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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.

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.

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 an earlier investigation (Mathur, 1997a; 1997b), the author had developed a simulation program for predicting the thermal and hydrodynamic performance of the automotive heat exchangers. The performance of finned tube condenser and evaporator was simulated and compared with the experimentally obtained data. The simulated performance for both condenser and evaporator was in good agreement with the experimental data. In this paper, the performance of serpentine condenser and evaporator is simulated by using the computer program developed earlier by the author. None of the original correlations for predicting the heat transfer, pressure drop, void fraction are changed. However, the computational methodology had to be changed as the flow in a serpentine heat exchanger is different than in finned tube heat exchangers. The working fluid used in this investigation is R-134a. The simulated performance is compared with the experimentally obtained data on the calorimeter tests.

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 on a parallel flow condenser with HFO-1234yf as the working fluid on an AC system bench. This refrigerant is being considered as an alternative refrigerant for mobile air conditioning systems (MACS) to address the global warming concerns. A condenser 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. 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 was used with HFO-1234yf. Detailed test results have been presented in this paper.

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.

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.

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.

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.

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.

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.

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.

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.