What Factors Affect Heat Transfer Coefficient?

What affects overall heat transfer coefficient?

The factors affecting overall heat transfer coefficient are : Physiochemical properties of fluids ( both cold and hot ) such a viscosity , density, specific heat, thermal conductivity.

Geometry of the exchanger ( equivalent length and heat exchanging area ) Velocity of flowing fluids..

What is the heat transfer coefficient of air?

Convective Heat Transfer Coefficient for Air The convective heat transfer coefficient for air flow can be approximated to. hc = 10.45 – v + 10 v1/2 (2) where. hc = heat transfer coefficient (kCal/m2h°C) v = relative speed between object surface and air (m/s)

What are the three factors affect the heat transfer that is necessary to change an object’s temperature?

Answer: Experiments show that the transferred heat depends on three factors—the change in temperature, the mass of the system, and the substance and phase of the substance.

How do you find the coefficient of convective heat transfer?

Common units used to measure the convective heat transfer coefficient are:1 W/(m2 K) = 0.85984 kcal/(h m2 ° C) = 0.1761 Btu/(ft2 h ° F)1 kcal/(h m2 ° C) = 1.163 W/(m2 K) = 0.205 Btu/(ft2 h ° F)Btu/hr – ft2 – °F = 5.678 W/(m2 K) = 4.882 kcal/(h m2 ° C)

Does heat transfer coefficient depend on material?

The heat transfer coefficient is a very important parameter during the thermal application, and depends on many parameter such as the materials of fluid temperature. But the other important group of parameters effect on the heat transfer coefficient are flowing properties, geometry and thermal conditions.

Can the overall heat transfer coefficient be negative?

In case of constant wall temperature, using adiabatic wall temperature as reference temperature can result in negative heat transfer coefficient, which means the heat flux has a different direction with the defined driving temperature difference.

What factors affect heat transfer between a warm and a cool substance?

Which factors affect heat transfer between a warm and a cool substance? chemical composition of the substances. state of matter of the substances at room temperature. thermal equilibrium of the substances.

What is the heat transfer coefficient of stainless steel?

Typical heat exchanger materials and their thermal conductivitiesMaterialThermal Conductivity (W/m oC)Polypropylene0.1 – 0.22Red Brass (85 Cu – 15 Zn)159Stainless Steel, type 316 (17 Cr – 12 Ni – 2 Mo)16Stainless Steel, type 304 (18 Cr – 8 Ni)1618 more rows

Does heat transfer coefficient change with flow rate?

The heat transfer coefficient decreases by ˜10% with a threefold increase in the mass flow rate under these conditions, based on the commonly used Dittus-Boelter correlation for estimation of the heat transfer coefficient. … Doubling the mass flow rate will result in a 92% increase in the heat transfer coefficient.

What does a higher heat transfer coefficient mean?

The larger the coefficient, the easier heat is transferred from its source to the product being heated. In a heat exchanger, the relationship between the overall heat transfer coefficient (U) and the heat transfer rate (Q) can be demonstrated by the following equation: where. Q = heat transfer rate, W=J/s [btu/hr]

Does heat transfer coefficient increase with temperature?

So if velocity of flow is increased, heat transferred will increase. You can use Newtons law of cooling for a body which states- Heat tranferred= hA(Temp difference). Here heat tranfer has increased but temp diff and area remain same hence Heat tranfer coefficient must have increased.

What is average heat transfer coefficient?

Heat-transfer coefficient equal to the heat flow (Q) across the heat-transfer surface divided by the average temperature (Δt) and the area of the heat-transfer surface (F)

What does the convective heat transfer coefficient depend on?

The convective heat transfer coefficient is dependent upon the physical properties of the fluid and the physical situation. Values of h have been measured and tabulated for commonly encountered fluids and flow situations.

What are the 4 types of heat transfer?

Various heat transfer mechanisms exist, including convection, conduction, thermal radiation, and evaporative cooling.

What are the factors affecting heat transfer?

Factors that affect rate of heat flow include the conductivity of the material, temperature difference across the material, thickness of the material, and area of the material. Different materials have greater or lesser resistance to heat transfer, making them better insulators or better conductors.

What is the difference between heat transfer coefficient and overall heat transfer coefficient?

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. … The areas for each flow will be different as they represent the contact area for each fluid side.

How do you increase the coefficient of convective heat transfer?

To improve convective heat flow, increasing the area of contact either between the athlete or the apparel and the flow, as well as the speed of the flow is important. For cooling, materials selection and apparel designs can focus on allowing air to flow between the body and the apparel.