Amir Karimi

A review of available computer software packages for use in an undergraduate heat transfer course

Available computer software packages for use in an undergraduate or introductory graduate heat transfer course are reviewed. Brief introductions for using each of the software are provided. A comparison of these software packages highlighting the strengths and limitations of each software is also discussed. A few examples are included to demonstrate the application of the available software in analysis of heat transfer problems.Copyright

Understanding Why Engineering Students Take Too Long to Graduate

There is growing pressure on public colleges and universities to decrease the time students take to earn an undergraduate degree. There are many factors that slow students’ progress towards graduation. For example, urban universities may have a significant number of non-traditional students who don’t take a full load of courses required to graduate in four years. Also, some freshman students interested in engineering may not be prepared for college and are required to take remedial math and science courses. Engineering is a highly-structured program, often with a long sequence of courses requiring one or more prerequisites. If some courses aren’t offered each semester, this can delay progress toward graduation for some students. This paper examines graduating students’ academic records and surveys senior-level mechanical engineering students to identify some of the causes for the increased graduation times. Students provided detailed information such as their full- or part-time status, how many semesters left to graduation, whether they attended summer school, the courses they had difficulty passing, and other issues related to the length of time required to complete their degrees. Feedback from students is essential as universities look to improve graduation rates. The results presented are based on the data for the mechanical engineering program at a public institution in Texas. Although each institution is unique, the findings presented in this paper are expected to apply to similar institutions throughout the nation.Copyright

Using excel for the thermodynamic analysis of air-standard cycles and combustion processes

In an undergraduate course or a course-sequence in thermodynamics mechanical engineering students are introduced to air-standard power cycles, refrigeration cycles, and the fundamentals of combustion processes. The analysis of air-standard thermodynamic cycles or solving problems involving combustion processes requires the evaluation of thermodynamic properties either from ideal gas tables or equations developed based on the assumption of constant specific heats. Many students have a difficult time to distinguish the differences between the two property evaluation methods. Also, solving problems involving power and refrigeration cycles or parametric studies of combustion processes involve several steps of property evaluation and some steps require interpolation of data listed in the thermodynamic property tables. Also solution to problems requiring trial and error iterative procedure makes the solution process tedious and time consuming, if it is done manually. This paper provides several examples to demonstrate the effectiveness of Excel in solving problems involving air-standard cycles and combustion processes.Copyright

Use of Interactive Computer Software in Teaching Thermodynamics Fundamental Concepts

In recent years many publishing companies have provided optional computer software for engineering textbooks. Some of these software packages are tools for enhancing classroom instruction and others are capable of engineering analysis. Several software are currently available as an option with most engineering thermodynamics. They can be used for thermodynamic property evaluations and are extremely useful tools in analysis and design in introductory courses. They are also useful in teaching fundamental thermodynamic concepts. The most significant advantage of these software programs is that no prior knowledge of programming language is necessary in their applications. This paper will discuss the benefits associated with the use of computer software in introductory thermodynamics courses. Available software tools are compared and, in each case, their strengths and limitations are highlighted. The paper describes how one software tool has been integrated into our introductory thermodynamics course to teach the fundamental concepts. Several examples are provided.Copyright

Bringing Uniformity in Topic Coverage and Grading Fairness in Multiple Sections of an Engineering Course

In large engineering departments, multiple sections of an engineering course are typically offered during a single semester to accommodate student enrollment demands. At times, multiple sections of a single course are taught by the same instructor, but very often, they are taught by different instructors. Having different instructors teaching various sections of the same course provides opportunities for students to select the instructor of their choice. But it also may create unfairness in grades received by all students taking the same course. Since the grading scale can vary significantly among the instructors, the grade distribution in various sections of the same course can also vary significantly. Some students, who pass a course with one instructor, might not be able to pass the same course if the course is taken with another instructor. One way to resolve this problem is for the instructors to coordinate their efforts in the way they are teaching the course and evaluating student knowledge. In fall 2014, and spring 2015 two instructors who were teaching two sections of a senior level engineering course collaborated in providing a uniform coverage of course topics and coordinated their efforts in assessing knowledge of all students enrolled in both sections. They worked together to put similar emphasize on the topics covered in the course. The weight of each exam, homework assignments, and projects counted towards the final exam were agreed upon at the start of the semester. Exam questions were developed and graded by both instructors. The benefits of coordination in teaching and evaluating the student knowledge uniformly are discussed. Lesson learned in this experiment are also included.Copyright

Behavior of Internal Energy and Enthalpy of Fluids Along Isotherms and Isentropic Lines in the Compressed Liquid Region

It is a common practice to approximate the thermodynamics properties of fluids in the compressed liquid regions from their saturation properties. Most thermodynamics textbooks state that the specific volume, specific internal energy, and specific entropy in the compressed liquid region are functions of temperature only and are independent of pressure. Therefore, compressed liquid property tables are not provided for any substance, except for water, and compressed liquid properties are approximated by their saturated liquid properties at a given temperature. Recent examination of current practice in approximating compressed liquid properties has shown that the internal energy of fluids exhibits growing dependency on pressure with increases in temperature. This paper compares the behavior of internal energy and enthalpy four compressed fluids along isotherms with those behaviors along isentropic lines. Water, ammonia, methane, and propane are examined in this study. It is shown that effects of pressure on the internal energy and enthalpy of compressed liquids are much lower along isentropic lines than those along isotherms.Copyright

An Examination of the Behavior of Thermodynamic Properties in the Compressed Liquid Region

Most thermodynamic textbooks state that the specific volume, specific internal energy, and the entropy of fluids in the compressed liquid region are independent of pressure and vary only with temperatures. Therefore in the compressed liquid region, these properties at given pressures and temperatures are approximated by their saturated liquid properties at the given temperatures. Examination of property values in the compressed liquid region verifies that these assumptions are valid at low temperatures close to the triple point of the fluids. However, the data show that, with increasing temperature, the internal energy and entropy of fluids exhibit higher dependencies on pressure in the compressed liquid region. In a similar fashion, in most applications, it is assumed that the values of constant pressure specific heat (cp ) and constant volume specific heat (cv ) are approximately the same in the compressed liquid region. Again, examination of these properties in the compressed liquid region validates this assumption for water at low temperatures. However, with increasing temperatures away from the triple point, the deviations between the two specific heat values increase. For fluids other than water the values of cp and cv in the compressed liquid region are not very close, even at temperatures close the triple point. Thermodynamic property behavior of several common fluids in the compressed liquid region is examined in this paper. The paper presents data on the behavior of v, u, h, cp and cv in the compressed liquid region and establishes the range of pressures and temperatures in this region where it is valid to assume that the v, u, h, and s are functions of temperature only and the ranges for which the values of cp and cv can be assumed to be nearly the same.Copyright

Thermal Performance Comparison for Five Liquid Heat Sink Designs

Five high-flow liquid-cooled heat sink designs are compared for the cooling of a single chip CPU. Five distinctive design configurations are considered with regard to the introduction, passage, and extraction of cooling fluid. The typical water flow rate is about 3.8 liters per minute (lpm) with flow passages in the primary heat transfer area ranging from 2 to 0.1mm. The design configurations are summarized and compared, considering: the primary convective heat transfer area, flow passage streamlining, acceleration mechanisms, and nominal fluid velocity in the primary heat transfer area. Overall pressure drop and thermal resistance are compared for varying flow rates of water. At the nominal flow, the pressure drops ranged from 1 kPa to 20 kPa. In the restrictive designs, such as nozzles, flow acceleration accounts for the largest source of pressure drop. In some designs, a large fraction of the overall pressure drop is due to circuitous flow associated with the introduction and/or extraction of flow which contributes little to heat removal. At the nominal flow, the overall thermal resistance varied from 0.14 to 0.18 C/W. As flow rate increases the overall thermal resistance decreases. Results indicated that 80 to 85% of the total thermal resistance is due to conduction and about 15 to 20% attributed to convection at the nominal flow rate. There is minimal thermal benefit for flow rates beyond twice the nominal while this substantially increases fluid pumping requirements. This study highlights design features which yield above average heat transfer performance with minimal pressure drop for high-flow liquid-cooled heat sinks.Copyright

A New Approach in Approximating Thermodynamics Properties in Compressed Liquid Region

Currently it is a common practice to use saturated liquid properties to approximate thermodynamics properties of fluids in the compressed liquid region. In this practice it is assumed that specific volume, internal energy, and entropy of fluids in the compressed liquid region are functions of temperature only and pressure practically has very little or no effect on these properties. Therefore, these properties at a given temperature and pressure are approximated by the saturated liquid properties at the given temperature. In the current literature the approximation formula given for enthalpy in the compressed liquid region is expressed as h(T, p) = hf (T) + vf (T) [p – psat (T)], where the aim of the second term on the right hand side of the equation is to improve the accuracy of the approximation, when pressure is much greater than the saturation pressure. However, in a recent study of thermodynamic properties of water, Kostic has shown that the second term in the equation improves the accuracy of the approximation of the enthalpy only at temperatures below 100 °C. In fact, he has shown that the second term increases the error when the formula is used to approximate the enthalpy of water in the compressed liquid region at intermediate and high temperatures. Kostic’s investigation is expanded in this paper to include substances other than water. The study shows that in many situations pressure has a bigger influence on the internal energy than it does on enthalpy of fluids in the compressed liquids. This paper demonstrates that the current practice of approximating properties of fluids in the compressed liquid region is not accurate at all range of temperatures and pressures. It establishes the range of pressures and temperatures for which the current approximation method could be used with reasonable accuracies. It also proposes a new scheme for the approximation of thermodynamic properties in the compressed liquid region.© 2008 ASME

Challenges in Teaching Applied Thermodynamics

Most Mechanical Engineering programs offer a course in applied thermodynamics either as a requirement or as an elective for an undergraduate degree. Student success in this course depends on their preparation on fundamental concepts gained in an introductory course in thermodynamics. The divide in background knowledge among students creates a challenge for an instructor teaching the applied thermodynamics course. This paper explains how students’ background knowledge of the fundamental concepts is evaluated at the beginning of the semester. It provides a description of an approach adapted in teaching the course in order to close the gap in background knowledge among students. Through assessment results, this paper demonstrates how the adapted teaching method has improved student success. Other challenges for instruction and student assessment are discussed in this paper.Copyright