Questions tagged [heat-transfer]

Questions relating to the transfer of heat via the mechanism of convection, conduction, or radiation, in forms of systems (or your device) attempting to obtain thermodynamic equilibrium with another system (the environment or your other device)

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39 views

What could cause nichrome wire to overheat and melt?

Yesterday I wasn't careful enough with my popcorn maker and I managed to break it. The kernels probably restricted the air flow and something blew up. It stopped working and about 2 seconds after that ...
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34 views

Electric heating element inside refractory concrete

I'm thinking of making an electric pizza oven in my free time. My thinking at the moment is to have one kilowatt electric heating elements in the bottom as well as the top of pizza oven. I would like ...
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1answer
29 views

Fire rated EN 13501-1 B-s1/s2, d0 sheets

I'm trying to learn more about the type of sheets I can get for a project, I would of course go for polycarbonate if not for its price, currently the project with PC will cost \$600-\$700 but I'm ...
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1answer
49 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 $...
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2answers
281 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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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 ...
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19 views

How to model the kinetics of a reaction while its not being stirred in a batch reactor?

lets consider the following reaction: $$ A + B \rightarrow C $$ Where the rate of reaction ($r$) can be expressed as: $$ r = k*c_a*c_b $$ Where $c_i$ is the concentration of species $i$ and $k$ is the ...
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1answer
52 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. ...
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What can you coat/seal Gallium with?

If I were to make a sculpture out of Gallium, Ga melts at about 85 °F I think, would I be able to spray it with some sort of solvent based or not solvent based coating to help prevent it from breaking ...
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121 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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1answer
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Calculating the difference in heat loss from human body in different environments

I'm interested in personal cooling devices and would like to know if there's a way to make a rough estimate of rate at which you would need to extract heat from the body of an average male walking in ...
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1answer
39 views

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 ...
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Does a higher temperature difference result in a faster rate of heat transfer?

Suppose that I have a thermally insulated tank with hot air at a temperature of 400 C, and the tank is stored in a room with an ambient temperature of 25 C. I also have another identical insulated ...
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Recreate mini fractional distillation column for oil refinery

I am planning to recreate fractional distillation column in my warehouse, size not an issue however want to keep it as compact as possible (ideally should not exceed 8 meters high) Where can I find ...
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2answers
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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 ...
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3answers
58 views

Why materials with preferably a negative temperature coefficient for heating elements?

As far as I understood heating elements make use out of Joule heating. Hence, I wonder why one would preferably use materials with a negative temperature coefficient, therefore? Isn't it, that, the ...
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Significance of Radiation in Heat Transfer Problem

I am trying to calculate the significance of radiation heat transfer to a fluid for a particular geometry I am modeling in Ansys. I would like to leave out radiation in the model, but I want to ...
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1answer
27 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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1answer
58 views

Identify this textbook

I would really like to buy this textbook, but only see a scan of one chapter online. Could anybody help me identify the book? Thanks!
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87 views

How to compute wall heat flux q with just wall temperature

I am doing some simulation for natural circulation loop and have a heat rate q in the heating leg and a fixed temperature for the cooling leg. I know the heat rate for the heating section (128 W) and ...
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1answer
62 views

What would be the best setup to evaporate as much seawater as possible using the propane from a 1kg tank?

Out of curiosity, What would be the best setup to evaporate as much seawater as possible in using the propane from a 1kg tank? Will it be, Big pan, boil them all at once Small wide pan, boil them a ...
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2answers
77 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.
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Is there a way to make an air conditioner without venting heat outdoors?

Is there a way to make an air conditioner for when you can’t vent the heat outdoors? Can you trap the heat in an object or convert it to another form of energy? For example, could you transfer the ...
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1answer
31 views

Pre requisites for a course in Heat Transfer from Fluid Mechanics , for a Mechanical Engineering Bachelors Degree [closed]

Can anyone please tell me the topics I need to study from Fluid Mechanics, specially fluid dynamics to understand Heat Transfer in a better way?
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6answers
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Can aluminium foil be a thermal insulator?

I've searched on Google that aluminium foil can be a thermal insulator, but how does it work? From my thought process, it should've been a conductor because its a metal, right? But, some said that ...
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Thermal conductivity and the second law

I am having trouble figuring out the solution for part d. Can anyone give me a hint?
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0answers
28 views

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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0answers
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How would a realistic PV diagram look for a Beta-Type Stirling Engine?

Normally, most textbooks use the diagram below to describe an ideal Stirling Cycle. 1st comes isothermal expansion of gas, 2nd comes isochoric heat transfer to the regenerator, 3rd isothermal ...
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3answers
84 views

How do you imagine momentum?

If you want to explain it to a layman (who belongs to the science stream ofc!!) how do you explain it? Also, what is momentum transfer when it comes to fluid mechanics?
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2answers
42 views

Why do we consider a wavelength range when defining spectral emissive power of a blackbody?

The spectral hemispherical emissive power of a blackbody is the amount of thermal energy emitted in the form of EMW lying in the wavelength range of $\lambda$ to $\lambda + d\lambda$ via thermal ...
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2answers
53 views

Maximum rate of heat transfer in a balanced counter flow heat exchanger in NTU method

In effectiveness NTU method for heat exchangers, we have effectiveness of the heat exchanger defined as $$\epsilon = \frac{Q_{actual}}{Q_{max}}$$ Where $$Q_{max} $$ is the maximum rate of heat ...
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3answers
141 views

Improving ac efficiency in car

I live in Oklahoma. HOT in summer. I drive a small car. Honda Fit. Seems to me, a smaller cabin would cool faster than a larger one. If I "made my car cabin smaller," would the ac work ...
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1answer
30 views

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 ...
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1answer
51 views

Maximum rate of heat transfer in Effectiveness NTU method for a heat exchanger

The effectiveness NTU method is used for determining the heat transfer rate for a heat exchanger, with known inlet temperatures and surface area. It makes use of effectiveness which is defined as $$\...
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2answers
175 views

Homemade spray dryer - how to generate powerful hot air?

I am currently trying to create homemade spray dryer, Which is basically pumping hot air in a chamber where targeted liquid is sprayed, so that the water content could instantly evaporate, leaving ...
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1answer
42 views

Arithmetic and Log mean temperatuer difference of a double pipe heat exchanger with parallel flow

Consider a double pipe parallel flow heat exchanger, the mean temperature difference in this case turns out to be logarithmic because the temperature profiles are exponential. If we would have made ...
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0answers
31 views

How to model a condenser (heat exchanger) where both streams are two fluid mixtures?

As mentioned I would like to model a heat exchanger (using Python). In this case, the condenser/hx streams are both a mixture of O2 and N2 These are known for both streams: Inlet temperature Inlet ...
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3answers
69 views

Why does thermal conductivity of a pipe matter in a double pipe heat exchanger?

My understanding is that thermal conductivity is responsible for the time until something will heat up. For example, if you hold a copper bar over a candle it will quickly become hot at the other end. ...
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2answers
114 views

Aluminum or Copper, which one is better to control and maintain the temperature?

Friends, I am an EE/SW/Controls eng. Please, pardon me of perhaps incorrect terminologies. I am working on a R&D project: A chemical lab equipment has a 2" long metal pipe enclosed in ...
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3answers
89 views

How are heat exchangers normally calculated?

Most of the calculations that I find in books are about calculating the heat transfer rate, which I'm not sure why I would care about. What I imagine is the case in a real world situation is that I ...
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1answer
68 views

In a shell and tube heat exchanger, does reducing flowrate affect the outlet temperatures?

Let's say I have 2 exchangers that are completely the same, only difference being that one of them has half the number of tubes. Also let's assume the coolant is the same and has the same inlet ...
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0answers
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Trying to find the steady state temperature of air inside a semi-truck trailer?

To start, this is mostly a procedural question, so I'll be doing some handwaving for the numbers. Lets say I have a semi-truck trailer. It's insulated and refrigerated, and meant to transfer drink ...
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1answer
93 views

Out of the three types of Stirling Engines, which one is the most efficient and delivers the most amount of power?

I was thinking that the beta Stirling engine would be the most efficient as it has a displacer to block heat transfer from the hot to cold regions in between thermodynamic cycles. However, I heard ...
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1answer
62 views

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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1answer
80 views

In case of solvation , Who converts gaseous ions to aqueous ? Why do we even have gaseous but not solid ions?

We take Nacl and dissolve it in water. There is formation of $Na^+$ and $Cl^-$ gaseous ions along with 2H+ and $Cl^{2-}$ aqueous ions. Then , Na+ is attracted towards $Cl^{2-}$ and 2H+ is attracted ...
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43 views

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 ...
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2answers
59 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 ...
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2answers
67 views

What are some technical problems with generating electricity using a gas turbine or combustible engine at a gas flaring site?

Numerous oil and gas exploration sites practice flaring for safety and disposal of unwanted low calorific gases. However, instead of just standalone burning the gas, why can't a gas turbine or ...
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1answer
45 views

Do all thermoelectric generators (TEG) require two distinct metals?

Most thermocouples that I've seen being sold online consist of two separate metal wires connected at junctions. Many smaller thermoelectric generators consist of a combination of iron and copper or ...
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3answers
840 views

Mathematical derivation for 1st law of thermodynamics

Mathematical derivation for 1st law of thermodynamics : What I know : 1st law of thermodynamics is known as or derived as the conservation of energy . But how are the terms U , q and W derived from ...

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