Refrigerant Mass Flow Rate Calculation

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Refrigerant Mass Flow Rate Calculator

kW Tons (TR) BTU/hr
kJ/kg BTU/lb
Difference between Evaporator Outlet and Inlet Enthalpy.

Calculation Results

Mass Flow Rate (kg/s): –
Mass Flow Rate (kg/min): –
Mass Flow Rate (lb/min): –
Mass Flow Rate (lb/hr): –

Understanding Refrigerant Mass Flow Rate

The refrigerant mass flow rate represents the amount of refrigerant by mass that circulates through a refrigeration or air conditioning system per unit of time. It is a critical parameter in the design and analysis of HVAC systems, determining the sizing of compressors, expansion valves, and piping.

The Mass Flow Formula

The fundamental thermodynamic equation linking cooling capacity and mass flow rate relies on the concept of the Net Refrigerating Effect (NRE). The NRE is the change in enthalpy (energy content) of the refrigerant as it passes through the evaporator.

˙m = Q / Δh

Where:

  • ˙m = Mass Flow Rate (kg/s or lb/min)
  • Q = Total Cooling Capacity or Heat Load (kW or BTU/hr)
  • Δh = Net Refrigerating Effect (Enthalpyout – Enthalpyin) across the evaporator

How to Determine the Variables

To use this calculator effectively, you need two primary inputs:

  1. Cooling Capacity: This is the total heat load the system must remove. It is often measured in Tons of Refrigeration (TR), kilo-Watts (kW), or British Thermal Units per hour (BTU/hr).
  2. Refrigerating Effect: This requires knowing the thermodynamic properties of the specific refrigerant used (e.g., R-410A, R-134a). You subtract the enthalpy of the refrigerant entering the evaporator from the enthalpy leaving the evaporator. These values are typically found using a Pressure-Enthalpy (P-h) chart.

Example Calculation

Consider a commercial chiller utilizing R-134a with a required cooling capacity of 10 Tons.

  • Capacity (Q): 10 Tons. Converting to kW: 10 × 3.517 = 35.17 kW.
  • Enthalpy Data:
    • Enthalpy at Evaporator Outlet (hg): 400 kJ/kg
    • Enthalpy at Evaporator Inlet (hf): 250 kJ/kg
    • Net Effect (Δh): 400 – 250 = 150 kJ/kg

Calculation:
˙m = 35.17 kW / 150 kJ/kg = 0.2345 kg/s

This value determines the volume that the compressor must displace to maintain the cooling cycle.

Why Mass Flow Rate Matters

If the mass flow rate is too low, the system cannot absorb enough heat to meet the cooling load, leading to high indoor temperatures. Conversely, if the flow rate is excessively high compared to the components' capacity, it can lead to liquid flood-back into the compressor (damaging the equipment) or inefficient operation due to high pressure drops in the piping.

function calculateMassFlow() { // 1. Get Input Values var capacityInput = document.getElementById('coolingCapacity').value; var effectInput = document.getElementById('refEffect').value; var capacityUnit = document.getElementById('capacityUnit').value; var effectUnit = document.getElementById('effectUnit').value; // 2. Validate Inputs if (capacityInput === "" || effectInput === "") { alert("Please enter both Cooling Capacity and Refrigerating Effect."); return; } var capacity = parseFloat(capacityInput); var effect = parseFloat(effectInput); if (isNaN(capacity) || isNaN(effect)) { alert("Please enter valid numeric values."); return; } if (effect === 0) { alert("Refrigerating effect cannot be zero (divide by zero error)."); return; } // 3. Normalize to Base Units (SI: kW and kJ/kg) to calculate kg/s // Base Unit for Capacity: kW var capacityKW = 0; if (capacityUnit === 'kW') { capacityKW = capacity; } else if (capacityUnit === 'ton') { // 1 Ton = 3.51685 kW capacityKW = capacity * 3.51685; } else if (capacityUnit === 'btu') { // 1 BTU/hr = 0.000293071 kW capacityKW = capacity * 0.000293071; } // Base Unit for Effect: kJ/kg var effectKJKG = 0; if (effectUnit === 'kjkg') { effectKJKG = effect; } else if (effectUnit === 'btulb') { // 1 BTU/lb = 2.326 kJ/kg effectKJKG = effect * 2.326; } // 4. Calculate Mass Flow in kg/s // Formula: kg/s = kW / (kJ/kg) => (kJ/s) / (kJ/kg) = kg/s var flowKgS = capacityKW / effectKJKG; // 5. Convert Results to other units var flowKgMin = flowKgS * 60; var flowLbMin = flowKgMin * 2.20462; // 1 kg = 2.20462 lbs var flowLbHr = flowLbMin * 60; // 6. Display Results document.getElementById('resKgS').innerText = flowKgS.toFixed(4); document.getElementById('resKgMin').innerText = flowKgMin.toFixed(3); document.getElementById('resLbMin').innerText = flowLbMin.toFixed(3); document.getElementById('resLbHr').innerText = flowLbHr.toFixed(2); document.getElementById('resultDisplay').style.display = 'block'; }

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