Open Access Original Research Article

Numerical Study of the Air Conditioning of a Room by a Two-phase Thermosyphon Loop Using Meteorological Data from Mamou (Guinea)

Abdoulaye Diallo, Xavier Chesneau, Idrissa Diaby, Djanfar El-Maktoume

Physical Science International Journal, Page 1-20
DOI: 10.9734/psij/2021/v25i1130289

This paper presents a numerical study of the air-conditioning of a room by a two-phase thermosyphon loop using meteorological data from the Mamou region (Guinea). The room is composed of a rectangular roof and a passenger compartment in the form of a parallelepiped. In addition, the air-conditioning unit that operates with methanol is composed of an evaporator, a condenser, a riser and a downcomer. The heat transfer modelling governing the habitat model and the air conditioning loop is based on the nodal method. The coupling of the system is done by convective transfer between the internal air of the habitat and the surface of the evaporator. The equations are solved by the implicit finite difference method. Thus, this resolution made it possible to determine the influence of the parameters on the model. This work presents results of the habitat with and without the air-conditioning loop for typical days in March of Mamou. These results show that the use of the air conditioning loop can contribute to lowering the internal air temperature. The value of the maximum temperature of the indoor air of the habitat with the air conditioner is about 299 K while that of the air without air conditioner is about 303 K. The variation of parameters such as temperature, wall thickness, incident solar flux, air exchange rate and evaporator surface has a significant impact on the operation of the air conditioner and on the temperature of the conditioned room. A low wall thickness or a high air exchange rate contributes to the temperature increase in the room. For a wall thickness of 10 cm, 15 cm or 40 cm, the air temperatures are 301.5 K, 297 K and 296.9 K respectively. However, for a habitat without an air conditioner the temperature is 303 K when the wall thickness is 15 cm.

Open Access Original Research Article

Modeling Heat Transfers in a Typical Roasting Oven of Burkina Faso

David Namoano, Abdoulaye Compaoré, Ousmane Ouédraogo, Gaël Lassina Sawadogo, Drissa Ouedraogo, Serge Wendsida Igo

Physical Science International Journal, Page 21-33
DOI: 10.9734/psij/2021/v25i1130290

This work concerns a numerical study of heat transfers in a typical roasting oven in Burkina Faso. The numerical methodology is based on the nodal method and the heat transfer equations have been established by performing a heat balance on each node. The equations obtained were then discretized using an implicit finite difference scheme and solved by the Gauss algorithm. The numerical results validated by the experiment show that the heat transfers within the oven are mainly influenced by the gas flow, the ambient temperature, the flame extinction time and the wind speed. Increasing gas flow rate and increasing ambient temperature increase the oven cavity temperature. The increase in wind speed causes a significant drop in the oven cavity temperature after the first 15 minutes of operation. Beyond a wind speed of 3m/s, we observe a convergence of the oven cavity temperatures towards a limit value. Regardless of the time the flame is extinguished, the gas flow rate, the ambient temperature and the wind speed, the oven cavity temperature drops rapidly towards the ambient temperature.

Open Access Original Research Article

Form Space: A New Understanding of Space in the Theory of Relativity [Shorter] Form Space in the Theory of Relativity

Runsheng Tu

Physical Science International Journal, Page 34-46
DOI: 10.9734/psij/2021/v25i1130291

What is the physical mechanism by which space contracts due to motion? Theory of relativity is reluctant to answer this question. The reason is that this physical mechanism threatens the principle of relativity. The side effects of theoretical mathematical form system have not been reported. This side effect is mainly the proliferation of mathematical formal concepts (and/or conclusions) that violate mathematical logic and do not correspond to facts. Through a series of thought experiments, it reveals the spatial difficult related to concept proliferation that have never been reported in the special theory of relativity — There is a logical contradiction in the concept of "when mutual observation, always is observed ruler shortening". The existence of such contradictions or spatial difficulties is a side effect of the above. According to the relation of mass-velocity of relativity and quantum mechanics, the conclusion that the moving object shrinks in all directions due to the motion is deduced. Deeper understanding of space time is provided and it is exposed that the areas of further research topic on the space time continuum and their role in the proper understanding of relativity theory.

Open Access Original Research Article

Experimental Results of Cooking Tests in the Dry Season in a Subequatorial Country Using a Box-type Solar Cooker with an Inclined Receiving Surface Fitted with a Flat Reflector

D. Soro, M. Sidibé, K. Emmanuel Kone, Amal Bouich, B. Marí, Siaka Toure

Physical Science International Journal, Page 47-55
DOI: 10.9734/psij/2021/v25i1130292

In this work, a box-type solar cooker with an inclined receiving surface with a flat reflector is designed and manufactured with less expensive materials available in the local market. Cooking tests were carried out during the great dry season in the south of Côte d'Ivoire, a subequatorial country, to assess the performance of the system. During these tests, the illumination (E) and temperatures at different places of the solar cooker were measured. The absorber temperature (Ta) rose above 100°C, which made it possible to cook eggs and yam stew with fish. The results obtained for these tests are satisfactory and very encouraging because the cooker produced allows sufficient temperatures to be reached for healthy cooking of food.

Open Access Original Research Article

Characterisation of the Vertical Wind Profile According to the Stability Classes of the Atmosphere in Conakry, Guinea

Kalil P. Mathos, Hagninou E. V. Donnou, Guy H. Hounguè, Basile B. Kounouhewa

Physical Science International Journal, Page 56-82
DOI: 10.9734/psij/2021/v25i1130293

The characteristics of the vertical wind profile and the wind potential study on the Conakry site for each atmospheric stability class were investigated in this study. Wind speed and air temperature data recorded over the period from January 2001 to December 2019 at 10 m and 50 m above the ground at daily (50 m) and hourly (10 m) scales were used. The wind shear parameters were determined from the logarithmic and power law. Based on the Newman and Klein wind shear model, a new formulation of this parameter was proposed as a function of the Obukhov length at order 2 and calibrated from the measurements using the simplex algorithm of Nelder and Mead. From the Weibull parameters obtained for the stable and unstable period of the atmosphere, the available wind potential at Conakry was estimated from 10 m to 80 m. The results indicate that the annual average of the ground roughness length is 1.7 x 10-2 m. The annual average of the ground friction velocity is 0.19 m.s-1. The atmosphere remains stable at the Conakry site from 09 p.m. to 10 a.m. and unstable from 10 a.m. to 09 p.m. The proposed wind shear formulation gives a better estimation of the wind speed in function of altitude with the lowest values of RMSE and MAE (4.5x10-4 ; 3.8x10-4) m.s-1 in stable and unstable periods (0.09 ; 0.07) m.s-1 compared to some models found in the literature. The mean annual wind shear coefficient in stable period is 0.26 and in unstable period 0.28. The annual mean shape parameter from 10 m to 80 m above ground in stable period is between 1.25 and 1.64, and during unstable period, it varies from 1.55 to 2.07. The annual mean scale parameter at 10 m and 80 m above ground is   (3.9; 7.10) m.s-1 (unstable atmosphere) and (2.45; 4.41) m.s-1 when the atmosphere is stable. The annual average of the energy production under a convective atmosphere at 10 m and 80 m is estimated at 72 W.m-2 and 301 W.m-2 respectively. During the night cycle, this annual production varies from 28 W.m-2 (10 m) to 93 W.m-2 (80 m). Based on these results, the Conakry site is suitable to host medium-sized wind power plants for electricity and water production.