# What is Convection: Definition and 194 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.

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1. ### Thermodynamics: Cooling of a heated block of iron in contact with air

Φ = 𝜑S (dQ/dt) = k*S*dT avec dT = (1500 + 273.15) - (40 + 273.15) = 1460 [k] avec dQ = - 0.24 [kg] * 440 [j/(kg * k)] * 1460 [k] = - 154176 [j] donc, -(154176)/dt = 40 [W/(k * m²)] * 0.0062 [m²] * 1460 [k] = 362.08 [W]
2. ### I Granules On The Sun: Photosphere Or Convection Zone?

Are the granules that we see on the Sun actually in the photosphere? Or are they actually just the top of the convection zone, with the photosphere beginning just above them? Or is the photosphere simply defined as the top edge of the convection zone where the granules are present, having...
3. ### A Granular convection (particle distribution) calculation

Hi All, Am new here came particularly hoping for some guidance I need to calculate theoretically, how different types of particles (shown below) distribute in a granular convection Condition: Large surface or open surface Types of particles: 1) Low volume, Low density particle 2) High...
4. ### Engineering Average heat transfer coefficient (forced convection)

So firstly, I don't understand if the mass flow rate is for steam or for water. If it is for water, I know I can find the heat transfer rate using equation:Q=mcdeltaT. But then I don't know how to find h (the average heat transfer coefficient) because I don't know the surface area (As). I can...
5. ### Convection current in electricity

So, I randomly came upon this in a textbook that I was skimming and I think I have a very very surface ideea of what it's about but I want to read and know more in order to understand the fenomenon in much more detail. Any help in any form would be much appreciated! P.S.: This is my first post...
6. ### 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
7. ### (CFD) Problem with C code for 1D linear convection equation

This is my c program below. Again everything works as expected up until the highlighted lines or the second for loop. When i run my program to output the arrays contents i get bizarre numbers that are not correct. # include <math.h> # include <stdlib.h> # include <stdio.h> # include <time.h>int...
8. ### 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...
9. ### Convection powered bladeless fan style ventilation?

I'm still trying to understand the operation of these fans. How does the geometry downstream influence the flow. Specifically, there is an 8" ventilation tube in the ceiling of my warehouse. I'm thinking that I can extend it until it is 3/4 of the way to the floor. If I crack open an overhead...
10. ### I Heat transfer coefficient and convection

I would like to fully understand two parameters involved in convection heat transfer systems. I have read the document https://fenicsproject.org/pub/tutorial/sphinx1/._ftut1005.html, and I am interested in the parameters ##r## and ##s## in eq. 69. As far as I understand, when one solves the...
11. ### Deriving the 1-D Linear Convection Equation

With the assumptions of Inviscid flow, no pressure gradient and no body force terms in 1-D Navier Stokes becomes 1-D nonlinear convection equation; And if we assume velocity of wave propagation is constant value c, equation becomes 1-D linear convection equation; This is online derivation and...
12. ### Natural convection enhanced by a "chimney effect"

It has been suggested to me that the ability of the heatsink shown below to remove heat from its base (orange) by natural convection could be enhanced by closing the open side (pink) shown in the figure below. Assume a lid (pink) of non-conductive/isolating material. I think the idea is that...
13. ### 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...
14. ### I What are the real-world applications of convection?

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...
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### A Non-homogenous convection equation

Does anyone know if there are solutions to the following PDE $$u_t + u_x = f(x,t)$$ If not in a general context, what if ##f(x,t) = \delta(x-at)/(x-at)##? Please let me know if you have any information. Method of characteristics?
16. ### B Convection in Stars: The Role of Mass and Structure in Fuel Consumption

As most people know, massive stars such as blue giant of Wolf-Rayet stars are short lived,only for a few million years.well tiny stars such as red dwarfs seems to be immortal by human’s prospective, and indeed they can live up to a trillion years! Most people thought it was only caused by the...
17. ### 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...
18. ### 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...
19. ### 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...
20. ### A 1D Convection Diffusion Equation - Inlet Mixing Effect

I have a working Matlab code solving the 1D convection-diffusion equation to model sensible stratified storage tank by use of Crank-Nicolson scheme (without εeff in the below equation). As indicated by Zurigat et al; there is an additional mixing effect having a hyperbolic decaying form...
21. ### 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...
22. ### Simplifying the Natural Convection Heat Transfer Correlation

Homework Statement An appropriate correlation for heat transfer by natural convection from a horizontal pipe to the atmosphere is Nu=0.53Gr^0.25 Pr^0.25 Where, Gr= (αp^2 d^3 (T_1-T_f )g)/μ^2 And Pr⁡〖= (C_p μ)/k〗 Show the above correlation can be simplified to h...
23. ### Exam help regarding heat exchanger, forced convection questions

hello, im in bachelors mechanical engineering programme and my thermodynamics papers are in few days one question is related to heat exchangers or forced convection, but our professor has hinted that in the exam the question regarding heat exchanger, forced convection will be a case study of a...
24. H

### Transient Energy Balance for Heating a Tank of Water

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...
25. ### A Difference between conduction & convection current density?

Hello Everyone, Could anyone please explain the difference between the conduction current density (J=σE) and the convection current density (J=ρvd)? I really appreciate any examples or applications to further elaborate these two theories. Note: vd is the particles' average drift velocity...
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### 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...
27. 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...
28. 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...
29. ### Convection Diffusion Equation

I'm tinkering with the Convection Diffusion Equation (a second order differential equation) to model a temperature behavior in proximity to a heat source in a water bath. Just to get going I solved the system for some arbitrarily chosen boundary conditions. The result is that the temperature at...
30. N

### I What is convection in a serpentine flow field?

Hi all. Rather than a physics student, I'm a translator, and tucked into a piece I'm translating from Japanese is an obscure (to me) physics reference. The sentence goes something like, "It seems a type of convection is taking place amid the serpentine flow of my memory." If someone could...
31. ### 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.
32. ### Thanks in advance.Heat Transfer Modeling: Get Insight for Physical Intuition

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...
33. ### Compressible inviscid vorticity convection w Rankine Vortex

Homework Statement The compressible inviscid vorticity convection equation: $$\frac{D(\frac{w}{\rho})}{Dt}=(\frac{w}{\rho})\cdot \nabla U + \frac{1}{\rho}\nabla P \times \nabla (\frac{1}{\rho})$$ differs from the incompressible version in two important ways : 1) The convected quantity is...
34. ### I Forced convection over a cylinder

I am building an apparatus to measure how does fluid speed effect heat transfer from solid on fluid. fluid runs over a cylinder which inner side is kept at a constant temperature. A calculation for surface temperature profile was made for a similar eaxperiment were a flat plate was used instead...
35. ### Earth's Core Dynamics - Convection

Hi all, I am interested in rotating convection. Anyone know of any open questions, or where to find research topics in this area? Cheers.
36. ### 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?
37. ### Cooling Steel Die for Contact Cooling of Aluminium - Advice Needed

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...
38. ### Understanding Convection Heat Transfer in a 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...
39. ### A Modeling diffusion and convection in a complex system

I am trying to come up with an analytical solution (even as a infinite series etc.) for the following diffusion-convection problem. A thin layer of gel (assumed rectangular) is in direct contact with a liquid layer (perfusate) flowing with velocity v in the x direction (left to right) just...
40. ### 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...
41. ### I Diffusion and convection in a moving fluid

In a fluid moving at constant velocity V, a concentration will undergo diffusion and convection $$U_t=\alpha^2 U_{xx}+VU_x$$ I understand that in this situation you can transform to a moving coordinate system and the convection term will disappear and you can solve for diffusion alone and...
42. ### Computational model for solution convection due to density difference

I am a corrosion engineer and I am trying to model localised corrosion, where saturated (dense) salt solutions flow over less dense solutions. I am aware of the Rayleigh-Benard convection model, where hot water rises and cool water sinks (e.g. boiling water on a hob). Is there a well known...
43. ### 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...
44. ### 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...
45. ### 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...
46. ### Processes in Convection cells / magma intrusion

Yes this is a bit broader question but I want to know which processes play their role in movement of magma. If one wants to model magma movement through rocks, which processes should one not miss at all and which equations discuss these processes?. As a starter I can that we can use Navier...
47. ### 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)...
48. ### What is the mechanism of heat transfer and air flow in coffee roasters?

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...
49. ### Convection coefficient for an annular finned pipe

Hi. I am stuck on a project on calculation of heat convection transfer coefficient for a annular finned pipe. All parameters [Diameter of pipe, diameter of fins for each case, the distance between fins, fin thickness, pipe length and fin number] are determined. And I have two book Fundamentals...
50. ### 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...