The principle of heat preservation performance of insulated tableware

Analysis of the Principle of Heat Preservation Performance of Insulated Tableware

The core of insulated tableware lies in reducing heat loss through three major mechanisms: heat conduction inhibition, heat convection blocking and heat radiation reflection. Its performance is jointly influenced by material properties, structural design and process details. The following analysis is carried out from three aspects: thermodynamic principles, structural design and material application:

First, thermodynamic principles and heat transfer paths

Heat conduction inhibition

Principle: Heat is transferred from the high-temperature zone to the low-temperature zone through solid materials, and the rate of transfer depends on the thermal conductivity (λ) of the material. For instance, the thermal conductivity of air (0.026 W/(m·K)) is much lower than that of stainless steel (15 W/(m·K)), so a vacuum layer or low-density material can significantly reduce heat conduction.

Case: The traditional insulated cup adopts a double-layer stainless steel structure, with a vacuum in the middle to eliminate air convection and conduction, reducing the heat conduction rate to less than 1/1000 of that of the single-layer structure.

Blocking of thermal convection

Principle: When a fluid (such as air) is heated, it expands and rises; when it cools, it contracts and sinks, forming convection and resulting in heat loss. Convection can be suppressed by enclosing a space or filling it with low-fluidity media (such as foaming materials).

Case: The interlayer of the insulated lunch box is filled with polyurethane foam. Its closed-cell structure can prevent air flow, reducing heat convection loss by more than 90%.

Thermal radiation reflection

Principle: High-temperature objects radiate energy outward in the form of electromagnetic waves. Materials with high reflectivity (such as silver and aluminum) can reflect the radiant heat back into the interior.

Case: The inner wall of insulated tableware is coated with a silver layer, which can increase the infrared radiation reflectivity to over 95%, reducing radiant heat loss.

Second, the influence of structural design on thermal insulation performance

Multi-layer composite structure

Double-layer vacuum structure: The outer layer of stainless steel and the inner layer of food-grade material are isolated from heat conduction and convection through the vacuum layer, making it suitable for cup and pot tableware.

Three-layer sandwich structure: outer layer (protective layer) + middle layer (vacuum/foaming layer) + inner layer (heat conduction layer), taking into account both strength and thermal insulation performance.

Sealing and heat insulation design

Sealing rings: Silicone or rubber sealing rings can prevent air convection. For instance, the threaded sealing structure of a thermos can reduce heat loss by 30%.

Heat insulation cover: Use low thermal conductivity materials (such as PP plastic) or add an air layer to reduce heat loss from the top.

Shape optimization

Short and stout design: It increases the surface area to volume ratio, but needs to balance portability and heat preservation.

Narrowing of the neck: Reducing the opening area and lowering the loss of heat convection and radiation.

Third, material selection and process optimization

Low thermal conductivity material

Stainless steel: 304 or 316 stainless steel has a moderate thermal conductivity and combines strength and corrosion resistance, but it needs to be used in conjunction with a vacuum layer.

Glass: High borosilicate glass has a low thermal conductivity (1.2 W/(m·K)), but it is fragile and needs to be strengthened through a double-layer structure or coating.

Plastics: Plastics such as PP and PE have low thermal conductivity (0.1-0.3 W/(m·K)), but poor temperature resistance, making them suitable for low-temperature insulation scenarios.

Vacuum layer and foaming layer

Vacuum layer: It eliminates air convection and conduction through vacuuming, but requires high-strength materials and sealing processes.

Foaming layer: The interlayer is filled with foaming materials such as polyurethane and polystyrene. The closed-cell structure can effectively insulate heat.

Reflective coating

Silver plating layer: Silver is plated on the inner wall through physical vapor deposition (PVD) technology, with a reflectivity of over 95%.

Ceramic coating: It has both reflective and wear-resistant properties, but it is relatively expensive.

Fourth, quantitative indicators of thermal insulation performance

Insulation efficiency

Initial temperature difference: The temperature difference between 65℃ hot water and room temperature (25℃) is 40℃.

Temperature difference after 6 hours: High-quality insulated tableware can maintain a temperature difference of more than 30℃, that is, the water temperature is not lower than 55℃.

Heat loss rate

Conduction loss: Calculated based on the thermal conductivity of the material and its thickness, for instance, the heat conduction loss of 1mm stainless steel is 0.15W/℃·m².

Convective loss: It is related to the sealing performance. When not sealed, the loss rate can reach 5 to 10 times that of the sealed state.

Radiation loss: Related to the surface emissivity, the silver plating layer can reduce the radiation loss to 1/20 of the untreated surface.