Heat Definition and 1000 Threads

  1. Beanyboy

    Exploring the Relationship Between Color and Temperature in Thermal Measurements

    There's a passage in Kumar's (excellent) book, "Quantum", which has me confused. He notes that Planck is aware that as the temperature of a heated poker rises, the colours change from red through to bluish white. Later in the passage, he refers to Herschel's earlier work on the relationship...
  2. M

    I What is the solution to the heat equation with a constant added?

    I have seen how to solve the heat equation: $$ \frac{ \partial^2 u(x,t) }{\partial x^2} = k^2 \frac{ \partial u(x,t) }{\partial t} $$ With boundary conditions. I use separation variables to find the result, but i don't know how to solve the equation plus a...
  3. Cassius1n

    Heat loss in a conductor based on Fourier's law

    Homework Statement Find the admissible current density Jadm for a wire that has no insulation and also for a wire that has two layers of insulation and compare it to Jadm for the case when the wire has only one layer of insulation.2. The attempt at a solution and equations In the image I've...
  4. F

    What is the Specific Heat of an Ideal Blackbody?

    Hello, I was thinking about how a blackbody (and any other type of body) eventually reaches a steady-state, constant and finite temperature once the absorbed energy is equal to the emitted energy. The specific heat of a substance indicates the temperature change causes by the...
  5. Krushnaraj Pandya

    Change in temperature when a gas is in a moving container

    Homework Statement Some gas at 300K is enclosed in a container. Now the container is placed on a fast moving train.is the change in temperature of the gas the same as the change dT observed when train suddenly stops? Homework Equations 1/2mv^2=dU?? or dU=0?? The Attempt at a Solution...
  6. C

    Heat released during combustion at constant pressure vs volume

    Greetings! I've been brushing up on some thermodynamics recently and came across a perplexing sentence in my notes and text from undergrad. It says that for a combustion reaction, such as the combustion of heptane: C7H16 (l) + 11O2 (g) ---> 7CO2 (g) + 8H2O (l) That this process carried out at...
  7. T

    Seawater sample temperature control – heat exchanger design

    I’m designing a system where a sea water sample must have its temperature controlled between near its freezing point (-2°C) and +30°C to simulate sea temperatures. To control it, the sample will be in contact with a block, which will be controlled by an external circulating water bath. The image...
  8. cosmik debris

    Why does a resistive wire heat up from current flow?

    The kinetic energy of electrons in a conductor is roughly 9 orders of magnitude greater than the kinetic energy from the drift velocity of the electrons. It seems that the kinetic energy from the drift velocity is not enough to account for the heating, where does the heat energy come from? Cheers
  9. K

    Flow inside pipe, heat transfer

    Homework Statement A 5m long heated pipe is used heat up water from 15°C to 65°C. Water flow through the pipe is 10liter/min. The heating gives a constant heat flow in all parts of the pipes surface. The inner and outer diameter of the pipe is 30 and 50 mm, respectively. Calculate the heat...
  10. K

    Can a Heat Balance be Achieved with Constant Condensation Temperature?

    Homework Statement If you have a heat exchanger with a cooling fluid and a fluid that condenses, and the fluid condenses over the entire heat exchanger i.e. its temperature is constant. How can one make a heat balance in such a case, when dT is 0 for the condensing fluid but not the other? i.e...
  11. EastWindBreaks

    Heat transfer boundary condition

    Homework Statement I am confused on how it's using the surrounding temperature minus the surface temperature as its the other way around in the Newton's law of cooling, Doing that would change the sign of convection right? I don't see the reason to do that, since if left side is hotter, then...
  12. T

    Explain what is meant by an 'overall heat transfer coefficient

    Homework Statement (I) Explain what is meant by an 'overall heat transfer coefficient'. (II) Explain what is meant by fouling and what its effect will be on the value of the overall heat transfer coefficient. 
 Homework Equations None provided. The Attempt at a Solution (I) The overall heat...
  13. S

    Steady state heat flow: radiation and conduction

    Homework Statement One end of a solid cylindrical copper rod 0.200 m long and 0.0250 m in radius is inserted into a large block of solid hydrogen at its melting temperature, 13.84 K. The other end is blackened and exposed to thermal radiation from surrounding walls at 500.0 K. (Some telescopes...
  14. P

    Finite difference conjugate heat xfer: internal flow

    Hi. I have been trying to solve this problem that has been keeping me up at night for a coupe weeks at least. If anyone can help me, I would be greatly appreciated. Hot air enters a cylindrical duct. The duct has some R-value and radiation and convection is being accounted for on the outside...
  15. K

    Heat transfer in a fin with constant volume

    Assume we have a cylindrical fin which has the effective length of L and its efficiency is given by the equation: $$η=exp(-0.32mL)$$ where $$m=\sqrt{\frac{hP}{kA}}$$ where P is perimeter and A is the cross sectional area of the fin. If the volume of the fin remains constant, which of the...
  16. J

    Thermodynamics - Hypothermia - Heat loss

    Homework Statement A careless farmer sends this sheep out to graze on a very cold winter day when the temperature is -10oC. The sheep's coat has a thickness of 4.7 cm and a surface area 1.3 m2. Calculate the rate of heat loss from the sheep on this cold day. Assume that heat is lost only...
  17. T

    Negative Heat Sink thermal resistance

    I'm currently developing a heat sink for a product that produces up to 150 W max power dissipation. I'm currently getting a negative thermal resistance for the heat sink. I don't think that is possible.. I'm not sure how to move on at this point to properly design a heat sink to meet the heat...
  18. UMath1

    Heat Engine Efficiency and Entropy

    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...
  19. Rafe Zayed

    Energy of Waste Heat: Is Exergy of Steam Less?

    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?
  20. jdawg

    Engineering Heat and Mass Transfer: Thermal Radiation Circuit

    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...
  21. K

    Heat Question -- Temperature rise of a hiker on a long hike

    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...
  22. A

    Specific heat capacity of a solid material

    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...
  23. S

    Calculating Specific Heat Capacity

    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...
  24. C

    Modeling a Heat Source with the 2D Heat Equation

    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...
  25. B

    Thermodynamics - temperature, pressure and heat

    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...
  26. maajdl

    Heat exchanger and the second principle

    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...
  27. EastWindBreaks

    Derivation process? (Heatsink Fin Heat Conduction Equations)

    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...
  28. jdawg

    Heat and Mass Transfer: Nodal Networks

    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...
  29. T

    Exploring the Energy Transfer of Light and Heat in Matter

    I read that atoms transition from electronically excited to vibrationally excited. But how?
  30. Ilya Furman

    How Much Heat is Produced by Radioactive Waste?

    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...
  31. lc99

    What is the specific heat of the metal in this specific heat problem?

    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...
  32. komarxian

    Chemistry: Heat of Sublimation and Hydrogem Bonds Problem

    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...
  33. Likith D

    Heat in Crowded Places: Origin and Explanation

    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...
  34. House

    Understanding the Molar Heat Capacity of an Ideal Gas

    We know that for an ideal gas the differential of the internal energy function is: dU = n Cv dT But is Cv the molar heat capacity or not?
  35. Aleoa

    Understanding the Heat Energy of Springs: Exploring Feynman's Explanation

    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...
  36. W

    Heat transfer within a laptop computer from CPU and GPU

    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...
  37. H

    Heat and work when temperature increases by 1 degree

    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 =...
  38. T

    Heat Transfer II -- What is the purpose of a silvered coating?

    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...
  39. T

    Heat Transfer II -- How heat is lost from a hot surface to the surrounding air?

    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...
  40. T

    Simplifying the Natural Convection Heat Transfer Correlation

    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...
  41. A

    Hot metal lid on cool surface has resistance when pulled up

    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?
  42. M

    Which of these materials will heat up faster and why?

    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...
  43. T

    Heat Transfer and Combustion -- A furnace wall consists of three layers of material

    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...
  44. T

    How is Heat Transferred Through a Reheating Furnace Wall?

    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...
  45. P

    Calculating Heat Transfer in a Water Bath with a Changing Volume and Temperature

    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 ×...
  46. Shadow89

    Optimal values for power in an induction heater?

    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...
  47. P

    How Efficient Can a Radiative Heat Engine Be for a Moon Base?

    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...
  48. voltech444

    Auto/Motor ORC Waste Heat Scroll Expander DIY

    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...
  49. HethensEnd25

    Fin/Fan heat exchanger mass and energy balance

    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...
  50. Facial

    What is the main source of Earth's internal heat?

    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...
Back
Top