Heat transfer Definition and 947 Threads

Homework Statement a copper pot's radius is 12 cm, the thickness is 5 mm. It is placed on the stove for boiling, if the temperature of the stove is 115 oC while the water is 100 oC. How much of water that evaporates per minute Homework Equations ΔQ/Δt = (A)(k)(ΔT) / (L) Q=mcΔT The Attempt...

Homework Statement [/B] We are heating a semi-infinite slab with a laser (radius of a stream is ##a##), which presents us with a steady surface heating (at ##z=0##), everywhere else on the surface the slab is isolated. How does the temperature change with time? Look at the limit cases: at ##t...

Hi all. I don't have as much experience with thermal analyses in ANSYS, and I can't quite figure out a problem that I'm working on. I'm trying to find the temperature distribution in a box that has a circle in the center. I want to define constant temperature b.c.'s at the walls and the circle...

Does anyone here have experience with COMSOL? I want to model a system where i have a fluidic channel containing warm fluid running through a block and I want to analyze the heat transfer from the channel into the block . To establish the warm fluid I put an initial temperature condition at...

Homework Statement Would really appreciate if you could lend me a hand with this tube and shell exercise.[/B] m=0.24kg/s ##D=2.5*10-2m## ρ=850 kg/m^3 cp=2000 J/kg*K μ=2*10-4 kg/m*s λ=0.3W/m*k Homework Equations Dittus-Boelter:Nu=0.023*Re0.8*Prn where n=0.4 heating and n=0.3 for cooling, so in...

Homework Statement I have a confusion regarding areas. Usually in fluid flow I am using the A=(pi*D^2)/4 However in heat transfer we usually use A=pi*D*L Could you please explain this?I mean in first case(fluid flow) it is cross sectional area and in the 2nd case(heat transfer) is like the...

Homework Statement I would really appreciate if you could give me some hints regarding what exactly to do at iv)[/B] iv) Given formulas: Homework Equations f(y)=(ro*R^5/E*t^2) The Attempt at a Solution we know that f(y)=0.75 1ton TNT=4.184*10^9 J ro=1.003kg/m^3 We have the above...

Homework Statement Homework Equations The Attempt at a Solution I do not know exactly how to start this problem. I would really appreciate it if you could give me some hints. I know that e^ - t/tau=T(t)-Twall/Ti-Twall where tau=m*cp/hA where h=convective heat tr.coeff and T(t) is desired temp...

Hi Guys While studying physics for my masters (doing it in material science engineering), huge amount of questions appeared. First, let's imagine two experiments 1) One enclosure with perfect reflective walls (R=1 over the entire thermal radiation spectra) at a temperature T1 and a body inside...

Homework Statement Problem data:[/B] http://imgur.com/a/hEz16 Homework Equations Rconduction=ln(rout/rin)/2*pi*Length*thermal conduct Rconvection=1/2*pi*Length*routside*convective heat transfer outside =>Qconduct=2*pi*Length*thermal conduct*(Tin-Tout)/ln(rout/rin)...

Homework Statement Hello, I am struggling with this heat transfer and fluid flow problem.I would really appreciate if someone could have a look over what I have done on it. I am not sure if what I have done is correct ,I would really appreciate if you could tell me if it is correct or wrong.And...

Homework Statement I would really appreciate if someone could help me out with this exercise in fluid flow/heat transfer ,because I really struggling with it.Below I am attaching photo of problem+table with values. Thank you in advance !Homework Equations Question link:[/B]...

Hello all, I have a question regarding heat transfer. When the Biot number is small (<0.1) a mass can be regarded as lumped. Which means that the temperature is the same everywhere in the mass. Now if the Biot number is larger than 0.1 (say around 0.5-0.8) and I still do a lumped system...

So, i was studying some fin design in a heat transfer course , and then came the part where the efficiency is to be calculated, then i noticed that when he calculated the surface area and the sides of a rectangular fin weren't included, so i searched and i found out that it was neglected...

Homework Statement I'm unsure of what exactly is changing the heat transfer direction in the triangular fin. Homework Equations $$q_{x} = -kA(x)\frac{dT(x)}{dx} (1)$$ $$q_{x+dx} = -kA(x)\frac{dT(x)}{dx} - k\frac{d}{dx}[A(x)\frac{dT(x)}{dx}] (2)$$ $$dq_{conv} = h(x)dS(x)P[T(x) - T_{∞}] (3)$$...

Hi guys, I need help with heat transfer calculations The scenario is : Installing a coil around a hot pipe and extract the heat from the hot pipe to heat the fluid flowing through the coil. The whole assembly is insulated. I need methods/formulas to calculate the amount of heat transferred so...

Hi all! I'm analyzing a fermenter and the water cooling system that cools it down. In analyzing this I've found kW and kWh required to cool down the fermenter using Q = dt*cp*m However when I try to find the overall heat transfer coefficient U using the data, I find that it varies with...

Hi, I'm working on a project and would like some help regarding heat transfer and heat conductivity. Any help would be appreciated, I'm more or less a layman. If I wanted to use heat from the sun to heat water via a metal conductor, does the size of the heat sink have proportional heating...

Hello, I have here a complex question. My background is Chemistry and Optoelectronics. I wasn't the best when we were studying Thermodynamics at uni so I have some knowledge-gaps. Anyways, here is my problem. Can somebody explain me the whole process of the convection in the coffee roaster. So...

For an airflow experiencing a large heat transfer, say a delta of ~600 degrees celsius, I assume compressible effects cannot be ignored. I am struggling however with some conceptual elements, such as how the pressure gradient changes along the flow when compared with compressible and inviscid...

Hi. I would like to ask a simple question. Here is the link of the file I study on. Immediately before the formula 4.9 for Biot number. Lc=V/As but I cannot understand it and I think it is not clear enough. How it appears, for what the word "characteristic" stands for, for example a pipe? For...

Dear All, I am facing a problem in Ansys Ansys issue. I am solving a model (Transient Thermal Analysis (Heat Flow from Hydrothermal Vessel)) in Ansys 16.2 Workbench While reaching modeling stage, and upon running the simulation, program gives an below errorAn error occurred while starting...

Homework Statement [Update: just realized that the LMTD is a temperature difference, so my question was not valid] :P Calculate the logarithmic mean temperature difference (LMTD) to heat water flowing through a tube from 21 C (Ti) to 40 C (Te) if the tube has a fixed temperature of 45 C (Ts)...

Natural convection always occurs opposite of gravity due to buoyancy; but I am confused as ice is solid so how could possibly convection even contribute to the heat transfer. I doubt about air movements nearby block that may contribute to greater heat transfer rate in case of hot block placed...

I'm looking to model the heat transfer by conduction from the aperture to the base of a compound parabolic dish (CPE). Here's what I have so far, thanks to CFDFEAGURU's solution for a cone at https://www.physicsforums.com/threads/heat-transfer-by-conduction-in-a-truncated-cone.368972/ let θ =...

Hi all. I'm currently working on a problem where I have to determine individual and overall heat transfer coefficients for a vertical cylinder with water flowing on the inside and steam on the outside (parallel flow), studying the cases of free and forced convection. I only have four...

Hello all, I am working on a few test scripts to test the life of a hydraulic cylinder. (It is a mechanically operated cylinder and has a positive displacement) The testing will involve thousands of continuous pump and retraction operations, due to which the temperature of the piston seal and...

Homework Statement In each of the following, state and explain which container will have the hotter liquid after thirty seconds: a) You pour equal amounts of of hot coffee into two cup s from a percolator. The cups are the same general size and shape. One is made from heavy china one is made...

Homework Statement A metal sphere is subjected to a heat flux, 5000 W/m2. It is originally at 20 C. How long does it take to heat to 90 C? D = 5 cm density = 8522 kg/m3 cp = 0.385 kJ/kg-K k = 104 W/m-k Homework Equations rate of heat input = rate of heat accumulation -k*A*dT/dr = m*cp*dT/dt...

Have been slightly racking my brains trying to remember the basics of this, but have a quick and probably pretty simple heat transfer problem. Was in a discussion Two standard 1000 liters square enclosed plastic HDPE containers (1m x 1m x 1m). One is filled up 800 liters (some air present at...

I am asked to simulate a 2-D coupled problem in COMSOL(Navier stokes with Heat transfer) of a simple room. I'm not sure if COMSOL already has preexisting physics for navier stokes and heat tranfer that I could use directly but I am provided with two differential equations and boundary...

I don't understand why heat transfer from hot reservoir to the system is considered reversible in case when Treservoir = Tsystem + dT but it's considered irreversible in this case: Treservoir = Tsystem + ΔT Where dT is infinitesimal difference while ΔT is finite difference in temperature...

Homework Statement Suppose you walk into a sauna that has an ambient temperature of 57.0°C. Calculate the rate of heat transfer to you by radiation given your skin temperature is 37.0°C, the emissivity of skin is 0.95, and the surface area of your body is 1.60 m2. I solved this first part and...

Hi all, I am new here, and want to thank you for help in advance! I am working on a project and need some help - I need to figure out surface temp on an object at some distance from the heat source: I need some help getting started. Is it going to be: Heat transfer (radiation) + Heat...

Homework Statement A solar heater is used to warm 150 kg of water by 30 K. The intensity of solar radiation is 6000 Wm-2 and the area of the panels is 4.0 m2. The specific heat capacity of the water is 4.2 * 103 J/kg/K. Estimate the time this will take, assuming a solar panel efficiency of...

Homework Statement Two rigid, insulated tanks are connected with a pipe and valve. One tank has 0.5 kg air at 200 kPa, 300 K and the other has 0.75 kg air at 100 kPa, 400 K. The valve is opened, and the air comes to a single uniform state without any heat transfer. Find the final temperature...

Hey guys, I'm really stuck right now 1. Homework Statement Habitable exoplanet: Now we will include a convective heat flux (H), with H being proportional to the difference between the atmospheric and ground surface temperature, $$H=c_p(T_a-T_p)$$ with c = 1.2 Wm−2K−1. Calculate the temperature...

If the temperature of the wall is homogeneous i.e. the entire wall has the same temperature: T1 being the temperature of the left wall and T2 being the temp of the right wall, how will heat transfer take place? Can convection occur here? If yes then how will the bulk motion be set up? I am...

Hi, I'm trying to calculate energy loss between two areas. One area is -25C and another is +15. The contact area(door) is 20m^2. Is convective heat transfer formula the right way to calculate it, or what should I use? I want to find out the how many kW I need to keep cold area at -25 when the...

Homework Statement A hot reservoir with a temperature of 653 K is 0.7 m away from a cold reservoir with a temperature of 399 K. The two reservoirs are insulated from each other except for a rod of brass (k = 109 W/m-K) that has a cross-sectional area of 0.07 m2. The entire system is allowed to...

Hi, there. I remember when I was in the University (mech. engineering), I had an exam on partial differential equations about heat transfer in a cylinder. We had to determine the temperature distribution. I remember the conditions were that the cylinder was insulated in the side area, had a...

Homework Statement Since the 1980's a total of 20 x 10^22 J of additional energy has been absorbed by the worlds oceans. This is 90% of the additional heat our planet is storing as a consequence of global warming. The surface area of the worlds oceans is 361,900,000 km^2 and we will assume this...

Usually it is said that loss of heat through a chunk of material because of conduction is proportional to difference in temperature and inversely proportional to thickness of material. E.g. if I got a wall to ΔQ = K*S*ΔT/D. where ΔQ - is energy flow through material. K - constant characteristic...

My textbook says that net rate of heat transfer due to radiation is εσA(T^4-To^4) but i couldn't understand it. Rate of emission is εσAT^4 and rate of absorption is aσATo^4 so net rate of heat transfer must be εσAT^4-aσATo^4(where T is the temperature of body and To is the temperature of...

Dear members, Some days ago, I received the following exercise but I have never studied thermodynamics before and I don't know very well where to start, the exercise is about Heat Transfer and the Finite Difference Method and I must program the solution using Petsc and C++. About the Finite...

I am trying to understand the concept of convective heat transfer. I plugged in some values into the convective heat equation and ended up with q = 40. Now, I don't know what that means. What does that tell me about how long it would take to bring a given volume of air around a hot surface to...

Hello, forum! I'm just starting a new course on heat transfer and we're using Incropera's book. Last time I studied heat transfer was in my transport phenomena course, using BSL, so it was kind of a culture shock using the new book, because the methods used are kind of different in some cases...

Freon is used every day to reduce temperature by compressing the gas then releasing the pressure. The Question is dose radiation from the sun (witch would be high pressure) steal energy from the objects it comes in contact with in space (witch is low pressure), Thus contribute to the loss of...

Homework Statement A thick wall cylinder having a thermal conductivity of 60W/mK has a 75mm inner diameter and is 2.5mm thick. The pipe carries water at 90 degrees celsius inside and the outside is surrounded by air at 20 degrees celsius. The heat transfer coefficients inside and outside the...

Hi All, I have a situation were I need to evaluate the heat transfer coefficient of a horizontal surface. The surface has tubes within although I first used "flow across a bank of tubes", this has been untrue due to the air flow coming from above the surface flowing vertically (and...