CFD investigation of effect of nanofluid filled Trombe wall on 3D convective heat transfer

A numerical investigation was carried out on the effect of carbon nanotube(CNT)-water-nanofluid-filled Trombe wall on heat transfer and fluid flow inside a 3 D typical room.Time depending governing equations are considered with applying hot temperature at the left surface(collector) of the Trombe wall.The left wall(glazing) of the room and a square part(window) at the right wall are considered at cold temperature.The effects of Rayleigh number and the nanofluid volume fractions and the Trombe wall height on the temperature field,flow structure and heat transfer rate,are studied.The results show that the addition of nanoparticles and the increase of the Trombe wall height,enhance the heat transfer considerably and affect the flow structure and the temperature field.

Preparation of Palygorskite-based Phase Change Composites for Thermal Energy Storage and Their Applications in Trombe Walls

Palygorskite/paraffin phase-change composites were prepared by the combination of purified palygorskite clay and sliced paraffin. Then, this composite was used in the Trombe wall to improve its energy storage ability. Further, its energy storage ability was compared to that of ordinary concrete wall through contrastive test. The experiments show that palygorskite clay is a type of clay mineral with strong adsorption ability, and the purity of natural palygorskite clay can reach up to 97.1% after certain purification processes. Paraffin is well adsorbed by palygorskite, and the test results show that the optimal adsorption ratio is palygorskite： paraffin = 2：1（mass ratio）. Palygorskite/paraffin phase change composites can be obtained by using palygorskite as the adsorbing medium to adsorb paraffin. The composite materials exhibit good heat storage（release） performance, which can store heat with increasing environment temperature and release heat with decreasing temperature. This property not only increases the inertia to environment temperature change, but also promotes the energy migration in different time and space, thus achieving a certain energy-saving effect. The application of palygorskite/paraffin phase change composite materials to the Trombe wall can significantly reduce the fluctuation of indoor temperature and enhance the thermal inertia of indoor environment. From the aspect of energy storage effect, the Trombe wall fabricated using PCMs is significantly superior to the concrete wall with the same thickness.

Numerical Study of Mixed Convection in a Photovoltaic Trombe Wall Channel Coupled with a Solar Chimney Integrated into a Building for Habitats Passive Cooling

The solar chimney can generate airflow through the living space of the building to provide cooling. Hence, solar energy represents the best renewable, environmentally friendly source of energy that can be used for heating and cooling of houses. The present paper reports the numerical study of the performance of the mixed convection in the associated hybrid Photovoltaic/Thermal chimneys integrated into building for natural habitat ventilation. The front side glass plate of the chimneys is heated by a non-uniform daily solar radiation flux. Air is considered to be the cooling fluid. The stream fucntion-vorticity formulation with a finite difference numerical discretization solution scheme has been adopted. The system of algebraic governing equations is solved by Thomas algorithm method. The aim of the present paper is to study and to predict the dynamic fields and particularly of the mass flow rate of the air thermosiphon drawing in the associated hybrid Photovoltaic-Thermal chimneys integrated into a building for passive cooling in the habitats. The effects of the governing parameters, namely Reynolds number (30 ≤ Re ≤ 200), Rayleigh number (103 ≤ Ra≤ 105), the integrated chimney width on the fluid flow and the heat transfer characteristics, are studied in detail. The local Nusselt number, streamlines, isotherms, PV cells electrical efficiency and the outlet velocity at the top of the channels are the results represented versus the above controlling parameters.

Trombe walls with porous medium insertion and their influence on thermal comfort in flats in Cusco,Peru

The Trombe wall is a passive indirect heating system which should be used in Cusco,Peru to improve thermal conditions against the typical frosts and low temperatures during winter in the high Andean regions.Due to this problem,the use of a modified Trombe wall with insertion of porous medium is proposed to improve thermal comfort in flat buildings in Cusco.This research aims to analyse and compare the performance of dwellings without Trombe wall,with traditional Trombe wall,and with Trombe wall with glass and plastic pellets insertion in thermal comfort improvement.Autodesk■CFD was used to simulate and analyse the system.The simulation was performed with three prototype flats(55 m^(2),75 m^(2) and 95 m^(2))for six months of the year.From the results obtained,the level of thermal comfort in the traditional scenarios is low with an average PMV of-1.86,in the scenarios with Trombe wall is good and in the scenarios with Trombe wall with insertion of porous medium is slightly better than the previous one,reaching an average PMV of+0.10 and a temperature of 21.90℃.The study carried out is important because it represents an efficient eco-sustainable heating alternative that improves the thermal comfort sensation in houses during the coldest months of the year.

Thermal comfort in a building with Trombe wall integrated with phase change materials in hot summer and cold winter region without air conditioning

Trombe wall and phase change materials(PCMs)are two effective ways to regulate indoor thermal comfort.However,Trombe wall surfers from overheating in summer and PCMs suffer from low heat transfer rate caused by the limited thermal conductivity.To compensate the shortcomings of the two methods,this paper proposed a Trombe wall system integrated with PCMs.Based on a light-weight building envelope in Changsha,China,the thermal comfort of 10 kinds of Trombe wall systems with PCMs with a melting temperature of 18-28℃ were studied.Taking the integrated indoor discomfort duration(I_(D)),integrated indoor discomfort degree-hour(I_(DH)),indoor air temperature(T_(in)),PCM liquid fraction(γ)and heat flux across wall(q)as evaluation indexes,the indoor thermal comfort was assessed in hot summer and cold winter region.Results show that the Trombe wall helped PCMs complete the phase change process effectively.Trombe wall with PCM25 next to the wall inner surface possessed the lowest annual I_(D) and I_(DH),as 2877 h and 12,974℃·h,respectively.Compared with the values in a traditional building,the I_(D) and I_(DH) were reduced by 7.01% and 14.14%.In order to give full play to the heat storage and heat release of the Trombe wall with PCMs,PCMs with phase change temperature 7℃ lower than the peak ambient temperature in summer or 8℃ higher than the winter night temperature was recommended according to regional climate conditions.

A Novel Combined Trombe Wall System for Village Houses in Cold Regions of China

Trombe walls have significant energy-saving features and are therefore of great interest to researchers.However,additional research about the Trombe wall is needed to reduce indoor temperature fluctuations and to improve thermal behavior under different climatic conditions.A new Trombe wall system was proposed which uses Venetian blinds and a basement.The field tests were conducted to compare the thermal performance of four types of rooms:(ⅰ)no Trombe wall(control),(ⅱ)classical Trombe wall(TW),(ⅲ)Trombe wall with Venetian blinds(TW+VB),and(ⅳ)Trombe wall with Venetian blinds and a basement(TW+VB+B).The field measurements were conducted during the winter near Shihezi City in northwest China.The objective of this study was(ⅰ)to evaluate the thermal performance of a novel Trombe wall system under different operation conditions,and(ⅱ)to confirm the optimal angle of Venetian blinds during the heating period.The results demonstrated that the TW+VB+B system effectively reduced indoor temperature fluctuations after sunset.Furthermore,during the daytime,the average air temperatures in the test rooms were 13.6℃higher in the TW+VB+B system than in the control.The average temperature at the air outlet in the TW+VB+B system was 4.9℃higher than that in the TW+VB system during the daytime,and the average predicted mean vote(PMV)of the test room was 1.02 units greater in the TW+VB+B system than in the control.The thermal efficiency remains in the range of 40%-65%when the Venetian blind angle was set at 45°.In conclusion,the experiment results showed that the TW+VB+B system can not only reduce indoor temperature fluctuations but also improve thermal performance in winter.Both the heating energy consumption in buildings and pollutants emission in the environment were lessened through the application of this passive solar energy-saving technology.Therefore,this can provide valuable insights for improving the thermal performance of the novel Trombe Wall system in such village houses.

Optimization Study of Active-Passive Heating System Parameters in Village Houses in the Southern Xinjiang Province

Aiming at the problems of large energy consumption and serious pollution of winter heating existing in the rural buildings in Southern Xinjiang,a combined active-passive heating system was proposed,and the simulation software was used to optimize the parameters of the system,according to the parameters obtained from the optimization,a test platform was built and winter heating test was carried out.The simulation results showed that the thickness of the air layer of 75 mm,the total area of the vent holes of 0.24 m^(2),and the thickness of the insulation layer of 120 mm were the optimal construction for the passive part;solar collector area of 28 m^(2),hot water storage tank volume of 1.4 m^(3),mass flow rate of 800 kg/h on the collector side,mass flow rate of 400 kg/h on the heat exchanger side,and output power of auxiliary heat source of 5∼9 kWwere the optimal constructions for active heating system.Test results showed that during the heating period,the system could provide sufficient heat to the room under different heating modes,and the indoor temperature reached over 18°C,which met the heating demand.The economic and environmental benefits of the system were analyzed,and the economic benefits of the systemwere better than coal-fired heating,and the CO_(2) emissionswere reduced by 3,292.25 kg compared with coalfiredheating.The results of the study showed that the combinedactive-passiveheating systemcouldeffectively solve the heating problems existing in rural buildings in Southern Xinjiang,and it also laid the theoretical foundation for the popularization of the combined heating systems.

A Study of Passive Solar House Design

This paper deals with the investigation of the principles of passive solar house design, passive solar systems, and techniques for solar house design. It is expected that the research is to be of momentous significance to the design and construction of passive solar house, and may make contribution to the massive energy efficient housing construction in our country.

Numerical Study of Classical and Composite Solar Walls by TRNSYS

The laboratory LAMTI has worked for several years on the study and the optimization of the thermal performances of passive solar walls like solar Trombe wall. These components of the buildings envelope have very complex behaviour because they are the seat of various coupled heat transfers modes and are subjected to the random variations of the meteorological parameters. Using the finite difference method （FDM） and starting from experimental results recorded during several years, a simulation model was developed and validated concerning the ＂composite＂ Trombe wall. In order to make this work more accessible to the community of the heat engineers, it appears interesting to build a simulation model which can be integrated into the library of elements of the TRNSYS software. A ＂Type＂ was thus carried out and the results obtained compared with those of the FDM model. In this work we compare the obtained results with these two numerical ways. The assumptions and the results of simulations are also confronted with those of an existing module in TRNSYS （Type 36） established for the ＂classical＂ Trombe wall. The study shows that the models that we developed are very precise and that certain assumptions must be used with a lot of precautions. The advantages of the composite Trombe solar wall compared to the Classical Trombe wall are highlighted for cold and/or cloudy climates.