Convection Definition and 178 Threads

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...

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...

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...

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...

Realising that all is not well when we're just moving not thinking, I began to think about a trivial thing which has been around me for too long. What actually is convection? If it is governed by difference in density causing the masses to flow, is this not atleast distantly, similar to a...

I am trying to design a heat exchanger for a stratified hot water tank which means that the heat transfer on that side of the exchanger will be totally dependent on free convection. I plan on using a shell and tube set-up but I have no idea on how to calculate the required mass flow rate from...

Hi, Its been a while since I had my thermal heat transfer classes and I am a little skeptical on what I remember. Im trying to insulate a copper block, the sides are covered by an insulating material which has a low thermal conductivity (they are touching). Howver there is a surface on the top...

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...

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...

Hello, my problem is the following: I have an iron bar, which can be heated by convection through an electric cable with power Q. I want to know the temperature of the iron bar after 1 hour has passed, both in the case when the power is turned on and when it is off (Q=0). the input parameters...

hello I have a liquid or gas inside a metallic box (eg. stainless steel 5mm thick) how can I increase its temperature without heat convection or conduction?

Hi, I shall be grateful if someone can throw light on the heat transfer processes taking place through in this very simple example. Consider the attached image (pdf). See figure (c) which I have also marked in red block. It is pot lying on a hot plate. I want to know the heat transfer...

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...

Hi, I know, there is a stability condition for solving the Convection-Diffusion equation by Finite Difference explicit/implicit technique, which is \Delta t<=(\Delta x)^2/(2*D) for one-dimensional or \Delta t<=((\Delta x)^2+(\Delta y)^2)/(8*D) for two-dimensional problem, where D is the...

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...

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...

Dear all, I have a hard time in understanding the fundamentals of convection. Let's say we blow a fan over a hot surface. From fluid mechanics, I know that there is a velocity boundary layer due to the viscosity and no slip condition. The velocity gradient is kinda parabolic. Ok...

Homework Statement The goal is to derive the heat equation with convection, ut=α2uxx-vux but for the case where u(x,t) instead models concentration changes by diffusion and convection. The idea is to use conservation of mass to do this. Homework Equations We are given: Change of mass inside...

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...

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...

I just read the following about the evolution of stars: "When reaching point 2 in the HR-diagram, the radius of the star has been increasing so much that the surface temperature is close to 2500 K which is a lower possible limit. When reaching this limit, the dominant mechanism of energy...

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...

Hi my names Oliver and I'm new to this but I am currently studying engineering, maths and physics A levels and as part of my engineering I have to create an innovative product. My idea is a saucepan with a built in device to stir the contents without the need for human interaction. So far I've...

Homework Statement Determine the thermal conductivity of a metal (assume linear heat distribution at steady-state, and well insulated), given, Thot = 96.8 Tcold = 29.5 There is also: 13.7 W being pumped in at one end. Water convecting heat away on the other end. Homework Equations...

I am trying to calculate heat transfer from an inclined flat plate under free convection conditions. I am referring to Fundamentals of heat and mass transfer (Incropera / DeWitt). The equations and a spreadsheet which can be used to find a solution can be found at...

Homework Statement 4 rectangular long fins are assembled on a 40x40x6 mm aluminum heat sink with the fins being 30 mm long, t=4 mm in thickness and 40 mm wide. The system generates 3 W and the room temp is maintained at 20 c. What is the temperature of the substrate surface that holds the...

When convection currents are illustrated they are often painted as arrows with red and blue color, the red one being the direction of warmer currents and the blue ones being the direction of cooler currents. See for example this picture: But how does this go together with the fact that heat...

I'm trying to do a rough calculation to find the "operating temperature" of a concrete floor. I've found a paper that discusses calculations for rate of heat loss from the slab to the earth: here. (It's a Word file - don't freak out.) Which gave me a fairly reasonable figure of ~2400Btu/hr...

Can you guys give me example for conduction, convection, radiation energies ?

Hi everyone, I am currently undertaking my honours year in physics focusing on atmospheric physics. I am wondering if anyone knows where I can get a model to determine how much energy is moved to the top of the troposphere by deep convective "hot towers". I wish it was as simple as...

Homework Statement I have a question about part b for this question: In the solution apparently h1 and h2 are a function of temperature as shown here: However, I thought the convection heat transfer coefficient is a constant. I have done some problems where it is constant but in this...

I'm wondering with the circular fin, with uniform cross section area with given length and diameter. both ends are attached to surfaces. is there a general equation to find the heat rate by convection of the fin side surface. I tried to relate all the conditions and ended up with a equation that...

I am wondering if in a case where the air velocity comes from one face as shown in the picture. Can I assume the whole area going along the channel will be subject to the same convective coefficient? Thanks

Hi, please could someone explain how a convection current occurs. There are a few different explanations I have come across which in my view are not consistent. Warm air rises, becomes less dense and due to its buoyancy will rise. What mechanism causes the cooler air to replace this air? Some...

Homework Statement It is often stated that heat sinks, radiators, and the like require proper spacing of fins/pins/etc., especially when relying on natural convection. There is a formula from Rohsenow and Bar-Cohen that allows one to calculate the proper spacing between rectangular fins in...

Homework Statement I just completed a lab in class where we heated a copper pipe and measured the temperatures at 25 different locations. Each of these locations is called a node. The goal is to find the convection losses by using the First Law (qc1 + qc2 + qc3 + qc4 + qrad + qconv = dECV/dt)...

I have a difficult problem on my research exploration for math. I am modeling the convection currents of boiling water in a pot, which is heated by an electric stove. There is a constant supply of energy at 8000 watts (the average for a stove) that heats the pot from the bottom of the pot...

I have a difficult problem on my research exploration for math. I am modeling the convection currents of boiling water in a pot, which is heated by an electric stove. There is a constant supply of energy at 8000 watts (the average for a stove) that heats the pot from the bottom of the pot...

Here we have question with answer Could please explain to me the answer of this question ? and can explain to me why we don't use area 2pi . r^2 because we have pipe ? and how we can know this combined modes ? I mean conduction and radiation ? In addtion , As I know s = the...

I'm trying to figure out the convection coefficent between aluminum 4032 and steel in w/m^2*k 400w-500w? No Reason being I'm running a simulation of a thermal loaded aluminium detail, that is in contact with a steel plae. The upper part is heated by an external source. I need the...

Hi. Suppose I have 2 cylindrical bodies of the same radius and length - one is a good thermal conductor, while the other is a bad conductor. The upper end in each case is kept at a constant temperature T1, while the lower end is in contact with a steel disk of same radius, which is in free...

Calculating convection movement. Is there a simple way of calculating the mass flow inside a torus as a result of a difference in temperature. Asuming the torus is placed vertically and the heat source and sink placed in this way. Thank you very much. Cold side ( o ) Hot Side

Homework Statement Hi everyone, I'm working on an assignment and am totally stumped by this question: A horizontal cylinder is heated electrically. The cylinder is supplied with a current at a DC Voltage. Using the data supplied and allowing for both natural convection and radiation...

Hi PhysicsForums. I have a question. I was looking through a manual for an industrial grade PC, which is fanless, with the CPU mounted directly onto the chassis which is practically one large heatsink. When considering side-mount applications for this PC, I noticed that the manual had a...

whats would be typical value for free air convection heat transfer coefficient at high temperature of 1000 degree c? let say i have a vertical cylinder of diameter 5 cm and 3 cm high. and i heat it to 1000 degree c. the room temperature is 20c . what would the convection heat transfer...

Hello, I was trying to see if anyone knew a site where I could find directions on how to do Rayleigh–Bénard convection from home. I found this book on google books and it started to tell me then the pages jumped from 6 to 9. Any info would be appreciated. Thanks

Hello everyone, For the purpose of my study I would like to know the relation between Pressure and Convection Heat Transfer. Especially the rough pressure when the convection becomes less significant. I did not find satisfying results on the forum. I have to study the global heat transfer...

Convection heat transfer rate decided by Newton's cooling law doesn't have a relative velocity between the fluid and the solid surface term. But intuitively doesn't blowing faster on a hot surface make it cool quicker?

Hello, I have an interesting question about water natural convection without an external heat source. Say we have a high tower filled with water. The tower walls don’t allow any heat to escape or enter the system. There is a constant gravitational force present in a system (g-force). At the...

I'm looking for the analytical solution for the 1D convection diffusion equation with a constant heat flux. Boundary conditions: The domain I'm looking at is x from 0 meters to 1 meter. The temperature at x=0 is T=0 degrees Celsius. At x=1, T=100 C. I'm given the equation...