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).
In deriving the Carnot Efficiency, the assumption is made that theoretically most efficient engine will generate no net entropy, meaning that the entropy that enters the system during heat absorption must equal the entropy that leaves the engine during heat rejection. Why is the case? Why would...
Suppose a combined cycle power plant is made using waste heat as the heat source for second cycle.let the second cycle working fluid be steam.Is it possible that the exergy of waste heat is less than exergy of steam at any point of the powerplant?
Homework Statement
1.) A piece of bread (ε = 0.85) is being toasted in a toaster, as shown below. The heating element of the toaster consists of a wire 2 mm in diameter that is wound to approximate cylinders spaced 2 cm apart. This element acts as a blackbody. The housing for the toaster is...
Homework Statement
A 80.4 kg hiker uses 212 kcal hr-1 (3 s.f.) of energy whilst hiking. Assuming that 20% of this energy goes into useful work and the other 80% is converted to heat within the body, calculate the temperature change, in units of Kelvin (K), of the hiker's body during a 1.6 hour...
Homework Statement
A 4.80 kg piece of solid material is heated from 16.4C to 219C (3 s.f.) using 787 kJ of energy (3 s.f.).
Assuming an efficiency of 0.383 for the heating process, and that the material does not melt, calculate the specific heat capacity of the material.
Homework Equations...
Homework Statement
A 4.96 kg piece of solid material is heated from 16.7oC to 234oC (3 s.f.) using 725 kJ of energy (3 s.f.).
Assuming an efficiency of 0.342 for the heating process, and that the material does not melt, calculate the specific heat capacity of the material.
m = 4.96 kg
change...
Homework Statement
Hi,
So I have a perfectly insulated rectangular plate and I trying to use the 2D heat equation in conjunction with numerical finite diference methods and MATLAB to see how the temperature changes throughout the plate. My issue is with the heat source. I am supposed to decide...
Homework Statement
The initial state of 0.1 mol of an ideal monatomic gas is P0=32 Pa and v0=8m3. The final state is P1=1 Pa and V1=64m3. Suppose that the gas undergoes a process along a straight line joining these two states with an equation P=aV+b, where a =31/56 and b=255/7. Plot this...
Hello,
I am developping a Python (/Pyomo) package for simulation and optimization of some industrial processes.
I want to create global (simplified) models for heat exhangers (and more) and avoid differential equations.
(to decrease the number of variables of the problem)
Most often the...
Homework Statement
I don't understand the derivation of the right side of the last equation.
Homework EquationsThe Attempt at a Solution
I got to this point, I also don't understand why it did not include C_2 for the variation of temp. along the fin.
I am guessing the right side is the...
Homework Statement
So this is more of a really vague conceptual question, I'm sorry if it doesn't really make sense. I'm in the stage of learning this where I don't quite understand things well enough to form a proper question.
I'm a little bit confused about nodal networks in heat and mass...
To begin, I am not sure whether or not this is the correct location for this post since I am a complete greenhorn to this forum (just joined today!).
I ask how much heat is produced by radioactive waste because I was wondering if it was viable to reuse all the tons of stored radioactive waste...
Homework Statement
A 12.0 g sample of a metal is heated to 90.0 °C. It is then dropped into 25.0 g of water. The temperature of the water rises from 22.5 to 25.0 °C. The specific heat of water is 4.18 Jg-1°C-1.
Calculate the specific heat of the metal. Express your answer in Jg-1°C-1
Homework...
Homework Statement
Using the heats of fusion and vaporization for water, calculate the change in enthalpy for the sublimation of water:
H2O(s) --> H2O(g
Using the delta H value given in Exercise 24 and the number of hydrogen bonds formed to each water molecule, estimate what portion of the...
So, I have noticed that when people are crowded in small rooms, it feels hot. In fact, everyone in the crowd feels hot and starts sweating. I am wondering about the origin of all this heat.
I do know that by first law of thermodynamics, if two people touch each other and if one of them feels...
In an ideal reversible case, a spring is a simple perpetual machine ; in order to introduce the slowdown of a spring in a real case and the consequent heat development in the spring, Feynman writes (here par. 4.4):
"Inside a spring or a lever there are crystals which are made up of lots of...
Hello all
I have a practical question regarding heat transfer within my laptop. My laptop uses a shared-heatpipe design, meaning that my CPU and GPU are connected by a common piece of copper, and then each chip goes off to its own heatsink/fan.
While playing games, I was monitoring the...
Homework Statement
Kinetic energy per mol is 3/2KTHomework Equations
Q = nC##\Delta##T
U = Q + W
W = -P##\Delta##V
The Attempt at a Solution
1) internal energy = 3/2NKT
2) heat needed to increase temperature of 1 mol ideal gas by 1 degree at constant volume?
Since constant volume, W = 0
Q =...
Homework Statement
(a) What is the purpose of a silvered coating, usually of a good conductor, on the outside of most insulation?
The Attempt at a Solution
[/B]
The silver coating on the outside of most industrial pipes and lagging (Insulation) is primarily to reduce the surface’s...
Homework Statement
(a) Explain how heat is lost from a hot surface to the surrounding air.
The Attempt at a Solution
We will assume as there has been no other stipulation that the effect of radiation is negligible and thus we are taking purely about conduction.
We will also assume as there...
Homework Statement
An appropriate correlation for heat transfer by natural convection from a horizontal pipe to the atmosphere is Nu=0.53Gr^0.25 Pr^0.25
Where,
Gr= (αp^2 d^3 (T_1-T_f )g)/μ^2
And
Pr〖= (C_p μ)/k〗
Show the above correlation can be simplified to
h...
I placed a hot metal lid on a cool surface. When i tried to pull it up, it had a lot of resistance, i had to really try to pull it up. I could hear sounds under the lid, I'm guessing it was boiling water.
What do you think could have caused this resistance?
Hello,
I am doing a high school EEI to investigate the impact that the material of a cup has on the temperature of water inside the cup when left outside in the sun.
The cups I am using are:
Glass
Steel
Plastic
Paper
Theoretically, if I poured the same amount of water into each of the cups...
Homework Statement
A furnace wall consists of three layers of material as shown below.
The thermal conductivities are:
Firebrick = 1.15 W m–1 K–1
Insulating brick = 0.17 W m–1 K–1
Ordinary brick = 0.62 W m–1 K–1
Calculate:
(i) the thermal resistance of each layer
(ii) the heat loss per...
Homework Statement
A small reheating furnace wall consists of 200 mm of firebrick. The inner surface of the wall is at a temperature of 320 °C and the outside temperature is 35 °C. Calculate the rate at which heat is transferred, by conduction, through unit area of the wall. The thermal...
Homework Statement
A cylinder is fitted with a piston and is in thermal contact with a heat bath at 273K. Initially the volume in the cylinder is filled with 10kg of pure H2O and about half of this is liquid and the other half is solid. The piston is lowered so as to reduce the volume by 2 ×...
I really want to build a simple but powerful induction heater for hobby blacksmithing.
Metal shaping and the design of the cooling system within the coils are not a problem.
I need help understanding the electronics
Obviously I must first use a transformer as a safety against "backlash" to the...
Homework Statement
The emission of radiation from the Sun’s disc is observed to peak at 0.5 μm wave- length and that from the Moon’s disc at 10.0μm. A heat engine to power a Moon base is to be constructed using radiation collected from the Sun. What is the maximum theoretical efficiency of such...
I bought a A/C scroll compressor from a 2005 Toyota Prius. I want to convert it into a expander to use in a ORC waste heat recovery system. If I can get it working on the bench, then it's my dream to put it on a hybrid vehicle, most likely another Prius since I own 2. The electricity it...
I am currently working on a project which requires a mass and energy balance on a fin/ fan heat exchanger. The problem I am running into is finding how to apply the fin efficiency to find out the amount of hea tbeing dissipated through the fins. The hot fluid is water and the cooling fluid is...
I've been wondering about this question for some time now. There are the following two contributors:
~~~~~~~~~~~~~~
1. Heat left over from the planet's initial formation. In the early 19th century Lord Kelvin estimated the temperature based on a homogenous sphere of uniform initial temperature...
<< Mentor Note -- poster reminded to use the standard Template >>
Question Three
A pipe of outside diameter 200 mm is lagged with an insulating material of thermal conductivity 0.06 W m-1 K-1 and thickness 75 mm. The pipe carries a process fluid at a temperature of 300 °C and the average...
Question - Four
A pipe carrying superheated steam at 300 °C has an outside diameter of 120 mm and is lagged with two layers of insulating material. The first layer (adjacent to the outer pipe wall) is 25 mm thick and has a thermal conductivity of 0.072 W m-1 K-1. The second layer (covering the...
Hello guys,
I have a problem with my work!
I have a furnance that have a "heat exchanger" to heat the air that will be used on the burners!
(You can work every value close to 1 atm pressure on the entire exercice)
The furnance is 1100~900 ºC
The fan sends in a tube 7500m^3 air per hour...
Hello everyone !
I am currently looking for a way to find the heat of vaporization of Acrylonitrile butadiene styrene
I can not find any papers or source about it, so maybe I thought there is some chemistery table that could help ? Do you have any ideas/sources ? Thank you !
Homework Statement
117 J of energy is supplied as heat to 2.00 moles of an ideal gas at constant
pressure, the temperature rises by 2.00 K. Calculate the molar heat capacity at
constant pressure C_p,m and the molar heat capacity at constant volume C_v,m
for the gas. Is the gas monatomic or...
Question:
A pipe of outside diameter 200 mm is lagged with an insulating material of thermal conductivity 0.06 W m–1 K–1 and thickness 75 mm. The pipe carries a process fluid at a temperature of 300 °C and the average temperature of the outer surface of the lagging is 45 °C.
(a) Estimate the...
1. The problem
What is the resultant temperature when 100g of steam at 100°C is passed through 500g of ice at -20°C.Homework Equations
Q=mCDeltaT[/B]
The Attempt at a Solution
I am not sure whether both the quantities will combine to from water
Can black body retain it`s absorbed heat energy? If yes, then why we can not convert this energy into a usefull form such as into electric energy as solar do?
Homework Statement
If Cp for an ideal gas is 35.4 J/mol⋅K, which of the following is Cv for this gas?
a. 12.5 J/mol⋅K
b. 20.8 J/mol⋅K
c. 29.1 J/mol⋅K
d. 27.1 J/mol⋅K
e. 43.4 J/mol⋅K
Homework Equations
ΔH = ΔE + Δ(PV) = Q + W + Δ(PV), and for ideal gas, ΔH = nCvΔT + Δ(nRT) = nCvΔT + nRΔT =...
Homework Statement
How much heat in joules is needed to raise the temperature of 7.0 L of water from 0°C to 78.0°C? (Hint: Recall the original definition of the liter.)
Homework Equations
How much heat in joules is needed to raise the temperature of 7.5 L of water from 0°C to 87.0°C? (Hint...
If the universe keeps expanding and eventually ends in a "big freeze" or heat death, does this contradict the third law of thermodynamics?
The third law of thermodynamics states that a crystal at absolute zero has zero entropy. Since the entropy of the universe can never decrease, as the age...
Hi guys,
I am newbie on thread and currently working on a project
I need some help on the Heat flow on multiple walls.
Here is the setup (see figure below)
The first wall is a Steel material which has a 350C temperature(1kwatts) and the an Air Gap is present then followed by a Plastic wall...
Homework Statement
I'm a little bit stuck with this exercise.A small body with temperature T and emissivity ε is placed in a large evacuated cavity with interior walls kept at temperature Tw. When Tw-T is small, show that the rate of heat transfer by radiation is
$$...
Homework Statement
A 0.25 kg piece of ice at -30 C is warmed by an electric heater and the following graph of temperature is produced. Assume that there has been no loss of energy to the surroundings.
- Use the info on the graph to determine the power output of the heater
- Explain how long...
I have a long steel uninsulated cylinder filled with hydraulic fluid (let's say it's mineral oil), and I need to figure out how many barrel heaters to clamp onto it in the winter months to prevent the steel surface temperature from dropping under 40 degrees Fahrenheit. My question is, how do I...
Homework Statement
A 1.75m long PVC pipe with a thermal conductivity of 0.19 W/mK has an internal diameter of 3mm and an external diameter of 5.5mm. Inner temperature is 298K and outer temperature is 273K. Calculate the heat transfer rate through the pipe and thus the decrease in the inner...