外文原文-基于表面扩散现象的太阳能除湿机.pdf

454 Ind Eng Chem Process Des Dev 1905 24 454 457 measured rate of moisture removal Acknowledgment We are grateful to M Mori and Y Nakane for their assistance in the experimental work and to Sumitomo Aluminium Smelting Co La for the supply of activated alumina Financial support was provided by the Iwatani Naoji Foundation 1979 and the Ministry of Education Science and Culture of Japan for Grant in Aid for Special Project Research No 421011 1979 and Grant in Aid for Energy No 505556 1980 Nomenclature a parameter D surface diffusion coefficient m2 h Dsapp apparent surface diffusion coefficient m2 h Dso parameter m2 h EaO differential heat of adsorption kJ mol Eal heat of vaporization kJ mol ES1 activation energy for migration in all layers above first Hi humidity of air at inlet of diffusion cell kg kg Ho humidity of air at outlet of diffusion cell kg kg P permeability of capillary condensate kg Pa l m l h PO parameter kg Pa m l h l p partial pressure of water vapor Pa p saturated vapor pressure Pa Q flow rate of air m3 h q amount adsorbed kg kg qm monolayer amount adsorbed kg kg R gas constant J k l mo1 l R rate of moisture removal kg m 2 h 1 layer kJ mol Sc specific surface area of c a illary condensed phase m2 kg S area of activated alumina plate m2 T temperature K Vc volume of capillary condensed phase m3 kg VT total pore volume m3 kg VH humid volume m3 kg Greek Letters A effective thermal conductivity W m l K l papp apparent density kg m3 T mean holding time for migration in first layer s T mean holding time for migration in all layers above first 4 degree of saturation of a void Literature Cited Kapur J C Solar Energy 1880 4 39 Kimura K Tabata M Matsuura H Abstracts of the Annual Convention of Architecture of Japan 1977 127 Okazaki M Ito I Toei R AIChESymp Ser 1878 No 163 164 Okazaki M Tamon H Toei R AICh J 1881 27 262 Oisen T G Solar Heating and Cooling A National Forum University of Miami School of Continulng Studies Miami FL 1978 Robinson H I Houston S AIChESymp Ser 1980 No 76 139 Rush W F Symposium Papers Energy From the Sun Institute of Gas Technology Chicago IL 1976 Satcunanathan S So Brier G C Solar Technology for Building StamW is C Ed Royal Institute of British Archltects Publication Limited Lon don England 1977 Tamon H Kyotani S Wada H Okazaki M Toei R J Chem Eng Jpn 188la 14 136 Tamon H Okazaki M Toei R AIChE J 1881b 27 271 S T specific surface area m F kg layer s Registry No Alumina 1344 28 1 Received for review November 18 1983 Accepted August 6 1984 Development of a Solar Powered Dehumidifier Based on the Surface Diffusion Phenomenon Hajime Tamon and Ryoro Toel Department of Chemical Engineerlng Kyoto Universliy Kyoto 606 Japan A new solar powered dehumidifier based on surface diffusion using a desiccant such as activated alumina was proposed to decrease the latent heat in an air conditionlng system The prototype dehumidifier with an activated alumina plate of 0 25 m2 area was constructed and operated by receiving solar energy in summer The experimental data from the prototype apparatus indicated that the dehumidifier proposed in the present work can be scaled up and can be used in summer The analysis was made from the viewpoint of the simultaneous heat and mass transfer to determine the optimum structure of the dehumidifier Introduction The summer climate of Japan is very hot and humid A considerable amount of moisture in the air is taken off by condensation in air conditioning units and about 40 of the energy consumption for air conditioning is the latent heat of condensed water Therefore a new solar powered dehumidifier is proposed to save the latent heat load in air conditioning We proposed a new solar powered dehumidifier based on the surface diffusion phenomenon through a desiccant such as activated alumina and conducted a fundamental experiment to verify the principle of its dehumidification method Tamon and Toei 1985 The purpose of this paper is to estimate the practical use of the proposed dehumidifier A prototype dehumidifier was constructed 0196 4305 85 1 l24 0454 01 50 0 and operated in summer An attempt was made to de termine the structure of the dehumidifier by computer simulation on the basis of simultaneous heat and mass transfer in order to obtain the maximum rate of moisture removal Experimental Section We verified the proposed dehumidification method using a very small scale apparatus Tamon and Toei 1985 However a halogen lamp and a thermoelectric cooler were used instead of the sun and the cooling water in this ex periment It is now necessary that a prototype dehumi difier be constructed and operated in summer to verify its practical use Experimental Apparatus and Procedure Figure 1 shows a schematic diagram of the experimental apparatus 0 1985 American Chemical Society Ind Eng Chem Process Des Dev Vol 24 No 2 1985 455 2 5 b 7 2 Ad 12 10 Figure 1 Schematic diagram of prototype dehumidifier 1 sun 2 outside air 3 humidified air 4 dehumidifier 5 tempera ture controlled bath 6 cooling water 7 cooling unit 8 dehu midified air 9 dew point hygrometer 10 room air 11 rotameter 12 blower 13 circulation pump c 9 t 6 7 6 7 Figure 2 Detailed drawing of dehumidifier 1 Pyrex glass 2 activated alumina plak 3 brass perforated plate 4 brass cooling water pipe 5 bottom plate 6 air in 7 air out 8 cooling water in 9 cooling water out The dehumidifier has an activated alumina plate area of 0 25 m2 One side of the activated alumina plate receives heat from the sun and the other side is cooled by water running through a pipe The intensity of solar radiation was measured by a Gorezynski actinometer Eikoseiki Co Ltd MS 800 The flow rate and humidity of air at the inlet and outlet were measured by a rotameter and a dew point meter using a quartz oscillator Yokogawa Electric Works Model 2586 respectively The rate of moisture removal was calculated by eq 1 1 Figure 2 shows a detailed drawing of the dehumidifier unit This unit has an activated alumina plate of area 0 05 m2 length 0 5 m width 0 1 m Other physical properties of this plate have been reported in the previous paper Tamon and Toei 1985 D r y graphite powder with a maximum diameter of 1 pm was sprayed on the surface of the activated alumina plate 2 to obtain high absorp tivity for solar energy If the contact resistance for heat transfer between the activated alumina plate 2 the brass perforated plate porosity 0 58 3 and the brass cooling pipe 4 is large the heat from the sun is not completely removed by the cooling water Therefore thermocement Nichias Corp Thermocon R that is an adhesive with good thermal conductivity was used to glue the brass perforated plate 3 to the brass cooling pipe 4 Epoxy resin including aluminum powders was also used to glue the activated alumina plate 2 to the brass perforated plate 3 Five u n i t s shown in Figure 2 were placed in series to remove the moisture of air in the prototype dehumi difier Ekperimental Results The prototype experiment was carried out in summer 1982 The rates of moisture re moval were measured under the following experimental conditions the flow rates of air were 317 and 500 cm3d the temperature of outside air was 29 34 C the relative humidity at the inlet of the dehumidifier was 50 80 the flow rate of cooling water was 39 cm3 s and the controlled temperature of cooling water was set between the dew point temperature and the wet bulb temperature of the outaide a i r The measured rate of moisture removal ranged from 0 045 to 0 08 kgm 2 h 1 in the prototype dehumidi fication experiment One example of the experimental results is shown in Figure 3 This figure indicates the time change of air temperature humidity of inlet and outlet air R Hi HJQ uHS Time Figure 3 Experimental results with prototype dehumidifier 1 H inlet 2 H outlet 3 T outside air 4 R rate of moisture removal 5 T higher temperature side 6 T lower temperature side 7 Z intensity of solar radiation Solar energy Y Figure 4 Coordinates of transport equation temperature of both sides of the activated alumina plate rate of moisture removal and the intensity of solar radi ation on Sept 3 1982 From this real time performance of the prototype dehumidifier it is found that moisture removal is possible and the proposed dehumidifier is ef fective From the rate of moisture removal in the prototype experiment it was determined that a large area activated alumina plate is needed to decrease the latent heat load in an air conditioning system Such a system would not be available for high rise buildings at present but would function for a house When the amount of condensed water in an ordinary home air conditioning system is 0 3 kg h the area of the activated alumina plate would need to be from 4 to 6 m2 Theoretical Considerations Fundamental Equations Simultaneous heat and mass transfer equations based on three assumptions have been presented in the previous paper Tamon and Toei 1985 Here the fundamental equations for heat and mass transfer are similarly prescribed The prototype apparatus is simplified as shown in Figure 4 The heat transfer equations are given by at 0 5 x 5 lr3 and ly3 I y 5 lY4 3 at 0 5 x 5 lX2 and 0 4 y I 1 J or 1 1 I x I 4 2 and Z 1 5 y 5 1 2 or 0 5 x 4 Zx3 and lY2 I y I Z where the boundary conditions are 4 456 Ind Eng Chem Process Des Dev Vol 24 No 2 1985 at lX2 d x Sl and y lY2 Table I Conditions of Computer Simulation at 0 I x I lX2 and y 0 at x lX2 and 0 I y I lyz aT aY XI h3 T T 5 7 at 0 I x I 1 and y lY1 or 0 5 x I 1 and y ly2 8 aT XI h3 T T ax at x l and 1 I y I ly2 aT aY A h3 T Tgz I at 0 I x I l and y ly4 and aT 0 10 dX at 0 5 x I lr3 and y ly4 The mass transfer equation becomes at 0 I x I lX3 and ly3 I y 5 ly4 where the boundary con ditions are 4 Q1 4 y Ly3 12 at lX2 5 x 5 lx3 and y ly3 9 Qz 4Iy ly4 13 at 0 I x I lx3 and y ly4 a4 o ax at x 0 or x lx3 and at 0 5 x I 1 and y ly3 Equations 10 14 and 15 show that the activated alu mina plate is insulated for heat or mass transfer If the adsorbed water distributions are obtained by solving eq 2 15 the rate of moisture removal R can be calculated by It is noted that the transport properties such as A and D are functions of the adsorbed amount of moisture q anc temperature T Accordingly we should solve the above equations by taking into account the dependence of X and D on q and T The values of A and D be calculate2 by using our procedure Tamon and z 1985 Results of Computer Simulation The structure of a dehumidifier such as the thickness of the activated alumina plate and the pitch of the cooling water pipes can be determined by a computer simulation to obtain the maximum moisture removal Here the pitch 2lX3 is the distance between the centers of cooling water pipes as shown in Figure 4 Table I shows the conditions of a computer simulation intensity of solar radiation kJ m 2 h a temperature of air outside C humidity of air outside kg kg velocity of air on both sides of activated alumina plate temperature of cooling water C velocity of cooling water m s thickness of activated alumina plate mb thermal conductivity of perforated plate W m leh thermal conductivity of cooling water pipe W m h pitch of square cooling water pipes me one side length of square cooling water pipes inner thickness of cooling water pipe in 0 002 m s m 2931 30 0 021 5 0 26 1 0 0 005 205 205 0 100 0 010 0 002 This value waa varied from 2931 to 8793 kJ m 2 h and other values were kept constant in Figure 7 bThis value was varied from 0 002 to 0 015 m in Figure 5 This value was varied from 0 02 to 0 60 m in Figure 6 0 1 I I I I I I1 0 5 1 0 1 5 AI cm o o Ij Figure 5 Influence of thickness of activated alumina plate on rate of moisture removal Influence of Thickness of Activated Alumina Plate on Rate of Moisture Removal The thickness of the activated alumina plate is changed from 0 2 to 1 5 cm and other values are constant as shown in Table I Figure 5 indicates the change of the rate of moisture removal when the thickness of the plate is changed The rate of moisture removal gradually decreases with increasing thickness As the thickness A1 increases the temperature difference across the sides of the plate becomes large and the dif ference of amount of moisture adsorbed Aq also becomes large This increase of Aq is not large compared with the increase of Al Therefore the driving force for surface diffusion dq dl decreases with the thickness of the plate because of the nonlinearity of the adsorption isotherm of moisture on the activated alumina If the thickness of the plate Al doubles the temperature difference at both sides of the plate AT nearly doubles The difference of the relative humidity of air across the sides of the plate A p p does not however double In addition the dif ference of amount of moisture adsorbed Aq is smaller than A p p8 as shown by the adsorption isotherm Ta mon and Toei 1985 Consequently the driving force for surface diffusion dqldl decreases with the thickness of the activated alumina plate Al as does the rate of moisture removal The thickness of activated alumina plates which can be produced at present is from 0 3 to 1 5 cm In the case where one side length of the square cooling water pipe is 1 4 cm and the pitch of cooling water pipes is 10 0 cm the rate of moisture removal is 0 078 kg m 2 h 1 for a 0 3 cm thick activated alumina plate Influence of Pitch of Cooling Water Pipes on Rate of Moisture Removal The pitch of the cooling water pipes was varied from 2 0 to 60 cm and other values were kept constant as shown in Table I Figure 6 shows the plot of the rate of moisture removal vs the ratio of the one side length of the square cooling pipe and the pitch of the cooling pipes for the case where the activated alumina plate is 0 5 cm thick The rate of moisture removal increases Ind Eng Chem Process Des Dev Vol 24 No 2 1985 457 for the ratio of one side of the cooling water pipes and the pitch of the cooling water pipes should be 3 5 When the thickness and the ratio are 0 3 cm and 3 5 the rate of moisture removal is 0 0794 kg m 2 h 1 In this work an activated alumina plate was used as the adsorbent plate The rate of moisture removal calculated on the basis of the simulating condition listed in Table I is 0 0702 kg m 2 h 1 If the thermal conductivity of the activated alumina becomes half the rate of moisture re moval becomes 0 0961 kg m 2 h 1 Therefore it is necessary that an adsorbent plate which has small thermal conduc tivity and large surface diffusion coefficient is developed Conclusion A prototype dehumidifier with an activated alumina plate of 0 25 m2 area was constructed and operated by receiving solar energy in summer The experimental data from the prototype apparatus indicated that the dehu midifier proposed by us can be scaled up and can be used in summer The analysis was made from the viewpoint of the simultaneous heat and mass transfer to determine the optimum structure of the dehumidifier The calculated results agreed well with the experimental values Acknowledgment We are grateful to Y Nakane for his assistance in the simulation work to Sumitomo Aluminium Smelting Co Ltd for supplying the activated alumina plate and to Kurimoto Ltd for construction of the prototype dehu midifier Financial support was provided by the Ministry of Education Science and Culture of Japan for Grant in Aid for Development Scientific Research No 56850218 1981 and the Iwatani Naoji Foundation 1979 o calculated 2L 0 0 6 20 40 f I Figure 6 Influence of pitch of cooling water pipes on rate of moisture removal 0 1 3 c d 4 0 5000 10000 I W m 2 h Figure 7 Influence of intensity of solar radiation on rate of mois ture removal with this ratio and decreases for a value of the ratio greatxx than 3 Thus the rate of moisture removal changes and has a maximum value as shown in Figure 6 As for a short pitch of cooling water pipes heat removal at the lower temperature side of the activated alumina plate is enough to increase the amount of moisture ad sorbed The surface diffusion coefficient also becomes larger and the rate of moisture removal is increased In the part of the activated alumina plate where the cooling water pipe is attached moisture transfer does not take place It is believed that the rate of moisture removal decreases when this ratio is smaller than 3 Influence of Intensity of Solar Radiation on Rate of Moisture Removal The intensity of solar radiation was varied from 2931 to 8793 kJ m 2 h 1 and other values were kept constant as shown in Table I Figure 7 shows the plot of the rate of moisture removal vs the intensity of solar radiation In the case where the intensity of solar radiation is below 5024 kJ m 2 h 1 the rate of moisture removal increases with this intensity On the other hand where this intensity is above 5024 kJ m 2 h 1 this rate decreases This result can be interpreted as follows For the former case large temperature differences occur on both sides of the activated alumina plate and the gradient of the amount of moisture adsorbed increases For the latter case because the heat removal is not large enough the temperature of the activated alumina plate becomes high Thus the surface diffusion coefficient is small and the rate of moisture removal decreases For example the