Heat exchanger thermal calculation

First of all, you can consider placing the gas test on the tube side of the aftercooler and the water side on the shell side, because generally the gas pressure of the compressor aftercooling is relatively high, and the pressure drop requirements are not so stringent. However, in your case, the gas should be placed on the shell side. Of course, you can also do calculations on the tube side. Then you must determine whether there is water precipitation, determine the gas side physical parameters (it is very important to fully understand the gas components), and calculate the heat transfer surface area through the heat transfer balance equation. According to your The pre-designed tube bundle form first estimates the heat transfer coefficient, and finally determines the cooling element size parameters based on the heat transfer area. Finally, the correlation is used to back-calculate the heat transfer coefficient, pressure drop, heat transfer margin, etc. Iterate the final optimization result repeatedly and make full use of the gas measurement pressure drop. At the same time, increase the gas side heat exchange area (in a limited space), increase the gas side flow rate and other means to improve the heat transfer efficiency. In addition, structural aspects must also be fully considered, such as the impact of the inlet and outlet pipes, etc.

Looking at the parameters, we can see that the air is dry air. From the import and export problems, we can find the physical parameters of the air. The average temperature is 82.5°. Remember that the specific heat is 1.005 Q=150/60* 1.293 * 1.005 * (125-40)=276KW

We usually put the air on the shell side and let the water flow through the tube side (the heat exchanger is of tube-fin type and the fins are of positive corrugated type) and water is precipitated during the cooling process, so this is more complicated because the centrifuge is a 3-stage compression and the inlet air state of the compressor is: The inlet air temperature is 35°C, the pressure is 0.1MP, and the relative humidity is 70%. There are two coolers in the middle two stages, and water is precipitated. I think that after the third stage of compression, the gas state that enters the post-cooling state is already saturated humid air. If it is saturated humid air, it cannot be calculated as dry air alone. The heat released by the precipitated water must be included. What do you think of vivo1314?

Sir, if you want to calculate whether the heat exchange area is appropriate, you must first tell everyone what form of heat exchanger it is. The heat transfer effect of heat exchangers with different structures is different. The heat transfer effect of the heat exchanger is also related to the flow rate, that is, to the specific structure of the heat exchanger. It is difficult to determine the parameters you gave. I can only know a heat load, and why is your gas side pressure drop so big? 150KPa? It’s too big! And your water inlet is 32 degrees Celsius, and the air outlet is 40 degrees Celsius. This industrial and mining industry is quite harsh.

If there is water precipitation, it must be divided into several parts. The compressor is the first part. The change in physical properties of the gas coming out of the compressor must be calculated. This part is calculated based on the relative humidity, pressure, temperature of the gas entering the compressor, the gas inlet pressure, the gas inlet and outlet temperature, and the gas mass flow rate. Check the data table to calculate the entry. The partial pressure in front of the compressor port, the water content before the gas enters the compressor, the partial pressure entering the cooler, and the temperature at which water begins to separate - determine whether there is water precipitation - calculate the partial pressure after the gas leaves the cooler, the water content after the gas leaves the cooler, and the h1-h2 value - get the total power of the mixed gas (= (h1-h2 value)* Gas mass flow rate), water precipitation amount (= water content before the gas enters the compressor - water content after the gas leaves the cooler) - Substitute the gas specific heat to calculate the total gas power according to the heat transfer equation - Get the condensed water power ； The following steps should be calculated according to conventional methods. This involves the performance parameters of your cooling components, so I won’t continue. We have equipped many heat exchangers for the compressor industry. Generally, this calculation is done using a small program compiled by EXCEL.

The pressure drop is a bit too big. Normally it should be between 200-400Pa, which is more reasonable. However, the factory requires that one type of compressor only needs to use one kind of aftercooling, which is difficult to handle. I took the highest possible pressure value at the compressor outlet and the highest temperature value of the inlet air. This seems a bit unreasonable, because the horsepower of the motor is different for one type of compressor, and the air inlet environment is different, resulting in a relatively large difference in the medium working conditions of the three-stage exhaust. As for the temperature of the medium, it must not change. Another special thing is that the gas flow rate at the compressor exhaust port is very high. Now, the heat exchanger is gradually being blown by the wind. The fin after-cooling designed by Lao Mei that we are currently using is not high enough to upload data, so we can only briefly describe it. What we use is the so-called tube-fin heat exchanger, and its structure is: There are as many holes as there are in each fin, and then each fin and all the tubes are welded together with soldering. Inside the water pipe, this heat exchanger should be considered a special high-finned one. The number of fins is very large (more than 1,000 fins). The ratio of the heat exchange area of ​​the fins to that of the light tube can reach 20: 1 or more. I have consulted some people before, but there seems to be no better way to calculate thermal calculations for this type of heat exchanger. I considered using the most severe working conditions to calculate the heat load, and then calculated the heat transfer area based on common shell and tube heat exchangers. Then, I converted the fin heat transfer area into a light tube heat transfer area according to a certain ratio, and compared the difference between the two. To determine whether the heat exchanger can meet the requirements. wode * aohei, can you leave your email address and I can send you the drawings for my reference?

First of all, you need to find out your design points accurately. There are several design points for compressors, one is the minimum guaranteed working condition, the other is the worst working condition, and sometimes there are other working conditions. We often provide Siemens compressors with the data sheets they provide. In fact, the worst working condition data sheet they provide is not necessarily the one with the largest heat exchange area. You have to calculate it separately. In addition, your comparison method is unreasonable for the heat exchange area. The heat exchange area can be calculated based on the shape of the fins, and there is no need to compare it with the light tube. For comparison, in addition, your cooling element involves a heat transfer coefficient correlation, which must be based on experimental data. If it is a mature process, data in this area should be available. Pressure drop is not the most important factor for the aftercooler. You can compare A larger pressure drop will not have much impact, because there is no interstage cooler at the back and it is directly connected to the factory. What you need is to make full use of water to measure the pressure drop, reduce the diameter of the cooling pipe, lengthen the heat exchange pipe, and make full use of it to get the optimal heat transfer result.

What the poster wants to know is the amount of heat exchanged. According to whether there is a phase change in the state of the heat exchange medium, it can be calculated based on the specific heat.

Aftercoolers are generally made of tubes. You can just calculate the area based on the heat.

This is quite troublesome and requires the use of professional software, such as HTRI and HTFs.

This also depends on the structure type of the aftercooler you want to calculate. Generally, the aftercooler of a centrifuge is made of fins and through-tubes, as well as the specifications and materials of the tubes and fins. It is recommended to choose K=120 first and calculate it. Our company usually chooses this size.

It can be seen that the 6th floor is an expert in this field.