Tagged Questions
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0answers
21 views
Find the workdone to increase the temperature of an ideal gas by 300c if gas is expanding under [closed]
Find the work done to increase the temperature of an ideal gas by $30^o C$ if gas is expanding under the condition $V \propto \dfrac{t^2}{3}$.
0
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1answer
679 views
Beginner Thermal Dynamics Question [closed]
A syringe is set up filled with air (mainly N2 and O2) as shown in the diagram below. The surface area of the syringe is 15.3 cm2. The initial pressure inside the syringe is Pi = 114 kPa and the ...
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0answers
27 views
Calculating the change in entropy in a melting process
I have a homework question that I'm completely stumped on and need help solving it.
I have a $50\, \mathrm{g}$ ice cube at $-15\, \mathrm{C}$ that is in a container of $200\, \mathrm{g}$ of water at ...
0
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1answer
44 views
Calculating the coefficient of thermal expansion in liquid
I am trying to write a matlab function that calculates the coefficient of thermal expansion of water from a given temperature. From what I understand the thermal expansion coefficient is calculated as ...
0
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0answers
23 views
Calculate the amount of water needed to extinguish a vehicle fire? [closed]
Essential Data:
Petrol has a calorific value 45000 KJ/Kg
Temperature at which petrol burns ~ 300 Degrees Celcius
Specific heat Capacity of Water = 4.2 KJ/Kg
Specific heat Capacity of Steam = 2.0 ...
0
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1answer
40 views
What happens to pipe outlet temperature here?
I have a fluid flowing through a pipe in the ocean and there is heat transfer from the ocean to the fluid in the pipe. I prepared a simulation and the results show that if I increase the mass flow ...
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0answers
30 views
What is the meaning of $h_L - h_H$ for a heat engine?
My problem gives me a Carnot cycle heat engine with water as its working fluid, with $T_H$, $T_L$, and the fact that it starts from saturated liquid to saturated vapor in the heating process.
I need ...
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1answer
88 views
Sensible heat question (solving for temperature)
If $55 034.175 \rm{kJ }$ of heat are transferred to $150 \rm{kg}$ of ice at a temperature of $-12.15 ^\circ \rm{C}$, calculate the temperature of the resulting water.
Using $Q = mc(t_2-t_1)$ or ...
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0answers
32 views
Height of a piston in a heated cylinder containing H2O
I'm a first time user and I hope I won't be too enigmatic asking the following question:
I have a cylinder (radius= $6$ $\text{cm}$) with a frictionless piston on top of it and inside $30$ $g$ of ...
3
votes
4answers
362 views
why does a larger thermal conductivity provide a smaller temperature gradient?
I was thinking about Fourier's Law in heat transfer today and for some reason I am just not understanding the relationships it gives us. Fourier's tells us that if the heat transfer rate is kept ...
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2answers
2k views
What is the characteristic length of a cylinder
I have a cold cylinder that is submerged in hot water and I need to find the convective heat transfer coefficient. I can do the whole process but I am stuck finding the characteristic length. I found ...
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1answer
459 views
Heat Exchanger Calculation
I have a tank of oil at 55 degrees c. I plan to run a copper pipe 8mm in diameter (1mm thickness) into a coil 15m long inside the tank. For all purposes of assumption, the copper pipe is perfectly ...
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1answer
96 views
I need help with this question on Heat Capacity
A calorimeter has a Heat Capacity of $70 J/K$. There is $150g$ water with a temperature of $20^oC$ in this calorimeter. In this, you put a metal cube of $60g$ with a temperature of $100^oC$. The ...
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0answers
168 views
Simple heat transfer question [closed]
You add an unknown volume of milk of $5.2 ^\circ C$ to a cup of coffee ($40 mL$ of water, temperature: $80.3 ^\circ C$). After a while of stirring the temperature reaches $73.2 ^\circ C$. The ...
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0answers
53 views
Experimental Physics [closed]
A heater and thermocouple are used to measure and control the temp. T of a sample at $T_{0}=250^{o}C$. A feedback circuit supplies power P to the heater according to the equation $P=P_{0}+G(T_{0}-T)-D ...
1
vote
1answer
260 views
ratio between work and heat [closed]
I am really stuck on a problem in my textbook:
Water is heated in an open pan where the air pressure is one atmosphere. The water remains a liquid, which expands by a small amount as it is heated. ...
1
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1answer
103 views
Temperature and latent heat
Building a bronze stature we make a mold and pour in the liquid bronze when the bronze hardens we remove the mold.
The mold is made of 3 Kg of steel and the statue has a mas of 1 Kg. The specific ...
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1answer
113 views
Determine the flow and amplitude equation for thermal energy (with Del operator)
It is a question vector calculus and Maxwell's laws. I put it this way. Let's say, we are working in a $3$-Dimensional space ( e.g $x\cdot y\cdot z = 4\cdot3\cdot2$, a certain room/class of that size ...
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2answers
658 views
Specific heat capacity
Which of two objects at the same tempreature can cause more intense burns when you touch it: the one with the greater specific heat capacity or the one with the smaller specific heat capacity and why?
...
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2answers
138 views
Using CO2 to air condition a room
I'm trying to determine how much dry ice or liquid nitrogen I would need to cool 3300 cubic feet, about 90,000 liters of air, from about 100F (37.78C or 310K) to about 90F (26.67C or 299.81K). I'm ...
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vote
1answer
257 views
How would I calculate the convection coefficient in transient convection?
So I have faced a problem dealing with transient conduction and I need a little help with the problem solving concepts. I need to determine how long it would take to reach the final temperature but I ...
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2answers
299 views
Transient radiation--heating a slab
Hey guys I really need help on this problem.
A ceramic slab of dimentions 5cm x 10 cm x .25 cm has to be heated to $177\,^{\circ}{\rm C}$. The ceramic slab travels on a conveyor belt traveling at ...
2
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2answers
140 views
How would I go about solving this transient convection problem if the mean fluid temperature is constantly changing?
Let's say I have a ceramic slab on a conveyor belt that is initially at $450\,^{\circ}\mathrm{C}$ and there is air being blown over it at a speed of $35 \frac{m}{s}$ with an ambient temperature of ...
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1answer
134 views
2d or 1d conduction in this scenario?
There is a rectangular fin attached to a heat exchanger with a base temperature of 350K. The fin has uniform properties and experiencesa uniform heat generation. It also experiences heat transfer with ...
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1answer
162 views
At what point can we assume the tip of a fin is adiabatic?
Let's say there is a fin that is 1mm thick, extends 8mm from the surface, and is 10 mm wide. The fin is exposed to a moving fluid. Can we assume the adiabatic tip condition and use the characteristic, ...
1
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1answer
459 views
In what situations do I use the characteristic length of a fin to find the surface area?
So I'm learning about fins in heat transfer and it seems that there are two separate formulas for the surface area of a rectangular fin of length L, width w and thickness t. The fin is attached to a ...
2
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1answer
627 views
Confused with stress, strain and linear thermal expansion
Four rods A, B, C, D of same length and material but of different
radii r, 2r , 3r and 4r respectively are held between two rigid
walls. The temperature of all rods is increased by same ...
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0answers
166 views
Is the $mL_c$ value for triangular and rectangular fins the same value?
I am looking at the solutions that my professor put up and I feel that he did something wrong. Here is the question and I will give my stab at the solution so you can see why I think that it is wrong.
...
2
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1answer
270 views
How do I find average temperature given a temperature distribution?
I was told to find the temperature distribution of a wire with a current going through it. So I found $$T(x)=T_{\infty}-\frac{\dot{q}}{km^{2}}[\frac{cosh(mx)}{cosh(mL)}-1]$$
I need to find the ...
0
votes
1answer
177 views
When to use Heat Diffusivity eqn and when to use Fourier's law to find temperature distribution?
Let's say that there is a circular conical section that has diameter $D=.25x$ without any heat generation and I need to find the temperature distribution.
Originially I thought I could use the heat ...
2
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0answers
403 views
When do I know if energy stored in an object is 0 or nonzero? (Heat transfer)
There is uniform internal heat generation at $\dot{q}=5\times10^{7} \frac{W}{m^{3}}$ is occurring in a cylindrical nuclear reactor fuel rod of 50 mm diameter and under steady state conditions the ...
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1answer
271 views
Temperature change effected by electric heater [closed]
A 40-gallon electric water heater has a 10kW heating element. What will the water temperature be after 15 min of heating if the start temp is 50F degrees.
There must be an equation. I can't find it ...
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1answer
271 views
Given two boiling temperatures and pressures, how can I find the latent heat?
I am given the fact that at a certain pressure a liquid boils at a corresponding temperature, at a different pressure it boils at a different temperature, and then I am asked to find the latent heat ...
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3answers
260 views
Problem with an electricity / thermodynamics assignment
I've been trying to figure this one out for a while on my own, so I'd like to ask for your help if you could offer some.
The task states:
A heater made out of a wire with a diameter $R = ...
1
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0answers
95 views
To determine the age of the Earth by the cooling of the centre of the Earth [closed]
I was given an exercise to make a simple model that suggests that the age of the Earth is 78000 years old.
My current starting point is
$$u_{tt} = u_{xx}$$
so a wave equation. So in polar ...
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4answers
12k views
Heat transfer calculated from the specific heat formula
Say I have 10g of silver, whose specific heat is known to be 0.235. I've heated it up from 50.0C to 60.0C. How much heat has been transferred?
The equation is:
$$ Q = C_pm\Delta t $$
where Cp is ...
0
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1answer
378 views
Heat & thermodynamics question based on heat loss [closed]
A Sphere A is placed on a smooth table.Another sphere B is suspended as shown in the figure.Both the spheres are identical in all respects.Equal quantity of heat is supplied to both spheres.All ...
