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Convective heat transfer coefficients experimental estimation and its impact on thermal VOL 5 N M 2. building design for walls made of different Mexican building materials. Alguns dos principais fatores que determinam a confiabilidade do projeto t rmico de um edif cio s o as propriedades. de transfer ncia de calor e t rmicas N o h dados experimentais dispon veis na bibliografia internacional relacio. nados com propriedades de transfer ncia de calor por convec o para os materiais de constru o mais utilizados. portanto pela primeira vez algumas medidas relacionadas com propriedades de transfer ncia de calor por convec o. para os materiais de constru o mais utilizados foram realizadas para ajudar a otimiza o do processo de design. t rmico de edif cios Apresentamos dados experimentais sobre os coeficientes de transfer ncia de calor convectivo. para paredes de diversos materiais de constru o na posi o vertical e horizontal usando uma ferramenta poderosa. como um t nel de vento, Tijolo vermelho tepetate calc rio adobe e paredes de teste concretos de 0 46 x 0 56 x 0 06 m foram fabricados. bem como um prot tipo de testes para mont los e avaliar os seus coeficientes de transfer ncia de calor por convec o. As medi es foram realizadas no t nel de vento para o intervalo de um 2 10 m s velocidade do vento Os valores re. portados oscilam entre 14 71 W m2K dependendo do material da parede e de posi o bem como a velocidade do vento. O impacto do uso de dados experimentais contra dados recomendados pelos padr es mexicanos no projeto t rmico de. um edif cio foi avaliada atrav s de simula es com o software Energy 10 estimando se discrep ncia do consumo de. energia para um edif cio em quatro locais no M xico com diversificada radia o solar clim tica e global condi es. Palavras chave convec o coeficientes de transfer ncia de calor t nel de vento a irradia o solar global mate. riais de constru o,1 Introduction, Many international studies about convection heat transfer exist which consider for example the convective coefficients. for heated plates Rebay et al 2002 or roof mounted flat plate solar collectors Sharples and Charlesworth 1998. Studies about convection heat transfer in buildings are focused mainly on developing theoretical models Sartori 2006. Mirsadeghi et al 2012 and a little on experimental measurements of convective heat transfer coefficients for some. building elements like roofs Clear et al 2003 considering only geometrical and wind velocity aspects but not the. kind of building material used The main weakness of actual international bibliography is that studies are not focused. on the kind of building material of which is done the building element and also just a small range of wind velocity. 1 5 m s has been analyzed Hagishima and Tanimoto 2003 Modelling of natural convection in vertical and tilted. photovoltaic applications was carried out by Lau et al 2012 A method to calculate wind profile parameters of the wind. tunnel boundary layer is described by Liua et al 2003 Two different building envelope systems 2x4 stick frame buil. ding Structural Insulated Panel SIP building were constructed from a thick layer of polystyrene foam sandwiched. between two fiber cement boards and the other one was a wood building model under simulated environmental loads. generated by the 12 fan Wall of Wind WoW at Florida International University FIU The low speed wind flow field. was simulated using the 12 fan WoW at FIU The simulation conducted in this study was targeted at a preselected eave. height with wind speeds of 6 7 11 2 15 6 20 1 m s to investigate the convective heat transfer under normal weather. investigaci n y desarrollo, conditions The measurements were conducted on the roof and one of the side walls of the building models at different. wind speeds and three wind angles of attack A plot has a mild positive slope which indicates that the wind induced. convection heat loss increased as the wind speed increased by only a small amount over the roof surface and with AOA. 0 only 1 to 1 5 W m2K 45 7 to 16 W m2K and 90 8 to 9 W m2K on side walls Chowdhury and Suksawang. 2012 In Latin American context experimental studies about convection heat transfer properties of building materials. have not been carried out except for only a few exceptions consisting of qualitative analyses about thermal performance. of walls with at real climatic and solar irradiation conditions Corral et al 2004. The vast majority of buildings that are built in developing countries do not have adequate air conditioning 27. equipment to maintain indoor air conditions within the ranges of human hygrothermal comfort This means that the. building itself by design orientation materials and devices must protect the occupants of moisture and thermal. concreto y cemento,discomfort, To improve the thermal design of buildings and achieve thermal comfort of the occupants with minimum power. consumption there is the official norm NOM 008 ENER 2001 Ministry of Energy 2001 in Mexico Its main objective. seeks to provide the items and information through which restricts the heat gain of a building through its envelope in. order to rationalize the use of energy in cooling systems For heat gain calculation this standard proposes the use of a set. of values for the thermal and heat transfer properties of the most common building materials such as concrete and red. ENERO juNio 2014 Convective heat transfer coefficients experimental estimation and its impact on. thermal building design for walls made of different Mexican building materials. brick Many of these values were obtained from international literature and have not been measured for the specific type. of material and under climatic conditions prevailing in Mexico An example is the convective heat transfer coefficient. for which only four default values are given regardless the type of building material or local wind conditions. The usual wind speed in Mexican cities is between 0 to 6 m s but in coastal and others locations wind speed can. reach up to 9 11 m s at different levels of frequency Ministry of Livestock and Hydraulic Resources 1981. For these reasons measurements of convective heat transfer coefficients of diverse building materials were carried. out for wind velocities of 2 4 6 8 and 10 m s This paper presents the measurements of these heat transfer coefficients. of horizontal and vertical walls made of red brick tepetate limestone adobe and concrete. 1 1 Background, Newton s cooling law expresses the convection heat transfer for a hot plate.
Convective heat transfer coefficients depend on many factors including velocity temperature and the kind of fluid The. hydrodynamic boundary layer thickness is Holman 1998. When a plate is warm over its entire length the thermal and hydrodynamic boundary layer thicknesses are correlated. by Holman 1998, Considering a laminar flow regime the local convective heat transfer coefficient for a hot plate is Holman 1998. An evaluation of the heat transfer convection along a hot plate surface is only possible through the average convective. heat transfer coefficient Holman 1998,investigaci n y desarrollo. Also local convective heat transfer coefficient for a hot plate with laminar parallel air flow is given by Holman. 28 2 Experiment, To measure the convective heat transfer coefficients of walls we built a testing prototype consisting of a heater an. insulated box cavity and a base to mount the proof walls Fig 1. concreto y cemento, Convective heat transfer coefficients experimental estimation and its impact on thermal VOL 5 N M 2. building design for walls made of different Mexican building materials. Figure 1 Drawing of the testing prototype for the estimation of convective. heat transfer coefficients, The heater consisted of three 1500 W resistors connected in a parallel circuit and mounted on a steel structure A 6 x 10 4 m.
thick copper plate of length 0 3 m and width 0 4 m was placed on the three resistors to improve the heat flow toward the. proof wall The box was made of 4 x 10 4 m thick aluminum walls thermally insulated by 0 02 and 0 05 m thick layers of. ceramic fiber and expanded polystyrene EPS respectively The base to mount the proof walls was made of steel bars. The box container had exterior dimensions of 0 6 x 0 7 x 0 2 m and internal dimensions of 0 46 x 0 56 x 0 15 m. The test walls were built from red brick blocks tepetate limestone and adobe each of which were pasted with a. mixture of cement sand and lime Also a concrete wall with a compressive strength of 200 kg cm2 similar to those. used in ceilings was built The test wall dimensions were 0 46 x 0 56 m and the thickness for the red brick tepetate. and concrete walls were 0 06 m while the adobe wall thickness was the larger 0 08 m because this material was the. weakest Fig 2 shows a picture of a red brick wall mounted on the testing prototype. investigaci n y desarrollo,concreto y cemento, Figure 2 A red brick wall mounted on the testing prototype. ENERO juNio 2014 Convective heat transfer coefficients experimental estimation and its impact on. thermal building design for walls made of different Mexican building materials. Table 1 Density and thermal conductivity of building materials used for test walls. Material Density kg m3 Thermal Conductivity k W mK. Red Brick 1595 12 0 61 0 74,Tepetate 1023 47 1 047 0 93. Adobe 1306 66 0 93 0 582,Concrete 2161 29 1 3 2 6, Table 1 contains density and thermal conductivity of the building materials used for built the test walls The density. of building materials was experimentally estimated by water displacement method whereas conductivity values were. taken from Mexican and international bibliography American Society of Heating Refrigerating and Air Conditioning. Engineers 2001 Ministry of Energy 2001, The experimental measurements for the estimation of convective coefficients were carried out within the wind tunnel. of the Institute of Engineering UNAM The wind tunnel is of the closed circuit type and has a rectangular test section. of 1 70 x 1 13 x 0 77 m and a 75 hp engine Temperature data were collected through a system of sensors manufactured. with LM35AH semiconductors and connected to a data acquisition device AT MIO 16E IO Multi I O from National. Instruments, The vertical displacement of the sensors was achieved by means of a mechanism installed at the roof of the test.
section basically consisting of an endless screw Fig 3 a mounted on an aluminum base Two vertical bearers of steel. were coupled to the aluminum base to sustain the sensor system which consisted of a pair of horizontal Lucite bars. fastening five temperature sensors Fig 3 b,investigaci n y desarrollo. Figures 3a and 3b Mechanism for mounting the sensor system as well as for movement. concreto y cemento,at different heights above the wall tests. The testing prototype and hence the test wall mounted on it was installed horizontally and vertically inside the test. section of the wind tunnel such that the shorter length of the wall 0 46 m was parallel to the air flow direction Sensors. were situated on the wall surface 0 23 m stream wise from the main edge An exterior view of the wind tunnel s test. section is shown in Fig 4 during a test with the prototype in horizontal position. Convective heat transfer coefficients experimental estimation and its impact on thermal VOL 5 N M 2. building design for walls made of different Mexican building materials. Figure 4 View of prototype testing within the test section of the wind tunnel. The heater was switched on for 60 minutes during a warming up process without any air flow and then a stream. of air wind parallel to the surface of the test wall was produced Its speed was measured by a hot wire anemometer. EXTECH brand model 407 123 Once the temperature readings stabilized the transitional stage ranged from 330 to. 1820 seconds depending on the material wind speed and position of the wall the sensor system was moved vertically. in regular steps of 1 5 mm above the surface of the wall To estimate the convective heat transfer coefficient we applied. Eq 1 where the temperature values were the average of the sensor system readings. 3 Impact on the building s thermal design process, To estimate the impact of using experimental data in a building s thermal design process a simulation was performed. using the Energy 10 software version 1 5, The E 10 thermal simulation engine executes hourly thermal and daylight performance calculations based on hourly. weather data for the site in question the building description and the operating characteristics The software provides. investigaci n y desarrollo, a detailed evaluation of solar gains through windows heat flowing in and out of walls thermal storage in all building.
materials and heating ventilation and air conditioning system HVAC performance The simulation calculates the. heat transfer from point to point within the building every 15 min throughout a simulated year The thermal analysis. is carried out using a thermal network mathematical modeling approach the HVAC analysis is in steady state and the. daylight analysis uses a split flux method For the thermal network representation of heat flow among building elements. the energy is exactly balanced at each node of the network Such a simulation is based largely on the central difference. of finite difference equation solutions HVAC is quasi steady and is quite detailed accounting for both sensible and. latent energy transfers Iteration is performed at each time step to ensure consistency between the thermal loads and 31. systems simulations, The house used for this simulation was a 70 m2 apartment with a concrete ceiling a mosaic ceramic floor and. concreto y cemento, 16 cm thick brick walls The orientation was north to south with four 3 mm thick single pane soda lime glass win. dows facing north and four facing south The ratio of window to wall area was 20 The simulation process compared. the energy consumption for the building when Mexican standard recommended data were used against the energy. consumption when the experimental data were used The apartment in both cases was considered to be inhabited by 5. persons The simulation also considered the use of heating by electrical resistances as well as air conditioning equip. ment with a direct expansion cycle and a COP of 2 6 The geographic locations used in this simulation were Mexico. ENERO juNio 2014 Convective heat transfer coefficients experimental estimation and its impact on. thermal building design for walls made of different Mexican building materials. city Chihuahua city located in the north central part of Mexico Mexicali city located in the northwest of Mexico. and Merida city located in the southeast of Mexico all of them with very different weather conditions Table 2 shows. the annual average and extreme values of temperature as well as the average relative humidity Ministry of Livestock. and Hydraulic Resources 1981 and global horizontal solar irradiation Almanza et al 1992 for each locality The. interval of comfort temperature was taken as 22 25 5 C. 4 1 Convective heat transfer coefficients, Temperature profiles were measured to determine the thickness of the thermal boundary layer The results for a ho. rizontally positioned red brick wall and a wind speed of 8 m s are shown in Fig 5 and they are in agreement with. temperature profiles reported in other studies Davies et al 2005 As can be seen the main air temperature change. occurred over the first 4 5 mm, Figure 5 Temperature profile for a horizontal red brick wall with an 8 m s parallel air flow. investigaci n y desarrollo, Table 2 Climatic and irradiation data for four different Mexican localities.
Longitude Latitude Temperature C Annual Daily average. Locality W deg N deg Annual Maximum Minimum average of through the year. 32 average extreme extreme relative of global solar. humidity irradiation MJ m2,concreto y cemento,Mexico City 99 16 19 2 15 6 33 5 0 5 58 9 17 7. Chihuahua 106 06 28 6 18 4 47 0 12 8 45 0 21 3,Mexicali 115 45 32 6 22 3 49 6 7 0 38 2 19 8. Merida 89 63 20 9 26 5 43 0 7 0 72 0 16 9, Convective heat transfer coefficients experimental estimation and its impact on thermal VOL 5 N M 2. building design for walls made of different Mexican building materials. The same behavior was observed in all the walls for wind speeds of 6 8 and 10 m s Employing Eq 2 to. calculate the hydrodynamic boundary layer thickness and considering that Pr 0 708 we obtained a 0 0037 m. thickness If we used Eq 3 the thermal boundary layer thickness was 0 0041 m representing an 8 8 discre. pancy compared to the 0 0045 m experimental result This discrepancy is easily explainable by two factors the. roughness of the wall surface and the error in measurements of the vertical distance between the sensors system. and wall surface, For low wind speeds 2 and 4 m s after the sensors were moved a distance beyond the boundary layer thickness. as predicted by Eq 3 the air temperature readings still showed a downward trend thus we assumed that free flow. temperature was not yet attained Such behavior of the air temperature was more notorious with the horizontal concrete. wall and a 2 m s airflow because even at the highest possible vertical displacement of the sensors system 0 0078 mm. the sensor readings still showed a slight downward trend therefore we were not able to measuring the boundary layer. thickness because of the design limitations of our system Fig 6 shows an example of this case for a horizontal concrete. wall and a 4 m s wind velocity The free flow temperature is reached but this measurement is shifted some millimeters. beyond that predicted by Eq 3, Figure 6 Temperature profile for a horizontal concrete wall with a 4 m s parallel air flow.
investigaci n y desarrollo, Being that the parameter Gr Re5 2 for horizontal walls and Gr Re2 for vertical walls ranged 2 2 x 10 4 3 9 x 10 5. and 3 6 x 10 2 9 1 x 10 3 respectively for low wind speed 2 and 4 m s we do not consider the mixed convection to. explain the widening of thermal boundary layer because these values for the parameters exclude the effects of natural. convection for a Pr 0 708 Martynenko and Khramtsov 2005. Such a behavior is explained by the humidity content of the test walls For porous building materials like red brick. or adobe a great part of the water content was evaporated during the 60 minute warming process For a concrete wall 33. the evaporation was more sluggish because of the wall s low porosity Consequently for high wind velocities the. evaporated water was not yet detected by the top sensors but for low velocities the air stream was not capable of dragging. concreto y cemento, the evaporated water coming out from the test wall This hypothesis is supported by the high thermal conductivity of the. concrete compared with the other building materials and the correspondingly larger amount of heat coming out from. the concrete wall towards the air Therefore the temperature of air near the wall surface rises quickly the density. and Reynolds number Re diminish and the viscosity increases causing an augmentation of the Prandtl number. Pr and the thickness of the hydrodynamic and thermal boundary layers This augmentation is supported by the low. speed of the heat carriers air particles that results in an overheating of such heat carriers as they absorb more heat. ENERO juNio 2014 Convective heat transfer coefficients experimental estimation and its impact on. thermal building design for walls made of different Mexican building materials. during their time of travel along the surface of the wall Thus Eq 4 was not used as an alternative method to calculate. the convective heat transfer coefficients of the test walls since the thicknesses of the thermal boundary layer estimated. from the temperature profiles were distorted by the evaporated water coming out of the test wall. From Fig 6 in concordance with thermal boundary layer theory the temperature curve diminishes suddenly in. the 3 mm nearest to the wall surface however between 3 and 24 mm the curve is constant at a value above the free. flow temperature This disruption is due to the influence of water steam coming out of the test wall on the air tempe. rature For the 25 39 mm interval the influence of the water steam decreases as the temperature curve decreases. slowly until finally vanishing at 40 mm the temperature behavior is practically constant i e free flow temperature. is reached, Table 3 summarizes the results for test walls of red brick tepetate adobe and concrete in both horizontal and ver. tical position always considering an air flow parallel to the surface of the wall Heat losses from the box enclosing the. electric resistances were estimated for each test considering metallic areas exposed to the air flow from the steel base. for walls and using the convection heat transfer model described by the Eq 6 Thus heat losses were considered for. the calculation of convective heat transfer coefficients and ranged between 8 2 18 4 for tests with horizontal walls. and 11 6 25 9 for tests with vertical walls Five different tests were made in each case so that in Table 3 the standard. deviation of the estimated values of the convective coefficient is also included. Table 3 Convective heat transfer coefficients W m2K for red brick tepetate adobe and concrete. Wind velocity m s,2 4 6 8 10,Horizontal position,Red Brick h 17 48 19 89 28 49 28 62 31 45. 2 14 2 73 5 23 5 39 6 50,h 14 67 24 71 25 63 31 21 37 87.
1 71 1 31 0 21 1 93 1 33,h 19 73 23 04 26 45 26 48. Concrete 0 15 0 36 0 27 1 99,Vertical position,Red Brick h 19 09 29 44 36 89 49 46. 2 34 3 02 1 44 4 15,investigaci n y desarrollo,Tepetate h 22 74 40 88. 2 29 10 46,h 25 19 34 95 46 54 49 76,2 62 1 09 1 11 6 39. h 24 92 33 36 34 21 62 83 71 98,Concrete 3 22 1 67 2 94 2 10 5 59.
If we compare the values in Table 3 with those proposed by the Mexican standards Ministry of Energy 2001 it is. possible to see a substantial difference 200 400 However the values in Table 3 are similar to experimental data. concreto y cemento, reported in some international studies for flat plates and a wind velocity interval of 1 5 m s Hagishima and Tanimoto. 2003 Sharples and Charlesworth 1998 Sartori E 2006 makes a comparison between several of the experimentally. obtained equations currently used for convective heat transfer coefficients in flat surfaces and based on the principles of. boundary layer theory suggests an equation that tries to reach a consensus between all the results Using this equation. Sartori evaluates the convective coefficient for a wind velocity interval of 2 5 m s and the results range between 4. and 25 W m2K which is consistent with our data, Convective heat transfer coefficients experimental estimation and its impact on thermal VOL 5 N M 2. building design for walls made of different Mexican building materials. A graph of Nu vs Re for a horizontal red brick test wall with parallel air flow is presented in Fig 7 Table 4 con. tains the equations that relate the numbers Nu and Re obtained for each wall considered as well as their respective. correlation coefficient, Figure 7 Re vs Nu graph for a horizontal red brick test wall with parallel air flow. 4 2 Energy 10 Simulation, Fig 8 presents the simulation results for a building with red brick walls in Mexico City This location experiences a. mild climate throughout the year A great energy consumption in such an apartment is because air conditioning heating. and cooling and energy is also required for illumination of the building defined by the term lights Other sources of. consumption include the energy required for heating water and running electrical devices. investigaci n y desarrollo, Table 4 Equations that relate the Nu and Re numbers for red brick tepetate adobe and concrete.
test walls considering Pr 0 708,Test Wall Equation Correlation. Coefficient R2,Red Brick Horizontal Nu 3 4817 Re0 3894 0 9186. Vertical Nu 0 0042 Re 94 223 0 9892,Tepetate Horizontal Nu 0 6353 Re0 5465 0 9576. Adobe Vertical Nu 300 51 ln Re 2988 8 0 9807,Concrete Horizontal Nu 5 1141 Re0 3444 0 9478. concreto y cemento,Vertical Nu 0 0052 Re 89 453 0 8986.
Results from the simulation reveal a decrease of 22 5 in the building energy consumption when experimental data. are used as opposed to the case when Mexican standard recommended data are used During the simulations only the. values of thermal convective properties of building materials were modified to compare both cases experimental and. Mexican standard properties data so the diminution on energy consumption of the building that resulted from simu. ENERO juNio 2014 Convective heat transfer coefficients experimental estimation and its impact on. thermal building design for walls made of different Mexican building materials. Table 5 Percentage difference in building energy consumption when experimental data are used. as opposed to the case when Mexican standard recommended data are used. Locality Percentage Difference,Red Brick Tepetate Adobe. Mexico city 22 5 13 9 23 1,Chihuahua 10 3 14 2 12 8. Mexicali 9 9 11 0 9 8,Merida 14 5 16 3 25 0, Figure 8 Simulation results of annual energy consumption for a building with red brick walls in. investigaci n y desarrollo,Mexico City, lations is due mainly to the used value for the thermal convective coefficient Percentage differences were calculated. for the other localities too and the results are shown in Table 4 The fact that the percentage differences are positive. means that the building energy consumption when experimental data are used was less than for the case when Mexi. can standard recommended data are used Therefore we could have an error of 22 5 at least during the process of. thermal design of a building when inappropriate data is used Depending on type of weather as well as solar irradiation. 36 conditions of the locality where building will be constructed an inadequate choice of values for convective heat transfer. coefficients can lead to greater error,concreto y cemento.
5 Conclusions, The main conclusion is that has been used successfully a wind tunnel to obtain heat transfer coefficients for different. building materials This establishes a methodology for other researchers could use it with other building materials. fabricated in their countries, Convective heat transfer coefficients for walls made of different building materials were experimentally measured in. vertical and horizontal position The obtained values are in agreement with theoretical and experimental data reported. Convective heat transfer coefficients experimental estimation and its impact on thermal VOL 5 N M 2. building design for walls made of different Mexican building materials. internationally for low wind speeds 1 5 m s However some of the main contributions of this work are that generates. new experimental data of convective heat transfer coefficients for walls also they were measured for a wider range of. wind velocities 2 10 m s and considering a variety of building materials red brick adobe limestone and concrete. For the measurement of convective coefficients of building materials it is important to consider the humidity content. of the wall because it influences the air temperature readings near the wall surface and therefore distorts the measurement. of the temperature profile Therefore a determination of the thermal boundary layer is not possible. From the simulation results we can deduce that for the cases examined erroneous higher energy consumption is. predicted when Mexican standard recommended data are used in the thermal design process of a building instead of our. experimental data This situation could generate an overdesign of air conditioning equipment and other mistakes that. directly impact on energy consumption in buildings with associated economic and environmental consequences. Acknowledgment, The authors would like thank the financial support of Direcci n General de Asuntos del Personal Acad mico from Na. tional University of Mexico DGAPA UNAM through the project IN 109505 Julio Gonzalez and Ceferino Figueroa. help during the measurements in the wind tunnel Lauro Santiago make the system for acquisition data. References, Almanza R Estrada V Barrientos J 1992 Actualization of the Mexican Republic s global solar irradiation maps. No 543 Engineering Institute Series UNAM in Spanish M xico pp 37. American Society of Heating Refrigerating and Air Conditioning Engineers 2001 Fundamentals Handbook E U A. Chowdhury A G and Suksawang N 2013 Development of Hurricane Resilient Composite Structural Insulated Wall. Systems for Residential Buildings August 1 2012 Florida hurricane loss mitigation program 2012 Annual Report. January 2013, Clear R D Gartland L and Winkelmann F C 2003 An empirical correlation for the outside convective air film.
coefficient for horizontal roofs Energy and Buildings 35 pp 797 811. Corral M Gallegos R and Luna A 2004 Experimental study of construction systems for most typical walls in housing. at warm climate regions Proceedings of XXVIII National Week of Solar Energy ANES Oaxaca City M xico. Davies M Martin C Watson M and Ni Riain C 2005 The development of an accurate tool to determine con. vective heat transfer coefficients in real buildings Energy and Buildings 37 pp 141 145. investigaci n y desarrollo, Hagishima A and Tanimoto J 2003 Field measurements for estimating the convective heat transfer coefficient at. building surfaces Building and Enviroment 38 pp 873 881. Holman J P 1998 Heat Transfer C E C S A First Ed M xico. Lau G E Sanvicente E Yeoh G H Timchenko V Fossa M M n zo C Giroux Julien S 2012 Modelling of natural. convection in vertical and tilted photovoltaic applications Energy and Buildings 54 pp 810 822. Liua G Xuanc J and Parka SU 2003 A new method to calculate wind profile parameters of the wind tunnel boundary. layer Journal of Wind Engineering and Industrial Aerodynamics 91 pp 1155 1162. concreto y cemento, Martynenko Oleg G and Khramtsov Pavel P 2005 Free Convective Heat Transfer Springer The Netherlands. Ministry of Energy 2001 Official Mexican Standard NOM 008 ENER 2001 Energetic Efficiency in buildings shell. of nonresidential buildings Official Daily of the Federation in Spanish M xico. ENERO juNio 2014 Convective heat transfer coefficients experimental estimation and its impact on. thermal building design for walls made of different Mexican building materials. Ministry of Livestock and Hydraulic Resources 1981 Mexican Climatologic Averages 1951 1980 in Spanish. Mirsadeghi M C stola D Blocken B Hensen J L M 2013 Review of external convective heat transfer coefficient. models in building energy simulation programs implementation and uncertainty Applied Thermal Engineering 56. pp 134 151, Rebay M Lachi M and Padet J 2002 Mesure de coefficients de convection par m thode impulsionnelle influence. de la perturbation de la couche limite International Journal of Thermal Sciences 41 pp 1161 1175. Sartori E 2006 Convection coefficient equation for forced air flow over flat surfaces Solar Energy 80 9 pp. Sharples S and Charlesworth P S 1998 Full scale measurements of wind induced convective heat transfer from a. roof mounted flat plate solar collector Solar Energy 62 2 pp 69 77. Nomenclature,A Area of plate in contact with the fluid m2. Gr Grashof number,Nu Nusselt number,Re Reynolds number.
Tf Fluid temperature K,Tw Hot plate temperature K,h Convective heat transference coefficient W m2K. hx Local convective heat transfer coefficient W m2K. k Thermal conductivity of air W mK,q Rapidity of heat transference W. x Distance from the main edge m,Hydrodynamic boundary layer thickness m. t Thermal boundary layer thicknesses m,investigaci n y desarrollo.

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