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# ExampleSolutions - 2.7 6Energy Balance on a Flow System...

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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, well-insulated 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⋅:=Δz25 m⋅:=gΔz⋅245.166Jkg=v1v2=(approximately 0 in large vessels)p1p2=(both vessels open to atmosphere, no pressure changes)ΣFJkg:=(assume friction losses minimal)H188.14kJkg⋅:=(enthalpy at 21C from saturated Steam Tables)ρ110.0010020 m3⋅kg1-⋅:=ρ1998kgm3=(from sat Steam Tables)mrVrρ1⋅:=mr11.09kgs=(mass flow rate)Energy from Pump:Energy from Heat ExchangerWs8.5kWmr:=Ws766.53Jkg=dQ255 kW⋅mr:=dQ23kJkg=H2H1Ws+dQ+:=H2111.9kJkg=Temperature Estimate from Enthalpy (interpolate from Steam Tables)2725-() 111.9104.89-()⋅113.25104.89-25+26.677=Implies t2= 26.7 C2.7- 7Mechanical-Energy Balance in Pumping Soybean Oil. Soybean oil is beingpumped through a uniform-diameter pipe at a steady mass-flow 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.ΣFWsgΔz⋅Δpρ+Δv22+-=ρoil919kgm3⋅:=Ws209.2Jkg⋅:=Δp172.4 kPa⋅103.4 kPa⋅-:=Δz3.35 m⋅:=Δv2=ΣFWsgΔz⋅Δpρoil+-:=ΣF101.3Jkg=2.7- 9Pressure Measurements from Flows. Water (998 kg/m3) is flowing at the rate of1.676 m/s in a 3.068-in 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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ExampleSolutions - 2.7 6Energy Balance on a Flow System...

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