lagging
DESCRIPTION
Lagging- Heat Transfer EquipmentTRANSCRIPT
Introduction
Lagging or Thermal insulation :
This is the reduction of heat transfer between objects in thermal contact. Thermal insulation can be achieved with specially engineered methods or processes, as well as with suitable object shapes and materials.
material types
There are three main types of thermal insulation materials:• Fiberglass• Cellulose• Spray in polyurethane foam
Application of Insulation MaterialsI. BuildingsBuilding insulations also commonly use the principle of small trapped air-cells e.g. fiberglass (specifically glass wool), cellulose, rock wool, polystyrene foam, urethane foam, vermiculite, perlite, cork, etc.
Piping Insulation
SpacecraftRe-entry through the atmosphere generates very high temperatures due to compression of the air at high speeds. Insulators must meet demanding physical properties beyond their thermal transfer retardant properties. E.g. reinforced carbon-carbon composite nose cone and silica fiber tiles of the Space Shuttle.
• AutomotiveInternal combustion engines produce a lot of heat during their combustion cycle. This can have a negative effect when it reaches various heat-sensitive components such as sensors, batteries and starter motors. As a result, thermal insulation is necessary to prevent the heat from the exhaust reaching these components.
Energy Loss costs
Energy losses costs will depend on the following:• Heat loss from the pipe
Pipe diameterTemperatures of inside and outsideInsulations
• Cost of the fuel• Boiler efficiency
Economic laggingCost of the Insulation will depend on:• Insulation material• Insulation thickness• Pipe Length• Labour costs
Critical Radius of Insulation
The variation of the heat transfer rate with the outer radius of the insulation r2 is shown in the figure.
Thus, insulating the pipe may actually increase the rate of heat transfer from the pipe instead of decreasing it when r2< rcr .
𝒓𝒄𝒓𝒊𝒕𝒊𝒄𝒂𝒍=𝒌𝒉
Question
An electric wire is wrapped with a 3mm thick plastic cover. If thermal conductivity of Plastic is k=0.15 W/mK and outside h= 24 W/m2K.
Explain the heat loss of the system if the insulation resistance is doubled.What happens if the thickness is tripled.
Question
Calculate the critical radius of insulation for a material of k=0.17 W/mK surrounding a pipe and exposed to a room air at 20 °C with h = 5 W/m2K
Calculate the heat loss from this pipe if the pipe diameter is 5 cm and the inside of the pipe is at 200 °C. (Select a suitable thickness for the insulation)