# Convection Definition and 37 Discussions

Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convection is unspecified, convection due to the effects of thermal expansion and buoyancy can be assumed. Convection may also take place in soft solids or mixtures where particles can flow.
Convective flow may be transient (such as when a multiphase mixture of oil and water separates) or steady state (see Convection cell). The convection may be due to gravitational, electromagnetic or fictitious body forces. Heat transfer by natural convection plays a role in the structure of Earth's atmosphere, its oceans, and its mantle. Discrete convective cells in the atmosphere can be identified by clouds, with stronger convection resulting in thunderstorms. Natural convection also plays a role in stellar physics. Convection is often categorised or described by the main effect causing the convective flow, e.g. Thermal convection.

Convection cannot take place in most solids because neither bulk current flows nor significant diffusion of matter can take place.

View More On Wikipedia.org
1. ### How do I get the Convection Coefficient for steam in a jacketed vessel?

Please could someone point me in the direction of an equation/ book I can use to obtain the convection coefficient for steam in a heating jacket. Steam is at 1 bar pressure. I think I need to use a dimensionless number. Thanks
2. ### Heat transfer problem for a long rectangular bar

Summary:: Determine the temperature distribution in a bar (very long– 2D) with rectangular cross section, in steady state, with imposed flux at one face, convection at the opposing face (Tinf, h), and imposed temperature (T1) at the two remaining walls. I am trying to find the analytical...
3. ### Cooling nozzle - convection power

Hi, when modeling convective cooling in FEA one needs to define film coefficient ##h## and ambient temperature ##T_{amb}##. The software calculates convective heat flux using this data and current surface temperature ##T_s##: $$q=h(T_{s}-T_{amb})$$ However, modeling of moving cooling nozzle may...
4. ### I Convection applications

Hello guys, I'm a physics graduate student and recently I've questioned myself about convection when reading about heat transmission processes. At least throughout my life, whenever I heard someone talk about convection, there were examples related to air and water convection currents, however...
5. ### Calculating the Power Dissipation of a Wire

I'm having trouble verifying an experiment I ran to determine the power dissipation of a heating element. 13.15W of power was applied to 3ft nichrome wire. Temperature readings were collected until they stabilized at 128.5F (room temp was 70F). I want to create a mathematical model of the system...
6. ### I Rotation profile for radiative zone of Sun - convection

I am exercising on Stellar Physics topics and in particular the questions below: 1) First of all on the rotation profile for the radiative zone: I know that unlike the convective zone, where the rotation varies mainly in latitude (faster at the equator than at the poles), the radiative zone...
7. ### Entropy in the Brazil Nut Sorting Effect

In Brazil Nut effect /Granular convection the large grains move upward and the smaller ones go downward. This sorting is supposed to reduce the multiplicity of this system. But according to the second law of thermodynamics, entropy and multiplicity of the system should increase. I am looking...
8. ### Natural Convection vertical heated flat plate

1. I am using FEA modelling for a vertical heated flat plate and I need to compare theoretical results with the FEA s/w modelling results. I have completed the model in FEA s/w and I'm getting different values for temperatures and because I can't work out theoretical values then I do not know...
9. H

### Transient energy balance

Homework Statement In an industrial process, a tank containing 200 liters of water must be heated from a temperature of 293 K to 372 K at a constant pressure. There is a negligible change in the volume of the water. The water is stirred during this process to maintain a uniformly distributed...
10. U

### Somewhat Complicated Thermal Problem

Problem Description: I have a solar panel of some surface area, material, and thickness mounted to an enclosure. The panel is isolated from the enclosure at some distance with a multitude of materials (air, insulation, plastic, metal) between the back surface of the panel and interior volume...
11. V

### Help to determine convection coeficent or temperatures

Homework Statement This is more like a design problem, I'm to evaporate water at 20°C and 2000 psi(Tsat=335.472°C), I have the heat flux the water is going to absorb during heating, and If that flux remains constant during all the length then, how can I find the surface temperature for the...
12. V

### How calculate the Heat flux requiered to evaporate sub cool water

Homework Statement I was trying to validate a calculation I didusing ANSYS fluent, it's about a flow of water that enters a tube, the tube is 16m long and is being heated with a Heat Flux of q'=1077328,47 [W/m^2], now after the simulation runs and I check the results I find out that the steam...
13. ### How can the neutral outer core generate a magnetic field?

Even if the outer core is convecting and conductive it is still charge neutral, so how can a Magnetic field be generated? Maxwells Equation say there needs to be net charge moving for a Magnetic field to be generated.
14. ### Heat transfer modeling

Hello everyone, I was hoping to get some insight on a model I am trying to create. Quick background in case it is important, I am now working at a new internship I landed for the summer doing some modeling and what not on areas of physics I have never worked on before. It has also been a few...
15. ### Nusselt number for a developing turbulent flow in the entrance region

Anyone knows if i can calculated Nusselt number for a developing turbulent flow in the entrance region for a duct/ tube?
16. ### Contact Cooling

Hi, I am designing a system to cool aluminium through contact cooling. I have a steel die with 9x 20mm diameter cooling chambers. Water is pumped through the chambers which cools the steel die and hopefully the aluminium sitting on top of it. I am looking to find the temperature of the...
17. ### Convection heat exchanger

Hello guys, in the question attached, my understanding is that there is a heat transfer that heats the fluid from an initial at the input, to at the output. This heat transfer is via convection from walls of temperature . Firstly, . Because the walls are and the fluid is of a lower...
18. ### Energy use, conductive-convective layers and air films

Homework Statement The door of a refrigerator is 1.5 m high, 0.80 m wide and 6.0 cm thick. Its thermal conductivity is 0.21Wm-1 degrees Celsius-1. a) what is the heat loss per hour through the door neglecting convection effects? b) Air is usually still inside the refrigerator so there will be a...
19. ### Air velocity inside a pipe (natural convection)

Hi guys, I'm doing some research in papers and literature to solve this problem but I've not found anything useful. I want to know the air velocity inside a pipe by the only effect of natural convection. I've attached a picture of the system right here: I hope you can help me to find the...
20. ### H (heat transfer coefficient) problem

I have a cuboid shaped box. It is being used as a chilling tank in my refrigeration system based on Evan Perkins cycle. For heat load calculation I tried to calculate the heat leakage in the sysyem. So I considered conduction and natural convection. I am in preliminary stage, so no use of...
21. ### Heat convection in liquid nitrogen

Hello, I am trying to achieve a range of temperature (below 0 degC) by heating up liquid nitrogen (77K) with an electric heater (100W) inserted into a copper block. How do I calculate the time taken (t) for the nitrogen vapour to reach temperature T (say 100K). The liquid nitrogen is poured into...
22. ### Heat Transfer Pipe Problem dilemma

Homework Statement Problem data:[/B] http://imgur.com/a/hEz16 Homework Equations Rconduction=ln(rout/rin)/2*pi*Length*thermal conduct Rconvection=1/2*pi*Length*routside*convective heat transfer outside =>Qconduct=2*pi*Length*thermal conduct*(Tin-Tout)/ln(rout/rin)...
23. ### Heat Transfer and Air Flow

Hello, I have here a complex question. My background is Chemistry and Optoelectronics. I wasn't the best when we were studying Thermodynamics at uni so I have some knowledge-gaps. Anyways, here is my problem. Can somebody explain me the whole process of the convection in the coffee roaster. So...
24. ### Ice will melt faster which case -- over or below hot block?

Natural convection always occurs opposite of gravity due to buoyancy; but I am confused as ice is solid so how could possibly convection even contribute to the heat transfer. I doubt about air movements nearby block that may contribute to greater heat transfer rate in case of hot block placed...
25. ### Heat Transfer Coefficients: Free and Forced Convection

Hi all. I'm currently working on a problem where I have to determine individual and overall heat transfer coefficients for a vertical cylinder with water flowing on the inside and steam on the outside (parallel flow), studying the cases of free and forced convection. I only have four...
26. ### Heat transfer through AL shield by radiation & convection

Hi all, I am new here, and want to thank you for help in advance! I am working on a project and need some help - I need to figure out surface temp on an object at some distance from the heat source: I need some help getting started. Is it going to be: Heat transfer (radiation) + Heat...
27. ### Thermal-expansion coefficients, convection as function of T

I have two questions on fine points of thermal physics. 1. Is an isotropic solid's volume-expansion coefficient beta exactly equal to 3 times its linear-expansion coefficient alpha, or is it only approximately equal? Some textbooks (Fischbane, Walker, Young) say the relation is exact, while...
28. ### Earth's Energy balance including a convective component

Hey guys, I'm really stuck right now 1. Homework Statement Habitable exoplanet: Now we will include a convective heat flux (H), with H being proportional to the difference between the atmospheric and ground surface temperature, $$H=c_p(T_a-T_p)$$ with c = 1.2 Wm−2K−1. Calculate the temperature...
29. ### Heat Transfer in glass pane windows

If the temperature of the wall is homogeneous i.e. the entire wall has the same temperature: T1 being the temperature of the left wall and T2 being the temp of the right wall, how will heat transfer take place? Can convection occur here? If yes then how will the bulk motion be set up? I am...
30. ### Thermal Resistance due to Convection Heat Transfer

Homework Statement 1) A typical wall construction for a single-family residence might consist of 0.375 inches of outer sheathing (insulating board, hardwood siding, etc.), 3.5 inches of mineral fiber insulation and then a 0.375 inches inner surface (gypsum, etc.). Typical thermal...
31. ### Heat Loss Through a Box with a hole in it

This is mainly just a theoretical question: say you have a rectangular box made of styrofoam (one of those ice cooler things) and it is levitating in air at room temperature conditions. It also has one hole at the top of the container so that heat can get out of it. Inside the box is a lightbulb...
32. ### Thermal Physics: Cooling by both Conduction & Convection

Hi all, I am not sure if the is the right place to post the question being new to the forum, but I am looking for some help with a heat transfer experiment that I ran for my honours thesis. Essentially the aim is to determine if warmed saline fluid bags taped to 3 different types of tree barks...
33. ### Explain convection heat transfer using kinetic theory

I am trying to explain the convection heat transfer and the mass transfer related (buoyancy of the heated part of the gas) using only kinetic theory of gases , I mean using only collisions between molecules of the gas. The environment is the usual one : a hot wall in contact with a gas...
34. ### Home Improvement Project & PV=nRT

I live in an attic apartment and have been suffering a problem lately. Convection seems to be pushing (nasty kitchen smelling) air up to my apartment from my neighbors who live below me in the same building. This nasty air current primarily seems to be coming from a specific crawl space inside...
35. ### Need explanation on Chracteristic Length in heat convection

Hi, I am working on constructing a thermal circuit where I am using the concept of natural convection from a vertical hot plate in the shape of a DVD. In order to calculate the Grashoff number, I have to use the characteristic length. What should I take as my characteristic length? The disc OD...
36. ### Need some helps for a Heat Exchanger Optimization project

Hello fellow PF members, My teammates and I are working on a project in our Heat Transfer class. It is extremely broad (open ended) and we are not very sure how we should get this project up and going. 1) Project description: We are given an Air Cooled Rankine Cycle. Cooling water, at 70 °C...
37. ### Convection between two plates

Homework Statement From my lecture notes, here are the equations for convection between two plates. I have derived equations 9.6, 9.7 and 9.8. But for 9.4 there's a problem when gravity becomes involved. Homework Equations Navier stokes: ## \rho \frac{D \vec u}{D t} = -\nabla p + \mu...