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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18 views

HVAC Condensor Liquid Level/Ratio Estimate

Let's say I have a simple condenser inside of a HVAC system with 1 point of entry(Super-heated Vapour) and 1 point of exit(Saturated Liquid) for my refrigerant r134a. A pipe passes through it with ...
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42 views

Does a Peltier device conduct heat when turned off?

If I put a Peltier device between a heat source and a heat sink (Peltier turned off), How well will it conduct heat? as opposed to lets say a copper block? Thank you
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How do I calculate final equilibrium temperature of a pot of water on a stovetop vs. after I add food to it?

So I'm trying to come up with a simple hack to heat up food in a water bath to hopefully +-1ºC of a target temperature, but I really don't understand the physics of it all so much. I'm pretty sure I ...
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73 views

I want to dissipate 3 kW of heat with an air conditioner. How big of an air conditioner do I need?

So the title says it all. I have a room (4 m x 4 m x 2.5 m) which is closed.(Actually there is a window and I could add a 50 cm panel fan if needed as an exhaust if that will help.) I have some ...
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1answer
22 views

Heating an uninsulated campground building with high ceiling and radiant floor in New England

We have a beautiful dining hall designed for summer camp use, which we want to keep warm enough for group activities in the winter. The chosen heat is radiant floor, hoping to keep temperatures ...
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1answer
39 views

Can't tesla turbine work on air heated by solar concentration? [closed]

If we heat air along a pipe that's tilted at 30° to the horizontal using parabolic troughs, the air should rise upwards (I'm not sure how fast or powerfully) and then connect the outlet at the top ...
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54 views

Why is Carnot Factor defined as 1 - (T(cold) / T(hot))

This is the proof I've found for the Carnot Factor: $$S = \frac{Q}{T} \qquad \qquad (1)$$ $$S_{in} = S_{out}\qquad \qquad (2)$$ Because entropy stays the same when ...
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Determining length of interstage cooling coils for removal of heat

I'm currently trying to determine the length of cooling tube required to remove a specific amount of heat from my exothermic reactor in stages. I'm aware I need to use the equation $Q = UA \theta_{...
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Volumetric Flow Rate calculation

I am getting stuck in a problem where 20% of 8 tonnes of the reactor fuel(thermal nuclear reactor) is removed 2 months after shutdown( the reactor was in operation for 30 years and then got shutdown) ...
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1answer
76 views

How to calculate heat loss across a process pipe with perpendicular air flow

My thermodynamics knowledge is extremely rusty, so I would appreciate some guidance on how to solve this problem. As illustrated here, I have a process pipe (steel) with a gas flowing through it (blue)...
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52 views

How to evenly heat stainless type 304 steel bar to approximately 200F?

I need to heat stainless bar stock prior to bending in a forming machine. I would like to reach approximately 200 degrees F. The material is stainless type 304/304L, 3/16" thick. We are heating ...
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33 views

Does a photon impart energy on a surface (to raise its temp) if it goes THROUGH that surface?

Hi so I have this senior design project involving cooling human skin as it is irradiated by an infrared LED. Human skin not only is super absorbent to IR, but that IR goes THROUGH the thickness of it ...
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19 views

How can we determine that the flow in a wind tunnel reaches the steady-state condition?

I am investigating the flow and heat transfer over a cylinder in a wind tunnel. I want to record the data that I need to calculate the flow characteristics, But how can I make sure that the steady-...
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1answer
41 views

How to compute velocity distribution in the developing boundary layer on the cylinder

Air flows perpendicular to the axis of a cylinder $a=1$ cm in diameter. Air speed upstream of the cylinder is $U=6.72$ mm/s and its kinematic viscosity is $2.1×10^{-5}$ at 350 K. I want to obtain the ...
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Optimizing flue gas temp for maple syrup evaporator

I have a simple maple syrup evaporator. Fuel is burned in a firebox located under 1mm stainless steel pans containing maple sap--which becomes syrup once enough water is evaporated. After passing ...
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2answers
107 views

Why does accuracy of temperature PID controller drop over time and how to eliminate it?

What am I trying to control? I have a container with approximately 3*2*6 meters (width, height, length). I am controlling through PID the ...
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1answer
36 views

Why do binary cycle geothermal power plants have so low efficiency?

Well, a binary cycle geothermal power plant utilizes the low temperature of the primary liquid to generate heat. I found out that they are only 10% to 15% efficient. Is the continuous flow of the ...
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1answer
37 views

Heat rate through composite wall with non-constant thermal conductivity

I just started a job working with cryogenics and I am trying to solve an interesting heat conduction problem that I was hoping someone could help me along with. I have a structure that spans from room ...
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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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40 views

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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2answers
32 views

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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46 views

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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40 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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201 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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3answers
40 views

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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31 views

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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40 views

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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1answer
24 views

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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1answer
21 views

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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2answers
149 views

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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24 views

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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2answers
59 views

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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28 views

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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1answer
18 views

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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1answer
51 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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3answers
230 views

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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25 views

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
63 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
34 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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25 views

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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1answer
32 views

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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32 views

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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113 views

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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1answer
49 views

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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1answer
48 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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164 views

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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63 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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1answer
34 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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53 views

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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3answers
40 views

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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