Evaluation of pressure measurement components of heat exchanger

In order to obtain reliable and accurate pressure values, we used two types of pressure measurement components in the experiment. At the four inlets and outlets of the heat exchanger, 0.4 precision pressure gauges were installed respectively. At the same time, all the connection points of each section of the heat exchanger were Install a pressure sensor, each pressure sensor is individually calibrated, the calibration range is 0.1 to 2. SMPa, the accuracy is ± 0.5. In the experiment, the system volume flow was measured using a float flow meter (LZ1600, Tianjin Instrument Factory) with an accuracy of 1.5 In addition, in order to control the operating conditions of the refrigerator, the resistance wire is wound on the evaporator and powered by a DC power supply to simulate the cooling capacity of the refrigerator to achieve different operating conditions.

The temperature and pressure data measured during the experiment are recorded and processed by a data acquisition system (Keithley, Model 2700). Because the concentration of the mixture will change under different conditions in the experimental project, the concentration of the mixture must also be measured in the experiment. The concentration of the mixture is measured by gas chromatography. Regarding this part of the work, another report will be made 141. The measurement accuracy of the concentration of the mixture is 0.5.

Because the insulation measures in the experimental system use low vacuum, and the leads of various measuring devices will cause a certain amount of heat leakage in the refrigerator, which will cause the temperature measurement to deviate from the ideal insulation condition, and finally the inaccuracy of the entire experimental data will reach ± ​​15 .Compressor aftercooler counterflow heat exchanger throttle valve evaporator from compressor. Data analysis The experiments in this paper were conducted for three typical refrigeration temperature zones (18OK-ZOOK, 120K-15K and 80K-10K). In the experiment, the mixture working fluid component selection, temperature and pressure range are completely consistent with the actual refrigeration system. Therefore, the experimental measurement results can be directly used in the design of real systems. During the specific experiment, when the pressure, temperature and flow rate were kept constant for at least one hour, the system reached a stable operating state.

If the above formula is satisfied. At the same time, the heat transfer characteristic description: the △ boundary in the above formula is the apparent logarithmic average temperature difference (ALMTO) of the i-th heat exchanger. Since the physical and physical changes of each small heat exchanger are relatively small, the logarithmic average temperature difference The difference between the high and low pressure inlet and outlet temperature of the heat exchanger is calculated, and the difference between the average logarithmic average temperature difference here is called the apparent logarithmic average temperature difference; ki is the average heat transfer coefficient of the i-th heat exchanger, Koveral is the The heat transfer coefficient of the heat exchanger; Q, and Q are the heat exchange amount of the i-th heat exchanger and the entire heat exchanger; △ is the integrated logarithmic average temperature difference of the entire heat exchanger, which is determined by the apparent The number average temperature difference is obtained by weighted average heat exchange load; A is the heat exchange area of ​​the i-th heat exchanger.

It can be seen from the above results that the specific heat transfer characteristics of the heat exchanger are very sensitive to the mixture used, and the composition of different mixtures determines the basic working characteristics of the heat exchanger. At the same time, because the heat exchanger is working in a complete refrigeration system, the different operating conditions of the entire system also have a great influence on the heat exchanger such as temperature distribution, heat exchange amount, heat transfer temperature difference and apparent heat transfer coefficient .