With an increase in length of pipe, both pressure drop and thermal performance increase. The corresponding values of friction factor were calculated by using. The decrease in air flow velocity and increase in diameter of pipe results in decrease in pressure drop. No slip condition with smooth wall was assumed at the inner surface of the pipe. The value of Prandtl number for thermo-physical properties of air.7 C was calculated.717. ( 8 ) and ( 17 ) that both NTU and p are proportional to the length of the pipe, and the designer can use NTU/ L and p/L as the main performance measures to determine the required length of pipe for design purposes. Analysis and modeling of eahe, the development of the model of the eahe system involves the use of basic heat transfer equations. To evaluate the overall thermo-hydraulic performance of a specific configuration, the J-factor, introduced by De Paepe and Janssens ( 2003 ) was used. It was observed that Nusselt number increases with increase in Reynolds number. Zhang ( 2009 ) presented in his PhD thesis that in conventional earth-to-air heat exchanger (etahe) systems, it is typical to have buried ducts with 10 cm h D h) are at an order of magnitude of 100. The combination of pipe length and diameter has to be optimized. A longer pipe of smaller diameter buried at a greater depth and having lower air flow velocity results in an increase in performance of the eahe system. So, it is better to have several tubes of small diameter over which the flow rate is divided. Outlet boundary conditions, in a subsonic flow regime, the relative pressure at the outlet of the eahe pipe was defined as equal to zero atm. In this paper the NTU method is used. (6) If a pipe of infinite length ( A ) is used, option
the air will be heated or cooled to the wall temperature. Since the correlations were all derived for fully developed turbulent air flow, ideally, they are expected to yield similar values for the same operating condition. This may be due to different experimental conditions, which were adopted to derive the correlations, for example, the surface roughness of the experimental ducts. The variation in earthair heat exchanger effectiveness as a function of number of transfer units is shown in Fig. This result in a changing Reynolds number,. The large discrepancies indicate that a suitable correlation has to be selected if one uses any of the existing models to simulate the performance of an eahe system. The thermodynamic properties (density and specific heat capacity) and transport properties (dynamic viscosity and thermal conductivity) of air were to be defined at static temperature of air at inlet.
A large number of pipes are beneficial. Bhopal, it is defined for mean soil properties. And it must be known by the designer so that the selection of size and number of pipes can be initiated. The mass flow rate of air is an important parameter. The use of basic heat transfer equations is more suitable to determine the geometrical dimensions of the system. TTmAmathrms expleftzleftfracpi 365alphasrightfrac12right cos leftfrac2pi alphasrightfrac12rightright 2 shiza papers where.
Simulation OF, earth -TO-, aIR heat exchanger.Building, Civil and Environmental.PDF, earth air heat exchanger system can be used effectively to reduce heat energy demand of buildings in cold and dry winter weather.
exchanger The author has developed a onedimensional model of the eahe system. T in C at inlet were to be defined. L The relative gain in effectiveness is very small after the value of NTU becomes more than. The temperature on the surface of the pipe is uniform in the axial direction.
The Prandtl number is given by: P_rfracmu c_mathrmpK (16) where c p is the specific heat of air (J/kg-K) Results and discussion The thermo-physical properties of materials used in design calculations of eahe are shown in Table 1 (Bisoniya.Assuming that the internal surface of PVC pipes used in the eahe system is smooth, the N u correlations given by De and Janssens ( 2003 ) can be used to simulate the performance of the system.Once the design output is fixed, the heat transfer equations are manipulated to meet the desired output in terms of input parameters.