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In the previous issues, we have studied the principles, characteristics, structure and installation and use methods of plate heat exchangers. In this issue, we will take a closer look. Design selection of plate heat exchangers and application in heat flow field.
Plate heat exchanger selection criteria and key points
1. Selection criteria
Principle 1: Look at the plate type
1. The plate type or corrugated type should be based on the heat exchange Depends on the actual needs of the location.
2. For situations where the flow rate is large and the pressure drop is small, the plate type with small resistance should be selected. On the contrary, the plate type with large resistance should be selected.
3. According to the fluid pressure and temperature, decide whether to choose the assembly type or the brazing type.
4. When determining the plate type, it is not advisable to choose a plate with a single plate area that is too small to avoid too many plate numbers, a small flow rate between plates, and a too low heat transfer coefficient. It is more suitable for larger heat exchangers. Pay attention to this topic.
Principle 2: Look at the process and flow channels
p> The process refers to a set of parallel flow channels in a plate heat exchanger in which a medium flows in the same direction, while the flow channel refers to the medium flow channel formed by two adjacent plates in the plate heat exchanger. Under normal circumstances, several flow channels are connected in parallel or series to form different groups of cold and hot medium channelsRwandans EscortTogether.
The process combination form should be determined based on heat transfer and fluid resistance calculations and meeting process conditions. Try to make the convective heat transfer coefficients in the cold and hot water flow channels equal or close to Rwanda Sugar to obtain the best heat transfer effect. Because the heat transfer coefficient obtains a larger value when the convective heat transfer coefficients on both sides of the heat transfer surface are equal or close to each other. Although the flow rate between the plates of the plate heat exchanger is different, when calculating the heat transfer and fluid resistance, the average flow rate is still used for calculation. Because the “U”-shaped single-flow receiver is fixed on the compression plate, it is easy to disassemble and assemble.
Principle 3: Check the pressure drop check
When designing and selecting a plate heat exchanger, there are generally certain requirements for the pressure drop, so it should be checked. If the calibrated pressure drop exceeds the allowable pressure drop, the design selection calculation needs to be carried out again until the process requirements are met.
2. Key points for selection
1. Flow rate and value:
①. Heat exchange pipe network flow rate: refers to the inlet and outlet pipes, see the flow rate table.
②. Unit main pipe flow velocity: when the pipe diameter Rwanda Sugar ≦ 80, choose 1m/s, when ≧ 100, RW EscortsSee flow chart.
③. Corner hole flow velocity: maximum 6m/s (four inlets and outlets).
④. Flow velocity between plates: 0.4 ~ 0.8m/s (L type 0.8, M type 0.6, H type 0.4).
2. Heat exchange area:
Refers to the area of the heat exchanger. The area of the single plate * the number of heat exchange plates involved (the total number of plates minus two)
① Calculation of the heat exchange area:
Heat exchange area = heat transfer amount/heat transfer coefficient/logarithmic average temperature difference/fouling coefficient
②. Calculation of heat transfer amount:
Change Rwandans EscortHeat = building area * heating target (i.e. heat load, see target table)
3. Media parameters:
① , District heating: hot gas heating/geothermal heating: 110/75 ℃ – 50/75
②. District heating: geothermal heating: 110/75 ℃ – 40/50 ℃
③. Building air conditioning: fan coil heating: 110/75 ℃ – 50/60 ℃
Rwanda Sugar ④. Domestic hot water : Rwandans Escort Bath, kitchen, laundry room: 70/50 ℃ – 10/55 ℃
⑤. Swimming pool water supply: swimming Pool constant temperature water supply: 110/70 ℃ – 10/40 ℃
⑥, Rwanda Sugar Daddy Super high-rise air conditioning and refrigeration: cold water conversion : 7/11 ℃ – 8/Rwandans Sugardaddy12 ℃
Methods and formulas for plate heat exchanger selection calculation Nowadays, software selection is generally used for plate heat exchanger selection calculations. The conventional hand calculation methods and formulas are as follows:
(1) Find the heat load Q
Q=G.ρ.CP.Δt
(2) Find the inlet and outlet temperatures of hot and cold fluids
t2 =t1+ Q /G .ρ .CP
(3) Hot and cold fluid flow rate
G=Q / ρ .CP .(t2-t1 )
(4) Find the uniform temperature difference Δtm
p> Δtm=(T1-t2)-(T2-t1)/In(TRW Escorts1-t2)/(T2- t1) or Δtm=(T1-t2)+(T2-t1)/2
(5) Select plate type
If all plate types are selectedWhen completed, the results will be analyzed.
(6) From the K value range, calculate the plate number range Nmin, Nmax
Nmin = Q / Kmax .Δtm .F P .β
Nmax = Q / Kmin .Δtm .F P .β
(7) Get the number of plates N (Nmin≤N≤Nmax)
If N has reached NmaxRwanda Sugar Daddy
a>, do (5).
(8) Take the process combination form of N. If the combination form is finished, do (7).
(9) Find Re, Nu
Re = W .de/ ν
Nu =a1.Rea2.Pra3
(10) Find a, K heat transfer area F
p> a = Nu .λ/ de
K= 1 / 1/ah+1/ ac+γc+γc+δ/λ0
F=Q /K .Δtm .β
( 11) Calculate the required number of plates NN from the heat transfer area F NN
NN= F/ Fp+ 2
(12) If N
(13) Calculate the pressure drop Δp
Eu = a4.Rea5
Δp = Eu .ρ.W2 .ф
Rwandans Sugardaddy(14) If Δp>Δ Yes, do (8);
If Δp ≤ Δ Yes, record the result and do (8).
Note: 1. (1), (2), and (3) are calculated based on known conditions.
2. When T1-t2=T2-t1, use Δtm = (T1-t2)+(T2-t1)/2
3. The modification coefficient β is generally 0.7~0.9.
4. Pressure drop modification coefficient ф, single process ф = 1 ~ 1.2, two process, three process ф = 1.8 ~ 2.0, four process ф = 2.6 ~ 2.8.
5.a1, a2, a3, a4, a5 are constant coefficients.
Choosing a plate heat exchanger means choosing the area of the plates. There are two important ways to choose it, but these two All are difficult to understand. The simplest is to apply the formula:
Q=K×F×Δt
Q——heat load
K——heat transfer coefficient
F—— Heat exchange area
Δt——Heat transfer temperature RW Escorts difference (commonly used logarithmic temperature difference)
Heat transfer coefficient Depending on the structure of the heat exchanger itself, each plate with different flow channels has its own empirical formula. If it is not strict, it can be 2000~3000. The finally calculated area of the plate exchange must be multiplied by a certain coefficient, such as. 1.2.
Application of plate heat exchanger in heat circulation field
District heating system
Combined heat and power system
Geothermal water heating system
Instantaneous domestic hot water system
Instant heating feature
Guaranteed useRwanda Sugar Daddy Households can have hot water supply anytime and anywhere. The system is compact and does not require storage tanks. It requires a larger boiler capacity and a larger heat exchanger. .
Semi-instantaneous domestic hot water system
Semi-instantaneous heating characteristics
It requires a smaller boiler capacity and a smaller heat exchanger. Bacteria are easy to grow in the storage tank and require additional Storage tanks are installed in the place.
Swimming pool constant temperature maintenance system
Solar hot water system
Cooling and air conditioning system
Condenser side utilization:
1 Cooling tower water cooling condensed water
2 Sea water, river water or well water cooling condensed water
3 Ethylene glycol cooling condensed water
4 Short circuit refrigeration unit RW EscortsSystem
5 Underground cooling/heat source system
6 Heat recovery system
The condensate water side heat exchanger can play the following roles:
Protect the condenser from Contamination, scaling and corrosion
Replace the condenser with cooling water side pressure
Can be used during the seasonDo not run the refrigeration unit when conditions permit
Able to achieve heat recovery
Save expensive additives
Cooling tower water cooling condensed water
Seawater, river water, or well water cooling condensed water
Ethylene glycol cooling condensed water
Short-circuit refrigeration unit system
Groundwater cooling/heat source system
Heat recovery system
Utilization of evaporation side:
1 Pressure relay system
2 Separate cooling circulating water (no pressure relay function)
3 Ice storage system
4 District cooling system
5 Ceiling cooling system
Evaporation The heat exchanger on the unit side can play the following roles:
Prevent the refrigeration unit from being exposed to high pressure (pressure relay system)
a>Reduce the use of expensive and inefficient additives
Separate the cooling water system to ensure that the local system is highly clean (electronic components give birth)
Reduce the damage and loss caused by leakage
Pressure Relay system
Separate cooling circulating water system
Ice storage system
Basic elements of ice storage system design:
Settings Rwanda Sugar Air conditioning requirements
Operation plan
Full ice storage system
Partial ice storage system
Refrigeration unit as the main system
Storage Rwandans EscortIce-based system
District cooling system
Ceiling cooling system
Other application plans for air conditioning systems
1 Summer and summer cooling and heat conversion
p> 
2 Chilled water pre-cooling system
Advantages of plate heat exchangers in cooling and air conditioning systems
1. High heat transfer coefficient, logarithmic temperature difference can reach 0.5 degrees.
2. Small size , light weight, easy to install, can be placed on the equipment layer
3. Easy to install, easy to clean external dirt
4. Sturdy structure, can withstand high working pressure, up to 3.0MPa. > 5. High heat exchange efficiency, reduced operating costs
6. Low fixed investment
Basic principles of plate heat exchange units
The high-temperature water (secondary return water) flowing through the user’s heat sink passes through After the filter is decontaminated, it is pressurized by the circulation pump and enters the heat exchanger. RW Escorts receives the heat released by the primary heating medium and reaches the water supply setting. After the temperature is reached, it flows to the heating pipe network to provide heat to users;
The source flows through the primary heat network (primary water), passes through the filter, the regulating valve, and enters the heat exchanger to release heat (secondary water). It returns to the heat source (secondary return water) from the heat medium return pipe to be heated and then participates in circulating heat exchange again;
The water replenishment pump performs constant-pressure replenishment of the secondary circulating water system in a timely manner according to the operating conditions of the system.
Review editor: Tang Zihong
Original title: Technology: Design selection of plate heat exchangers and application of heat flow fields
Article Source: [Microelectronic Signal: Communication Power Technology, WeChat Official Account: Communication Power Technology] Welcome to add tracking and follow! Please indicate the source when transcribing and publishing the article.
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