Search Results

Internal corrosion resistance of radiators and heaters is becoming more important as automotive manufacturers seek durability past 10 years, and as the usage of aluminum heat exchangers spreads to markets with poorly maintained engine coolant fluid from a corrosion inhibition standpoint. Simulated Service Corrosion Tests (SSCT) are used to evaluate the resistance of three aluminum alloys to tube failure in various corrosive water and depleted coolant conditions. The paper documents results from such tests that lead to two major conclusions: (1.) A weakly inhibited Oyama water solution with a silicated North American engine coolant is highly effective in ranking internal liner alloys for their pitting corrosion resistance, and (2.) AA7072 lined tubes exhibit superior pitting corrosion resistance compared to 1XXX lined tubes. Electrochemical test data obtained in a simulated pit electrolyte and the bulk test solution are utilized to develop an understanding of the SSCT results.

Simulation of passenger compartment climatic conditions is becoming increasingly important as a complement to wind tunnel and field testing to help achieve improved windshield de-icing performance while reducing vehicle development time and cost. Windshield de-icing simulation involves not only geometric complexity but also interactions between airflow and two modes of heat transfer, namely, heat conduction and convection. In the present study, CFD is employed to numerically simulate windshield de-icing performance. The general-purpose CFD package Fluent is used to perform the numerical simulation. Two CFD analysis methodologies, windshield de-icing pattern analysis and windshield de-icing process analysis, are discussed. The validation is presented by comparing the CFD predicted windshield de-icing patterns with windshield de-icing tunnel test. The present full 3-D CFD windshield de-icing simulations demonstrated reasonable agreement with available tunnel test data.

This paper chronicles a heat exchanger development project that utilized an integrated development process. A combination of full-scale heat exchanger performance testing, flow visualization experiments, and computational fluid dynamics methods were used in concert to investigate flow phenomena in multilouver fins. The primary goal of this project was to confirm the flow and heat transfer enhancement mechanisms at work in multilouver fins. A second goal was correlation of flow visualization, CFD, and traditional full-scale heat exchanger testing. Excellent agreement was found between the three methods.

Computational Fluid Dynamics (CFD) analysis has been used extensively in the design of automotive HVAC systems with the objective of optimize system performance and shorten the product development time. In this paper, the three dimensional Navier-Stokes code STAR-CD was used to determine the overall system pressure drop and velocity field, as well as, individual component pressure and velocity field. In addition, a better insight into the flow characteristics of the HVAC system has been obtained through the CFD analysis. Thermal performance of the HVAC module can also be achieved through the use of user supplied subroutines, which model the thermal effects of heat exchangers. In this paper, two specific systems were analyzed. The first system consisted of a simplified plentum, multiple inlet designs, blower, and evaporator core. The main focus of this analysis was placed on inlet design.

Vehicle acceleration induced pressure spike on the high side of an Air Conditioning (AC) system is causing considerable concerns, especially for systems with high efficiency compressors. Head pressure surge in the order of one to two hundred pounds per square inch can be observed within a time span of 10 seconds or less. As the industry moves to meet increased system durability standards and passenger comfort requirements, clear understanding of the underlying mechanisms is required so that the impact of the head pressure spike can be minimized or eliminated. The present investigation seeks to understand the mechanisms of the head pressure spike phenomenon through both experimental and mathematical analyses. Experimentally, extensive testing has been conducted in environmental wind tunnel. Our mathematical analysis is based on the mass conservation principle for the refrigerant flow through the high side of an AC system.

Concerns about global warming and climate change, combined with the inclusion of HFCs in the Kyoto Protocol as controlled gases, obligate the automotive air conditioning industry to assess the global warming impact of its HFC-134a emissions and develop cost effective mitigation strategies. One option would be replacing HFC-134a with a refrigerant with lower overall global warming impact. This paper demonstrates the feasibility of a secondary loop A/C system in automotive applications. The value of such a system is that it excludes refrigerant from the passenger compartment, thereby allowing the use of non-inert alternate refrigerants, such as hydrocarbons. It includes actual on-vehicle comparisons of A/C cooling performance and system energy requirements for secondary loop versus the current HFC-134a system. Also included is an assessment of the global warming impact advantage offered by a secondary loop A/C system.

The paper deals with potential augmentation of the present R134a automotive air conditioning system with the intent to lower its total equivalent warming impact (TEWI) which is a source of concern from the standpoint of environmental benignity of the system. It is identified that the most effective augmentation strategy includes (1) increase in compressor isentropic efficiency, (2) increase in condenser effectiveness, (3) decrease in lubricant circulation through the system, (4) decrease in air side pressure drop in evaporator through improved condensate management, (5) increase in condenser airflow, (6) decrease in air conditioning load via permissible increase in the amount of recirculated air through the passenger compartment and (7) reduction in direct emission of R-134a from the system through conservation and containment measures. The effect of each of these augmentations on the coefficient of performance (COP) of the system is quantified in a rigorous fashion.

In recent years, Global Warming Potential (GWP) has become as important as Ozone Depletion Potential (ODP) when evaluating a potential refrigerant. Increasing concern over GWP of HFC-134a and its effect on the environment have led international heating, ventilation and air conditioning, and refrigeration (HVAC & R) industries to look at other options. This study documents an assessment of some of the options. It describes simulated performance of R152a and hydrocarbon refrigerants and their potential as alternative refrigerants to HFC-134a in mobile air conditioning systems. In addition, a comparative assessment of the performance of a secondary loop system using these refrigerants is provided.

Simulation of passenger compartment climatic conditions is becoming increasingly important as a complement to wind tunnel and field testing to help achieve improved thermal comfort while reducing vehicle development time and cost. Delphi Harrison Thermal Systems has collaborated with the University of California, Berkeley to develop the capability of predicting occupant thermal comfort to support automotive climate control systems. At the core of this Virtual Thermal Comfort Engineering (VTCE) technique is a model of the human thermal regulatory system based on Stolwijk’s model but with several enhancements. Our model uses 16 body segments and each segment is modeled as four body layers (core, muscle, fat, and skin tissues) and a clothing layer.

The focus of the present paper is the energy efficient automotive air conditioning system, which ipso facto is also environmentally friendly from the standpoint of global warming impact. Two efficiency enhancement strategies are presented - one entailing the use of judicious amount of recirculated air and another relying on reduction in the amount of reheating of the chilled air employed in the conventional system. The first strategy, referred to as the air inlet mixture strategy, reduces the air conditioning load by mixing proper amount of recirculated air with the outside air. The second strategy, referred to as the series reheat reduction strategy, reduces reheating of chilled air under low to moderate load conditions. Analytical relations are presented for the determination of reduction in air conditioning load due to mixing of outside air with varying amounts of recirculated air as well as due to reduction in the series reheat.

Simulation of passenger compartment climatic conditions is becoming increasingly important as a complement to wind tunnel and field testing to help achieve improved thermal comfort while reducing vehicle development time and cost. Thermal analysis of a passenger compartment involves not only geometric complexity but also strong interactions between airflow and three modes of heat transfer, namely, heat conduction, convection, and thermal radiation. The present full 3-D CFD analysis takes into account the geometrical configuration of the passenger compartment including glazing surfaces and pertinent physical and thermal properties of the enclosure with particular emphasis on glass properties. This CFD analysis is coupled with a thermal comfort model in the Virtual Thermal Comfort Engineering (VTCE) Process that was described in [1].