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Unformatted text preview: 2.7 6Energy Balance on a Flow System with a Pump and Heat Exchanger. Waterstored in a large, wellinsulated storage tank at 21.0 C and atmospheric pressure isbeing pumped at steady state from this tank by a pump at the rate of 40 m3/hr. Themotor driving the pump supplies energy at the rate of 8.5 kW. The water is used as acooling medium and passes through a heat exchanger, where 225 kW of heat is addedto the water. The heated water then flows to a second large, vented tank, which is 25 mabove the first tank. Determine the final temperature of the water delivered to thesecond tank.kPa1000 Pa:=25 m heater 2 1 Q T1= 21 C T2= ? Vr40m3hr:=kJ103J:=z25 m:=gz245.166Jkg=v1v2=(approximately 0 in large vessels)p1p2=(both vessels open to atmosphere, no pressure changes)FJkg:=(assume friction losses minimal)H188.14kJkg:=(enthalpy at 21C from saturated Steam Tables)110.0010020 m3kg1:=1998kgm3=(from sat Steam Tables)mrVr1:=mr11.09kgs=(mass flow rate)Energy from Pump:Energy from Heat ExchangerWs8.5kWmr:=Ws766.53Jkg=dQ255 kWmr:=dQ23kJkg=H2H1Ws+dQ+:=H2111.9kJkg=Temperature Estimate from Enthalpy (interpolate from Steam Tables)2725() 111.9104.89()113.25104.8925+26.677=Implies t2= 26.7 C2.7 7MechanicalEnergy Balance in Pumping Soybean Oil. Soybean oil is beingpumped through a uniformdiameter pipe at a steady massflow rate. A pump supplies209.2 J/kg mass of fluid flowing. The entrance abs pressure in the inlet pipe to thepump is 103.4 kN/m2. The exit section of the pipe downstream from the pump is 3.35 m above the entrance and the exit pressure is 172.4 kN/m2. Exit and entrancepipes are the same diameter. The fluid is in turbulent flow. Calculate the friction lossin the system. The density of soybean oil is 919 kg/m3.FWsgzp+v22+=oil919kgm3:=Ws209.2Jkg:=p172.4 kPa103.4 kPa:=z3.35 m:=v2=FWsgzpoil+:=F101.3Jkg=2.7 9Pressure Measurements from Flows. Water (998 kg/m3) is flowing at the rate of1.676 m/s in a 3.068in ID horizontal pipe at a pressure of p1= 68.9 kPa abs. It thenpasses to a pipe having an ID of 2.067 in....
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 Spring '08
 Smith
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