The video shows that in case of improperly designed recuperator, the сross section of the heat exchanger is not fully used. This might lead to an overestimated resistance of the corresponding channel, and in some cases, to possible emergency situations.
The latter is possible, for example, if the last in a rowgas channels allow hot gas to pass through, and the last in a row air channels do not let through (surfaces washed by hot gas are not cooled).
Visualization of gas flow pattern makes it possible to eliminate design errors primarily for diffusers and confusors of heat exchangers.
In this example, the heat exchanger OPT 325/0,684-25/4,5 is selected for research.
- Weight 500 kg
- Output power: 100 kW
- Used for heating premises
- Payback period: 11.5 months
- Flue gas temperature: 325o С
- Temperature of heated air: 25o С
The video shows the trajectories of the cooling airflow in the longitudinal section of the heat exchanger. Lower temperature of streams is colored blue, highertemperature iscolored red respectively.
For more detailed information, the video shows the same air flow trajectories in the longitudinal section plane of the recuperator. There are visible areas of the airduct with practically no air flows, for example, several gaps after air flows turn the corner of connecting ducts. The main factor is the high speed of the air flows, which forces the flows to “fly” near the gaps virtually without reaching them, which leads to low efficiency of the gaps.This fact should be taken into account when designing recuperators for specific flow rates of cooling gases.
The video shows the speed trajectories of the masses of cooling medium. Blue color indicates flows with minimum speed, red color shows maximum possible speed. The low velocity area of the mediumcan be clearly seen near the «inefficient» gaps.
This figure shows the scaled temperature field of the cooling medium in the middle of the plane of thelongitudinal section on the temperature.
This figure shows the surfacetemperature of the heat exchanger. There are visible places of local overheating of the walls, which must be taken into account when designing.
The figure shows the wall surface temperature field. There are visible areas of local overheating of the walls, which must be taken into account when designing. The temperature scale is preserved in relation to the previous figure.
The figure shows the wall surface temperature field. There are visible areas of local overheating of the walls, which must be taken into account when designing. The temperature scale is preserved in relation to the previous figure.
The video shows the trajectories of the cooling medium flow, taking into account the speed for the case of the same heat exchanger, however, withthe air inlet and outlet dimensions along the X axis reduced by 2 times. There is noticeable decrease in speed of the medium flow near the outlet of the recuperator. This fact also reduces the efficiency of the recuperator, and also leads to an increase in resistance to the course of the cooling medium. The speed scale coincides with the speed scale in the first case.
The video shows the trajectories of thecooling medium flow, taking into account the speed for the case of the same heat exchanger, however, with the heights of air inlet and air outlet reduced by 2 times, as well as the height of the duct. There is a noticeable increase in the number of «inefficient» gaps, as well as an increase in the speed of the cooling medium flow in the connecting ducts and, consequently, in the second pass of the recuperator. This fact also reduces the efficiency of the heat exchanger and leads to an increase in the resistance to the course of the cooling medium. The speed scale coincides with the speed scale in the first case.
Therefore, it is important to model gas flows after the preliminary calculation to approve the final design of the recuperator.
