Cooling Definition and 646 Threads

Say there is a cup of coffee at 80ºC and you allow it to cool down. Eventually the cup of coffee will become at room temperature (if anyone knows the equation for this fluctuations of temperatures I'd love to see it) what is causing it to go from these temperatures? What are the principles are...

For dealing with different types of loss of coolant accident (LOCA), pressurized water reactors (PWR) have emergency core cooling system (ECCS). ECCS are simply redundant pumps to inject water into core to cool fuel, thus preventing fuel melting in case of an accident (hypothetical) that involve...

Homework Statement A hot solid sphere of initial radius ##a## with a uniform initial temperature ##T_{0}## is allowed to cool under stagnant air at ambient temperature, ##T_{\infty}## . Assume the temperature within the sphere is uniform throughout the cooling process. Show that under...

Homework Statement One method for cooling a gas is adiabatic throttling (Joule-Thomson Experiment). Another method is a reversible adiabatic expansion. Show that if the initial and final pressures are the same, the difference in temperature obtained by the second method is always higher. Hint...

If electric current passes from relatively good conductor to a much worse conductor (resistance), electrons start to loose energy and dissipate it as heat. Does opposite effect take place? I mean, when electrons pass from some poor conductor to a much better conductor, will they absorb energy...

What happens if a metal is heated and cooled at the same point at the same time?? will it expand or contract??

Homework Statement On a clear night, the loss of infrared radiation to space causes the loses 10 m of the atmosphere to cool by 5 K over 10 Hrs. Assuming a density of 1.25 kg^-3 for the air, what is the net rate of heat loss by radiational cooling, in Wm^-2 (Answer: 1.74 W m^-2)Homework...

As I understand it, a virus like HIV for example cannot survive more than a few degrees below normal body temperature. Is it possible, therefore, to reduce the whole body core temperature, under controlled conditions, to well below the virus survival threshold temperature, thereby killing the virus?

When dealing with power losses from engine to drive wheel(s) i ignored losses other than straight friction, can cooling and alternator losses be taken as roughly a percentage of the cars engine power ? Thanks Dean

Fourier's law of thermal conduction states that \mathbf{j}=-k\nabla T, where \mathbf{j} is the heat flux. Integrating both sides of this equation over a closed surface gives the equation \frac{dQ}{dt}=-k\int \nabla T \cdot d\mathbf A. If there is a temperature discontinuity across this...

I have been looking into a number of things related to Reaction Engine's Sabre Engine Program for their Skylon hypersonic aircraft. I find the program absolutely fascinating as the technological development looks like it is on track to revolutionize air and space flight in the coming decades...

Hi. I have a closed container about 1.1L in volume and within this chamber is a continuous heat source. I am trying to regulate the container temperature without purging out or fanning the air contained inside the chamber out. I want the air within the chamber to circulate and I thought of...

I know that in the pursuit of low noise amplifiers, the cooler the better, generally speaking. But when does it make sense to try and go through the work required to cool an amp? One of my passions is radio astronomy. I have a good collection of LNA's around of various types and an eight foot...

I need convincing that evaporative cooling is refrigeration in the sense of a heat engine run backwards. It has the outward appearance of refrigeration. Take perspiration, for example. Your body temperature drops even though the ambient air temperature is hotter. It requires work. You need a...

Good Morning, First, let me preface my question by stating that I do not have a background in physics so my question my or may not be ignorant. I simply have a curiosity and I am having trouble finding any results. My question is regarding air conditioners and cooling energy usage. Given...

Homework Statement I have an "abstract" problem. Calculate the maximum cooling capacity for forced air cooling of a room. The room contains two computers that each has a energy usage of 1 kW. v_air_in=75m^3/h v_air_out=30m^3/h Homework Equations As the cooling is done by ventilation...

Hello, I was in a discussion with a Friend regarding cooling systems for computers. We were discussing different air cooling methods for CPUs and he claimed that if the fan was moving at high enough RPMs that the heat transfer from heat sink to the surrounding air would drop in efficiency. He...

Hello, I am trying to calculate the surface cooling rate from the sides of a round tin can using Rayleigh, Prandtl and Grashof numbers but I'm getting a ridiculously high result, and I'm hoping someone could run through my numbers to tell me where I'm going wrong. Posting my question is...

Newton's Law of Cooling states that the rate of cooling of an object is proportional to the temperature difference between the objects and its surroundings. Suppose that a roast turkey is taken from an oven when its temperature has reached $200^oF$ and is placed on a table in a room where the...

I have a fairly large (for household use) 7.5HP electric motor driven two-stage air compressor, which charges the receiving 80 gallon tank to a limit of 175PSI. There is a short 3/4" diameter copper pipe that connects the pump to the tank. I have not measured, but guesstimate that the...

Hi everybody! Well, these are just two basic questions that are bothering me. 1.When it is said that, for example, a Cryocooler has 1W of cooling power at 4.2K, what does it really mean? To me, the action of "cooling" depends on the material that it's being cooled down. So, for different...

Hi Guys! How come this could happen: The temperature of water runs through the radiator can't be lower than the temperature blows through the radiator. Am I wrong? Is there a significant effect of increasing the amount of fans in this case? Thanks a lot!

I am interested in knowing whether what changes would happen at the molecular and atomic level, to a material subjected to Cooling. 1. Does the minimum temperature that can be achieved has limit? 2. Is it Zero Kelvin? 3. If so, is it a global standard for minimum temperature for any material...

I have an airtight container, the "hot-box", filled with air from outside. I close the two valves to the outside air, and let the sun heat it up. Once it reaches a certain temperature/pressure: I open/unlock a one-way check-valve that leads to a shaded/water-immersed coil of copper tubing...

Discuss two measures that can improve the cooling efficiency.

Consider that you are cooling a mass of steel from 1,000 °C to 920 °C. To accomplish this a water flow of 2,000 liters/min is required, and the water outlet temperature increases 10 °C. The water pressure at the inlet is 5 kg/cm2. Now suppose that you increase 30% the water pressure by means...

If you stop cooling a resistor and stop current simultaneously then what happens to the temperature of the resistor in the next few moments? My question is actually about whether a computer CPU will continue to heat up at all when the computer is switched off (Stopping any power to the CPU, so...

Hey everyone! I am working on improving natural draft counter flow cooling tower efficiency as my final year B.E. project. I came across a research paper that said that at transverse cross section of the tower, above drift eliminators, the air velocity decreases from the periphery to the...

Hello, I would like to know how to calculate how long the phase transition when cooling lasts. So basically how long the latent transition lasts. I really don't have any ideas how this could be calculated, although I would assume it is function of the mass. Any help is much appreciated.

I've been a bit confused about when/why an expanding gas cools. Here is what I've heard so far: Refrigeration systems work based on using heat that is used merely to break attraction of molecules of liquids at their boiling point (eg, freon released through an expansion valve gets cooler...

At 9am , a thermometer reading 70ºF is taken outdoors, where the temperature is 15ºF. At 9:05am, the thermometer reading is 45ºF. At 9:10am, the thermometer is taken back indoors, where the temperature is fixed at 70ºF. (a). Find the reading at 9:20am (b). when the reading, to the nearest...

The two kettles contain a boiling aqueous solution. They must be cooled to room temp as fast as possible (otherwise adverse chemical reactions will take place). Only one pump and one cooling coil are available. It would seem the second kettle would fill up. However, would the increased...

The kinetic energy of gas molecules or atoms is: (3/2)kTN/M where k is Boltzman constant, T is absolute temperature, N is avogadros number and M is molecular weight. The formula is derived from http://en.wikipedia.org/wiki/Kinetic_theory. Assume that the gas is steam with M = 18 kg/mol at 373K...

I have a practical problem that I am trying to solve regarding using air chambers. I hope someone can help me with the problem. I have two air chambers connected by a tubing and a valve. One is pumped to a low pressure, chamber A (~30 kPa), and the other is at near atmospheric pressure...

I have a 10x20 shed. It has a chipboard floor, and below that is about 8" of open space, which wind will blow through. If needed, I can close it off - but I cannot insulate it. My main concern is not with heating the room, although that would be a nice benefit. By far, my concern is with...

Homework Statement The world's most active volcanos, such as the Kilauea volcano in Hawaii, can disgorge about 5 ✕ 105 m3 of 1000°C lava per day. What is the rate of heat transfer out of the Earth by convection if this lava has a density of 2800 kg/m3 and eventually cools to 32°C? Assume that...

Homework Statement hello friends,i have to do a project about calculations of cooling of a car engine.i don't know what to do or where will i start.can you offer me some links or books about this area please.how can i find how many wats of heat, say, a 100 kw engine, releases. Homework...

Homework Statement By how many degrees will your body cool if you evaporate away 10g of water? Specific heats of water and water vapor are, respectively, 4.18 J/gC and 2.00 J/gC. Heat of vaporization of water is 40.7 kJ/mol. Heat of fusion of water is 6.03kJ/mol. Assume a 100kg person who is...

OK, before I get into the main question, I figure I should give a little background. First off, this is not something that is going to be made for real. It's for a flight simulator called Orbiter (found here), and in particular for a personal project to update and improve upon the existing...

Homework Statement How much time does it take a planet with surface temperature of 100K and a radius of 500 km to cool down to 50K, ignoring solar heating. Assume E_thermal = 3/2 NkT and that the surface radiates as a blackbody. Calculate this by using the relationship between thermal energy...

Hi, I am new to the forum and would like your thoughts and idea on a project I am currently working on as a chemical engineering student. I have to design a cooling system for a distillation column using water pumped from a pond nearby. I have been given the distance to pump this water and...

Homework Statement A homicide victim is found to have a temperature of 31°C at the stroke of midnight. At 1:00AM his temperature dropped to 29°C. Assuming that the temperature of the room stays at 20°C, when did the murder take place? Homework Equations - The Attempt at a Solution...

Hi, If we took the blood of all people here on Earth and made a ball of it (r=200, T = 310 K) how long would it take for it to cool down to ~ 285 K in vacuum (absent of sunglight)? How long would it take to cool down in air, with reasonable conduction speeds?

Hello, I am a final Year undergrad in B.Sc in Electronics. I am going to apply for a Summer Research (2months period )in Lasers in other institutions and I am thinking to work on Laser Cooling. I have to specify a short, innovative project idea. I have gone through courses in Quantum...

Homework Statement A hot solid body is immersed into a large body of water which is a 4 degrees C. After one hour the body's temperature is measured at 40 degrees C, after 2 hours at 15 degrees. Assuming that Newton's law of cooling applies and that the water body is mixed constantly and...

Hello, In my Differential Equations class we are learning about modelling with first order differential equations. We learned that Newton's Law of Cooling breaks down when the temperature of the object is approaching the temperature of the room its in. You eventually get to a point where you...

Law of cooling states that the rate of loss of heat by a body is directly proportional to the excess temperature of the body above that of its surroundings. The equation of determining temperature in time T(t)=Ta+(T0-Ta)*e^kt (Ta-ambient temperature, T0-initial temperature, k-heat transfer...

A decent "k" value for Newton's law of cooling for water? Recently I've been trying to cool some water to a specific temperature from boiling. It doesn't have to be super accurate (within about 5° degrees Fahrenheit or 2° Celsius) but the only thermometer I have access to is just for ambient...

how can i calculate the require time for an air-conditioning unit to cool from 30 degree celcius to 22 degree celcius? others parameter can be ignore, i would like to know the formula used and the principal of calculation. thanks

Here is the question: I have posted a link there to this topic so the OP can see my work.