# A piston–cylinder device initially contains 0.A m3 (A is the digit in your SID ****ABC, if A is 0 or 1, then take the next higher digit between B or C) of air at 100 kPa and 80 °C.

**Element 011: MOD002684 (Thermofluids) Assessment**

**QUESTIONS: Element 011: MOD002684 (Thermofluids) Assessment**

**1.**

**Part A**

A piston–cylinder device initially contains 0.**A** m^{3} **(A** is the digit in your SID ******ABC**, **if A is 0 or 1, then take the next higher digit between B or C****) **of air at 100 kPa and 80 °C. The air is then compressed to 0.1 m^{3} in such a way that PV = constant. Determine the work done during this process. ** (5 Marks)**

**Part B**

The air enters the compressor at a temperature of 280 K with an enthalpy of 280.13 kJ/kg and is compressed steadily to 400 K with an enthalpy of 400.98 kJ/kg. The mass flow rate of the air is 0.0**A** kg/s **(A** is the digit in your SID ******ABC, ****if** **A is 0, then take the next higher digit between B or C****) **and a heat loss of 16 kJ/kg occurs during the process. Determine the necessary power input to the compressor when:

a) the changes in kinetic and potential energies are negligible.** (7 Marks)**

b) the air velocity at entry is 100 m/s and exit is 150 m/s but potential energy is negligible. **(7 Marks)**** **

Provide a reflective commentary underpinning the KEY conceptual elements in solving problem Q1 Part B (maximum 100 words) **(6 Marks**** **

**2.**

**Part A:**

Heat is transferred to a heat engine from a furnace at a rate of 100 MW. If the rate of waste heat rejection to a nearby river is **BC** MW **(BC **are the digits in your SID ******ABC****).** Determine the net power output and the thermal efficiency for this heat engine. **(8 Marks)**

**Part B**

A heat source at 800 K loses 2000 kJ of heat to a sink at (*a*) 500 K and (*b*) **ABC** K **(ABC** are the digits in your SID ******ABC, ****for those who has SID number A = 0 or 1 or 2, replace A by 7****)** (shown in Figure Q2B). Determine which heat transfer process is more irreversible based on the entropy calculation. ** (11 Marks)**

**Figure Q2B**

Provide a reflective commentary underpinning the KEY conceptual elements in solving problem Q1 Part B (maximum 100 words)

**(6 Marks)**** **

**3.**

An ideal Otto cycle has a compression ratio of 8. At the beginning of the compression process, air is at 100 kPa and 17°C, and **ABC** kJ/kg (**ABC** are the digits in your SID ******ABC, for those who has SID number A = 0 or 1 or 2, replace A by 7)** of heat is transferred to air during the combustion process. Determine:

a) the pressure and temperature at the end of the compression process **(8 Marks)**

b) the thermal efficiency of the cycle **(3 Marks)**

c) the net output work of the cycle per kg of air** (4 Marks)**

d) the mean effective pressure for the cycle** (4 Marks)**

Assume C_{v}=0.718 kJ/kg.K and C_{p}=1.005 kJ/kg.K for air.

Provide a reflective commentary underpinning the KEY conceptual elements in solving this problem (maximum 100 words)**(6 Marks)**

**4.**

A fuel with a chemical formula C_{8}H_{1A} **(A** is the digit in your SID ******ABC, if A is an odd number, choose the next even number****)** is burned with dry air. The volumetric analysis of the exhaust products gases on a dry basis are CO_{2}: 10.02%, O_{2}: 5.62%, CO: 0.88% and N_{2}: 83.48%.

Determine

- the air–fuel ratio

**(15 Marks)**

- the percentage of theoretical air used
**(4 Marks)**

Provide a reflective commentary underpinning the KEY conceptual elements in solving this problem (maximum 100 words)**(6 Marks)**

**5. Element 011: MOD002684 (Thermofluids) Assessment**

**Part A:** Choose the correct option.

**5A1.** For the same compression ratio, the efficiency of diesel cycle is........Otto cycle (provide reason)

- Greater than

ii. Less than

iii. Equal to

iv. None of the above

** (2 Marks)**

**5A2:** Which of the following is true for a steady flow system? (provide reason)

i. mass entering = mass leaving

ii. mass does not enter or leave the system

iii. mass entering can be more or less than the mass leaving

iv. none of the mentioned

**(2 Marks)**

**Part B**

A rigid tank contains **BC** kg **(BC** is the digit in your SID ******ABC****)** of water at 90°C. If 80% by mass of the water is in the liquid form and the rest is in the vapour form. Determine

- the pressure in the tank
**(2 Marks)**

- the dryness fraction of the mixture
**(3 Marks)**

- the total volume of the tank
**(3 Marks)**

- the internal energy (
*U*)**(3 Marks)**

- the enthalpy (
*H*)**(2 Marks)**

- the entropy (
*S*)**(2 Marks)**

Provide a reflective commentary underpinning the KEY conceptual elements in solving problem Q5 Part B (maximum 100 words)

**(6 Marks)**

**6. Element 011: MOD002684 (Thermofluids) Assessment**

A certain gas of 2 kg is kept at **BC** **(BC** is the digit in your SID ******ABC****)** °C in a constant volume chamber of 0.3 m^{3 }capacity. Heat is transferred to the gas until the temperature is of the gas reached to100 °C. The gas has *c _{p}* = 1.968 kJ/kg-K and

*c*= 1.507 kJ/kg-K. Universal gas constant 8.314 kJ/kg-mol K. Determine:

_{v}- the molecular weight
**(3 Marks)**

- the gas constant
**(2 Marks)**

- the work done
**(3 Marks)**

- the heat transferred
**(2 Marks)**

- the change in internal energy
**(3 Marks)**

- the change in enthalpy
**(3 Marks)**

- the change in entropy

**(3 Marks)**** **

Provide a reflective commentary underpinning the KEY conceptual elements in solving this problem (maximum 100 words)

**(6 Marks)**

**Element 011: MOD002684 (Thermofluids) Assessment**

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