Influence of Capillary Length of High and Low Temperature Test Chamber on Parameters of Refrigeration System
1. Influence on suction and exhaust temperature and pressure
With the same charge amount, the shorter the capillary, the larger the refrigerant flow rate, so the suction temperature and exhaust temperature will decrease; Similarly, when the capillary is constant, the larger the charge amount is, the larger the refrigerant flow rate is, and the suction temperature and exhaust temperature also decrease.
However, with the increase of flow, the inspiratory pressure also rises. For the exhaust pressure, the shorter the capillary is, the smaller the filling amount is. When the capillary length is constant, the higher the charge amount is, the higher it is.
2. Influence on condensing temperature and pressure
When the refrigerant charge is constant, the shorter the capillary tube is, the condensation temperature and pressure decrease.
When the capillary length is constant, the higher the charge amount, the higher the condensing temperature and pressure.
3. Influence on evaporation temperature and pressure
The shorter the capillary, the greater the evaporation temperature and pressure.
When the capillary length is constant, the higher the charge amount, the higher the evaporation temperature and pressure.
4. the influence of supercooling and superheat
When the refrigerant charge is constant, the longer the capillary is, the higher the supercooling degree and the superheat degree are.
When the capillary length is constant, the higher the charge amount, the greater the supercooling degree and the smaller the superheat degree.
5. Influence on cooling capacity, power consumption and performance coefficient EER
When the refrigerant charge is constant, the longer the capillary length, the smaller the power consumption, but the cooling capacity is also smaller, the EER is smaller.
When the charge amount increases to a certain extent, because of the influence of heat exchange temperature difference, the cooling capacity increases, and the EER also increases.
6. Design points of capillary system
(1) On the high pressure side, the reservoir is generally not used, in fact, whether the reservoir is used does not depend on what kind of throttling device, but depends on whether the operation of the entire system is needed, such as heat pump system, shutdown pump system.
(2) In the suction tube, it is best to use a gas-liquid separator.
Because when the capillary system is shut down, the high and low pressure side will balance and the evaporator will accumulate refrigerant liquid, the gas-liquid separator can prevent liquid shock and refrigerant migration.
(3) The high pressure side can accommodate all the refrigerant charged, which is to prevent the capillary blockage when the damage to the high pressure piping system and compressor.
(4) In the high load condition of the evaporator, because the capillary system can be fed back to the condenser side, the condenser should take into account whether the condensing pressure will be too high under this condition, so it is necessary to increase the condensing heat transfer area.
(5) The pipe between the condenser outlet and the capillary inlet should not accumulate refrigerant liquid.
One is that when the compressor is shut down, this part of the refrigerant liquid will evaporate because of the pressure drop, flow into the evaporator and condense, thus bringing some heat to the refrigeration space, which may have an impact on the closed space of the refrigerator, for the air conditioning, this part of the heat can be ignored;
Another is that this will delay the time of the balance of the high and low voltage side, which may cause problems when the low torque compressor starts again, which can generally be solved by increasing the delay in the control (in fact, this is also good for reducing the impact of the starting current on other electrical appliances or the grid).
(6) The capillary inlet must be filtered to prevent clogging, especially the HFC refrigerant used now, which is required to add a dryer in design.
(7) Before the refrigerant enters the capillary, it is best to have a certain degree of undercooling, which can be added to the evaporator by adding a section of undercooling tube, or generating heat exchange with the suction tube, so that the gas flash in the capillary is minimal, thereby increasing the cooling capacity and ensuring the refrigerant flow.
However, it should be noted that at low temperature conditions, the undercooling may be too large because there is a little return liquid in the suction tube, which increases the capillary flow rate, and in turn increases the undercooling degree, which may eventually cause the return liquid.
How to Control the Uniformity of Temperature and Humidity When the High and Low Temperature Test Chamber is Loaded?
High and low temperature test chamber "load" refers to the weight of our test product, or the product needs to be energized to test its heat is referred to the load. The "load" in the high and low temperature chamber is divided into non-heating load and heating load, and the test product that is not powered on or powered on is called non-heating load. This load has no effect on the temperature and humidity range of the constant temperature and humidity test chamber as a whole, but only affects the time of rising and cooling or rising and falling humidity. The test product that needs to be powered on and emits heat is a heating load, which has a relatively large impact on temperature and humidity, and the load that different temperature points or humidity points can withstand is not the same.
It is very important to select the appropriate test equipment when the product is undergoing temperature test.
1, The test range must be required to meet the product failure possibility test range, that is, whether it is a high temperature chamber or a low temperature chamber or a temperature and humidity test chamber or a thermal shock test chamber should be able to meet the extreme temperature conditions specified in the test requirements.
2, Ensure the volume of the test sample, it should not be greater than the working volume of the test equipment 1/5 of the principle standard to select the test equipment.
3, In order to ensure the uniformity of temperature in the test area, the convection mode of the test chamber is customized according to the heating power of the sample. The natural convection of hot air is used, which is especially suitable for drying powder, and most of the test equipment adopts the forced circulation of hot air. The difference in the temperature distribution of the equipment has a great impact on the test results. When a large sample is used, or the number of samples tested at the same time is large, the test results will vary greatly with the different locations, so the temperature uniformity of the equipment should be selected as best as possible. The uniformity performance of the high and low temperature alternating and humidity test chamber of the macro exhibition instrument can reach ≤0.5°C.
4, To prevent the sample heat absorption or heat release caused by heat radiation or heat load in the test area, the heating or refrigeration system device of the equipment has no effect on the temperature equalization and cooling rate of the sample during the test.
We can not be empty when using the high and low temperature test chamber, we will more or less place the test sample, and the user - generally after the test sample put into the heat is not too much concept, in order to avoid the temperature can not reach, can not fall down or rise and cool slowly this kind of situation, so we recommend that when purchasing equipment, to its heat requirements, or place the material, weight, size of the sample to tell the manufacturer, which will effectively help the test to make the test effect better.
Use Principle of High and Low Temperature Test Chamber Low Temperature and Constant Temperature Tank
Because of its own circulation system, the uniformity of temperature field is very high, and more and more experiments are applied to the low temperature constant temperature tank. Mainly used in petroleum, chemical, electronic instrumentation, physics, chemistry, biological engineering, medicine and health, life science, light industrial food, physical property testing and chemical analysis and other research departments, colleges and universities, enterprise quality inspection and production departments, to provide users with a hot and cold controlled, uniform and constant temperature field source for test samples or products to perform constant temperature test or test. It can also be used as a heat source or cold source for direct heating or cooling and auxiliary heating or cooling.
What are the precautions for using a low temperature or constant temperature tank?
1, Before the use of low temperature constant temperature tank, the tank should be added to the liquid medium (pure water, alcohol, methyl silicone oil), the medium liquid level should be less than 20mm workbench, otherwise the power will damage the heater.
2, The selection of liquid medium in the low temperature constant temperature tank should comply with the following principles:
When the operating temperature is below 5 ° C, the liquid medium is generally alcohol;
When the operating temperature is 5 ~ 85℃, the liquid medium is generally water;
When the working temperature is 85 ~ 95℃, the liquid medium can choose 15% glycerol aqueous solution, which can reduce the evaporation of water;
When the operating temperature is higher than 95 ° C, oil is generally selected as the liquid medium, and the open cup flash point value of the selected oil should be higher than the operating temperature of 50 ° C or more; Generally, methyl silicone oil with low viscosity is used.
3, Power supply: 220V50Hz, the power supply should be greater than the total power of the instrument, the power supply must have a good "grounding" device.
4, The instrument should be placed in a dry and ventilated place, and there are no obstacles within 300mm around the instrument.
5, When the thermostat working temperature is high, should be careful not to open the cover, hands do not enter the groove, to prevent hot injury.
6, After using, all switches are placed in the off state, cut off the power.
7, Avoid acid and alkali substances into the tank corrosion coil and inner liner.
8, The instrument should do a good job of regular cleaning work, long-term use, empty the media in the tank, and wipe clean, keep the workbench and the operating panel clean.
9, Often pay attention to observe the liquid level in the tank, when the liquid level is too low, the liquid medium should be added in time.
10, Liquid external circulation, customers should pay special attention to the fastness of the connection of the leading pipe, strictly prevent falling off, so as to avoid liquid leakage.
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