Arquivo de categoria Cross flow heat exchanger

Here’s a breakdown of the temperature profile for a cross flow heat exchanger, specifically when both fluids are unmixed:

🔥 Cross Flow Heat Exchanger – Both Fluids Unmixed

➤ Flow Arrangement:

• One fluid flows horizontally (say, hot fluid in tubes).
• The other flows vertically (say, cold air across the tubes).
• No mixing within or between the fluids.

📈 Temperature Profile Description:

▪ Hot Fluid:

• Inlet temperature: High.
• As it flows, it loses heat to the cold fluid.
• Outlet temperature: Lower than inlet, but not uniform across the exchanger due to varying contact time.

▪ Cold Fluid:

• Inlet temperature: Low.
• Gains heat as it flows across the hot tubes.
• Outlet temperature: Higher, but also varies across the exchanger.

🌀 Because of the crossflow and no mixing:

• Each point on the exchanger sees a different temperature gradient, depending on how long each fluid has been in contact with the surface.
• The temperature distribution is nonlinear and more complex than in counterflow or parallel flow exchangers.

📊 Typical Temperature Profile (schematic layout):

                ↑ Cold fluid in
        │
  High  │       ┌──────────────┐
  Temp  │       │              │
        │       │              │ → Hot fluid in (right side)
        │       │              │
        ↓       └──────────────┘
      Cold fluid out           ← Hot fluid out

⬇ Temperature Curves:

• Cold fluid gradually heats up — the curve starts low and arcs upward.
• Hot fluid cools down — starts high and arcs downward.
• The curves are not parallel, and not symmetrical due to crossflow geometry and varying heat exchange rate.

🔍 Efficiency:

• The effectiveness depends on the heat capacity ratio and the NTU (Number of Transfer Units).
• Generally less efficient than counterflow but more efficient than parallel flow.

A cross flow heat exchanger with both fluids unmixed refers to a type of heat exchanger where two fluids (hot and cold) flow perpendicular (at 90°) to each other, and neither fluid mixes internally or with the other. This configuration is common in applications like air-to-air heat recovery or automotive radiators.

Key Features:

• Cross flow: The two fluids move at right angles to each other.
• Unmixed fluids: Both the hot and cold fluids are confined to their respective flow passages by solid walls or fins, preventing any mixing.
• Heat transfer: Occurs across the solid wall or surface separating the fluids.

Construction:

Typically includes:

Enclosed channels for the second fluid (e.g., water or refrigerant) to flow inside the tubes.

Tubes or finned surfaces where one fluid (e.g., air) flows across the tubes.

Common Applications:

• Radiators in cars
• Air-conditioning systems
• Industrial HVAC systems
• Heat recovery ventilators (HRVs)

Advantages:

• No contamination between fluids
• Simple maintenance and cleaning
• Good for gases and fluids that must remain separate