Jiangsu Bink teaches you how to understand the plate heat exchanger selection parameter list
In our many years of sales of plate heat exchanger products, we noticed that many customers do not pay attention to the selection parameter list issued by the plate heat exchanger manufacturers, or it is not clear on the selection parameter list. The significance of the data, can not judge the correctness of the heat exchanger selection scheme issued by the heat exchanger manufacturer, whether it is good or bad, thus causing many hidden dangers in the use of the heat exchanger and the heat exchanger operating system. Caused a lot of unnecessary trouble and economic loss. Therefore, Jiangsu Bingke solemnly reminds all new and old customers:
1, be sure to pay attention to the heat exchanger scheme that does not provide heat exchanger selection parameter table and drawings, please choose carefully.
2, must pay attention to the review of the plate heat exchanger selection parameter table and supporting drawings.
These two must pay attention to reduce a lot of unnecessary losses for you! Below we will first teach you how to understand the plate heat exchanger selection parameter list.
1, if you get and see the design selection parameter table (hereinafter referred to as the design book), the content is a foreign language version or a Chinese and foreign version at the same time, congratulations! Because at least the description:
a, the heat exchanger manufacturer you choose can provide you with this heat exchanger product should be a foreign imported brand, the plate type technology used will definitely not be a very backward plate type ;
b, this heat exchanger product has advanced design software that matches the product to provide technical support, which can accurately optimize the selection.
So, if your foreign language level is not very good, you can't read the foreign language design book, you don't have to worry about it, you can ask the designer of the heat exchanger to translate it for you. This translation service is free!
2, when you get the design book, the first thing to check is the fluid name on the design book, heat load (also called heat transfer), flow rate, fluid inlet and outlet temperature, fluid pressure loss, Whether the sheet material of the heat exchanger product, the material of the gasket, and the pressure rating data of the product are consistent with the data provided by you and the technical requirements of the proposed specifications. If it does not match, please do not hesitate, you can directly ask the designer of the heat exchanger to redesign or make a reasonable explanation according to the data and technical specifications you requested. This is the responsibility and obligation of the heat exchanger designer, and it is also your evasion. The most direct and effective method and approach to late trouble due to product design errors.
3, combine the parameter data in the design book, from a technical point of view to verify whether the design is reasonable, from the economic point of view to consider whether the design is appropriate. First, let's take a look at what items are generally found in design books:
a, fluid name is the name of the two media entering the heat exchanger for heat exchange, if this is wrong, the design is completely wrong.
b, fluid flow The medium that participates in heat exchange inside the plate heat exchanger is generally liquid or gas. Their flow is also divided into volume flow and mass flow. The flow rate calculated by the input selection software during general selection is the mass flow. So for liquids, if you are providing volumetric flow, you should confirm the density of the liquid to calculate the mass flow corresponding to the volume flow. For gases, it should be determined whether the volume flow is the flow at standard pressure or the flow at the working pressure and is converted to the corresponding mass flow. If you provide volumetric flow, the mass flow on the design book is unit-converted and the data should match the data you provide. If there is a phase change in the fluid involved in heat exchange on one side, such as steam condensation, refrigerant evaporation, etc., the fluid flow rate in the design book is actually the condensation mass flow rate or the evaporation mass flow rate.
c, fluid inlet temperature / fluid outlet temperature the fluid side where the temperature is reduced, called the hot side inlet and outlet temperature, also called the primary side; The side of the fluid where the temperature rises is called the cold side inlet and outlet temperature, also called the secondary side. According to the purpose of the heat exchanger to be used, it can be divided into the inlet and outlet temperature of the process target side and the inlet and outlet temperature of the non-process target side. The process inlet side inlet and outlet temperature of the cycle heating or circulating cooling conditions must often be determined by data parameters such as the total volume of the fluid supplied by the customer, the initial temperature, the final required temperature, and the time required for circulating heating or cooling. These four temperatures on the design book should be consistent with the data you provide.
d, fluid working pressure is also called operating pressure or operating pressure. This data directly affects the determination of the pressure rating of the plate heat exchanger and the choice of plate type. In general, the actual operating pressure of the fluid multiplied by a factor of 1.2 should not exceed the design pressure rating of the product. At the same time, you must understand that for plate heat exchangers, shallow corrugated plate type products have high pressure bearing capacity, deep and wide corrugated plate type products have low pressure bearing capacity; and heat exchangers with a large number of plates Low pressure capacity. Heat exchangers with a small number of plates have high pressure bearing capacity; the smaller the pressure of the heat exchanger, the lower the pressure bearing capacity, and the smaller the diameter of the heat exchanger, the higher the pressure bearing capacity. You can tell the heat exchanger designer which type of plate is available for you according to the pressure rating of the heat exchanger product you need, and consider whether the number of plates is reasonable and the size of the heat exchanger product ( Whether the caliber is large or not, is it reasonable?
e, fluid pressure drop is also known as pressure loss, drag drop, pressure loss. The pressure drop refers to the pressure difference. In a plate heat exchanger, it refers to the difference between the operating pressure of the fluid entering the heat exchanger and the heat exchanger. The larger the pressure drop, the higher the flow velocity in the inner plate channel of the heat exchanger, the higher the Reynolds coefficient, the stronger the turbulent flow and the smaller the heat exchange area. On the contrary, the lower the flow velocity in the inner plate channel of the heat exchanger, the lower the Reynolds coefficient, the weaker the turbulent flow, and the larger the heat exchange area. Unless you have a clear pressure drop control range requirement, the general heat exchanger designer will default to a heat exchanger design with a pressure drop of no more than 100kpa. In principle, the pressure drop should be no less than 50kpa. If the value of the pressure drop shown in the design book is too low, it means that the heat exchanger product design margin of this scheme is too large, the selected model may be unreasonable, the designed product has low heat exchange efficiency, the fluid passage is easy to scale, and is blocked. Causes the corrosion rate to increase. That is to say, if you spend more money, it will shorten the maintenance cycle of the heat exchanger, increase the maintenance cost and reduce the service life.
f, fluid flow rate is divided into nozzle flow rate and plate flow rate. Nozzle flow rate: For different materials, the maximum allowable flow rate limit for the media is different due to the different ability to resist scouring. In most cases, the higher the flow rate, the stronger the corrosion, which will cause damage to the protective film, causing impact, abrasion, and cavitation corrosion. However, it is advantageous for the concentration of the battery to corrode, to reduce the local corrosion at the gaps and dead corners, and to prevent chlorine pitting of aluminum and stainless steel. Flow rate between plates: The flow rate between heat exchanger plates is generally not more than 1.5 meters per second, and the flow rate between plates should not be too low. The flow rate between plates is too low, which means that the heat exchanger design is unreasonable, the model is too large, and the flow rate is large. Low and the number of plates is too large, the fluid passage is prone to fouling, blockage, and corrosion. Generally, only the data of the nozzle flow rate is reflected in the design book. When the data is higher than 2.5 m/s, it is recommended to select the metal material for the flanged bushing. That is to say, the fluid flow rate is actually an important data that you can't ignore.
g, heat exchange is also called heat load, heat transfer power. Heat exchange amount = hot side fluid specific heat * hot side fluid flow rate * hot side fluid inlet and outlet heat exchanger temperature difference = cold side fluid specific heat * cold side fluid flow rate * cold side fluid inlet and outlet heat exchanger temperature difference. Please note that this fluid flow refers to the mass flow! The unit is kg/s. If it is the calculation of the heat exchange capacity of water, you only know the volume flow rate of water and the temperature requirements for inlet and outlet. We will tell you a formula for calculating the heat load of heat exchange (unit KW) = water inlet and outlet temperature difference * volume flow (m 3/h)/coefficient 0.86 This does not need to check the specific heat data of the water!
h, heat exchange area heat exchange area refers to the common contact area of the two materials that exchange heat with each other. In theory, without setting a clear process goal, that is, without a clear temperature setting requirement, the heat exchange area is larger, the heat exchange effect is better, and the heat exchange temperature is closer. However, as the heat exchange area increases and the number of plates increases, the fluid pressure drop and the flow velocity between the plates are greatly reduced. The low pressure drop and the flow velocity between the plates reduce the heat exchange efficiency of the product, and the fluid passage is easy. Fouling, clogging, corrosion, and reduced product life. Therefore, selecting a plate heat exchanger of a suitable area can greatly extend the service life of the product and reduce the cost of procurement and maintenance of the customer. Do you understand? That is to say, the view that most customers think that the heat exchange area is bigger and better is not completely correct. If it is small, it will not work. If it is too big, it is a good choice. With a small investment to achieve a large effect, reducing the cost of the later is your wise choice.
i, heat transfer coefficient heat transfer coefficient is related to the heat exchanger shape, flow path depth, medium properties, medium flow rate, etc. Heat transfer coefficient = heat transfer amount / (heat exchange area * logarithmic temperature difference of design conditions). It can be seen from the formula that the heat transfer coefficient is inversely proportional to the heat transfer area when the heat exchange amount is determined and the heat transfer design condition is determined. On the heat exchanger design selection parameter list issued by our Jiangsu Bingke Heat Exchange Equipment Co., Ltd., you will find two heat transfer coefficients, one of which is the design heat transfer coefficient, which is the maximum value of the theoretical heat transfer coefficient. One is the running heat transfer coefficient, which is the maximum value of the actual heat transfer coefficient of the design. These two data, you can calculate by the previous formula, you can know the heat exchange area of the heat exchanger you need and the actual heat exchange area of the heat exchanger in the design. If you find that the heat exchange area you calculated is inconsistent with the heat exchange area on the design book, huh, you can think about why?
j, fouling coefficient is also known as fouling thermal resistance, which indicates the value of the heat transfer efficiency of the heat transfer surface of the heat transfer device due to deposits. Under normal circumstances, the heat exchanger will inevitably gradually appear some kind of dirt after operation, which will lead to the gradual formation of the thermal resistance of the dirt, resulting in a corresponding reduction in the heat transfer coefficient of the heat exchanger, which promotes the heat transfer performance of the heat exchanger. deterioration. In the design of the heat exchanger, the larger the fouling coefficient is set, the larger the heat exchange area is. You may see that this item in our design book shows 0. That is because when the heat exchanger is selected, the default setting is 0 unless the customer proposes the fouling factor data. When the fouling coefficient is 0 by default, the design margin should be no less than 5%-10% when designing the heat exchanger. That is to say, even if a part of the passage is blocked or the scale is severely fouled, it is still necessary to ensure the normal heat exchange of the heat exchanger and reduce the number of times of disassembly, cleaning and maintenance of the heat exchanger.
k, design margin is the minimum design margin set by the design input and the actual design margin of the heat exchanger obtained after calculation. The actual design margin is not less than the minimum design margin. Generally, the normal design margin should be controlled at 10%-20%, in order to maintain the heat transfer capacity of the heat exchanger to meet the requirements of the process in order to prevent the scale or blockage of the heat exchanger. The time when the heat exchanger is stably operated reduces the number of maintenance of the heat exchanger disassembly cleaning and reduces the maintenance cost. Need to remind you that there are usually many manufacturers who do not put design margins when designing products, or adjust the design margin from 0 to customer requirements. Such a scheme has a small heat exchange area and is relatively inexpensive. However, because there is no design margin after the heat exchanger starts to run, once the product is fouled or blocked, it will not meet your heat transfer process requirements, and you only have two choices, or frequent disassembly. Cleaning and maintenance, either by adding plates, by increasing the design allowance to reduce the frequency of cleaning and maintenance of the heat exchanger, you can calculate the specific value of this hidden post-cost. Therefore, Jiangsu Bingke recommends that you require at least 10% of the design allowance for heat exchanger design selection.
l, logarithmic temperature difference is also called logarithmic mean temperature difference or heat transfer temperature difference. The larger the value, the smaller the heat transfer area required, and vice versa. The required heat exchange area is large.
m, fluid flow direction is divided into countercurrent and downstream, the standard heat exchanger design is generally countercurrent heat transfer, hot side fluid up and down, cold side fluid Go in and out. In special cases, the hot side fluid can also be moved in and out, and the cold side fluid can be moved in and out as long as the hot side fluid is kept.