Effect of the high and low pressure of circulating return water on heat exchange efficiency
Thread Content
A high pressure of the circulating water can promote turbulence of the circulating water inside the heat exchanger, thereby improving the heat exchange efficiency； So what is the impact of backwater pressure on heat exchange?
Generally speaking, if the supply water pressure is high, the return water pressure should also be relatively high, right? If the supply water pressure is high and the return water pressure is low, it indicates that the resistance of the heat exchanger is somewhat high.
If the return water pressure is adjustable, reducing it will affect the water volume in the heat exchanger. Improve heat exchange efficiency. (In the case of insufficient circulating water volume)
The return water pressure is generated by the return water network; therefore, a high return water pressure will inevitably lead to a decrease in the pressure difference, which in turn reduces the heat exchange efficiency of the heat exchanger.
Ultimately, it comes down to the water flow rate used in the heat exchanger. When the pressure difference between the supply water and return water is high, there are two possible reasons: 1. The return water pressure decreases; in this case, the amount of water flowing through the heat exchanger is higher, resulting in greater heat transfer. The turbulent flow within the heat exchanger leads to a higher heat transfer coefficient, thereby improving the efficiency of heat transfer. 2. If the total return water pressure remains unchanged, it might be due to blockages inside the heat exchanger. However, since the total supply pressure is connected to the entire system, it is almost impossible to determine whether a heat exchanger is clogged based on the total supply pressure.
It needs to be kept at a relatively appropriate pressure difference; if the pressure difference is too large, the flow rate will increase, which affects the heat exchange efficiency
The pressure of the return water is generally related to the height of the inlet pipe of the cooling tower above the ground level; the higher the height, the greater the pressure. There is no inevitable connection between the pressure of the return cooling water and its flow rate – it depends on the layout of the piping system. This can be understood by looking at Bernoulli’s equation.
7# Lazy caster: The pressure of the return water can be controlled by the opening degree of the valve on the pipeline of the return circulation tank
It is necessary to conduct a specific analysis of the reasons behind the changes in the pressure of the circulating water inlet and outlet in order to determine their impact on heat exchange. (If the heat exchange tubes are blocked, the heat exchange efficiency may not improve.) Of course, a higher flow rate of the circulating water within the heat exchange tubes increases turbulence, thereby raising the convective heat transfer coefficient and enhancing heat transfer. In principle, that’s how it is. In actual engineering analysis, it is also necessary to determine the relative magnitudes of the thermal resistance of the heat exchange tube wall, the convective thermal resistances on both sides, and the fouling thermal resistance, in order to assess the extent of this enhancement effect.
First, it is necessary to determine what is causing the increase or decrease in the return water pressure. If the increase in the pressure difference before and after the heat exchanger is due to blockages in the heat exchanger, then cleaning the heat exchanger should be considered. I would like to ask why some companies use pressurized return water, while others do not There is a pipeline network for pressurized return water, and there is also a pipeline network for non-pressurized return water. I fully agree with what was said on floor 5.