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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How to calculate the ideal and realistic estimate of thermal efficiency of absorption chiller?

How Can I calculate the ideal and a realistic estimate of the thermal efficiency of the system (thermal, electrical and water) per 1 kWh chilling energy (removed from the chilled water)? What is the ...
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Is it possible to find heat flux without emissivity value?

In this question there is a value given for absorptivity of infrared radiation however in order to work out a value for heat flux emitted from the solar panel in order to answer part (a) surely I'd ...
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Where water goes in split air conditioner system in “dry” mode?

In split air conditioners, there are two tubes connecting the indoor unit and the outdoor unit. According to the generic schematics I find online (like this one), they are part of the closed circuit ...
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What are the factors I need to over/under estimate cost of heating in a box-like room? [closed]

For economic purposes, I am interested in studying the equilibrium of heat in a typical rectangular room from various sources, such as a classic radiator or vents. If I have a radiator sitting next to ...
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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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189 views

Furnace Combustion Air Properties

My house is heated by a condensing natural gas furnace that is rated as 92% efficient. It has the option to draw combustion air directly from outside. I know the main advantage of this is avoiding ...
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Is thermal conductivity a property that affects the use of an alloy in high-temperature applications?

I'm interested in the effect of thermal conductivity on the choice of materials used for high temperature applications such as turbines. For the particular case of Nickel-Chromium alloys (such as René ...
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What if ammonia is used as a refrigerant for a refrigerator?

I have a refrigerator whose compressor configuration is: power- 10hp compression ratio- 10:1 I do not have expertise in this field, but I am curious if I use ammonia as a refrigerant instead of HFC-...
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What power lasers can be used to heat fabrics to 70 degree Celsius?

For a project that I was building I wanted to heat fabrics to 70 degree Celsius using lasers. Since fabric is a very wide term for now I was looking to draw heat patterns on 100% cotton T-shirt and ...
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Thermal Resistance

I am trying to complete the following question. But feel it is not correct, so need some help. Given that heat transfer via convection off a planar wall is given by: Write out the combined thermal ...
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How does the change in temperature of water in a tube depend on the angle that the tube makes with the gravitational field/the horizontal?

Let's imagine a tube that is open at one end and is filled with water. A constant source of heat is applied to a specific spot somewhere at the middle of the tube, for a example a preheated soldering ...
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Heat transfer Calculation, for Cooling for an aluminium box

To go into more detail, I basically have a controller and its housing is basically an aluminium box that I need to add heat sinks to. But first I need to calculate how much heat is being dissipated by ...
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Networked Control

Considering the air conditioning system for three rooms B, A, and C. Room A is in the center while rooms B and C are on the left and right sides respectively. What is the coupling value (N) I should ...
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Heat Exchanger Design (Log Mean Temp Difference or Epsilon NTU Method)

I am trying to design two heat exchanger interfaces (shell and tube) that transfers heat to and from an intermediate heat pipe. The picture below gives a general idea of the problem I am trying to ...
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Is there a relationship between temperature and pressure of a refrigerant?

When searching for a pressure temperature relation for a refrigerant a chart appears. But I was wondering are these charts made by experimenting on the refrigerant or is there a relationship which can ...
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Empirical correlation for low reynolds convective heat transfer coefficient

I am looking for a heat transfer coefficient for a shape (rectangular cross section preferred, could estimate with flow over flat plates) in 2 m/s cross flow. I have found a few empirical correlations ...
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46 views

Is there a way by which one could determine the required temperature difference for stirling engine?

I am trying to make a stirling engine. I did some research work and also reviewed some books but the problem is that a great deal of information on this engine is qualitative, rather than quantitative....
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What is the maximum temperature that could be achieved by a heat-pump and will it affect its efficiency?

I did some research and found out that one of the applications of a heat pump is as a water heater which means that it could achieve a temperature of about 100-degree Celsius. Will changing the ...
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Rate of heat loss from a water tank

I'm doing a project for which I need to calculate heat dissipation from a water tank. I'm not well versed in thermodynamics and I can't find any place where this has been answered. I don't know the ...
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1answer
55 views

Theoretical maximum pressure from combusting LPG

I am curious how to find or estimate the theoretical maximum pressure that the combustion of a LP gas, such as propane, can produce inside of a constant volume, such as in a cylinder. I know what the ...
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1answer
33 views

What material might by used to 'staple' coils down in this stovetop element?

I have the stovetop element shown in the image below. If you look at the coils, they're fixed down by what look like little staples. I'm wondering what material those staples might be. The surface ...
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how to obtain solution of this bessel equation using Frobenius method

Given this equation: $$ \frac{1}{r}\frac{d}{dr}\bigg(r \frac{dT}{dr} \bigg) - \bigg(\frac{2h}{bk} \bigg)(T-T_a) = 0 $$ I can let $x=r\sqrt{(2h/bk)}$ and $z=T-T_a$ to obtain the bessel equation using ...
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How is heat transfer calculated for an aqueous salt solution?

I am familiar with using $\dot{Q}=c_p\cdot\dot{m}\cdot\Delta T$ to calculate the heat transfer rate of a fluid given a singular value for specific heat capacity (such as with water), but how do I go ...
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Increase in internal energy and temperature

A banquet hall (150 m3) is to be used for a formal dinner for 20 persons. Each person occupies 0.075 m3 of space and has an average heat transfer rate of 500 kJ/hr. If the AC system fails, determine ...
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Does venturi effect helps in reducing temperature of a room?

I clearly didn't understand how this works, but the explanation and claim that it reduce the temperature of room by 5°c made me wonder, here I am trying to understand the Venturi-effect on temperature ...
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Determining the final surface temperature and final gas temperature flow through a tube in a room

I am trying to calculate the final temperatures as stated above. There is hot gas flowing through a tube that is insulated and inside of a room (no wind). I will try to walk you through my thought ...
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46 views

What's the setpoint of the temperature on the primary side of a heat exchanger?

I have a heat exchanger with known flows on priamry and secondary sides - $\dot m_p$, $\dot m_s$, known temperature in $t_{si}$ and a desired temperature out on the secondary side $t_{so}$. How to ...
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Disc Brakes - Swept Area , why is larger better?

I am trying to understand why a bigger swept area on disc brakes provides higher braking force for the same force being exerted on the brake lever/pedal by the rider. If we use the same exact brake ...
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62 views

Setting up a radiation heat transfer problem

I am trying to solve a radiation heat transfer problem. The problem is set up like this: Two spherical shells of radius R whose surfaces are separated by a distance R. One shell, call it A, has a ...
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33 views

Is there any unilateral heat exchanger?

I don't know if this is even possible or not but are there any pads that can transfer/exchange heat from one side to the other side unilaterally? I mean that the heat could be transferred from one ...
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How much time to melt marshmallow under heat lamp?

Using the Specific Heat Formula, I found that I need to apply 612J of heat to melt 18g of marshmallow. Marshmallow has a specific heat of 2 J/(g*C), melting point of 98.6°F, and a starting room ...
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Material selection of heating element

I am interested in heating coils which are heated using Ohmic/Joule/resistive heating - specifically, how the material for the heating coil is selected. When I read about heating coil materials - ...
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As a rugged and waterproof device, how does gopro dissipate heat?

I am new to designing rugged + waterproof products. I am curious about how to dissipate heat when the electronics are running and the ambient environment is even hotter. It seems like the mode of heat ...
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1answer
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If you have a small fan that blows hot air, and a larger fan that blows cold air against it, what happens to the hot air?

For context, I have a laptop that has a fan that sucks in cold air from the top on the left side (for cooling the cpu), and a fan that blows hot air out the bottom on the right side (for cooling the ...
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103 views

Water Cooling a Personal Computer

I intend to water cool my next PC. There are three areas of heat production in a PC - the CPU, the GPU and the motherboard itself. Would it be more effective to treat these three areas separately (...
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Can wet welding be done in mineral oil?

I'm interested in knowing whether or not submerged welding can be done in fluids other than water, specifically mineral oil in this case. The reason I want to know is that I'm looking into designing ...
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When is a heat exchanger worth it?

I am currently working on a huge industrial process for a student project and we need to transfer around 25MW of energy between dozens and dozens of streams, some larger and some smaller ones. Many ...
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57 views

Most efficient orientation of exhaust vents on top plate of chassis for air flow with regard to heatsink fins?

I'm looking for some advice from an ME or anyone who understands heat transfer,convection, etc. I'm currently laying out in Inkscape a top panel for an audio amplifier I'm building. Now, my question ...
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Heat loss calculation and Energy Balance

The image shows the CAD model of the annealing zone in a galvanization simulator. The zone is electrically heated with a AC current of 5597A at 2.09V. This whole zone is surrounded by insulating ...
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One dimensional U-Factor Calculation - How to determine indoor / outdoor film resistances

Can someone clarify the ASHRAE Fundamental 2017 (SI Units) (See Below) Indoor and Outdoor film resistances. The manual states that it comes from Table 3 and in the description of table 3 it states &...
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Diffusion Pump Copper Cooling Coil Repair

I bought a Varian VHS-4 oil diffusion pump off of ebay about a year ago. The pump was stored outside by the people I bought it from so it suffered mostly cosmetic issues. Recently I have acquired all ...
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Determining the heat capacity of an X-Band transmitter

I am conducting a thermal analysis of an X-Band transmitter that will form part of the payload in a CubeSat. The goal is to determine how long the X-Band transmitter can operate before it will ...
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Heat Conduction/Convection Along discontinuous tube

I have a question regarding heat conduction/convection. I have a metallic tube over which a rope heater is wound, supplying power. A glass tube and a 2nd metallic tube lies at the exit of the first ...
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77 views

Simulation of temperature in insulated box

I have a box outside that I want to insulate such that the temperature inside the box doesn't drop below 10°C given outside temperatures of (in the most extreme case - at night) -10°C. Inside the box ...
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61 views

How to calculate heat and mass transfer rates from an enclosed box?

I'd like to know if it's possible to calculate the heat and mass transfer rates from a small volume to the environment. Let's assume there is a box with a small opening at the top. The air inside the ...
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234 views

Safe temperature thresholds for #2 HDPE and #5 PP plastic

It would be convenient to use a temperature adjustable heat plate (element)/mug warmer for the massive amount of blender bottles accumulated over the years. What are safe thresholds to safely warm the ...
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Adding a black plastic layer to increase retained heat in compost

I have some invasive climbing weeds to break down into compost. I don't want to discard the biomass, but I do want to thoroughly kill all the weeds and ideally the seeds over a period of months. The ...
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Effects of Solar Shield on Electronics Enclosure

I am designing a prototype of an electronics package that will sit out on a pole in the sun 24/7 with a max ambient temperature of 50˚C and at 30˚N latitude. It produces 50W of internal heat ...
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50 views

How can I calculate the airflow needed for a fan to cool a system?

The airflow needed for a system to sustain itself at 80°C with 25°C ambient temperature can be calculated with this formula: ...
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72 views

How effectively will this evaporation setup cool down the water?

I devised a setup, and I show it in the diagram below. Suppose I have these specifications: Water in the bottle is 5 liters and it's initial temperature is 28°C. The bottle capacity is 6 liters. The ...

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