ELECTRIC DUCT HEATERS Ap plicat ion: Heat ing of a i r a nd of Ga se s Figure 1: Typical sketch of a “Through Duct Heater” GENERAL CHARACTERISTICS The electric duct heaters have been developed to satisfy the need of temperature controlled air or gas flows which is present in several industrial processes. The are designed to be inserted into ventilation ducts, tubes, ovens or autoclaves and are directly flown by the process air or gas. The heating elements are finned to increase the heat exchange. However, if the heated fluid contains particles which could clog the fins, the duct heater is manufactured using smooth heating elements. These products are designed by our technical department on the basis of customer provided functional requirements. Design is supported by purpose-developed software that allow to define the design parameters and to verify the corresponding thermodynamic performances. The analysis yields a precise picture of the heater operating conditions. The iteration between design and analysis leads to define: 1. the specific power 2. the resulting pressure drops 3. the maximum sheath temperature and, consequently, the safety devices to be used 4. the materials to be used in the construction 5. The duct heater main dimensions 6. the thermodynamic behaviour of the duct heater in the different operational conditions that are foreseen The air duct heaters can be of two types: “Through Duct heaters” (that become an integral part of the for ventilation duct system) “Plug-in Duct heaters” (which are coupled with a flange to the plant) A typical sketch of a “Through Duct Heater” is shown in Figure 1, the one of a “plug-in” heater Is shown in Figure 2. In both cases the heating elements are mounted using threaded bushings which make maintenance operations easy. TECHNICAL DATA (see also Figure 1 and Figure 2) B x H Flow channel dimensions Overall width Overall height Flange overall envelope Contact box depth Contact box height Frame width Supporting Baffle Female sleeve for power cable glands Female sleeve for signal cable glands Figure 2: Typical sketch of a “Plug-In Duct Heater” Fluid Electric Heaters The manufacturing experience built up in several years of operation in the market, coping with the most different applications, enables us to suggest to our customers materials and technical solutions which are best suited to the application of interest. The results of the thermodynamic calculations, performed to prove the capability of the duct heater to operate as requested, are provided already as part of the offer. p a g e 1/8

ELECTRIC DUCT HEATERS Ap plicat ion: Heat ing of a i r a nd of Ga se s HIGH TEMPERATURE DESIGN CONCEPT SPECIAL CONSTRUCTIONS In some cases, the high operating temperature impose a construction which foresees a “distancing” of the electric contact box (“cold head” construction). In these cases each element is fixed both to the plant coupling surface and to the contact box structure using a threaded bushing complete with seal and nut (see Figure 3) If the operating temperature is too high (i.e. > 300 °C) to guarantee tightness by means of seals, the “cold head” construction can be realised introducing...

ELECTRIC DUCT HEATERS Ap plicat ion: Heat ing of a i r a nd of Ga se s DATA REQUIRED FOR A CORRECT DEFINITION OF AN ELECTRIC DUCT HEATER To design an electric duct heater a set of data is required. The availability of all the data is a pre-requisite for an optimum sizing and for a precise definition of the heating power. Table 1 hereunder summarises the required data. Table 1: data required to design an electric duct heater Design Data Thermodynamic Data If the fluid is not air and is not a common gas, please specify the thermodynamic characteristics at, at least, three different temperatures...

ELECTRIC DUCT HEATERS Ap plicat ion: Heat ing of a i r a nd of Ga se s Figure 5: typical scheme of a MAXIMA duct heater CATALOGUE STANDARD DUCT HEATERS Many applications do not present complex heating needs but, on the other hand, require to limit the duct heater lead time and cost as well as to insure the constant availability on stock of exchange heating elements. MAXIMA duct heaters have been conceived just to respond to these needs: they are through duct heaters, suitable to heat air in the velocity range 2.5 to 5 m/s and to offer a wide range of heating powers (from 2.5 to 315 kW). These...

ELECTRIC DUCT HEATERS Ap plicat ion: Heat ing of a i r a nd of Ga se s 4. Verify the temperature increase that is available in the case of interest employing the following formula: HOW TO SELECT A MAXIMA DUCT HEATER MAXIMA duct heaters can be selected from the list shown in Table 2. To identify the one that best suits your needs, you must know the following data: Air flow rate Q (or air velocity V) Required temperature increase (∆T) Ventilation duct section The selection procedure is the following: 1. identify, amongst the proposed duct heaters, those having a duct section (B x H – see Figure...

ELECTRIC DUCT HEATERS Ap plicat ion: Heat ing of a i r a nd of Ga se s Table 2: available MAXIMA duct heaters Fluid Electric Heaters Minimum flow rate (Qmin) m3/h Temperature coefficient (Coeff_T°) °C m3/h

ELECTRIC DUCT HEATERS Ap plicat ion: Heat ing of a i r a nd of Ga se s Table 2: available MAXIMA duct heaters (continued) Fluid Electric Heaters Minimum flow rate (Qmin) m3/h Temperature coefficient (Coeff_T°) °C m3/h

ELECTRIC DUCT HEATERS Ap plicat ion: Heat ing of a i r a nd of Ga se s Table 2: available MAXIMA duct heaters (continued) Minimum flow rate (Qmin) m3/h Temperature coefficient (Coeff_T°) °C m3/h Fluid Electric Heaters