Flat radiator tubes for technological uses

Transcription

1 Flat radiator tubes for technological uses IOAN CĂLDARE*, IOAN GIURCA**, CORNEL MUNTEA**, DORIN CRISTIAN NĂSTAC*** * Mechanic Engineering Department, Technical University of Cluj-Napoca ** Building Services Engineering Department, Technical University of Cluj-Napoca *** Building Services Engineering Department, Transilvania University of Braşov Boulevard Labour, no , , Cluj-Napoca Romania ioan.caldare@rezi.utcluj.ro Abstract: Use of radiator tubes in processes other than those for heating rooms is less study by the specialized papers. This article presents the possibility of using flat radiator tubes for dry heat sterilization of hazardous medical waste. In order to create these hospital waste dry heat sterilization systems, the TUBRADSPIT.BAS computation software was designed. This software calculates the heat flows and dimensions the system. At the same time, the software allows us to perform simulations by modifying the working parameters. Key-Words: plane radiation tubes, heat transfer by radiation, heat sterilization, hazardous medical waste. 1 Introduction At international level, the heat transfer through radiation is a well-known phenomenon, thus several books [5], Ph.D. theses [4], as well as articles published in specialized magazines [2], [3] have been written on this subject. In the last time, in Romania, several doctoral theses appeared, concerning radiation heating systems with radiator tubes [6], [1]. Usually, these radiator tubes are used in order to heat industrial shop floors or other very high buildings. Use of radiator tubes in processes other than those for heating rooms is less study by the specialized papers. In this article, we present the use of flat radiator tubes used for the dry heat sterilization of hazardous medical waste. Thus, we propose to perform the dry heat sterilization of hazardous medical waste using a quasi-isothermal radiator tube placed over a conveying belt, thus permitting the heating by thermal radiation. This technical solution is an affordable alternative to the technical solution concerning high pressure vapor sterilization. 2 Flat radiator tubes used in material drying or heating technological processes Radiator tubes used in material drying or heating technological processes have many advantages, first of all the fact that the primary heat source is not in direct contact with the material treated. An extraordinary efficiency may be obtained by using flat radiator tubes. A first analysis of using flat radiator tubes was made in a paper where the authors used the flat radiator tube in order to dry enamel. Flat radiator tube may be actually used industrially in many fields, due to the fact that the modern calculation methods allow a thorough exactness in assessing and dimensioning the processes. In order to obtain a uniform temperature of the radiator tube and implicitly a uniform heat flow, a quite important prerequisite of the drying processes, we have used a radiator tube with internal gas recirculation, as the one presented in figure 1. ISBN:

2 Fig.1 Radiator tube with internal gas recirculation The interior separating wall works as a radiation display, compensating the temperature decreasing effect in the exhaust area of the gases from the radiator tube. This technical solution was applied for drying certain types of enamel requiring very strict temperature uniformity conditions, because small temperature variations lead to important variations of the colors obtained. 3 Progressive heating radiator tube A new technical solution, applicable in modern technological conditions, is the use of the progressive heating radiator tube. The progressive heating may be regulated on sections, thus allowing a very fine adjustment of the temperature of radiator tube the active wall. For the progressive heating, one may use long flame burners, but a much more efficient solution may be obtained by using flat radiators as burners. The principle scheme is presented in figure 2. The physical phenomenon is the following: the surface of the flat radiators, namely the burning surface type (also called invisible flame burning), has a burning temperature amounting to o C. One cannot decrease the temperature under 800 o C, because the methane s flaming point is of 780 o C, and over 1200 o C the costs of the ceramic materials representing the active surface of the radiator are too high. air flat radiator receiver inferior surface of the flat radiator Fig. 2 Radiator tube with flat radiators ISBN:

3 4 High temperature radiation sterilization An interesting application, quite actual, is to turn hazardous medical waste not harmful by using dry heat sterilization. At present, Romanian legislation does not allow «intra muros» burning of hospital waste, requiring that the hazardous medical waste be burnt regionally, limiting the minimum quantity of waste to be incinerated to 3000 tons/year. As a city hospital, with several hospitals depending on it, generates 0.15 kg of contaminated waste/bed/day, and therefore for 1000 beds we have 150 kg/day and 54 tons/year respectively (150 kg/day), it results that the incineration solution can be put into practice only at the regional, county level. Therefore the solution for ecologically solving the waste neutralization at the hospital level is the heat sterilization. The classical high pressure vapor sterilization has some big technological disadvantages, while the microwave sterilization supposes high costs. High temperature radiation sterilization is a flow, easy to control and affordable technology. One forecasted radiant panel sterilization systems, but these ones have the disadvantage of the difficulty of conducting a heating source high temperature process. In this case it is necessary to precise the temperature limits that the material to be sterilized may take: as a lower limit, we shall obviously have the sterilization lower limit of about 150 o C; the upper limit is given by the decomposition temperature of certain organic materials composing the waste (paper, cellulose materials, plastic material) and one care certainly set this to 280 o C. Therefore, the acceptable temperature range is relatively small, o C. For such a small range, the direct flame radiation technology is much too difficult to be conducted, but a radiator tube system presents a low temperature of the radiator tube on the one hand, and on the other hand the temperature is easily controllable using an automated system. 5 Calculating heat flows necessary to dry the hazardous waste and to heat it up to the sterilization temperature Taking into account the thermal system presented in figure 2, if there is an equality between the surfaces of the radiant panel and those of the radiator tube, one notices that the radiation surface of the flat radiator tube shall have a temperature, according to the radiation display theory, of: Ttr = ( Te + 273) ( Tr + 273) 273[ o C] (1) where: Ttr is the surface of the flat radiator tube [ o C]; Te - superficial temperature of the radiant panel [ o C]; Tr - temperature of the material submitted to sterilization [ o C]. burning gases flat radiator, Te inferior surface of radiator tube, Ttr receiver, Tr Fig. 3 Thermal system with flat radiators Having these data it is possible to calculate the heat flows necessary to dry the hazardous waste and to heat it up to the sterilization temperature, as well as to perform a study concerning the possibility of variations of temperature at the surface of flat radiators and at the inferior surface of the radiator tube depending on the needs of the technological sterilization process. ISBN:

4 6 Process physical, mathematical and computation model In order to obtain a physical image of the forecasted system, it was necessary to elaborate a process physical, mathematical and computation model. The software, available under the name of TUBRADSPIT.BAS, developed in a modern programming system with conversational possibility, may simulate the functioning of a hospital waste sterilizer according to various functioning parameters. In order to exemplify the size of a real hospital waste sterilization system with radiant flow with flat radiator tube, we further on present a table of values. Table 1 Size of a real hospital waste sterilization system with radiant flow with flat radiator tube Temperatures in the flat tube system Le = 0.3 Ltr = 0.3 Lr = 0.6 Radiant panel temperature o C Receiving surface temperature o C Radiator tube display temperature o C Heat flows Transmitter s transmission coefficient 0,850 0,850 0,850 0,850 0,850 Receiver s transmission coefficient 0,650 0,650 0,650 0,650 0,650 Useful radiant specific heat flow W/m Useful radiant specific heat flow kw/m 2 20,767 29,799 41,462 56,222 74,584 Useful width of the treatment conveyor m 0,6 0,6 0,6 0,6 0,6 Waste s height on the conveyor m 0,2 0,2 0,2 0,2 0,2 Conveyor s speed m/s 0,5 0,5 0,5 0,5 0,5 Waste volume per second m 3 /s 0,060 0,060 0,060 0,060 0,060 Waste density kg/m 3 0,200 0,200 0,200 0,200 0,200 Waste flow kg/s 0,012 0,012 0,012 0,012 0,012 Waste flow kg/h 43,200 43,200 43,200 43,200 43,200 Heating to 105 o C Waste specific heat kj/kg/k 2,093 2,093 2,093 2,093 2,093 Heating range ( o C) K 85,0 85,0 85,0 85,0 85,0 Heating heat flow kw 2,135 2,135 2,135 2,135 2,135 Humidity elimination Waste s absolute humidity kg/kg 0,500 0,500 0,500 0,500 0,500 Water flow to be eliminated kg/s 0, , , , ,00600 Water vaporization heat kj/kg Heat flow in order to eliminate water kw 12,558 12,558 12,558 12,558 12,558 ISBN:

5 Conveyor s weight (neoprene 10 mm) kg/s 0,003 0,003 0,003 0,003 0,003 Neoprene specific heat kj/kg/k 1,424 1,424 1,424 1,424 1,424 Heat flow for heating the conveyor 85 K kw 0,363 0,363 0,363 0,363 0,363 Useful heat flow to be eliminated kw 15,056 15,056 15,056 15,056 15,056 Heat losses (50 % output) kw 15,056 15,056 15,056 15,056 15,056 Total heat flow to be eliminated kw 30,112 30,112 30,112 30,112 30,112 Radiant panel dimensions Necessary radiant panel surface m 2 1,450 1,010 0,726 0,536 0,404 Panel width m 0,3 0,3 0,3 0,3 0,3 Panel total length m 4,8 3,4 2,4 1,8 1,3 7 Results and result interpretation In fig. 4 we present the diagram of the necessary radiator tube surface depending on the temperature of the radiant bodies. Temperature of the radiator tube s display, Le = 0,3, Ltr = 0.3, Lr = Temperatures [ o C] Surface of radiant panels [m 2 ] Temperatures in the radiant system, in oc Temperature of radiant panel, in oc Fig. 4 Diagram of the necessary radiator tube surface depending on the temperature of the radiant bodies For such a configuration of the radiator system one notices a relatively high temperature of the radiator tube material, which means that it must be manufactured out of allied steel, which is usually made for the initial section in case of all radiator tubes. Still, the radiant panel length, namely the length of the active section of waste drying conveyor, has a technically normal value of de m. If one forecasts a lower temperature of the radiator tube, one must accept its widening and the lengthening of the active conveyor track. By recalculating the system for the parameters leading to a decrease of the radiator tube temperature, one obtained the results presented in the above table. ISBN:

6 Table 2 System recalculation for the parameters leading to a decrease in the radiator tube temperature Temperatures in the flat tube system Le = 0.3 Ltr = 0.6 Lr = 0.6 Radiant panel temperature o C Receiving surface temperature o C Radiator tube display temperature o C Heat flows Transmitter s transmission coefficient 0,850 0,850 0,850 0,850 0,850 Receiver s transmission coefficient 0,650 0,650 0,650 0,650 0,650 Useful radiant specific heat flow W/m Useful radiant specific heat flow kw/m 2 13,845 19,866 27,641 37,481 49,723 Useful width of the treatment conveyor m 0,6 0,6 0,6 0,6 0,6 Waste s height on the conveyor m 0,2 0,2 0,2 0,2 0,2 Conveyor s speed m/s 0,5 0,5 0,5 0,5 0,5 Waste volume per second m 3 /s 0,060 0,060 0,060 0,060 0,060 Waste density kg/m 3 0,200 0,200 0,200 0,200 0,200 Waste flow kg/s 0,012 0,012 0,012 0,012 0,012 Waste flow kg/h 43,200 43,200 43,200 43,200 43,200 Heating to 105 o C Waste specific heat kj/kg/k 2,093 2,093 2,093 2,093 2,093 Heating range ( o C) K 85,0 85,0 85,0 85,0 85,0 Heating heat flow kw 2,135 2,135 2,135 2,135 2,135 Humidity elimination Waste s absolute humidity kg/kg 0,500 0,500 0,500 0,500 0,500 Water flow to be eliminated kg/s 0, , , , ,00600 Water vaporization heat kj/kg Heat flow in order to eliminate water kw 12,558 12,558 12,558 12,558 12,558 Conveyor s weight (neoprene 10 mm) kg/s 0,003 0,003 0,003 0,003 0,003 Neoprene specific heat kj/kg/k 1,424 1,424 1,424 1,424 1,424 Heat flow for heating the conveyor 85 K kw 0,363 0,363 0,363 0,363 0,363 Useful heat flow to be eliminated kw 15,056 15,056 15,056 15,056 15,056 Heat losses (50 % output) kw 15,056 15,056 15,056 15,056 15,056 Total heat flow to be eliminated kw 30,112 30,112 30,112 30,112 30,112 ISBN:

7 Radiant panel dimensions Necessary radiant panel surface m 2 2,175 1,516 1,089 0,803 0,606 Panel width m 0,3 0,3 0,3 0,3 0,3 Panel total length m 7,2 5,1 3,6 2,7 2,0 In fig. 5 we present the diagram of the necessary radiator tube surface, depending on the radiant body temperature Temperature of the radiator tube s display, Le = 0,3, Ltr = 0.6, Lr = 0.6 Temperatures [ o C] Temperatures in the radiant system, in oc Temperature of radiant panel, in oc Surface of radiant panels [m 2 ] Fig. 5 Diagram of the necessary radiator tube surface, depending on the radiant body temperature 8 Conclusion Dry heat sterilization of hazardous medical waste may be accomplished by using a quasi-isotherm radiator tube placed above a conveyor, and the heating is made by heat radiation. In order to create these hospital waste dry heat sterilization systems, the TUBRADSPIT.BAS computation software was designed. This software calculates the heat flows and dimensions the system. At the same time, the software allows us to perform simulations by modifying the working parameters. Depending on the burning temperature on the radiant panel and depending on the width rations between the radiators, the radiator tube and the receiving conveyor, one shall obtain different necessary lengths of radiant panels and different temperatures of the radiator tube surface. This technical solution is an affordable alternative to the technical solution concerning high pressure vapor sterilization. References: [1] Cǎldare, I., Contributions to the study of heating with low temperature radiant tubes (in Romanian), Doctoral Thesis, Technical University of Cluj-Napoca, Cluj-Napoca, [2] Dudkiewicz, E., Jezowiecki, J., The influence of orientation of a gas-fired direct radiant heater on radiant temperature distribution at a work station. Energy and Buildings, 43, 2011, pp [3] Dudkiewicz, E., Jezowiecki, J., Measured radiant thermal fields in industrial spaces served by high intensity infrared heater. Energy and Buildings, 41, 2009, pp [4] Manolescu, M. - Modélisation des échanges radiatifs dans des cavités complexes a l'aide d'outils infographiques. Application a la qualification des ambiances radiatives, Thèse de doctorat, INSA de Lyon, ISBN:

8 [5] Perlmutter, M., Siegel, R. - Thermal Radiation Heat Transfer, McGraw-Hill, New York, [6] Ţoropoc, S., M., Contributions to the study of heating systems through high temperature radiation, with radiator tubes, (in Romanian), Doctoral Thesis, Technical University of Constructions, Bucharest, ISBN: