Heat transfer is a thermal engineering discipline that concerns the generation, use, conversion, and exchange of heat and heat energy between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and energy transfer through phase changes. Engineers also consider the mass transfer of different chemical species, whether cold or hot, to achieve heat transfer. While these mechanisms have different characteristics, they often occur simultaneously in the same system.
Heat conduction, also called diffusion, is the direct microscopic exchange of the 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 environment reach the same temperature, at which time they are in thermal equilibrium. Such heat transfer always occurs spontaneously from an area of high temperature to another region of lower temperature, as explained by the second law of thermodynamics.
Law I of thermodynamics states that energy is eternal, cannot be created and cannot be destroyed. Energy can only change from one form to another. Based on this theory, you can change the heat energy to other forms as you like provided you fulfill the law of conservation of energy.
However, the reality is not the case. Energy cannot be changed as you wish. For example, you drop an iron ball from a certain height.
When an iron ball falls, its potential energy is transformed into kinetic energy . When an iron ball hits the ground, most of its kinetic energy is transformed into thermal energy and a small portion is turned into sound energy.
Now, if you reverse the process, which is the iron ball you heat so it has heat energy equal to the heat energy when the iron ball hits the ground, is it possible that this energy will turn into kinetic energy, and then turn into potential energy so that the iron ball can rise?
This event is not possible even if your iron ball is heated until it melts. This shows that the process of changing the form of energy above can only take place in one direction and cannot be reversed.
A process that cannot be reversed is called an irreversible process . The process that can be reversed is called a reversible process. The events above inspired the formation of the second law of thermodynamics. Law II thermodynamics limits which energy changes can occur and which cannot occur.
This restriction can be expressed in various ways , including, the second law of thermodynamics in the statement of heat flow: “Heat flows spontaneously from high temperature objects to low temperature objects and does not flow spontaneously in the opposite direction”; second law of thermodynamics in the statement about the heat engine: “
It is not possible to make a heat engine that works in a cycle that merely absorbs heat from a reservoir and converts it entirely into external effort “; the second law of thermodynamics in the entropy statement: “Total entropy of the universe does not change when a reversible process occurs and increases when an irreversible process occurs”.
Now from the basic law of thermodynamics above, on this occasion I want to share, how heat transfer takes place using a lubricant as a heat transfer oil.
while other heat transfer media (water) I will discuss on another occasion.
This heat-conductive lubricant is usually applied to industries where in the production process heat is needed for the catalyst in making bonds between chemical elements in the process so that it can be bonded better and tightly or perfectly
What are the basic criteria that a Heat Transfer Oil must have?
Non-flammable and volatile. This means that the lubricant must have a high flash point.
Not easily damaged carbon chains / lubrication bonding elements. The broken carbon chain can be seen from the change in color from its original color to dark (oxidized). This means that the base material of the lubricant must come from the processing of petroleum containing long carbon chains
Easily absorbs heat and provides heat and has stable properties (temperature range is not large). Because heating is more evenly distributed, the risk of fire can be reduced, which may occur due to heat which directly hits the materials being processed.
Easy to move /
move means the lubricant can carry heat from the heat source to the media to be heated by transferring the pump
It is not corrosive and can carry impurities in the heating system.
Things that must be considered in a heating system that uses a heat transfer oil:
Please note that the circulation system is totally closed to prevent oxidation, pollution and evaporation.
The flow rate of the lubricant must remain controlled to prevent certain places from overheating (usually between 1.5 – 3 meters per second)
Example image: Heat exchanger system using a heat transfer oil as a heat carrier
Heat Transfer Oil, as a heat exchanger, is considered by some to be a better alternative to overcoming the problem of water quality and the limited temperature of the system owned by the water system. besides that there are several other advantages as seen in the following table
The advantages of using heat transfer oil compared to other systems, can generally be seen as follows:
Efficiency, many people believe that heat-conductive lubricants have an efficiency of 5 to 8% better than the use of conventional steam systems, this is because in conventional steam systems there are many heat losses such as in steam traps 6% to 14% depending on the length of the installation pipe of the system . Besides heat loss in water blowdown up to 3%, and heat loss in deaerator up to 2%.
Certification, to operate a pressurized steam system requires certification of both the operator who runs it and the installation itself, in many countries this is a law that must be obeyed so that it impacts on operational costs.
Unlike pressurized steam systems, almost all heat installations using heat-conducting lubricants operate at atmospheric pressure. The pressure on this system is only limited to the pressure of the circulating pump used, which only ranges from 2-4 bar.
Corrosion, the steam system is very susceptible to corrosion, air and salt contained in water are the main components causing corrosion. Vapors are also very abrasive to metals because there is no luminance.
The heat transfer system used to heat the lubricant is non-corrosive and has the same lubricating properties as the lubricating oil so that it does not cause corrosion and abrasion on the metal.
Maintenance, due to the absence of steam traps, condensate returns, and chemical dosing on boiler water in heating systems that use heat-conductive lubricants, automatically the maintenance is also less.
Environmentally friendly, more environmentally friendly compared to steam boilers whose use of water must be processed mechanically and chemically so that the disposal of waste water must be safe for the environment.
Safety, unlike steam boilers that require high pressure for high operating temperatures, thermal fluid heaters operate at atmospheric pressure so it is very safe. The pressure that occurs in the thermal fluid heaters system is only due to the pressure of the circulating pump and not the pressure due to the pressure needed to reach the desired working temperature.
Temperature control, Temperature control in the lubricant heating system is carried out directly at the temperature of the lubricant, so it is more accurate than the steam boiler which is regulated by regulating the working pressure of the system
The costs, investment and operating costs of a heating system using a heat transfer lubricant are relatively lower compared to steam boilers.
PT Indira Mitra Boiler – Specialist Expert in Project Boiler Marine Heater ,Marine boilers used in ships today are mostly for auxiliary purposes in vessels that run on marine diesel engines or diesel electric propulsion. In case of ships using steam turbines (mostly found in high speed vessels used by navies), boilers are a part of the main propulsion system. However, in this article, we will focus on auxiliary boilers, boilers used for running auxiliary systems in a ship.