Shell-and-tube heat exchangers with hundreds of tubes housed in a shell are commonly used in practice for heat transfer between two fluids. Such a heat exchanger used in an active solar hot- water system transfers heat from a water-antifreeze solution flowing through the shell and the solar collector to fresh water flowing through the tubes at an average temperature of 60 degree C at a rate of 15 L/s. The heat exchanger contains 80 brass tubes 1 cm in inner diameter and 1.5 m in length. The roughness of brass tubing is epsilon 1.5 times 10^-6 m. Determine the pressure drop across a single tube. Calculate the pumping power required by the tube-side fluid of the heat exchanger. After operating for a long time. 1-mm-thick scale builds up on the inner surfaces with an equivalent roughness of 0.4 mm. For the same pumping power input determine the percent reduction in the flow rate of water through the tubes. Solution solution: 1)here for calculating pressure loss is given by dP=f(L/D)*density*V^2/2 Q=15/80=.1875 l/s or 1.875*10^-4 m3/s D=.01 m L=1.5 m e=1.5*106-6 m velocity is given by V=Q*4/pi*D^2=2.3873 m/s Re=VD/kinematic viscosity=23873.241 here for terbulent flow friction factor is given by f=1.325/{ln[e/3.7D+5.74/Re^.9]}^2 so we get f=.02510 here pressure drop is given as dP=f(L/D)*density*V^2/2 dP=10728.74 N/m2 where pumping power is W=Q*dP/1000=2.011*10^-3 kw 3)when scale are deposited then flow velocity is given by reduced diameter=d1=.01-.002=8*10^-3 m velocity=1.875*10^-4*4/pi*d1=3.7301 m/s reynolds number is Re1=29840.8 friction factor is for e1=4*10^-4 m f1=.07284 pressure drop=dP1=95016.55 N/m2 for same power flow rate is W=Q1*dP1/1000 Q1=2.1164*10^-5 m3/s hence percent reduction in flow rate is for single tube %reduction=(Q-Q1/Q)*100=88.75%.

1. Should the US conform to international standards?
Solution
Yes, US should conform to International Standards.
The International Accounting Standards Board (IASB) has achieved “almost” worldwide
acceptance and adoption of its precious and hard-delivered (that is, more than 30 years in the
making) “baby”—International Financial Reporting Standards (IFRS), a comprehensive set of
financial reporting standards. However, that “almost” is a very significant one: the US, the
largest capital market in the world, is still reluctant to fully incorporate IFRS into its financial
reporting system, despite the recognition of IFRS on all continents during the last ten years. So
US should conform to International Standards