According to the theory of boiling heat transfer in the evaporator of an air conditioner, different types of heat exchangers such as nucleate boiling, membrane boiling, and convective heat transfer may occur in the evaporator, and from the perspective of two-phase flow, the evaporator may There are different flow forms such as a bubble flow, a bulk flow, an annular flow, and a single-phase flow.
The evaporator can be divided into two zones according to the state of the refrigerant in the ideal refrigeration cycle and the flow heat transfer condition: a two-phase boiling zone and a superheated gas zone. In the two-phase boiling zone, the temperature of the refrigerant gradually decreases along the length of the tube, and in the superheated gas zone, the temperature of the refrigerant gradually increases along the length of the tube.
From the point of view of the actual refrigeration cycle and versatility, there is often a process in which the supercooled liquid absorbs heat into a saturated liquid in the inlet section of the evaporator, so it is necessary to increase the liquid area, that is, to establish a three-zone model of the evaporator.
For the single-phase zone, the parameter variation is small and the average value is easy to be used. The one-dimensional distributed parameter model of the concentrated parameter model or less segmentation unit can be used. For the two-phase zone, the material parameters of the heat exchange tube vary greatly, and more divisions can be adopted. One-dimensional distribution parameter model of the unit.
Regardless of the model used in each partition, it can be assumed that the evaporator model is a one-dimensional flow heat transfer model consisting of several micro-elements.
Nozzle flowmeter is a fluid flow measurement device that consists of a tapered nozzle arrangement within a pipeline.
The device is designed to increase the velocity of the fluid with a corresponding decrease in pressure. A measurement of the difference between upstream and nozzle pressure gives an indication of the flow rate.
Applications of Flow Nozzle
1．It is used to measure the flow rates of liquid discharged into the atmosphere.
2．It is usually used in situations where suspended solids have the property of settling.
3．It is widely used for high pressure and temperature steam flows.
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