Questions tagged [convection]

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How do I calculate the amount of watts that a heating element needs inside a box?

I have an aluminium box (6 mm thick) of about 13.6 m³. Inside the box is a ventilator that can move 140 m³/h and I want to keep the temperature inside this box at about 30 °C. The box is to be placed ...
Magne Nysæther's user avatar
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How to calculate internal convection loss in a sealed container?

Say I have a box with a 1m x 1m x 1m interior wall dimension. The side walls and the floor are 10cm of styrofoam, with a thermal conductivity of 0.03 W/m K. The top is 1cm thick opaque plastic with ...
DaleCloudman's user avatar
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Heat convenction through double pipe

I have a realistic scenario which involves a double contained PP plastic pipe which a section of the pipeline is placed outdoor. What I want to determine if insulation is required at all. The media is ...
Dfhaa_DK's user avatar
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What effect does airflow rate have on heat dissipation if the initial heat varies proportionally to the airflow rate?

If I have a server rack consuming 10 kW of power in an empty room with A/C, what effect does the rate of airflow from the rack's exhaust have on the temperature in the room and the load on the HVAC? I ...
Chris's user avatar
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Nusselt number equations for external flow over a single finned tube heat exchanger

I am designing a heat exchanger that will utilize a singular finned tube of around 2" diameter with 4 fins per inch that are 3/4" tall and .03" thick. I am looking at finding the ...
Brad Lasley's user avatar
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Implementing convective boundary conditions for 1-dimensional finite difference computation of heat equation

I am simulating heat transfer through a 1-dimensional wall with convection on both sides. For the wall, I implemented a finite difference model like this: $$ u(x, t + ∆t) ≈ u(x, t) + c [u(x + ∆x, t) − ...
Dave's user avatar
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Does 'Jet Impingement Cooling' always cool?

I understand that by using jet impingement cooling, we can achieve a high convective heat transfer rate, but there is also a stagnation region where the kinetic energy of the jet will be converted to ...
GRANZER's user avatar
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Heat transfer in open equalization tank

I have to cool waste water in equalization tank (open tank) from 60 C to 30 C. Here is the information about the waste water: [![enter image description here][1]][1] [1]: https://i.stack.imgur.com/...
Stud Course's user avatar
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Correlations for convection coefficients in tubes at high Reynolds numbers

I am looking for a correlation to calculate the heat transfer coefficient for a convection problem for turbulent flow in a tube at high Reynolds numbers of > 5×106. This is where the Gnielinski ...
Felix's user avatar
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Can a steel plate reach -20°C due to radiative cooling when the ambient temperature is 2°C?

Conditions: there is a steel plate insulated at the bottom and facing the clear night sky, the ambient air temperature is 2°C, the cosmic microwave background radiation is 3K, and the convective heat ...
Miya's user avatar
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How do I get the temperature of a stainless steel pipe that's being heated by a direct current?

I'm working on the following problem: Use a stainless-steel pipe with an internal diameter of 0.016m and a length of 2.5 m to conduct a convective heat transfer experiment. During the experiment, the ...
Miya's user avatar
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What would be the advantage of using Colburn j factor instead of h (heat transfer coefficient)

Why do researchers use the Colburn j factor vs. Re when presenting the thermal performances of a heat exchanger? A graph of the heat transfer coefficient h vs. Re wouldn't be sufficient? What are the ...
Hélène's user avatar
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Modeling 1D Transient Heat Transfer: Wall/Room interface

Consider a 1D adiabatic room (of volume V) with a wall conducting heat on its left side. The wall is solid and heat conduction in it is driven by the common heat equation. There is convection at the ...
Camille Chaize's user avatar
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Why heat transfer happens only via conduction in this case?

Why heat transfer between a heated flat plate and a fluid happens via conduction only and not convection, when the fluid is present below it? Consider a plate under which a fluid is present and it ...
Harshit Rajput's user avatar
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Heat transfer coefficient in forced convection and its dependence of temperature

I'm working on a Ansys Fluent of an Aluminium coil annealing furnace with the goal of estimating the heat transfer coefficients at different temperatures and ventilator/fan speed conditions. The ...
Ash's user avatar
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Mean temperature of a fluid in a pipe

Consider a pipe in which a fluid flows such that the pipe is at a higher temperature than the fluid. At any cross section of the pipe we get a varying temperature profile. We can define a mean ...
Harshit Rajput's user avatar
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Does forced convection account for energy transfer in this case?

I have to confess that thermodynamics is not a friend of mine. My system consists of a volatile droplet sitting on a thermally conductive substrate. The energy balance comprises heat lost due to ...
Toadie_76's user avatar
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Isn't the Newton's cooling law for heat convection too macroscopic for CFD simulations?

In CFD (Computational Fluid Dynamics) simulations, the space is discretised into a huge number of tiny cells and, therefore, one has the opportunity to use a model of heat transfer that takes into ...
Élio Pereira's user avatar
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301 views

Can the Whitaker Nusselt number correlation be used for a hot sphere in convection with cool air?

The Whitaker Nusselt number correlation (equation 4 here if you don't know it) seems to not be applicable for when the viscosity of the fluid gets higher away from the surface, but it seems to get ...
William G Martin's user avatar
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Minimizing home heating costs [closed]

I live in an old rental house with 12 foot ceilings and zero ceiling fans. I am trying to conserve as much energy as possible as heating costs are expensive. I have placed plastic on all of my windows ...
Kasi Darnell-Tibbs's user avatar
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Calculating Thermal Convection Coefficient

I am designing a heat sink, the diameter of the hole is 6mm. and the diameter of the fibre rod is 1.2mm. The material I am using is aluminium, with thermal conductivity of 230. The ambient ...
Dugong98's user avatar
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In this scenario, if I continue to increase the length of heat exchanger how will the temperatures change?

Consider a counter flow double pipe heat exchanger inside which the cold fluid enters at 20 degrees Celsius and hot fluid enters at 100 degrees Celsius. Initially the length of the heat exchanger is ...
Harshit Rajput's user avatar
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1 answer
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Is this value of critical Reynolds number also valid for ducts?

In internal flow, when a fluid flows inside a circular pipe, the most practical value of critical Reynolds number is taken as 2300. I was wondering if this number is also the same for non circular ...
Harshit Rajput's user avatar
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2 answers
91 views

How to visualise/measure airflow in sauna?

I'd like to visualise/measure the flow of air in sauna to optimise the ventilation. Is there a way to colour the air (non-toxic!!!) so I may watch the flow? Or is there any other accessible technology ...
Honza Zidek's user avatar
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Errors obtained in the numerical solution of the 1D convection-diffusion equation

I have been trying to solve the 1D convection-diffusion equation In implementing the above, I have tried to follow closely the method described here: https://uk.mathworks.com/support/search.html/...
gary105's user avatar
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Analytical solution for the 1D convection-diffusion equation

The Ogata and Banks analytical solution of the convection-diffusion equation for a continuous source of infinite duration and a 1D domain: where C [mol/L] is the ...
gary105's user avatar
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1 answer
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surface temperature due to constant heat flux

Imagine a hollow cylinder with the outside surface exposed to air (convection). If there is a constant heat flux on the inside surface how would I calculate both the inside and outside surface ...
mani shekar's user avatar
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Why do we consider the normal component of velocity in a flux and not the original direction of velocity?

Below is the equation of convective flux of an arbitrary property that is carried by particles. When particles move they carry their property along with them. Given a fixed surface in space, in order ...
user134613's user avatar
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How to calculate heat loss across a process pipe with perpendicular air flow

My thermodynamics knowledge is extremely rusty, so I would appreciate some guidance on how to solve this problem. As illustrated here, I have a process pipe (steel) with a gas flowing through it (blue)...
Phizzy's user avatar
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Empirical correlation for low reynolds convective heat transfer coefficient

I am looking for a heat transfer coefficient for a shape (rectangular cross section preferred, could estimate with flow over flat plates) in 2 m/s cross flow. I have found a few empirical correlations ...
sam232423232's user avatar
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As a rugged and waterproof device, how does gopro dissipate heat?

I am new to designing rugged + waterproof products. I am curious about how to dissipate heat when the electronics are running and the ambient environment is even hotter. It seems like the mode of heat ...
Wei Xun He's user avatar
1 vote
0 answers
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Heat Conduction/Convection Along discontinuous tube

I have a question regarding heat conduction/convection. I have a metallic tube over which a rope heater is wound, supplying power. A glass tube and a 2nd metallic tube lies at the exit of the first ...
arodor's user avatar
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2 answers
256 views

How to calculate heat and mass transfer rates from an enclosed box?

I'd like to know if it's possible to calculate the heat and mass transfer rates from a small volume to the environment. Let's assume there is a box with a small opening at the top. The air inside the ...
Sergio's user avatar
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Heat transfer for a copper rod

For a copper rod heated by a heat gun, why might the temperature of the rod continue to increase for a short time after the heat gun has been removed as the heat source? With reference to transient ...
Joe's user avatar
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1 answer
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How to consider the dimension of a cylinder when computing its radiative budget?

I am trying to derive a heat budget model to estimate the temprature of very small a stationary vertical cylinder (1mm) under environmental conditions. Imagine a wooden stick. Simply put, I have R = ...
MorningGlory's user avatar
1 vote
1 answer
205 views

Wire heating and heat transfer in a cylindrical pattern

I have a series of copper coils with ¼” cooling plates between each coil. The cooling plates will be manufactured from aluminum and cooled using copper tubing. There are seven in series, and a plate ...
alcopo63q's user avatar
1 vote
1 answer
252 views

Heat Transfer in Different Wire Configurations

I am trying to create a program which estimates the final temperature of a magnet made of copper wire. I have different configurations in mind, but I will start off with a straight square wire with a ...
alcopo63q's user avatar
1 vote
0 answers
295 views

Minimum distance between long curtains and radiator for good air flow?

It's a known fact that you cannot place a curtain near a radiator because it will trap hot air behind the curtain and also block cold air from going through the radiator from bellow. But obviously ...
Yuri Borges's user avatar
3 votes
1 answer
2k views

What is the difference between the wave equation and the advection equation?

I am trying to understand what is the difference between the wave equation ad the advection equation? Bot the equation seems to move a quantity. While in literature it is said that the advection ...
GRANZER's user avatar
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Ventilation requirements of a closed housing of a video wall

Our company builds rather large video walls that are driven by computers next to them. In one of our current project the size of the installation is 21 55" displays side by side in portrait mode and 4 ...
PepitoSh's user avatar
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1 answer
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convection query

I am attempting some convection analysis for research I am doing. I was wondering someone could kindly confirm whether I am on the right track. The calculation is based up air being passed over a flat ...
85l00k85's user avatar
1 vote
1 answer
87 views

Convection Heat Transfer

I am working on a problem at the moment and would appreciate some of your expertise regarding this issue. If you see the image below, I am trying to calculate heat transfer from a fluid entering a ...
85l00k85's user avatar
0 votes
1 answer
334 views

Most effective heat transfer in a vertical pipe with small top/bottom temperature difference?

What would be most effective way to transfer heat in the following situation? Specific conditions: A vertical cylinder or pipe, 30-100cm long, 5-10 cm in diameter, heavily thermally insulated except ...
Colin Stark's user avatar
1 vote
0 answers
357 views

Calculating heat transfer in a cooling loop

Imagine a closed pipe like below, filled with a liquid. The pipe is copper. Then imagine a small point heat source of X watts applied to the outside of the pipe in the position shown. Heat warms the ...
Paul Uszak's user avatar
1 vote
1 answer
187 views

Characteristic dimension for combining free and forced convection?

I have a situation that I have a combination of free and forced convection over a cylinder. Remembering back from heat transfer, to combine these I use the formula $$Nu_{\mathrm{comb}}^n = Nu_{\...
user1543042's user avatar
2 votes
1 answer
129 views

Can I neglect kinetic energy when modeling convective heat transfer for viscous, low mach airflow? Why or why not?

I'm looking at convective heat transfer for air flow over a solid at Ma=0.2. At this speed, it is plausible to model the flow as incompressible because of small density variations in the air. ...
Paul's user avatar
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2 votes
1 answer
777 views

Convective heat transfer coefficient in finite difference method boundary conditions

Suppose there is a cubic material with an internal heat source ($\Delta q / \Delta t =$ Constant), and is immersed in a sufficiently large amount of water. Now I would like to use finite difference ...
Xiangxi Meng's user avatar
5 votes
1 answer
730 views

How to determine if mass transfer convection is natural or forced?

I know that forced convection requires some external bulk flow, but is there an equation to determine which form of Convection is dominant? I looked around and found the Richardson number $\mathrm{Ri}=...
user4785's user avatar
2 votes
1 answer
427 views

Heat transfer characteristics in narrow rectangular channel

Please take a look at following figure: System considered is a narrow rectangular channel of 2.5 mm depth (W x L is 60 mm x 150 mm). Since channel has low depth, it can be considered as mini-channel. ...
user1768201's user avatar
4 votes
1 answer
1k views

Heat Transfer coefficient calculation for hot air flow inside rectangular duct

I am working on modeling of air-heater component. A simplified representation of system is as follows: Cold air flow enters steel duct at one end. Inside duct is Calrod heating element shaped as ...
user1768201's user avatar