The heat transfer coefficient increases when the fluid velocity increases (better mixing in the turbulent boundary layer, thinner laminar su-blayer). A turbulent flow increases the amount of air resistance and noise; however, a turbulent flow also accelerates heat conduction and thermal mixing.

ΔTm =

1. ΔTm =
2. = 94.9 °F. 0.10536.
3. The preliminary area estimate of the heat exchanger can now be calculated as: A = Q / (U x ΔTm) =
4. A = 2, 035, 000 Btu/hr.
5. = 178.7 ft² (120 Btu/h.ft².°F).(94.9°F)
6. The required mass flow rate of water can be calculated from Q = m.Cp. ΔTm: Rearranging:
7. m = Q…… = Cp x ΔTm.
8. m = (2,035,000 Btu/hr)

Tf. = bulk fluid temperature away from the surface, (K) The convective heat transfer coefficient is an experimentally determined parameter that depends upon the surface geometry, the nature of the fluid motion, the properties of the fluid, and the bulk fluid velocity.

Heat Transfer

Under turbulent flow conditions, the increase in heat transfer rate is more significant than that under laminar flow conditions. This is due to the increase in the Reynolds number of the flowing fluid in turbulent flow.

The interpretation of relation [3] is that if the pressure drop, for example, is increased four times, the heat transfer coefficient becomes 4^1/3 = 1.59 times higher than the original value, i.e. a 59% increase. Note that these proportionalities only apply to fully turbulent flow.

In temperature programming, the flow rate will decrease as the column temperature increases. This decrease is due to the increased viscosity of the carrier gas at higher temperature.

How Pressure & Temperature Changes Affects Flow Meter Accuracy in Gas Flow Measurements. In gas flow measurement, the density of the gas changes as pressure and temperature change. This change in density can affect the accuracy of the measured flow rate if it is uncompensated.

More distance between molecules means less mass in a given volume. If mass flow is kept constant, and temperature increases, volume flow increases to pass the same amount of mass (molecules) across the sensor. Fig. 1: Increased volumetric flow due to temperature increase T2 > T1 , constant mass flow and pressure.

At high Reynolds number, the increase in the viscosity is compensated by force convection and the increase in the volume fraction of nanoparticles which results in an increase in heat transfer is in coincidence with experimental results.

In general, liquids tend to get “thinner” when their temperature increases. For example, honey and oil tend to flow better at higher temperatures. Therefore, increasing temperature decreases viscosity. In general, the liquids tend to expand when their temperature increases.

Viscosity is defined as the resistance to flow! Viscosity of often referred to as the thickness of a fluid. You can think of water (low viscosity) and honey (high viscosity).

The units of dynamic viscosity are: Force / area x time The Pascal unit (Pa) is used to describe pressure or stress = force per area This unit can be combined with time (sec) to define dynamic viscosity.