课程名称︰热力学
课程性质︰必修
课程教师︰黄信富 教授
开课学院：工学院
开课系所︰机械工程学系
考试日期（年月日）︰2015/11/12
考试时限（分钟）：120
是否需发放奖励金:是
试题 :
1.(50pts)
The turbocharger of an internal conbustion engine consists of a
turbine and a compresser. Hot exhausts gases flow through the turbine to
produce work and the work output from the turbine is used as the work input
to the compressor. The pressure of ambient air is increased as it flows
through the the compressor. The purpose of a turbocharger is to increase
the pressure of air so that more air gets into the cylinder, and more fuel
can be burned, creating more power.
Exhaust air enter the turbine at 400°C and 120kPa at the rate of
0.02kg/s and leave at 350°C. Air enters the compressor at 50°C and 100kPa
and leaves at 130kPa at a rate of 0.018kg/s. The compressor increases the air
pressure with a side effect: It also increases the air temperature, causing
the possibility of an engine knock. To avoid this, an aftercooler is placed
after the compressor to cool the warm air by cold ambient air before it enters
the engine cylinders. It is estimated that the aftercooler must decrease the
air temperature below 80°C if knock is to be avoided. The cold ambient air
enters the aftercooler at 30°C and leaves at 40°C. Disregard any frictional
losses in the turbine and the compressor and treating the exhaust air as air,
determine (a)(30pts) the temperature of the air at the compressor outlet
(b)(20pts) the minimum volume flow rate of ambient air to avoid knock.
图示：
http://i.imgur.com/OL9WcD0.jpg
2.(25pts)
Two tanks (A and B) are seperated by a partrition. Initially tank A
contains 2-kg steam at 1Mpa and 300°C while B contains 3-kg saturated
liquid-vapor mixture at 150°C with a quality of 50%. The partition is removed
and the two sides are allowed to mix until the mechanical and thermal
equilibrium are established. If the pressure at final state is 300kPa,
determine:
(a)(16pts) the temperature and quality of steam(if mixture) at the final state
(b)( 9pts) the amount of heat lost from the tanks.
图示：
http://i.imgur.com/r5U8Lli.jpg
3.(25pts)
An insulated 8-m^3 rigid tank contains air at 600kPa and 400K. A valve
connected to the tank is now opened, and air is allowed to escape until the
pressure inside drops to 200kPa. The air temperature during this process is
maintained constant by an eletric resistence heater placed in the tank.
Determine the eletrical energy supplied to air during this process.
Gas constant R = 0.287 kPa * m^3 / kg * K
图示：
http://i.imgur.com/o0XHhMg.jpg