UPSC Combined Geo-Scientist, Mains · 2024 · Mains Paper III
Q1(g). Calorific value of a fuel
Question
What do you understand by the calorific value of a fuel?
Answer in brief
The quantity of heat liberated when unit mass (solid, liquid) or unit volume (gas) of a fuel is burnt completely in oxygen; gross value with steam condensed, net value with water leaving as vapour.
Key points
- Calorific value: heat liberated when unit mass (solid or liquid) or unit volume (gas, at STP) of a fuel is burnt completely in oxygen.
- Higher (gross) calorific value: products cooled to room temperature and steam condensed, so the latent heat of water is included.
- Lower (net) calorific value: water leaves as vapour; LCV = HCV − 0.09 H × 587 kcal kg⁻¹.
- Determination: bomb calorimeter for solids and liquids; Boys or Junkers calorimeter for gases; estimate by Dulong’s formula.
- It is the chief measure of fuel quality: efficiency, price and the rank of a coal.
The full model answer
As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.
Coverscalorific valuegross calorific valuenet calorific valuebomb calorimeterDulong formulafuel
All parts of Question 1
- 1(a) Percentage relative error of a balance reading5 marks
- 1(b) Partition ratio k′ and relative retention α5 marks
- 1(c) Transmittance from Beer’s law5 marks
- 1(d) Identifying a magnesium compound from its thermogram5 marks
- 1(e) Properties needed in a detector for X-ray fluorescence5 marks
- 1(f) Generation of the plasma in the ICP torch5 marks
- 1(g) Calorific value of a fuel5 marks
- 1(h) AAS and ICP compared: accuracy, interferences, detection limit5 marks