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Internal thermal conditions and cooling load of the buildings intensely depend on outdoor conditions. Outdoor conditions of the building are not constant during a day, so assumption of constant thermal conditions for indoor is not proper. It seems that using adaptive temperature panels proportional to the variations of outdoor conditions decreases the energy consumption in comparison with constant temperature cooling panels. In this paper the effects of adaptive temperature metal panels are investigated on energy consumption of the buildings and thermal comfort conditions of the occupants. Results of hourly analysis show that, in Tehran with maximum relative humidity of 65%, in buildings with north and south orientations, we do not need cooling systems in nearly 10 hours of a day, in remains we can provide thermal comfort conditions by radiant ceiling cooling panels with natural ventilation and without any anxiety about condensation on the panels. However, in buildings with east or west orientations we do not need to air conditioning and cooling systems in only 7 hours of a day. In these buildings condensation is inevitable in some intervals of system operation during a day. In these periods, we can decrease the probability of condensation by using mechanical ventilation. Results also demonstrate that cooling energy consumption is decreased of 29 to 45% depending on the orientation of building.

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Radiative heat transfer must be considered in retail refrigerators with glass doors. Some methods have been proposed for reducing radiative losses, like usage of double glased windows filled with argon or other types of transparent material with low emissivity in infrared band. For evaluation of thermal radiation in commercial refrigerator compared to infiltration loss, thermal conduction and facilities loss, a three dimensional model has been developed. In this model all wall surfaces are isothermal and evaporator with specific temperature located in roof. The radiative properties of glass are considered as actual. The results show that decreasing internal temperature of cabinet incentive radiation losses. These losses are almost independent of window surface temperature. Increasing of emissivity factor of evaporator, causes increasing of thermal radiation flux of evaporator which can be used in design improvement. Radiation flux of each surface have been compared with convection flux. This comparison show the importance of covering windows in unutilized times.

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In cold season, draught or undesired local cooling sensation in ankle and neck region is one of the most frequent cases of complaint of the occupants. A person who are subjected to draughts in winter, tend to elevate the room temperature to counteract the cooling sensation, thereby increasing the energy consumption. In naturally ventilated buildings, draught is due to windows and other cold surfaces in the room. Draught is dependent on the air speed and on the magnitude of turbulence intensity. Serious draught complaints can often occur at mean speeds lower than those recommended by standards when turbulence intensity is high. So investigation of undesired local cooling in floor heating systems is very important, although in these systems the mean air speed is not significant. In this paper, the effects of size of window on draught are investigated in floor heating systems. Results demonstrated that, undesired thermal discomfort caused by local cooling phenomenon in floor heating systems is negligible. At the end, the probability of occurrence of local cooling phenomenon in floor heating systems is compared to vertical heating panels. Thereby the floor heating systems are more effective than the vertical heating panels in aspect of thermal comfort and energy consumption.

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- The effect of panel height on performance of ceiling radiant cooling system has been studied. Investigation has been done by employing solution of conservative equations, together with the radiant and thermal comfort equations. Calculation is performed for the typical hottest day of Tehran. Vapour condensation is one of the most important problems whit these systems. Therefore effect of panel height on condensation has been also studied, in a residential place with several different ranges of ventilation rate. The results show that appropriate design of the panel height can significantly reduce the rate of condensation.

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There is a full connection between the electrochemical quantities of a fuel cell and the curves of the temperature and primary materials at the catalyst region. These quantities are strongly linked to the mass and heat transfer phenomena in the other regions. In the present paper, the lattice-Bolzmann method, as a microscale model with good computational capabilities in the problems such as the fuel cell, has been utilized to simulate the fluids flow and heat transfer in a two-dimensional cross section of a proton exchange membrane fuel cell including the channel, bipolar plate, gas diffusion layer and catalyst of the cathode and the electrochemical characteristics in the catalyst layer have been analyzed. By representing a method for estimation of the changes in the concentration along the channel, the serpentine arrangement has been modeled. The results reveal the essential role of the bipolar plate on the quantities at the catalyst layer.

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Internal immobilization of fractured parts of bone depends on the drilling of fracture site and screw fixation of implanted devices to the bone. During drilling, the temperature may rise allowable temperature of 47°C and causes irreversible thermal necrosis. This study is concerned with methods of drilling to determine the best processing condition to minimize the osteonecrosis. Drilling tests were performed with two drilling techniques: conventional, and high speed drilling on the bovine femur and increase of temperature in drilling site, duration of temperature raise and thrust force were measured. The result for conventional drilling shows that in all processing conditions, the generated heat is over the allowable limit, which makes thermal necrosis inevitable. On other hand, it was found that increase of cutting speed of drill bit to 7000 rpm, leads to considerable decrease of thrust force and increase of heat dissipation with chips, simultaneously and leads to decrease of local temperature raise in drilling site. But with more increase of rotational speed of drill bit, because of not sensible change in drilling force and considerable increase of friction between chips, drill bit body and drilled hole, amount of temperature elevation is increased.

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The main goal in design of heating, cooling and air conditioning systems is to provide thermal comfort. In present study, performances of radiant cooling ceiling system and stratum ventilation have been studied separately and together to provide the overall and local thermal comfort conditions. Therefore, using computational fluid dynamics, indices PMV (predict mean vote) and PPD (predict percent dissatisfied) has been studied as two overall thermal comfort parameters. Also, vertical temperature gradient and draft risk has been studied as two indices dissatisfaction of¬¬ local thermal comfort. According to the results of this study, combining stratum ventilation and radiant cooling ceiling caused a uniform distribution of overall thermal comfort conditions. Also vertical temperature gradient decreases and there is no draft risk. Therefore combining stratum ventilation and radiant cooling ceiling is introduced as the new Strategy and application ability to provide the proper conditions to achieve overall and local thermal comfort.

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In this article, after the design of a CCHP system for office buildings in Tehran, a mathematical analysis of the CCHP system following thermal demand management in comparison to separate system is presented. In order to have a comprehensive evaluation of the performance of the CCHP system, four criteria including primary energy saving, CO2 emission reduction, operational cost reduction and rate of return are employed for a typical office building in Iran. Also a sensitivity analysis of rate of return based on increasing natural gas and electric price is performed. Results show that the CCHP system with selling electricity to grid has much better performance than separate system when all of the criteria are involved. Also without selling electricity to grid the CCHP system achieves more benefits than separate system but these benefits are less than the benefits of the situation with selling electricity to grid. The sensitivity analysis shows that in the situation with selling electricity to grid, with increasing natural gas and electric price the ROR will be increased but in the situation without selling electricity to gird, with 40% increase in natural gas price the ROR will become less than Interest Rate.

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The problem of bone fracture in medicine due to an accident, aging or diseases, has existed from times when humans started to work and activity. The process of bone drilling is an essential part of internal immobilization in orthopaedic and trauma surgery. The force required to chip formation in drilling process, resulting in heat generation in drill site that leads to the occurrence of thermal necrosis. This research experimentally investigates the effect of ultrasonic vibration on thrust force in drilling of bovine femur bone. This method induces high-frequency and law-amplitude vibration in the feed direction during cutting, and has the potential to spread tiny cracks in bone and decrease friction leading to reduce of cutting forces and also increase the speed of chip disposal leading to reduction of machining forces, totally. Experimental results demonstrate that ultrasonic assisted drilling of bone produces fewer thrust force than conventional drilling and rotational speed of 1000 rpm is the optimal speed to achieve at minimum thrust force for all feed rates. Moreover, this method is due to the force independence of the feed rate in the rotational speed of 1000 rpm, is applicable in orthopedic surgery.

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In this article, a mathematical analysis of a CCHP system following electrical demand management and thermal demand management in comparison to separate heat and power system for an office building in Tehran is presented. In the thermal demand management, two modes including with selling electricity to grid and without selling electricity to grid are investigated. In order to have a comprehensive evaluation of the performance of the CCHP system, four criteria including primary energy saving, CO2 emission reduction, operational cost reduction and rate of return are employed for a typical office building in Iran. Also the AHP method is used to specify the best operation mode of the CCHP system when all of the criteria are involved. Results show that from the energy and environmental viewpoints, the CCHP system following thermal demand management with selling electricity to the grid is the best operation mode. But the CCHP system following electrical demand management has the maximum rate of return. For the all of the operation modes, the CCHP system has lower operational cost than SHP system throughout the year. From an integrated view point, the CCHP system following thermal demand management with selling electricity to the grid is the most attractive option.

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In the present paper, cooling performance of a hybrid system of air underground channel and direct evaporative cooler to provide cooling load for residential spaces was investigated in summer and its performance evaluation was studied for Tehran,Iran. The study was performed in hottest day of the year in Tehran which has hot and dry condition. At first, mathematical modeling of the hybrid system components was developed then by using the mathematical modeling, outlet air temperature distribution of any component of the proposed hybrid system was calculated. The obtained results imply that air temperature drops about 10°C in underground air channel and 6°C in direct evaporative cooler. andAccording to the obtained temperatures and thermal comfort zone, it was found that the hybrid system is capable in the hottest days of the year to provide thermal comfort for the residental occupants in Tehran. Then, by calculation of the system efficiency, it was found that the efficiency is more than 1 which indicate high performance of the hybrid system. Eventually by comparison between efficiency of the hybrid system and direct evaporative cooler it was found that efficiency of the hybrid system is 45 percent more than direct evaporative cooler. Also the system efficiency is higher than conventional mechanical systems efficiency and it is eco-friendly because of the system is passive. Thus according to present work, the proposed hybrid cooling system could be a suitable alternative for conventional HVAC systems.

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Compliance mismatch is one of the reasons of the coronary artery bypass graft (CABG) failure. The purpose of this study is to investigate the effect of compliance mismatch on the End to Side bypass graft. In order to model non Newtonian behavior of the blood flow, the Carreau–Yasuda model was employed and the graft and artery wall was assumed to be isotropic and modeled as a linearly elastic. In this study also the effects of blood rheology and wall distensibility on the wall shear stress distribution and velocity profile were investigated. The results of the simulation show that the maximum deformation occurs in the critical position of graft-artery junction and compliance mismatch cause smaller wall deformation in comparison to the cases in which the materials of the graft and artery are the same which leads to a higher intramural shear stress in graft-artery junction. The anastomotic wall deforms in a way that always tends to separate the graft and artery. Wall shear stress distribution on the bed centerline and the toe of the bypass graft indicates that the differences between the homologous and non-homologous material case are visible only when the internal pressure is lower than the external one. In the distal location of the artery after the toe of the anastomotic, the values of wall shear stress in the homologous material case are lower than the non-homologous material one.

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In the present study the validity of two conventional Nusselt number definitions were investigated using analytical and numerical methods for convection heat transfer in a pipe partially filled with porous media. The first definition is denoted as Nu_1 (x)=(2R(∂T/∂r)_(r=R))⁄((T_w-T_m (x)) ) and the second one follows: Nu_2 (x)=(2Rq_cond^'')⁄(k_ref (T_w-T_m (x)) ). The Nusselt number resulted from these two definitions was investigated analytically in a pipe for different porous configurations. The results show that the calculated Nusselt numbers using these two definitions, are different in porous media boundary arrangement. In the first definition, the heat transferred to the fluid flowing thorough the porous media is not considered, so the Nusselt number which is calculated via this definition cannot demonstrate the physics of heat transfer phenomenon properly. The boundary arrangement of porous in a pipe with turbulent flow is simulated numerically and the Nusselt number was calculated by the two definitions. The calculated Nusselt from the first definition shows that the Nusselt number increases as the heat conduction coefficient of porous grows which is not a proper expression of physics of this problem. So, the first definition of the Nusselt number is not proper for porous boundary arrangement in a pipe. However, with investigating of the second definition, it is seen that with increasing the porous heat conduction coefficient, the Nusselt number increases which this result is physically valid; therefore the second definition is more appropriate for the porous media boundary arrangement.

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Development and application of high-speed underwater vehicle is the cause for considering super-cavitating flows by many researchers. Frictional drag decreases and vehicle’s velocity increases due to cavity generation. The objective of the present research is to find the coefficients of an optimized equation to estimate cavity length around a submercible vehicle equipped with a wedged-shaped cavitator which has important practical applications. For this purposes, the super cavitation phenomena has been simulated numerically around three bodies with different geometry. At first stage, to validate the results of numerical simulation of present work a well-established experimental result of a cylindrical body with hemispheric cap is used for comparison. This comparison is used for parameters effecting numerical method, turbulence flow model and mass transfer model. As this comparison is confirmed, the simulation is continued at second stage for super cavitation phenomena initiation around a wedged-shaped cavitator with two 15 and 45 degrees angle. At third stage, the super cavitation flow is analyzed around a submersible body equipped with a wedged-shaped cavitator. The cavity length and related coefficients are obtained for three cases using different cavitation numbers. The developed equation is similar for all cases with different coefficients. The averaged Navier-Stokes equations are solved in transient case using finite volume method. Different mass transfer models with turbulent flow models are used at different conditions. The numerical results are validated with experimental results of other researchers. Comparison is encouraging.

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In the present study, a new analytical model for Earth to Air Heat Exchanger is presented. To this end, transient energy equation is solved employing duhamel's theorem and the soil temperature distribution is achieved with the concept of G function. Then, the outlet temperature will be achieved by solving the energy equation along the length of heat exchanger. In comparison to previous models, the present results are in better agreement with those obtained experimentally. Parametric investigation and feasibility study of this system in Tehran has been made using this analytical model for summer season with two different input temperatures. Parametric investigation showed for each mass flow rate, the corresponding optimum diameter is gained. It is observed that optimum diameter is a function of mass flow rate and operation time and independent of soil and input temperature of heat exchanger. For major mass flow rate supply, utilization of heat exchangers with minor mass flow rate is suggested; accordingly the temperature of heat exchanger is decreased. The depth and distance between heat exchangers can be calculated by the present model. It is also revealed this system can solely supply thermal comfort in continuous summer operation for cities with cold climate and low annual average temperature.

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In present study, heat transfer in double-tube heat exchanger filled with metal porous material has been investigated. In contrast to the most of previous studies, fluid flow is considered turbulent in heat exchanger which is in a good agreement with the practical performance of these exchangers in the industry. Fluid flow and heat transfer equations have been discretized on a collocated grid by the means of finite volume method with simple algorithm. Discretized equations are solved with a numerical program in FORTRAN language in order to study the effect of porous material parameters and Reynolds of fluid flow on the heat transfer in double-tube heat exchanger. According to the results and analysis of porosity in the range of 0.8 to 0.95 as well as pore diameter of 1 mm up to 6 mm and diverse types of porous material, it is observed that the decrease in porosity, the increase in pore diameter and use of copper porous material (with high heat conduction coefficient), increase heat transfer. In the best case, overall heat transfer coefficient enhances up to 7 times. Moreover, the results reveal that the heat transfer enhancement ratio have no distinct difference with changing Reynolds number of turbulent flow in the range of 10000 to 80000. Performance evaluation criteria, which investigate the effects of pump lost power and thermal power, depicts that with using porous material the value of the pump lost power is of major importance which can be decrease by increasing the porous pore diameter.

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This paper presents a new analytical model to study the thermal behavior of borehole heat exchangers (BHE) in short time periods. Transient heat transfer considered inside the borehole and at the ground around the borehole, transient heat conduction is considered inside the borehole and ground around the borehole. For this purpose, the analytical solution has been developed in two stages. First, a new analytical equation is provided for the short-time thermal response of the BHE (dimensionless G-function). In the second phase, the outlet temperature calculation using the G-function is described. Inside the borehole, the analogy between thermal and electrical conduction is used for derivation heat balance equations. For this purpose, a new equivalent thermal network for modeling of the heat transfer inside the borehole is developed. In ground around the borehole, the conduction equation in the radial direction is considered. The governing equations are solved by Laplace transform. Finally, the mean fluid temperature and short thermal response of the BHE is computed. Then in the second phase, the outlet temperature in the on and off times of the system is calculated using the G-function. The solution of the proposed analytical model is compared with experimental measurements. Results show that the outlet temperature of the analytical model matches very well with the reference experimental measurements.

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The correct placement of supply air inlets and pollution extraction outlets play an important role in increasing indoor air quality and reducing the amount of pollution in enclosed car parks. In this paper the effect of exhaust locations, exhaust height and parking dimensions on indoor air quality of car park is investigated with numerical simulation. For this purpose conservation equations are solved with openFoam. For validation, air flow and pollution is simulated in a simple car park and compared with experimental results. In the next section, the effect of exhaust vent locations on increasing indoor air quality is investigated and is compared with other solutions. The result of numerical simulation indicates that, if inlets and exhausts are located in end sides of car park and if exhaust vent locations are in the optimized height, the indoor air quality in the car park is increased.in this paper, the graph of CO concentration in different heights is explained and by using it, the optimum range for exhaust vent locations is proposed. Moreover the standard criteria for using jet fans is expressed and the results showed that, for ventilation of car parks with length more than criterion, jet fans should be used.

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Cavity length estimation is important as supercavity condition is generated. The cavity length is function of cavity number and is calculated by relations deduced from experimental results which are different from each other and are not driven from analytical approaches. Literature survey shows that correlations based on cavity length in relation with Reynolds and cavity numbers have not been attempted. The present work purpose is to estimate analytical based relations for cavity length with respect to mass transfer, continuity and momentum conservation equations. This effort which has been conducted by order of magnitude method resulted in three relations. The first analytical based relation calculates cavity length versus cavity number. The obtained relation shows that cavity length is proportional with the inverse square root of cavity number. The second analytical relation calculates cavity length in respect to Reynolds number. It shows cavity length has proportional relation to Reynolds square root. The third analytical relation considers cavity number in respect to Reynolds number. The third relation shows that cavity number has inverse relation to Reynolds number. Unknown coefficients values of the relations obtained through comparison with the already existed experimental results. These analytical relations which are appropriate alternative to experimental based relations estimate cavity length in respect to cavity and Reynolds number.