Understanding the three types of heat transfer will help you insulate smarter and not just throw money at expensive energy bills like most people. There are three types of heat transfer: conduction, convection, and radiation. All three of these should be addressed if you want an effective insulation design for your old home.
Heat is always trying to move toward cooler areas. In the winter we fight to keep the heat in, and in the summer we strive to keep it out. When it comes to insulating buildings, conductive heat has very little effect.
An example of conductive heat would be putting a pot of water on the stove and turning the stove on high. The heat transfers directly from the stove top to the pot, and again from the pot to the water causing the water to boil. Conductive heat transfer occurs when a cooler item comes into contact with a warmer item.
The heat flows into the cooler item until a temperature equilibrium is reached. Just like electricity is conducted along electric lines, conductive heat is transferred much the same way. Break the connection and the flow stops. How to Stop Conductive Heat: Use a thermal break where possible.
Allow air space or place insulation like rigid foam between building elements to prevent thermal bridging and stop the flow of conductive heat. How about the huge temperature difference in the shade versus in the sun? Radiant heat is the answer. Radiation keeps the earth warm during the day, and in its absence at night, things cool down quickly. In southern climates, a huge portion of your air conditioning bill is caused by radiant heat. Regular foam or fiberglass insulation does little to stop this kind of heat transfer.
How to Stop Radiant Heat: Install a radiant barrier inside surfaces of your home that receive direct sunlight. Radiant barrier can make a huge difference placed on the underside of a roof or any other exterior wall. Think of a hairdryer, and you have a pretty good idea of what convective heat is. Convective heat affects houses by air infiltration. Hot air escaping through leaky windows, doors without weatherstripping, gaps in framing, siding, sheathing, roofing or anything really! Old houses are big leaky sieves sometimes.
They breathe and constantly exchange air with the outside. Some air exchange is necessary for a healthy home, but you want to control when and where the air is being swapped. How to Stop Convective Heat: Stop the airflow and you stop convection. Weatherstrip windows and doors, caulk exterior trim boards, install outlet gaskets most switch plate covers are a big source of air infiltration and can be fixed easily with this inexpensive productuse spray foam to fill larger gaps.There are three types of heat transfer that can occur and cause your van to heat up or cool down at different rates.
When insulating your van, it is important to know these three types, how they work, and how you can manipulate them to make your vanlife experience more comfortable. Radiation Radiation is heat that can be transferred between two areas without any contact to the heat source; either through the air or within a vacuum. In a van, radiation occurs most prominently through the windows. If you park a car with large windows in direct sunlight, the inside of the vehicle will heat up quickly.
This is because radiant heat transfers easily through glass. Radiant heat can redirect off reflective surfaces, preventing heat from getting through. When you place a reflective sunshade on the windshield of your car, heat from the sun bounces off the shade back outwards rather than continuing into your van. There are many materials to protect against radiant heat transfer. Metals like aluminum reflect heat, as well as materials like Reflectix and Infrastop.
Types of Heat Transfer
To keep your van cool, place a reflective material like Reflectix on your windows with the shiny side facing out. To keep the van warmer during the winter months, place Reflectix on the windows with the shiny side facing in. If you are running a heater inside for example, the heat will bounce off the shiny side, and back into the vehicle rather than escaping out. Conduction occurs when heat is transferred through an object.
When cooking with a cast iron skillet, you can feel the handle get hot even though that handle is not touching the fire. The metal framing of your van walls are excellent conductors of heat. Without any insulation, a van sitting directly in the sun will heat up fast. The inside metal can be hot to the touch because heat is transferred very efficiently through the outside walls. The reverse is true when it comes to cold cold. If you hold a metal bucket full of ice, it will quickly draw the heat out of your hands.
If you hold a foam bucket full of ice, the heat will stay in your hands. Different materials have different levels of conduction. In general, the more porous a material is, the less it conducts heat because air is a poor conductor. Nothing resists conduction better than a vacuum; this is why vacuum insulated mugs work so well. Heat cannot transfer through a material that is not there. But it is hardly possible to create a durable, leak free vacuum in something like a van.
Carpet, foam or wool are poor conductors of heat; meaning it is not easy for heat to transfer through them. The higher the R-value, the harder it is for heat to transfer through a material. Aluminum has a low value of R R-values are measured per inch of material.
One inch of wool has a value of R Without insulation, metal cars will get cold fast in the winter because of their low R-value. To prevent a van from getting too cold inside, you can insulate the walls, ceiling and floor with materials that prevent cold air from the outside transferring to the inside of your van.Cooling an electrical enclosure involves processes for transferring heat from inside the enclosure and discharging it to the surrounding air.
Various heat transfer mechanisms exist, including convection, conduction, thermal radiation, and evaporative cooling. Enclosure cooling involves a combination of heat transfer mechanisms. The primary mechanisms used for cooling electrical enclosures are as follows:. Passive cooling, the reliance on natural conduction, convection and radiation, is suitable for lightly loaded enclosures that have relatively large surface areas and good ventilation.
The ambient air temperature must be lower than the enclosure temperature. This method is not suitable for temperature-sensitive components in high ambient temperatures. The effectiveness of convection can be increased by the use of fans that increase the flow of air through the enclosure.
Cool air is drawn into the bottom of the enclosure and hot air discharged at the top. Fans should be fitted with filters to limit the ingress of dirt that could harm components.
To ensure the electrical components do not get too hot, the ambient temperature must be well below the maximum desired enclosure temperature. Heat pipes, first developed in the s, are an almost energy-free method of enclosure cooling. A heat pipe consists of an evacuated copper tube partially filled with a fluid such as alcohol or water.
Due to the low pressure, the fluid at the bottom of the pipe boils when it absorbs heat from the air inside an enclosure. The vapor rises to the top of the tube, where it is cooled by the air outside the enclosure and condenses.
The condensed fluid then returns to the bottom of the tube and the cycle repeats. The only energy needed is for small fans to circulate air around the hot and cold ends of the heat pipe. Air conditioning also utilizes evaporation, but in a slightly different way. A refrigerant liquid, under pressure, is passed through an expansion device. The hot gas is then compressed and passed through a condenser coil, where the gas liquefies, giving up its heat to the air outside the enclosure.
Heat Transfer Mechanisms Enclosure cooling involves a combination of heat transfer mechanisms. The primary mechanisms used for cooling electrical enclosures are as follows: Conduction: This is the transfer of heat through a solid. For example, heat generated inside an emclosure is transferred to the outer surface by means of conduction.
Convection: Convection is the transfer of heat from a surface by means of a fluid such as air. Natural convection occurs as air is heated: it expands, rises, and is replaced by cooler air. The amount of convection may be increased by using a fan to increase the flow of air.
Radiation: This is a process where energy is radiated through the air by means of electromagnetic radiation. Evaporation: The latent heat of a fluid can be used to transfer heat by absorbing the energy required to evaporate that fluid. The heat absorbed is released by allowing the fluid to condense outside the enclosure.Heat is transfered via solid material conductionliquids and gases convectionand electromagnetical waves radiation. Heat is usually transfered in a combination of these three types and seldomly occurs on its own.
For example, the thermal environment of a building is influenced by heat fluxes through the ground conductionand the building envelope mostly convection and radiation. Convection is heat flux through liquids and gases. Examples of convective heat flux are:. Sensing principle in heat flux based mass flow sensors. Learn more. Conduction is heat flux through solid materials. Examples of conductive heat flux are:. Thermal influences in precision instruments. Measurement of heat output from chemical reactors.
Radiation Radiation is heat flux through electromagnetic waves. Examples of radiative heat flux are:. Measurement of solar power. Conduction, Convection and Radiation The three types of heat transfer Heat is transfered via solid material conductionliquids and gases convectionand electromagnetical waves radiation.
Convection Conduction Radiation. Examples of convective heat flux are: Feeling much colder when it is windy. Examples of conductive heat flux are: Touching a hot cup of coffee Thermal influences in precision instruments.
Learn more Measurement of heat output from chemical reactors. Examples of radiative heat flux are: Feeling hot when standing close to fire. Previous: Definition of Heat Flux. Next: Heat Flux Measurement Techniques.Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy heat between physical systems. Heat transfer is classified into various mechanisms, such as thermal conductionthermal convectionthermal radiationand transfer of energy by phase changes.
Engineers also consider the transfer of mass of differing chemical species, either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system. Heat conduction, also called diffusion, is the direct microscopic exchange of kinetic energy of particles through the boundary between two systems.
When an object is at a different temperature from another body or its surroundings, heat flows so that the body and the surroundings reach the same temperature, at which point they are in thermal equilibrium. Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature, as described in the second law of thermodynamics.
Heat convection occurs when bulk flow of a fluid gas or liquid carries heat along with the flow of matter in the fluid. The flow of fluid may be forced by external processes, or sometimes in gravitational fields by buoyancy forces caused when thermal energy expands the fluid for example in a fire plumethus influencing its own transfer.
The latter process is often called "natural convection". All convective processes also move heat partly by diffusion, as well. Another form of convection is forced convection.Different modes of Heat Transfer
In this case the fluid is forced to flow by use of a pump, fan or other mechanical means. Thermal radiation occurs through a vacuum or any transparent medium solid or fluid or gas. It is the transfer of energy by means of photons in electromagnetic waves governed by the same laws.
Conduction, Convection and Radiation
Heat is defined in physics as the transfer of thermal energy across a well-defined boundary around a thermodynamic system.
The thermodynamic free energy is the amount of work that a thermodynamic system can perform. Enthalpy is a thermodynamic potentialdesignated by the letter "H", that is the sum of the internal energy of the system U plus the product of pressure P and volume V.
Joule is a unit to quantify energywork, or the amount of heat. Heat transfer is a process function or path functionas opposed to functions of state ; therefore, the amount of heat transferred in a thermodynamic process that changes the state of a system depends on how that process occurs, not only the net difference between the initial and final states of the process.
Thermodynamic and mechanical heat transfer is calculated with the heat transfer coefficientthe proportionality between the heat flux and the thermodynamic driving force for the flow of heat. Heat flux is a quantitative, vectorial representation of heat-flow through a surface.
In engineering contexts, the term heat is taken as synonymous to thermal energy. This usage has its origin in the historical interpretation of heat as a fluid caloric that can be transferred by various causes,  and that is also common in the language of laymen and everyday life. The transport equations for thermal energy Fourier's lawmechanical momentum Newton's law for fluidsand mass transfer Fick's laws of diffusion are similar,   and analogies among these three transport processes have been developed to facilitate prediction of conversion from any one to the others.
Thermal engineering concerns the generation, use, conversion, and exchange of heat transfer.
As such, heat transfer is involved in almost every sector of the economy. By transferring matter, energy—including thermal energy—is moved by the physical transfer of a hot or cold object from one place to another. A practical example is thermal hydraulics.Heat transfer occupies a field which comprises a wide range of functions, from the simple processes of objects heating and cooling to advanced thermodynamic concepts in thermal physics.
In order to understand how a drink cools in the summer or how heat travels from the sun to the Earth, you must grasp these basic principles of heat transfer on a fundamental level. The Second Law of Thermodynamics states that heat transfers from an object of a higher temperature to that of a lower temperature. The higher energy atoms and thus higher temperature move toward the lower energy atoms lower temperature in order to maintain equilibrium known as thermal equilibrium.
Heat transfer occurs in order to maintain this principle when an object is at a different temperature from another object or its surroundings. When particles of matter are in direct contact, heat transfers by means of conduction. The adjacent atoms of higher energy vibrate against one another, which transfers the higher energy to the lower energy, or higher temperature to lower temperature.
That is, atoms of higher intensity and higher heat will vibrate, thereby moving the electrons to areas of lower intensity and lower heat. Fluids and gases are less conductive than solids metals are the best conductors due to the fact that they are less dense, meaning that there is a larger distance between atoms. Convection describes heat transfer between a surface and a liquid or gas in motion. As the fluid or gas travels faster, the convective heat transfer increases.
Two types of convection are natural convection and forced convection. In natural convection, fluid motion results from the hot atoms in the fluid, where the hot atoms move upwards toward the cooler atoms in the air--the fluid moves under the influence of gravity. Examples of this include the rising clouds of cigarette smoke, or heat from the hood of a car that rises upwards.
In forced convection, the fluid is forced to travel over the surface by a fan or pump or some other external source. Radiation not to be confused with thermal radiation refers to the transfer of heat through empty space. This form of heat transfer occurs without an intervening medium; radiation works even in and through a perfect vacuum.
For instance, energy from the sun travels through the vacuum of space before the transfer of heat warms the Earth. Heat transfer forms an integral part of education in relevant subjects, such as in the curriculum of chemical or mechanical engineering.
Manufacturing and HVAC heating, ventilating and air cooling are examples of industries that rely heavily on thermodynamics and principles of heat transfer. Thermal science and thermal physics are higher fields of education that deal with heat transfer. Brian Neese is a writer living in Rockford, Ill. He has a B. Neese enjoys writing on a number of different levels, from the academic to applied environments. About the Author. Copyright Leaf Group Ltd.Heat Transfer. Heat always moves from a warmer substance to a cooler substance.
For example, holding an ice cube will make your hand begin to feel cold in a few seconds. But is the coldness in the ice cube moving to your hand? This is one of the ways that heat is transferred. There are three types of heat transfer: radiation, conduction, and convection. The transfer of energy through space is called radiation. Heat transfer by radiation takes place with no direct contact between a heat source and an object.
Other familiar forms of radiation include the heat you feel around a flame or open fire. Heat transfer within a material or between materials that are touching is called conduction. Heat moves from the hot soup and the pot to the particles that make up the spoon. The particles near the bottom of the spoon vibrate faster as they are heated, so they bump into other particles and heat them, too.
Gradually the entire spoon heats up. When your hand touches the spoon, conduction transfers heat from the spoon directly to your skin. Then you feel the heat. Conduction is responsible for some of the heat transfer inside Earth. Conduction heats the spoon and the pot itself. Heat can also be transferred by the movement of fluids—liquids and gases. Convection is heat transfer by the movement of currents within a fluid.
During convection, heated particles of fluid begin to flow.