Heat transfer coefficient issues in heat exchangers
Thread Content
I would like to ask everyone: Multiple tubes are submerged in water inside a container (the water does not wash against the tubes); heat transfer oil flows through these tubes, causing their temperature to drop, while the temperature of the water rises and it turns into steam that is then expelled from the container. How should the overall heat transfer coefficient be calculated? I first calculate the heat loss coefficient within the tubes, then assume a temperature for the tube walls and use the average temperature to calculate the heat loss coefficient outside the tube walls, followed by a verification step. The heat exchange at the tube walls occurs through natural convection in a large volume of air; however, the results I obtain are incorrect. Therefore, I seek advice from those who are more experienced in this area – this is my first time calculating the heat transfer for such a heat exchanger
Calculated based on forced oil-water convection, with the water flow rate determined by the evaporation amount.
Since there is phase change outside the pipe, it cannot be calculated using natural convection. What was said on the second floor is correct: the flow rate can be determined based on the amount of evaporation, and the thermal resistance outside the pipe can be calculated using the evaporation rate; thereafter, this value can be combined with the thermal resistance inside the pipe, and the results should be fairly similar.