Convection Definition and 178 Threads

Hello Wondering if anyone can help me towards finding an equation to calculate the heat transfer due to forced convection? Can't seem to find a good source for one at all, needs to be referenced for my MEng project. Currently have for natural convection: Q = h A (ΔT) Thank you...

Hello everyone, So I am an Aero-Thermo Intern at Pratt and Whitney, and my supervisor gave me the following problem to set up a mathematical Excel model for the temperature gradient inside an enclosed box with a heat source underneath it to be used in thermal analysis of an engine component...

I am trying to develop a spreadsheet to calculate a convection coefficient with altitude as one of the inputs. What variables should I consider? The most obvious are pressure and temperature, but I'm sure there is more to it than that.

in refrigerators, why cooling boxes are kept at top?

Homework Statement A silicon chip measuring 5mm by 6mm and of thickness 1mm is embedded in a ceramic substrate. At a steady state, the chip has an electrical power input of 0.3W. The top surface of the chip is exposed to a coolant whose temperature is 20°C. The heat transfer coefficient for...

Homework Statement Solve u_t -k u_xx +V u_x=0 With the initial condition, u(x,0)=f(x) Use the transformation y=x-Vt Homework Equations The solution to the equation u_t - k u_xx=0 with the initial condition is u(x,t)=1/Sqrt[4\pi kt] \int e^(-(x-y)^2 /4kt)f(y) dy The Attempt at a...

Hello, PhysicsForums! I've been discussing what little I know of plate tectonics with someone and the other party has suggested that convection cells within the mantle (assuming convection really occurs at all) should eventually move such that they no longer push more matter up through...

I need some clarification regarding the following formula: Qconv = Pn x Qs x b x ϕ this equation is used to determine the cooking appliance's convective heat output in kw, 'b' and 'ϕ' are coefficients easily determined. I am confused whether to use the actual capacity of the appliance for...

the bottom. Would it still obey the laws of convection, how would it?

Hi I'm trying to workout the velocity of air inside a pipe that's sealed and ten meters long. I've found this Air Velocity vc = 0.65 [g l dt / (273 + te)]1/2 (1) where vc = velocity in center of airflow (m/s) g = 9.81 - acceleration of gravity (m/s2) l = vertical distance from bottom of...

Homework Statement Consider a flat plate subject to parrallel flow (top and bottom) characterized by u∞ = 5 m/s and T∞ = 20°C. Determine the average convection heat transfer coefficient and convective heat transfer rate with an L = 2m long and w = 2m wide flat plate for airflow and...

Dear all I got a value of 37 for h ( convection heat transfer ) Does it consider as free or natural convection heat transfer coefficient? Thanks in advance ! And Sorry its not a Homework problem :)

I am confused as to how heat transfer really works. I've read all about conduction/convection/radiation. Radiation makes sense to me, electrons enter a higher band, come back down and give off energy in the form of EM waves. These waves can then be absorbed by other atoms causing electrons to...

Hello everyone, I am trying to model the flow of steam through a vertical cylinder. Ultimately I would like to find the surface temperature as a function of the length of the pipe. I am assuming the steam cools as it moves upward along the length of the pipe and it is a steady-state process...

Hi all, I have a unique problem that I need some direction on. I have a .5x.5x.75 meter adiabatic chamber. No heat loss from chamber walls to the atmosphere. Inside the chamber there is an electrical flat heater plate .5x.05 meter with constant 100W. A fan blows air over the heater bar at...

A person is standing near heater .How is he getting heat?

I used to think that the heat does rise even in solid metals with no gas/liquid around (No density argument is possible then.) But couldn't find anything describing or even verifying it. I'am pretty sure the gravitationally induced anharonicity in the atomic core potentials should have at...

In my book I'm reading about heat, specifically convection. There is an image of a person with a drink in their hand, suntanning while a fan blows on them. I get that the drink represents conduction, the sunlight is radiation, but how is the fan convection?

I have a question... Suppose you have a thin and long rectangular piece of aluminum. You heat one end (pt A). The thermal resistance (steady state) from one end (pt A) to the other (pt B) would be θ=ΔT/W Where W= Watts of heat energy. ΔT = temperature of ptA - temperature of ptB...

Homework Statement A thin rod of length ∏ is heated at one end to temperature T_0. It is insulated along its length and cooled at the other end by convection in a fluid of temperature T_f . Find the transient and steady-state temperature distribution in the rod, assuming unit thermal diff...

Ok, I have some questions to answer for this lab report, and one of them has left me clueless. The experiment was as follows: An apparatus is made of a rectangular circuit (of known dimensions) of tubes filled with water with thermometers visible at various points throughout the circuit. No...

hi, if i have a cylindrical rod of copper and i heat is at one end face while the other surface areas are open to the atmosphere then besides the conductivity of copper i will also need the convective heat transfer coefficient to analyse the setup. my question is : how do can we estimate...

I need to develop a simple model in Comsol, but I have no experience with it. I need to see what the convective currents and velocity fields are at certain temperatures in a glass optical fiber. I have the information about the fiber and its dimensions. The fiber is going to be at around its...

I have a heating element. This heating element is placed on a wall. If I want the heat to be supplied horizontally would a relflector blocking the top of the heating element work? to prove this are these two statements below correct?? 1. Heat rises so by blocking the top of the heating...

Hey, I was having this very silly problem in heat transfer. Please could you see what's going wrong ! I am working on defrost water tray modelling. In that, the water collected during defrost is heated by the compressor o/p coil so as to aid evaporation. I was trying to find out the heat...

For extended surface or fin, how do we find the convection coefficient ? Explain some general idea? thanks

The problem is as follows: \frac{\partial u}{\partial t}=k\frac{\partial^{2}u}{\partial x^{2}}+c\frac{\partial u}{\partial x}, -\infty<x<\infty u(x,0)=f(x) Fourier Transform is defined as: F(\omega)=\frac{1}{2\pi}\int_{-\infty}^{\infty}f(x)e^{i\omega x}dx So, I took the Fourier...

I'm learning c++ and currently trying to write a little programme for 1D linear convection (wave equation). I have managed set all boundary and initial conditions as well as a mesh. But I have reached the point where I can't understand why the program does what it does. In red I...

I'm studying the effect of a magnetic field on a non-conducting fluid, such as liquid oxygen or liquid hydrogen. As I know a convective flow can be driven, if the extern magnetic field is strong enough. The extern magnetic field can be uniform or nonuniform, but the effect of convection is much...

Hi, I've did an experiment today, a forced convection in circular tube where the heat flux is constant along the length. my result seems not follow what it should be.. [PLAIN]http://img688.imageshack.us/img688/8015/expresult.png what I'm wondering is shouldn't it in a fully...

Hi All, I'm trying to understand heat so I'm going to say what I understand and ask you to please tell me if I am correct. Thank you. Radiative Heat - This is heat transferred in the form of electromagnetic radiation and does not need a medium. If in a vacuum, the radiation will travel...

Hi all, I have recently observed a very strange thing (or rather, I shall say unexpected phenomenon). When I deposited some charged micro-particles between 2 electrodes (vertical plates) with a DC bias in hexadecane oil, I expected the negatively charged particles to go to the positive...

Hello, Do you have any idea where I could find my formula for the Grashof N°, Nu and Heat? Thank you very much for your help Steve

Homework Statement A vertical steam pipe of outside diameter 7.5 cm and height 4 m has its outer surface at the constant temperature of 950C. The surrounding air is at atmospheric pressure and at 200C. How much heat is delivered to the air by natural convection in 1 hr? Homework Equations...

Hello! I'm currently reading papers about ferrofluids and trying to understand the physics behind this topic. I do understand, that if we consider a vertikal temperature gradient, we get a antiparallel magnetization gradient. The ferrofluid with a the higher magnetization will move to the...

Hello, everyone! I could not imagine what force makes this convection under concentration gradients , no matter how hard I thought. Maybe we can use principle of entropy increase to explain it, but that is not vivid to me. anyone can help me? Thans!

Hello, I am having some problems with COMSOL multiphysics 3.5a. I am using 2D weakly compressible flow with general heat transfer and am trying to model a natural convection loop. The Approach I have taken is to use properties of the material for a certain range of temperatures to...

Hey I've got this question and the answer that is giving is 219.12 but i keep getting 319 could someone please help me out here's the question. Consider a person standing in a room. The room air temperature is maintained at 22OC at all times. The inner surface of the walls, floors and the...

Hi, I have a pseudocode I would like to try and implement and understand the programming of it in python. The physics and maths of the case is no problem, but the implementation of the code in Python is something I'm not familiar with. The problem is a simple 1D linear convection using...

Homework Statement Two large thin aluminum plates, the first polished (emittance = 0.05 and the second painted black, are placed horizontally outdoors, where they are cooled by air at 283K. The heat transfer coefficient is 5 W/m^2-K on both the top and bottom. The top is irradiated with 750...

So this is my current problem: I have block of solid material that separates two bodies of gas. The temperature of all three is known (and presumably all different). The solid material is also being heated, equally throughout its volume. I want to know the instantaneous heat transfer...

I am working on a problem involving heat transfer from a horizontal pipe in air. I am having trouble with it and not getting the solution I expect, and I think it is because of the convection component of the heat transfer. The general formula I am following for convection from a horizontal pipe...

Homework Statement A flow of air at 27C and 1 atm is hydrodynamically fully developed in a 1c I.D pipe with uav=2m/s. Plot(to scale) Tw,Tb, qw as a function of the distance x after Tw is changed or qw is imposed. a) in the case for which Tw=68.4 C = constant b) in the case for which qw=378...

Hello, I am working on a case in which I'm trying to calculate the heat load of a house (actually mine). I want to be sure that the calculations were done correctly during the design phase. Disregarding the methods at various web sites (most of which are commercial), i'm doing it in a...

Hello! thanks in advance for any help you can throw my way! I am in my masters year of an Acoustical Engineering course in the UK. We have been set a group design project to with essentially setting up a forced convection cycle in a room in order to redistribute the heat from a radiator and...

Homework Statement A tent being considered for cold-weather conditions has insulation on the top and sides with a conductivity, k = 0.040 W/(m*K) and a thickness, l = 0.50 cm. The tent (and surrounding medium) has the following conditions: a heater (inside the tent) producing heat at a rate...

The other day I was at a football match and I had a cup of tea in a styrofoam cup. The tea was practically boiling - far too hot to drink, but the cup was only warm to the touch. I know that if the tea had been in a china cup or mug it would hve been uncomfortably hot to pick up. Why does the...

Both are near silent and 100% (in)efficient, but does the convection heater (with the electric coil where heat rises naturally) make the room more stuffy as I've sometimes heard, or perhaps even deplete oxygen?

I am trying to calculate the length of a pipe needed for an air cooling system I have found the following formulas: R=1/(h*a) where h is the convection coefficient and a is the surface area. h=Nu*(k/L) where Nu is the nusult number and k is the thermal conductivity. a=π*d*L where d is the...

I have a transformer in a box that is cooled using natural convection. There are louvered openings on the box to pull cool air in the bottom and let heated air out of the top. How do I determine how much heat is actually leaving the enclosure? Info that I have is the area of the enclosure, the...