Will the heat transfer coefficient for turbulent flow be less than for laminar flow?
The heat transfer coefficient increases when the fluid velocity increases (better mixing in the turbulent boundary layer, thinner laminar su-blayer). However, the heat transfer coefficient will still decrease along the length of the surface, but to a lesser degree than for laminar flow.
Why does heat transfer coefficient increase with velocity?
In this mode, heat transfer is because of the mass transfer. As our common sense suggests, more the velocity, more the rate of mass transfer and hence more is the rate of convective heat transfer. Hence heat transfer coefficient increases with the increase in the velocity of the fluid.
Does heat transfer increase 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.
What is a good heat transfer coefficient?
As mentioned earlier in the article the convection heat transfer coefficient for each stream depends on the type of fluid, flow properties and temperature properties. Some typical heat transfer coefficients include: Air – h = 10 to 100 W/(m2K) Water – h = 500 to 10,000 W/(m2K).
Does overall heat transfer coefficient change with temperature?
This in turn influences the heat transfer coefficient, despite possible identical temperature differences. 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.
How do you increase overall heat transfer coefficient?
To increase heat-transfer rates, the velocity through a jacket can be increased by recirculating the cooling or heating liquid. For simple jackets without baffles, heat-transfer will be mainly by natural convection and the heat-transfer coefficient will range from 200 to 400 W/m2 °C.
Which of the following has the lowest overall heat transfer coefficient?
Which one is having the lowest value of overall heat transfer coefficient? Explanation: Overall heat transfer coefficient for air condensers is 780 W/m2 K while that of steam condensers, air to low viscosity liquids and feed water heaters are 5000 W/m2 K, 600 W/m2 K and 8500 W/m2 K.
What is the absorptivity of the gray body?
What is the absorptivity of the gray body? Explanation: Gray body absorbs a certain fixed percentage of impinging radiations. Explanation: In this case reflection is regular. For such bodies reflectivity is unity and transmissivity is equal to zero.
How do you calculate the number of heat exchangers on a tube?
4.0 – HEAT EXCHANGERS CALCULATIONS:
- The main basic Heat Exchanger equation is: Q = U x A x ΔTm =
- The log mean temperature difference ΔTm is: ΔTm =
- (T1 – t2) – (T2 – t1) = °F.
- T1 = Inlet tube side fluid temperature; t2 = Outlet shell side fluid temperature;
- ln (T1 – t2) (T2 – t1)
What are the two types of heat exchangers?
There are two main types of regenerative heat exchangers—static heat exchangers and dynamic heat exchangers.
Why counter flow heat exchanger is better than the parallel flow?
Counter flow heat exchangers are inherently more efficient than parallel flow heat exchangers because they create a more uniform temperature difference between the fluids, over the entire length of the fluid path.
What is effectiveness NTU method?
The effectiveness-NTU method is very useful for all the flow arrangements (besides parallel flow and counterflow ones) because the effectiveness of all other types must be obtained by a numerical solution of the partial differential equations and there is no analytical equation for LMTD or effectiveness, but as a …
Which heat transfer process requires no medium?
radiation
Which of the following is the fastest process of heat transfer?
Radiation
Why conduction is only possible in solids?
Conduction can takes place in Solids,liquids and gases. But it is maximum in solids as their atoms and molecules are located closer. Metals are the best solids to conduct the heat as they have tightly packed atoms which can pass the kinetic energy and the free electrons to the near by atoms and leads to conduction.
What type of heat transfer is heating food in a microwave?
Microwave radiation utilizes short, high-frequency waves that penetrate food, which agitates its water molecules to create friction and transfer heat. If you’re heating a solid substance, this heat energy is transferred throughout the food through conduction, while liquids do so through convection.
When something is really hot How do molecules move?
Cold things have slow-moving molecules, while hot things have fast-moving molecules. In fact, temperature is really a measurement of molecule speed. For a cold thing to get warm, its molecules have to speed up. Heat moves in three different ways — conduction, convection, and radiation.
What kind of heat transfer happens when the sun is heating your body?
Review for Heat Transfer Quiz
| A | B |
|---|---|
| Convection | The transfer of heat by the movement of a fluid. |
| Feeling the sun’s heat on your face is an example of which kind of heat transfer? | Radiation |
| What kind of heat transfer occurs when you put a heating pad on your injured knee? | Conduction |