Muhammad M Rafique | The University of Adelaide (original) (raw)

Papers by Muhammad M Rafique

The liquid desiccant cooling system is found to be a good alternative of conventional air conditi... more The liquid desiccant cooling system is found to be a good alternative of conventional air conditioning system for better control of both latent and sensible loads. The major component of a liquid desiccant cooling system is desiccant dehumidifier which controls the latent cooling load. In this paper a mathematical model for rotary type liquid desiccant dehumidifier commonly known as desiccant wheel has been presented. The desiccant wheel has a cylindrical shape with a number of identical narrow circular slots distributed uniformly over the rotor cross section. The slots are filled with a porous medium carrying the solution of liquid desiccant, to make the absorbing surface. The absorption and regeneration performance of the desiccant dehumidifier is discussed in this paper for different operating conditions. The wheel performance curves which help to determine the air outlet conditions and coefficient of performance (COP) of the system are drawn for a wide range of wheel thickness (0.06-0.6m), air mass flux (1-8 kg/m 2 .s), and regeneration temperature (60-85 o C). A reduction of about 30% in outlet humidity ratio is observed with an increase in the wheel thickness from 0.06 to 0.2m. The computed results show that better supply air conditions can be obtained to provide human thermal comfort in the hot and humid climate with effectiveness of the system largely dependent on air flow rate, wheel thickness and humidity ratio of process air.

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In this article, the current energy consumption of Pakistan is presented and the issue of securit... more In this article, the current energy consumption of Pakistan is presented and the issue of security of electrical energy supply is discussed. The power sector has been looked from variety of aspects such as, demand and supply gap, diminishing energy sources, energy security, and increasing energy costs. Furthermore, the status of energy and potential of renewable sources of energy has been discussed as sustainable alternative. In addition, the roles of different sectors in the promotion and development of renewable energy technologies have been discussed. The renewable energy future prospects are encouraging in Pakistan with a total renewable energy potential of about 167.7 GW which is more than enough to meet the total electricity demand of the country. This vast potential of renewable sources of energy could be utilized to overcome the energy shortage which has not been utilized properly due to lack of policies and infrastructure. The diversification of existing energy resources and exploration of new sources is an important aspect to be considered in order to have a sustainable power development and its implementation in the country.

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The control of air conditioning latent and sensible load separately by using a desiccant dehumidi... more The control of air conditioning latent and sensible load separately by using a desiccant dehumidifier operating in conjunction with evaporative cooler can reduce the air conditioning power requirement significantly. This system can also utilize the alternative resources of energy such as solar, waste heat, and natural gas effectively. In this article a mathematical model of desiccant evaporative cooling has been developed and the performance of the system is analyzed for its feasibility under the climatic conditions of Dhahran, Saudi Arabia. Different performance curves have been drawn to get optimum values of parameters under different operating conditions. Some new parameters such as sensible energy ratio have also been introduced for better prediction of system cooling capacity. The results showed that the proposed system is suitable and feasible solution to meet the high cooling demands for the conditions of Dhahran, Saudi Arabia with performance largely dependent on optimum selection of operating parameters.

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Now days, air conditioning systems are a must for almost every commercial and residential buildin... more Now days, air conditioning systems are a must for almost every commercial and residential building to achieve comfortable indoor conditions. The increasing energy demand, and increasing oil prices and pollution levels raise the need for alternative air conditioning systems which can efficiently utilize renewable energy resources. The liquid desiccant-based air conditioning method is pollution free and thermal energy-based cooling techniques can use low grade thermal energy resources like solar energy, waste heat, etc. These systems have an additional advantage of cleaning bacteria and fungi from the air. In this paper, a newly proposed rotary liquid desiccant air conditioning system has been investigated theoretically. Most direct contact liquid desiccant cooling systems have the problem of desiccant carryover which can be eliminated using the proposed system. The effects of various key parameters and climatic conditions on the performance of the system have been evaluated. The results showed that if the key parameters of the system are controlled effectively, the proposed cooling system has the ability to achieve the desired supply air conditions. The system can achieve high coefficient of performance (COP) under different conditions. The dehumidifier has a sensible heat ratio (SHR) in the range of 0.3–0.6 for different design, climatic, and operating conditions. The system can remove latent load efficiently in applications which require good humidity control.

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Air high in humidity leads to uncomfortable conditions and promotes the growth of different fungi... more Air high in humidity leads to uncomfortable conditions and promotes the growth of different fungi and bacteria, which may cause health problems. The control of moisture content in the air using traditional air conditioning techniques is not a suitable option due to large consumption of primary energy and hence emission of greenhouse gases. The evaporative cooling technology is a cost effective and eco-friendly alternative but can provide thermal comfort conditions only under low humidity conditions. However, the evaporative cooling method can be used effectively in conjunction with desiccant dehumidifiers for better control of humidity. Such systems can control the temperature and humidity of the air independently and can effectively utilize the low-grade thermal energy resources. In this paper, the theoretical analysis of desiccant based evaporative cooling systems is carried out for five cities in Saudi Arabia (Jeddah, Jazan, Riyadh, Hail, and Dhahran). It has been observed that the coefficient of performance (COP) of the system varies from 0.275 to 0.476 for different locations. The water removal capacity of the desiccant wheel is at its maximum for the climatic conditions of Jazan and at its minimum for Hail. The effect of climatic conditions of five cities on regeneration temperature, air mass flow rate, and potential of solar energy has been evaluated using RET Screen software.

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Due to the direct utilization of thermal energy and possibility of using renewable energy resourc... more Due to the direct utilization of thermal energy and possibility of using renewable energy resources, the interest of using desiccant wheel for air conditioning application is increasing rapidly. The thermally driven desiccant cooling systems are environmental friendly and have a great potential to reduce the peak electricity demand. The high initial cost of these system as compared to the conventional units can be reduced at designing stage through selection of suitable cycle, size reduction, and flow optimization. The aim of this paper is to develop a mathematical model for the desiccant wheel to predict its dynamic performance. The model is numerically stable and easy to simulate. The desiccant wheel performance has been discussed under different operating parameters. The effect of mass flow rate on heat and mass transfer coefficient has also been studied. Results showed that, an optimum value of operating parameters like mass flow rate and regeneration temperature should be selected for better performance of the system. In addition, transient variation of vapor adsorption rate has also been discussed.

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Due to the direct utilization of thermal energy and possibility of using renewable energy resourc... more Due to the direct utilization of thermal energy and possibility of using renewable energy resources, the interest of using desiccant wheels for airconditioning application is increasing rapidly. The thermally driven desiccant cooling systems are environmental friendly and has a great potential to reduce the peak electricity demand. During the experiments the inlet and outlet parameters in the dehumidifier can be easily measured. However, in theoretical analysis it is difficult to predict the relationship between these parameters because of the complexity of combined heat and mass transfer process. In this paper a statistical analysis using Minitab software is used to predict the functional relationships between the input and output parameters in the dehumidifier. The factorial analysis is first carried out to eliminate the factors which does not affect the response, significantly. Then, the regression analysis is carried out to analyze the effect of significant operating variables (independent) on the moisture absorption rate in the dehumidifier and to develop a relationship between dependent and independent variables. Regression analysis shows that the inlet air humidity ratio, ratio of mass flow rates, and regeneration temperature cause significant variation (P<0.01) in the absorption rate.

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It is important to decrease the energy cost of heating, ventilating and air conditioning (HVAC) s... more It is important to decrease the energy cost of heating, ventilating and air conditioning (HVAC) systems without compromising indoor air quality and comfort conditions due to the rising cost of fossil fuels and other environmental concerns. Liquid desiccant cooling systems are one of the alternatives in this regard which is not only environmental friendly (no use of any refrigerant which deplete ozone layer) but at the same time make a good use of alternative sources of energy like, solar, biomass etc. This paper presents different commercially available liquid desiccants and their composites which combines the properties of two or more desiccant materials for better performance. A good desiccant should have better moisture absorption capability and lower temperature of regeneration. This paper also includes the different configurations of liquid desiccant dehumidifiers and their advantages as well as drawbacks. Some new configurations of liquid desiccant dehumidifiers have been introduced which greatly improves the system overall performance. Moreover, a summary of the performance parameters has been made to analyze the system performance. This review is meaningful for the research and technical development process of liquid desiccant technology.

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The scarcity of fresh water is an issue which need special attention as most of the world populat... more The scarcity of fresh water is an issue which need special attention as most of the world population suffers from clean water shortage which results in a lot of diseases and deaths. The aim of the work is to come up with a relatively cheap, portable and efficient system that can produce pure water by utilizing solar energy. The approach involve the experimental investigation of single sloped solar still with and without phase change material in winter season under climatic conditions of Dhahran, Saudi Arabia. Initially solar still was tested with different depth of water without phase change material and performance analysis are carried out on the basis of various factors that include solar intensity, ambient temperature, water temperature, and glass temperature, temperature of inlet water, and depth of water. The still was then tested with phase change material for the comparative analysis under same prevailing conditions. The purpose of using phase change material is storage of available solar energy during the day which can be used after the sunsets and solar still can work for longer period of time. The results showed that solar still with phase change material can produce the fresh water for longer period of time during the day (even after the sunset) as compared to the solar still without phase change material.

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Books by Muhammad M Rafique

The conventional vapor compression air conditioning systems remove moisture from the air by cooli... more The conventional vapor compression air conditioning systems remove moisture from the air by cooling to a very low temperature. This dehumidified air is then reheated to an appropriate supply temperature for occupants comfort. These two processes of excessive cooling and reheating of process air remarkably increase the air conditioning load. To avoid the excessive waste of energy an alternative way to achieve desired moisture reduction is the use of liquid desiccant dehumidification system in which a desiccant material absorbs moisture from the humid air. Thermal energy is used to regenerate the desiccant material and cycle continues. A good desiccant should have better moisture absorption capability and lower temperature of regeneration. Different types of new desiccant materials with high dehumidification performance have been proposed in past few years. These materials have the potential to improve the performance of liquid desiccant cooling systems because of lower heat input required for regeneration. In this article, liquid desiccant cooling systems have been discussed from variety of aspects including the need of liquid desiccant technology as an alternative way of cooling, working of liquid desiccant cycle, as well as developments of this technology. The research indicated that the technology of liquid desiccant cooling has a great potential of energy saving and providing human thermal comfort conditions in hot and humid climatic conditions with the utilization of alternative energy resources.

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Thermal cooling using low-grade energy resources such as solar energy, waste heat, biomass is one... more Thermal cooling using low-grade energy resources such as solar energy, waste heat, biomass is one of the key solutions to the environmental degradation and fast depletion of primary energy resources. Liquid desiccant-based evaporative cooling is an environment-friendly and cost-effective alternative to the conventional airconditioning systems due to its energy-saving potential. The idea of a liquid desiccant evaporative cooling system is to combine liquid desiccant dehumidifi-cation with an evaporative cooling system in order to advance the overall system performance and to utilize clean and renewable energy resources. In this chapter, desiccant-enhanced evaporative cooling systems have been discussed from variety of aspects including background and need of alternative cooling systems, concept of desiccant-based evaporative coolers, system configurations, as well as developments of technology. The research indicates that the technology of liquid desiccant-based evaporative cooler has a great potential of providing human thermal comfort conditions in hot and humid climatic conditions at the expense of less primary resources of energy as compared to conventional cooling systems. Furthermore, recent developments for liquid desiccant dehumidifiers and evapo-rative cooling technology along with future view of research in the field of des-iccant cooling technology have been presented.

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Conference Presentations by Muhammad M Rafique

The quality and cleanliness of indoor air is affected by moist surrounding when relative humidity... more The quality and cleanliness of indoor air is affected by moist surrounding when relative humidity of the air is above 70% which may leads to the growth of fungi and bacteria. Apart from this issue of indoor air quality, the presence of humidity cause inefficiencies in cooling devices. One alternative way to this problem is the use of desiccant dehumidifier to absorb/adsorb moisture from the hot and humid air. In this paper a cooling system using solid desiccant dehumidifier is presented for hot and humid climatic conditions. The objective of this investigation is to study and compare the performance of desiccant cooling system operating on two different cycles (ventilation and recirculation) in hot and humid climatic conditions. The average values of different performance parameters such as COP, cooling load and regeneration load are compared for the both cycles. The results showed the system operating under the ventilation cycle has a better coefficient of performance as compared to the recirculation cycle because of the less input/regeneration heat required. The value of these operating parameters have also been calculated in this analysis.

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With the increase in cooling load demand and environmental concerns, some alternative cooling tec... more With the increase in cooling load demand and environmental concerns, some alternative cooling technology is required along with conventional cooling systems. Desiccant cooling technology is a suitable alternative in this regard and gives good control of both temperature and humidity. Moreover these systems can exploit thermal energy such as, solar energy in a very efficient way instead of electric energy. A typical solid desiccant cooling system combines a desiccant wheel composed of some sorption material and a sensible cooling system. It is an environment friendly system because no refrigerant is being used which depletes the ozone layer. The main purpose of this study is to analyze the performance of a solid desiccant cooling system with indirect evaporative cooler for the climatic zone of Dhahran, Saudi Arabia. Three months (April, June, and August) have been selected to observe the performance of the system. It has been observed after theoretical analysis that solid desiccant cooling system is a good and suitable option for human comfort in humid and hot climate conditions. The results showed that maximum regeneration power required is for month of April and minimum for August. It has also been observed that by bypassing 30-75% regeneration air before it enters the heater increase the system coefficient of performance (COP) remarkably.

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Due to the direct utilization of thermal energy and possibility of using renewable energy resourc... more Due to the direct utilization of thermal energy and possibility of using renewable energy resources, the interest of using desiccant wheels for airconditioning application is increasing rapidly. The thermally driven desiccant cooling systems are environmental friendly and has a great potential to reduce the peak electricity demand. During the experiments the inlet and outlet parameters in the dehumidifier can be easily measured. However, in theoretical analysis it is difficult to predict the relationship between these parameters because of the complexity of combined heat and mass transfer process. In this paper a statistical analysis using Minitab software is used to predict the functional relationships between the input and output parameters in the dehumidifier. The factorial analysis is first carried out to eliminate the factors which does not affect the response, significantly. Then, the regression analysis is carried out to analyze the effect of significant operating variables (independent) on the moisture absorption rate in the dehumidifier and to develop a relationship between dependent and independent variables. Regression analysis shows that the inlet air humidity ratio, ratio of mass flow rates, and regeneration temperature cause significant variation (P<0.01) in the absorption rate.

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