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Heat Transfer - Engineering

Q1:

The Graetz number is concerned with the

A mass transfer between a gas and a liquid.

B absorption with chemical reaction.

C heat transfer in turbulent flow.

D heat transfer in laminar flow.

ANS:D - heat transfer in laminar flow.

The Graetz number (Gr) is concerned with the: c) heat transfer in laminar flow. The Graetz number is a dimensionless parameter used in heat transfer analysis, particularly in situations involving laminar flow. It represents the ratio of thermal diffusion timescale to the flow timescale in a system. In the context of heat transfer in laminar flow, the Graetz number helps characterize the relative importance of conduction and convection in the heat transfer process. It is defined as: ReGr=δL​×Re Where:

  • L is a characteristic length scale (such as the length of the system),
  • δ is the thermal boundary layer thickness,
  • ReRe is the Reynolds number.
A high Graetz number indicates that conduction dominates over convection, which is often the case in laminar flow situations. Therefore, the Graetz number is particularly relevant for analyzing heat transfer phenomena in laminar flow regimes.