A heat exchanger sizing calculator is a tool used to determine the required size of a heat exchanger based on various inputs. Heat exchangers are essential in many industries for transferring heat between two or more fluids. The right size ensures efficiency and effectiveness in thermal management.
Purpose and Functionality
The primary goal of a heat exchanger sizing calculator is to help engineers and designers select the correct size of a heat exchanger. This is crucial because an improperly sized heat exchanger can lead to inefficiency, higher energy costs, and potential equipment failure. The calculator takes into account different factors like heat duty, temperatures, and fluid properties to determine the necessary heat transfer area.
Inputs Required
To use the calculator, you need to provide the following inputs:
- Heat Duty (Q): The amount of heat that needs to be transferred, typically measured in kilowatts (kW) or BTU/hr.
- Inlet and Outlet Temperatures (T1, T2): The temperatures of the hot and cold fluids entering and leaving the heat exchanger, measured in degrees Celsius (°C) or Fahrenheit (°F).
- Specific Heat (Cp): The heat capacity of the fluid, measured in kJ/kg·°C or BTU/lb·°F.
- Density (ρ): The mass density of the fluid, measured in kg/m³ or lb/ft³.
- Flow Rates (m1, m2): The mass flow rates of the hot and cold fluids, measured in kg/s or lb/hr.
- Overall Heat Transfer Coefficient (U): The heat transfer coefficient for the exchanger, measured in W/m²·°C or BTU/hr·ft²·°F.
Calculations
The calculator uses a formula to determine the required heat transfer area. The main steps are:
- Calculate the Log Mean Temperature Difference (LMTD):
- ΔT1 = Th,in−Tc,outT_{h,\text{in}} – T_{c,\text{out}}Th,in−Tc,out
- ΔT2 = Th,out−Tc,inT_{h,\text{out}} – T_{c,\text{in}}Th,out−Tc,in
- ΔTlm = ΔT1−ΔT2ln(ΔT1ΔT2)\frac{\Delta T1 – \Delta T2}{\ln \left( \frac{\Delta T1}{\Delta T2} \right)}ln(ΔT2ΔT1)ΔT1−ΔT2
- Calculate the Required Area (A):
- A = QU⋅ΔTlm\frac{Q}{U \cdot \Delta Tlm}U⋅ΔTlmQ
Step-by-Step Example
Suppose you have the following data:
- Heat duty Q=100 kWQ = 100 \text{ kW}Q=100 kW
- Inlet temperatures: Th,in=120∘CT_{h,\text{in}} = 120^\circ\text{C}Th,in=120∘C, Tc,in=30∘CT_{c,\text{in}} = 30^\circ\text{C}Tc,in=30∘C
- Outlet temperatures: Th,out=90∘CT_{h,\text{out}} = 90^\circ\text{C}Th,out=90∘C, Tc,out=60∘CT_{c,\text{out}} = 60^\circ\text{C}Tc,out=60∘C
- Overall heat transfer coefficient U=500 W/m2⋅∘CU = 500 \text{ W/m}^2\cdot^\circ\text{C}U=500 W/m2⋅∘C
1. Calculate ΔT1 and ΔT2:
- ΔT1 = 120−60=60∘C120 – 60 = 60^\circ\text{C}120−60=60∘C
- ΔT2 = 90−30=60∘C90 – 30 = 60^\circ\text{C}90−30=60∘C
2. Calculate LMTD:
- ΔTlm = 60−60ln(6060)\frac{60 – 60}{\ln \left( \frac{60}{60} \right)}ln(6060)60−60
- As ΔT1 equals ΔT2, the LMTD simplifies to ΔT1 or ΔT2, which is 60°C.
3. Calculate Required Area:
- A = 100,000500⋅60≈3.88 m2\frac{100,000}{500 \cdot 60} \approx 3.88 \text{ m}^2500⋅60100,000≈3.88 m2
Relevant Information Table
| Parameter | Value | Unit |
|---|---|---|
| Heat Duty (Q) | 100 | kW |
| Inlet Temperature (T1) | 120 | °C |
| Outlet Temperature (T2) | 90 | °C |
| Overall Heat Transfer Coefficient (U) | 500 | W/m²·°C |
| Required Area (A) | 3.88 | m² |
Conclusion
A heat exchanger sizing calculator is a valuable tool for designing and selecting heat exchangers. By inputting relevant data such as heat duty, temperatures, and fluid properties, users can determine the appropriate size of the heat exchanger. This ensures efficient heat transfer and helps prevent problems associated with incorrect sizing. Proper use of the calculator contributes to better system performance and energy savings.