Question

PROBLEM 3 (45 points) The condenser of a large steam power plant is a heat exchanger in which steam is condensed to liquid water. Assume the condenser to be a parallel flow shell-and-tube heat exchanger consisting of a single shell and 1x10 tubes, each executing two passes. The inner diameter of tubes is D = 50 mm and its thickness is 5 mm (Do not ignore the thickness). The steam condenses on their outer surface. Thermal conductivity of the tube is estimated to be 20 W/m- K. The heat transfer rate that must be effected by the exchanger is Q = 2.5x 10' W, and this is accomplished by passing cooling water through the tubes at a rate of 2x10 kg/s. The water enters at 30C, while the steam condenses at 90 C. The average velocity of steam on the tube surface is 1 m/s. Assumption: - Steam flow on the outer surface of the tube is assumed to be external forced flow. - Water flow on the inner surface of the tube is assumed to be internal forced flow. - Negligible heat transfer between heat exchanger and surroundings. - Negligible kinetic and potential energy changes. - Constant properties. (a) (5 pts) List fluid properties (density, dynamic viscosity, specific heat, thermal conductivity, Prandtl number) with units for steam and water that need to be used throughout this problem and state the temperature at which the fluid properties are evaluated. Use 45 as the bulk mean temperature for the water. Don't forget the units! Steam Temperature used Density Dynamics viscosity Specific heat Thermal conductivity Prandtl number Water Temperature used Density Dynamics viscosity Specific heat Thermal conductivity Prandti number (b) (5 pts) What is the temperature of the cooling water emerging from the condenser?

Answer 1

3. single shell n= No. of tubes a lot p= noi of passes=2 w Inner drauseter (D) = 50 urus Thickness it t)= sunus, Ktuble = 20w/usk Heat transfer rate = Q = 215x10? Heat transfer in single tube in single pass (@j = 2,5x107 104 x 2 Q = 125 x103 W water is = 200 Kg/A Enterance temperature (TIJ = 300 Straus. condensing teusperature (T) = 90°C (Vaug) steaus = im

la) fluid properties water steaus 45°C Teuspexafused Teusperature used goc used Density 10.423 (kg/u3) Dynamics Viscosity 12x10-5 (pa-A) specific heat 1.9919 (K7686) The rrusal 0.020 Conductivity (whunt prandtl 1.195 Number Density 991 (Kg/u3), Dynamics viscosity: 10.6x10-3 (Pars) specific heat 4.18 The rusal conductivity 0.632 (Whusk) prandal Nuusber 3.97 M. Cp prandal Nuusber (1) K

(b) Heat transfer (Q.) = Ens Cp (Tarto) 2.5X107 = 2x102x4-180(T2-30) Tz = 30+ 59.8086 89.8086°C