Book - School of Science and Technology

192 Heat emitting equipmentTable 7.7 Emission from radiators in an isothermal enclosure: proportions radiant and convectiveProportion (%)Radiator type Radiation ConvectionSingle panel 50 50Double panel 30 702 column 30 704 column 19 816 column 17 83Convector/radiator 10±15 90±85(a) (b) (c)Figure 7.15 Aluminium radiatorsThe material and production techniques are such in each case that a clean smooth finishis provided but the problem of metal corrosion remains. One manufacturer provides aninhibitor which is inserted in capsule form during radiator construction, for release wheninstallation is complete and hot water activates the curing process. Other manufacturersrecommend the use of special additives to a system which has any mixture of metals.Radiators generallyIt is generally best to site radiators under windows in order to meet architectural, socialand technical demands. Architectural, to avoid the presence of foreign objects on anotherwise unblemished wall, social to give freedom for furniture arrangement and toavoid the need for frequent redecoration to hide dirty marks from convection currents. Intechnical terms, siting under a window is preferred because:. heat is provided where most needed, at the point of maximum heat loss. cold `negative' radiation is countered at source and direction by hot `positive' radiation. the temperature gradient in a room with radiators fitted below windows is less than ifthey were sited elsewhere. marking of a wall surface by dust carried in rising convection currents is avoided.In circumstances where it is not possible to site a radiator below a window, it is anadvantage to fit a shelf above the heated surface. Provided that the jointing to the wall issound and that adequate end shields are fitted, the shelf will reduce the wall stains caused bythe dust entrained in rising convection currents. Such a shelf, if fitted not less than 80 mmabove the top of the radiator, will reduce output by only about 4%.