Heating water from 20°C to 100°C using an open fire for cooking and washing is a daily task in the developing world. Approximately one-third of the world’s population uses an open fire with a heat transfer efficiency of approximately 5%. Consider the difference between cooking with wood and cooking with braided grass. a. Assume the wood has 25% moisture and 0.8% ash on an as-received basis. The bulk density of stacked wood is 45% of the density of the wood. Assume that the dry, ash-free composition of the wood is 51.2%, 5.8%, 42.4%, 0.6%, and 0% for C, H, O, N, and S, respectively. The dry density of the wood is 640 kg/m3 . The dry, ash-free HHV of the wood is 19.7 MJ/kg. What is the as-received LHV of the wood (MJ/kg)? What is the as-received density of the wood (kg/m3 )? What is the as-received bulk density of the wood (kg/m3 )? What is the bulk volume (L) and weight (kg) of wood needed to heat 5 L of water? b.Some cultures use braided grasses for cooking. Assume the grass has 2% moisture and 10% ash on an as-received basis. Assume that the dry, ash-free composition of the grass is 49.4%, 5.9%, 43.4%, 1.3%, and 0.0% for C, H, O, N, and S; respectively. The bulk density of braided grass is 20% of the density of the grass. The dry density of the grass is 250 kg/m3 . The dry, ash free HHV of the grass is 17.4 MJ/kg. What is the as-received LHV of the grass (kJ/kg)? What is the as-received density of the grass (kg/m3 )? What is the as-received bulk density of the grass (kg/m3 )? What is the bulk volume (L) and weight (kg) of grass needed to heat 5 L of water? c. Report your results in a table comparing wood and grass. What are your observations?
Heating water from 20°C to 100°C using an open fire for cooking and washing is a daily task in the developing world. Approximately one-third of the world’s population uses an open fire with a heat transfer efficiency of approximately 5%. Consider the difference between cooking with wood and cooking with braided grass.
a. Assume the wood has 25% moisture and 0.8% ash on an as-received basis. The bulk density of stacked wood is 45% of the density of the wood. Assume that the dry, ash-free composition of the wood is 51.2%, 5.8%, 42.4%, 0.6%, and 0% for C, H, O, N, and S, respectively. The dry density of the wood is 640 kg/m3 . The dry, ash-free HHV of the wood is 19.7 MJ/kg. What is the as-received LHV of the wood (MJ/kg)? What is the as-received density of the wood (kg/m3 )? What is the as-received bulk density of the wood (kg/m3 )? What is the bulk volume (L) and weight (kg) of wood needed to heat 5 L of water?
b.Some cultures use braided grasses for cooking. Assume the grass has 2% moisture and 10% ash on an as-received basis. Assume that the dry, ash-free composition of the grass is 49.4%, 5.9%, 43.4%, 1.3%, and 0.0% for C, H, O, N, and S; respectively. The bulk density of braided grass is 20% of the density of the grass. The dry density of the grass is 250 kg/m3 . The dry, ash free HHV of the grass is 17.4 MJ/kg. What is the as-received LHV of the grass (kJ/kg)? What is the as-received density of the grass (kg/m3 )? What is the as-received bulk density of the grass (kg/m3 )? What is the bulk volume (L) and weight (kg) of grass needed to heat 5 L of water?
c. Report your results in a table comparing wood and grass. What are your observations?
Trending now
This is a popular solution!
Step by step
Solved in 4 steps with 27 images
How is it that the LHV of wood is higher than the grass? when grass has 15.312MJ/kg and wood has 14.6714MJ/kg.
by Bartleby Expert
