Experimental and Mathematical Research of Convection Heat Transfer for a High Integral Finned Tube Heat Exchanger

This research exhibits an experimental and numerical investigation for the characteristics of heat transfer by utilizing an integral and smooth high finned tube and shows how the integral high fins affect in improving the transfer of heat. In the experimental work, the experimental rig consists of a cold water loop, a hot air loop and the trial part which is a concentric parallel flow double pipe heat exchanger. The first test smooth tube made of brass has external and internal diameter (32 mm) and (22 mm), respectively, the second test section made of the same material has external fins, the third test section possesses internal fins, and the fourth test section has internal and external fins. The dimensions of the fin are (2 mm) in thickness, (2 mm) in height and pitch (2.5 mm) center to center. And, the water flow rates are (6, 8, 10, 12 and 14 L/min). The inlet water to the trial tube was at temperatures (15, 25, 35, and 45oC). The investigational results manifested that the air side heat transfer coefficient of the smooth tube was lesser than the integral high finned tube. The ratio of improvement when using the integral high finned tube was (47.5%, 60.5% and 67.5 %). Numerical simulation was applied on the current heat exchanger to study both the transfer of heat and the field of flow by using ANSYS, FLUENT15 package. Steady state, Newtonian flow, incompressible and three dimensional analyses were assumed. The comparison between experimental work and numerical results elucidated a good agreement.

Rack-Level Thermosyphon Cooling and Vapor-Compression Driven Heat Recovery: Evaporator Model

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.

Selection of a Heat Exchanger for a Small-Scale Liquid Air Energy Storage System

This paper presents the results of a theoretical analysis of a heat exchanger design for the challenging application of a small-scale modified Linde-Hampson cycle liquid air energy storage system (LAESS). A systems engineering approach was taken to determine the best heat exchanger alternative for incorporation into an existing LAESS. Two primary heat exchanger designs were analyzed and compared: a finned tube heat exchanger (FTHE) design and a printed circuit heat exchanger (PCHE) design. These designs were chosen as alternatives due to the gas-to-gas cooling that occurs in the heat exchanger, and material selection was based on the requirement for the heat exchanger to withstand the cryogenic temperatures required for the system to produce liquid nitrogen. Thermodynamic analysis was conducted using the ε-NTU method and fin theory to determine the dimensional requirements for the finned tube heat exchanger and a trade-off study was conducted to compare the alternatives. Based on the results from the study, the PCHE was the preferred alternative due to an inherent small footprint, comparable cost to manufacture, simple integration into the LAESS and inherent safety features that are critical when working with high pressure systems. Future work will include subsystem and system integration and testing to obtain a consistently functional prototype that produces liquid nitrogen.