diameter. The inside heat transfer coefficient is 3210 W/m²K. Neglecting fouling coefficients, determine the required tube length.

Data: Water: C_p = 4182 J/kgK, density = 998.1 kg/m³

Steel: k = 40 W/mK

Ans. 4.37 m
7. A concentric tube heat exchanger uses water (C_p = 4178 J/kgK), which is available at 15^oC to cool ethylene glycol (C_p = 2650 J/kgK) from 100 to 60^oC. The water flow rate is 0.5 kg/s and glycol flow rate is each 1.0 kg/s. Determine the effectiveness of the exchanger.

Ans. 0.597

1¹ Incropera and DeWitt, Fundamentals of Heat and Mass Transfer, Wiley, 6^th ed., 2007

Directory: ~tknguyen
~tknguyen -> Previous Exams che31301 mass transfer spring 2011 quiz #1 I

Download 34.28 Kb.

Share with your friends: