A gas is leaking from a rigid tank into the air. Which of the following represen

Question

A gas is leaking from a rigid tank into the air. Which of the following represents the BEST energy balance?

d(nU) = Hdn

(nU) = Hn

U = Q + W

H = Q + W

Which of the following is the first step to solving a thermodynamics problem?

Identify your system as steady or unsteady-state.

Write the mass and energy balances.

Identify system boundaries and select open or closed.

Identify the variables required to specify the states

High pressure steam flows through an adiabatic turbine to steadily produce work. Write the best energy balance for solving this problem.

U = PV + W + mv2/2

Hout*mout - Hin*min + W = d(mU)/dt

U = Q + W

H = Q + W

A gas is filling a rigid tank from a supply line. Which of the following represents the BEST energy balance?

H = Q + W

(nU) = Hn

U = Q + W

d(nU)= Hdn

a

d(nU) = Hdn

b

(nU) = Hn

c

U = Q + W

d

H = Q + W

Which of the following is the first step to solving a thermodynamics problem?

a

Identify your system as steady or unsteady-state.

b

Write the mass and energy balances.

c

Identify system boundaries and select open or closed.

d

Identify the variables required to specify the states

High pressure steam flows through an adiabatic turbine to steadily produce work. Write the best energy balance for solving this problem.

a

U = PV + W + mv2/2

b

Hout*mout - Hin*min + W = d(mU)/dt

c

U = Q + W

d

H = Q + W

A gas is filling a rigid tank from a supply line. Which of the following represents the BEST energy balance?

a

H = Q + W

b

(nU) = Hn

c

U = Q + W

d

d(nU)= Hdn

Explanation / Answer

Answer to question 1

We will make use of first law of thermodynamics to solve this problem.

dU =Q +W

Where, dU is the change in internal energy

Q = Heat exchange

W = work done

Hence the right answer should option (c) Which is the general energy balance

Answer to question 2

First thing to solve a thermodynamics problem is to specify the Boundary ,i.e, to define the system and the surrounding And Hence see whether the system is a closed system or an open system. Once that is defined we can apply mass and energy balance and than apply conditions such as steady or unsteady state problem

Hence the correct option is (C)

answer to Question 3

Here the system is an open system and we have flow work. Hence we will have use overall energy balance and apply steady state approximation.

Hence the correct option is (b)

Answer to question (4)

Here again same as question 1

We will make use of first law of thermodynamics to solve this problem. and than depending on further data provided we can further simply or alter the 1st law

dU =Q +W

Where, dU is the change in internal energy

Q = Heat exchange

W = work done

Hence the right answer should option (c) Which is the general energy balance

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