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Chapter 8, Problem 81C(choose chapter or problem)
Problem 8.81C
Outdoor air is to be preheated by hot exhaust gases in a cross-flow heat exchanger before it enters the furnace. Air enters the heat exchanger at 101 kPa and at a rate of . The combustion gases enter at at a rate of and leave at . Determine the rate of heat transfer to the air and the rate of energy destruction in the heat exchanger.
Questions & Answers
QUESTION:
Problem 8.81C
Outdoor air is to be preheated by hot exhaust gases in a cross-flow heat exchanger before it enters the furnace. Air enters the heat exchanger at 101 kPa and at a rate of . The combustion gases enter at at a rate of and leave at . Determine the rate of heat transfer to the air and the rate of energy destruction in the heat exchanger.
ANSWER:
Step 1 of 9
Air is preheated by hot exhaust gases in a cross-flow exchanger. The rate of heat transfer and the rate of energy destruction in the heat exchanger are to be determined.
Assumptions
1. Steady operating conditions exist.
2. The heat exchanger is well-insulated so that heat loss to the surroundings is negligible and thus heat transfer from the hot fluid is equal to the heat transfer to the cold fluid
3. Changes in the kinetic and potential energies of fluid streams are negligible .
4. Fluid properties are constant.