Heat transfer Definition and 947 Threads

Scenario A: An icicle on the eaves of Uncle Ivan’s dacha in far off Verkhoyansk vaporizes a number of water vapor molecules at an ambient temperature of -80°C. Over the succeeding months, one of these molecules makes its random way to the surface of a cloud droplet over Ouagadougou. Along the...

When I pour two different liquids at different temperatures, into the same container, the temperature will be uneven at the start but then will approach equilibrium. Similarly, the concentrations of each liquid will be uneven but when mixing is complete, there will be the same concentrations...

Having difficulty remembering how to model a simple heat transfer equation for a liquid tank/piping system and wondering if anyone can provide some quick help. I have a 1000L tank of water that is heated by a 1kW heater (target temp of 43°C). The piping system (outside of the tank), holds 100L...

Considering one dimensional heat conduction we may write the Fourier's law of heat conduction in the x-direction as, ##\dot{Q}_{x}=-kA\Big(\frac{∂T} {∂x}\Big)## where, ##\frac{∂T} {∂x}## is the temperature gradient which is basically the slope of the temperature curve on a T-x diagram...

Hi, I have to check the buckling of a beam in fire. To do this I am following the below stages: 1. Conduct a heat transfer analysis ( transient ) for 30 minutes in fire , to find out the temperature history of the beam. Please not the temperature of the beam is not uniform 2. perform 6 runs...

Hi, I'm looking for some help regarding heat transfer through some sandwiched materials. We have a pneumatic cylinder with the stainless steel 303 cylinder rod attached to a block of aluminium 6082 t6 50mm high x 40mm wide x 10mm deep. This block is attached to a block of polyurethane, shore...

hi im supposed to simulate a vcsel laser for my thesis i got problem in selecting physics.. i should check its heat transfer and threshold current but i don't know which physics should i choose ! does anyone know about vcsel's physical structure in Comsol ? by the way does anyone know that how...

1. Homework Statement We want to heat up 200 liters of water in a bathtub from 15 ◦C to 30 ◦C. The temperature is increased by adding marble stones to the water. The initial temperature of the marble stones is 773, 15 K. Assume that the marble is rigid, with the heat capacity cm = 0.88 J ·K−1...

I'm setting up a thermal resistance network to determine the heat loss through the insulated wall of a heated fuel/crude oil tank but i can't seem to find values for the convective heat transfer coefficient of the fuel oil (kerosene) or the crude oil at elevated temperatures. I have only found...

I am trying to design a heat exchanger for a stratified hot water tank which means that the heat transfer on that side of the exchanger will be totally dependent on free convection. I plan on using a shell and tube set-up but I have no idea on how to calculate the required mass flow rate from...

Homework Statement A pipe of internal radius r1=0.03 m is built to have conductivity variable with radius: k=ar2, where a=250 Wm/K. 1) Find the critical radius r2 for the maximum heat transfer by convection from its external surface if the heat transfer coefficient is h2=30 W/m2K. Homework...

Hey, long time reader, new user. I have a probably simple fin question. If you all don't mind. I honestly just need to nail down the equations. Don't quite need a solution. A fan blows air over the top surface of a hot electronic component (size of 10 mm x 10 mm) with an average convective...

Hello, I will try and provide as much detail to the problem as I can with the hope someone can help me solve this. We are currently working on a wireless project that contains high electrical currents, because of this the box the electronics are enclosed in experience quite a temperature rise...

Hello, I am working a designing a cooking pot with thermoelectrics integrated into the design. I am trying to find the heat flow through the pan to estimate how much electricity the design will produce. First off some constants - The design has a base area of .0491 m2, or a diameter of 25 cm...

If hot air passing through a tube which is exposed to the atmospheric temperature is to be cooled at a certain temperature, fins are installed to increase the heat transfer from the hot air, which one is better design? to install the fins inside the pipe or outside the pipe ? and why?

Homework Statement a small lump of ice at 0 degrees celsius falls to the Earth's surface. when the hailstone hist the surface, all of the kinetic energy of the hailsotne is transferred to thermal energy in the ice. calculate the minimum speed of the hailstone so that it just melts when it hits...

Homework Statement Perform a one-dimensional energy balance for the heating of a fluid through a hot pipe in order to develop a differential equation that governs the variation of the mean temperature of the fluid along the length pipe. The pipe has an inner diameter D and length L; its walls...

Homework Statement Water flowing at the rate 3.5 kg s−1 through a tube with an inner diameter of 2 cm is to be heated from 20 to 40◦C. If the tube wall temperature is maintained at 90◦C, determine the length of the tube required. Homework Equations Q'=Cp*m*(DeltaT) Q=2*pi*r*L*Q' The Attempt...

Homework Statement A thin flat plate 2m×2m is hanging freely in air. The temperature of the surroundings is 25°C. Solar radiation is falling on one side of the plate at the rate of 500 W/m2. What should be the convective heat transfer coefficient in W/m2°C, if the temperature of the plate is...

Hi everyone. I have here a problem understanding the stability of heat transfer through radiation. I'll give you some background, and later on I'll describe the physical problem. Background I am simulating the unsteady radiative heat transfer between mutually visible surfaces of objects through...

What physical interpretation can we draw from the thermophysical property of thermal diffusivity? How might we visualize the true physical meaning of this property and relate it to its definition?

Hello, Consider this exemple: At y = 0 It is said that the heat is transferred by conduction because the fluid has a velocity equal to 0 (no-slip conditions). But the temperature of the fluid for y=0 is equal to Ts(temperature of the surface) so how come there's a gradient in the temperature...

Hello, PF! Recently, while reading chapter 10 (microscopic energy balances) of the second edition of BSL, I found a minor discrepancy which is confusing me, especially when considering the mathematical analogies of heat and mass transfer. In section 10.1, the authors introduce Newton's law of...

Homework Statement A reversible heat engine produces work from the temperature difference that exists between a mass of m = 9 kg of an ideal gas (cv = 716 J/kgK, R = 287 J/kgK) in a rigid container and a heat reservoir at THR = 285 K. The only heat transfer interaction experienced by the...

Hello, Let's say the temperature of an object is constant and equal to 20 °C. If we put this object to a surrounding which has a temperature of 25 °C, than there's heat transfer from the surrounding to object by convection. If q is the heat transfer (in Watt) than after a specific time (Δt)...

Homework Statement One kg of Refrigerant 22 initially at p1=0.9 MPa, u1=232.92 kJ/kg, is contained within a rigid closd tank. The tank is fitted with a paddle wheel that transfers energy to the refrigerant at a constant rate of 0.1kW. Heat transfer from the refrigerant to its surroundings...

Hello, Heat transfer through finite temperature difference is known a irreversible process because heat cannot be transferred from cold to hot temperature without doing any additional work. But, how this transfer affect the efficiency of the system? How this heat transfer decrease the amount of...

Hello, i have a simple question regarding a problem I am solving. Here it is: A 4x4m flat plate maintained at a constant temperature of 80 degree Celsius subjected to parallel flow of air at 1 atm,20 degree celsius and 10m/s.The total drag force acting on the UPPER surface of plate is measured...

Homework Statement A specific type of ideal gas has a specific heat capacity at constant pressure (cp=cv+R) that is a function of temperature T, such that cp=0.5+876T, where cp has units of J/kg/K and T has units of K. The gas, which is initially at T1 = 294 K and P1 = 1x105 Pa, undergoes a...

Which of the two books would you pick as an undergraduate engineering student if you were to study the subject of Heat and Mass Transfer entirely on your own? 1. Heat and Mass Transfer: Fundamentals and Applications by Cengel & Ghajar 2. Fundamentals of Heat and Mass Transfer by...

Hello all. I want to do some experiment but I thought I would go over this theoretically before trying out and now I have a doubt. Homework Statement I have a driver which produces say 600mA. I connect the driver to one end of Nichrome Wire. And the other end of Nichrome wire is in contact...

Homework Statement How much heat is radiated in water per sq cm, from a block of copper at 250 C and 1200 . Homework Equations e= 0.6 Hr= (Area)(e)(5.67x10^-8 W/m^2K^4)(temperature)^4 The Attempt at a Solution i'm sorry, i don't know how to solve this one...

Homework Statement 1) A typical wall construction for a single-family residence might consist of 0.375 inches of outer sheathing (insulating board, hardwood siding, etc.), 3.5 inches of mineral fiber insulation and then a 0.375 inches inner surface (gypsum, etc.). Typical thermal...

Homework Statement A copper wire has a diameter of 204.3 mil (1 mil = 0.001 in) and a resistance per unit length of 8.31x10^-4 ohm/m. The wire is coated with plastic insulation with thermal conductivity k = 0.20 W/(m K). The upper temperature limit of the plastic is 400 K. The air surrounding...

Two metal rods, one silver and the other gold, are attached to each other. The free end of the silver rod is connected to a steam chamber, with a temperature of 100oC, and the free end of gold rod to a ice water bath, with a temp of 00 C. The rods are 5.0 cm long and have a square cross-section...

Q. Regards infrared radiation, conduction and convection, is infrared radiation the starting point, the fundamental source of heat energy (thermal energy), and the fundamental source of the other two? I’m thinking that the Sun predates the Earth by 30 million or so years so the first heat...

Consider the heat equation dT/dt - aΔT + v⋅∇T = S where S is a source term dependent of the radiation intensity I and the temperature T. The fluid velocity v is prescribed. We also consider the radiative transfer equation describing the radiative intensity I(x,ω,t) where ω is the ray direction...

Homework Statement The ice is placed in water, we know the surface area A, emissivity of both ice and water, Stefan-Boltzmann constant and the temperature of both ice and water. What is the equation for heat transfer rate between water and ice? Homework Equations Heat transfer rate by...

Hello, I am looking for the general direction that I need to go to calculate the following: The time-dependent change of temperature of a finite, but continuous, mass of air moving across a water/air boundary. Let's say you have 150 degree F air moving at 0.007m^3/s over a relatively infinite...

For a general cooler or heater, the calculations for heat transfer are based on the tube side and shell side. So 1) For a reboiler would the vaporizer be the "shell" since that's where the heat transfer occurs? 2) How do you account for the phase change? I used Q = m*cP*dT to calculate duty...

Lets assume an exchanger that is 100% efficient (no heat loss). Duty (Q) and LMTD is known. Your overall heat transfer coefficient (U) is dependent on your transfer coefficients on the shell and tube side, and the resistance of the pipe walls (we're going to ignore entrance effects and fouling)...

Good evening people of PF! I have recently encountered a problem from Himmelblau's Basic Principles and Calculations in Chem. E. which asks to set up an energy balance for a tank, and then non-dimensionalize the differential equation before solving it. It's not the most complex task, but it's...

Hello, my problem is the following: I have an iron bar, which can be heated by convection through an electric cable with power Q. I want to know the temperature of the iron bar after 1 hour has passed, both in the case when the power is turned on and when it is off (Q=0). the input parameters...

Hello, I have completed my bachelors degree in Mechanical Engineering and will be joining for my masters degree in mechanical engineering shortly. I am planning to become a drilling engineer in the petroleum industry. So in order to achieve my goal, what are the recommended courses that i...

If I have a large steel box that is 27ft x 8ft x 8ft and has 7 in thick walls with 4 non-insulated windows each 1ft by 1ft, where does heat escape from inside the box, is it the windows and the walls? So if the inside temperature needs to be 72 F and the outside air is 0 F how much heat would...

Hi, We are doing radiation analysis using solidworks simulation..And as a part of this project i need to validate it theretically..Hope i will get some help here.. Its cylindrical vacuum furnace,where inside strip type heating elements are placed which are connected to transformer of 60kW.After...

Homework Statement A solid, 2.00 kg cube of nitrogen at -220.0oC is added to a 1.00 kg mixture of ice and water at 0.00 oC. If the final temperature of the mixture is -100.0 oC, how much ice was there in the original mixture? Homework Equations e=mct e=mLv/f The Attempt at a Solution...

Homework Statement Getting an expression for the convective heat tarnsfer coefficient. Homework Equations See attached images The Attempt at a Solution I have been reading about the boundary layers. Here is an extract of my notes corresponding to thermal boundary layer and consequently my...

Hi All, I'm trying to understand the radiation mode of heat transfer. I have been reading the book by Incropera - "Fundamentals of heat and mass transfer" and have a few very basic questions. 1) Firstly, thermal radiation is the energy emitted by matter that is at non-zero temperature...

1. The problTfem statement, all variables and given/known data Determine the result when 100g of steam at 100C is passed into a mixture of 200g of Water and 20g of ice at exactly 0C in a calorimeter which behaves thermally as if it were equvalent to 30g of water. Homework Equations FInding the...