Comparisons between heat pipe, thermoelectric system, and vapour compression refrigeration system for electronics cooling

Passive systems such as air for electronics cooling have now effectively reached their limits. This paper evaluated three comparable systems for electronics cooling, including heat pipe (HP, passive system), thermoelectric (TE) and vapour compression refrigeration (VCR) systems (active systems). Mathematical model has been built for the heat pipe and the thermoelectric system respectively. Measurements have been conducted to validate the model and to compare the performance among a HP, a single stage TE system and a two-stage TE system, a combination of the HP and the TE system, and a VCR system using an oil-free linear compressor. Close agreements between the modelling and measurements have been achieved in terms of electric power input and cooling capacity at various temperatures. The HP improved the cooling capacity and the coefficient of performance (COP) of the TE system by 53% and 42% respectively at a cold end temperature of 10 °C. Heat pipe is more attractive for cooling large devices at higher temperatures. Two-stage TE system can be used for cooling devices at lower temperatures. VCR system is capable of dissipating much higher heat flux (200 W/cm2 ) at lower temperature than all other technologies

Weak Convergence to Stochastic Integrals for Econometric Applications

Limit theory involving stochastic integrals is now widespread in time series econometrics and relies on a few key results on function space weak convergence. In establishing weak convergence of sample covariances to stochastic integrals, the literature commonly uses martingale and semimartingale structures. While these structures have wide relevance, many applications in econometrics involve a cointegration framework where endogeneity and nonlinearity play a major role and lead to complications in the limit theory. This paper explores weak convergence limit theory to stochastic integral functionals in such settings. We use a novel decomposition of sample covariances of functions of I(1) and I(0) time series that simplifies the asymptotic development and we provide limit results for such covariances when linear process, long memory, and mixing variates are involved in the innovations. The limit results extend earlier findings in the literature, are relevant in many econometric applications, and involve simple conditions that facilitate implementation in practice. A nonlinear extension of FM regression is used to illustrate practical application of the methods

Weak convergence to stochastic integrals for econometric applications

Limit theory involving stochastic integrals is now widespread in time series econometrics and relies on a few key results on functional weak convergence. In establishing such convergence, the literature commonly uses martingale and semimartingale structures. While these structures have wide relevance, many applications involve a cointegration framework where endogeneity and nonlinearity play major roles and complicate the limit theory. This paper explores weak convergence limit theory to stochastic integral functionals in such settings. We use a novel decomposition of sample covariances of functions of I (1) and I (0) time series that simplifies the asymptotics and our limit results for such covariances hold for linear process, long memory, and mixing variates in the innovations. These results extend earlier findings in the literature, are relevant in many applications, and involve simple conditions that facilitate practical implementation. A nonlinear extension of FM regression is used to illustrate practical application of the methods.</jats:p

Experimental study of R1234yf as a drop-in replacement for R134a in an oil-free refrigeration system

R1234yf is a synthetic refrigerant with global warming potential (GWP) of 4 and similar thermodynamic properties to R134a. This paper experimentally compares the performance of R1234yf with R134a in an oil-free vapour compression refrigeration (VCR) system. The oil-free VCR system consisting of oil-free linear compressors, an off-the-shelf condenser and an evaporator with an electric heater avoids the impact of oil lubricant on the heat transfer so that the two refrigerants can be appropriately compared with each other. Experiments for two refrigerants were carried out for compressor strokes of 9-13 mm, operating frequency of 32-38 Hz, pressure ratios of 2- 4, and condenser temperatures of 40-50 °C with refrigerant charge of 250 g. The experimental results show that the coefficient of performance (CoP) of R1234yf is 20% lower than R134a with condenser temperature of 40 °C and evaporator temperature of 0 °C. The volumetric efficiency of R1234yf is 5% lower than R134a with condenser temperature of 40 °C and evaporator temperature of -1.5 °C. Results of evaporator pressure drop, superheat, power input, and cooling capacity are also reported

Prospects of Cytomegalovirus-Specific T-Cell Receptors in Clinical Diagnosis and Therapy

Human cytomegalovirus (HCMV) is responsible for widespread infections worldwide. In immunocompetent individuals it is typically latent, while infection or reactivation in immunocompromised individuals can result in severe clinical symptoms or even death. Although there has been significant progress in the treatment and diagnosis of HCMV infection in recent years, numerous shortcomings and developmental limitations persist. There is an urgent need to develop innovative, safe, and effective treatments, as well as to explore early and timely diagnostic strategies for HCMV infection. Cell-mediated immune responses are the primary factor controlling HCMV infection and replication, but the protective role of humoral immune responses remains controversial. T-cells, key effector cells of the cellular immune system, are critical for clearing and preventing HCMV infection. The T-cell receptor (TCR) lies at the heart of T-cell immune responses, and its diversity enables the immune system to differentiate between self and non-self. Given the significant influence of cellular immunity on human health and the indispensable role of the TCR in T-cell immune responses, we posit that the impact of TCR on the development of novel diagnostic and prognostic methods, as well as on patient monitoring and management of clinical HCMV infection, will be far-reaching and profound. High-throughput and single-cell sequencing technologies have facilitated unprecedented quantitative detection of TCR diversity. With these current sequencing technologies, researchers have already obtained a vast number of TCR sequences. It is plausible that in the near future studies on TCR repertoires will be instrumental in assessing vaccine efficacy, immunotherapeutic strategies, and the early diagnosis of HCMV infection

Characteristics of a novel moving magnet linear motor for linear compressor

Linear compressors consisting of linear motor and suspension spring have been widely used for cryogenic and refrigeration systems. This paper characterises a novel moving magnet linear motor for linear compressor including magnet spring, motor force, resonant frequency and overall performance. First, the static force of the linear motor was modelled using FEA (Finite Element Analysis) method for various excitation current and armature positions. A specific test rig was built to measure the motor force and to verify the results from FEA simulation. The magnet spring was found to be 1.3 N/mm for peak stroke. The magnet spring effect was taken account into the calculation of the resonant frequency, which mainly depends on mechanical spring and gas spring. The linear compressor using the proposed linear motor and flexure springs was instrumented for measurements of the resonant frequency at different pressure ratios and strokes. Good agreement was shown between the calculated and measured resonant frequencies for various conditions. The high efficiency novel magnet linear motor is very attractive for linear compressor

Modelling and Measurement of a Moving Magnet Linear Motor for Linear Compressor

For the purpose of efficiency improvement, a linear motor that performs a linear reciprocating motion can be employed to directly drive the piston in a reciprocating refrigeration compressor without crankshaft mechanism. This also facilitates the modulation of cooling capacity as the stroke and frequency can be readily varied in response to heat load. A novel design of moving magnet linear motor for linear compressor was analyzed in the paper. A finite element analysis (FEA) model was built to simulate the characteristics of the linear motor. Current and displacement signals were measured from a test rig and were defined in the transient FEA model. Transient motor force was simulated with the FEA model and good agreements are shown between the results from the FEA model and interpolated shaft force from static force measurements. Major Losses, such as copper loss and core loss were also computed. Motor efficiency decreased from 0.88 to 0.83 as stroke increased from 9 mm to 12 mm, while the pressure ratio remained unchanged. Comparisons were made between the present moving magnet linear motor and moving coil linear motors. Generally, the moving magnet linear motor demonstrates higher efficiency than moving coil motors, which have significantly higher copper loss. The present moving magnet design with simple structure could be further optimized to improve motor efficiency

Current <i>i</i>_<i>q</i> waveform at L₀ = 2L.

(a) Traditional model current iq; (b) Improved model current iq.</p

Comparison between the waveforms of the variable torque current and speed, when a two times inductance mismatch exists between the traditional and improved models.

(a) Traditional model current id/q; (b) Improved model current id/q; (c) Traditional model speed n; (d) Improved model speed n.</p

Current <i>i</i>_<i>d</i> waveform at L₀ = 2L.

(a) Traditional model current id; (b) Improved model current id.</p