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1. RACK-LEVEL THERMOSYPHON COOLING AND VAPOR-COMPRESSION DRIVEN HEAT RECOVERY: COMPRESSOR MODEL

   Khalid, R. ; Amalfi, R.L. ; Wemhoff, A.P. ( October 2021 , Proceedings of the ASME 2021 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems InterPACK2021)

   This paper introduces a novel thermal management solution coupling in-rack cooling and heat recovery system. System-level modeling capabilities are the key to design and analyze thermal performance for different applications. In this study, a semi-empirical model for a hermetically sealed scroll compressor is developed and applied to different scroll geometries. The model parameters are tuned and validated such that the model is applicable to a variety of working fluids. The identified parameters are split into two groups: one group is dependent on the compressor geometry and independent of working fluid, whereas the other group is fluid dependent. By modifying the fluid-dependent parameters using the specific heat ratios of two refrigerants, the model shows promise in predicting the refrigerant mass flow rate, discharge temperature and compressor shaft power of a third refrigerant. Here, the approach has been applied using data for two refrigerants (R22 and R134a) to achieve predictions for a third refrigerant’s (R407c) mass flow rate, discharge temperature, and compressor shaft power, with normalized root mean square errors of 0.01, 0.04 and 0.020, respectively. The normalization is performed based on the minimum and maximum values of the measured variable data. The technique thus presented in this study can be usedmore »to accurately predict the primary variables of interest for a scroll compressor running on a given refrigerant for which data may be limited, enabling component-level design or analysis for different operating conditions and system requirements.« less
2. Design and Thermal Analysis of a 3D Printed Impingement Pin Fin Cold Plate for Heterogeneous Integration Application

   https://doi.org/10.1109/TCPMT.2022.3185401  

   Hoang, Cong Hiep ; Azizi, Arad ; Fallahtafti, Najmeh ; Rangarajan, Srikanth ; Radmard, Vahideh ; Arvin, Charles ; Sikka, Kamal ; Schiffres, Scott ; Sammakia, Bahgat ( June 2022 , IEEE Transactions on Components, Packaging and Manufacturing Technology)

   Miniaturization and high heat flux of power electronic devices have posed a colossal challenge for adequate thermal management. Conventional air-cooling solutions are inadequate for high-performance electronics. Liquid cooling is an alternative solution thanks to the higher specific heat and latent heat associated with the coolants. Liquid-cooled cold plates are typically manufactured by different approaches such as: skived, forged, extrusion, electrical discharge machining. When researchers are facing challenges at creating complex geometries in small spaces, 3D-printing can be a solution. In this paper, a 3D-printed cold plate was designed and characterized with water coolant. The printed metal fin structures were strong enough to undergo pressure from the fluid flow even at high flow rates and small fin structures. A copper block with top surface area of 1 inch by 1 inch was used to mimic a computer chip. Experimental data has good match with a simulation model which was built using commercial software 6SigmaET. Effects of geometry parameters and operating parameters were investigated. Fin diameter was varied from 0.3 mm to 0.5 mm and fin height was maintained at 2 mm. A special manifold was designed to maximize the surface contact area between coolant and metal surface and therefore minimize thermalmore »resistance. The flow rate was varied from 0.75 L/min to 2 L/min and coolant inlet temperature was varied from 25 to 48 oC. It was observed that for the coolant inlet temperature 25 oC and aluminum cold plate, the junction temperature was kept below 63.2 oC at input power 350 W and pressure drop did not exceed 23 Kpa. Effects of metal materials used in 3D-printing on the thermal performance of the cold plate were also studied in detail.« less
3. Phase Equilibria, Diffusivities, and Equation of State Modeling of HFC-32 and HFC-125 in Imidazolium-Based Ionic Liquids for the Separation of R‑410A

   Morais, Ana Rita ( September 2020 , Industrial engineering chemistry research)

   Growing concerns about the global warming potential of hydrofluorocarbons (HFCs) has led to increasing interest in developing technologies to effectively recover and recycle these refrigerants. Ionic liquids (ILs) have shown great potential to selectively separate azeotropic HFC gas mixtures, such as R-410A composed of HFC-32 (CH2F2) and HFC-125 (CHF2CF3), based on solubility differences between the refrigerant gases in the respective IL. Isothermal vapor−liquid equilibrium (VLE) data for HFC-32 and HFC-125 were measured in ILs containing fluorinated and nonfluorinated anions using a gravimetric microbalance at pressures ranging from 0.05 to 1.0 MPa and a temperature of 298.15 K. The van der Waals equation of state (EoS) model was applied to correlate the experimental solubility data of each HFC refrigerant/IL mixture. The solubility differences between HFC-32 and HFC-125 vary significantly depending on the choice of IL. The diffusion coefficients for both HFC refrigerants in each IL were calculated by fitting Fick’s law to time-dependent absorption data. HFC-32 has a higher diffusivity in most ILs tested because of its smaller molecular radius relative to HFC-125. Based on the calculated Henry’s law constants and the mass uptake for each system, [C6C1im][Cl] was found to have the highest selectivity difference for separating R-410A at 298.15more »K.« less
4. Phase Equilibria, Diffusivities, and Equation of State Modeling of HFC-32 and HFC-125 in Imidazolium-based Ionic Liquids for the Separation of R-410A

   Morais, Ana Rita ( September 2020 , Industrial engineering chemistry research)

   Growing concerns about the global warming potential (GWP) of hydrofluorocarbons (HFCs) has led to increasing interest in developing technologies to effectively recover and recycle these refrigerants. Ionic liquids (ILs) have shown great potential to selectively separate azeotropic HFC gas mixtures such as R-410A composed of HFC-32 (CH2F2) and HFC-125 (CHF2CF3), based on solubility differences between the refrigerant gases in the respective IL. Isothermal vapor−liquid equilibrium (VLE) data for HFC-32 and HFC-125 were measured in ILs containing fluorinated and non-fluorinated anions using a gravimetric microbalance at pressures ranging from 0.05 to 1.0 MPa and a temperature of 298.15 K. The van der Waals Equation of State (EoS) model was applied to correlate the experimental solubility data of each HFC refrigerant / IL mixture. The solubility differences between HFC-32 and HFC-125 vary significantly depending on the choice of IL. The diffusion coefficients for both HFC refrigerants in each IL were calculated by fitting Fick’s law to time-dependent absorption data. HFC-32 has a higher diffusivity in most ILs tested due to its smaller molecular radius relative to HFC-125. Based on the calculated Henry’s law constants and the mass uptake for each system, the [C6C1im][Cl] was found to have the highest selectivity difference formore »separating R-410A at 298.15 K.« less
5. RACK-LEVEL THERMOSYPHON COOLING AND VAPOR-COMPRESSION DRIVEN HEAT RECOVERY: CONDENSER MODEL

   Khalid, R. ; Amalfi, R.L. ; Wemhof, A.P. ( October 2021 , Proceedings of the ASME 2021 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems InterPACK2021)

   This paper is focused on the modeling of a brazed plate heat exchanger (BPHE) for a novel in-rack cooling loop coupled with heat recovery capability for enhanced thermal management of datacenters. In the proposed technology, the BPHE is acting as a condenser, and the model presented in this study can be applied in either the cooling loop or vapor recompression loop. Thus, the primary fluid enters as either superheated (in the vapor recompression loop) or saturated vapor (in the cooling loop), while the secondary fluid enters as a sub-cooled liquid. The model augments an existing technique from the open literature and is applied to condensation of a low-pressure refrigerant R245fa. The model assumes a two-fluid heat exchanger with R245fa and water as the primary and secondary fluids, respectively, flowing in counterflow configuration; however, the model can also handle parallel flow configuration. The 2-D model divides the heat exchanger geometry into a discrete number of slices to analyze heat transfer and pressure drops (including static, momentum and frictional losses) of both fluids, which are used to predict the exit temperature and pressure of both fluids. The model predicts the exchanger duty based on the local energy balance. The predicted values ofmore »fluid output properties (secondary fluid temperature and pressure, and primary fluid vapor quality and pressure) along with heat exchanger duty show good agreement when compared against a commercial software.« less