Questions tagged [thermal-conduction]

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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 ...
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1 answer
42 views

Volume of air going through a hole with a temperature difference, and kWh of energy

Let's say we have a square hole of 2cm x 2cm in a wall. The inside temperature is 20°C, the outside temperature is 10°C, so $\Delta T = 10$. This creates a flow of air. Let's say the velocity is $1\ ...
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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 ...
-1 votes
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Heat Transfer Problem - Cooling of water through aluminium coil

I am trying to figure out how to compute the outlet temperature of water that goes through a coil and is cooled down by an aluminium block. The goal of this system is to cool down the water, by ...
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1 answer
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Blower door DIY test

Since in my area there is no way to do a blower door test for a house, I was thinking to do a DIY blower door test. Here is my test scenario: Preheat the house before testing to have 10 degree ...
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 ...
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2 answers
315 views

High thermal conductivity in soft, fleece-like textiles

Fleeces typically exhibit low thermal conductivity, and are often used in winter clothing for their insulating properties. I am seeking a material for a radiant heat application that is soft to the ...
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1 answer
57 views

heat flow in a annular cylinder of insulating material

Maybe this belongs in DIY, because ... I'm trying to analyze the amount of heat required to prevent water supply pipes from freezing. The pipes would be protected by electrical heating tape and ...
1 vote
1 answer
244 views

Analytical solution of thermal stress in a bi-metallic cylinder

As a side project I have looked to solve using Python an analytical solution for one-dimensional transient heat transfer in a thick cylinder with cladding on the inside surface, wherein the fluid in ...
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29 views

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 ...
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1 answer
26 views

Minimizing heat transfer to the contents of a non-airtight pipe

Consider the following simple (half)pipe setup: The grey part is a galvanized-steel half-pipe. The green part consists of the ABS plastic non-airtight top lid and an internal layer of ABS plastic ...
2 votes
2 answers
59 views

R value of a hole?

Suppose I have a room, 10x10x10m with insulated walls (R-value: 4) and a single double-pane window 1x1m (R-value: 0.35). Now the total thermal power required to keep the room at a desired temperature ...
1 vote
1 answer
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Can $R$ value be estimated by change in temperature over time?

Suppose a closed sphere with a hull and an $R$-value of $10$ m2 K/W and a radius of $1$ m. Suppose the temperature inside of the sphere is Ti, the temperature outside is To. The inside temperature is ...
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1 answer
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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 ...
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Configurating heat transfer between parts

I am new to Ansys, so sorry if I have some misunderstood parts. I am doing a Steady-state Thermal simulation of a PCB with some of its components. I am currently simulating only the highlighted ...
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95 views

Water through a Copper-Coil Heat-Exchanger: How much tubing will be enough?

I am making a hot-water tank for a boat. Within it will be a copper-coil heat-exchanger. Because copper tubing can be rather expensive, I am trying to better understand the design beforehand, and ...
1 vote
2 answers
239 views

Heat transfer: does the heat generated in a cable get transferred to the electrical components?

I have a 1000 V, 50 sq mm, double insulated (XLPE) copper conductor cable. This cable is being connected to a power electronic component. The current flowing through it is 230 Amps DC. The cable ...
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1 answer
3k views

How to calculate temperature rise on AC induction motor in an evaporative cooler centrifugal blower?

A neighbor recently asked me if his evaporative air conditioner was running correctly because he felt the blower drive motor and it was too hot to leave his hand on it for long. I was surprised to ...
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40 views

Diffusor for uniform illumination

I have an LED with a beam angle of 120° and I need to illuminate an area in the shape of a circle with a radius of 3.5 mm. My objectives are as follows: Achieve a uniform illumination of the circle (...
1 vote
1 answer
67 views

What is the ideal theoretical construction for an insulative box to keep my frosty beverages frosty?

What is the ideal construction for an insulative box to keep my frosty beverages frosty? I am interested in finding the theoretical maximum as well as the practical maximum. I was sitting on my back ...
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0 answers
44 views

How to correctly use the thermal conductivity coefficient formula?

I'm trying to help a friend. We are trying to use the formula below to calculate the thermal conductivity coefficient of a composite material (styro-bamboo). Q=100 Watts, d (or thickness)= 20mm, A= ...
1 vote
3 answers
8k views

Calculating R-value from temperature differential

A home windows installation rep gave me a quote today and conducted the following temperature differential demonstration. Alice pointed a heat gun (with a surface temperature of 165F) at the interior ...
1 vote
1 answer
518 views

How to calculate the thermal conductivity of a composite material

Very new to thermal conductivity calculations, so I'm aware there are already queries on here that may cover this, but I'm struggling to apply them to this instance. I'm trying to calculate the U-...
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33 views

approximate equation for temperature drop near wall in contact with fluid

I am concerned about the following problem and so far I am not able to find a solution. Let us consider an environment at a temperature $T_a$ and the inner surface of a not insulating wall in contact ...
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23 views

U-value for suspended ground floor

I'm about to finish U-value calculation for a house (an assignment for the Sustainable Technology for Buildings module) but I can't understand the formula. I've got all the data except from "ln&...
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1 answer
39 views

Why Ball-Grid Arrays are More Heat Resistant

I read that for Ball-Grid Arrays, the BGA's act like a thermal dissipator because there are more channels, so it is more heat resistant as opposed to Thin-Quad Flat Pack which uses pins. Is this ...
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0 answers
137 views

Calculating Glass Wool Insulation Thickness

I intend to calculate required thickness of glass wool insulation for a hot vessel. I know the temperature inside the vessel, the acceptable temperature at the surface of the vessel (after insulation),...
0 votes
1 answer
166 views

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 ...
1 vote
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Equivalent Resistance Between Two Points in a Wye Network

I am interested in learning how to calculate the equivalent resistance between two points in a wye circuit for application to thermal networks (i.e. I'd like to calculate the equivalent thermal ...
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2 answers
53 views

Human lying on a cooled mat - ballpark estimate of heat transfer rate

Hardware builder and youtuber Naomi Wu came up with this idea to help people with acute heat stress due to very hot and possibly moist weather: Instead of cooling all the air in a room, just place the ...
1 vote
3 answers
85 views

Through which medium is most of the heat transferred down (downwards) a glass tube filled with water: the glass walls or the water column?

If a much hotter object is attached to the tube from the outside, and the heat in question is transferred to the part of the tube that is below the source of heat, so there is no convection. The ...
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1 answer
827 views

Calculate Thermal Conductivity of Layered Structure

I am having a problem determining the thermal conductivity of a layered sample. The sample is made of two materials, one whose thermal conductivity is known (λ-1) and one whose thermal conductivity is ...
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1 answer
63 views

What is the thermal conducivity of Air between two plates?

What is a rough cut figure I could use to determine what the thermal conductivity of 10mil and/or 20mil of air sandwiched between two plates (perfectly conducting)? I understand that convection dies ...
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2 answers
278 views

Thermal oil in Boiler not reaching desired temperature

The thermal oil Feroline U in Boiler is not gaining the desired temp of 240 Degrees. We have physically measured the temp using digital thermometer at a distance of 20 cm where the boiler temp sensor ...
1 vote
1 answer
53 views

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 ...
1 vote
1 answer
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Heat Diffusion and Specific heat

Consider two slabs - Slab A and Slab B, insulated on "latereal" faces as shown, initially at the same temperature, and having identical dimensions. The slabs at t= 0 are brought in contact ...
1 vote
1 answer
1k views

Why different characteristic dimension for Biot Number and Fourier Number?

In unsteady heat conduction analysis, Biot Number and Fourier Number are given as follows: $$Bi=\frac{h L_c}{K}$$ $$Fo=\frac{\alpha t}{L_c^2}$$ where $L_c$ is the characteristic dimension or length ...
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1 answer
212 views

Critical Radius of Insulation

Consider a long pipe inside which a hot fluid flows. The pipe is exposed to ambient air which is at at some temperature $T_\infty$. Let the inner radius of the pipe is $r_1$ and the outer radius is $...
5 votes
2 answers
366 views

Why does the author assume the temperature to remain constant, in this case, along the axial direction?

This is in regards to steady heat conduction taking place in a pipe. Within the pipe a hot fluid flows and heat transfer first takes place via convection to the pipe and then via conduction within ...
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1 answer
222 views

What causes the temperature to drop at the interface when two slabs are brought in contact?

Consider two slabs made up of different materials which are brought in contact with each other as shown. Thermal energy is supplied from the left, and it flows through the two slabs towards right. ...
1 vote
1 answer
354 views

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 ...
1 vote
0 answers
152 views

Time required for balls to cool down

Two balls A and B, made of different materials, having the same radius, are initially heated to the same temperature $T_i$ and then are kept in the same environment which is at a temperature $T_\infty$...
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1 answer
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Thermal Conductivity and Energy gain

I have a two part question: Part 1: I understand thermal conductivity as The measure of a material's ability to allow thermal energy transfer to it, from it and within it via conduction My very first ...
2 votes
2 answers
123 views

What and why thermal diffusivity?

I understand the following properties: Thermal Conductivity: It tells how well thermal energy can get transferred to a material, from a material and within the material. A material with higher thermal ...
1 vote
1 answer
107 views

Best metal for solar energy collection in an evacuated tube solar water heater

I am building an evacuated tube array for a solar water heater and I am selecting the materials to use for the tubing and the collectors (the places connected to the tubing that help absorb the solar ...
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2 answers
583 views

Examples of two dimensional heat conduction problems

Can anyone give me some examples from real life, where the heat transfer can be modelled as two dimensional. Also if one could explain why we can model it as 2 dimensional.
2 votes
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Question regarding evaluating 1D heat transfer PDE

My question regards cooling of an object using 1D-heat transfer with fixed surface temperatures. First I need to find the solution to this PDE: Based on the conditions, I worked out that the ...
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1 answer
73 views

In a warmer/sunnier climate, window (or roller shutters) superior to curtains?

When -on a hot day- the sun is incident on a window covered from the outside by a closed window shutter, the resulting heat is absorbed by the layers of air surrounding the shutter, subsequently ...
1 vote
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Cold Plate Thermal Resistance

I am designing a cold plate that will have 4 Power Modules Mounted on it. The total power loss from the modules is 5000W(1250W per Power Module). I have simulated the results on ANSYS Fluent and ...
1 vote
3 answers
281 views

How to calculate the volume of air required to keep electrical box cool?

I have a steel electrical box that is 15 cm x 15 cm x 10 cm. The weight of the box is 1kg. Inside the box is a relay that loses 30 Watts of heat while in operation (it's attached to a heat sink that ...