Real-Time Cooling Power Attribution for Co-Located Data Center Rooms with Distinct Temperatures and Humidities

At present, a co-location data center often applies an identical and low temperature setpoint for its all server rooms. Although increasing the temperature setpoint is a rule-of-thumb approach to reducing the cooling energy usage, the tenants may have different mentalities and technical constraints in accepting higher temperature setpoints. Thus, supporting distinct temperature setpoints is desirable for a co-location data center in pursuing higher energy efficiency. This calls for a new cooling power attribution scheme to address the inter-room heat transfers that can be up to 9% of server load as shown in our real experiments. This article describes our approaches to estimating the inter-room heat transfers, using the estimates to rectify the metered power usages of the rooms’ air handling units, and fairly attributing the power usage of the shared cooling infrastructure (i.e., chiller and cooling tower) to server rooms by following the Shapley value principle. Extensive numeric experiments based on a widely accepted cooling system model are conducted to evaluate the effectiveness of the proposed cooling power attribution scheme. A case study suggests that the proposed scheme incentivizes rational tenants to adopt their highest acceptable temperature setpoints under a non-cooperative game setting. Further analysis considering distinct relative humidity setpoints shows that our proposed scheme also properly and inherently addresses the attribution of humidity control power.

Two-Dimensional Modeling of Heat Transfers in a Ventilated Test Cell Built with Various Local Materials

The main objective of this work is to find a material that attenuates heat transfer and provides an acceptable indoor environment in the habitat of countries with a hot and dry climate like Burkina Faso. The absence of thermal regulations in Burkina Faso leads to the development of buildings constructed with materials that do not provide thermal comfort. This study therefore aims to compare the thermal performance of local materials such as BLT, BTC, concrete block and adobe in order to propose a material adapted to the hot climate. In this work, a modelling and simulation is conducted with the COMSOL software. The modelling is done on a building of dimensions 4m×3m×3m, built successively with cut laterite block (BLT), compressed earth block (BTC), hollow concrete block, and adobe. As for the simulation, it concerns the evolution of the internal and external temperature of the building. The heat flows on the Northern and Southern sides are neglected due to the overhang of the roof. The results obtained show that the cell built with BTC allows a 4°C reduction, the one built with BLT a 2°C reduction and the one built with adobe a 1.5°C gain compared to the one built with concrete block. Thus, the material that best meets the criteria is BTC.

Characteristic of heat transfer nanofluid of Al2O3 improved by ZrO2 addition

Efforts to replace conventional fluids as coolants for heat transfers with new fluids are continuously being made to improve heat transfer efficiency. Nanofluids are currently widely studied around the world as candidates for conventional fluids substitutes. In this research, the synthesis of Al2O3-ZrO2 nanocomposites for heat transfer nanofluid applications was carried out. The synthesis of the nanoparticles was conducted by the hydrothermal method. Here, we used ZrO2 to improve the characteristics of Al2O3. The results of XRD analysis showed that the nanocomposite had an Al2O3 gamma structure. The Al2O3 nanoparticles and Al2O3-ZrO2 nanocomposite have a crystallite size of 7.41 nm and 6.84 nm, respectively. The addition of 0.1 % ZrO2 decreased the crystallite size and BET particle size and increased the zeta potential, hence the stability of the nanofluids. The increase of stability increased the heat transfer coefficient of the Al2O3 nanofluids, making them suitable for heat transfer.

Heat and moisture transfer in wall-to-floor thermal bridges and its influences on the insulation performance

The moisture modifies the characteristics of heat transfer in building envelopes. Multiple factors, including the distinct hygric properties of various material, gravity, etc., affect the moisture content, resulting in a non-uniform distribution of water vapour in different parts of the envelope (e.g. column, beam, the main part of exterior walls). Usually, the more water vapour in a material, the higher the thermal conductivity, resulting in more heat transfers here. Moreover, condensation easily occurs where there is wet, marking such parts have risks both on structural safety and mould growth. The wall-to-floor thermal bridge (WFTB) occupies the largest area among all kinds of thermal bridges that formed by frame structures. In this study, we aimed to quantify the influence on heat loss through WFTB when the moisture transfer in envelopes is considered. The average apparent thermal resistance of WFTB (R TB, ave) was defined to access the insulation performance of WFTB in practical application. The results of transient numerical simulation indicated that when the moisture transfer is considered, the insulation performance of building envelopes decreases significantly, while the adverse effect of WFTB on heat insulation becomes less pronounced. The results indicated that the measures of insulation for WFTB should be reconsidered when the moisture transfer is considered.

Effect of Couple Stress Fluid in an Irregular Couette Flow Channel: An Analytical Approach

The work embodied in this paper presents the combined effects of Soret, chemical reaction, and Dufour on Couette flow in an irregular channel for dusty viscoelastic couple stress fluid. The behavior of the boundary layer is studied with the help of Brinkman-Forchheimer's extended Darcy model as a momentum equation for the unsteady, incompressible dusty viscoelastic fluid. The heat transfers are considered due to the radiation absorption parameter and Dufour effect, the mass transfer influenced by the chemical reaction, and the Soret effect. The boundary conditions of the problem and leading equations of the physical problem are solved by a similarity transformation, and the consequent ordinary linear differential equations are solved by the perturbation method. The obtained results are shown graphically. The computational results show a good agreement between our values and a particular case of the earlier work.

Analysis of Non-Symmetrical Heat Transfers during the Casting of Steel Billets and Slabs

The current automation of steelmaking processes is capable of complete control through programmed hardware. However, many metallurgical and operating factors, such as heat transfer control, require further studies under industrial conditions. In this context, computer simulation has become a powerful tool for reproducing the effects of industrial constraints on heat transfer. This work reports a computational model to simulate heat removal from billets’ strands in the continuous casting process. This model deals with the non-symmetric cooling conditions of a billet caster. These cooling conditions frequently occur due to plugged nozzles in the secondary cooling system (SCS). The model developed simulates the steel thermal behavior for casters with a non-symmetric distribution of the sprays in the SCS using different boundary conditions to show possible heat transfer variations. Finally, the results are compared with actual temperatures from different casters to demonstrate the predictive capacity of this algorithm’s approach.

Numerical Investigation of New Cooling Method for Clinker Flow in Opposite Direction with Airflow at Different Height Ratios

Several parameters affect the properties of Portland cement and one of these parameters is the cooling rate of the clinker. If the effectiveness of the cooling method of the clinker increases, a good enhancement in the properties of Portland cement will be found. Depending on the new cooling method suggestion by Nasr et. al. [20], the counter pattern of air clinker flow was studied using (FLUENT 6.3.26). The dimensions of the cooling room in grate cooler, the constant mass flow rate of both clinker and air, different height ratios, and different clinker porosity were considered in this numerical work. The results show that the heat transfers in the first half of the cooling room (0 < X < 0.9 m) is larger than that in the second half (0.9 < X < 1.8 m), and this leads to an increase in the temperature of outlet air so can benefits from it in the heating of furnace. When the clinker and air are flowing in the counter direction, the cooling method is more beneficial when compared with that of parallel flow because the exiting clinker has a great rate of cooler and the air exits from the grate cooler is loaded with large thermal energy. Finally, it can design the best length of gate according to the required clinker temperature at the outlet side, and this results to reduce the cost of the cooling process according to the temperature distribution results at (0 < X > 1.8m) for different porosity and H.R values.

Finite Physical Dimensions Thermodynamics Analysis and Design of Closed Irreversible Cycles

This paper develops simplifying entropic models of irreversible closed cycles. The entropic models involve the irreversible connections between external and internal main operational parameters with finite physical dimensions. The external parameters are the mean temperatures of external heat reservoirs, the heat transfers thermal conductance, and the heat transfer mean log temperatures differences. The internal involved parameters are the reference entropy of the cycle and the internal irreversibility number. The cycle’s design might use four possible operational constraints in order to find out the reference entropy. The internal irreversibility number allows the evaluation of the reversible heat output function of the reversible heat input. Thus the cycle entropy balance equation to design the trigeneration cycles only through external operational parameters might be involved. In designing trigeneration systems, they must know the requirements of all consumers of the useful energies delivered by the trigeneration system. The conclusions emphasize the complexity in designing and/or optimizing the irreversible trigeneration systems.