H. J. Sauer

Experimental investigation of thermal conductance of finned tube contacts

Abstract An experimental study was conducted to investigate the contact conductance of plate finned tubes. The basic theory of thermal contact conductance supports the use of measurable parameters including interference, fin spacing, fin thickness, tube hardness, and tube diameter as prediction parameters. Thirty-one coils were tested in a vacuum chamber. A correlation was developed that predicts the thermal contact conductance. The heat transfer results of the experimental study are presented.

Nucleate Boiling Performance of Refrigerants and Refrigerant-Oil Mixtures

Current and previous studies by the authors and others have shown that the carry-over on oil in refrigeration systems can have a significant influence of the boiling performance in the evaporator of refrigeration systems. This investigation was conducted primarily to develop a general correlation equation for predicting the heat transfer coefficient for refrigerants and refrigerant-oil mixtures under pool boiling conditions. Experimental results were obtained to establish the validity of the correlation equation.

Thermal contact conductance of a phase-mixed coating layer by transitional buffering interface

The thermal contact conductances of metallic joints having phase-mixed coating layers applied by a novel transitional buffering interface technique was investigated. This study is restricted to relatively low contact pressure and to microhardness (P/H) ratios, 10~ < PlH < 6 x 10~, where very little data exist. These results are extremely useful for some applications such as electrical contacts in spacecraft. The purposes of this work were 1) to conduct an experimental study to examine four different coating materials, two pure materials, and two phase-mixed materials; and 2) to develop a theoretical model for a phase-mixed coating layer to predict the thermal contact conductance under the first-load cycle. The theoretical model included both the thermal and mechanical (microhardness) aspects of the contact problem. An extensive experimental program was carried out employing four different coating materials, as well as a broad range of surface roughness and microhardness. In order to obtain more robust coatings than conventional methods with better endurance, an adhesion test was conducted to investigate the adhesive strength of transitional buffering interface (TBI) coating layers.

Formulation of High-Temperature Properties for Moist Air

This paper presents the formulations for the thermodynamic properties of moist air at temperatures from −40 to 320°C, humidity ratios from 0 to 1 kg/kgda, and pressures from 0.069680 (corresponds to altitude of 3000 m) to 5 MPa. Real gas behavior is modeled using the virial equation of state. Up-to-date values for the virial coefficients of both air and water vapor are used to accurately predict the behavior of moist air. Equations are derived and results are presented for humidity ratio, specific volume, enthalpy, entropy, wet- and dry-bulb temperatures, and relative humidity. In addition, saturation data are presented for humidity ratio, specific volume, enthalpy, entropy, and compressibility. The formulation and calculations presented herein extend the range of psychrometric moist air data with humidity ratios up to 1 kg/kgda and temperatures up to 320°C.

Thermal Constriction Resistance of Phase-Mixed Metallic Coatings

A phase-mixed coating using plasma-enhanced deposition onto a cold surface can offer excellent characteristics of adhesion of coatings to a wide range of base materials, and very close control of coating thickness. These physical characteristics are of great importance to the control of surface contact situations and in particular to the thermal constriction resistance of contact joints, with many applications in thermal control systems. Analytical expressions were developed for the thermal constriction resistance of cylindrical contact spots in such coatings. The thermal constriction parameter was presented in the dimensionless form as a function of the contact geometry, coating thickness, and thermal conductivity ratio of the two different coating materials. Finally, the results of analytical thermal constriction resistance were compared with experimental investigation using copper-carbon and silver-carbon phase-mixed coating materials. Conclusions on selecting phase-mixed coating materials were based solely on the thermal point of view. 11 refs., 7 figs., 2 tabs.

Availability and Irreversibility

Whereas the first law of thermodynamics concerns the quantity of energy, the second law deals with the quality. Because work (organized energy) is the highest-quality (or lowest-entropy) form of interaction among systems, it is also the most valuable form of energy and should therefore be one important index used to rank energy-conversion processes. The second law permits the definition of a property called available energy—the maximum amount of theoretical work that can be produced from the energy of a system. Unlike energy, available energy can be consumed in a process. The goal of energy conversion, therefore, should be to minimize the consumption of available energy. In this chapter we examine this property.

Flow Resistance Characteristics of Airflow Control Dampers (RP-1157)

This paper presents the experimental results of the performance of various types of HVAC system airflow control dampers over a wide range of types, installations, and operating conditions. Three hundred and sixty-eight tests have been conducted with the data and results discussed herein. The main fundamental performance parameter for predicting the flow rate through a partially opened damper is the pressure loss coefficient as a function of the degree of damper opening. Major variables included the type of damper, blade movement, manufacturer, installation, approach velocity, and total system pressure drop. Results should prove very useful for HVAC system designers in the proper selection of airflow modulating dampers.

Gaseous Mixing Characteristics of Parallel Blade Damper Combinations (RP-1045)

Concern for indoor air quality continues to have a significant impact on the design and operation of heating, ventilating, and air-conditioning (HVAC) systems. A major player in the performance of such systems is the flow control damper, particularly with the current popularity of the variable air volume type of system. Mixed air damper systems with economizer control have been used for many years to provide energy savings and to provide ventilation air for building occupants. It is often assumed that sufficient mixing of the outdoor air and return air occurs if parallel blade dampers properly aligned are used. However, it has been found that some mixed air dampers do not provide proper mixing of air under cold outdoor air temperature conditions. If the thermal mixing is inadequate to prevent coil freezing, there may also be inadequate mixing of oxygen and gaseous contaminants that could lead to poor indoor air quality (IAQ). This paper includes guidelines for the selection of mixed air damper configurations that provide proper mixing of airstreams. Configurations that do not provide proper mixing are also identified.

Combined Solar and Internal Load Effects on Selection of Heat Reclaim-Economizer HVAC Systems

This study looks at potential energy savings of such combined systems with particular emphasis on the effects of the solar load (amount of glass) and the internal load level (lights, people, appliances, etc). These results strongly demonstrate the necessity of complete engineering evaluations if proper selection and operation of combined heat recovery and economizer cycles are to be obtained. This paper includes the basic methodology for making such evaluations