Dr. Jignesh R. Mehta

The power is very vital factor for development of any nation. Energy resources are limited in stock and its present consumption rate is in increasing trend. There fore energy efficiency and energy conservation are prime important. More over the technology largely used today to produce electricity from coal causes significant negative environmental impacts. Energy and exergy analysis are used to analyse the performance of thermal systems. Energy analysis deals with quantity aspect whereas exergy an alysis deals with quality and quantity aspects of energy. Exergy analysis focuses on magnitude and location of energy loss. In this analysis energy efficiency, exergy destructions, exergy efficiency and turbine heat rates are evaluated at 40%, 50%, 60%, 70 % and 80 % Maximum continuos rating condition of steam turbine. Analysis shows that operating turbine at 80 % MCR attract plant heat rate improvement by 1356.72 kJ/Kwh, which reduce environmental CO2 emission by 1907.79 kg/h, SO2 emissio...

Liquid desiccant (LD) based air conditioning technology is a promising eco-friendly technology with valuable features like high density energy storage and electrical energy saving. Air is dehumidified in air- LD contacting device in this system. Performance of rotating disk type contacting device (RDCD) is simulated in this work using aqueous potassium formate solution as LD. Finite difference method is used for this purpose and suitable heat and mass transfer models and empirical correlations are used. This work would be helpful in choosing the right parameters for RDCD for the given performance criterion.

ABSTRACT There is rapid growth in demand for air conditioning due to rising population and economic development. This technology should diversify and utilize alternative source of energy like solar energy for sustainable development. Liquid desiccant based air conditioning system (LDAC) is adaptable to solar thermal energy and has advantages like high density energy storage and low regeneration temperature. Regenerator in LDAC system removes moisture from LD absorbed in air dehumidifier. Various regenerators in literature like air scavenging regenerators and collector cum regenerator are discussed. These regenerators are compared and their pros and cons are given. The paper presents the topic in digestible form and provides a perspective to a professional in the field or a person who would like to start doing research in the field.

The thermal behaviour of valve regulated lead acid batteries with an evaporative cooling-based thermal management system is experimentally examined during the charging process of an E-bike. The thermal behaviour of valve regulated lead acid batteries is investigated during charging process with three different cooling strategies: evaporative cooling-based battery thermal management system, pre-cooling + battery thermal management system, and natural convection. The valve regulated lead acid batteries from the OREVA ALISH E-bike were used for testing. A portable evaporative cooling system was built for investigation based on available space on the E-bike. The results show that the developed evaporative cooling-based battery thermal management system kept temperatures between 1.5°C and 2.2°C below ambient during the charging process. The temperature of the battery during the charging process is increased slightly, by 1.6°C during the pre-cooling + battery thermal management system coo...

Abstract Contacting device is a system that bring air and water in contact with each other in evaporative cooling systems while it brings liquid desiccant and air in contact with each other in case of liquid desiccant-based air conditioning systems. They should provide high surface area density for heat and mass transfer and also provide high heat and mass transfer rates in smaller volume with lower electrical power consumption. A novel design of contacting device is presented in this work, where plastic porous cylindrical contact media is used and unlike previous designs, the liquid pool in lower part of the device is eliminated. This would help to utilize the contact surfaces more effectively and reduce power consumption of motor used for rotation of the media as compared to earlier designs in literature. The novel contacting device and the experimental set up were developed and preliminary testing was done. The contact media is 230 mm long with diameter equal to 145 mm, providing surface area density equal to 445 m 2 /m 3 . In a preliminary experiment, the device provided evaporative cooling rate up to 288 W and effectiveness of 33.1%. The performance can be further improved by increasing mass flow rate of water for better wetting, increasing surface density by decreasing porosity and increasing path length of air.

There is need to investigate alternate cooling technologies to reduce greenhouse gas emissions and ozone depletion. Liquid desiccant (LD) based air conditioning (LDAC) system is one such promising alternative. Solar thermal energy can be used to regenerate the dilute LD in regenerator of an LDAC system. Solar still is a simple and low parasitic power device for above job. Simulation of performance of solar still for water desalination and 60% aqueous potassium formate regeneration for weather of Ahmedabad, India is done. Experiments are also performed on a FRP solar still with 1 m 2 area. Water evaporation-condensation rate of 2.5 kg reduced to 1.2 kg in LD regeneration experiments due to water vapour pressure suppression by presence of salt in later case. Liquid desiccant temperatures are much higher for LD regeneration than water desalination, particularly in experiments due to low air velocities. Lower air velocities resulted in lower yield for water desalination but higher yield...

A large part of industrial energy need consists of process heating around 100oC temperature. Some of the process heating applications like washing, pasteurization, bleaching, dyeing etc. can be catered to using low temperature solar steam generator. A novel heat pipe based evacuated glass tube solar collector, HP_SC, is developed and fabricated at Heat Pump Laboratory at IIT Bombay, HPL_IITB. This efficient, light weight, low cost non-tracking collector can be mounted on existing roof or can be integrated with roof in new construction. Performance tests of a 7.0 m2 HP_SC generating saturated steam at 1 bar and 100oC with tap water as feed are reported. Six hour average efficiency was in the range of 48 to 54% for average global insolation in the range of 685 to 719 W/m2. Average steam generation rate was 2.2 to 2.6 kg/h with collection of 2.43 to 2.85 kWh/m2 heat over 9 h test period. The paper also includes test results of a three module 10.5 m2 HP_SC while heating water from about...

High peak loads in summer and negative environmental impact are the limitations of using electrical energy for air conditioning. A 3 TR liquid desiccant based solar air conditioner conceived at Heat Pump Laboratory at IIT Bombay HPL_IITB, would maintain indoor conditions at 25+2 C and 50+10% RH while operating in Mumbai. It would also produce potable water and heat tap water to 50 C. Regeneration of liquid desiccant would be carried out in two stages, high temperature regeneration (HTR) and low temperature regeneration (LTR) in order to achieve COP of around one. This paper presents performance of LTR being developed for the solar air conditioning system. The focus is on lowering the parasitic power consumption of the LTR and making it compact and cost effective. In this design of LTR, regeneration air circulation occurs by natural draft. Wetting of contacting media is independent of flow of desiccant, eliminating need for recirculation pump and associated power. Rotating contacting...

ABSTRACT Growing demand for air conditioning and pollution concerns related with production of electrical energy have compelled researchers to investigate new technologies for air conditioning. Liquid desiccant based air conditioning technology is adaptable to pollution-free renewable energy source like solar energy. It has additional advantages like air washing and high density energy storage. Use of solar energy for air conditioning is logical as higher availability of solar radiation matches with higher demand for air conditioning in summer. A novel evacuated tube collector (ETC) with heat pipes is developed in the Heat Pump Laboratory at IIT Bombay (HPL_IITB). In spite of being a not-tracking type, temperatures much beyond the range of flat plate or conventional ETC can be achieved and liquids can even be boiled in this collector. This collector was used as regenerator for liquid desiccant based solar air conditioning system. Objective of this work was to demonstrate and investigate performance of this solar collector with in-situ regeneration. Liquid desiccant was preheated in solution heat exchanger and pumped into the solar regenerator. Steam and regenerated liquid desiccant at outlet of collector were separated and steam was condensed downstream to the collector. Average thermal COP of 0.82 over 5 h experiment period could be achieved with single stage regeneration and insolation range from 509 to 752 W/m2. Parasitic power consumption was less than 40 W, which works out to be 1.5% of the regeneration duty. Solar collector efficiency up to 44.7% was achieved at 117 °C regeneration temperature and 719 W/m2 global radiation along with distilled water production of 5.14 kg/h.

The fossil fuel stocks are limited and create pollution when consumed. We need to use them very rationally. Energy has quality as per second law of thermodynamics. Exergy analysis gives insight into quality of energy (exergy) lost in a given system. Exergy analysis focuses on magnitude and true location of energy loss. More effort need to be applied to place where there is more exergy destruction. This work is an energy and exergy analysis of a 43 MW captive co-generation steam power plant at a chemical plant. The co-generation plant produces power and steam from turbine can be used for process heating. Energy and exergy analysis is carried out for all individual components of the plant like boiler, turbine, condenser etc. Major exergy destruction is seen in combustor and heat recovery system. Frequent soot blowing and excess air control are recommended to improve performance of this plant. This can improve boiler efficiency by 2.2% and also reduce environmental emissions significan...

In today's world where there are energy crises, there is a need to conserve the same. In order to conserve the energy, it is imperative to utilize its available forms as per the requirement that arise from the end user. In this paper, modeling and optimization of a Combined Cooling, Heating and Power (CCHP) plant is done wherein minimization of Exergy Destruction is set as an objective function. Electric and Cooling demands are specified for the plant in the beginning and depending upon the same, the decision variables over a span of 24 hours are achieved after optimization procedure imposed. The CCHP system has thermal, electrical, mechanical and chemical components. It does mean that multiple energy domains exist. The objective function chosen takes care of the same which is the main advantage of using it in optimization procedure.

Better indoor environmental quality at lower energy consumption and less environmental impact are the goals of researchers working in the field of air conditioning. Liquid desiccant based air conditioning (LDAC) system seems to have good potential as an alternative air conditioning system for achieving above goal. Dehumidifier of an LDAC system is an air-liquid desiccant contacting device responsible for air conditioning. Most of the times, the dehumidifier used in LDAC systems is an adiabatic device. High LD flow rate necessary in such systems increase parasitic power consumption in these systems. An internally cooled dehumidifier cools LD as well as air helping to achieve sensible cooling as well as reducing flow rate of LD. Development and analysis of such a device is a bit difficult and getting more attention only recently. The current work focuses on the internally cooled dehumidifier and presents a review of the work reported in literature. This work provides direction and a g...

Lower electrical power consumption and greenhouse gas emission would help to make the technology of air conditioning more sustainable. In present work, a conventional finned tube cooling water coil for air conditioning application was integrated with a liquid desiccant distribution and collection system to work as an internally cooled liquid Desiccant-Air contacting device. More than two-fold rise in latent cooling could be achieved as compared to only chilled water at 16.5 o C temperature. This shows that by use of liquid desiccant, the total cooling provided by a cooling coil can be increased and latent cooling can be significantly enhanced at higher cooling water temperatures.

Demand for air Conditioning demand is continuously growing due to expansion of
middle class and higher comfort expectations. But, higher electricity demand for air
conditioning lead to problems like high peak electrical power deficit and pollution concerns
related to thermal power plants. Low energy alternative air conditioning systems are getting
attention of researchers and policy makers due to these concerns. The alternative
technologies should also use eco-friendly working fluids. Evaporative cooling is one such
eco-friendly low energy cooling technology. High effectiveness, low cost and compact heat
and mass exchangers play an important role in making such technologies competitive with
conventional technologies. Wire mesh media is getting renewed interest from researchers as
they can provide above mentioned favorable properties.
This paper describes a novel contacting device using highly porous cylindrical shape rotating
media made from wire screens. The device is very compact and small in size, 110 mm
diameter x 750 mm length. The surface area density of the device is as high as 527 m2/m3. It
uses a DC motor and DC fan for its operation and thus can run on solar PV cells. In its
present form it can serve as spot cooling device using evaporative cooling concept.
Preliminary testing was carried out in the month of March at Vadodara, India. It provided a
cooling at a rate of 69.5 W consuming around 10 W power. The effectiveness was found to
be 49% at 16 rpm speed of motor and face velocity of air equal to 1.67 m/s. Lower speed of
motor and higher speed of fan was found to be advantageous. The device is expected to
perform better in dry and hot summer conditions and at higher fan speeds. Low electrical
power consumption, low air side pressure drop, least chances of carryover of liquid and
prospective high effectiveness are the important features of this device.

Alternative air conditioning technologies using low grade or renewable energy sources need to be investigated and promoted in order to address issues of sustainable and environment friendly development.  Liquid desiccant dehumidification technology is a promising alternative to conventional air conditioning systems, particularly for reducing power consumption for fresh air dehumidification.  Integrated liquid desiccant dehumidification-fan coil unit system (iLDD+FCUs) was developed and demonstrated in this work.  It showed good energy saving potential as dedicated outdoor air conditioning system (DOAS).  Dehumidification could be achieved without cooling the air below its dew point temperature along with enhancement of the cooling capacity of the FCU.

There is rapid growth in demand for air conditioning due to rising population and economic development. This technology should diversify and utilize alternative source of energy like solar energy for sustainable development. Liquid desiccant based air conditioning system (LDAC) is adaptable to solar thermal energy and has advantages like high density energy storage and low regeneration temperature. Regenerator in LDAC system removes moisture from LD absorbed in air dehumidifier. Various regenerators in literature like air scavenging regenerators and collector cum regenerator are discussed. These regenerators are compared and their pros and cons are given. The paper presents the topic in digestible form and provides a perspective to a professional in the field or a person who would like to start doing research in the field.

Craving for higher comfort and rise in living standards in various societies have led to higher demand for air conditioning. Energy consumption is related with climate change. Desiccant based air dehumidification systems can run with waste heat or renewable source of energy. Liquid desiccant (LD) based air conditioning systems are many times conceived as complicated and costly. A novel but simple internally cooled LDAD system is developed, integrated and tested in this work. Outdoor air was passed through the coil, thus making it essentially a study of fresh air enthalpy removal. Temperature range of 14 to 22oC was used for cooling water, which can be catered by a single stage vapour absorption refrigeration system on lower side or cooling tower on the higher side. The cooling capacity of the system increased up to 54%, compared to conventional chilled water coil. Latent heat fraction removed was also higher, showing usefulness of the system for higher latent load applications. Higher air velocity was found to give higher cooling capacity, while moisture removal per kg of air and effectiveness were higher at lower air velocities.