Final answer:
To determine the temperature of the entering steam in a heat exchanger, one should refer to the saturation temperature corresponding to the given pressure from steam tables. The rate of heat transfer in the heat exchanger can be calculated using the first law of thermodynamics for steady-state processes with the given mass flow rates and temperatures of the steam and air.
Step-by-step explanation:
The student is asked two questions: to determine the temperature of entering steam and to calculate the rate of heat transfer for a counterflow heat exchanger where steam condenses and air is heated.
Temperature of Entering Steam
The entering steam has a quality of 0.9, which means it is 90% vapor and 10% liquid by mass. At a pressure of 0.05 MPa, the saturation temperature of steam can be found from steam tables. Since the steam is saturated, its temperature will be at the saturation temperature corresponding to 0.05 MPa.
Rate of Heat Transfer
To find the rate of heat transfer, we'll use the first law of thermodynamics for a steady-state process, ignoring kinetic and potential energy changes:
- The mass flow rate of the steam: 1.5 kg/min
- The mass flow rate of the air: 100 kg/min
- The air's inlet and exit temperatures: 30°C and 60°C, respectively
- The specific heat at constant pressure for air (cp): 1.005 kJ/kg*K
Using the energy balance for the control volume that involves these two streams, we can calculate the rate of heat transfer, which is the energy per unit time, in kilowatts (kW).