How to calculate the heat exchanger area
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Does that person have a table for calculating heat exchangers? This post was last edited by The wise are free from confusion on 2009-1-4 09:57.]
Does this thing really need a table? It can be calculated just by doing the math casually
The heat exchange area is calculated by multiplying the outer diameter of the heat exchange tube by 3.14 and then by its length.
You might have misunderstood what the original poster meant! The poster probably needs the method for calculating the heat exchange area in thermodynamic calculations!
For thermal calculations, it’s better to ask in the process section; I don’t see any hope here
Thank you. Currently, waste engine oil is preheated using heat transfer oil (in a shell-and-tube configuration). I need help calculating the overall heat transfer coefficient K
In fact, what’s truly praiseworthy is having knowledge of high-end equipment, understanding the origins of various process parameters, and being aware of the complete design process behind such equipment. It is also necessary to learn more about technical skills
Those in charge of equipment don’t need to take this into account; as long as the process calculation requirements are met, that’s sufficient!
Search on the forum for common uses of pressure vessels. It’s in xls format; I don’t have it on my computer right now, so I can’t give it to you. Sorry!
Ultimately, it comes down to the selection of the heat transfer coefficient K value. Empirical values are generally used, and these must be verified through actual tests before a final decision can be made. Therefore, the empirical values provided in books can only serve as a reference.
Those who work with equipment also need to have some knowledge of manufacturing processes; otherwise, it’s impossible to communicate with customers. Only by knowing both oneself and the opponent can one succeed in every situation.
I’ll give you a few formulas; I hope they will be helpful to you. For floating-head heat exchangers and fixed-tube-sheet heat exchangers: A=πd(L-2δ-0.006)n. For vertical thermosyphon heat exchangers: A=πd(L-2δ-0.006). For U-tube heat exchangers: A=πd(L-δ-0.003)n. In these formulas, A represents the calculated heat exchange area in m2; d is the outer diameter of the heat exchanger in meters; L is the length of the heat exchange tubes in meters; δ is the thickness of the tube sheet in meters; and n is the number of rows of heat exchange tubes
To determine the design heat transfer area, you first need to know the total heat transfer amount, the average heat transfer temperature difference, the average heat transfer coefficient. There is also a heat transfer efficiency associated with the total heat transfer amount; the heat transfer area is equal to the total heat transfer amount divided by the temperature difference and then divided by the heat transfer coefficient. This value represents the design area. If you want to verify whether this area is correct, you can use the diameter of the tube multiplied by a coefficient, then multiplied by the length and by the total number of tubes – this method works as well too. The value of this coefficient varies depending on whether the diameter used in the calculation is the outer diameter or the inner diameter. I forgot to mention that 3.14 is also a factor that needs to be taken into account. Last edited by liulinger on 2009-1-4 15:20.]
Q=kA△T can be regarded as a general formula for heat transfer; it’s just that different correction factors are added in various situations. For the specific calculation method, refer to the process manual, which provides detailed step-by-step instructions and guidance on parameter selection. Good luck!
The heat transfer coefficient k in this case needs to be determined based on the different methods of collection as well as the different heat exchange media on both sides; the original poster can refer to heat exchange manuals for more information
No need for that. For thermodynamic formulas, it’s sufficient to consider the thermal resistance in a simple way
How can one determine the value of k in thermodynamic formulas without looking it up? The values obtained through pure calculation using these formulas differ significantly from those observed in practical applications!
Does it refer to the heat exchange area? This is simple. Perimeter of the outer surface of the heat exchange tube × Effective length of the heat exchange tube (this length does not include the thickness of the baffle plates or the length extending into the tube sheet) × Number of heat exchange tubes.
There are various types of heat exchangers made from polymer materials, such as tube bundle types, shell-and-tube types, etc.; they can be used for both heating and cooling. The method for calculating the heat exchange area is as follows:
I. Method for calculating the theoretical area
● Heating
1. Calculate the heat transfer amount Q (in W·h):
Q = 1.16β·γ·c·V · (T2 – T1)
Where β is the heat loss coefficient (1.1–1.3), γ is the density of the solution (kg/L), c is the specific heat capacity of the solution (kcal/kg), V is the volume of the solution (L), T1 is the initial temperature of the solution (°C), and T2 is the final temperature of the solution (°C).
2. Calculate the heat exchange area S (in m²):
S = Q / (ΔT·κ·h)
Where Q is the heat transfer amount (W·h), h is the heat exchange time (h), κ is the heat exchange coefficient (200–350 W/m²·°C), and ΔT is the average temperature difference (°C). The method for calculating ΔT is as follows:
– For heat exchange involving latent heat (e.g., when the heat medium is steam):
ΔT ≈ (Ty – Tx) / ln
Where Tz is the saturation steam temperature (°C), Tx is the initial temperature of the solution (°C), and Ty is the final temperature of the solution (°C).
– For heat exchange involving sensible heat (e.g., when the heat medium is hot water):
ΔT ≈ ln(T2/T1)
Where T1 is the inlet temperature of the heat medium (°C), T2 is the outlet temperature of the heat medium (°C), Tx is the initial temperature of the solution (°C), and Ty is the final temperature of the solution (°C).
● Cooling or freezing
1. Calculate the heat transfer amount q (in W):
q = β·V·I
Where β is an additional coefficient (1.1–1.3), V is the operating voltage (V), and I is the operating current (A).
2. Calculate the heat exchange area S (in m²):
S = q / (ΔT·κ)
Where q is the heat transfer amount (W), κ is the heat exchange coefficient, and ΔT is the average temperature difference (°C). The method for calculating ΔT is as follows:
– For direct cooling inside a tubular bundle:
ΔT ≈ (T2 – T1) / ln
Where T is the process temperature (°C), T1 is the inlet temperature of the coolant (°C), and T2 is the outlet temperature of the coolant (°C).
– For external circulation cooling in a shell-and-tube design:
ΔT ≈ ln(T2/T1)
Where T1 is the inlet temperature of the coolant (°C), T2 is the outlet temperature of the coolant (°C), Tx is the inlet temperature of the solution (°C), and Ty is the outlet temperature of the solution (°C).
★ Ln represents the natural logarithm.
★ T2 mainly depends on the relationship between the flow rate of the circulation pump and the heat transfer amount.
II. Method for verifying the calculated area
S = d × 3.14 × n × L × m
Where d is the nominal diameter of the capillaries (m), L is the average length of the capillaries (m), n is the number of capillaries per group of heat exchangers, and m is the number of groups of heat exchangers.
III. Notes
The heat exchange coefficient depends not only on the method of heat exchange, the material of the heat exchanger, and the specifications of that material (especially the wall thickness), but also on various factors such as the state of the solution (e.g., whether it is stirred or not). Generally, for heating with hot water or cooling with a refrigerant, the heat transfer coefficient can take the lower limit value ； For steam heating, the upper limit can be chosen
I. Method for calculating the theoretical area
● Heating
1. Calculate the heat transfer amount Q (in W·h):
Q = 1.16β·γ·c·V · (T2 – T1)
Where β is the heat loss coefficient (1.1–1.3), γ is the density of the solution (kg/L), c is the specific heat capacity of the solution (kcal/kg), V is the volume of the solution (L), T1 is the initial temperature of the solution (°C), and T2 is the final temperature of the solution (°C).
2. Calculate the heat exchange area S (in m²):
S = Q / (ΔT·κ·h)
Where Q is the heat transfer amount (W·h), h is the heat exchange time (h), κ is the heat exchange coefficient (200–350 W/m²·°C), and ΔT is the average temperature difference (°C). The method for calculating ΔT is as follows:
– For heat exchange involving latent heat (e.g., when the heat medium is steam):
ΔT ≈ (Ty – Tx) / ln
Where Tz is the saturation steam temperature (°C), Tx is the initial temperature of the solution (°C), and Ty is the final temperature of the solution (°C).
– For heat exchange involving sensible heat (e.g., when the heat medium is hot water):
ΔT ≈ ln(T2/T1)
Where T1 is the inlet temperature of the heat medium (°C), T2 is the outlet temperature of the heat medium (°C), Tx is the initial temperature of the solution (°C), and Ty is the final temperature of the solution (°C).
● Cooling or freezing
1. Calculate the heat transfer amount q (in W):
q = β·V·I
Where β is an additional coefficient (1.1–1.3), V is the operating voltage (V), and I is the operating current (A).
2. Calculate the heat exchange area S (in m²):
S = q / (ΔT·κ)
Where q is the heat transfer amount (W), κ is the heat exchange coefficient, and ΔT is the average temperature difference (°C). The method for calculating ΔT is as follows:
– For direct cooling inside a tubular bundle:
ΔT ≈ (T2 – T1) / ln
Where T is the process temperature (°C), T1 is the inlet temperature of the coolant (°C), and T2 is the outlet temperature of the coolant (°C).
– For external circulation cooling in a shell-and-tube design:
ΔT ≈ ln(T2/T1)
Where T1 is the inlet temperature of the coolant (°C), T2 is the outlet temperature of the coolant (°C), Tx is the inlet temperature of the solution (°C), and Ty is the outlet temperature of the solution (°C).
★ Ln represents the natural logarithm.
★ T2 mainly depends on the relationship between the flow rate of the circulation pump and the heat transfer amount.
II. Method for verifying the calculated area
S = d × 3.14 × n × L × m
Where d is the nominal diameter of the capillaries (m), L is the average length of the capillaries (m), n is the number of capillaries per group of heat exchangers, and m is the number of groups of heat exchangers.
III. Notes
The heat exchange coefficient depends not only on the method of heat exchange, the material of the heat exchanger, and the specifications of that material (especially the wall thickness), but also on various factors such as the state of the solution (e.g., whether it is stirred or not). Generally, for heating with hot water or cooling with a refrigerant, the heat transfer coefficient can take the lower limit value ； For steam heating, the upper limit can be chosen
The following is the formula for calculating the heat transfer coefficient K: 1/K = 1/α1 + R1 + δ/λ + 1/α2 + R2, where α1 is the heat transfer film coefficient on the high-temperature side； α2—Heat transfer film coefficient on the low-temperature side ； R1—High-temperature side fouling thermal resistance ； R2—Fouling thermal resistance on the low-temperature side ； δ—Heat exchange tube wall thickness ； λ—is the thermal conductivity of the heat exchange tube. As for the calculation of the heat transfer film coefficient on each side, it is quite complex. It’s definitely impossible to explain it here.