Heater sizing

Fire uihe area required and heater size (shell diameter, shell length, fire luhe rating, coil length and number of passes). 

Figure 4 shows how variations in the electric heater size affect the relative contributions of the heated element and the main (unheated) converter to the overall HC conversion performance of the EHC system for the case of 20 s heating at 2500 W. As expected, the HC conversion over the heater increases with increasing heater volume. With a large electric heater, however, the conversion performance of the main converter (as given by the difference between the dashed and solid curves in Fig. 4) is predicted to be substantially lower than that with a small-volume heater, so that the best overall conversion performance (i.e., lowest tailpipe emissions) can be obtained in the regime of small heater volumes. 

Discussion Note that if the water bath is heated electrically, a 4,6 kW resistance heater vrill be needed just to make up for the heat loss from the top surface. The total heater size will have to be larger to account for the heat losses from the side and bottom surfaces of the bath as v/ell as the heat absorbed by the spray paint cans as they are heated to 50°C. Also note that water needs to be supplied to the bath at a rate of 5.24 kg/h to make up for the water loss by evaporation. Also, in reality, the surface temperature will probably be a little lower than the bulk water temperature, and thus the heat transfer rates will be somesvhat lower than indicated here. 

Based on the tuned models, equipment performance could be evaluated and compared with design. The models could then be readily adapted to simulate an additional process fired heater (to unload the methanol superheater) and to evaluate it s inpact on the overall MTG unit performance. Multiple case studies were performed to determine optimum heater size with regard to maximising heat recovery and providing unit heat balance flexibility. The additional heat balance flexibility allows the ZSM-5 catalyst outlet temperature to be reduced hence maximising gasoline yield. 

Effect of Heater Size. Heated surfaces of small dimension tend to give higher critical heat fluxes than do surfaces of large size. Lienhard and Dhir [155] suggest a characteristic length scale L above which the critical heat flux becomes independent of the heater size. L is given by... 

One could also choose the proper heater size to have 70 percent conversion in some chosen time—say 20 min. Here, Eqs. (d) and (e) would have to be solved iteratively for the unknown value of q. Actually, after the above range of simulations were available, a simple interpolation is possible the result is qA = 8 kW. 

Bimetal Overload Relays. Traditional NEMA-style bimetal overload relays share the heater mterchangeabihty of the melting-alloy type. They may also have the ability to adjust up or down the equivalent of one heater size, or about +15 percent. lEC overloads are bimetal type, but have nonreplaceable integral heaters. To compensate for this, these units can typically be adjusted +20 to 25 percent. Bimetal devices use the heat generated to cause deflection of one or more bimetal strips. Once this deflection is great enough, the trip mechanism is operated. 

Check heater sizing and also check ambient temperature. 

Recheck ratings and heater size. Correct if necessary. 

Effect of Heater Size on Nucleation Temperature and Nucleation Time... 

Themial Bubbles, Figure 13 Effects of heater size on nucleation temperature and nucleation time at r = 1,66 ms [13]... 

Deng PG, Lee YK, Cheng P (2006) An experimental study of heater size effect on micro bubble generation. Int J Heat Mass Transf 49 2535-2544... 

One could also select the proper heater size to achieve 70 % conversion in a given time — say, 20 min. In such a case equations (8.2.A-d) and (8.2.A-e)... 

---