Plate Heat Exchanger Design Equation & Calculation Method
Plate Heat Exchanger Calculation method or some call it sizing of a plate heat exchanger can be simplified to two formula and by using constant figures for certain fluid combinations.
Step ➀ - Determine Heat Load
Qhot = ṁhot Cphot (Tin hot - Tout hot) = Qcold = ṁcold Cpcold (Tout cold - Tin cold)
Q: Heat load, kW
ṁ : Flow rate, kg/h
Cp : Specific heat, kJ/kg℃
T : Inlet/outlet temperature, ℃
ṁ = W (m3/h) x ρ (kg/m3)
W : Volumetric flow rate
ρ : Density
This calculation is done at first to determine how much Heat Load we are considering for heat transfer within this equipment. Your purpose maybe cooling, or heating, or even both at the same time. The heat load of cooling means the amount of heat load removed from the cold fluid during heat transfer in the equipment. Likewise, heat load heating means how much heat receive on the cooling fluid side. Based on this understanding, the amount heat removed from the hot stream is equal to the amount received for the cold stream.
Step ➁ - Determine Logarithmic Mean Temperature Difference (LMTD)
T: Temperature, ℃
if Tin hot - Tout cold = Tout hot - Tin cold ,
ΔT = Tin hot - Tout cold = Tout hot - Tin cold
The logarithmic mean temperature difference (also known as log mean temperature difference, LMTD) is used to determine the temperature driving force for heat transfer in flow systems, most notably in heat exchangers. The LMTD is a logarithmic average of the temperature difference between the hot and cold feeds at each end of heat exchanger. For a given heat exchanger with constant area and heat transfer coefficient, the larger the LMTD, the more heat is transferred.
Step ➂ - Determine surface area required
Q = A U ΔT
Q : Heat Load, kW (Amount of heat that will be transferred for the equipment)
U : Heat Transfer Coefficient W/m2K (Varies depend on combination of fluid, plate material, thickness, fouling factors as well as corrugation design that affect turbulence and heat transfer ability)
ΔT :LMTD, ℃ (value as per step ➁)
A : Heat transfer area, m2 (This value to be determined)
This formula purpose is for us to determine Surface area (A) of the plates required, considering values of the heat transfer.
Plate Heat Exchanger Calculation Example
Water-Water application
| Water | 25 ℃ → 15 ℃ | 150 m3/h |
| Pure Water | 12 ℃ ← 7 ℃ | *** m3/h |
① Heat Balance
Q = ṁhot Cphot (Tin hot - Tout hot) = ṁcold Cpcold (Tout cold - Tin cold)
= [150 x 1000] x 4.186 (25 – 15) = [Wcold x 1000] x 4.186 (12 – 7)
= 1,744 kW ↔ Wcold = 300 m3/h
② Logarithmic Mean Temperature Difference (LMTD)
③ Heat Transfer Principal Equation
Q = A U ΔT = A x 5,000 x 10.3 = 1,744,167
| Application | Approx. U Value |
|---|---|
| Water - Water | 5,000 - 8,000 W/m2 . ℃ |
| Water - Brine | 2,000 - 3,000 W/m2 . ℃ |
| Steam - Water | 3,000 - 4,000 W/m2 . ℃ |
| Oil - Water | 300 - 800 W/m2 . ℃ |
- Approximate U-Value for difference applications
- Apply in Step ➂
④ Number of Heat Transfer Unit (NTU)
If less than 1.5 = LOW (Select LX-Series)
⑤ Number of Plates per unit
Pressure Drop
While we can determine the minimum surface area required for the heat transfer. In actual operation, pressure drop is an important factor that affects flow rate. PHE with narrow gaps and corrugation will contribute to certain amount of pressure drop. The accumulated pressure drop across the flow line against the pump will result of the flow rate.
Prior to sizing any new PHE, sales engineer will confirm with user what is the allowable pressure drop. User will confirm on the pump ability against all the pressure drop include PHE’s contribution, and see the flow rate that can be achieved. If this step is not conducted properly, it will result in lower flowrate due to too much pressure drop in the line against the pump. Lower flowrate also will cause heat transfer not achievable. These are the common error when heat exchanger is sized smaller to cost down but cannot achieve performance.
In order to achieve reasonable pressure, drop, Plate heat exchanger has many different gaps, corrugation angles to meet customer needs. Sometimes, number of plates are added to increase plate channels to reduce pressure drop to the allowable. These are the important things to consider other than the calculation.
Web Simulator
In recent years designs are more transparent and also users can do it by themselves using our web simulator. Accurate values are preloaded into the software that anyone can use it. Simulation can be done without tedious calculation of heat transfer coefficient and allowable pressure drop.
FAQs
How is heat exchanger design calculated? ›
Solution: The surface area per tube will be: Sa = πDL = π (3/12) (10) ft² = 7.854 ft² - (D – tube diameter in ft). The number of tubes required would thus be: n = 178.7 ft² = 22.7 tubes (23 or 24 tubes).
How do you calculate heat capacity of a heat exchanger? ›Heat capacity is the amount of heat necessary to change the temperature of a substance by 1.00°C. In equation form, heat capacity C is C=mc, where m is mass and c is specific heat.
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 10 13 Rule 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).
How do you calculate design flow rate? ›Design flow calculation is as follows: Design flow = PDWF + GWI + RDI = 14.9 + 0.6 + 7.5 = 23.0 L/s, which, for this example, is equivalent to 1.5*PDWF.
How do you calculate heat exchanger effectiveness? ›- From fluid's properties, calculate the maximum (qmax) and actual heat transfer (q).
- Determine the ratio between the heat capacities of the fluids, Cr = Cmin / Cmáx.
- Calculate the effectiveness as the ratio of the heats, ε = q/qmax.
The formula is: Room volume x Delta T x Air Changes per Hour x . 018.
What is the formula for calculating heat capacity? ›Heat Capacity of an object can be calculated by dividing the amount of heat energy supplied (E) by the corresponding change in temperature (T). Our equation is: Heat Capacity = E / T.
What is the easiest way to calculate specific heat capacity? ›The specific heat capacity is the heat or energy required to change one unit mass of a substance of a constant volume by 1 °C. The formula is Cv = Q / (ΔT ⨉ m) .
How do I calculate heat capacity? ›q = m×sp_heat×Δt where: q = amount of heat, measured in joules(J). C = 1 degree K. m = mass, measured in grams Δt = temperature change, °C or K. The heat capacity, C, of a substance is the amount of heat required to raise the temperature of a given quantity of the substance by 1 degree.
What is heat exchanger rules of thumb? ›
In heat transfer engineering, rules of thumb are used to estimate the optimum design performance of a heat exchanger; weighing the capital cost (CAPEX) with the operating cost (OPEX) of its performance. Many times a minimum approach temperature (pinch temperature) is used to approximate the optimum design point.
Which two standards are generally used for heat exchanger design? ›There are various standards, codes and quality control guidelines that apply to the design and manufacture of heat exchangers. These include industry codes such as ASME, PD500 and EN13445, manufacturing standards like TEMA and API, plus standards such as ISOs.
What is the maximum temperature difference in a heat exchanger? ›WHAT TEMPERATURES AND PRESSURES CAN A HEAT EXCHANGER WITHSTAND? They range up to 1000°C and 1000 bars. It all depends on the technologies used.
What is an acceptable pressure drop in plate heat exchanger? ›If it is possible to increase the allowable pressure drop, and inci- dentally accept higher pumping costs, then the heat exchanger will be smaller and less expensive. As a guide, allow- able pressure drops between 20 and 100 kPa are accepted as normal for water/water duties.
What is an acceptable pressure drop in heat exchanger? ›Normal operation: 137.93 kPa (20 psi) Maximum: 689.66 kPa (100 psi) Pressure drop across heat exchanger: approximately 48 kPa (7 psi)
How do you calculate Reynolds number in heat exchanger? ›The Reynolds number (Re) of a flowing fluid is calculated by multiplying the fluid velocity by the internal pipe diameter (to obtain the inertia force of the fluid) and then dividing the result by the kinematic viscosity (viscous force per unit length).
How big of a plate exchanger do I need? ›Re: Sizing a plate heat exchanger? You will want to get a 5x12" or 5x13" plate. 20 plate will work fine unless you are very near the limits on boiler water flow. If you are, going with a 30 plate will usually work without needing to get a larger pump.
What formula is Q MC ∆ T? ›The amount of heat gained or lost by a sample (q) can be calculated using the equation q = mcΔT, where m is the mass of the sample, c is the specific heat, and ΔT is the temperature change.
What is the equation for the rate of plate motion? ›Remember, a rate of movement (velocity) can be calculated if you know the distance traveled and the time it took to make the "trip," according to the following formula: velocity = (distance traveled) / (travel time), or more simply, v = d / t.
What is the sizing of plated heat exchanger? ›Plate heat exchangers can vary significantly in size. Available sizes range from: 9.7 x 32 x 51 mm (or 0.97 x 3.2 x 5.1 cm) at the lower end. 524.4 x 112 x 24.1 mm (or 52.44 x 11.2 x 2.41 cm) at the higher capacity end.
Can you oversize a plate heat exchanger? ›
Going too big wont hurt anything but if you go too small you will have to replace it with a bigger one. also going oversize will get you a little hotter water on the secondary side.
How do you determine the shell diameter of a heat exchanger? ›The equivalent diameter is calculated along (instead of across) the long axes of the shell and therefore is taken as four times the net flow area as layout on the tube sheet (for any pitch layout) divided by the wetted perimeter.
How much flow is required for heat exchanger? ›In many process applications, a flow rate of 2.5 to 3 gal/min per cooling ton is sufficient to achieve turbulent flow through a heat exchanger.
How do you calculate specific heat capacity? ›The formula for specific heat capacity, C , of a substance with mass m , is C = Q /(m ⨉ ΔT) . Where Q is the energy added and ΔT is the change in temperature.
How to calculate temperature? ›The Temperature Conversion Formula
The conversion formulas we use are the standard ones that are used in most textbooks. To convert temperatures in degrees Fahrenheit to Celsius, subtract 32 and multiply by .5556 (or 5/9). To convert temperatures in degrees Celsius to Fahrenheit, multiply by 1.8 (or 9/5) and add 32.