The concept of flow coefficient, for the valve, the choice of flow coefficient and the choice of caliber is corresponding, the valve flow coefficient is the coefficient used when the flow is calculated, the symbols used are very complex, in fact, the United States and Japan use Cv symbol and concept. Europe uses Kvs symbol and concept, UK uses fp, international unit should be Kv, and Kv is also the traditional flow coefficient code of China's regulating valve. In the international standard, the Kv value is defined as the hourly cubic meter flowing through the regulating valve when the pressure drop is 1 Bar. The calculation of the flow coefficient has the following formula:
Where: Q - maximum flow m3/h
G—specific gravity (usually 1)
P1—inlet pressure bar
P2 - outlet pressure bar
â–³P=P1-P2 bar
And the relationship between Cv and Kv is as follows:
Cv=1.17Kv, in fact it is accurate to say that Cv=1.167Kv, and Kv and Kvs are equivalent.
Theoretically speaking, in different air-conditioning loops, the ΔP value is different and it is a dynamically changing value, and the impact on the Cv/Kv calculation is still relatively large. When the valve is in the same kilogram level, the larger the ΔP is, the smaller the corresponding caliber is, and the greater the controllability of the medium is, but the smaller the flow capacity is, the smaller the valve size is, the less the system is. Capacity requirements, on the other hand, the valve will need to provide a large pressure difference through the system to maintain sufficient flow, increase the load of the pump, the valve is vulnerable; valve diameter is too large to make the control performance deteriorate, easy to shock and oscillation system , And the investment will increase. If the valve is too big or too small, the life of the control valve will be shortened and the maintenance inconvenience will be caused.
Therefore, we choose the valve pressure drop as much as possible, and the size of the pressure drop in the system operation is best to be constant, this can also ensure the constant flow characteristics of the valve, to ensure that the PI regulation has a good effect, when the pressure The larger the proportion of the drop in the pressure drop of the total supply and return water pressure, the smaller the influence of pressure fluctuation on the magnitude of the pressure drop. However, the pressure drop should not be too large. Consider the maximum allowable pressure drop and allowable pump pressure. Therefore, experience has shown that it should generally be chosen such that the pressure drop at full valve opening is equal to or close to 50% of the total pressure drop between the supply and return water. The pressure difference for the general supply and return system is 2-4 Bar. This pressure drop on the air conditioning valve is generally selected as 1-2Bar.
After the pressure drop, we also need to know the rated flow of the valve. Sometimes the design institute will give it directly or we can calculate it based on the cooling capacity.
The amount of cold and flow can be calculated according to the following formula:
Cold or calorie calculation
The amount of cooling (or heat) of the equipment (or device) is calculated as follows:
Q=G×C×△t/3600
G=L×Ï
In the formula:
Q---- cold or heat, KW;
L--- volume flow of the fluid, m3/h;
G--fluid mass flow rate, T/h;
Ï --- the bulk density of the fluid, T/m3;
C---- specific heat of the fluid, J/Kg;
△ t ---- Import and export fluid temperature difference, °C.
The specific heat of water is 4184 J/Kg.°C
So we can choose the valve after calculating the Cv/Kv value. The valve's rated value is slightly larger than the calculated value.
According to the different backlight sources, LCDs can be divided into two types: CCFL displays and LED displays.
Misunderstanding:
Many users believe that liquid crystal displays can be divided into LEDs and LCDs. To some extent, this understanding is misguided by advertisements.
The LED display on the market is not a true LED display. To be precise, it is an LED-backlit Liquid Crystal Display. The liquid crystal panel is still a traditional LCD display. In a sense, this is somewhat fraudulent. nature! South Korea`s Samsung was once convicted by the British Advertising Association as violating the country`s advertising laws because its [LEDTV" LCD TVs were suspected of misleading consumers. For liquid crystal displays, the most important key is its LCD panel and backlight type, while the LCD panels of displays on the market generally use TFT panels, which are the same. The difference between LEDs and LCDs is only their backlight types: LED The backlight and CCFL backlight (that is, fluorescent lamps) are diodes and cold cathode lamps, respectively.
LCD is the acronym for Liquid Crystal Display, which means "liquid crystal display", that is, liquid crystal display. The LED display refers to a type of liquid crystal display (LCD), that is, a liquid crystal display (LCD) with LED (light emitting diode) as the backlight source. It can be seen that LCD includes LEDs. Corresponding to the LED display is actually a CCFL display.
(1) CCFL
Refers to a liquid crystal display (LCD) with CCFL (cold cathode fluorescent lamp) as the backlight source.
The advantage of CCFL display is good color performance, but the disadvantage is higher power consumption.
(2) LED
Refers to a liquid crystal display (LCD) that uses LEDs (light emitting diodes) as a backlight source, and generally refers to WLEDs (white light LEDs).
The advantages of LED displays are small size and low power consumption. Therefore, using LEDs as a backlight source can achieve high brightness while taking into account lightness and thinness. The main disadvantage is that the color performance is worse than that of CCFL monitors, so most professional graphics LCDs still use traditional CCFL as the backlight source.
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