Zacharias B Maroulis

• Professor (Full) at National Technical University of Athens

Cogeneration is a cost-effective technology, and modern greenhouses are considered one of the best applications for it due to their energy intensity. Taking into account that in such cases the production cost is significantly affected by the cost of energy, the potential of combined heat and power (CHP) has already been examined and proved in pract...

A systematic method to evaluate the economic operating performance of existing combined heat and power (CHP) or combined cooling heat and power (CCHP) generation systems is applied. Two key performance indicators are selected to evaluate both the technical and the economic performance, based on operating recording data; the capacity factor and the...

A simple effective model is proposed for the day-ahead electricity market. The model considers the main factors which govern the process, predicts the seasonal and daily variation of electricity demand, renewable production, system marginal price, and merit order effect. The accuracy of the model is increased by fitting to historic data of the Hell...

Modern greenhouses are good candidates for combined cooling, heating and power generation (CCHP) systems. An analytical framework to assess the affordability of such systems for two different problems, is proposed; (a) the grassroots problem, i.e. the CCHP system is designed along with the greenhouse, and, (b) the retrofit problem, i.e. the additio...

The significant penetration of renewables, in the Hellenic electricity system, during the last 12 years, was based on feed-in tariff-supporting schemes, according to the compliance to European Directives. The characteristics of this penetration are presented and analyzed in this paper based on real data. Photovoltaics, wind parks, hydroelectric pla...

This paper presents an analytical methodology of evaluating the economic viability of a CCHP system, over three alternative configurations: (1) boiler and electric chiller, which have been extendedly analyzed in literature, (2) boiler and gas driven absorption chiller and (3) reversible heat pump, which have been slightly investigated in comparison...

Phenolic content, antioxidant activity and sensory characteristics of vegetable-enriched extrudates were investigated as a result of extrusion conditions, including extrusion temperature (140-180 °C), screw rotation speed (150-250 rpm) and feed moisture content (14-19 % w.b.). Broccoli flour and olive paste was used in mixtures with corn flour at a...

Recently, an interesting experiment was completed in Greece concerning photovoltaic penetration into the electricity production sector. Based on the relevant laws and in accordance to the related European directives, an explosive penetration process was completed in less than three years, resulting in a 7% share of photovoltaics in electricity prod...

Following the tendency of replacing common food snacks with healthier food products, extruded snacks with corn flour and broccoli (4-10%) or olive paste (4-8%) were investigated in this study. The effect of material characteristics, including feed moisture content (14-19%), and broccoli or olive paste concentration, and extrusion conditions, includ...

The growing consumers’ demand for healthier snacks is of high importance and is driving research and industry towards developing novel ready to-eat expanded products. Thus, it would be interesting to enrich these products with additives that possibly lead to highly nutrient products. In the present study, extruded snacks based on corn flour enriche...

Moisture is one of the most damaging factors of buildings. Masonries moisture content is defined by a delicate equilibrium established between the building and the environment. First order mathematical models can describe satisfactory phenomena like capillary rise and drying kinetics. Their advantages lie on the fact that they are general and inclu...

The present study examines the addition of dehydrated broccoli or olive paste to corn flour for the production of extrudates with increased value and superior quality. Extrudates were prepared using a twin-screw extruder, operated at different conditions, including screw speed (150 rpm, 200 rpm, 250 rpm) and extrusion temperature (140 °C, 160 °C, 1...

The principles and techniques of process economics can be applied to food processing by evaluating the economics of a particular food process. Material and energy balances, sizing of process equipment, and cost data on raw materials, labor, and utilities are used in the design of new food processes, and in economic evaluation of industrial processi...

This work addresses the problem of optimal design of trigeneration plants and discusses the factors that affect the operation and the feasibility of investment. The effect of various operation parameters and energy tariffs structures are studied and the performance of a trigeneration plant is presented and evaluated versus the investment size. A ne...

A multi-objective optimization method was developed for the design of trigeneration plants. The optimization is carried out on technical, economical, energetic and environmental performance indicators in a multi-objective optimization framework. Both construction (equipment sizes) and discrete operational (pricing tariff schemes and operational str...

Summary  Apparent density, true density, specific volume and internal porosity were investigated during vacuum dehydration of banana, apple, carrot and potato, at various moisture contents and pressures. The pressure was found to effect significantly the apparent density and porosity of the materials examined, while for the true density, this effec...

Additional types of silicone biopolymers are widely used in maxillofacial prosthetics. Therefore, the knowledge of the solar radiation’s effect on their structural stability is highly important. Four different industrially synthesized biomaterials were examined, called Episil Europe 1, Europe 2, Europe 3 and Africa 3, which were exposed to solar ra...

Moisture diffusivity is the most crucial property in drying calculations. Literature data are scarce due to the variation of both experimental measurement techniques and methods of analysis. The effect of using different methods of analysis on the same experimental drying data is examined in this work. Detailed and simplified mathematical models, i...

A generic structural model to estimate the effective thermal conductivity of granular foods is proposed based on a distribution coefficient. It is assumed that granular food materials in bulk can be considered as a two-phase system containing granules and an interstitial air phase, and while the granules are also be considered as a two-phase system...

A wide variation of the reported experimental data of thermal conductivity of solid food materials makes difficult their utilization in food processing applications. The published values of thermal conductivity of various foods were classified and analyzed statistically to reveal the influence of material moisture content and temperature. Empirical...

Heat transfer coefficient data in food processing were retrieved from literature and classified per process and material. Most of the data were available in the form of empirical equations using dimensionless numbers. All available empirical equations were transformed in the form of Heat Transfer Factor vs. Reynolds Number (jH=aRe). In the case whe...

Recently reported heat and mass transfer coefficient data in drying were retrieved from literature and were classified per dryer type and material. Most of the data were available in the form of empirical equations using dimensionless numbers. All available empirical equations were transformed in the form of Heat or Mass Transfer Factors versus Rey...

Published experimental data on thermal conductivity of food materials are scattered, and their utilization in food processing operations is difficult. Data of thermal conductivity for various foods in recent literature were classified and analyzed. The results of more than 100 food materials, classified in 11 food categories, are presented. The res...

Recently published values of rheological properties of fluid fruit and vegetable puree products were retrieved from the literature and analyzed. The results of more than 10 materials are presented, concerning the reported ranges of variation of Consistency Coefficient and Flow Behavior Index, together with the corresponding ranges of variation of c...

Moisture loss and oil adsorption kinetics, structural properties (apparent density, true density, specific volume and internal porosity), color changes and viscoelastic behavior (compression tests, crispness) were investigated during deep fat frying of french fries. The effect of frying conditions (oil temperature, sample thickness and oil type), d...

The seasonal moisture transfer to and from the walls of a building is the most important factor concerning the deteriorating effect of moisture in buildings envelopes. The presented simulator takes into account the (a) moisture transfer mechanisms to and from the building (capillary rise, drying, etc.), (b) wall configuration (materials and size),...

Recently published values of food properties, such as true density, apparent density, and porosity, in various foods were retrieved from the literature, classified, and analyzed. Data for more than 130 food materials classified into 11 food categories are presented. These ranges of data are reported as a function of material moisture content and te...

Computer-aided design is based on computer simulators, whereas computer simulators are based on process modeling. The basic terms, such as modeling, simulation, and design, are dened in Table 5.1. Modeling is the procedure of translating the physical laws of a process to mathematical equations to analyze or design the process. Simulation is the app...

The thermal conductivity (k) of gelatinized high-amylose and high-amylopectin starches was determined, using the heated probe method. The granular starches, mixed with distilled water at 1 to 4 kg water/ kg dry solids, were gelatinized at 120°C. Similar k values which varied from 0.434 to 0.548 W/mK in the temperature range 30 to 70°C were obtained...

Published values of food properties, such as true density, bulk density, and porosity in various foods were collected from the literature and classified in a previous work. These values of the true density were processed in order to reveal the influence of material moisture content and temperature. A simple mathematical model, relating true density...

Structural properties, such as apparent density, true density, expansion ratio and porosity, of extruded corn grits were measured. Corn grits were extrusion-cooked in a Prism extruder with varied feed rate (1.16–6.44 kg/h), screw speed (150–250 rpm), product temperature (100–260 °C) and feed moisture content (12–25 kg/100 kg wet basis). A simple ma...

A systematic analysis of published food industries cost data is used (a) to estimate the appropriate factor models for rapid cost estimation in food plant design, and (b) to reveal the particular food industry characteristics for supporting various techno-economic studies.

Moisture is one of the most deteriorating factors of buildings. The deteriorating effect of moisture occurs mainly during the drying phase, not in the wetting phase. Environmental factors, such as air temperature, air humidity, and air velocity affect drying. An experimental air dryer of controlled drying air conditions was used to investigate the...

Moisture is one of the most deteriorating factors of buildings. The masonry moisture content depends on hygroscopic equilibrium between building materials and environment. Moisture sorption (adsorption and desorption) isotherms of 4 sandstones, 2 bricks, and 6 plasters were determined at 15, 25, and 35°C. A modified Oswin equation was used to predi...

There is a wide variation of the reported experimental data of moisture diffusivity of solid food materials, making difficult their utilization in drying and other applications. Recently published values of moisture diffusivity in various foods were retrieved from the literature, and they were classified and analyzed. The results of more than 100 f...

Moisture is one of the most deteriorating factors of buildings. The deteriorating effect of moisture occurs mainly during the drying phase, and not in the wetting phase. Appropriate parameters of the drying kinetics are required for the building materials. Environmental factors, such as air temperature, air humidity, and air velocity affect drying....

Recently published data of drying kinetics and drying constant in various foods were retrieved from the literature, and they were classified and analyzed. The results of more than 35 food materials classified in eight food categories are presented. The results concern the reported range of variation of drying constant data together with the corresp...

The effect of air conditions (air temperature, air humidity and air velocity) and characteristic sample size on drying kinetics of various plant materials (potato, carrot, pepper, garlic, mushroom, onion, leek, pea, corn, celery, pumpkin, tomato) was examined during air drying. A first-order reaction kinetics model was used, in which the drying con...

A mathematical model is proposed to simulate brackish karstic springs. Rainfall data constitutes model input information while output information is the discharge and the chloride concentration of the water versus time. The model was constructed by considering the mass and mechanical energy balance on the hydrodynamic analog, which includes three r...

Published data on the surface heat transfer coefficients in food processing operations have been selected from the literature, organized into a database, and presented. Useful information concerning the proposed equation, the system geometry, the experimental conditions, the range of application, and the relevant references, are tabulated.

Olive-mill cake is one of the most widespread biomaterials for bioenergy exploitation in Greece. It is a sludge-type material, produced as byproduct from olive-mill extraction process. Its energy content is higher than 15 MJ/kg db and it can be used for direct burning, after drying. The drying process of olive cake is examined in the present paper....

A generic structural model to predict the effective thermal conductivity of fruits and vegetables during drying is proposed. The model was applied successfully in the case of apple. It combines a generic structural model for shrinkage and the distribution factor concept for thermal conductivity. The shrinkage coefficient and the distribution factor...

An empirical model was developed to predict the water loss and solid gain during osmotic dehydration of apple, banana and kiwi fruit. The model is based on a first-order kinetic equation, in which the rate constant is a function of the main process variables (speed of agitation, solute concentration, size of fruit and process temperature). This mod...

Mass transfer coefficient data in food processing were retrieved from literature and classified per process and material. Most of the data were available in the form of empirical equations using dimensionless numbers. All available empirical equations were transformed in the form of mass transfer factor versus Reynolds number (jM = a Re). Average e...

The viscoelastic behaviour of french fries during deep fat frying after two different types of drying pre-treatment (air drying and osmotic dehydration) was examined under uniaxial compression tests. The stress-strain data of the compression test were modelled using a simple mathematical model, containing parameters such as the maximum stress (σmax...

The effect of duration of pre-drying on structural properties (apparent density, true density, specific volume and internal porosity) and color parameters (lightness, a, b) of fried potatoes was also investigated. The results showed that pre-drying pre-treatment had a significant effect on oil uptake and moisture loss, as well as structural propert...

Osmotic dehydration as a pretreatment before frying in order to produce low-fat french fries was examined. A relationship between frying kinetics and the type of solution used for osmotic dehydration before frying of french fries has been developed. The effect of osmotic dehydration on the structural properties (apparent density, true density, spec...

There is a wide variation of the reported experimental data of moisture diffusivity of solid food materials, making difficult their utilization in drying and other applications. Published values of moisture diffusivity in various foods were retrieved from the literature, and these were classified and analyzed statistically to reveal the influence o...

The following structural properties of dehydrated apple, banana, carrot and potato were examined during rehydration: true density, apparent density, porosity and specific volume. Samples were dehydrated using five different drying methods: conventional, vacuum, freeze, microwave and osmotic; after which they were rehydrated in an air dryer at 50 °C...

The effect of frying conditions on the colour changes during deep fat frying of french fries has been investigated. The Hunter colour scale parameters redness, yellowness and lightness were used to estimate colour changes during frying as a function of the main process variables (oil temperature, oil type and sample thickness). A first-order kineti...

The viscoelastic behaviour of french fries during deep fat frying was examined under uniaxial compression tests, as a function of the main process variables (oil temperatures, oil type) for various frying times. The stress–strain data of the compression test were modelled using a simple mathematical model, containing parameters such as the maximum...

The problem of designing wind parks has been addressed in terms of maximizing the economic benefits of such an investment. An appropriate mathematical model for wind turbines was used, taking into account their construction characteristics and operational performance. The regional wind field characteristics for a wide range of sites have been appro...

Summary We tested the hypothesis that an optimum method of drying fruit could be designed. The effect of the method used for drying on colour of apple, banana, potato and carrot was investigated for five different methods of drying: conventional, vacuum, microwave, freeze and osmotic drying. Colour characteristics were studied by measuring lightnes...

The effect of drying methods on the rheological behaviour of dehydrated apple, banana, carrot and potato was examined by uniaxial compression tests on cylindrical specimens. Samples were dehydrated using four different drying methods: osmotic, conventional, vacuum and freeze drying. After drying samples at varying final moisture, the contents were...

Drying related properties of apple are evaluated for various different drying methods (namely, convective, vacuum, microwave, osmotic and freeze drying), and their corresponding process conditions. The examined properties are drying kinetics, equilibrium material moisture content, density, porosity, color and viscoelastic characteristics. The effec...

The effect of pretreatment on color of convective dried products (namely apple, banana, potato and carrot) was investigated. Five different types of pretreatment were taken into consideration; microwave, osmotic, sulfite, water blanching and steam blanching. Color characteristics were identified by measuring the color parameters (namely, Lightness...

The problem of designing small hydroelectric plants has been properly analysed and addressed in terms of maximizing the economic benefits of the investment. An appropriate empirical model describing hydroturbine efficiency was developed. An overall plant model was introduced by taking into account their construction characteristics and operational...

Color and sorption characteristics of osmotically treated and air dried apple and banana were studied during air drying at 70C. The color parameters: Lightness (L), Redness (a) and Yellowness (b) were studied, using a Hunter Lab chromatometer. A first order kinetic model was fitted to the experimental data adequately for color parameters, while sor...

The rheological behavior of osmotically dehydrated apple and banana was examined under uniaxial compression and relaxation tests of cylindrical specimens. Compression and relaxation tests were performed, following air drying of osmotically pre-treated samples, at various moisture contents ranging from 0.1 to 1.5 kg/kg dry basis. The maximum stress...

A relationship between moisture loss and oil adsorption with frying time during deep fat frying of french fries has been developed. A first order kinetic equation was used, in which the rate constant is a function of the main process variables (oil temperature, sample thickness and oil type). This model was applied to a wide range of experimental d...

Apparent density, true density, specific volume and internal porosity were investigated during deep fat frying of french fries. The effect of frying conditions (oil temperature, sample thickness and oil type) on the above properties was examined. A simple mathematical model was used to correlate the above properties with oil and moisture content. F...

The textural properties of apple, banana, carrot and potato were experimentally determined by uniaxial compressive tests of cylindrical specimens at a constant deformation rate of 5mm/min. Compression tests were performed, following air drying, at various moisture contents ranging from 0.2 to 6 kg/kg db. The tests were performed using a universal t...

Design of conveyor-belt dryers constitutes a mathematical programming problem involving the evaluation of appropriate structural and operational process variables so that total annual plant cost involved is optimized. The increasing need for dehydrated products of the highest quality, imposes the development of criteria that, together with cost, de...

The performance of a pharmaceutical pressure sensitive adhesive, whose liquid formulation is based on a multicomponent mixture of solvents, has been examined during two peel adhesion types of tests (90° dynamic adhesive strength peel test and 180° release liner peel test). The experiments were carried out under various drying temperatures, initial...

Drying kinetics of volatile organic solvents have been examined during the drying process of a pharmaceutical coating containing a multicomponent mixture of ethyl acetate, n-heptane, propanol-2, and toluene. A complete set of experiments was performed in two drying apparatuses, a laboratory air-dryer and an oven dryer, for a wide range of drying te...

Viscoelastic behaviour of dehydrated products during rehydration of apple, banana, carrot and potato was examined under uniaxial compression tests. Samples were dehydrated with four different drying methods: conventional, vacuum, freeze and osmotic-freeze drying and after that they were rehydrated in an air dryer at 50°C and 80% air humidity. Compr...

The operational performance of a paper production plant can be significantly improved by appropriate process interventions. This paper deals with energy aspects of the most important section of such a plant, the paper drying section. A significant intervention that would lower the operational cost of the drying process is proposed. It refers to the...

The effect of microwave and microwave-vacuum drying on some quality properties such as density, porosity, color and viscoelastic behavior of dehydrated apple, banana, carrot and potato was investigated. It is concluded that microwave drying and moreover microwave-vacuum drying tends to increase the product porosity and to prevent the color damages...

Mass transfer phenomena were investigated during osmotic dehydration of apple, banana and kiwi in glucose and sucrose osmotic solution. A complete set of experiments was performed for a wide range of temperature, sample size, speed of agitation, osmotic agent concentration and immersion time. An empirical model, based on a first order kinetic equat...

The use of computers to perform simulations of chemical engineering processes has lead to the development of software tools that perform most tedious computations in the field of process analysis, mathematical modeling and design. In the case of dryers, these mathematical programming aspects can be dealt in a straightforward way. The mathematical m...

Solar energy exploitation for assisting the operation of reverse osmosis (RO) seawater desalination plants was investigated. A hybrid solar-assisted steam cycle was designed in order to provide the required shaft work to drive the RO plant high pressure pump. Two problems have been analyzed. The design problem concerned the determination of the opt...

Structural properties such as particle density, bulk (or apparent) density and porosity of apple, banana, carrot and potato were investigated after freeze-drying under various drying conditions. The materials were freeze-dried at various pressures, to achieve sample temperature ranging between −50 and −5 °C. For temperatures above the glass transit...

Viscoelastic properties for carrot and potato were experimentally determined by stress relaxation tests using uniaxial compressive tests of cylindrical specimens at various deformation rates (5,10 and 20 cm/min). Stress relaxation tests were performed following conventional drying at 70°C and 15% humidity for various moisture contents ranging from...

The effect of drying conditions on color changes of apple, banana, carrot and potato during conventional and vacuum drying was investigated. The Hunder color scale parameters redness, yellowness and lightness were used to estimate color changes during vacuum and conventional drying at 50, 70 and 90°C. Air humidity during conventional drying was reg...

The paper presents a mixed-integer nonlinear programming (MINLP) approach to construction and operational optimization of carbon-in-pulp (CIP) processes related to hydrometallurgical gold recovery plants. In this plant section, gold in the form of aurocyanide complex ions is adsorbed on the active sites of carbon particles. This takes place in a se...

Microwave vacuum drying kinetics of three fruits (namely, apple, kiwi and pear) were studied by introducing an one-parameter empirical mass transfer model, involving a characteristic parameter (drying constant), as a function of process variables. The model was tested with data produced in a microwave oven equipped with vacuum apparatus, using non-...

The effect of drying method on bulk density, particle density, specific volume and porosity of banana, apple, carrot and potato at various moisture contents was investigated, using a large set of experimental measurements. Samples were dehydrated with five different drying methods: conventional, vacuum, microwave, freeze and osmotic drying. A simpl...

The steady-state process simulator developed by Kiranoudis et al. has been used for the detailed simulation of sulfuric acid pressure leaching of laterite ores for the extraction of nickel and cobalt, and aqueous pressure oxidation of pyrites for the recovery of gold. Advanced hydrometallurgical process models for the specific unit operations invol...

Flowsheeting is an important engineering activity, arguably the most important, because it is the basis for analyzing process interactions within a specific flowsheet. An effective flowsheeting program can enhance the design procedure, and thus, improve the entire decision-making strategy. A number of requirements make the development of a flowshee...

The steady-state process simulator developed by Kiranoudis et al. has been used for the detailed simulation of the Bayer process flowsheet. It consists of the digestor/flash section as well as the precipitation and washing circuits. Advanced hydrometallurgical process models for the specific unit operations involved were developed and are appropria...

A short-cut model suitable for the estimation of the overall wind park efficiency was developed. Its parameters were estimated by fitting the predictions of a detailed explicit kinematic wake model for a wide range of wind velocities, number of turbines utilized, relative distances of turbines and various types of commercial wind turbines. An empir...

A mathematical model for the semi-batch operation of industrial dryers with trucks and trays is presented and analysed. Design aspects are discussed concerning problems involving both single dryer and systems of parallel dryers. In both cases, optimum flowsheet configuration and operation conditions are sought and verified by appropriate formulatio...

Drying kinetics of four Fruits (namely, apple, pear, kiwi and banana) were studied by introducing an one-parameter empirical mass transfer model, involving a characteristic parameter (drying constant), as a function of process variables. The model was tested with data produced in a laboratory dryer, using non-linear regression analysis. The investi...

Wind power exploitation for assisting operation of reverse osmosis desalination plants was investigated. Two problems have been analyzed: the design determining optimum plant size with respect to membrane and turbine type for different production capacity levels and various site characteristcs. Operational aspects of already installed wind-powered...

A mathematical model for predicting three-dimensional, two-phase flow, heat and mass transfer inside fluidized-bed dryers has been developed. The model consists of the full set of partial-differential equations that describe the conservation of mass, momentum and energy for both phases inside the dryer, and is coupled with correlations concerning i...

A design method for reverse osmosis desalination plants has been developed. It incorporates rigorous mathematical models for the prediction of the performance of various process units (reverse osmosis modules, pumps, energy recovery turbines) employed in the flowsheet and taken into account the network structure using an appropriate superstructure,...

Fluidized bed and rotary dryers are two popular types of dryers utilized in almost every area of dryine. In this study, both dryers are analysed regarding their design and operational performance, so that they could be compared in a straightforward way. The mathematical models describing the convective drying process were evaluated for both types o...

A software package for process and total site integration, as well as, utilities design (grass roots and retrofit) is presented. The system, operating under MS Windows®, effectively integrates all functions of process integration, co-current simulation, and total site integration in a common environment, fully supported by interactive graphics scre...

A system for real-time management and optimisation of industrial utilities facilities is presented. The system, given the demand from the process (steam of various levels, power), optimally allocates the load to the available utilities equipment (boilers, turbines, etc.) and external sources (national power grid). The utilities plant is considered...

Design and study of operational performance of convective industrial dryers are a strong indicator in the last stages of the selection procedure. This problem is addressed in a straightforward way for the three most popular types; conveyor-belt, fluidized bed and rotary dryers. Design was carried out by appropriately optimizing the total annual cos...

A design method for reverse osmosis seawater desalination systems has been developed. It incorporates rigorous mathematical models for the prediction of the performance of the various process units (reverse osmosis modules, pumps, energy recovery turbines) employed in the flowsheet and takes into account the network structure using an appropriate s...

Design and operational performance of convective industrial dryers are an important field of chemical engineering, which is still governed by empiricism. This article addresses the design vs. operation problem for three basic types of continuous convective industrial dryers: conveyor-belt, fluidized bed, and rotary. Design procedures determined the...