课程名称︰化工热力学
课程性质︰化工系大二必修
课程教师︰林祥泰 教授
开课学院：工学院
开课系所︰化工系
考试日期（年月日）︰2018.10.15
考试时限（分钟）：120 min
试题 :
Each problem worth 5 credit points.
1. Answer the following questions.
(a) How our world would be different if energy were not a conserved quatitiy?
(b) How our world would be different if entriopy were a conserved quantity?
(c) What is equilibrium? Provide your answer with and without using the second
law (i.e. the concept of entropy), respectively.
(d) What is a reversible process? Provide your answer with and without using
the second law (i.e. the concept of entropy), respectively.
(e) What are the 5 principles commonly used by chemical engineers for process
analysis?
(f) Explain the ingredients of total energy of a material (i.e. how one can
determine the total energy of it).
2. An electric heater is a device that converts electricity to heat. Suppose
the heater consumes electricity with a constant power of W and the room
temperature is T (T is constant due to heat loss from the room to the
environment).
(a) Write the mass, energy, and entropy balance equaitons for the electric
heater.
(b) Determine the coefficient of performance of the electric heater.
(c) Is it possible to have a reversible process when heating with an electric
heater? Explain your reasons.
3. Another way to heat a room is to use a heat pump where a compressor is used
to transfer heat from the outside (with an ambient temperature Ta) to the room
(with a constatnt temperature T, and T > Ta).
(a) Write the mass, energy, and entropy balance equations for the electric
heater. (应该是pump?)
(b) Determine the coefficient of performance of the heat pump.
(c) Is it possible to have a reversible process when heating with a heat pump?
Explain your reasons.
4. A metal block of total heat capacity Cp in initally at a temperature T1,
which is higher than the ambient temperature Ta. Suppose the rate of heat
transfer from the metal to air is described by Q = h(T - Ta) and the change in
internal energy and entropy of the metal woth temperature can be estimated as
dU = Cp*dT and dS = Cp* dlnT, respectively.
(a) Write the mass, energy and entropy balance equation of the metal block.
(b) Determine the temperature of the metal as a function of time, i.e., T(t).
(c) Determine the total entropy generation of the process when the system
reaches equilibrium.
(d) If a magic machine is used to extract work during the cooling of metal,
determin the maximum work that can be obtained.
*5&6的A,S,V都是molar的*
5. The total derivative of Helmholz free energy is
dA = -SdT - PdV
(a) What should be the question marks in the folloing equations?
╭δA ╮ ╭ δA ╮ ╭ δ S ╮ ╭ δ ? ╮
│──│ = ? │─── │ = ? │ ─── │ = │───│
╰δT ╯? ╰ δV ╯? ╰ δ V ╯? ╰ δ ? ╯?
(b) Derived all the Legendre transform fuctions of the Helmhlotz free energy.
6. A cleaver student solved the total derivative of Helmholtz free energy in
problem 5 and obtained
a
A(T,V) = - ── - RTln[(V-b)* T^(3/2)]
V
where a and b are constants.
(a) Derive the expression of pressure as a function of T and V.
(b) Derive the expression of entropy as a dunction of T and V.
(c) Derive the experssion of internal energy as a function of T and V.