ANFIS modelling of a natural convection greenhouse drying system for jaggery: an experimental validation

The aim of the current research work is to generate an adaptive-network-based fuzzy inference system (ANFIS) model so as to forecast the jaggery temperature, the greenhouse air temperature and the moisture evaporation for drying of jaggery inside the greenhouse for natural convection mode. The experiment was conducted separately for 0.75 and 2.0 kg of jaggery pieces having dimensions of 0.03×0.03×0.01 m³ for complete drying. The jaggery was dried in a roof-type even span greenhouse with a floor area of 1.20×0.78 m². An ANFIS model was developed in MATLAB software so as to calculate the jaggery temperature, the greenhouse air temperature and the moisture evaporated and was also used to forecast the thermal performance of the greenhouse on the basis of solar intensity and ambient temperature. This model was experimentally validated. It was shown that the analytical and experimental results for jaggery drying are in good agreement.     

On the selection of shape and orientation of a greenhouse: Thermal modeling and experimental validation

In this study, five most commonly used single span shapes of greenhouses viz. even-span, uneven-span, vinery, modified arch and quonset type have been selected for comparison. The length, width and height (at the center) are kept same for all the selected shapes. A mathematical model for computing transmitted total solar radiation (beam, diffused and ground reflected) at each hour, for each month and at any latitude for the selected geometry greenhouses (through each wall, inclined surfaces and roofs) is developed for both east-west and north-south orientation. Computed transmitted solar radiation is then introduced in a transient thermal model developed to compute hourly inside air temperature for each shape and orientation. Experimental validation of both the models is carried out for the measured total solar radiation and inside air temperature for an east-west orientation, even-span greenhouse (for a typical day in summer) at Ludhiana (31°N and 77°E) Punjab, India. During the experimentation, capsicum crop is grown inside the greenhouse. The predicted and measured values are in close agreement. Results show that uneven-span shape greenhouse receives the maximum and quonset shape receives the minimum solar radiation during each month of the year at all latitudes. East-west orientation is the best suited for year round greenhouse applications at all latitudes as this orientation receives greater total radiation in winter and less in summer except near the equator. Results also show that inside air temperature rise depends upon the shape of the greenhouse and this variation from uneven-span shape to quonset shape is 4.6 °C (maximum) and 3.5 °C (daily average) at 31°N latitude.     

Thermal modelling of asymmetric overlap roof greenhouse with experimental validation

Global solar radiation availability model and thermal model for newly designed asymmetric overlap roof shape (AORS) greenhouse are presented and experimentally validated. Instantaneous solar radiation flux is utilised in a dynamic thermal model to ascertain the hourly plant and inside air temperature. The AORS is also compared with the previously developed two best greenhouse shapes. An experimental validation of both the models is carried out for the measured instantaneous solar radiation, plant and inside air temperature for a typical day in summer at Ludhiana (31°N and 77°E), Punjab, India. During the experimentation, a tomato crop was grown inside the greenhouse. From the results, it can be inferred that an east–west orientation AORS greenhouse should be preferred due to a lesser solar radiation capture in summer months. The predicted plant and air temperatures are in good agreement with the measured data having a root mean square error of 4.69 and 3.7, respectively.     

Thermal modeling of a greenhouse integrated to an aquifer coupled cavity flow heat exchanger system

A thermal model is developed for heating and cooling of an agricultural greenhouse integrated with an aquifer coupled cavity flow heat exchanger system (ACCFHES). The ACCFHES works on the principal of utilizing deep aquifer water available at the ground surface through an irrigation tube well already installed in every agricultural field at constant year-round temperature of 24 °C. The analysis is based on the energy balance equations for different components of the greenhouse. Using the derived analytical expressions, a computer program is developed in C⁺⁺ for computing the hourly greenhouse plant and room air temperature for various design and climatic parameters. Experimental validation of the developed model is carried out using the measured plant and room air temperature data of the greenhouse (in which capsicum is grown) for the winter and summer conditions of the year 2004–2005 at Chandigarh (31°N and 78°E), Punjab, India. It is observed that the predicted and measured values are in close agreement. Greenhouse room air and plant temperature is maintained 6–7 K and 5–6 K below ambient, respectively for an extreme summer day and 7–8 K and 5–6 K above ambient, respectively for an extreme winter night. Finally, parametric studies are conducted to observe the effect of various operating parameters such as mass of the plant, area of the plant, mass flow rate of the circulating air and area of the ACCFHES on the greenhouse room air and plant temperature.     

Thermal modeling of solar stills: an experimental validation

Expressions for water and glass temperatures, yield and efficiency of both single and double slope multiwick solar distillation systems in quasi-steady state conditions have been derived. The analysis is based on the basic energy balance for both the systems. A computer model has been developed to predict the performance of the solar stills. Experimental validation of the thermal model has been carried out by using modified heat transfer coefficients. Internal heat transfer coefficients have been evaluated based on both inner and outer glass cover temperatures for typical days namely January 22, and June 19, 2001 in Delhi. A fair agreement has been observed between theoretical and experimental results by using the modified internal heat transfer coefficients based on inner glass cover temperature.     

Thermal modelling and experimental validation of ground temperature distribution in greenhouse

A periodic analysis for daily and monthly variations of ground temperature with depths is presented both under greenhouse and bare surface conditions of Delhi and for bare surface condition in other climates of India in order to design an efficient earth to air heat exchanger for greenhouse system. Calculations were carried out for a typical winter and summer day of Delhi in year 2000. Predicted values of ground temperature at 1 m depth were in fair agreement with experimental values under both conditions. Ground temperatures at various depths inside greenhouse were found to be on an average 7–9°C and 3–6°C higher than bare surface for daily and monthly variations respectively. Copyright © 2004 John Wiley & Sons, Ltd.     

Computer model and its validation for prediction of storage effect of water mass in a greenhouse: a transient analysis

In the present paper, an attempt has been made to develop a computer model based on transient analysis of the greenhouse. The model predicts room air temperature, storage water temperature and the thermal energy storage effect of a water mass in a low cost, passive greenhouse. Analytical expressions, based on an energy balance for each component, have been derived in terms of climatic as well as design parameters. Numerical computations have been done on typical days for the months from December 1999 to June 2000 at New Delhi. It has been observed that (i) there is a significant thermal energy storage effect of the water mass on room temperature and (ii) TLL, which is found to decrease with an increase in the mass of storage water, varies with month of year. An experimental validation of the developed model has also been demonstrated. The predicted room and water temperature show fair agreement with experimental values.     

Thermal modeling and heat management of supercapacitor modules for vehicle applications

Temperature has a huge influence on supercapacitor cells and modules ageing. Consequently, thermal management is a key issue concerning lifetime and performance of supercapacitor modules. This paper presents thermal modeling and heat management of supercapacitor modules for vehicle applications. The thermal model developed is based on thermal-electric analogy and allows the determination of supercapacitor temperature. Relying on this model, heat management in supercapacitor modules was studied for vehicle applications. Thus, the modules were submitted to real life driving cycles and the evolution of temperatures of supercapacitors was estimated according to electrical demands. The simulation results show that the hotspot is located in the middle of supercapacitors module and that a forced airflow cooling system is necessary.     

Experimental investigation of the drying characteristics of a mixed mode natural convection solar crop dryer with back up heater

A mixed mode natural convection solar crop dryer with a backup heater was designed and constructed from locally available materials and used to dry freshly prepared pineapples under four drying Scenarios for drying to correspond to specified drying periods for four typical seasons in Ghana. The experiments were devised for the material moisture content to be monitored continuously till the desired moisture content of between +106% and 184% (d.b) was achieved. In solar heating mode of operation, results show that the thermal mass was capable of storing part of the absorbed solar energy but the quantities involved are insufficient to sustain night drying. It was possible to dry a batch of pineapples in each mode of operation. The dryer reduced the moisture content of pineapple slices from about; 924% to 106% in 19 h; 1049% to 184% in 10 h; 912% to 155% in 7 h; and 1049% to 144% (d.b) in 23 h, for drying in Scenarios 1, 2, 3 and 4, respectively. The average moisture pickup efficiency values obtained were 27%, 24%, 11%, and 32% for drying in Scenarios 1, 2, 3, and 4, respectively.     

Thermal analysis of natural convection and radiation in porous fins

In this study, the effects of radiation and convection heat transfer in porous media are considered. The geometry considered is that of a rectangular profile fin. The porous fin allows the flow to infiltrate through it and solid-fluid interaction takes place. This study is performed using Darcy's model to formulate heat transfer equation. To study the thermal performance, three types of cases are considered viz. long fin, finite length fin with insulated tip and finite length fin with tip exposed. The theory section addresses the derived governing equation. The effects of the porosity parameter S_h, radiation parameter G and temperature ratio C_T on the dimensionless temperature distribution and heat transfer rate are discussed. The results suggest that the radiation transfers more heat than a similar model without radiation.     

Mathematical modeling of convective drying: Lumped temperature and spatially distributed moisture in slab

The present study describes the modeling and simulation of the drying process. The model considers fundamentals of the drying process and takes internal resistance to moisture into account. The main connotation of this study regards the possibility of employing a new analytical method for simultaneous heat and mass transfer. The proposed model considers the evaporative heat transfer at the surface of product. The validation of the model is made with a set of numerical and experimental results reported in the literature for carrot sliced in slab form. The results reveal that there is nearly perfect match between the temperature and moisture obtained by the analytical model and the numerical solution.     

Annual thermal performance of greenhouse with an earth–air heat exchanger: An experimental validation

In this paper the thermal model given by Ghoshal and Tiwari has been validated by round-the-year experimental work at IIT Delhi, New Delhi (28° 35′N, 77° 12′E), India. The correlation coefficient and root-mean-square percentage deviation have been computed for each month for validation of the thermal model. The values are 0.99% and 4.24% for the greenhouse temperature with an earth–air heat exchanger (EAHE) in the month of January. Statistical analysis shows that there is fair agreement between predicted and experimental values. An effort has also been made to optimize the working hours of an EAHE to obtain maximum heating/cooling potential. The non-operational hours of an EAHE are 252 and 279 for February and March months, respectively. The maximum value of heating potential (11.55 MJ) and cooling potential (18.87 MJ) has been found during off sunshine (8 pm–8 am) hours and peak sunshine hours (8 am–8 pm), for a typical day in the month of January and June.     

Solar drying of wastewater sludge: A review

Drying constitutes an important process for wastewater sludge management, as it can reduce the mass and the volume of the product and consequently the cost of storage, handling and transport. During constant operating conditions, the drying kinetic of the sludge has shown mainly: a constant drying rate, one or two falling rate periods and a final short period with variations along the process of the physical properties of the product with the appearance of shrinkage and cracks phenomena. Solar drying was benefit as using free solar energy can reduce the cost of the operation. On the other hand, it plays an important role for the pathogen reduction until Environmental protection Agency (EPA) recommendations. In some studied cases, the value of 1000 CFU g⁻¹ DS, which represents the EPA Class A pathogen requirement, for fecal coliform was attained. The general design of used solar dryers was constituted of: a greenhouse made with transparent material and a floor, where the product is speared in thick layers. Furthermore, fans and ventilations can be used in order to have homogeneous distribution of the air inside the greenhouse with replacement of humidified air with fresh one. Automatic or handle mix of the product was used once or for several times a day. In order to increase the performances of the drying system, other ways such as heating the floor using solar water heater, infrared lamps, using heat pumps or adding thermal energy storage systems were also tested. Covered solar drying has given better results than open solar drying. However, the origin of the wastewater sludge affects the obtained results. Alternatively, modeling drying systems was effectuated using heat and mass balances, applied for the air and the dried product. Solar drying of wastewater sludge has given satisfactory results.     

Thermal performance evaluation of a four pan jaggery processing furnace for improvement in energy utilization

The jaggery making from sugarcane is one of the traditional process industries contributing to the local employment and entrepreneurship opportunities to the rural population. Jaggery is a condensed form of sugarcane juice produced by evaporation of moisture. Bagasse which is internally generated during juice extraction from sugarcane is used as the fuel for evaporation in a jaggery furnace. Any efficiency improvement in the thermal performance of a jaggery furnace leads to bagasse saving which provides additional revenue for the jaggery manufacturer.     

Formulation and validation of a mathematical model of the microclimate of a greenhouse

A mathematical model MICroclimate of GREENhouse (MICGREEN), consisting of set of algebraic equations, was developed. The equations were written for four components of the greenhouse viz. cover, inside air, canopy surface and bare soil surface. It was assumed that the greenhouse air is well mixed, thermal properties of materials of construction do not change with time and solar radiations pass through cover without absorption. The values of dimensions and material properties of the greenhouse constructed at the Research Farm of Department of Soil and Water Engineering, Punjab Agricultural University, Ludhiana were put in these equations. The inputs to the model are ambient air temperature, solar radiations on normal surface, solar radiations on earth's surface, temperature of the soil under canopy and temperature of the soil at a depth of 6 cm. A computer program was written in C++ language. The equations were solved using Gauss–Seidal Iteration method. The outputs of the model are greenhouse cover temperature, inside air temperature, canopy temperature and bare soil temperature. The relative humidity of the inside air is predicted from the predicted inside air temperature with the help of psychrometric chart. To validate this model, experiments were conducted on greenhouse to obtain data during winter as tomato crop was being grown. The results of computer model were compared with the experimental results and agreement was found between the measured and predicted values.     

An experimental study of natural convection in a differentially heated cavity through a 2D-PIV system

This paper provides an experimental analysis of the natural convection in a differentially heated H side square enclosure. The cavity is full of air and is heated by a hot strip with a height of H/2. The effect of the position of this source on the dynamic structures generated by the natural convection heat transfer was analyzed at the steady state and under laminar conditions. The experimental apparatus is a 2D-PIV system while the experimental data consist of vector maps, velocity maps and streamlines at different Rayleigh numbers. During the study the presence of two small vortexes was noted on the upper surface of the source. These are dependent both on the Rayleigh numbers and on the position of the strip.     

Numerical and experimental analysis of convection heat transfer in passive solar heating room with greenhouse and heat storage

In this paper, heat transfer and air flow in passive solar heating room with greenhouse and heat storage are studied. Thermal insulation of solar heating room has significant effects on temperature distribution and airflow in the heating chamber of this solar system. Heat transfer and air flow in a rock bed, which is used as solar absorber and storage layer, are also studied. If porosity is kept within certain range, increasing the rock size causes an increase of the capability of thermal storage and heating effects; increasing the porosity of thermal storage materials results in an increase of the bed temperature but a decrease of the rock mass. The specific heat capacity and thermal conductivity have a remarkable effect on the average temperature of rock bed. All these factors should be taken into account when designing a solar heating system.     

Thermal modeling of integrated roof air heater for passive solar space heating of a non-air-conditioned building

This communication presents the periodic heat transfer analysis for solar space heating of an unconditioned building with an integrated roof air heater. The system consists of an air duct within the roof such that the air is continuously or intermittently forced to circulate the cooler room air through the inlet of the air duct. Time dependence of the air flow is represented by a step function of time for daily operation and, hence, has been expressed as a Fourier series in time. The analysis takes into account air ventilation, ground heat conduction and furnishings. The effects of depth of the air duct from the outer surface of the roof and the magnitude and duration of air flow rate on indoor air temperature have been studied for a typical cold winter day in Delhi. It is seen that a time dependent air flow through the duct is desirable from the point of view of increasing the indoor air temperature in the case of a bare roof. However, in the case of a blackened and glazed roof, continuous air flow is needed for increasing the room air temperature. The results are desirable from the point of view of efficient space heating of solar passive buildings.     

The potential for heat pumps in drying and dehumidification systems II: An experimental assessment of the heat pump characteristics of a heat pump dehumidification system using R114

An experimental heat pump dehumidifier is described. Actual coefficients of performance (COP)_A are plotted against the gross temperature lift (T_CO - T_EV) for various bypass ratios and air velocities. Interpolated values of (COP)_A for a specified temperature lift were obtained by fitting each set for various dry bulb temperatures of air leaving the humidifier using a linear equation. These values of (COP)_A are plotted against the linear velocity of the air stream approaching the evaporator at different dry bulb temperatures. The curves show a maximum of (COP)_A at approach velocities in the region of 1·6 ms^?1.