Search Results

The author has developed UV based photocatalytic air purification system (Mathur, 2021, 2122, 2023) that can eliminate all pathogens from the cabin air including COVID-19. In this study, the focus is to determine the risk of infection due to pathogens/germs in the cabin of an automobile. Author has determined the risk of infection by using Wells-Riley model and conducted CFD analysis to determine propagation of virus in cabin as a function of: 1 Cabin Volume & Number of Occupants (Wells-Riley Model in OSA mode): (i) Cabin volume from: Small Sedan, Large Sedan and a SUV; with 4 occupants (males & females); Number of infector 1; Air flowrate (m3/min); (ii) A 15-seater minibus – with 10 occupants (males); Number of infectors 1 & 2; Air flowrate (m3/min) 2 CFD to simulate 4 occupants and 1 infector in an automotive cabin – Current investigation is for talking, coughing and sneezing with blower off in Recirc mode wit (i) Infector in the front seat; (ii) Infector in the rear seat.

Per - and polyfluoroalkyl substances – known as PFAS are man-made chemicals that do not occur naturally. PFAS are widely used, long lasting chemicals, components of which break down very slowly over time. Scientific studies have shown that exposure to some PFAS in the environment may be linked to harmful health effects in humans and animals. Because of their widespread use and their persistence in the environment, many PFAS are found in human and animals’ blood all over the world and are present at low levels in a variety of food products and in the environment. PFAS are found in water, air, fish, and soil at locations across the nation and the globe. Both refrigerants (HFC-134a & HFO-1234yf) that are currently used in mobile air conditioning systems (MACS) create PFAS. Hence, various countries are looking into banning chemicals that create PFAS. Natural refrigerants are being proposed as alternative refrigerants as they do not create PFAS.

The author has been conducting research on UV based photocatalytic air purifier systems for the past 5 years to eliminate living organic germs, bacteria, pathogens, etc. from the cabin air. An HVAC system has been developed by using a filter impregnated by titanium di-oxide (TiO2) with UV lights to improve and maintain cabin air quality. The author has designed and constructed a 3rd generation HVAC unit for cabin air purification for automobiles that is based on UV photocatalytic process by using UV-C LEDs to eliminate viruses that typically exist in conditioned space. The author has conducted tests with HVAC unit to determine power consumptions of air purification systems. An HVAC unit that employs a HEPA (high efficiency particulate air filter) filter is compared with the same HVAC unit with UV & titanium dioxide based photocatalytic system. The pressure drops of the HEPA, particulate and TiO2 filters have been investigated that contribute to the overall energy consumption.

The author has been conducting research on UV based photocatalytic air purifier systems for the past 5 years to eliminate living organic germs, bacteria, pathogens, etc. from the cabin air. An HVAC system has been developed by using a filter impregnated by titanium di-oxide (TiO2) with UV lights to improve and maintain cabin air quality. The designed system can be used for conventional vehicles, EVs, ride sharing and for autonomous vehicles. The author has designed and constructed a 3rd generation HVAC unit for cabin air purification for automobiles that is based on UV photocatalytic process by using UV-C LEDs to eliminate viruses that typically exist in conditioned space.

In a photocatalytic air purifier system, the catalyst that cleans the air is typically titanium dioxide and it is energized by ultraviolet (UV) light. When UV light shines on the titanium dioxide, electrons (negatively charged particles inside atoms) are released at its surface. The electrons interact with water molecules (H2O) in the air, breaking them up into hydroxyl radicals (OH·), 9which are highly reactive, short-lived, uncharged forms of hydroxide ions (OH−). These small, agile hydroxyl radicals then attack bigger organic (carbon-based like virus) pollutant molecules, breaking apart their chemical bonds and turning them into harmless substances such as carbon dioxide and water. Current investigation uses the above principle to kill living organic germs, bacteria; pathogen, etc. from the cabin air in recirculation mode. A HVAC system has been developed by using a filter impregnated by titanium di-oxide (TiO2) with UV lights to improve and maintain cabin air quality.

Carbon dioxide exhaled by occupants remains within the cabin during operation of HVAC unit in recirculation mode. The CO2 inhaled by the occupants goes into their blood stream that negatively affects occupant’s health. ASHRAE Standard-62 (1999) specifies the safe levels of carbon dioxide in conditioned space for humans. The CO2 concentration limit per ASHRAE is 700 ppm over ambient conditions on a continuous basis. Based on the test data, at worst case scenario (idle condition where body leakage will be a minimal) results in CO2 concentrations of 1601, 2846, 4845 and 6587 ppm respective for 1 to 4 occupants in 30 minutes. Author has also conducted test by imposing ASHRAE standard-62. A controller was programmed for operating the blower unit’s intake door to go from recirculation to OSA mode when the measured carbon dioxide ppm level goes above 1100 ppm. The door stays in OSA mode until the cabin carbon dioxide falls to approximately 500ppm.

Author has developed a correlation to predict condensation heat transfer coefficients for refrigerant condensation in an automotive parallel flow condenser. This is a first correlation in the open literature for HFO-1234yf to predict heat transfer coefficients for an automotive condenser. The system refrigerant mass flowrate was varied from 180 to 475 kg/hr; inlet refrigerant qualities from 1 to exit qualities of 0. The tests were conducted at an average condenser saturation temperature of 50°C and the oil circulation ratio was maintained at 3%.

Carbon dioxide exhaled by occupants remains within the cabin during operation of HVAC unit in recirculation mode. The CO2 inhaled by the occupants goes into their blood stream that negatively affects occupant’s health. ASHRAE Standard 62 specifies safe levels of carbon dioxide in conditioned space for humans. The CO2 concentration limit per ASHRAE is 700 ppm over ambient conditions on a continuous basis. In a recent investigation the author had developed a model to predict cabin carbon dioxide concentrations for recirculation mode as a function of time, number of occupants, vehicle speed, body leakage characteristics, occupant lung capacities and concentrations of the carbon dioxide coming out from occupant’s mouth, blower position and vehicle age. This developed model has been modified to simulate cabin airflows from 100% recirculation mode to 100% outside air mode, i.e., for any percentage of partial recirculation.

In recent years, start-stop systems have been implemented by many OEMs for improvement of fuel economy. When the engine stops, the occupant comfort typically deteriorates. Hence, the climate and fuel economy engineers are struggling to combine the passenger comfort and fuel economy. Especially in a vehicle cabin where the thermal environment becomes unsteady and highly non-uniform due to a start-stop. It is difficult to adapt any comfort evaluation index that have already been well established for a stationary/uniform space in building type environment in comparison to a vehicle cabin interior. The existing standard of ISO-14505-2 does not consider this for vehicle cabin interior condition. Hence, the authors have developed the occupant’s comfort prediction method under highly non-uniform condition and unsteady conditions and have established a new methodology [1].

Author has developed a correlation to predict flow boiling heat transfer coefficients for refrigerant evaporating in an automotive evaporator. This is a first correlation in the open literature for HFO-1234yf to predict heat transfer coefficients for automotive evaporator. The refrigerant mass flux was varied from 500 to 1200 kg/m2.s; heat flux was varied from 2 to 6.2 kW/m2; inlet refrigerant qualities from 0 to 40% and exit qualities of about 95%. The tests were conduct at 4.4 °C and the oil circulation ratio was maintained at 3%. Experimental data has been used with MINITAB software, Version 16.1.0 to develop this correlation. Multivariate nonlinear regression analysis has been done to develop this correlation. Experimental data along with refrigerant properties, hydraulic diameter that affects Reynolds number, Prandtl number and other appropriate variables have been used to develop this correlation. Details of the newly developed correlation have been presented in the paper.

Recently the author (Mathur, 2017) had presented a model to predict cabin carbon dioxide concentrations as a function of time, number of occupants, vehicle speed, body leakage characteristics, occupant lung capacities and concentrations of the carbon dioxide coming out from occupant’s mouth, blower position and vehicle age. The developed model was validated by the author for mid-sized vehicles (vehicles from D-segment). The simulated data was within ±11.5% of the experimental data. In this paper the author has used the developed model to predict cabin CO2 concentrations for vehicles from B, C & D segments. Or in other words, the effect of the cabin volume will be investigated on the rate of build-up of cabin CO2 concentrations. Experimental tests were conducted on these vehicles and are compared to the simulated data. Detailed results have been presented in the paper.

Water drainage characteristics are dependent on the design of the evaporator: specifically the design of the fins and plates along with hydrophilic coating. A part of the hydrophilic coating washes off with the moisture that condenses over the evaporator core from the air-stream. Hence, water drainage characteristics of an evaporator changes with the vehicle mileage or the age of the vehicle. Since a part of the hydrophilic coating washes away, more water is retained within the evaporator at this condition. Hence, the effectiveness of the evaporator drainage deteriorates with the age of the vehicles. At this condition, the contact angle measured at the plate increases. Author has conducted an experimental study to measure the effectiveness of hydrophilic coating from evaporators taken out from arid (9 cores) and humid areas (16 cores) as a function of vehicle mileage or vehicle age. Contact angles and water retention were measured for a number of evaporators from different OEMs.

The EPA has issued regulations in the Final Rulemaking for 2017-2025 Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards (420r12901-3). This document provides credits against the fuel economy regulations for various Air Conditioning technologies. One of these credits is associated with increased use of recirculation air mode, when the ambient is over 24°C (75°F.). The authors want to communicate the experiences in their careers that highlighted issues with air quality in the interior of the vehicle cabin. Cabin contamination sources may result in safety and health issues for both younger and older drivers. Alertness concerns may hinder their ability to operate a vehicle safely.

The author has developed a model that can be used to predict build-up of cabin carbon dioxide levels for automobiles based on many variables. There are a number of parameters including number of occupants that dictates generation of CO2 within the control volume, cabin leakage (infiltration or exfiltration) characteristics, cabin volume, blower position or airflow rate; vehicle age, etc. Details of the analysis is presented in the paper. Finally, the developed model has been validated with experimental data. The simulated data follows the same trend and matches fairly well with the experimental data.

Water drainage characteristics of an evaporator changes with the age of the vehicle. This is due to the fact that with time, a part of the hydrophilic coating washes off with the moisture that condenses over the evaporator core from the air-stream. Hence, the effectiveness of the evaporator for water drainage deteriorates with the age of the vehicle. At this condition more water is retained in the evaporator as the contact angle increases. Author has conducted experiments with evaporators from multiple vehicles from different OEMs. These evaporators were analyzed to determine the effectiveness of the hydrophilic coating as a function of time or vehicle age. This is the first paper in the open literature that deals with the vehicle mileage or vehicle age with the evaporator plate contact angle and surface coating of an evaporator.

Field tests were conducted on a late full sized sedan with the HVAC unit operating in both Recirculation and OSA modes to monitor build-up of the CO2 concentration inside the cabin and its influence on occupant’s fatigue and alertness. These tests were conducted during 2015 summer on interstate highways with test durations ranging from 4 to 7 hours. During the above tests, fatigue or tiredness of the occupants (including CO2 levels) was monitored and recorded at 30 min intervals. Based on this investigation it is determined that the measured cabin concentration levels reaches ASHRAE (Standard 62-1999) specified magnitudes (greater than 700 ppm over ambient levels) with three occupants in the vehicle. Further, the occupants did show fatigue when the HVAC unit was operated in recirculation mode in excess of 5 hours. Further details have been presented in the paper.

In last 10 years or so, a number of OEMs are designing vehicles with start-stop function to save energy and to reduce pollution. For these systems, the situations in which air-conditioning systems are used have been changing with a significant increase in adoption of idle-time reduction systems (no idling-system). Blower fan remains operating at idle condition while compressor stops in most cases for these systems. In this case, the air temperature at the vent outlets increases. The increase in the air temperature under range of thermal boundary conditions around the evaporator causes a concern of odor to occur. This paper describes and explains experimental studies on changes in heat and humidity at the air outlets according to the switching operation of compressor and root cause analyses of odor coming from air-conditioning system for vehicles with start-stop function.

Proper flow distribution on the windshield and side windows is critical for adequate visibility while driving. Fog or ice which forms on the windshield is the main reason of invisibility and leads to major safety issue. It has been shown that proper clear visibility for the windshield could be obtained with a better flow pattern and uniform flow distribution in the defrost mode of the automobile heating, ventilation, and air-conditioning (HVAC) system. In this study, a three dimensional numerical model of a car cabin with full HVAC system was developed using Star-CCM+, a commercial CFD package. The Reynolds-Averaged Navier-Stokes equations (RANS) approach with the realizable two-layer k-ε turbulence model was employed for simulating the airflow field on the windshield for the defrost mode. The HVAC unit, ducts and defroster grille were included in the analysis in detail and the air distribution on the windshield was studied.

Experimental studies have been conducted to determine the energy stored in vehicle's Cockpit Module (CPM) at cold soaking conditions for a MY2012 production vehicle. Detailed analysis has been done in this paper to show the influence of energy stored in various components (e.g., Instrument panel, HVAC system, heat exchanger, wire harness, etc.) contained within the CPM unit. Experiments conducted show that the instrument panel stores the maximum amount of energy at a given temperature.

Experimental studies have been conducted to determine the energy stored in vehicle's Cockpit Module (CPM) at high ambient and at high solar heat loads for a MY2012 production vehicle. Detailed analysis has been done in this paper to show the influence of energy stored in various components (e.g., Instrument panel, HVAC system, heat exchanger, wire harness, etc.) contained within the CPM unit. Experiments were conducted to show the amount of energy stored at high ambient and solar conditions.