Mohamed A. Antar

Thermoeconomic considerations in the optimum allocation of heat exchanger inventory for a power plant

Abstract Thermoeconomics is defined as the integration of thermodynamics with economics of thermal systems. In this paper, we discuss the thermoeconomics of heat exchanger units in a power plant for cost based optimal design conditions. In this regard, unit cost parameters of hot and cold end heat exchangers in distributing the heat transfer surface area of the power plant are considered for minimum total cost of the heat exchangers. A closed form expression is given in terms of unit costs of the conductances of both heat exchangers, and the results are presented in terms of a unit cost ratio, G , and the hot and cold end heat exchangers costs. The results demonstrate a strong dependence of the total cost function on the absolute temperature ratios as well as the hot to cold end conductance cost ratio. It is also shown that for the case of equal unit costs of the hot and cold end heat exchangers, the total conductance is equally divided between the two heat exchangers.

An improved model for multiple effect distillation

Abstract Increasing global demand for fresh water is driving research and development of advanced desalination technologies. As a result, a detailed model of multiple effect distillation (MED) is developed that is flexible, simple to implement, and suitable for use in optimization of water and power cogeneration systems. The MED system is modeled in a modular method in which each of the subcomponents is modeled individually and then instantiated as necessary in order to piece together the complete plant model. Modular development allows for studying various MED configurations (such as forward feed, parallel feed, etc.) with minimal code duplication. Use of equation-oriented solvers, such as Engineering Equation Solver and JACOBIAN, rather than sequential solvers, simplifies the coding complexity dramatically and also reduces the number of required approximations and assumptions. The developed model is compared with four prominent forward feed MED models from literature. Through parametric analysis, it is ...

On the Use of Spreadsheets in Heat Conduction Analysis

Detailed methodology and different techniques for simply utilizing the widely available and user friendly spreadsheet programs in heat conduction analysis are presented. Evaluation of analytical and numerical solution of heat conduction problems via spreadsheets is investigated. Detailed techniques of obtaining spreadsheet numerical solutions for one- and two-dimensional steady and transient heat conduction problems are introduced. A new technique of marching the transient numerical solution with time, in a single layer spreadsheet, for one- and two-dimensional heat conduction is explained. Creating macros that automate the spreadsheet processes, particularly calculations, is detailed. Utilization of the powerful graphical facility that is built in the spreadsheets to graphically represent the obtained solutions is outlined.

Thermoeconomic Considerations in the Optimum Allocation of Heat Transfer Inventory for Refrigeration and Heat Pump Systems

Thermoeconomics is defined as attaching monetary values to heat exchanger conductances of a given plant. In this study, optimum allocation of heat transfer inventory for heat exchangers in a refrigeration system with specified power input or cooling capacity, and for a heat pump with specified heating capacity is investigated. The ratio of hot- to cold-end conductance unit cost ratio, G, was considered in the analysis as an additional parameter of considerable importance to the designer. A closed-form expression is given in terms of unit cost of conductances of both the heat exchangers. The results show a strong dependence of the total cost on the absolute temperature ratios as well as the hot-to the cold-end conductance cost ratio. It is demonstrated in the illustrative example that for G=0.1, the conductance of the hot-end heat exchanger is about three times the cold-end heat exchanger.

Boundary Layer Flow About and Inside a Liquid Sphere

A finite-difference scheme has been developed to solve the boundary-layer equations governing laminar flows around and inside a spherical fluid droplet moving steadily in another immiscible fluid. Using this scheme, results not available in the literature have been obtained for circulating droplets at intermediate and high interior-to-exterior viscosity ratios (μ * ) and large values of the external flow Reynolds number (Re). Detailed results over the range 1.01 ≤ μ * ≤ ∞ (solid sphere) and 100 ≤ Re ≤ 10000 are presented for the velocity profiles outside and inside the droplet, the interface shear stress, the external flow separation angle, the droplet surface velocity and the drag coefficient.

Spreadsheet Modelling of Transient Three Dimensional Heat Conduction with Various Standard Boundary Conditions

A method of analysing transient three-dimensional heat conduction problems using spreadsheets is described. An implicit numerical scheme is used and user-defined macros are designed and executed in a single-layer sheet. The method allows the use of all standard boundary conditions such as constant surface temperature, specified heat flux, thermal insulation, convection and/or thermal radiation. This method seems to be convenient for both practising engineers as well as undergraduate students since it enables them to solve engineering problems numerically without complicated programming. The method also allows the user to incorporate nonlinear boundary conditions such as thermal radiation with no further simplification which otherwise would require further effort to model. The method was received by engineering students and hence was useful as an educational aid that can be applied in other fields of engineering applications.

Experimental investigations on the performance of an air heated humidification–dehumidification desalination system

Abstract Experiments on a single- and two-stage air-heated humidification–dehumidification desalination system (HDD) driven by solar energy are conducted. The system is built on the seashore of Dhahran, Eastern Province of the Kingdom of Saudi Arabia. In this harsh climate, natural water sources are absent. Currently, Saudi Arabia uses desalination to augment its water supply. It is ranked the first worldwide in water desalination. However, the current large-scale desalination plants are fossil-fuel-driven and consume large amount of energy. Since there is abundance of solar energy in the region, attempts are made to utilize the solar energy to produce fresh water on a small scale for remote areas. The HDD systems have received considerable attention as an effective way to produce fresh water in remote areas where receiving water through pipelines is a challenge. The system used in this study is a solar air heated, closed-water closed-air cycle that can be adjusted to operate in a single-stage or two-stag...

Performance of Air Gap Membrane Distillation Unit for Water Desalination

Due to water scarcity in the Arabic gulf region, water desalination technologies are considered extremely important. The present work represents a fundamental study on the effect of basic operating and design variables on the flux of an air gap membrane distillation (AGMD) unit for water desalination. The flat sheet, channeled air gap membrane distillation module was designed and manufactured locally. The effect of feed flow rate, feed temperature, coolant water temperature, the air gap width, and the water salinity on the module flux are investigated. Analytical model for heat and mass transfer is used to predict the flux and the model results are compared to the experimental ones. Results showed that the technique has good potential to be used for water desalination. The permeate flux is increased by increasing feed flow rate, feed temperature, decreasing the air gap width, decreasing coolant temperature, and decreasing salinity of feed water. For a given feed flow rate, the width of the air gap and the feed water temperature are found to be the most effective parameters in increasing the distillate flux. Predicting the permeate flux with analytical models for heat and mass transfer showed good agreement with experimental results.Copyright

The entropy generation for a rotating sphere under uniform heat flux boundary condition in forced‐convection flow

Purpose – The purpose of this paper is to investigate the problem of entropy generation around a spinning/non‐spinning solid sphere subjected to uniform heat flux boundary condition in the forced‐convection regime.Design/methodology/approach – The governing continuity, momentum, energy and entropy generation equations are numerically solved for a wide range of the controlling parameters; Reynolds number and the dimensionless spin number.Findings – The dimensionless overall total entropy generation increases with the dimensionless spin number. The effect of increasing the spin number on the fluid‐friction component of entropy generation is more significant compared to its effect on heat transfer entropy generation.Research limitations/implications – Since the boundary‐layer analysis is used, the flow is presented up to only the point of external flow separation.Practical implications – Entropy generation analysis can be used to evaluate the design of many heat transfer systems and suggest design improvemen...

Entropy generation due to forced convection fluid flow about a solid sphere

The problem of entropy generation for laminar fluid flow around a solid sphere subjected to uniform heat flux is investigated numerically using a finite-difference technique. The governing continuity, boundary-layer momentum and energy equations were solved. The resulting velocity and temperature profiles were used to compute the local and average entropy generation around the sphere. The two components of the entropy generation, i.e., friction entropy generation and heat-transfer entropy generation, were calculated separately, compared to each other, and the total entropy generation was calculated. The effect of the controlling parameters such as Reynolds number, fluid Prandtl and Eckert numbers on entropy generation were investigated and presented.