Acoustic padding and combustor resonance

1. The triangle foam on the acoustic panels for noise absorption: The triangle height determines what is the frequency being absorbed, the triangle foam material determines the absorption factor
2. The  flame in the combustor tube excites multiple frequencies. The frequency corresponding to quarter wave length of the combustor tube will be amplified because of resonance from the combustor tube. 

Orifice type flow meter

How to Build a Low-Cost Orifice Plate Mass Flow Meter for Compressed Air (0.07–0.2 kg/s) – Completely DIY in India

If you need to measure compressed air mass flow in the range 0.07 to 0.2 kg/s (roughly 250–700 m³/hr at 6 bar) in a 1-inch pipeline, and you cannot afford a ready-made thermal/Coriolis meter (₹1.5–3 lakh), here is a proven, fully fabricable orifice-plate-based solution that costs only ₹25,000–₹30,000.

Service Conditions

• Fluid: Dry compressed air
• Mass flow range: 0.07 – 0.2 kg/s
• Pipe size: 1 inch Schedule 40 (ID = 27.3 mm)
• Max gauge pressure: 5 bar → ~6 bar(a)
• Max temperature: 60 °C

Step-by-Step Design Calculations

1. Selection of β ratio

Chosen β = 0.50 (best compromise between accuracy and pressure loss)

Orifice bore d = 0.5 × 27.3 = 13.65 mm → 13.6 mm (easy to machine)

2. Expected Differential Pressure

Density at 6 bar(a), 60 °C ≈ 6.27 kg/m³

Using ISO 5167-2 formula →

• At 0.2 kg/s → ΔP ≈ 11.2 kPa ≈ 1140 mmWC
• At 0.07 kg/s → ΔP ≈ 140 mmWC

This range is perfectly measurable with commonly available Indian DP transmitters.

3. Final Orifice Plate Specification

Parameter	Value
Pipe ID (Sch 40)	27.3 mm
Orifice bore (d)	13.6 ± 0.02 mm
β ratio	0.50
Plate thickness	3–4 mm
Material	SS304
Taps	Corner taps
Bevel	45° on downstream side
Permanent pressure loss	≈ 55% of ΔP (≈ 600 mmWC max)

Fabrication Drawing (Give This to Any Local Workshop)

• Plate size: 80 mm OD circular or 50×50 mm square with handle tab
• Centre hole: 13.6 mm reamed
• Downstream face: 45° bevel
• Upstream face: polished (Ra < 0.4 µm)
• Weld two 6 mm SS nipples on pipe for corner taps

Recommended Instruments (Easily Available in India – 2025 prices)

Parameter	Make & Model	Range	Approx Price
Differential Pressure	WIKA A-10 / Waaree / Galaxy	0–2000 mmWC	₹9,000–12,000
Cheap mechanical option	Galaxy Magnehelic type	0–2000 mmWC	₹3,500–5,000
Gauge Pressure	WIKA 233.50 / H Guru	0–10 bar	₹1,200–2,000
Temperature	Pt-100 RTD or bimetallic	0–100 °C	₹800–1,500

Field Calculation Formula (Mass Flow)

Mass flow (kg/s) = 0.000178 × √(ΔP in mmWC) × √(P_abs in bar × 288/(T+273))

You can put this formula in Excel or display live value using Arduino + 4-20 mA DP transmitter.

Total Estimated Cost (India – Nov 2025)

• Orifice plate + welding: ₹4,000
• DP transmitter: ₹10,000
• Pressure & temperature gauges: ₹3,000
• Tubing, valves, manifold: ₹5,000
• Optional display/logging: ₹4,000
• Total: ₹25,000 – ₹30,000 only

Is Thermal Mass Flow Meter Easier to DIY?

Absolutely NOT.

• You still need to buy the sensing element (₹15,000–40,000)
• Complex electronics & calibration required
• Not truly DIY

Orifice plate + DP cell + P&T compensation is the cheapest, most robust and 100% locally fabricable solution in India.

Lecture notes on aerodynamics

 

Animation of pole movement for mechanical rotor, gyroscopic effect

 

Animation of components of Active magnetic bearing supported flywheel

 

Animation of thrust AMB operation

Thrust magnetic bearing single axis, operation

 

Animation of the radial AMB operation

 

Radial active magnetic bearing operation