The Experts below are selected from a list of 236781 Experts worldwide ranked by ideXlab platform
Ahmed Elsayed - One of the best experts on this subject based on the ideXlab platform.
-
effects of contact resistance and metal additives in finned tube adsorbent beds on the performance of silica gel water adsorption chiller
Applied Thermal Engineering, 2013Co-Authors: Ahmed Rezk, Raya Aldadah, Saad Mahmoud, Ahmed ElsayedAbstract:Recently interest in adsorption cooling Systems has increased due to their capability to utilise low grade heat sources and environmentally friendly refrigerants. Currently, most of the commercially available adsorption cooling Systems utilise granular packed adsorbent beds. Enhancing the heat transfer process inside the adsorbent bed will improve the overall efficiency of the adsorption System. Using recently developed empirical lumped analytical simulation model for a 450 kW two-bed silica gel/water adsorption chiller, this paper theoretically investigates the effects of various adsorbent bed heat transfer enhancement techniques on the adsorption System cooling capacity. Firstly, coating the first adsorbent layer to the metal part and packing the rest of adsorbent granules to eliminate the thermal contact resistance between heat exchanger metal and granules while keeping the same level of permeability. Secondly, adding metal particles to the adsorbent in order to enhance the granules thermal conductivity. The effective thermal conductivity of adsorbent/metal mixtures were determined and validated by comparing it with published experimental data. Also, the combined effect of using both techniques simultaneously was investigated. All these investigations were carried out at various adsorption bed fin spacing. Results of the combined techniques showed that the enhancement in the cooling capacity and System Coefficient of performance (COP) increased with increasing the fin spacing ratio to reach maximum of 25% and 10% respectively at fin spacing ratio of 2.
-
Effects of contact resistance and metal additives in finned-tube adsorbent beds on the performance of silica gel/water adsorption chiller
Applied Thermal Engineering, 2013Co-Authors: Ahmed Rezk, Raya K. Al-dadah, Saad Mahmoud, Ahmed ElsayedAbstract:Recently interest in adsorption cooling Systems has increased due to their capability to utilise low grade heat sources and environmentally friendly refrigerants. Currently, most of the commercially available adsorption cooling Systems utilise granular packed adsorbent beds. Enhancing the heat transfer process inside the adsorbent bed will improve the overall efficiency of the adsorption System. Using recently developed empirical lumped analytical simulation model for a 450 kW two-bed silica gel/water adsorption chiller, this paper theoretically investigates the effects of various adsorbent bed heat transfer enhancement techniques on the adsorption System cooling capacity. Firstly, coating the first adsorbent layer to the metal part and packing the rest of adsorbent granules to eliminate the thermal contact resistance between heat exchanger metal and granules while keeping the same level of permeability. Secondly, adding metal particles to the adsorbent in order to enhance the granules thermal conductivity. The effective thermal conductivity of adsorbent/metal mixtures were determined and validated by comparing it with published experimental data. Also, the combined effect of using both techniques simultaneously was investigated. All these investigations were carried out at various adsorption bed fin spacing. Results of the combined techniques showed that the enhancement in the cooling capacity and System Coefficient of performance (COP) increased with increasing the fin spacing ratio to reach maximum of 25% and 10% respectively at fin spacing ratio of 2.
Ahmed Rezk - One of the best experts on this subject based on the ideXlab platform.
-
effects of contact resistance and metal additives in finned tube adsorbent beds on the performance of silica gel water adsorption chiller
Applied Thermal Engineering, 2013Co-Authors: Ahmed Rezk, Raya Aldadah, Saad Mahmoud, Ahmed ElsayedAbstract:Recently interest in adsorption cooling Systems has increased due to their capability to utilise low grade heat sources and environmentally friendly refrigerants. Currently, most of the commercially available adsorption cooling Systems utilise granular packed adsorbent beds. Enhancing the heat transfer process inside the adsorbent bed will improve the overall efficiency of the adsorption System. Using recently developed empirical lumped analytical simulation model for a 450 kW two-bed silica gel/water adsorption chiller, this paper theoretically investigates the effects of various adsorbent bed heat transfer enhancement techniques on the adsorption System cooling capacity. Firstly, coating the first adsorbent layer to the metal part and packing the rest of adsorbent granules to eliminate the thermal contact resistance between heat exchanger metal and granules while keeping the same level of permeability. Secondly, adding metal particles to the adsorbent in order to enhance the granules thermal conductivity. The effective thermal conductivity of adsorbent/metal mixtures were determined and validated by comparing it with published experimental data. Also, the combined effect of using both techniques simultaneously was investigated. All these investigations were carried out at various adsorption bed fin spacing. Results of the combined techniques showed that the enhancement in the cooling capacity and System Coefficient of performance (COP) increased with increasing the fin spacing ratio to reach maximum of 25% and 10% respectively at fin spacing ratio of 2.
-
Effects of contact resistance and metal additives in finned-tube adsorbent beds on the performance of silica gel/water adsorption chiller
Applied Thermal Engineering, 2013Co-Authors: Ahmed Rezk, Raya K. Al-dadah, Saad Mahmoud, Ahmed ElsayedAbstract:Recently interest in adsorption cooling Systems has increased due to their capability to utilise low grade heat sources and environmentally friendly refrigerants. Currently, most of the commercially available adsorption cooling Systems utilise granular packed adsorbent beds. Enhancing the heat transfer process inside the adsorbent bed will improve the overall efficiency of the adsorption System. Using recently developed empirical lumped analytical simulation model for a 450 kW two-bed silica gel/water adsorption chiller, this paper theoretically investigates the effects of various adsorbent bed heat transfer enhancement techniques on the adsorption System cooling capacity. Firstly, coating the first adsorbent layer to the metal part and packing the rest of adsorbent granules to eliminate the thermal contact resistance between heat exchanger metal and granules while keeping the same level of permeability. Secondly, adding metal particles to the adsorbent in order to enhance the granules thermal conductivity. The effective thermal conductivity of adsorbent/metal mixtures were determined and validated by comparing it with published experimental data. Also, the combined effect of using both techniques simultaneously was investigated. All these investigations were carried out at various adsorption bed fin spacing. Results of the combined techniques showed that the enhancement in the cooling capacity and System Coefficient of performance (COP) increased with increasing the fin spacing ratio to reach maximum of 25% and 10% respectively at fin spacing ratio of 2.
Syed M Zubair - One of the best experts on this subject based on the ideXlab platform.
-
capacity control for refrigeration and air conditioning Systems a comparative study
Journal of Energy Resources Technology-transactions of The Asme, 2001Co-Authors: Maqsood Yaqub, Syed M ZubairAbstract:The capacity control of a vapor-compression refrigeration System is investigated for three different capacity control schemes. In a hot-gas by-pass control scheme, the refrigerant is by-passed from the compressor and injected back into the suction line to decrease the cooling capacity, whereas in cylinder-unloading scheme, one or more cylinders are unloaded to decrease the refrigerant mass flow rate in the System, which decreases the cooling capacity. However, in suction gas throttling, the suction gas throttled at the inlet of the compressor, decreases the refrigerant mass flow rate, and hence a corresponding decrease in the System capacity. These schemes are investigated for HFC-134a by considering finite size of the components that are used in the refrigeration Systems. The models consider the finite-temperature difference in the heat exchangers, thus allowing the variations in the condenser and evaporator temperatures with respect to capacity and external fluid inlet temperatures. A comparative study is performed among these schemes in terms of the System Coefficient of performance (COP), the operating temperatures, and percentage of refrigerant mass fraction as a function of the percentage of full-load System capacity.
-
Performance evaluation of hot-gas by-pass capacity control schemes for refrigeration and air-conditioning Systems
Energy, 2000Co-Authors: Maqsood Yaqub, Syed M Zubair, Jameel-ur-rehman KhanAbstract:The capacity control of a vapor-compression refrigeration System is investigated by injecting hot gas and liquid refrigerant into the suction side of the compressor. Three different possibilities for the by-pass schemes are investigated for HFC-134a by considering finite size of the components that are used in the refrigeration Systems. The model considers the finite-temperature difference in the heat exchangers, thus allowing the variations in the condenser and evaporator temperatures with respect to capacity and external-fluid inlet temperatures. It is demonstrated that the compressor discharge temperatures increase significantly when the hot-gas from the compressor discharge is extracted and injected (without any liquid injection) directly into the suction side of the compressor. A comparative study is also performed of these schemes in terms of the System Coefficient of performance (COP), operating temperatures and the refrigerant by-pass fraction as a function of the percentage capacity reduction.
-
thermodynamic analysis of capacity control schemes for refrigeration and air conditioning Systems
Energy, 1996Co-Authors: Maqsood Yaqub, Syed M ZubairAbstract:Cylinder unloading and suction-gas throttling schemes are studied to reduce the capacity of refrigeration and air-conditioning Systems when operating at reduced load. In the first scheme, an unloaded valve is used to unload one or more cylinders at part-load conditions. The unloading of cylinders reduces the mass-flow rate of refrigerant in the System and thus reduces the System capacity, whereas in suction-gas throttling, a throttling valve is needed before the compressor to reduce the mass-flow rate through the compressor. These schemes are discussed for HFC-134a and compared on the basis of the first and second laws of thermodynamics. A hot-gas by-pass capacity-control scheme is also examined in terms of System Coefficient of performance (COP) and irreversible component losses. It is found that the cylinder-unloading scheme is best and has the highest COP and minimum irreversible losses at any System capacity.
-
second law based thermodynamic analysis of hot gas by pass capacity control schemes for refrigeration and air conditioning Systems
Energy, 1995Co-Authors: Maqsood Yaqub, Syed M Zubair, Shamsul Hoda KhanAbstract:Abstract The automatic hot-gas by-pass technique is applied to reduce the capacity of refrigeration and air-conditioning Systems when operating at part load. In this scheme, hot gas from the compressor is extracted and injected into the suction side of the compresor through a hot-gas by-pass valve. Thus, the refrigerant gas by-passes the evaporator and reduces the System capacity. In this paper, three hot-gas, by-pass schemes for HFC-134a are discussed ad analyzed on the basis of the first and second laws of thermodynamics. A comparative study is performed of the schemes in terms of the System Coefficient of performance (COP) and irreversible component losses. Second-law-based thermodynamic analysis indicates that the total irreversible losses of the by-pass valve increase substantially as the capacity decreases.
-
thermodynamics of a vapor compression refrigeration cycle with mechanical subcooling
Energy, 1994Co-Authors: Syed M ZubairAbstract:Refrigeration and air-conditioning Systems, when operating under large temperature differences between the condenser and evaporator, consume significant amounts of energy. A vapor-compression refrigeration cycle with a mechanical subcooling loop to increase System performance and reduce energy consumption is investigated by using both the first and second laws of thermodynamics. Although the first-law (energy-balance) approach to System analysis shows improvement in the System Coefficient of performance (COP) with an increase in the temperature difference between the condenser and evaporator, it fails to locate sources of losses. Identifying and quantifying these sources can be a useful design tool, especially in developing or investigating new, more complex refrigeration cycles. A second-law analysis (in terms of irreversibility) has been carried out for both the simple and the vapor-compression refrigeration cycle with a mechanical subcooling loop. It is found that the performance of the System can be significantly improved by reducing the irreversibilities due to the expansion process. The low-temperature refrigeration System, when operating at the optimum subcooler saturation temperature, may have the following features: 1.(i) 85% reduction in power input2.(ii) 65% percent lower irreversibility rate3.(iii) 20% reduction in the total refrigerant flow-rate.
Saad Mahmoud - One of the best experts on this subject based on the ideXlab platform.
-
effects of contact resistance and metal additives in finned tube adsorbent beds on the performance of silica gel water adsorption chiller
Applied Thermal Engineering, 2013Co-Authors: Ahmed Rezk, Raya Aldadah, Saad Mahmoud, Ahmed ElsayedAbstract:Recently interest in adsorption cooling Systems has increased due to their capability to utilise low grade heat sources and environmentally friendly refrigerants. Currently, most of the commercially available adsorption cooling Systems utilise granular packed adsorbent beds. Enhancing the heat transfer process inside the adsorbent bed will improve the overall efficiency of the adsorption System. Using recently developed empirical lumped analytical simulation model for a 450 kW two-bed silica gel/water adsorption chiller, this paper theoretically investigates the effects of various adsorbent bed heat transfer enhancement techniques on the adsorption System cooling capacity. Firstly, coating the first adsorbent layer to the metal part and packing the rest of adsorbent granules to eliminate the thermal contact resistance between heat exchanger metal and granules while keeping the same level of permeability. Secondly, adding metal particles to the adsorbent in order to enhance the granules thermal conductivity. The effective thermal conductivity of adsorbent/metal mixtures were determined and validated by comparing it with published experimental data. Also, the combined effect of using both techniques simultaneously was investigated. All these investigations were carried out at various adsorption bed fin spacing. Results of the combined techniques showed that the enhancement in the cooling capacity and System Coefficient of performance (COP) increased with increasing the fin spacing ratio to reach maximum of 25% and 10% respectively at fin spacing ratio of 2.
-
Effects of contact resistance and metal additives in finned-tube adsorbent beds on the performance of silica gel/water adsorption chiller
Applied Thermal Engineering, 2013Co-Authors: Ahmed Rezk, Raya K. Al-dadah, Saad Mahmoud, Ahmed ElsayedAbstract:Recently interest in adsorption cooling Systems has increased due to their capability to utilise low grade heat sources and environmentally friendly refrigerants. Currently, most of the commercially available adsorption cooling Systems utilise granular packed adsorbent beds. Enhancing the heat transfer process inside the adsorbent bed will improve the overall efficiency of the adsorption System. Using recently developed empirical lumped analytical simulation model for a 450 kW two-bed silica gel/water adsorption chiller, this paper theoretically investigates the effects of various adsorbent bed heat transfer enhancement techniques on the adsorption System cooling capacity. Firstly, coating the first adsorbent layer to the metal part and packing the rest of adsorbent granules to eliminate the thermal contact resistance between heat exchanger metal and granules while keeping the same level of permeability. Secondly, adding metal particles to the adsorbent in order to enhance the granules thermal conductivity. The effective thermal conductivity of adsorbent/metal mixtures were determined and validated by comparing it with published experimental data. Also, the combined effect of using both techniques simultaneously was investigated. All these investigations were carried out at various adsorption bed fin spacing. Results of the combined techniques showed that the enhancement in the cooling capacity and System Coefficient of performance (COP) increased with increasing the fin spacing ratio to reach maximum of 25% and 10% respectively at fin spacing ratio of 2.
B Saleh - One of the best experts on this subject based on the ideXlab platform.
-
energy and exergy analysis of an integrated organic rankine cycle vapor compression refrigeration System
Applied Thermal Engineering, 2018Co-Authors: B SalehAbstract:Abstract In the present study, the performance of an integrated organic Rankine cycle-vapor compression refrigeration (ORC-VCR) System is investigated from the viewpoint of energy and exergy analysis. The System performance was represented by System Coefficient of performance (COPS), System exergy efficiency (ηe,sys), turbine pressure ratio (TPR), and total mass flow rate of the working fluid for each kW cooling capacity ( m t o t a l ). Many common and new hydrocarbons, hydrofluorocarbons, fluorocarbons, hydrofluoroethers, and hydrofluoroolefins were suggested as working fluids. The influences of various parameters such as the boiler, condenser, and evaporator temperatures, along with compressor and turbine isentropic efficiencies, on the System performance were also investigated. The results revealed that the best System performance was attained with the uppermost critical temperature dry working fluid. Among all suggested candidates, R602 is shown to be the most suitable working fluid for the ORC-VCR System from System performance and environmental issues viewpoints. However, due to its flammability, extra precautions should be taken. The highest COPS, ηe,sys, TPR, and the corresponding m t o t a l using R602 are 0.99, 53.8%, 12.2, and 0.005 kg s−1 kW−1, respectively at a condenser temperature of 25 °C and the typical values for the rest parameters.
-
parametric and working fluid analysis of a combined organic rankine vapor compression refrigeration System activated by low grade thermal energy
Journal of Advanced Research, 2016Co-Authors: B SalehAbstract:Abstract The potential use of many common hydrofluorocarbons and hydrocarbons as well as new hydrofluoroolefins, i.e. R1234yf and R1234ze(E) working fluids for a combined organic Rankine cycle and vapor compression refrigeration (ORC-VCR) System activated by low-grade thermal energy is evaluated. The basic ORC operates between 80 and 40 °C typical for low-grade thermal energy power plants while the basic VCR cycle operates between 5 and 40 °C. The System performance is characterized by the overall System Coefficient of performance (COPS) and the total mass flow rate of the working fluid for each kW cooling capacity ( m total ). The effects of different working parameters such as the evaporator, condenser, and boiler temperatures on the System performance are examined. The results illustrate that the maximum COPS values are attained using the highest boiling candidates with overhanging T-s diagram, i.e. R245fa and R600, while R600 has the lowest m total under the considered operating conditions. Among the proposed candidates, R600 is the best candidate for the ORC-VCR System from the perspectives of environmental issues and System performance. Nevertheless, its flammability should attract enough attention. The maximum COPS using R600 is found to reach up to 0.718 at a condenser temperature of 30 °C and the basic values for the remaining parameters.
