Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Maybe combine with [tag:statistical-mechanics].

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Why do $C_p$, $\alpha$ and $\kappa_T$ all approach to infinity when two phases coexist at the mean time?

My textbook (writed by Chinese) says that when two phases of a system coexist at the same time, this system's isobaric thermal capacity $C_p=T(\frac{\partial S}{\partial T})_p$, coefficient of ...
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1answer
13 views

What causes the buzzing sound when the electricity changes into heat?

When I turn on any kind of electric heating (kettle, cooker, heater, ...), it keeps producing a constant buzzing sound. What is the exact cause of that sound? Do the electrons of the electric ...
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Heating during expansion in Joule Thomson - Mechanism?

When a real gas(like H2,He) expands through a porous plug into free space, they heat up. How? How does it get the extra energy?
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2answers
27 views

Maxwell's area construction, why?

In the standard derivation of Maxwell's area construction (which can be found on page 4 of this pdf) the following equation is often written: $$G(p_1,T)=G(p_0,T)+\int^{p_1}_{p_0}Vdp $$ When the two ...
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1answer
158 views

Why does the equation for effectiveness of heat exchangers have $C_{\text{min}}$ in the denominator?

For an ideal heat exchanger of infinite length, $$ Q_{max}=m_{h}C_{h}\left[T_{h,i}-T_{o}\right]=m_{c}C_{c}\left[T_{o}-T_{c,i}\right] $$ \begin{eqnarray*} m_{h}C_{h}T_{h,i}+m_{c}C_{c}T_{c,i} & ...
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26 views

Why are glass beads used in a fractionating column?

Most sources do not go beyond saying that glass beads help increase the surface area for condensation of the liquid of the higher boiling point while using the method of Fractional Distillation to ...
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1answer
2k views

Why does friction produce heat?

What causes two objects sliding against each other to produce heat? Why don't they generate visible light or something else?
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12 views

Project Orion pusher plate computer modeling

Linked from the space.stackexchange forum: http://space.stackexchange.com/questions/15051/orion-project-npp-pusher-plate-computer-models-and-survivability Project Orion is discussed as if it is a ...
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34 views

2nd law of thermodynamics - simple steam power plant problem [on hold]

A steam power plant consists of a boiler, a turbine, a condenser and a pump. The temperature of the inner walls of the boiler is 350 °C and the temperature of the condenser cooling water is 20 °C. ...
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50 views

Would it be correct to state that all the forms of everyday matter (mountains, tables, buildings, people, etc.) are in a metastable state?

We had a fire going in the backyard of a friends house this weekend, and after thinking about the chemical reactions occurring in the wood (and anything else we threw into the pit), I started to ...
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Theoritical Electrical Energy of battery [on hold]

i m a student and looking for some answer related to my research, i m recently working on Ni-fe battery ie. nickel-iron battery. I would like to know what formula or law is applicable to calculate ...
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21 views

How can I get the exit temperature of water entered 100 degree in a pipe surrounded by 30 degree water?

Assume any value for: Length of the pipe The material of the pipe Velocity Heat transfer coefficient. I tried considering it as parallel flow heat exchanger but the water in this example isn't ...
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1answer
65 views

Thermal average, thermal fluctuations

I've a doubt concerning the physical meaning of "thermal average" and the "thermal fluctuation" in the canonical ensemble. Let's consider a very simple thermodynamic system: N particles, at fixed ...
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3answers
54 views

Why do Temperatures Equalize

I have some Oxygen at Temp A in one container and some Nitrogen at Temp B in another container. If I mix these two containers eventually both the Oxygen and Nitrogen will be at the same temperature. ...
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1answer
36 views

Confusion about inverse square law and temperature increase of an object

I know the inverse square law means that radiation intensity decreases in proportion to the radial distance from the source (I is proportional to 1/r^2). Does this apply to the temperature increase ...
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40 views

When does the Boltzmann distribution apply?

What are the requirements for a system to be described by the Boltzmann distribution in equilibrium? For example, should all the particles be identical? No attractors in the phase space? ...
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3answers
84 views

What ds>dQ/T mean?

I read the derivation on page 216 over here: https://www3.nd.edu/~powers/ame.20231/notes.pdf First it considers an irreversible process between state 1 and 2 followed by a reversible process between ...
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4answers
7k views

Is thermal/heat energy the same thing as internal energy?

I learned that internal energy of an object is the sum of the kinetic energy and potential energy of the molecules of the object. Is this energy the same thing as the heat energy the object contains?
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123 views

Amount of heat required to raise the temperature of a balloon which requires no energy for expansion?

Two moles of ideal helium gas are in a rubber balloon at $30^°C$. The balloon is fully expandable and can be assumed to require no energy in its expansion. The temperature of the gas in the balloon ...
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1answer
288 views

How to calculate the heat transfer rate between the liquid and the gas?

Let water (liquid) be in a chamber (with no heat transfer to the walls). The gas is the residual space above the liquid, meaning that the contact surface is the surface of the water. Given the gas ...
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2answers
25 views

U and PV changes in thermofluid processes

If we have a steady flow open system, how can we know the change in U and PV? I mean if we input work in the system, how can we know that the work goes to U increase or PV increase? Also, can you give ...
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1answer
406 views

Does a negative line tension in a 3-fluid immiscible interface make sense?

This question is inspired by this question/answer pair: Is this formula for the energy of a configuration of 3 fluids physically reasonable? Consider three immiscible fluids forming contact surfaces, ...
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201 views

Is the Boltzmann brain problem really clearly established as a problem?

Starting from the assumption of a cosmology in which Boltzmann brains dominate over evolved ones, it is not immediately obvious to me that there is a real problem, since only Boltzmann brains ...
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1answer
34 views

Room with open door and heater : use inside boundary conditions or heat source for PDE?

I want to model the stationary temperature in a room (=square) that has one open door (=side) is otherwise perfectly insulated is heated through a (circular) heater that is placed somewhere in the ...
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1answer
44 views

Thermofluid mechanics inclined plane

As shown in the attacked image, a tank has an inclined wall at an angle of 450 to the horizontal. On this wall, there is a 1m square door that is hinged at A and has a simple latch at B. The distance ...
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Maximum temperature possible on earth

What is maximum temperature that can we have on earth on a single day? Lets say an air mass is static over an area and there is no way for air mass to move, sun warming it up would increase ...
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40 views

Thermal Capacity

An electrical heating coil of power $P$ is used to transfer thermal energy to a body of mass $m$. In a time $t$ the body changes temperature by $\Delta T$ . What is the thermal capacity of the body?
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1answer
144 views

Heat balance: how to obtain T(t) with energy in the form u(T(t))

I have the heat balance equation for a cooling case in the form: $$\frac{dU(T(t))}{dt}=-J$$ with $U$: energy (J) $T$: temperature (K) $t$: time (s) $J$: heat flux leaving the system (W) I have ...
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1answer
35 views

Entropy for $N$ number of particles [on hold]

If there are $N$ number of non-interacting and distinguishable particles which have either Energy $E_1$ or $E_2$ , then a. What will be the entropy $S(n)$ for such system? ($n$ is the number ...
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1answer
17 views

Force applied between neighboring atoms resulting in increase in separation

I am attempting a past paper question in practice for an upcoming exam and I am a little lost with the following question: Using lennard Jones model for potential. An external force $F$ is applied to ...
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1answer
115 views

relation between speed and temperature in relativistic gas

What is the correct formulation of the relation between the speed and temperature in the relativistic kinetic gas? I have found one mentioned in problem 3.24 of the third edition of Pathria's ...
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1answer
39 views

Does density of air decrease or increase with altitude and relation of this with temperature?

I think the air density decrease as due to gravity more air woul be near the earth but as the hot air raises up doesn't it have momentarily increased the density at height (like in up troposphere) ...
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2answers
43 views

Increase in entropy principle

If we consider a system to undergo an irreversible process from state 1 to state 2 and a reversible process from state 2 to state 1, then through Clausius inequality $\int_{1}^{2} \frac{\delta ...
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Dimensional Analysis Problem [on hold]

In the formula: $$ P = nRT/(V-b)* e^{-a/(RTV)}\ $$ Find the dimensions of 'a' and 'b', where P = Pressure , n = No. of moles , T= Temperature , V = Volume and R = Universal gas constant.
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2answers
37 views

A 50 g Ice Cube with an initial temperature of -10°C is put in 400 g of water at 40°C. Find final temperature [on hold]

My calculations: $$Q_g + Q_l = 0$$ $$Q_g = -Q_l$$ $$mc\Delta T = -mc\Delta T$$ $$(0.05)(2100)(T_f+10) = -(0.4)(4200)(T_f-40)$$ $$105(T_f+10) = -1680(T_f-40)$$ $$105T_f + 1050 = -1680T_f + 67,200$$ ...
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Eddy current damping heat generation

Background According to this source (page 7): https://deepblue.lib.umich.edu/bitstream/handle/2027.42/109373/me450w10project16_report.pdf?sequence=1 the "braking" torque a magnetic field on a ...
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20 views

How does one compute the maximum height reached by the water droplets in this experiment and what is the theory behind such phenomenon? [on hold]

Hot Water Fountain - Partially fill a Mohr pipette with hot water. Cover the top of the pipette with your thumb. Turn the tip upwards and observe the fountain exiting the tip. Investigate the ...
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1answer
33 views

Are all heaters exactly as energy efficient as each other?

I many applications, efficiency is measured in terms of how much of the input energy is wasted generating heat instead of the actual type of energy you want. For example, lightbulbs generating heat ...
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1answer
22 views

relativistic temperatures energy assumptions

why is the assumption $k_bT>>mc^2$ made for relativistic temperatures, where did the kT come from and how is it related to mc^2?
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2answers
42 views

how can energy conservation equation be different in different situations?

Neglecting potential and kinetic energy: energy conservation equation in a closed system is dU=Q-W and in an open system with steady flow is dU+d(PressureEnergyPV)=Q-W or in other words dH=Q-W. How ...
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23 views

Relation between Canonical and Grand Canonical Ensemble for a two levels system

For a two-level system of classical non interacting distinguishable paricles, labelling energy levels as $+\epsilon, -\epsilon$, in the canonical ensemble I found for the partition function ...
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2answers
36 views

Thermodynamics : Heat transfer : Conduction or convection?

I have an hot object, that is place in a room of 20°C. My goal is to be able to estimate how warm the object will be in T seconds. To be able to do that, I must first understand what is really ...
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1answer
49 views

I can get a heating strip - why can't I get a cooling strip?

A typical heating strip is a flexible silicone material containing a resistive heater. However, I would like the opposite - something I can wrap around my experiment and use in a similar way to the ...
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1answer
29 views

First Law of Thermodynamics and Signs

I have a question in my text book about the first Law of Thermodynamics. It gives 3 situations with the systems for each in brackets: 1) Rapidly pumping up a bicycle tyre (air in the pump) 2) ...
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22 views

What are the calculations specifically needed for High Altitude Ballooning? [on hold]

I want to know the lifting gas needed to launch the vehicle including the positive lift I want to predict the possible retrieval site I want to know the burst altitude AND MAYBE ALL WITHOUT ...
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18 views

Ratio of the change of internal energy under the specified condition given below [on hold]

What will be the ratio of the change of internal energy of a diatomic gas U1 & U2 for a unit rise of temperature in constant pressure and volume respectively.
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3answers
65 views

Degrees of freedom and temperature

I quote the following lines directly from the Wikipedia page titled "Heat capacity": "...rotational kinetic energy of gas molecules stores heat energy in a way that increases heat capacity, since ...
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3answers
139 views

Why engines don't melt?

The temperatures of internal combustion engines are well above the melting points of the component materials. For example, temperatures can reach 2200° C whereas the melting point of aluminium is ...
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3answers
52 views

How does frost form above freezing temperature?

This is a follow-up to the best answer linked below: Why does ice form on bridges even if the temperature is above freezing? I've witnessed that phenomenon, recently. The temperature was above zero ...
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1answer
38 views

Is potential energy included in internal energy?

I thought internal energy is only the energy due to molecular motion and chemical bonds, but here it says it's also the potential energy of the system! Is that true?