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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.

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.

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 vehicle's AC system should not be operated in recirculation mode for extended periods of time due to build up of CO2 inside the vehicle cabin. This is the CO2 that is exhaled by the occupants of the vehicle. This CO2 is then inhaled by the occupants that goes into their blood streams which results in a negative impact on health. This becomes critical when a number of people are sitting inside the vehicle. Field tests were conducted on a MY 2003 vehicle in recirculation mode to monitor the build-up of the CO2 concentration inside the cabin as a function of number of occupants, vehicle speed and ambient temperatures. The vehicle was driven in Detroit Metro area in city and highway traffic conditions. Based on this investigation it is determined that the cabin concentration levels reaches ASHRAE (Standard 62-1999) specified magnitudes in first 5 minutes of driving with only one occupant in the vehicle.

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.

Experimental tests were conducted on a parallel flow condenser with HFO-1234yf as the working fluid on an AC system bench to determine average and local heat transfer coefficients during condensation of HFO-1234yf for mass flow rates that are typically encountered from idle to highway speeds (800 to 3000 rpms). A condenser from MY 2008 medium-sized sedan was used for this investigation. All original OEM parts were used with the alternate refrigerant. Same TXV set-point was used with HFO-1234yf. The magnitude of the measured heat transfer coefficient for condensation was found to be 8~12% lower in comparison to HFC-134a. The magnitudes of the pressure drop during condensation were of the same magnitude as HFC-134a system. The information from this investigation can be used to in the design of condensers for mobile air conditioning systems with HFO-1234yf as the working fluid.

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.

Field tests were conducted on a MY 2003 vehicle with the HVAC unit in OSA mode to monitor build-up of the CO2 concentration inside the cabin as a function of number of occupants, vehicle speed and ambient temperatures. These tests were conducted in the winter season by driving the vehicle in Detroit Metro area in city (Farmington Hills) and highway traffic conditions. Based on this investigation it is determined that the measured cabin concentration levels reaches ASHRAE (Standard 62-1999) specified magnitudes with four occupants in the vehicle. For this investigation, one to three occupants inside the cabin did not increase the level of cabin carbon dioxide to the levels specified by ASHRAE standard. A maximum concentration with four occupants was measured at 1700 ppm. The cabin concentration level would be higher for vehicles that have lower body leakages compared to this one.

Experimental tests were conducted to monitor cabin carbon dioxide concentrations by driving the vehicle in Farmington Hills & Detroit area. The number of occupants, vehicle speed, and type of driving (local traffic and highway conditions) are the major variables for this study. The tests were conducted during winter season with HVAC unit operating in foot and defrost modes. For foot and defrost modes, there are some noticeable differences in the magnitudes of the carbon dioxide concentration due to the airflow rates and mixing of air within the cabin. The measured peak cabin carbon dioxide levels in foot and defrost modes were found to be of similar magnitudes. However, the initial build-up rates of cabin carbon dioxide for defrost modes were higher in defrost modes in comparison to the foot mode. This is due to different mechanism of mixing of air within the cabin. This is explained in details in the paper.

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.

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. Flow boiling heat transfer coefficients were experimentally determined for HFO-1234yf for this laminate evaporator. Heat transfer coefficients have also been computed from standard correlations available from the open literature. The experimentally obtained heat transfer coefficients are within ±20% of the simulated data based on standard correlation (Kandlikar, 1990). Pressure gradients for these two fluids calculated from Lockhart and Martinelli (1949) correlation shows that the pressure gradients for HFO-1234yf are lower by 15%. Detailed results have been presented in this 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.

A computer program has been developed to optimize the performance of finned tube evaporators. The developed program is used to predict the thermal and hydrodynamic performance of finned tube evaporators. The model is based on a steady-state finite difference model. The correlations for predicting the heat transfer and pressure drop are used from the literature. Experimental data is used to validate the developed model for a finned tube evaporator with R-12 as the working fluid. The simulated performance for heat transfer rate is within ±8 %; and refrigerant pressure drop is within ±10 % of the experimental data. The simulated data shows that 66 % of the heat transfer area is occupied by flow boiling; 23 % by the dryout region; and remaining 11 % is controlled by single-phase vapor flow. Work is continuing on predicting the performance of serpentine and laminate type evaporators with R-134a as the working fluid.

A computer program has been developed to optimize the performance of finned tube condensers. The developed program is used to predict the thermal and hydrodynamic performance of finned tube condensers. The model is based on a steady-state finite difference model. The correlations for predicting the heat transfer and pressure drop are used from the literature. Experimental test data is used to validate the developed model for a finned tube condenser with R-134a as the working fluid. The simulated performance for the condenser heat transfer is within ±7%; and refrigerant pressure drop is within 10% of the experimental data. The simulated data for the condenser coil shows that 16% of the total heat transfer area is occupied by single-phase vapor flow where the superheated vapor are cooled to the saturated conditions; 72% by condensation; and the remaining 12% is controlled by the single-phase liquid flow which results in subcooling.

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.

The current investigation focuses on the heat pick up by the air as it flows into the cowl from one end to the blower unit intake. Tests were conducted on a number of current production vehicles. The following are the major conclusions from this study: 1 A study of 8 current production vehicles revealed that the cowl surface were significantly heated resulting in an increased air temperature as it flows into the blower intake through the cowl. 2 Based on the wind tunnel data, the sheet metal cowl channel is heated up to 50∼63 °C at highway speeds and up to 85 °C at idle. 3 Hence, in OSA mode the ambient air is heated up by the hot channel surface as it travels from the cowl inlet to the blower unit that result in increasing the evaporator loads by significant levels, thereby, increasing the vent outlet temperature. 4 Tests were conducted by removing the cowl cover to determine the maximum potential of improvements (to prevent air from being heated up in the cowl channel).

In this paper, the results from an experimental investigation to determine the water carryover characteristics from the evaporator coil during transitional airflows is presented. The tests were conducted at the following transitional operating conditions: blower speed low to medium; and blower speed low to high. For both of these tests the system operated at low blower speed for an extended period of operation before switching to either medium or high speeds. A laminate (plate type) evaporator with louvered fins with hydrophilic coating was used for this investigation. Tests were also conducted with a screen at the downstream face of the core to prevent water carryover. This test was conducted for the worst case scenario, i.e., when the blower speed was increased to high from an extended period of operation at low speed.

In this paper a methodology is presented to predict the water drop trajectories at a given fan operating condition (i.e., face velocity), coil height and for a range of water drop diameters. Water drop carry over horizontal distances have been calculated as a function of evaporator coil height, water drop diameters, and face velocities for an evaporator unit. The simulated data has been compared with the experimental data. Initial results have shown that the model can predict the water drop trajectories fairly well. The developed model can be used to calculate the maximum horizontal distances the water drops will be carried over with the airstream for a range of water drop diameters. This is very important information to the design engineers for properly designing the evaporator units.

The performance of a parallel flow condenser of a domestic vehicle was simulated by using the computer program developed earlier by the author (Mathur, 1997). None of the original correlations for predicting heat transfer, pressure drop, void fraction were changed. The working fluid used in this investigation was R-134a. The simulated performance was compared with the experimentally obtained data from the calorimeter tests. The simulated thermal and hydrodynamic performance was within ±6% of the experimental data. Detailed performance data has been presented in this paper. The performance of the same condenser was optimized by varying the number of tubes in a given pass by fixing all other variables, e.g., tube and fin pitch; tube geometry; height, length, and depth of the condenser; number of passes; and location of the inlet and outlet connections.