1. Plate heat exchangers definition
What is a plate heat exchanger ?
Plate and frame heat exchangers have a very specific design compared to other each exchangers : the fluid is split into wide but narrow channels in between thin plates. This allows to have a very high heat exchange coefficient and as a consequence a rather compact heat exchanger compared to other designs which can make them an interesting proposal when space or costs are a constraint. However such a design leads as a consequence to high pressure drop which will limit the application when high flow rates are involved.
This kind of heat exchangers have especially been popularized by the company Alfa Laval, people sometimes referring them as "Alfa Laval Plate Heat Exchanger". The most common design is to have the plates pressed against each other with gaskets in between. Such a design allows to open and clean very easily the exchanger which will be appreciable in situations where high fouling is expected or if regular cleaning is required for hygiene reasons (food industry). Using gaskets will limit the operating pressure and temperature so other designs with welded plates exist (brazed plate heat exchangers). They can operate in more extreme conditions but cannot be open for inspection and cleaning.
2. Calculation procedure : plate heat exchanger sizing
How to design a plate heat exchanger ?
2.1 STEP 1 : get the design data
The following data must be defined in order to size a plate and frame heat exchanger :
- Fluid properties (viscosity, specific heat... if possible as a function of temperature)
- Inlet and outlet temperature of each fluids (note : the procedure here is to size a heat exchanger knowing those data, but it can be adapted after, using Excel, to calculate the outlet temperature knowing the characteristics of the heat exchanger for example)
- Inlet pressure of fluids
- Allowable pressure drop
2.2 STEP 2 : calculate the required heat flux
The heat flux can be calculated knowing the flowrate, the in and out temperatures and the specific heat of the fluid, either on hot or cold side.
With
mc = mass flowrate on cold side (kg/s)
Cpc = specific heat of cold fluid
Tco = outlet temperature of cold side (K)
Tci = inlet temperature of cold fluid (K)
mh = mass flowrate on hot side (kg/s)
Cph = specific heat of hot fluid (J/kg/K)
Tho = outlet temperature of hot side (K)
Thi = inlet temperature of hot fluid (K)
It is then possible to approximate the size of the heat exchanger by estimating the overall heat transfer coefficient H.
H for plate heat exchanger is often in between 2 to 7 kW.m2.K-1.
H = overall heat exchange coefficient (kW.m2.K-1)
S = area of the heat exchanger (m2)
ΔTml (K)
The value of S can thus be calculated, as a 1st approximation of the heat exchanger size.
2.3 STEP 3 : calculating the number of plates required
This stage requires to have some references from suppliers, especially the size of plate they can supply, the max size of the heat exchanger when using a given plate, the design of the plate as well as the max flow the heat exchanger can handle.
From there, the Engineer can chose a plate size, design, and calculate the number of plates required.
N = S/s
With
N = number of plates required
S = total heat exchange area (m2)
s = size of a single plate (m2)
It is also possible to calculate the number of channels : n = (N-1)/2
2.4 STEP 4 : confirmation of the heat exchanger size
Now that a rough design of the plate and frame heat exchanger has been done, it is required to go in details of the many options available for the plates and use correlations that will allow to recalculate the heat transfer coefficient and then a required exchange area. The calculation will then be iterative until the calculated heat exchange area is equal to the assumed area.
A correlation giving the Nusselt number can be used :
With
Nu = number of Nusselt (-) = h.Dh/μ
Re = Reynolds number (-) = ρ.u.Dh/μ
a = coefficient depending on the corrugation of the plates (-)
b = coefficient depending on the corrugation of the plates (-)
Pr = Prandtl number = μ.Cp/λ
Prw = Prandtl number at the plate (wall) conditions
And
h = heat transfer coefficient (W.m-2.K-1)
μ = viscosity of the fluid (Pa.s)
ρ = density of the fluid (kg/m3)
u = velocity of the fluid in between 2 plates (m/s)
Cp = specific heat of the fluid (J/kg/K)
λ = thermal conductivity (W/m/K)
Dh = hydraulic diameter = [4*l*dplate] / [2*(l+dplate)] (m)
l = width of the plates (m)
dplate = gap in between 2 plates (m)
a and b depends on α the angle of the corrugations on the plates. The following table is from [Aydin] which is taking its source from [Kakac]
| Corrugation angle in ° | Re | a | b |
| <30 | <10 | 0.718 | 0.349 |
| <30 | >10 | 0.348 | 0.663 |
| 45 | <10 | 0.718 | 0.349 |
| 45 | 10-100 | 0.400 | 0.598 |
| 45 | >100 | 0.300 | 0.663 |
| 50 | <20 | 0.630 | 0.333 |
| 50 | 20-300 | 0.291 | 0.591 |
| 50 | >300 | 0.130 | 0.732 |
| 60 | <20 | 0.562 | 0.326 |
| 60 | 20-400 | 0.306 | 0.529 |
| 60 | >400 | 0.108 | 0.703 |
| >65 | <20 | 0.562 | 0.326 |
| >65 | 20-500 | 0.331 | 0.503 |
| >65 | >500 | 0.087 | 0.718 |
It is then possible to calculate the heat transfer coefficient h on both hot and cold side and then calculate the overall heat transfer coefficient H.
H = overall heat transfer coefficient (W.m-2.K-1)
hc = heat transfer coefficient on cold side (W.m-2.K-1)
Rfc = fouling resistance on cold side (K.W-1.m-2)
hh = heat transfer coefficient on hot side (W.m-2.K-1)
Rfh = fouling resistance on hot side (K.W-1.m-2)
e = thickness of the plates (m)
λ = thermal conductivity of the plate (W.m-1.K-1)
It is then required to compare H calculated with H assumed.
If Hcalculated = Hassumed, the calculation is valid, the size of the heat exchanger, with the total heat exchange area S is correct.
If Hcalculated ≠ Hassumed, then the calculation needs to be run again, this time using Hassumed as starting point, or, if values are really far, changing the design of the heat exchanger (plate size...) and running it again.
2.5 STEP 5 : Calculation of the pressure drop
The design defined in step 4 is only valid if the pressure drop on both sides is less than the allowable pressure drop. If yes, the design can be kept, if not, some design choices such as the size of the plate, corrugation, number of plates... Checking the pressure drop is especially important for gasketed plate heat exchanger which have a limited resistance to pressure compared to brazed plate heat exchangers.
2.6 STEP 6 : optimization and detail design
Even if the design done satisfies the process conditions, it may be possible to improve the design by making it less costly, more compact... the design procedure can then be re-run for the basic design calculated by changing the type of plate, size, number of plates...etc...
The procedure above will be helpful to get an idea but cannot be used to such details. It should be done with a specialized company. Detail design and construction drawing must always be done with the support of such a company.
Source
[Aydin] Report to department of chemical engineering, Middle East Technical University, Plate Heat Exchanger design, Aydin et al., 2016, https://www.slideshare.net/ervaldi/plate-type-heat-exchanger-design-62443113
[Kakac] Heat Exchangers, Selection, Rating and Thermal Design, Kakac et al, CRC Press
FAQs
How is plate heat exchanger efficiency calculated? ›
- 1 deg.C.
- 2 deg.C.
- 3 m3/h.
- 5 deg.C.
- 4 deg.C.
- 6 m3/h. Q1 = Density x Heat capacity x ( 1 - 2 ) x 3 / 3600 [kW] Q2 = Density x Heat capacity x ( 5 - 4 ) x 6 / 3600 [kW] (For water, density is 1000, and heat capacity is 4.186kJ/kg deg. C.)
There are generally two ways to evaluate the performance of heat exchangers. One is Log Mean Temperature Difference, abbreviated as LMTD, and the other is the Effectiveness NTU-method, denoted by ε-NTU.
How many plate heat exchanger do I need? ›Many customers ask, “how do you know what size plate exchanger to install in your domestic hot water tank?” A simple rule of thumb is 2 to 3 people in one house will determine a 10 plate. A 10 plate heat exchange is enough for 2 and 3 people.
What is the formula of plate? ›Width * Length * Thickness * Density = Weight.
How are plate rates calculated? ›To calculate Plate Cost, first you need to know the As Served cost of each ingredient in your menu item. The As Served cost is the cost of a single serving of that item. In order to find those costs, take the cost of a product and divide it by the number of portions you make from the item.
What is a good heat loss calculation? ›The general heat loss formula is: Q=U*A*ΔT, or in plain words, the heat loss of an area of size A is determined by the U value of the materials and the difference in temperature between inside and out (that is the difference in temperature of the two surfaces, not the two air temperatures, which might not be quite the ...
How is heat quality calculated? ›We wish to determine the value of Q - the quantity of heat. To do so, we would use the equation Q = m•C•ΔT. The m and the C are known; the ΔT can be determined from the initial and final temperature.
How can I improve my heat exchanger design? ›- Online and Offline Cleaning. ...
- Maintaining Heat Exchanger. ...
- Periodic Cleaning. ...
- Cleaning the PHE Manually. ...
- Minimizing the Fouling Factor. ...
- Analyzing and Addressing Issues in Heat Exchanger Efficiency.
Design Analysis: Calculating Heat Exchanger Area - YouTube
How many plates are in a plate heat exchanger? ›The two plates are welded together and gasketed to other pairs within the heat exchanger. This results in an easy to service heat exchanger and you're able to transfer more fluids throughout the system. Semi-Welded heat exchangers are great for transferring expensive materials due to their low risk of fluid loss.
What is 2/3 rule in heat exchanger? ›
The “two-thirds rule” from API RP 521 states: For relatively low-pressure equipment, complete tube failure is not a viable contingency when the design pressure of the low-pressure side is equal to or greater than two-thirds the design pressure of the high-pressure side.
Which heat exchanger design is the most efficient? ›Plate exchanger is the most efficient due to turbulent flow on both sides. High heat-transfer coefficient and high turbulence due to even flow distribution are important. However, a plate heat exchanger regenerator is restricted to low viscosities.
How are plate sizes calculated? ›Multiply the length and width, if they are given in inches, by the factor 2.54 to convert the dimensions into centimeters. For example, the plate dimensions are 5-by-3 inches that will be converted to 12.7 and 7.62 cm. Multiply the length by its width to calculate the plate surface area in square centimeters.
How many is 4 plates? ›Two plates is 225 pounds. Three plates is 315. Four plates is 405.
How do you calculate plate spacing? ›The area of the plate is determined by the common formula A=πr 2. Plug in the numbers to get A = π(0.089) 2 = 0.0249m 2. Convert the plate spacing (1mm) to meters by dividing by 1000.
How do I calculate rates? ›- Identify the measurements being compared. ...
- Compare the measurements side-by-side. ...
- Simplify your calculations by the greatest common factor. ...
- Express your found rate. ...
- Find the difference between the two data values. ...
- Divide the difference by the original number. ...
- Multiply the results by 100.
Tectonic plates move at rates that vary from less than 6 feet per 100 years to 66 feet per 100 years (1.83–20.1 m/100 years); and these rates may have been faster in the ancient past. At an average rate of 33 feet per 100 years (about 10 cm/year), a tectonic plate can move 62.5 miles (about 100 km) in 1 million years.
What is the approximate rate of plate? ›Plate Tectonics - A Scientific Revolution. The majority of the research shows that the plates move at the average rate of between approximately 0.60 cm/yr to 10 cm/yr.
How do you calculate heat loss in heat exchanger? ›- Q = U x A x ΔTm = The log mean temperature difference ΔTm is:
- ΔTm = (T1 – t2) – (T2 – t1)
- = °F. Where:
- T1 = Inlet tube side fluid temperature; t2 = Outlet shell side fluid temperature;
- ln (T1 – t2) (T2 – t1)
The value of sensible heat ratio is about 0.75 for the commonly used conventional vapor compression air-conditioning systems which means that 75% capacity of the system is used to control the sensible load and the remaining 25% for the latent load.
What is the most effective means of heat loss? ›
First, because the amount of energy it takes to vaporize water is so high (2.4 kJ/g), evaporation of water from skin or lungs is the most efficient way to lose body heat (Romanovsky, 2007a).
How is heat transfer per unit calculated? ›Q/t = kA((T1-T2)/l), where Q/t is the rate of heat transfer, k is the thermal conductivity of the material, A is the cross-sectional area, T1-T2 is the temperature difference, and l is the thickness.
How do you calculate specific heat capacity? ›GCSE Science Revision Physics "Specific Heat Capacity" - YouTube
How is heat capacity measured? ›To calculate heat capacity, use the formula: heat capacity = E / T, where E is the amount of heat energy supplied and T is the change in temperature. For example, if it takes 2,000 Joules of energy to heat up a block 5 degrees Celsius, the formula would look like: heat capacity = 2,000 Joules / 5 C.
What are the main factors to be considered for a heat exchanger design? ›Designing heat exchanger
The main factors affecting the performance heat exchanger tubes include: fluid velocity, tube diameter, converter tube shape (U or cross shape), converter layout order (horizontal or vertical), and Venting valve, material of tube sheet and channel and location order of input channel.
Increasing baffle cut or increasing shell side passes by increasing number of baffles will increase the velocity too if you can change the tube bundle construction. If you could have cooling water on tube side, then you could block some tubes to increase the velocity. This is done many a times.
How do you increase heat exchanger capacity? ›Increasing heat exchanger performance usually means transferring more duty or operating the exchanger at a closer temperature approach. This can be accomplished without a dramatic increase in surface area. This constraint directly translates to increasing the overall heat transfer coefficient, U.
Why plate heat exchanger is more efficient? ›A plate heat exchanger is the lowest cost option because it can achieve high heat transfer coefficients — with pure counter current flow — giving the most efficient heat transfer and lowest surface area.
Why plate type heat exchanger is used? ›Advantages of plate heat exchanger:
Heat transfer precision – improved temperature approach, true counter-current flow, 80-90% less hold-up volume. Low cost - low capital investment, installation costs, limited maintenance and operating costs. Greatest reliability - less fouling, stress, wear, and corrosion.
Plate heat exchangers are now common and very small brazed versions are used in the hot-water sections of millions of combination boilers. The high heat transfer efficiency for such a small physical size has increased the domestic hot water (DHW) flowrate of combination boilers.
What is 10 13 rule in heat exchanger? ›
Increase the shell-side design pressure up to 10/13 of the tube-side design pressure. (The logic behind this “10/13” rule is that the hydrotest is done, as per ASME, at 1.3-times the design pressure—it was popularly known as the ⅔ rule based on old code hydrotest pressure before the year 2000).
What are the 3 types of heats? ›We are here to clear the air on the three main types of heat provided by household heaters: convection, conduction and radiant - helping you to make a more informed decision.
How do you calculate plating area? ›Simply place an imaginary grid of 1” squares over the part, and count the whole squares. Then go around the perimeter and add up all the squares that are more than ½ full. Divide the total by 2 and add this to your total of completely filled squares.
How many plates are on a heat exchanger plate? ›The two plates are welded together and gasketed to other pairs within the heat exchanger. This results in an easy to service heat exchanger and you're able to transfer more fluids throughout the system. Semi-Welded heat exchangers are great for transferring expensive materials due to their low risk of fluid loss.
What is plate heat exchanger? ›A plate heat exchanger is used to transfer heat energy from one fluid to another. These fluids never encounter each other due to being separated by the heat exchanger.
How do you calculate plate development length? ›We go better with a practical example; with a thickness of 1,5 m/m and to calculate the development of the following sheet (see sketch) we will do the next calculation: 70 – (2 x 1,5) + 25 – (2 x 1,5) + 15 = 104 m/m is the length of the piece (before being bended).
How do you calculate the thickness of a plate? ›How to calculate the required bearing plate thickness to support a steel ...
What is the formula to calculate plate weight? ›∴ Weight of steel plate = Volume of steel plate x Density of steel. Weight of steel plate = 0.07 x 7850 = 549.5 Kg. Similarly, you can calculate the weight of different thicknesses of steel plates.
Why plate heat exchanger is more efficient? ›A plate heat exchanger is the lowest cost option because it can achieve high heat transfer coefficients — with pure counter current flow — giving the most efficient heat transfer and lowest surface area.
Why plate type heat exchanger is used? ›Advantages of plate heat exchanger:
Heat transfer precision – improved temperature approach, true counter-current flow, 80-90% less hold-up volume. Low cost - low capital investment, installation costs, limited maintenance and operating costs. Greatest reliability - less fouling, stress, wear, and corrosion.
Which heat exchanger design is the most efficient? ›
Plate exchanger is the most efficient due to turbulent flow on both sides. High heat-transfer coefficient and high turbulence due to even flow distribution are important. However, a plate heat exchanger regenerator is restricted to low viscosities.
What is a plate heat exchanger made of? ›The most frequently used materials for the plates are stainless steel (AISI 304, 316), titanium and aluminium. The corrugation on the plates forces the fluid on a tortuous path, setting a space between two adjacent plates b, from 1 to 5 millimeters.
What is hot plate principle? ›It is based on the principle that when rodents are placed onto a hot surface they will initially demonstrate the aversive effects of the thermal stimulus by licking their paws and, ultimately, by overt attempts to escape the environment (jumping).
What is 2/3 rule in heat exchanger? ›The “two-thirds rule” from API RP 521 states: For relatively low-pressure equipment, complete tube failure is not a viable contingency when the design pressure of the low-pressure side is equal to or greater than two-thirds the design pressure of the high-pressure side.
What is the most common type of heat exchanger? ›The shell-and-tube heat exchanger is probably the most common type found in industry. It is widely used in the process industries as well as in many types of HVAC equipment.
What is heat exchanger rating? ›In a rating problem, the geometry and size of the heat exchanger are fully specified. Entering flow rates and fluid temperatures are known. The job is to calculate the thermal effectiveness (heat transferred) and pressure drop of each stream. This is a quite straightforward problem, with one exception.