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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.

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.

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.

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%.

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.

To improve fuel consumption, hybrid system, turbo-charged engine, and clean diesel engine vehicles have been developed. These new systems require additional heat exchangers which reduces air flow rate within the heat exchangers of an engine cooling module. Consequently, power of cooling fan is increased. CalsonicKansei (CK) has developed a new cooling module “SLIM” (Single Layer Integrated cooling Module). This consists of a current condenser which is air-cooled and a new water-cooled condenser. This water cooled condenser is specifically designed to bring superheated refrigerant vapor to saturated conditions. The water-cooled condenser is located inside of the sub-radiator tank. The operation of the sub-radiator is to provide cooling to charge air cooler (CAC) and to water-cooled condenser. The switch of the operation is done automatically without any valve and any actuator.

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.

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.

An experimental investigation has been carried out to quantify the performance enhancements with a suction line heat exchanger (SLHX) in an AC system with HFO-1234yf as the working fluid. An off-the-shelf double pipe cross fluted SLHX is used for this investigation. System level bench tests are conducted with an AC system from a 2009 MY mid-sized sedan. The test results shows that the AC system performance with HFO-1234yf can be improve up to 8~9% in comparison to a baseline system without a SLHX.

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].

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.

Experimental investigations have been carried out to determine the AC system performance with HFO-1234yf as the working fluid. System level bench tests have been conducted with an AC system from a 2008 MY mid-sized sedan. The cabin interior condition is held constant at 20°C and 50% RH and evaporator airflow rate is varied from 5 to 9 m₃/min (83 to 150 lps). The dry bulb temperature for the engine compartment is varied from 25 to 45°C. The compressor speed is varied from 800 to 3000 rpm and the air velocity over the condenser is varied from 2 to 10 m/s (546 to 2730 lps). Detailed test results 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.

Tests were conducted with a laminate evaporator for an automotive application. The tests were conducted with HFO-1234yf as the working fluid on an AC system bench. A laminate evaporator from MY 2008 medium sized sedan was used for this investigation. Tests were first conducted with R-134a and were then repeated by maintaining each test condition by changing the working fluid from R-134a to HFO-1234yf. Charge determination tests were also conducted with the new refrigerant. The refrigerant was used as “drop-in” refrigerant in the existing system. All original OEM parts were used with the alternate refrigerant. Same TXV set-point and lubricant type and quantity was used with HFO-1234yf. The new refrigerant has advantages due to the refrigerant thermodynamic properties that helps reduce the pressure ratio. Detailed test results have been presented in this paper.

A number of experiments were conducted to determine oil accumulation rates for a single tank laminate evaporator with the tank at the top. The tank at the top results in a U-shaped evaporator plate design at the bottom where oil can collect under extreme operating conditions. A typical 4 pass laminate evaporator was used for testing. R-134a with an oil circulation ratio of 3% was used for this study. The AC system was run for extended periods (2∼4 hours) at different compressor speeds to simulate the variation of load on the evaporator. Evaporator samples were taken off from the test stand and weighed after recovering refrigerant. The evaporators were designed such that it could be isolated by shutting off valves at the inlet and the outlet connections.

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.

Experiments were conducted on laminate evaporator to determine the effect of the tank position on the evaporator heat transfer and pressure drop. The experiments were conducted on the evaporator calorimeter facility that is fully instrumented per ASHRAE specifications. A typical 4 pass laminate evaporator was used for testing. The refrigerant used for this investigation was R-134a. An oil circulation ratio of 2% was used for this study. The test conditions were: air inlet state was maintained at 27°C of dry bulb temp and 50% RH; average condensing and evaporation pressures were maintained at 15.5 & 1.96 kg/cm2 G, respectively with 5°C evaporator superheat and 5°C condenser subcooling; and air flow rate was varied from 120 to 480 m3/hr. The result shows that there is a significant impact of the tank position on the evaporator heat transfer rate and pressure drop.

In a recent study the author (Mathur, 2006) had conducted an experimental study by monitoring and collecting the tailpipe emissions (NOx, CO, HC) of the exhaust gases for automobiles, buses, and trucks at peak and off-peak hours for major roads and highways in Detroit metropolitan area. The current study focuses on the influence of the vehicle speed and ambient temperature on the amount of CO, HC and NOx entering into the vehicles' cabin in a controlled test environment. These tests have been conducted at CalsonicKansei North America's (CKNA) wind tunnel. Two sensors were installed in the vehicle to monitor outside and inside concentration of the above gases. The tests were conducted at a number of vehicle speeds to determine the influence on the amount of the gases entering into the cabin due to the response time of the actuator for the blower unit's air intake door.

The current investigation is focused on monitoring and collecting the tailpipe emissions (NOx, CO, HC) of the exhaust gases for automobiles, buses, and trucks. The experimental data has been collected to record the peak and off peak hour tailpipe gas concentrations levels for major roads and highways in Detroit metropolitan area. This was accomplished by mounting a sensor on the vehicle's cowl to record the concentration levels of the above gases. A second sensor was installed inside of the cabin to monitor the concentration levels of the above gases entering into the cabin due to the response time of the actuator for the blower unit's air intake door. The levels of the gas concentrations on Detroit metro highways are moderate to high in comparison to rural regions. The concentration levels are the worst on I-696 and North Western Highway10 inside of the tunnels and the areas where retaining walls are present on either sides of the highway.

An experimental investigation has been carried out to quantify the performance enhancements with a suction line heat exchanger (SLHX) in an AC system. An off-the shelf double pipe cross fluted SLHX is used for this investigation. System level bench tests are conducted with an AC system from a 2008 MY mid-sized sedan. The cabin interior condition is held constant at 25°C and 50% RH. The dry bulb temperature for the engine compartment is varied from 25 to 45°C. The compressor speed is varied from 800 to 3000 rpm and the air velocity over the condenser is varied from 2 to 10 m/s. Based on the tests conducted on the AC system without and with SLHX, system performance (COP) has been improved by 7%. Additional tests have been planned with modified SLHX.