Questions tagged [convection]

transport mechanism involving bulk motion of a medium

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347 views

A theoretical model for evaporation occurring when wind is blowing over the surface of water

I've recently done an experiment in which I was studying the variation of the cooling rate of hot water in a draft (wind). The air was blown directly over the surface of the water (kept in a ...
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627 views

Numerical Solution of the Propagation-Dispersion equation

I have asked this question on Computational Science and also on Mathoverflow, but no satisfactory answers so far. I thought maybe the physics community could shed some insight on the issue. I am ...
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3answers
159 views

Why doesn't convection break conservation of energy?

assumption: Warmer gas rises. (under gravity) assumption: A volume of gas cannot have uniform temperature, because gas with fully uniform temperature (all molecules having the same speed) has lower ...
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1answer
82 views

Coupling Navier-Stokes and stochastic models for particle tracking in micro-scale free convection?

I have been using a commercially available software to simulate laminar free convection in a specific small domain (let's use channel w/ heated lower wall as an example). The scale is approx 50-100 ...
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1answer
122 views

Can convection cells evolve in stably stratified fluid?

Assume stably stratified fluid but not in equilibrium, e.g. with non-constant temperature gradient for example. Can convection cells be present? Typical example of convection cells is Rayleigh–Bénard ...
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1answer
74 views

Determination of the thermal resistance of a molding tool with cooling channel

This is a section of cooling channels in injection moulding tools. I have tried to calculate the thermal resistance in this section with 2 methods, one analytical and one numerical. analytical ...
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166 views

Maximum temperature possible on earth

What is maximum temperature that can we have on earth on a single day? Lets say an air mass is static over an area and there is no way for air mass to move, sun warming it up would increase ...
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51 views

Vanishing viscosity in eqn. of heat transfer for free convection: on what argument?

In Landau's and Lifshitz' Fluid Mechanics on the derivation of the equation of heat transfer for free convection p. 218, they write In the thermal conduction equation (50.2), the viscosity term can ...
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135 views

Heat Generation in Watts per cubic meter - how to apply this to a volume?

Water is running through a pipe. The pipe is heated uniformly in order to heat the water running through the pipe. I want to calculate how much heat needs to be generated by the pipe in order to heat ...
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3answers
64 views

Relation between volume of a room and temperature inside

I don't know whether it is based on some people's assumptions or it is a fact that the smaller the room, the hotter it is (say, during summer), considering the heat is only supplied from outside the ...
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233 views

Heat transfer on Mars

SCENARIO: I have been tasked with finding the heat transfer across a composite wall on Mars. On the left of the wall there is air maintained at Earth atmospheric conditions and room temperature (101 ...
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289 views

Finding the temperature of the glass envelope in an incandescent light bulb

I've been trying to evaluate the temperature of an incandescent light bulb, using radiation for the filament and convection for the bulb, the radiation's equation works fine, but the problem is the ...
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61 views

Nusselt number in Rayleigh-Bénard convection derivation

I read, that for a box with length L, with heated bottom and cooled top and boundary layers of thickness $\delta$, the Nusselt number Nu can be approximated as $$ \text{Nu}= \begin{cases} 1,& ...
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86 views

Is the sensation of air movement inside a closed cornering car due to differences in air density

The scenario. At ambient temperature of 0degC to -5degC car sets off, engine warms up and heater is turned max temp and high blower on with recirculate feature (faster heating, no cold make-up air or ...
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64 views

Forced convection: temperature gradient in conical pipe

My situation involves a conical pipe of known dimensions and material composition. Warmer-than-ambient air is added to the small end at a steady, known flow rate. I'm hoping for a way to estimate ...
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34 views

Vertical wall at 3 different temperatures - do the same natural convection coefficient correlations apply?

I have an vertical enclosure that consists of 3 shelves, each with its own temperature and are thermally isolated from each other. We will call the shelves A, B, and C with A being the base shelf. The ...
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14 views

Convection current vs current created by an electromotive force acting on a charge

I am wondering if I can use the term 'convection current' for the current created by an electromotive force acting on a charge that sits on some rod that moves through a magnetic field. The convection ...
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22 views

1D Convective Heat Transfer

I am considering 1D convective heat transfer in a vertical heat pipe with a constant wall temperature Tw, with z varying from 0 to L. Applying the Boussinesq assumption, we arrive at the following ...
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1answer
29 views

What is the temperature profile of hot and cold fluids for a double pipe parallel flow heat exchanger?

In books, they just mention the temperature profile is exponential. Can someone help me come up with the exact temperature profile (the relation) for the hot and cold fluids in a double pipe parallel ...
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1answer
58 views

Is it wrong to derive Log mean temperature difference (LMTD) of a Heat Exchanger, this way?

I tried deriving the LMTD of a parallel flow double pipe heat exchanger by first finding the temperature profiles of the hot and cold fluid and then averaging them over the entire length of the Heat ...
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18 views

Thermal Boundary Layer

When we study convection in Heat Transfer then there a part where a fluid flows over a plate maintained at a temperature T. In this case heat transfer ocurrs both by conduction as well as convection ...
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27 views

Why does bologna inflate radially when on stove?

I noticed that when heating up bologna in any way it inflates at the center, while other stuff tends to let the air escape sideways, or inflates in different places, like an egg or sausage. Nothing so ...
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1answer
53 views

Navier-Stokes Convective term divergence of tensor is a row vector

Consider the convective term from the Navier-Sokes equation (e.g. Navier–Stokes momentum equation (conservation form) from https://en.wikipedia.org/wiki/Navier%E2%80%93Stokes_equations): $$ \nabla \...
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How does the speed/rate of convection currents in water in a tube affect the change to temperature of water at the upper end of the tube?

I have done some experiments in which I heated a burette filled with water by applying a preheated soldering iron to approximately the middle of the burette and measured how the temperature of water ...
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9 views

Convection/conduction simulation run from equal temp, but losing heat

I was investigating the effects of heated wall materials on outdoor air temperature and indoor air temperature with a certain software. The system is as the following: 1x1x1 meter cube of outdoor air ...
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Hypothetical: generating an inadvertent and transient magnetic field in a massive biodome

I am doing a thought experiment for a sci-fi novel and have a physics related question. I do have some elementary knowledge of physics from college. Before I ask my question, I need to establish a ...
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34 views

Can one model fluid flow only by using the convection–diffusion equation?

Modeling fluid flow in a coil seems very complicated, especially for turbulent flow. Having Navier-Stokes equations seems to be the right way to go, but I was wondering... can one use the convection-...
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71 views

How to obtain a solution for the following IBVP?

I am trying to solve the following advection-diffusion equation for transient flow conditions for radial flow. The governing equation is as follows. $$\frac{\partial T}{\partial t} = \frac{\partial^2 ...
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35 views

Quickest way to dry wet floor

I have spilled around one liter of water to wooden floor. I'm afraid wood will deform and pop out. What would be quickest way to dry it? I have wiped out what I could, but some water passed between ...
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19 views

Convective Air Velocity

Consider there is a hot plate which causes natural convection in a closed environment of air over the hot plate. Is there any exact formula to find velocity of air flow? If there is please cite the ...
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10 views

Convection powered bladeless fan style ventilation?

So as I understand it Bladeless fans use the Coandă effect of air hugging the walls of an expanding cylinder to creat a lower pressure zone that pulls additional air in through the center. My question ...
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25 views

Exponent of Lewis number in coupled heat-mass transfer problem

I am writing a small model of the coupling of heat and mass transfers in the nose and mouth. By solving the heat and mass balance equations, Lewis number expression appears that allows for coupling ...
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41 views

Limits to natural convection in a non-infinite medium

I'm trying to understand the temperature profile of a fluid in an underground vertical pipe without flow. The fluid is subject to a boundary condition of the form: $$Q = h[T_e(z) - T],$$ where $Q$ ...
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101 views

How much conduction, radiation and convection influence in a thermos flask?

It has been thoroughly repeated that thermos flasks prevent heat loss by minimizing heat conduction, radiation and convection from the bottle to its ambient. This has been answered in this SE. However,...
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141 views

Material Derivative in Fluid Dynamics and Bernoulli Flow

If a fluid flow, such as water, is incompressible then the convective derivative term in the material derivative is equal to zero. How then, in a Bernoulli flow where there is an increase in velocity ...
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410 views

Shear stress and surface heat transfer rate with various Pr values

I'm revising for my Fluid Mechanics exam, and came across a question that ask us to explain the behaviour of the shear stress and surface heat transfer rate with various Pr values. The question is ...
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1answer
597 views

Evaporation rate of water with forced convection

A steel pot (diameter 200 mm) is fully filled with water (2 kg of water) and the water is maintained at a constant temperature of 40°C by supplying heat from an electrical tabletop burner. Assume ...
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2answers
74 views

Air temperature equilibrium

Suppose an ideal airtight room, filled with air, no changes in volume, amount of air or energy. On the one hand, "hot air rises" (less dense, flotation, convection...) ((there's gravity, we are on ...
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1answer
94 views

Is there heat transfer through radiation in a drinking flask with styrofoam insulation?

Suppose we have a drinking flask with styrofoam between outer and inner walls. The heat can be transferred through styrofoam by conduction. Is the heat transferred by radiation as well? My lecturer ...
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1answer
48 views

Inertial reference frames in an atmospheric science context

A Hadley cell cycles air meridionally between the equator and 20 ◦ latitude. Assuming no zonal wind at the equator, what is the mean speed and direction of the trade winds at 20 ◦ ? My instructor ...
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1answer
102 views

Convection current

I am a master student (geology), I seek to ask how one can simulate convection current movement. What the difference between Boussinesq approximation and non Boussinesq approximation, and what are the ...
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1answer
42 views

How to have high agitation caused by high air flow while heating the same air?

It may not be possible but I am trying to create an environment that has decent air flow for agitation. I want that environment to receive heat though through convection so increasing temperature over ...
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2answers
300 views

Natural convection and buoyancy: What is a better description of $g$?

In their derivation of the Grashof number (Gr), Çengel and Ghajar make the following comment: Note that there is no noticeable gravity in space, and thus there can be no natural convection heat ...
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91 views

Stationary Heat Equation with Convective Boundary Conditions

Let's say that I know a fundamental solution for the Laplace equation in the whole plane: $$\nabla^2u(\mathbf{x})=\delta\quad \text{in the sense of distributions}$$ And I need a solution for the ...
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1answer
2k views

Source for Nusselt number correlation for cooling sphere under forced convection

I've been trying to find a Nusselt number correlation for a sphere cooling in a forced gas cross flow where the sphere temperature is much higher than the free stream temperature. I want something ...
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1answer
299 views

Which are the best books I can refer for turbulent heat transfer and its computation?

I am a graduate student. I wanted to do computation on heat transfer problem mainly heat convection. I am working on turbulent regime. Can you kindly suggest some good books so that I can get ...
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566 views

Heat transfer through convection in human body

How does the heat transfer takes place in human body through convection in these two situations. 1) when environment temperature is less than body core temperature($37^0C)$, say it is around $25^0C$. ...
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59 views

How complex is an energy balance for this problem?

Let's say I have an enclosed room in the shape of a box with forced airflow on the outer walls at an ambient temperature. Each end of the room (forward and rear) has a vent that ducts in warm air to ...
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1k views

Determine pipe outlet temperature without length?

Let's say I am flowing a fluid through a pipe that has a constant surface temperature. Is it possible to determine the heat flux on the inner surface without knowing the pipe's length when the only ...
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213 views

Fluid mechanics Grashoff number

When I derived the Grashof number (for natural convection at a vertical plate) starting with the ratio of buoyancy forces to viscous forces, I realized that I had set the Reynolds number to 1 (ie I ...