Brazed plate heat exchangers (BPHEX) are broadly used in water source heat pump systems for their large heat transfer capacity. Despite their high heat transfer rate, their high-performance rate tends to decrease sharply, due to fouling and they cannot be cleaned. So the thermal and fouling resistances of washable Shell and helically coiled tube heat exchangers (SCHEX) are designed and experimentally investigated in this study. Heat exchangers with two different tube types are studied and compared with a brazed plate heat exchanger. The overall thermal resistance coefficient of the heat exchangers as determined by using Wilson plots is 38% lower than that of the brazed plate heat exchanger at a Reynolds number of 2460. Fouling test results revealed that regular maintenance and physical cleaning can be used to maintain the thermal resistance of fouling of the washable heat exchanger at a level equal to or less than that of the brazed plate heat exchanger.

An experimental investigation on the characteristics of the convective heat transfer in the fully developing region of a circular straight tube with a constant heat flux was carried out with Al2O3 nanofluids. Stable nanofluids, which were water-based suspensions of Al2O3 nanoparticles, were prepared by two-step method. The effects of the thermal conductivity, viscosity, and heat capacity of the nanofluids on convective heat transfer were investigated. The result showed that the coefficient enhancement of the convective heat transfer in the Al2O3 nanofluids was increased with increasing fluid temperature compared to that of water at a volume fraction of 3.0% in the turbulent flow region. Thermal conductivity was increased from 8% to 20%, and the increment of convective heat transfer coefficient was enhanced from 14% to 30% with fluid temperature from 22 degrees C to 75 degrees C, respectively. We observed that the increment of convective heat transfer coefficient in nanofluids was much higher than that of the thermal conductivity at a given temperature condition. The enhancement of Brownian motion due to the decreasing kinematic viscosity led to a higher convective heat transfer coefficient at a higher temperature condition.

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Electronic products and systems are widely used in industrial network systems, control devices, and data acquisition devices across many industry sectors. Failures of such electronic systems might lead to unexpected downtime, loss of productivity, additional work for repairs, and delay in product and service development. Thus, developing an appropriate sensing technique is necessary, because it is the first step in system fault diagnosis and prognosis. Many sensing techniques often require external and additional sensing devices, which might disturb system operation and consequently increase operating costs. In this study, we present an on-chip health sensing method for non-destructive and non-invasive interconnect degradation detection. Bit error rate (BER), which represents data integrity during digital signal transmission, was selected to sense interconnect health without connecting external sensing devices. To verify the health sensing performance, corrosion tests were conducted with in situ monitoring of the BER and direct current (DC) resistance. The eye size, extracted from the BER measurement, showed the highest separation between the intact and failed interconnect, as well as a gradual transition, compared with abrupt changes in the DC resistance, during interconnect degradation. These experimental results demonstrate the potential of the proposed sensing method for on-chip interconnect health monitoring applications without disturbing system operation.

The design of tubes in heat exchangers has a significant influence on heat transfer coefficients (HTCs), affecting nucleate boiling at heat exchanger surfaces. Many researchers have explained heat transfer enhancement techniques applied to tubes by identifying empirical correlations, both dimensional and non-dimensional, for HTCs in terms of surface roughness factor, vapor density, and liquid density based on their experimental results. However, there has been a lack of research analyzing the mechanisms that affect the HTCs in depth. For example, the influence of bubble density, surface roughness factor, and the dynamics of bubble behavior have rarely been explained. In this regard, the present study focuses on mechanism analysis in terms of the value of HTC, specifically revealing the dynamics of bubble behavior. Additionally, this study reports the results of an experimental investigation of pool boiling heat transfer of R134a in a plain tube, a low-fin tube, and an enhanced (Thermoexcel-E) tube as well as results of examining the dynamics of bubble behavior observed on the surface of an enhanced tube. Ultimately, all these investigations aim to determine the heat transfer characteristics of the enhanced tube. In this study, however, circulated water flowing inside an evaporator is used as a heat source instead of a cartridge heater. The heat transfer enhancement ratio of the Thermoexcel-E tube is 2.69-4.13 in the range of heat fluxes tested when the values of HTC from the Thermoexcel-E tube are compared to counterparts from a plain tube. Meanwhile, analysis of the dynamics of bubble behavior observed on the surface of the enhanced tube allows determination of the enhanced tube's heat transfer characteristics. The findings of this study can provide the refrigeration industry with a basic framework for better design using high-efficiency evaporators.INDEX TERMS Nucleate boiling, heat transfer coefficient, enhanced tube, HFC-134a, bubble dynamics, viscosity.