An in-rack cooling system connected to an external vapor recompression loop can be an economical solution to harness waste heat recovery in data centers. Validated subsystem-level models of the thermosyphon cooling and recompression loops (evaporator, heat exchangers, compressor, etc.) are needed to predict overall system performance and to perform design optimization based on the operating conditions. This paper specifically focuses on the model of the evaporator, which is a finned-tube heat exchanger incorporated in a thermosyphon cooling loop. The fin-pack is divided into individual segments to analyze the refrigerant and air side heat transfer characteristics. Refrigerant flow in the tubes is modeled as 1-D flow scheme with transport equations solved on a staggered grid. The air side is modeled using differential equations to represent the air temperature and humidity ratio and to predict if moisture removal will occur, in which case the airside heat transfer coefficient is suitably reduced. The louver fins are modeled as individual hexagons and are treated in conjunction with the tube walls. A segment-by-segment approach is utilized for each tube and the heat exchanger geometry is subsequently evaluated from one end to the other, with air property changes considered for each subsequent row of tubes. Model predictions of stream outlet temperature and pressure, refrigerant outlet vapor quality and heat exchanger duty show good agreement when compared against a commercial software.
Thermoregulatory garments composed of liquid‐cooled plastic tubes have users ranging from astronauts to multiple sclerosis patients and are emerging as a flexible cooling solution for wearable electronics and high‐power robotics. Despite the plethora of applications, the current cooling systems are cumbersome to use due to their excessive size. In this work this issue is resolved by developing soft, thermally conductive silicone–aluminum composite tubes. To achieve optimal device performance, the material must be designed to balance the decrease in bulk thermal resistance and the increase in interfacial tube‐substrate resistance due to composite stiffening. Thus, to enable the rational design of such tubes, a closed form thermomechanical model that predicts cooling performance as a function of tube geometry and filler fraction is developed and experimentally validated. Predictions via this model and experiments are used to reveal how the tube's geometrical and material design can be adjusted to minimize the required length of tubing and maximize the heat extracted from a metallic surface and skin. Lastly, through a holistic analysis, this work demonstrates that besides significantly increasing overall cooling capability, the use of low‐resistance tubing can provide a multifold reduction in the cooling system size and enable novel operating modes.
more » « less- Award ID(s):
- 1724452
- NSF-PAR ID:
- 10457120
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials Technologies
- Volume:
- 4
- Issue:
- 7
- ISSN:
- 2365-709X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)An in-rack cooling system connected to an external vapor recompression loop can be an economical solution to harness waste heat recovery in data centers. Validated subsystem-level models of the thermosyphon cooling and recompression loops (evaporator, heat exchangers, compressor, etc.) are needed to predict overall system performance and to perform design optimization based on the operating conditions. This paper specifically focuses on the model of the evaporator, which is a finned-tube heat exchanger incorporated in a thermosyphon cooling loop. The fin-pack is divided into individual segments to analyze the refrigerant and air side heat transfer characteristics. Refrigerant flow in the tubes is modeled as 1-D flow scheme with transport equations solved on a staggered grid. The air side is modeled using differential equations to represent the air temperature and humidity ratio and to predict if moisture removal will occur, in which case the airside heat transfer coefficient is suitably reduced. The louver fins are modeled as individual hexagons and are treated in conjunction with the tube walls. A segment-by-segment approach is utilized for each tube and the heat exchanger geometry is subsequently evaluated from one end to the other, with air property changes considered for each subsequent row of tubes. Model predictions of stream outlet temperature and pressure, refrigerant outlet vapor quality and heat exchanger duty show good agreement when compared against a commercial software.more » « less
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