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The number of transfer units (NTU) method is used to calculate the rate of heat transfer in heat exchangers (especially parallel flow, counter current, and cross-flow exchangers) when there is insufficient information to calculate the log mean temperature difference (LMTD). Alternatively, this method is useful for determining the expected heat ...
Schematic drawing of a hydrometer. The lower the density of the fluid, the deeper the weighted float B sinks. The depth is read off the scale A.. A hydrometer or lactometer is an instrument used for measuring density or relative density of liquids based on the concept of buoyancy.
+100 °Bé (specific gravity, 3.325) would be among the densest fluids known (except some liquid metals), such as diiodomethane. Near 0 °Bé would be approximately the density of water. −100 °Bé (specific gravity, 0.615) would be among the lightest fluids known, such as liquid butane .
The heat transfer coefficient has SI units in watts per square meter per kelvin (W/(m 2 K)). The overall heat transfer rate for combined modes is usually expressed in terms of an overall conductance or heat transfer coefficient, U. In that case, the heat transfer rate is: ˙ = where (in SI units):
The Twaddell scale is a hydrometer scale used for measuring the specific gravity of liquids relative to water. On this scale, a specific gravity of 1.000 is reported as 0, and a specific gravity of 2.000 is reported as 200. [1]
Heat is the flow of thermal energy driven by thermal non-equilibrium, so the term 'heat flow' is a redundancy (i.e. a pleonasm). Heat must not be confused with stored thermal energy, and moving a hot object from one place to another must not be called heat transfer. However, it is common to say ‘heat flow’ to mean ‘heat content’. [1]
Dimensionless numbers (or characteristic numbers) have an important role in analyzing the behavior of fluids and their flow as well as in other transport phenomena. [1] They include the Reynolds and the Mach numbers, which describe as ratios the relative magnitude of fluid and physical system characteristics, such as density, viscosity, speed of sound, and flow speed.
A hygrometer is an instrument which measures the humidity of air or some other gas: that is, how much of it is water vapor. [1] Humidity measurement instruments usually rely on measurements of some other quantities, such as temperature, pressure, mass, and mechanical or electrical changes in a substance as moisture is absorbed.