Heat Exchanger Flow Rate Calculations

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Heat Exchanger Flow Rate Calculator

Calculate Mass Flow Rate Based on Heat Load and Temperature Delta

Required Mass Flow Rate:
Please ensure all fields are filled correctly and temperatures are not equal.
function calculateFlowRate() { var Q = parseFloat(document.getElementById('heatLoad').value); var Cp = parseFloat(document.getElementById('specificHeat').value); var T1 = parseFloat(document.getElementById('tempInlet').value); var T2 = parseFloat(document.getElementById('tempOutlet').value); var resultBox = document.getElementById('flowResultBox'); var errorBox = document.getElementById('errorBox'); var flowOutput = document.getElementById('flowRateResult'); var volOutput = document.getElementById('volumetricResult'); // Reset displays resultBox.style.display = 'none'; errorBox.style.display = 'none'; // Logic: Q = m * Cp * dT -> m = Q / (Cp * dT) var deltaT = Math.abs(T1 – T2); if (isNaN(Q) || isNaN(Cp) || isNaN(T1) || isNaN(T2) || deltaT === 0 || Cp === 0) { errorBox.style.display = 'block'; return; } var massFlowRate = Q / (Cp * deltaT); // Assume water density roughly 1000 kg/m3 for volumetric estimation var volFlowLitersPerSec = massFlowRate; // kg/s to L/s for water var volFlowLitersPerMin = massFlowRate * 60; flowOutput.innerHTML = massFlowRate.toFixed(4) + " kg/s"; volOutput.innerHTML = "Approx. " + volFlowLitersPerMin.toFixed(2) + " L/min (for water-like fluids)"; resultBox.style.backgroundColor = "#e8f6f3"; resultBox.style.display = 'block'; }

Understanding Heat Exchanger Flow Rate Calculations

In thermal engineering, calculating the correct flow rate is critical for sizing pumps, pipes, and the heat exchanger itself. The relationship between heat transfer and fluid flow is governed by the conservation of energy principle.

The Fundamental Equation

Q = ṁ × Cp × ΔT

  • Q (Heat Transfer Rate): The total energy moved between fluids, usually measured in kiloWatts (kW).
  • ṁ (Mass Flow Rate): The mass of fluid passing a point per unit of time (kg/s).
  • Cp (Specific Heat Capacity): The amount of heat required to change the temperature of 1 kg of fluid by 1°C. For water, this is approximately 4.18 kJ/kg·°C.
  • ΔT (Temperature Difference): The difference between the inlet (T1) and outlet (T2) temperatures of the fluid.

Practical Example

Suppose you have a cooling process where you need to remove 100 kW of heat. You are using water (Cp = 4.18) entering at 15°C and leaving at 25°C.

  1. Calculate ΔT: 25°C – 15°C = 10°C.
  2. Rearrange the formula: ṁ = Q / (Cp × ΔT)
  3. Calculate: ṁ = 100 / (4.18 × 10) = 2.39 kg/s.

Why Flow Rate Matters

If the flow rate is too low, the fluid may reach its boiling point or fail to carry away enough heat, leading to system failure. Conversely, if the flow rate is too high, you face increased pumping costs and potential erosion/corrosion within the heat exchanger tubes due to high velocity.

Important Considerations

  • Fluid Viscosity: High-viscosity fluids (like oils) require more energy to move and have lower specific heat capacities than water.
  • Fouling Factors: Over time, mineral deposits can reduce heat transfer efficiency, requiring higher flow rates or higher ΔT to maintain performance.
  • LMTD: While this calculator focuses on a single fluid stream, full heat exchanger design requires the Logarithmic Mean Temperature Difference (LMTD) to account for both the hot and cold streams.

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