P.K. Sahoo

Thermoeconomic optimization of a single effect water/LiBr vapour absorption refrigeration system

In this paper, the thermoeconomic theory is applied to the economic optimization of a single effect water/LiBr vapour absorption refrigeration system for air-conditioning application, aimed at minimizing its overall operation and amortization cost. The mathematical and numerical techniques based optimization of thermal system is not always possible due to plant complexities. Therefore, a simplified cost minimization methodology is applied to evaluate the economic costs of all the internal flows and products of the system by formulating exergoeconomic cost equations. Once these costs are determined, the system is thermoeconomically evaluated to identify the effects of design variables on costs and enables to suggest values of design variables that would make the overall system cost effective. Finally, an approximate optimum design configuration is obtained by means of sequential local optimization of the system, carried out unit by unit. The result compares this optimum with the base case and shows percentage variations in the systems operation and amortization cost.

Application of the exergetic cost theory to the LiBr/H2O vapour absorption system

Optimization of thermal systems is generally based on thermodynamic analysis. However, the systems so optimized often are not viable due to economic constraints. The Theory of Exergetic Cost, a thermoeconomic optimization technique, combines the thermodynamic analysis with that of economic constraints to obtain an optimum configuration of a thermal system. In this paper, this technique is applied to optimize a LiBr/H2O vapour absorption refrigeration system run by pressurized hot water for air-conditioning applications. The mathematical and numerical techniques-based optimization of thermal systems is not always possible due to plant complexities. Hence, a simplified cost minimization methodology, based on ‘Theory of Exergetic Cost’, is applied to evaluate the economic costs of all the internal flows and products of the system under consideration. As shown in this paper, once these costs are determined, an approximately optimum design configuration can be obtained.

A Critical Review on Solid Desiccant-Based Hybrid Cooling Systems

The present review provides scientific and technical support on how solid desiccant-based hybrid cooling can be a supplement to the commonly used vapor compression-based traditional air-conditioning systems to provide the indoor thermal comfort to the occupants. The existing design of standalone vapor compression system needs to be modified by integrating it with the solid desiccant-based dehumidification system to achieve better performance and economic feasibility by handling humidity and temperature separately especially in case of hot humid conditions. The present study is undertaken by considering variety of aspects including background and need for alternative cooling systems, system configuration as well as operational modes and current status of desiccant-based hybrid cooling technology. The review work also indicates that the technology of desiccant-based hybrid cooling has a great potential to provide thermal comfort especially in hot humid climate at the expense of lower energy consumption as compared to traditional cooling systems.

Performance analysis of hybrid solid desiccant–vapor compression air conditioning system in hot and humid weather of India

The performance of hybrid solid desiccant–vapor compression air conditioning system is studied for the typical hot and humid climatic zone of North India (Roorkee). The system consists of a rotary desiccant dehumidifier coupled with heat recovery wheel and a conventional vapor compression air conditioning system. A FORTRAN program was developed to calculate different psychrometric properties like humidity ratio, dry-bulb temperature, wet-bulb temperature, relative humidity, specific heat, etc. at each state point of the system on the basis of ambient and desired inside room conditions, room cooling load, sensible heat factor, and required air flow rate. The overall system performance has been evaluated in terms of the coefficient of performance and the dehumidifier effectiveness. The influence of variation in ambient conditions on regeneration temperature of desiccants has also been discussed. The simulated results are validated using experimental measurements. The present system has ensured a reduction of 79.15% in processing air humidity ratio at an outlet of the desiccant dehumidifier as compared to the outdoor humidity ratio. The results show that the performance of the system is significantly affected by the variations in ambient temperature and humidity ratio. Practical application : The proposed model of solid desiccant–VCR hybrid air conditioning system minimizes the energy usage in comfort cooling applications such as auditoriums, supermarket, hospitals, central library, offices, and lecture halls in hot and humid climate while maintaining an acceptable thermal comfort level and improving the performance. The proposed approach will give valuable insights to the researchers and building engineers to analyze the impacts of ambient conditions on the energy requirements and performance of solid desiccant cooling to ameliorate comfort, energy, and cost savings. Moreover, its potential contribution in environmental protection makes it more attractive at a time where depletion of energy resources and environmental degradation are of major concerns.

Flow Characteristics of Refrigerants Flowing Inside an Adiabatic Spiral Capillary Tube

An analytical model has been developed to predict the length of adiabatic capillary tubes used in domestic refrigerators and low-capacity residential air conditioners. The model predicts the length of two types of tubes—straight and spiral adiabatic capillary tubes. The proposed model is based on the homogenous two-phase flow model, which predicts the length of the adiabatic capillary tubes as a function of refrigerant mass flow rate, capillary tube diameter, degree of subcooling at capillary inlet, internal surface roughness, and the pitch of the Archimedean spiral. The existence of subcooled liquid at the entry of the capillary tube requires the computation of single-phase and then two-phase lengths of the tube. The McAdams et al. (1942) viscosity correlation has been used to evaluate the two-phase viscosity of the expanding refrigerant in the latter part of the capillary tube. All the thermophysical and transport properties of the refrigerants are evaluated by the REFPROP Version 7 database, which is based on the Carnahan-Starling-DeSantis equation of state. The simulation results are validated with the experimental findings of previous researchers. The performance of the above two geometries of adiabatic capillary tube is compared, and it is established that for the same state of refrigerants at the inlet and exit of the adiabatic capillary, spiral capillary is found to have a shorter length. Parametric study of the adiabatic capillary tubes is also carried out. Further, the effect of geometric and physical parameters has been presented in detail. A much smaller capillary tube is required when the eco-friendly refrigerants R-134a and R-152a are used in place of refrigerant R-12 for similar conditions across the adiabatic spiral capillary tube.

Exergy analysis of solid desiccant-vapour compression hybrid air conditioning system

This paper presents energy and exergy analysis of a solid desiccant vapour compression hybrid air conditioning system. Parametric study has been conducted at varying dead state properties and operating conditions to investigate their effects on the overall system performance. The obtained results show that the exergy efficiency of hybrid air conditioning system is 11.45%. The energy-based performance parameters such as the coefficient of performance (COP) and components effectiveness are also presented. The rotary desiccant dehumidifier and heater are found as major contributors to exergy performance of the system. The analysis provides us beneficial knowledge to determine theoretical upper limit of the system performance.

Experimental and Numerical Investigation of R-134a Flow through a Lateral Type Diabatic Capillary Tube

This paper presents the performance of R-134a through a diabatic capillary tube with lateral configuration. The paper is divided into two sections: (1) an experimental investigation of straight and helical diabatic capillary tubes and (2) a numerical investigation of the straight diabatic capillary tube. In the experimental investigation, the effects of parameters such as capillary tube diameter, capillary tube length, coil pitch, and inlet subcooling on the refrigerant mass flow rate through a diabatic capillary tube were studied. In addition to the parameters mentioned above, the mass flow rate through a diabatic helical capillary tube was also found to be a function of suction-line inlet superheat and heat exchange length. The suction-line inlet superheat in the present investigation is not a controlled parameter. A comparison of the results of diabatic helical capillary and adiabatic helical capillary tubes was also made. On the basis of acquired experimental data, a correlation to predict the refrigerant mass flow rate was proposed. It was found that the predictions of the proposed correlation are within ±5% agreement with the experimental data. In the numerical investigation, a mathematical model was developed by applying laws of conservation of mass, momentum, and energy to a straight diabatic capillary tube. These differential equations were solved numerically using a finite difference method. The developed model was validated with experimental data from previous and present research. Further, a comparison was also made between the proposed model and the models of Sinpiboon and Wongwises (2002) and Valladares (2007).

Solar Assisted Solid Desiccant—Vapor Compression Hybrid Air-Conditioning System

Solar assisted solid desiccant—vapor compression based hybrid space cooling system for building thermal comfort is made by integrating desiccant based dehumidification system as well as by use of solar heating system along with conventional VCR system. This is because in humid climates, excessive humidity during summer leading to inefficiencies of conventional cooling devices. Humidity increment in ambient air as well as ventilation requirement suddenly rises the latent load of the space to be cooled. Conventional VCR systems are not effective in handling both temperature and relative humidity of cooling air independently. The application of solid desiccant based hybrid cooling systems significantly ameliorates the humidity control irrespective of temperature of supply air. The application of renewable free energy like as use of solar energy for regenerating the desiccant used in desiccant wheel helps us to alleviate the major requirement of electric energy needed by conventional VCR air-conditioning system for hot sunny days. So, it ameliorates overall energy efficiency and reduces energy costs. Performance of solid desiccant—vapor compression based hybrid building space comfort cooling system has been evaluated during hot and humid period from April to September for the ambient conditions of the Roorkee for various important parameters such as temperatures of supply air, room air and regeneration air etc. Regeneration temperature is one of the most important parameters having the key role in changing the performance of desiccant based cooling system.

Ballooning of Pressure Tube Under LOCA in an Indian Pressurised Heavy Water Reactor

A study has been carried out by experimental simulation of the loss of coolant accident (LOCA) in an Indian pressurized heavy water reactor (IPHWR). The experiment has been carried out taking a completely voided fuel channel of Indian PHWR at 40 bar inside pressure as test-section. In order to simulate the rate of heat generation during LOCA, the pressure tube (PT) was electrically heated with a 12VDC/3500A rectifier. Initially the set-up was maintained at 300 °C temperature by resistance heating of PT. After attaining nearly steady state a step input of 21 kW electrical heating was given to the test-section which resulted in the temperature rise of PT with a gross rate of 2.8 °C/s. The ballooning deformation of test-section tube i.e. PT initiated at 575 °C temperature. With the progress of ballooning the rate of temperature rise was reduced due to high heat transmission to CT and subsequently to water in the tank surrounding CT. The pressure tube (PT) and calendria tube (CT) contact established at the average PT temperature of 680 °C. The contact was also confirmed from the average temperature profile of CT.Copyright