We develop a computational framework for D-optimal experimental design for PDEbased Bayesian linear inverse problems with infinite-dimensional parameters. We follow a formulation of the experimental design problem that remains valid in the infinite-dimensional limit. The optimal design is obtained by solving an optimization problem that involves repeated evaluation of the logdeterminant of high-dimensional operators along with their derivatives. Forming and manipulating these operators is computationally prohibitive for large-scale problems. Our methods exploit the lowrank structure in the inverse problem in three different ways, yielding efficient algorithms. Our main approach is to use randomized estimators for computing the D-optimal criterion, its derivative, as well as the Kullback-Leibler divergence from posterior to prior. Two other alternatives are proposed based on low-rank approximation of the prior-preconditioned data misfit Hessian, and a fixed low-rank approximation of the prior-preconditioned forward operator. Detailed error analysis is provided for each of the methods, and their effectiveness is demonstrated on a model sensor placement problem for initial state reconstruction in a time-dependent advection-diffusion equation in two space dimensions.we seek sensor placements that maximize the expected information gain in parameter inversion. Our approach, however, is general in that it is applicable to D-optimal experimental design for a broad class of linear inverse problems. ]. In particular, A-optimal experimental design for large-scale applications has been addressed in [3, 4, 17, 20-22, 24, 43]. Computing Aoptimal designs for large-scale applications faces similar challenges to the D-optimal designs. The use of Monte-Carlo trace estimators [7] has been instrumental in making A-optimal design computationally feasible for such applications.Fast algorithms for computing expected information gain, i.e., the D-optimal criterion, for nonlinear inverse problems, via Laplace approximations, were proposed in [31,32]. The focus of the aforementioned works was efficient computation of the D-optimal criterion. The optimal design was then computed by an exhaustive search over prespecified sets of experimental scenarios. We also mention [26-28] that use polynomial chaos (PC) expansions to build easy-to-evaluate surrogates of the forward model. The expected information gain is then evaluated using an appropriate Monte Carlo procedure. In [27,28], the authors use a gradient based approach to obtain the optimal design. In [44], the authors propose an alternate design criterion given by a lower bound of the expected information gain, and use PC representation of the forward model to accelerate objective function evaluations. However, the approaches based on PC representations remain limited in scope to problems with low to moderate parameter dimensions (e.g., parameter dimensions in order of tens).Efficient estimators for the evaluation of D-optimal criterion were developed in [38,39]; however, these works do not...