Thermodynamics And Heat Transfer
Thermodynamics and heat transfer are two areas of physics dealing with energy , ability to do work and heat transfer...
Thermodynamics and heat transfer are two areas of physics dealing with energy , ability to do work and heat transfer from body to body. The basis for solving problems in the field of thermodynamics is understanding what energy consumed by the system, how much work the system performs and how much energy is being wasted and in what form.
Heater warms the room, sealed refrigerator which freezes the products, fan responsible for cooling the electronic components of a robot, and more - all developed after the calculations in thermodynamics and heat transfer. Heat transfer and heat removal are very important in the field of robotics.
1 / 13
Thermodynamics And Heat Transfer
//
Heat Transfer
Heat transfer is a term that describes thermal energy flowing through a body with a high temperature to a body with lower temperature. Heat transfer can be made through three ways: 1. Heat Conduction 2. Heat Convection 3. Heat Radiation
In robotics and machine design , the two most common ways for heat transfer are conduction and convection.
Heat conduction
2 / 13
Thermodynamics And Heat Transfer
Heat conduction describes a situation in which heat is transferred between two bodies through direct contact. For example, an ice cube is placed on a hot surface. Heat passes from the hot surface to the ice cube. Thus the hot surface is cooled and the ice cube is melted. The formula for calculating the amount of heat that passes in transmission between two bodies is:
- Heat flux coming from the system .
- Heat conduction coefficient of the material.
-Sectional area of the material.
- Temperature difference between the two ends.
- Distance between two ends.
You can use the heat conduction coefficient tables .
3 / 13
Thermodynamics And Heat Transfer
From the above equation it’s easy to understand that if we want to cool bodies by conduction we need to make sure that the following conditions are met: Contact area between the entities should be as large as possible Temperature difference between the entities should be as large as possible A material with conduction coefficient as high as possible should be selected
4 / 13
Thermodynamics And Heat Transfer
Sometimes, there are several layers of materials exists, and the heat conduction analysis is the same as in two bodies (two layers). The layers can be made of different materials or even different section area. Below are a number of drawings that explain how to calculate the heat conduction between several bodies in contact:
General description of heat passing through the two ends of any material:
Serial connection of a number of substances that are arranged one after the other. All substances have the same cross-sectional area but different heat conduction coefficient. It can be seen that T1 temperature is higher than the rest of the points.
Parallel connection of several materials is arranged next to each other. The heat that passes through each material is different than the other due to differences in both the sectional area and the heat conduction coefficient. .
Heat convection describes a situation in which heat moves from one object to another (without touching each other). For example, wind flowing over a hot surface cools it (heat flows from the hot surface to the air).
- Heat flux coming from the system.
- Convection coefficient (depending on the fluid surrounding the material - the coefficient is for a fluid that is at rest. Example, a fan that makes transportation has forced convection coefficient other).
7 / 13
Thermodynamics And Heat Transfer
- Area exposed to convection.
- Ambient Temperature.
- Body Temperature.
Heat convection coefficients Tables can be used.
When analyzing and designing the heat transfer in a system, insulation is often used to isolate one of the bodies (hot or cold) and prevent heat flowing from/to that body. Adding an insulating layer has its pros and cons. The pro is to add a material that has a very low thermal conduction coefficient to prevent heat flowing from that body. But with that method, the total surface area is
8 / 13
Thermodynamics And Heat Transfer
increased. When increasing the surface area, the heat that body loses from air convection is higher. That why you’ll have to find the best ratio to reach an ideal insulation thickness. This ratio is called: “Critical insulation thickness”. The formula to calculate the critical insulation thickness is:
// - Heat convection coefficient of the material.
- Heat conduction coefficient of the material.
Another means to improve heat removal from a system is the use of cooling fins (heat sink). Adding cooling fins increase the area of contact with the air and thus increasing the transfer of heat through convection.
9 / 13
Thermodynamics And Heat Transfer
Heat Radiation Radiation heatrare transfer when (without transfer designing is touching very aerospace another in planning describes body) and and energy through adevelopment situation facilities. emission in which of of robots electromagnetic heatand moves machines from waves. one andThis object more type to common another of heat
Laws of thermodynamics
Thermodynamics deals with energy, work, energy conversion and utilization. The field of thermodynamics is based on a number of laws called the laws of thermodynamics: 1. The first law of thermodynamics - the conservation of energy in the system. Energy does not disappear and does not form for no reason. The difference between the first law of thermodynamics and the law of energy conservation is that in thermodynamics heat is reflected. Internal energy in a system equation is:
- Heat flows into the system.
- Work done on the system.
2. The second law of thermodynamics – A system will always strive for the highest entropy level
10 / 13
Thermodynamics And Heat Transfer
and lowest energy level. 3. Entropy is zero when the temperature is absolute zero (-273.15 degrees Celsius).
Processes and Thermodynamic States
System that is in thermodynamic equilibrium is a system that is in a specific state. To influence the system and change its state, a certain process has to be performed on the system. There are several types of processes in a thermodynamic systems: 1. Isobaric process - occurs when the pressure in the system remains constant 2. Isochoric process - occurs when the system volume remains constant 3.
11 / 13
Thermodynamics And Heat Transfer
Isothermic process - occurs when the system temperature remains constant 4. Adiabatic process - occurs while losing or aggregation of energy through heat 5. Isentropic process - a process reversible adiabatic 6. Isenthalpic process - takes place while enthalpy is maintained inside the system. 7. Steady-state process - takes place without changing the internal energy of the system
Written by Eran Cenciper (Robot-and-Machines-Design Webmaster)
