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  Faculty of EngineeringMechanical Engineering DepartmentThermodynamic[1] Sheet [2], Exercise [2] Forms of energy & energy transfer The First Law of Thermodynamics 1-1-What is being heated in a closed pan on top of a range while being stirred by a paddle wheel? During the process, 30KJ of heat is transferred to the water, and 5J of heat is lost to the surrounding air! he paddle-wheel wor a#ounts to 500$! #!Deter#ine the final energy of the sys-te# if its initial energy is 10J!%35!5KJ& '-( classroo# that nor#ally contains )0 people is to be air-conditioned with windowair-conditioning units of 5-W cooling capacity! ( person at rest #ay be assu#ed todissipate heat at a rate of about 3*0J+h! here are 10 light-bulbs in the roo#, eachwith a rating of 100W! he rate of heat transfer to the classroo# through the wallsand the windows is esti#ated to be 15,000J+h! f the roo# air is to be #aintained ata constant te#perature of '1., deter#ine the nu#ber of window air-conditioningunits re/uired!% ' units &3-( fan is to accelerate /uiescent air to a elocity of 10#+s at a rate of )   +s!Deter#ine the #ini#u# power that #ust be supplied to the fan! ae the density of air to be 1!1g+!%'3*W&)-.onsider a 1)00-g car cruising at constant speed of 20#+h! $ow the car starts to pass another car, by accelerating to 110#+h in 5 s! Deter#ine the additional power needed to achiee this acceleration! What would your answer be if that total #ass of the car were only 200 g? % 22! W, 3! W& Energy conversion efficiency 1-   What is #echanical efficiency? What does the #echanical efficiency of 100 percent#ean for a hydraulic turbine?'-4ow is the co#bined pu#p-#otor efficiency of a pu#p and #otor syste# defined? .anthe co#bined pu#p-#otor efficiency be greater than either the pu#p or the #otor efficiency?3-Defined turbine efficiency, generator efficiency, and co#bined turbine-generator efficiency!)-.an the co#bined turbine-generator efficiency be greater than either the turbineefficiency or the generator efficiency? 6plain!5-( 25-hp 7shaft power8 #otor that has an efficiency of 19 is worn out and is replaced bya high efficiency 25-hp #otor that has 5!)9! Deter#ine the reduction in the heat gain of the roo# due to higher efficiency under full-load conditions!  *-lectric power is to be generated by installing a hydraulic turbine-generator at a site 20 # below the free surface of a large water reseroir that can supply water at a rate of 1500g+s steadily! f the #echanical power output of the turbine is 00W and the electric power generation is 250 W, deter#ine the turbine efficiency and the co#bined turbinegenerator efficiency of this plant! $eglect losses in the pipes! 2-Water is pu#ped fro# a lae to a storage tan '0 # aboe at a rate of 20:+s whileconsu#ing '0!) W of electric power! Disregarding any frictional losses in the pipes andany changes in inetic energy, deter#ine 7a8 the oerall efficiency of the pu#p-#otor unit and 7b8 the pressure difference between he inlet and the e6it to the pu#p!
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