In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter. The various mechanisms of energy transfer that define heat are stated in the next section of this article.
Like thermodynamic work, heat transfer is a process involving more than one system, not a property of any one system. In thermodynamics, energy transferred as heat contributes to change in the system's cardinal energy variable of state, for example its internal energy, or for example its enthalpy. This is to be distinguished from the ordinary language conception of heat as a property of an isolated system.
The quantity of energy transferred as heat in a process is the amount of transferred energy excluding any thermodynamic work that was done and any energy contained in matter transferred. For the precise definition of heat, it is necessary that it occur by a path that does not include transfer of matter.Though not immediately by the definition, but in special kinds of process, quantity of energy transferred as heat can be measured by its effect on the states of interacting bodies. For example, respectively in special circumstances, heat transfer can be measured by the amount of ice melted, or by change in temperature of a body in the surroundings of the system. Such methods are called calorimetry.
The conventional symbol used to represent the amount of heat transferred in a thermodynamic process is Q. As an amount of energy (being transferred), the SI unit of heat is the joule (J).
Hi all,
I do an calorimeter experiment at temperatures around 40 mK. To get more grip on the time constants that are associated with the heat flows, I calculate the thermal resistance as well as the heat capitance of the materials in the set-up.
We assume that Newton's law of cooling is the...
Homework Statement
A steam heating system is used in winter season, The radiator of a steam heating system has a
volume of 25 liters and is filled with superheated water vapor at 200 kPa and 200C. At this moment both the inlet and the exit valves to the radiator are closed. After a while it is...
A building needs a certain amount of energy during a year (kWh) for room heating. An air to water heat pump has been installed to provide heat to a radiator system (55/40°C). How do I go about estimating how much of the yearly energy need the heat pump will cover? What confuses me is that the...
Hi,
I have an underwater monitor housing made out of carbon fiber and an acryllic Glass on the other side.
Over time the monitor heats up. I guess carbon fiber is a bad heat conductor :(. the Acryllic glass is almost 1cm thick. Does anybody have an advice on how to cool something like this...
Hello sir,
How to calculate the heat flux of titanium and aluminum?What are the essentials for doing the calculation?We are undertaking a project of multilayer coated cutting tool inserts..So we are in the need of this.
Regards,
Shankaralingam.
Homework Statement
A problem will ask for an amount of substance in kilograms to be raised to a certain temperature and the specific heat be given in J/g*K. The amount of substance is not required to be converted to grams to match the units in the specific heat to get the correct amount of...
If I have and object at a different temperature than the thermal/heat reservoir (whatever it's called) an heat flow will take place. If I write the entropy balance for the thermal reservoir it will be:
##\frac {dS} {dt} = \frac {\dot Q} T + \dot S_{gen}##
Now I remember something my professor...
Hello Physics Forum Users! I have an annoying situation with the Finite Heat Release Equation used to simulate combustion and expansion processes in an internal combustion engine. The equation is as follows:
Nomenclature:
P = Cylinder Pressure (kPa)
θ = Crank Angle (Deg)
k = Specific Heat...
Morning!
My question is this: If we consider a situation of mechanical collision, in the real world we shall observe certain loss of energy into heat or sound. Can we find mathematical equations to measure the amount of sound or heat produced using only mechanical variables, such as mass...
Homework Statement
The temperature distribution across a wall 0.3m thick at a certain instant of time is T(x)=a+bx+cx2, where T is in degrees Celsius and x is in meters, a = 200°C, b = -200°C/m, and c=30°C/m2. The wall has a thermal conductivity of 1W/m2K.
(a) On a unit surface area basis...
Homework Statement
Homework Equations
Cv=(f/2)R
The Attempt at a Solution
I have no problem getting the right answers. My question is this: If Cv=72.254 and if Cv = (f/2)R, that implies that f = 17.381. I understand that f represents the gas particle's degrees of freedom. How does this...
Homework Statement
A 529 g piece of copper tubing is heated to 89.5°C and placed in an insulated vessel containing 159 g of water at 22.8°C. Assuming no loss of water and a heat capacity for the vessel of 10.0 J/°C, what is the final temperature of the system [c of copper = 0.387 J/g · K]...
Fluid comes in at ##T_1## and comes out at ##T_2## and I know that heat is exchanged with steam at constant ##T_{steam}##.
If I want to know the Surface of the exchanger then
##US(T_{steam}-T_{fluid}) = \dot m_{fluid} cp_{fluid} (T_2-T_1)##
My question is, since ##T_{fluid}## changes, which...
Hi everyone,
I'm currently trying to build a solar cooker which can also be used during the night / the next day so I was wondering if I can get some advice about how it can be done, especially the material that I can use to store the heat.
I saw an article that said a professor from MIT had...
I have to build a small green house and to calculate if one heating wire is enough (or even too much...)
Just for my curiosity I would like to understand the physics implied in this.
The starting point is the desired dimensions: two modules of greenhouse with the following dimensions:
60 cm...
Hi everyone, I'm reading this paper about the solution of the heat equation inside an infinite domain: https://ocw.mit.edu/courses/mathematics/18-303-linear-partial-differential-equations-fall-2006/lecture-notes/fourtran.pdf
1) Please let me know if the following discussion is correct.
The...
Homework Statement
There is a waterfall 230m high, take acceleration due to gravity to be 10 m s-2 and the specific heat Capacity off water to be 4200 J Kg-1K-1
First find the speed of the water hitting before htitting the ground using the Principle of Conservation of energy
Second assume all...
Homework Statement
I am working on a problem where I need to determine the time taken for an air heater with an 8kW output to heat a volume of air of 9m^3 by 25C. I am neglecting all losses at the moment. It almost seems too simple in my mind that I'm concerned I'm overlooking...
hi, I met a problem about heat transfer in cylinder, if you can help, I will appreciate it.
The question is simple. I want to know the transient heat distribution in a cylinder with internal heating(constant temperature not constant flux). The boundary conditions comprises two constant...
Hello Guys,
I am a mechanical Engineer working on a semester project, to design a waste heat recovery system for a cement plant Air quenching cooler (AQC). For WHR i have to first design a AQC Boiler.
According to the Data provided by the plant incharge, Air at the exit of cooler has a volume...
I tested it by heating it up for 2 min on a electric stove and pour about 200 to 300 ml water in bowl and did a very quick dip in and out like that and when i touch it, it was cold same temperature as the water. I also test with aluminium but when I touch it, it was will hot I burnt my finger...
I have lots of batteries 12 volt charged by the sun what I need is something that would draw 100 watts and give heat when connected to a car battery? I have ac heating pads, 2000 watt hot water elements lots of copper wire, light bulbs any other ideas?
Homework Statement
You add 1500 cal of heat to a cup of water at 22.5ºC. The water has a mass of 500.0g. What is the final temperature of the water?
Homework Equations
Q=mcΔT
The Attempt at a Solution
so i tried solving it by finding the energy of the water
Q=(500g)(1.0cal/g)(22.5ºC)
Q=11250...
I have a practical engineering problem for which I really have no background on how to solve. I am looking for help, but don't even know what field of engineering would be likely to know the answer, so not quite sure where to ask. Any formulas that I might use to calculate the answer would...
If we have two identical objects each placed in rooms at 25°C room temperature. In the first room, the object is at 0°C. In the second room, the object is at 50°C. Which object will reach the room temperature of 25°C first?
Homework Statement
In an electric circuit, consisting of copper wires with cross section area of Sc=5mm2 and a temperature of t=25C, a lead fuse is added melting when the copper wire temperature increases by Δt=25C. Find the cross section area of the lead fuse wire Sl=x.
specific heat...
Homework Statement
Homework EquationsThe Attempt at a Solution
Effiency of a heat pump is given as ## \eta = \frac { T_h }{T_h – T_c} = 30 ##
W * 30/s = 6000*4.2 cal /s
Minimum consumption rate = W/s = 840 watt
Is this correct?
Homework Statement
A stainless-steel wire is 0.1 mm in diameter and 1 m long. If the outside of the
wire is held fixed at 20◦C, estimate the steady-state current passing through the wire
when the stainless steel at the centre of the wire begins to melt.Homework EquationsThe Attempt at a...
Every year since the 90's I come back to some of my pet topics in physics, like statistical physics.
This time it was the reading of a Wikipedia article on entropy that surprised me.
The derivation of the second law from the Gibbs entropy was unknown to me.
I didn't know how heat, how change of...
From previous threads I understand that perfectly rigid bodies cannot exist.
Two, perhaps, simple questions:
1. Can atoms be stretched or compressed?
2. Does a theoretically rigid/immobile object get warm when a changing forces are applied?
When computing the rise in temperature on a body due to mechanical work, if we stick to using SI units, do we need the conversion factor called mechanical equivalent of heat. That is, can we readily equate W = Q and hence W = m x C x ΔT . Where 'm' is the mass of the substance on which work is...
Homework Statement
A 2.45 kg aluminium pan at 155 C is plunged into 3.58 kg of water. If the entropy change of the system is 162 J/k, what is the initial temperature of the water?
Homework Equations
Q = mcΔT ΔS=mcln(T_2/T_1) Q_water + Q_Aluminium = 0
c water = 4184 J/kg*K c aluminium = 900...
hello,
im in bachelors mechanical engineering programme and my thermodynamics papers are in few days
one question is related to heat exchangers or forced convection, but our professor has hinted that in the exam the question regarding heat exchanger, forced convection will be a case study of a...
hello. Simple question here for somebody just learning the basics. On the atomic scale what’s the difference between agitation and heat? For example, diluting salt in water. If you increase the heat of the water, more salt dissolves. Stirring it also makes the salt dissolve more too it seems...
There are three geothermal systems that are commonly used: sry steam, flash steam, and binary cycle https://www.eia.gov/energyexplained/index.cfm?page=geothermal_power_plants . What are the efficiencies of the plants from best to least effecient on average?
Homework Statement
Homework Equations
q = mCat
The Attempt at a Solution
I'm kinda confused the different between Hrxn and q? I know the reaction warms the water with q=mcat = 150*4.18*(59.5-20)=24766.5 J. This is the heat released from 1.25 grams of Ca which is 0.03 moles of Ca. But, the...
Greetings!
I did the famous "Mass Lifter Heat Engine" experiment in which a mass is put at the top of a piston enclosed within a cylinder. The cylinder is connected to an aluminium canister of air and the air inside this canister expands and contracts the piston with thermal contact. We had 2...
Homework Statement
Homework Equations
q = mcat
mols*hvap
The Attempt at a Solution
To decrease temp from 70 to 56 degrees (bp), q=mcat = 1195.5
to convert this gas into liquid , must do mols * hvap = 29129 joules
to decrease temp from 56 to 0 thought, i get q= mcat = -7047 J (which is...
Hello. I am starting to learn about thermodynamics. (i'm going to use lower case "d" for delta)
Energy is neither created nor destroyed. So dU = 0 for the universe as a whole.
If the universe is constantly expanding, then it must be doing work on the vacuum around it, right? So W is a...
Looking to make a heat exchanger so that I can have a less than adequately antifreeze treated water (easily over 750 gallons, so very expensive) from the outdoor wood boiler constantly circulating through a water jacket, and heat an adequately treated fluid (glycol treated water) and can turn...
Homework Statement
An office with a volume of 52.5 m^3 uses a heat engine that outputs 1200 W. Suppose that, initially, the office has a pressure of 1 atm and 20 degrees Celsius before the heater is turned on. After 10 minutes (6000 seconds), what is the final air temperature?
Homework...
Homework Statement
I am having an issue, not with the maths but with the boundary conditions for this question.
A bar 10 cm long with insulated sides, is initially at ##100 ^\circ##. Starting at ##t=0##
Find the temperature distribution in the bar at time t.
The heat flow equation is...
Homework Statement
A copper pot with a mass of 0.500 kg contains 0.170 kg
of water, and both are at a temperature of 20.0°C. A 0.250-kg
block of iron at 85.0°C is dropped into the pot. Find the final temperature
of the system, assuming no heat loss to the surroundings.
Homework Equations
Q =...
Homework Statement
A thin electrical heater is inserted between a long circular rod and a concentric tube with inner and outer radii of 20 and 40 mm. The rod (A) has a thermal conductivity of kA = 0.15 W/(m*K), while the tube (B) has a thermal conductivity of kB = 1.5 W/(m*K) and its outer...
Homework Statement
show ## \rho c_m \frac{\partial T}{\partial t} = \kappa \frac{\partial^2T}{\partial x^2} -\frac{2}{a}R(T)##
where ##R(T)=A(T-T_0) ##
a) Obtain an expression for T as a function of x for the case of an infinitely long rod whose hot end has temperature ##T_m##
b) Show that the...
Homework Statement
What is H, the rate of heat absorbtion by an air conditioner with an EER of 8.3 that operates at 1800 W? Recall that 1Btu=1055J. Express your answer in joules per minute.
Homework Equations
H/P=EER
The Attempt at a Solution
H=EER*P
H=(8.3 BTU/HR/W)*(1800 W)
H=(14,940 BTU...
Homework Statement
One cylinder in the diesel engine of a truck has an initial volume of 640 cm3. Air is admitted to the cylinder at 30°C and a pressure of 1.0 atm. The piston rod then does 500 J of work to rapidly compress the air. What are its final temperature and volume?
Homework Equations...
Homework Statement
So, my textbook doesn't go over these type of problems for heat of atomization , so I am confused on how to write the chemical equations for them.
Question: The heat of atomization is the heat needed to separated gaseous atoms from a substance in its standard state. The...
Homework Statement
Heated iron with mass of 55.0 g was added to 100 mL of water at 20 degree Celsius. Assuming no energy transfer to the surroundings and that the final temperature of the system is 42.7 degrees C, calculate initial temperature of the iron.
Mass of Iron = 55.0 g
mass of Water =...