A dimensionless parameter used in calculations of heat transfer between a moving fluid and a solid body.
It is equal to hD/k, where h is the rate of heat loss per unit area per degree difference in temperature between the body and its surroundings, D is a characteristic length of the body, and k is the thermal conductivity of the fluid.
Origin
1930s: named after Ernst K. W. Nusselt (1882–1957), German engineer.