Subcooled freon-11 flow boiling in top-heated finned coolant channels with and without a twisted tape

An experimental study was conducted in top-heated finned horizontal tubes to study the effect of enhancement devices on flow boiling heat transfer in coolant channels. The objectives are to examine the variations in both the mean and local (axial and circumferential) heat transfer coefficients for circular coolant channels with spiral finned walls and/or spiral fins with a twisted tape, and improve the data reduction technique of a previous investigator. The working fluid is freon-11 with an inlet temperature of 22.2 C (approximately 21 C subcooling). The coolant channel's exit pressure and mass velocity are 0.19 M Pa (absolute) and 0.21 Mg/sq. ms, respectively. Two tube configurations were examined; i.e., tubes had either 6.52 (small pitch) or 4.0 (large pitch) fins/cm of the circumferential length (26 and 16 fins, respectively). The large pitch fins were also examined with a twisted tape insert. The inside nominal diameter of the copper channels at the root of the fins was 1.0 cm. The results show that by adding enhancement devices, boiling occurs almost simultaneously at all axial locations. The case of spiral fins with large pitch resulted in larger mean (circumferentially averaged) heat transfer coefficients, h sub m, at all axial locations. Finally, when twisted tape is added to the tube with large-pitched fins, the power required for the onset of boiling is reduced at all axial and circumferential locations

TEXAS POLICY EDUCATION

Agricultural and Food Policy,

Flow boiling with enhancement devices for cold plate coolant channel design

The use of flow boiling for thermal energy transport is intended to provide an alternative for accommodating higher heat fluxes in commercial space systems. The objectives are to: (1) examine the variations in both the mean and local (axial and circumferential) heat transfer coefficients for a circular coolant channel with either smooth walls, spiral fins, or both spiral fins and a twisted tape; (2) examine the effects of channel diameter and subcooling; and (3) develop an improved reduction analysis and/or suggest possible heat transfer correlation of the present data. Freon-11 is the working fluid. Two-dimensional (circumferential and axial) wall temperature distributions were measured for coolant channels with the above noted internal geometries. The flow regimes which are being studied are: (1) single phase; (2) subcooled flow boiling; and (3) stratified flow boiling. The inside diameter of all test sections is near 1.0 cm. Cicumferentially averaged heat transfer coefficients at several axial locations were obtained for selected coolant channels for a mass velocity of 210 kg/sq m s, an exit pressure of 0.19 MPa (absolute), and an inlet subcooling of 20.8 C. Overall (averaged over the entire channel) heat transfer coefficients were compared for the above channel geometries. This comparison showed that the channel with large pitch spiral fins had higher heat transfer coefficients at all power levels

Flow boiling with enhancement devices for cold plate coolant channel design

The effects of enhancement devices on flow boiling heat transfer in circular coolant channels, which are heated over a fraction of their perimeters, are studied. The variations were examined in both the mean and local (axial, and circumferential) heat transfer coefficients for a circular coolant channel with either smooth walls or with both a twisted tape and spiral finned walls. Improvements were initiated in the present data reduction analysis. These efforts should lead to the development of heat transfer correlations which include effects of single side heat flux and enhancement device configuration. It is hoped that a stage will be set for the study of heat transfer and pressure drop in single sided heated systems under zero gravity conditions

Test results at transonic speeds on a contoured over-the-wing propfan model

A semispan wing/body model with a powered highly loaded propeller has been tested to provide data on the propulsion installation drag of advanced propfan-powered aircraft. The model had a supercritical wing with a contoured over-the-wing nacelle. It was tested in the Ames Research Center's (ARC) 14-foot Transonic Wind Tunnel at a total pressure of 1 atm. The test was conducted at angles of attack from -0.5 to 4 deg at Mach numbers ranging from 0.6 to 0.8. The test objectives were to determine propeller performance, exhaust jet effects, propeller slipstream interference drag, and total powerplant installation drag. Test results indicated a total powerplant installation drag of 82 counts (0.0082) at a Mach number of 0.8 and a lift coefficient of 0.5, which is approximately 29 percent of a typical airplane cruise drag

An Analysis of Whole Farm Revenue Safety Net Options in Agriculture

Despite many years of experience, the federal government continues to seek a farm program that holds the potential for providing a politically acceptable safety net for farmers. This study demonstrates that, with the 2002 Farm Bill, AMTA, and marketing loan provisions continuing, a whole farm revenue safety net has the potential for simplifying existing farm programs, while enhancing the financial position of US farmers. There remains the need for further analysis of the impacts of the options analyzed on supply response by farmers.Agricultural and Food Policy,

SOUTHERN FARMERS EXPOSURE TO INCOME RISK UNDER THE 1996 FARM BILL

Arguably, since the 1930s, what farmers produced has been markedly influenced by farm programs. The 1996 farm bill affects farmers in terms of what they produce and their level of risk exposure. This paper investigates the farm level impacts of the 1996 farm bill on the South. Focus group perceptions of risk sources, observed acreage changes, and the farm level impact of increased price risk are evaluated.Agricultural and Food Policy, Agricultural Finance,

American Agriculture: What We Can Expect - National Symposium on the Future of American Agriculture, University of Georgia: August 1999

The Agricultural and Food Policy Center (AFPC) of the Texas A&M University System is pleased to be invited to address this symposium addressing the future of U.S. agriculture. As a participant in the FAPRI consortium, AFPC monitors the economic conditions of U.S. agriculture at the farm and ranch level. To accomplish this, AFPC maintains approximately 80 crop, dairy, beef and pork representative farms throughout the nation. In the interest of time, this paper will focus only on the economic condition of the 41 feed grain/oilseeds, wheat, cotton and rice farms through the year 2002. Anyone interested in the livestock operations, or more detail on the crop farms, are directed to the AFPC web site at http://afpc1.tamu.edu. The publications included at this site provide greater detail about the process AFPC employs to develop the representative farms, their structure and their financial characteristics.Agribusiness, Agricultural and Food Policy,

National Agricultural, Research, Extension, Education and Economics Advisory Board Southern Regional Listening Session - Small and Family Farms: Challenges and Needs Alcorn State University, Alcorn, Mississippi

The Agricultural and Food Policy Center’s (AFPC) primary purpose is to analyze the economic and financial impacts of alternative government policies on U.S. farming and ranching operations. This is accomplished through the maintenance of data necessary to simulate the economic and financial activities of more than 80 representative crop and livestock farms chosen from major production areas across the United States. Twenty of the 41 crop farms are located in the Southern region. A brief description of these crop farms and their location is summarized in Appendix A. The economic and financial observations reported in this paper are based on AFPC’s experience with the crop farms in the Southern region. The paper is organized into four sections. The first section summarizes the process used to develop the representative farms. The second section presents the crop farms in terms of total crop cash receipts and economic efficiency as measured by the ratio of total cash costs to receipts. The third section reports the economic and financial conclusions inferred by AFPC’s experience with these crop farms. The final section addresses research, education and policy implications drawn from the analysis.Agricultural and Food Policy,