Thermal insulation in Egypt

Insulation materials in Egypt and their thermal properties

نشر في 20 فبراير 2017 وآخر تعديل بتاريخ 08 ديسمبر 2022 .

Insulation materials and their thermal properties
Polyurethane foam
Expanded polystyrene
Fibreglass
Expanded perlite
Cork

The primary function of thermal insulation materials used in small fishing vessels using ice is to reduce the transmission of heat through fish hold walls, hatches, pipes or stanchions into the place where chilled fish or ice is being stored. By reducing the amount of heat leak, the amount of ice that melts can be reduced and so the efficiency of the icing process can be increased. As has already been discussed, ice is used up because it removes heat energy from the fish but also from heat energy leaking through the walls of the storage container. Insulation in the walls of the container can reduce the amount of heat that enters the container and so reduce the amount of ice needed to keep the contents chilled.

The main advantages of insulating the fish hold with adequate materials are:

to prevent heat transmission entering from the surrounding warm air, the engine room and heat leaks (fish hold walls, hatches, pipes and stanchions);

to optimize the useful capacity of the fish, hold and fish-chilling operating costs;

to help reduce energy requirements for refrigeration systems if these are used.

One of the best commercially available choices of insulation material for fishing vessels is polyurethane foam. It has good thermal insulating properties, low moisture-vapour permeability, high resistance to water absorption, relatively high mechanical strength and low density. In addition, it is relatively easy and economical to install.

Polyurethane foam is effective as an insulator because it has a high proportion (90 percent minimum) of non-connected closed microcells, filled with inert gas. Until recently, the inert gas most commonly used in polyurethane foams was R-11 (trichlorofluoromethane). However, the Montreal Protocol on Substances that Deplete the Ozone Layer has called for the phasing out of the use of CFCs such as R-11. Replacement foaming agents are being investigated at the present time, with hydrocarbons, hydrofluorocarbons and inert gases such as carbon dioxide being developed as substitutes.

Through polymerization styrene can be made into white pearls/beads of polystyrene plastic. These beads can then be expanded to form a foam known as expanded polystyrene. There are two main ways of making of expanded polystyrene: by extrusion and by moulding of slabs.

Extruded foams are made by mixing the polystyrene with a solvent, adding a gas under pressure and finally extruding the mixture to the required thickness. The extrusion process improves the characteristics of the final foam, such as its mechanical resistance, producing non-interconnecting pores and a more homogeneous material. The mechanical resistance of expanded polystyrene foams can vary from 0.4 to 1.1 kg/cm2. There are several grades of foams available with densities from 10 to 33 kg/m3, with thermal conductivities that are lower with the increase in density.

Fibreglass matting is also used as insulating material and offers the following advantages:

high resistance to fire;

high resistance to microbiological attack;

good resistance to most chemicals;

high heat resistance;

available in a variety of presentations (e.g. blankets, mats, loose fill and boards);

low thermal conductivity.

Fibreglass insulation is available in rolls of different thickness, also called blankets and mats. The width of the blankets and mats will depend on the way they are to be installed and some come faced on one side with foil or Kraft paper, which serve as vapour barriers.

Perlite is a volcanic rock containing from 2 to 5 percent bonded water. It is a chemically inert substance composed basically of silica and aluminium, but some impurities, such as Na2O, CaO, MgO and K2O, which are hygroscopic, can absorb moisture easily. Therefore, depending on the storage conditions and the quality of the perlite, moisture absorption can be minimized. The average density of expanded perlite is about 130 kg/m3 and its thermal conductivity is about 0.04 kcal m-1 h-1 °C-1 (0.047 W m-1 °C-1). The perlite is expanded by means of rapid heating at a temperature between 800 and 1 200 °C. The vaporization of the bonded water and the formation of natural glass results in the expansion of the perlite particles, which have a granular shape. Therefore, the main parameters that define the characteristics of expanded perlite are:

the origin of the mineral perlite;

the granulometric characteristics of the mineral before the expansion process;

the temperature of expansion.

Cork is probably one of the oldest insulation materials used commercially, and in the past it was the most widely used insulation material in the refrigeration industry. At present, due to the scarcity of cork-producing trees, its price is relatively high in comparison with other insulating materials. Therefore, its use is very limited, with the exception of some machine foundations to reduce the transmission of vibrations. It is available as expanded slabs or boards as well as in granular form, its density varies from 110 to 130 kg/m3 and it has an average mechanical resistance of 2.2 kg/m2. It can only be used up to temperatures of 65 °C. It has good thermal insulating effectiveness, is fairly resistant to compression and is difficult to burn.