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What materials are used in high temperature heat exchangers?

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High-temperature heat exchangers must withstand extreme thermal conditions, corrosion, and mechanical stress. Therefore, the materials used are carefully selected for their thermal stability, oxidation resistance, and mechanical strength. Common materials include:

  1. Stainless Steel (e.g., 304, 316, 310, 321)

    • Good corrosion resistance and mechanical strength

    • Suitable for temperatures up to ~800°C (depending on the grade)

  2. Inconel (e.g., Inconel 600, 625, 718)

    • A nickel-chromium alloy with excellent resistance to oxidation and creep at temperatures up to ~1000°C

    • Common in aerospace, chemical, and power plant applications

  3. Hastelloy

    • Nickel-molybdenum alloys known for corrosion resistance under severe conditions

    • Useful in high-temperature, chemically aggressive environments

  4. Titanium and Titanium Alloys

    • Excellent corrosion resistance, moderate high-temperature performance (~600°C)

    • Often used in heat exchangers exposed to seawater or aggressive chemicals

  5. Ceramics (e.g., Silicon Carbide, Alumina)

    • Extremely high temperature resistance (>1200°C)

    • Brittle, but ideal for specialized high-temp gas heat exchangers

  6. Carbon Steel

    • Cost-effective and strong, but less resistant to corrosion and oxidation

    • Typically used in applications below ~425°C

  7. Aluminum Oxide-Coated Metals

    • Coatings help extend the temperature range and protect from oxidation

how does air to air heat exchanger work in fresh air system

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In a fresh air system, an air-to-air heat exchanger is used to recover heat from outgoing indoor air and transfer it to the incoming fresh outdoor air—without mixing the two airflows. This improves indoor air quality while reducing heating or cooling loads. Here's how it works step-by-step:

How It Works in a Fresh Air System:

  1. Stale indoor air is extracted from rooms like kitchens, bathrooms, or general living spaces. This air is typically warm in winter or cool in summer, depending on indoor climate control.

  2. Fresh outdoor air is drawn in simultaneously. This air may be cold in winter or hot in summer, requiring conditioning.

  3. Both air streams pass through the air-to-air heat exchanger, but in separate, sealed channels:

    • The warm outgoing air transfers its heat (or coolness in summer) to the metal or membrane surfaces inside the exchanger.

    • The incoming cold air picks up that heat from the exchanger surfaces before entering the building.

  4. The two air streams never mix, ensuring clean, filtered air is delivered inside.

Benefits in a Fresh Air System:

  • Energy efficiency: Recovers 60–90% of heat that would otherwise be lost.

  • Improved indoor air quality: Constant supply of filtered, fresh air.

  • Comfort: Reduces temperature swings from direct outdoor air intake.

  • Humidity control (if an ERV is used): Some units also transfer moisture to balance indoor humidity.