There are three types of heat transfer: convection heat transfer, heat transfer, and radiation heat transfer. Convective heat transfer is due to the presence of temperature differences in the gas, resulting in convection of the gas, driving the transfer of energy; heat conduction is the energy transfer due to molecular motion; radiation heat transfer is the direct transmission of energy by rays that is infrared. As the insulating glass, its thermal insulation performance is mainly due to its internal gas in a closed space, the gas does not produce convection, and the thermal conductivity of the air is 0.028W/mK, which is the thermal conductivity of the glass is 0.77W/mK, which is 1/27th. Convective heat transfer and conductive heat transfer account for a small proportion of the energy transfer in hollow glass. To improve the thermal insulation performance of insulating glass, generally speaking, the thickness of the space layer is increased, and the air inside the insulating glass is replaced with a gas with a low thermal conductivity, so that the conduction heat transfer can be reduced, but the space layer is too large and will generate Convection of gas, increase convective heat transfer, reasonable space layer gap should be about 12mm; To reduce the radiative heat transfer, generally through the use of solar control, especially low-emissivity glass, to control all kinds of ray penetration, to reduce the radiant heat transfer the goal of.
A. Hollow glass insulation and sound insulation
As we all know, there are three ways of energy transmission: radiation transmission, convection transmission and conduction transmission.
Radiation transmission is the transmission of energy through radiation in the form of radiation. Such radiation includes radiation such as visible light, infrared light, and ultraviolet light, just like the transmission of solar light. Properly configured hollow glass and a reasonable thickness of the insulating glass spacer can minimize the transmission of energy through radiation, thereby reducing energy loss.
Convection is due to the temperature difference between the two sides of the glass, causing the air to fall on the cold side and rise on the hot side, creating convection of the air and causing the loss of energy. There are several reasons for this phenomenon: First, the poor sealing between the glass and the surrounding frame system causes the gas inside and outside the window frame to be exchanged directly to produce convection, resulting in the loss of energy; the second is the design of the internal space structure of the insulating glass. Irrationality leads to the convection of the gas inside the insulating glass due to the temperature difference, which leads to the exchange of energy, which results in the loss of energy. Third, the temperature difference between the inside and outside of the window constituting the entire system is large, resulting in the temperature difference between the inside and the outside of the insulating glass. Larger, the air by the role of cold radiation and heat conduction, first in the hollow glass on both sides of the convection, and then passed through the entire hollow glass in the past, the formation of energy loss. Reasonable hollow glass design can reduce the convection of the gas and reduce the convection loss of energy.
Conduction transfer is through the movement of the molecules of an object, which drives energy to move and achieve the purpose of transmission. It is like cooking with an iron pan and welding with an electric iron, and the conduction of insulating glass to energy is through the glass and its internal Air to finish. We know that the thermal conductivity of glass is 0.77 W/m2k. The thermal conductivity of air is 0.028 W/m2k. It can be seen that the thermal conductivity of the glass is 27 times that of air, and the presence of active molecules such as water molecules in the air is the influence on the conduction and convection transfer performance of the insulating glass energy. The main factor, thus improving the sealing performance of the hollow glass, is an important factor to improve the insulating properties of hollow glass.
B. Insulating glass prevents condensation, reduces cold radiation and safety
Because there is a desiccant inside the hollow glass that can adsorb water molecules, the gas is dry. When the temperature is lowered, the interior of the hollow glass will not be condensed. At the same time, the dew point on the outer surface of the hollow glass will rise. high. For example, when the outdoor wind speed is 5m/s, the room temperature is 20°C, and the relative humidity is 60%, 5mm glass begins to condense when the outdoor temperature is 8°C, while the 16mm (5+6+5) hollow glass is under the same conditions, The condensation occurs only when the outdoor temperature is -2°C, and the condensation of 27mm (5+6+5+6+5) three-layer hollow glass begins at an outdoor temperature of -11°C.
Because of the better insulation performance of the insulating glass, the temperature difference between the two sides of the glass is larger, and the effect of cold radiation can also be reduced; when the outdoor temperature is -10°C, the temperature in front of the indoor single-layer glass window is -2°C and hollow The temperature in front of the window is 13°C; in the same house structure, when the outdoor temperature is -8°C and the room temperature is 20°C, the 3mm ordinary single-glazed cold radiation area accounts for 67.4% of the indoor space, and the double layer is used. Hollow glass (3+6+3) is 13.4%.
The use of hollow glass can improve the safety performance of the glass. In the case of using the original glass of the same thickness, the wind-resistant compressive strength of the hollow glass is 1.5 times that of the ordinary single glass.