Table of Contents
What does overall heat transfer coefficient depend on?
Heat transfer coefficient depends on both the thermal properties of a medium, the hydrodynamic characteristics of its flow, and the hydrodynamic and thermal boundary conditions.
What is overall heat transfer coefficient?
The overall heat transfer coefficient, or U-value, refers to how well heat is conducted through over a series of resistant mediums. Its units are the W/(m2°C) [Btu/(hr-ft2°F)].
How do you find the overall heat transfer coefficient?
The overall heat transfer coefficient R = Resistance(s) to heat flow in pipe wall (K/W) Other parameters are as above. The heat transfer coefficient is the heat transferred per unit area per kelvin. Thus area is included in the equation as it represents the area over which the transfer of heat takes place.
What is overall and individual heat transfer coefficient?
The overall heat transfer coefficient (U) depends on individual heat transfer coefficients and the heat resistance offered by the tube-wall. We assume the coolant heat transfer coefficient (hcool) and the tube wall resistance remains constant.
Does overall heat transfer coefficient change with flow rate?
Doubling the mass flow rate will result in a 92% increase in the heat transfer coefficient. However, there is a concomitant increase in the pressure drop, proportional to the mass flow rate raised to 0.95.
Why does heat transfer coefficient increase with velocity?
Convection is the bulk transfer of fluids. In this mode, it is because of mass transfer. When there is an increase in velocity there will be an increase in mass transfer. When the mass transfer increases there is an increase in the heat transfer coefficient.
Is the overall heat transfer coefficient constant?
The heat transfer coefficient is therefore also dependent on the direction of heat flow. In contrast to the thermal conductivity, the heat transfer coefficient is not a material constant. The heat transfer coefficient depends, among other things, on the material combination solid/fluid.
Why is the overall heat transfer coefficient U not changing as much with flow rate?
UA will, in principle change if you vary the flow rates because heat transfer coefficients changes. However, for the above example with air/water, changing the water flow rate may not influence the U-value much, since the resistance on the water side is small as compared to air.
What happens when heat transfer coefficient increases?
For turbulent flow, the heat transfer coefficient increases with increasing mass flux (or Reynolds number). This is because higher velocity increases turbulence, which in turn provides a more efficient radial transport/mixing of heat.
How does heat transfer coefficient change with flow rate?
The rate heat transfer ΔQ is vary linearly with the flow rate. The flow rate could be either mass flow rate (m°) or volume flow rate (m°). The heat transfer always increases with the increase in flow rate.
Why does heat transfer coefficient increase with Reynolds number?
What is NTU in heat transfer?
The Number of Transfer Units (NTU) Method is used to calculate the rate of heat transfer in heat exchangers (especially counter current exchangers) when there is insufficient information to calculate the Log-Mean Temperature Difference (LMTD).
What is IC in stock market?
The information coefficient (IC) is a measure used to evaluate the skill of an investment analyst or an active portfolio manager. The information coefficient shows how closely the analyst’s financial forecasts match actual financial results.
What is unit of heat transfer coefficient?
The heat transfer coefficient has SI units in watts per squared meter kelvin: W/(m2K). Heat transfer coefficient is the inverse of thermal insulance.
How does heat transfer coefficient change with velocity?
Generally Heat transfer coefficient of fluid increases with the increase in Reynolds number or velocity of fluid when it flows through a pipe.