Principle and maintenance of automobile cooling system[汽车维修知识]

one,carwatercooling systemPrinciple of heat dissipation
As we all know, the engine is the heart of the car, and it generates a lot of heat when it works. This heat must be dissipated in time, otherwise it will affect the working efficiency of the engine, and in severe cases (such as working in a water shortage state) will damage the engine block until it is paralyzed.
Therefore, in general, cars are cooled by water to dissipate heat.The principle is to make the outer wall of the engine cylinder block into a heat sink and install it in a closed casing, through two water inlet and outlet pipes andWater tankConnection, in the loopWater pumpIt circulates under the action of the circulating water flow, and uses the circulating water flow to bring the high temperature on the engine block to the heat dissipation water tank installed in the front of the car. The fin-type heat dissipation method of the water tank is used to dissipate the heat into the air. The cooled circulating water flow is again Enter the heat dissipation part of the engine block.
Causes and consequences of reduced heat dissipation capacity
As can be seen from the above schematic diagram, the cooling water system of the entire engine has three heat exchange points: one is the heat dissipation part of the cylinder block. The expression and purpose of heat exchange is to take away the cylinder block with circulating water.pistonThe heat generated by work. The second is that after the near-boiling hot water flow enters the grid-shaped heat dissipation water tank on the inner wall, its heat is quickly transferred and dissipated to the aluminum or copper fins of the water tank. The third is the heat exchange generated by the high temperature on the surface of the water tank fins after absorbing the heat of the hot water by the airflow to the air for digestion.
From the above three heat exchange methods and principles, we can see that as long as the ability of any one of the heat exchanges is reduced, the heat dissipation of the engine piston cylinder will not meet the design requirements. If the heat exchange capacity of these three places decreases at the same time, it will seriously affect the output power of the engine, and increase the resistance of the piston movement, and the energy consumption will rise sharply. In the worst case, it will directly damage the cylinder and cause the engine to be scrapped. Therefore, if you don’t pay attention to these aspects of maintenance, the general vehicle will experience an increase in energy consumption, a decrease in power, and an increase in engine noise after driving 50,000 to 60,000 kilometers. Some will give an alarm and stall because the water temperature is too high. In summer, everyone often sees the back cover of the bus driving while the bus is running. That is because of the poor heat dissipation of the water tank.
So what causes the reduction in the capacity of these three heat exchange locations? Let's first look at the heat dissipation part of the cylinder block and the inner wall of the water tank. With the extension of the engine's use time, these two places where heat exchange occurs are the same as using aluminum or copper kettles in our daily life to boil water. A layer of brown solid object is condensed on the inner wall. It has two main components: one is the oxide produced by the chemical reaction of oxygen and metal in the water (and the higher the water temperature, the faster the formation of oxides). The thermal conductivity of copper or aluminum is less than 1/20. The other is calcium bicarbonate (commonly known as scale). Its formation on the metal surface is: Ca(HCO3)2=CaCO3↓+H2O+CO2↑, its thermal conductivity is even worse, less than copper or aluminum 1/40. You may have seen the phenomenon of metal kettle fouling, but you don't know the waste it brings. We have tried repeatedly, using a new kettle and a kettle that has been used for two years, add the same amount of water at the same temperature to it, and boil it on the same gas stove. The new kettle takes longer than the old one. Should be 13-15% shorter. In other words, the old kettle will use 13-15% more fuel. This is partly because of the waste of energy caused by the reduction of heat exchange capacity due to fouling. This is also the reason for the increase in fuel consumption after the car has traveled 50,000 to 60,000 kilometers.
The reduced heat dissipation capacity of the cooling water tank surface fins is also caused by the oxides formed by the chemical reaction between the metal surface and the moisture in the air, and the dust and oil inhaled during the driving of the vehicle cover its surface.
two,Car Air ConditionerPrinciple of cooling system
Many friends who drive have this feeling: After driving for a year or two, the cooling effect of the air conditioner is better at high speeds than at low speeds, and much better at low speeds than during traffic jams. When encountering traffic jams in direct sunlight, , The air conditioner is almost ineffective, and the energy consumption will increase, and the power will be significantly reduced. What is causing it?
"The law of conservation of energy" is something that everyone has learned in the physics class of middle school. The cooling capacity of the air conditioner per unit time in the room is always equal to the heat output of the outside.Therefore, the greater the cooling capacity of the air conditioner, the outdoor unitCondenserThe larger the (heat sink area), the matching relationship between them is determined during product design.