Convective Heat Transfer Coefficient For Air Flow

The heat transfer coefficient is considerably greater with liquid flows and greater again with two phase flows.

Convective heat transfer coefficient for air flow. However newton s law does approximate reality when the temperature changes are relatively small and for forced air and pumped liquid cooling where the fluid velocity does not rise with increasing temperature difference. Medium hydrocarbons 0 5 cp viscosity 1 cp 50 100. 200 700. H c 10 45 v 10 v 1 2 2 where.

Such a situation can be seen for example with a radiator. Convective air flow from a single heat source. Obviously the radiator transfers heat to the passing air. H cw heat transfer coefficient w m 2 c.

The convective heat transfer coefficient is dependent upon the physical properties of the fluid and the physical situation. Typical values of α are shown in table 1 from which it can be seen that increases in velocity generally result in increases in heat transfer coefficient so that α is smallest in natural convection and increases to 100 and more on flat surfaces with air velocities greater than around 50 m s. 250 750. 10 20.

200 700. Calculate the heat transfer rate from the pipe into the room if the room temperature is 72 o f. The convective heat transfer coefficient for the air is 18 btu hr ft 2 o f. H cw 12 12 1 16 v 11 6 v 1 2 2b where.

Q air flow volume m 3 s per meter surface width. Heaters no phase change heat transfer coefficients. Thermal resistance due to fouling deposits. Cold air flows past the radiator due free convection and is heated.

Increasing air flow increases convective coefficient and vice versa. Many applications involving convective heat transfer take place within pipes tubes or some similar cylindrical device. The convective heat transfer coefficient for air flow can be approximated to. 100 700.

Light hydrocarbons viscosity 0 5 cp 100 200. The rate of heat transfer between a solid surface and a fluid per unit surface area per unit temperature difference. Convective air flow volume at a vertical distance generated by the hot or cold surface can be calculated as. The convective heat transfer coefficient h can be defined as.

Q 0 019 g t e t s 273 t e 0 4 l 1 2 2 where. The heat transfer coefficient describes the convective heat transfer from a solid to a flowing fluid gas or liquid or vice versa. In classical natural convective heat transfer the heat transfer coefficient is dependent on the temperature. That value of 20w m2k for still air is probably a reasonable approximation for still air but at the temperatures you are looking at my guess is that you will have significant circulation due to natural convection induced by density differences due to the high temp.

H c heat transfer coefficient kcal m 2 h c v relative speed between object surface and air m s since. 1 kcal m 2 h c 1 16 w m 2 c 2 can be modified to. Some typical heat transfer coefficients include.